Significant acidification in major Chinese croplands

Combined BSA-Seq and RNA-Seq Analysis to Identify Candidate Genes Associated with Aluminum Toxicity in Rapeseed (Brassica napus L.)

Exchangeable aluminum (Al) ions released from acidic soils with pH < 5.5 inhibit root elongation of crops, ultimately leading to yield reduced. It is necessary to identify the quantitative trait locus (QTLs) and candidate genes that confer toxicity resistance to understand the mechanism and improve tolerance of rapeseed. In this study, an F2 segregating population was derived from a cross between Al-tolerance inbred line FDH188 (R178) and -sensitive inbred line FDH152 (S169), and the F2:3 were used as materials to map QTLs associated with the relative elongation of taproot (RET) under Al toxicity stress. Based on bulked segregant analysis sequencing (BSA-seq), three QTLs (qAT-A07-1, qAT-A07-2, and qAT-A09-1) were detected as significantly associated with RET, and 656 candidate genes were screened. By combined BSA and RNA-seq analysis, 55 candidate genes showed differentially expressed, including genes encoding ABC transporter G (ABCG), zinc finger protein, NAC, ethylene-responsive transcription factor (ERF), etc. These genes were probably positive factors in coping with Al toxicity stress in rapeseed. This study provides new insight into exploring the QTLs and candidate genes' response to Al toxicity stress by combined BSA-seq and RNA-seq and is helpful to further research on the mechanism of Al resistance in rapeseed.

Towards Sustainable Productivity of Greenhouse Vegetable Soils: Limiting Factors and Mitigation Strategies

Greenhouse vegetable production has become increasingly important in meeting the increasing global food demand. Yet, it faces severe challenges in terms of how to maintain soil productivity from a long-term perspective. This review discusses the main soil productivity limiting factors for vegetables grown in greenhouses and identifies strategies that attempt to overcome these limitations. The main processes leading to soil degradation include physical (e.g., compaction), chemical (e.g., salinization, acidification, and nutrient imbalances), and biological factors (e.g., biodiversity reduction and pathogen buildup). These processes are often favored by intensive greenhouse cultivation. Mitigation strategies involve managing soil organic matter and mineral nutrients and adopting crop rotation. Future research should focus on precisely balancing soil nutrient supply with vegetable crop demands throughout their life cycle and using targeted organic amendments to manage specific soil properties. To ensure the successful adoption of recommended strategies, socioeconomic considerations are also necessary. Future empirical research is required to adapt socioeconomic frameworks, such as Science and Technology Backyard 2.0, from cereal production systems to greenhouse vegetable production systems. Addressing these issues will enable the productivity of greenhouse vegetable soils that meet growing vegetable demand to be sustained using limited soil resources.

Inoculation with arbuscular mycorrhizal fungi improves plant biomass and nitrogen and phosphorus nutrients: a meta-analysis

Arbuscular mycorrhizal fungi (AMF) have profound effects on plant growth and nitrogen (N) and phosphorus (P) nutrition. However, a comprehensive evaluation of how plant N and P respond to AMF inoculation is still unavailable. Here, we complied data from 187 original researches and carried out a meta-analysis to assess the effects of AMF inoculation on plant growth and N and P nutrition. We observe overall positive effects of AMF inoculation on plant performance. The mean increases of plant biomass, N concentration, P concentration, N and P uptake of whole plant are 47%, 16%, 27%, 67%, and 105%, respectively. AMF inoculation induces more increases in plant concentrations and storage of P than N. Plant responses to AMF inoculation are substantially higher with single AMF species than with mixed AMF species, in laboratory experiments than in field experiments, and in legumes than in non-legumes. The response ratios of plant N and P nutrition are positively correlated with AMF colonization rate, N addition, P addition, and water condition, while unvaried with experiment duration. The biggest and smallest effect sizes of AMF inoculation on plant performance are observed in the application of nitrate and ammonium, respectively. Accordingly, this meta-analysis study clearly suggests that AMF inoculation improves both plant N and P nutrients and systematically clarifies the variation patterns in AMF effects with various biotic and abiotic factors. These findings highlight the important role of AMF inoculation in enhancing plant N and P resource acquisitions and provide useful references for evaluating the AMF functions under the future global changes.

Response of N, P, and metal ions in deep soil layers to long-term cultivation of rubber and rubber-based agroforestry systems

The growing demand for natural rubber products has driven the expansion of rubber plantations in recent decades. While much attention has been given to studying the long-term effects of rubber and rubber-based agroforestry systems on surface soil properties, there has been a tendency to overlook changes in soil properties in deeper layers. Our study addresses this gap by examining alterations in nitrogen (N), phosphorus (P), and metal ion levels in deep soil layers resulting from the prolonged cultivation of rubber and rubber-based agroforestry systems. We found notable shifts in soil NH4+ and NO3- concentrations within the 0-30 cm soil layer across different-aged rubber and rubber-based agroforestry systems. Particularly in mature systems, NO3- and available P levels were close to zero below 30 cm soil depth. Introducing Flemingia macrophylla into young rubber plantations increased soil NH4+ and NO3- in the 0-90 cm soil layer and available P in the 0-10 cm soil layer. Over the long term, cultivation of rubber plantations increased the depletion of total P in the 0-50 cm soil layer, available iron (Fe) and manganese (Mn) in the 30-90 cm soil layer, available copper (Cu) and zinc (Zn) in the 0-90 cm soil layer, accompanied by a decrease in soil pH and increase in exchangeable aluminum (Al) in the 0-90 cm soil layer. Notably, soil exchangeable Al levels exceeding 2.0 cmol kg-1 appeared to induce aluminum toxicity. Furthermore, soil pH below 5.2 triggered a sharp release of exchangeable Al within the 0-90 cm soil layer of rubber plantations, with soil available P nearing zero when exchangeable Al levels assed 7.3 cmol kg-1. Our findings underscore the profound impact of long-term rubber plantation cultivation on surface and deep soil properties. Addressing soil degradation in these deep soil layers poses significant challenges for future soil restoration efforts.

Bioavailability and ecological risk assessment of metal pollutants in ambient PM2.5 in Beijing

Metal pollutants in fine particulate matter (PM2.5) are physiologically toxic, threatening ecosystems through atmospheric deposition. Biotoxicity and bioavailability are mainly determined by the active speciation of metal pollutants in PM2.5. As a megacity in China, Beijing has suffered severe particulate pollution over the past two decades, and the health effects of metal pollutants in PM2.5 have received significant attention. However, there is a limited understanding of the active forms of metals in PM2.5 and their ecological risks to plants, soil or water in Beijing. It is essential that the ecological risks of metal pollutants in PM2.5 are accurately evaluated based on their bioavailability, identifying the key pollutants and revealing historic trends to future risks control. A two-year project measured the chemical speciation of pollution elements (As, Cd, Cu, Cr, Ni, Mn, Pb, Sb, Sr, Ti, and Zn) in PM2.5 in Beijing, in particular their bioavailability, assessing ecological risks and identifying key pollutants. The mass concentrations of total and active species of pollution elements were 199.12 ng/m3 and 114.97 ng/m3, respectively. Active fractions accounted for 57.7 % of the total. Cd had the highest active proportion. Based on the risk assessment code (RAC), most pollution elements except Ti had moderate or high ecological risk, with RAC exceeding 30 %. Cd, with an RAC of 70 %, presented the strongest ecological risk. Comparing our data with previous research shows that concentrations of pollution elements in PM2.5 in Beijing have decreased over the past decade. However, although the total concentrations of Cd in PM2.5 have decreased by >50 % over the past decade, based on machine model simulation, its ecological risk has reduced by only 10 %. Our research shows that the ecological risks of pollution elements remain high despite their decreasing concentrations. Controlling the active species of metal pollutants in PM2.5 in Beijing in the future is vital.

Impact of active root zone soil potassium levels on cotton yield and fiber quality under no tillage

Introduction

Potassium deficiency significantly hinders cotton growth and development, adversely affecting yield and fiber quality. Applying potassium fertilizer is a common practice to address potassium deficiency in the soil. However, the effectiveness of potassium fertilizer application depends on the appropriate soil potassium levels in cotton fields.

Methods

This study used a randomized block design with six different soil potassium levels and conducted experiments across 18 micro-zones in the field. This study aimed to investigate the response of cotton yield and quality to different soil potassium levels, to try to clarify the suitable soil potassium levels for cotton growth, so as to provide practical and effective help for determining the amount of potash fertilizer in the cotton field.

Results

The results showed that the seedcotton yield was increasing, with the soil potassium level increased under no tillage. There was no significant difference among K4, K5, and K6 on seedcotton yield, which were significantly higher than K1 and K2. As soil potassium levels increased, the proportion of autumn boll and the proportion of outer boll also increased, indicating that higher soil potassium levels support the better growth and development of cotton in the middle and late stages, leading to increased boll sets and higher yields. Additionally, the available potassium content in the 0-40-cm soil layer was significantly correlated with yield and yield parameters but not with fiber quality indices.

Discussion

It is concluded that K4 treatment could provide sufficient potassium to meet the growth and development needs of cotton. Potassium fertilizer application is recommended when the available potassium content in the 0-40-cm soil layer falls below 122.88 mg kg-1 in the cotton field.

The tonoplast-localized OsTIP2;1 is involved in aluminum detoxification in rice

Aluminum (Al) stress is a significant issue in acidic soils, severely affecting crop growth and yield. Rice is notably resilient to Al toxicity, yet the internal tolerance mechanisms remain inadequately addressed. Here, we examined the role of OsTIP2;1, a tonoplast-bound intrinsic protein (TIP), in rice's internal Al detoxification. Our findings reveal that OsTIP2;1 expression was quickly and explicitly activated by Al ions in roots but not in shoots. The OsTIP2;1-GFP protein localizes to the tonoplast in plant and yeast cells. Non-functional ostip2;1 rice mutants were more vulnerable to Al toxicity. In the roots, the ostip2;1 mutants exhibited considerably lower levels of Al in the cell sap, primarily the vacuolar contents, than in the wild-type plant. Moreover, the ostip2;1 mutants showed reduced Al accumulation in the roots but increased translocation to the shoots. Heterologous expression of tonoplast-localized OsTIP2;1 in yeast led to enhanced Al tolerance, suggesting that OsTIP2;1 facilitates Al sequestration to the vacuole. These findings indicate that OsTIP2;1 mediates internal detoxification by transporting Al into the vacuole in the root and restricting its transport to above-ground tissues, thus contributing to Al resistance in rice.

Impacts of long-term chemical nitrogen fertilization on soil quality, crop yield, and greenhouse gas emissions: With insights into post-lime application responses

The improvement in the agricultural production through continuous and heavy nutrient input like nitrogen fertilizer under the upland red soil of south China deteriorates soil quality, and this practice in the future could threaten future food production and cause serious environmental problems in China. This research is initiated with the objectives of evaluating the impacts of long-term chemical nitrogen fertilization on soil quality, crop yield, and greenhouse gas emissions, with insights into post-lime application responses. Compared to sole application of chemical nitrogen fertilization, combined application with lime increased soil indicators (pH by 6.30 %-7.76 %, Ca2+ by 90.06 %-252.77 %, Mg2+ by 184.47 %-358.05 %, available P by 5.05 %-30.04 %, and soil alkali hydrolysable N by 23.49 %-41.55 %. Combined application of chemical nitrogen fertilization with lime (NPCa (0.59), NPKCa (0.61), and NKCa (0.27) significantly improved soil quality index compared to the sole application of chemical nitrogen fertilization (NP (0.31), NPK (0.36), and NK (0.16). Compared to sole application of chemical nitrogen fertilization, combined application with lime increased grain yield by 48.36 %-61.49 %. Structural equation modeling elucidated that combined application of chemical nitrogen fertilization and lime improved wheat grain yield by improving soil quality. Exchangeable Ca2+, exchangeable Mg2+, pH, and exchangeable Al3+ were the most influential factors of wheat grain yield. Overall, the combined application of chemical nitrogen fertilization and lime decreased global warming potential (calculated from N2O and CO2) by 16.92 % emissions compared to the sole application of chemical nitrogen fertilization. Therefore, liming acidic soil in upland red soil of South China is a promising management option for improved soil quality, wheat grain yield, and mitigation of greenhouse gas emissions.

Application of nano-urea in conventional flood-irrigated Boro rice in Bangladesh and nitrogen losses investigation

Bangladesh stands third in global rice production while complete modernization of rice production is not fully enforced. The boon of nano agriculture might circumvent the challenge of increasing the yield with minimal ecological damage. Nanofertilizer might be one of the solutions to address the problem of modern agriculture confronting environmental hazards owing to the excessive use of synthetic fertilizers by farmers in Bangladesh. We synthesized nanourea by chemical co-precipitation (CP) and hydrothermal (HT) methods in an attempt to develop environmentally friendly nanofertilizers. We characterized the nanourea and confirmed the functionalization of nanohydroxyapatite (nHAP) with urea by scanning transmission electron microscopy (STEM)/EDS mapping. The CP method produced particle dimensions of 45.62 nm for length and 14.16 nm for width. In comparison, the readings obtained through the HT method were around 74.69 nm and 20.44 nm for length and width, respectively. The field application of nanourea demonstrated impressive results, indicating a significant relationship between the particle size of nanourea and its impact on several agricultural factors. The grain yield using traditional synthetic fertilizer (urea) ranged from 6.47 to 6.52 t ha-1 with a very low NUE of 35.8-36.34 %. Contrarily, the grain yield was found from 6.52 to 6.84 t ha-1 and the obtained NUE ranged from 57.58 to 71.0 % using nanourea of the same concentration calibrated with traditional urea by two methods. Additionally, nanourea treatments having 25 % less nitrogen (N) provided higher total N (TN) in grain suggesting possible nutritional enrichment while checking the yield penalty and substantial increase in N use efficiency (NUE). However, further upscaling of this research on a field scale is necessary to confirm the findings.

Estimating thresholds of nitrogen, phosphorus and potassium fertilizer rates for rice cropping systems in China

Determining the fertilization rate plays a pivotal role in agronomic practices as they directly impact yield targets, soil fertility, and environmental risks. In this study, we proposed a method that utilizes allowed ranges of partial nutrient balance and yield to estimate the threshold of nitrogen (N), phosphorus (P), and potassium (K) fertilizer applied to rice (Oryza sativa L.) fields in China. Based on a dataset of 6792 observations from rice fields, we determined the minimum and maximum rates of N, P and K suggested for single (mono-season rice), middle (summer-season rice rotated with winter-season upland crop), early and late (double-season rice cropping system) rice, ranging between 114-146 and 220-292 kg N ha-1 per season, 56-74 and 112-149 kg P2O5 ha-1 per season, and 170-230 and 329-347 kg K2O ha-1 per season, respectively. These values serve as the lower and upper fertilization thresholds, guiding yield goals and environmental protection. Furthermore, if rice straw is returned to fields, the demand for K fertilizer can theoretically decrease by 183 kg K2O ha-1, with corresponding decreases of 50 kg N ha-1 and 26 kg P2O5 ha-1, respectively. A recommended fertilization approach, excluding returned straw nutrients from the upper fertilization thresholds, suggested average application rates of 194 kg N ha-1, 105 kg P2O5 ha-1, and 157 kg K2O ha-1, which align well with the nutrient requirements of rice. Additionally, substituting organic N for chemical N is an effective approach to conserve chemical fertilizer N, potentially reducing chemical N usage by 20%-40%. Utilizing slow-release N is also a favorable option to enhance N use efficiency and optimize N balance. This study offers valuable insights into the development of fertilization restriction indicators, aiming to achieve a delicate balance between environmental impact and agricultural productivity through the adoption of balanced fertilization rates and utilization of organic residues.

Nitrate Starvation Induces Lateral Root Organogenesis in Triticum aestivum via Auxin Signaling

The lateral root (LR) is an essential component of the plant root system, performing important functions for nutrient and water uptake in plants and playing a pivotal role in cereal crop productivity. Nitrate (NO3-) is an essential nutrient for plants. In this study, wheat plants were grown in 1/2 strength Hoagland's solution containing 5 mM NO3- (check; CK), 0.1 mM NO3- (low NO3-; LN), or 0.1 mM NO3- plus 60 mg/L 2,3,5-triiodobenzoic acid (TIBA) (LNT). The results showed that LN increased the LR number significantly at 48 h after treatment compared with CK, while not increasing the root biomass, and LNT significantly decreased the LR number and root biomass. The transcriptomic analysis showed that LN induced the expression of genes related to root IAA synthesis and transport and cell wall remodeling, and it was suppressed in the LNT conditions. A physiological assay revealed that the LN conditions increased the activity of IAA biosynthesis-related enzymes, the concentrations of tryptophan and IAA, and the activity of cell wall remodeling enzymes in the roots, whereas the content of polysaccharides in the LRP cell wall was significantly decreased compared with the control. Fourier-transform infrared spectroscopy and atomic microscopy revealed that the content of cell wall polysaccharides decreased and the cell wall elasticity of LR primordia (LRP) increased under the LN conditions. The effects of LN on IAA synthesis and polar transport, cell wall remodeling, and LR development were abolished when TIBA was applied. Our findings indicate that NO3- starvation may improve auxin homeostasis and the biological properties of the LRP cell wall and thus promote LR initiation, while TIBA addition dampens the effects of LN on auxin signaling, gene expression, physiological processes, and the root architecture.

Soil organic carbon regulation by pH in acidic red soil subjected to long-term liming and straw incorporation

The manipulation of soil pH through liming and straw incorporation plays a pivotal role in influencing soil organic carbon (SOC) dynamics in acidic red soil. This study aimed to assess the impact of these practices on SOC and elucidate the relationship between SOC and pH. Over a 31-year field experiment, seven different fertilization treatments were implemented: unfertilized (CK), nitrogen and potassium fertilizers (NK), NK with lime (NKCa), nitrogen, phosphorous, and potassium fertilizers (NPK), NPK with lime (NPKCa), NPK with straw (NPKS), and NPKS with lime (NPKSCa). Results revealed that liming and straw incorporation significantly elevated soil pH by 0.13-0.73 units. Lime application boosted SOC and mineral-associated organic carbon (MAOC) by 20.2% and 28.7%, respectively, in NK treatment, whereas its impact on SOC in NPK and NPKS treatments were negligible. SOC witnessed a 17.1% increase with NPKS and a 15.2% increase with NPKSCa compared to NPK alone. Notably, NPKS and NPKSCa led to a significant surge in particulate organic carbon (POC) by 19.7% and 37.7%, respectively, albeit NPKSCa reduced MAOC by 14.9% relative to NPK. Linear regression analysis unveiled a positive correlation between POC and soil pH, while SOC and MAOC exhibited an initial rise at lower pH levels followed by stabilization as pH continuously increasing. A partial least squares path model showed two pathways through which pH influenced SOC: firstly, by positively affecting SOC through increasing Fe and Al oxides contents and enhanced aggregate stability, and secondly, by negatively influencing SOC through altered ratios of fungi/bacteria and Gram-positive bacteria/Gram-negative bacteria. In conclusion, the long-term effects of lime and straw application on SOC and MAOC were contingent upon soil pH, with more pronounced positive effects observed at lower pH levels. These findings underscore the importance of considering soil pH when implementing lime and straw strategies to mitigate acidification and regulate SOC in acidic red soil.

Effects of co-application of biochar and nitrogen fertilizer on soil profile carbon and nitrogen stocks and their fractions in wheat field

Applying biochar to nitrogen (N)-fertilized soils is recognized as an effective technique for enhancing soil carbon (C) accumulation and improving agroecosystem sustainability. However, the impact of co-application of biochar and N fertilizer on soil C and N stocks, as well as their fractions, within the 0-60 cm soil profile remains unclear. This study examined the soil C and N fractions as well as stocks in soil profiles, and the primary influencing factors in wheat field with different rates of biochar (0, 20 and 40 t ha-1; B0, B1 and B2) and N application (0, 180 and 360 kg N ha-1; N0, N1 and N2). The results revealed that compared to B0N0 treatment, biochar plus N application increased soil organic carbon (SOC) and dissolved organic carbon (DOC), while N application alone decreased microbial biomass carbon (MBC). SOC in topsoil (0-10 cm) and DOC in subsoil (40-60 cm) were more susceptible to biochar and N application. The combined application of biochar and N enhanced soil N fractions, with NO3--N having the highest sensitivity than the other N fractions, whereas biochar application alone decreased topsoil inorganic N content. Biochar and N application significantly altered soil C stocks (4.33%-42.20%) and N stocks (-1.24%-20.91%) within the 0-60 cm soil layers, and belowground biomass and SOC were the main influencing factors, respectively. The combination of moderate biochar (42.35 t ha-1) and N (277.78 kg ha-1) application was the most beneficial for soil C accumulation in the 0-60 cm depth. These findings indicate the positive impacts of co-applying of biochar and N in agroecosystems on soil C and N accumulations, and highlight the importance of C and N stabilization in both topsoil and subsoil under management practice.

Ryegrass uptake behavior and forage risk assessment after exposing to soil with combined polycyclic aromatic hydrocarbons and cadmium

Internalization of chemicals and the forage risks of ryegrass under the combined exposure to PAHs and Cd at environmental concentrations were studied here. The effect of soil pH was also concerned due to the widely occurred soil acidification and general alkali remediation for acidification soil. Unexpectedly, as same as the acid-treated group (pH 6.77), the alkali-treatment (pH 8.83) increased Cd uptake compared with original soil pH group (pH 7.92) for the reason of CdOH+ and CdHCO3+ formed in alkali-treated group. Co-exposure to PAHs induced more oxidative stress than Cd exposure alone due to PAHs aggregated in young root regions, such as root tips, and consequently, affecting the expression of Cd-transporters, destroying the basic structure of plant cells, inhibiting the energy supply for the transporters, even triggering programmed cell death, and finally resulting in decreased Cd uptake. Even under environmental concentrations, combined exposure caused potential risks derived from both PAHs and Cd. Especially, ryegrass grown in alkali-treated soil experienced an increased forage risks despite the soil meeting the national standards for Cd at safe levels. These comprehensive results reveal the mechanism of PAHs inhibiting Cd uptake, improve the understanding of bioavailability of Cd based on different forms, provide a theoretical basis to formulate the safety criteria, and guide the application of actual soil management.

Soil pH amendment alters the abundance, diversity, and composition of microbial communities in two contrasting agricultural soils

Soil microorganisms are the most active participants in terrestrial ecosystems, and have key roles in biogeochemical cycles and ecosystem functions. Despite the extensive research on soil pH as a key predictor of microbial community and composition, a limitation of these studies lies in determining whether bacterial and/or fungal communities are directly or indirectly influenced by pH. We conducted a controlled laboratory experiment to investigate the effects of soil pH amendment (+/- 1-2 units) with six levels on soil microbial communities in two contrasting Chinese agricultural soils (pH 8.43 in Dezhou, located in the North China Plain, Shandong vs pH 6.17 in Wuxi, located in the Taihu Lake region, Jiangsu, east China). Results showed that the fungal diversity and composition were related to soil pH, but the effects were much lower than the effects of soil pH on bacterial community in two soils. The diversity and composition of bacterial communities were more closely associated with soil pH in Wuxi soils compared to Dezhou soils. The alpha diversity of bacterial communities peaked near in situ pH levels in both soils, displaying a quadratic fitting pattern. Redundancy analysis and variation partition analysis indicated that soil pH affected bacterial community and composition by directly imposing a physiological constraint on soil bacteria and indirectly altering soil characteristics (e.g., nutrient availability). The study also examined complete curves of taxa relative abundances at the phylum and family levels in response to soil pH, with most relationships conforming to a quadratic fitting pattern, indicating soil pH is a reliable predictor. Furthermore, soil pH amendment affected the transformation of nitrogen and the abundances of functional genes involved in the nitrogen cycle, and methane production and consumption. Overall, results from this study would enhance our comprehension of how soil microorganisms in contrasting farmlands will respond to soil pH changes, and would contribute to more effective soil management and conservation strategies.

IMPORTANCE

This study delves into the impact of soil pH on microbial communities, investigating whether pH directly or indirectly influences bacterial and fungal communities. The research involved two contrasting soils subjected to a 1-2 pH unit amendment. Results indicate bacterial community composition was shaped by soil pH through physiological constraints and nutrient limitations. We found that most taxa relative abundances at the phylum and family levels responded to pH with a quadratic fitting pattern, indicating that soil pH is a reliable predictor. Additionally, soil pH was found to significantly influence the predicted abundance of functional genes involved in the nitrogen cycle as well as in methane production and consumption processes. These insights can contribute to develop more effective soil management and conservation strategies.

Deep Eutectic Solvents for Extraction and Preconcentration of Organic and Inorganic Species in Water and Food Samples: A Review

Deep eutectic solvents (DESs) have been developed as green solvents and these are capable as alternatives to conventional solvents used for the extraction of organic and inorganic species from food and water samples. The continuous generation of contaminated waste and increasing concern for the human health and environment have compelled the scientific community to investigate more ecological schemes. In this concern, the use of DESs have developed in one of the chief approach in the field of chemistry. These solvents have appeared as a capable substitute to conventional hazardous solvents and ionic liquids. The DESs has distinctive properties, easy preparation and components availability. It is not only used in scienctific fields but also used in quotidian life. There are many advantages of DESs in analytical chemistry, they are largely used for extraction and determination of inorganic and organic compounds from different samples. In previous a few years, several advanced researches have been focused on the separation and preconcentration of low level of pollutants using DESs as the extractants. This review summarizes the use of DESs in the separation and preconcentration of organic and inorganic species from water and food samples using various microextraction processes.

Effects of humic acid fertilizer on the growth and microbial network stability of Panax notoginseng from the forest understorey

Humic acid (HA) can substantially enhance plant growth and improve soil health. Currently, the impacts of HA concentrations variation on the development and soil quality of Panax notoginseng (Sanqi) from the forest understorey are still unclear. In this study, exogenous HA was administered to the roots of Sanqi at varying concentrations (2, 4, and 6 ml/L). Subsequently, the diversity and community structure of bacteria and fungi were assessed through high-throughput sequencing technology. The investigation further involved analyzing the interplay among the growth of sanqi, soil edaphic factors, and the microbial network stability. Our finding revealed that moderate concentrations (4 ml/L) of HA improved the fresh/dry weight of Sanqi and NO3--N levels. Compared with control, the moderate concentrations of HA had a notable impact on the bacterial and fungal communities compositions. However, there was no significant difference in the α and β diversity of bacteria and fungi. Moreover, the abundance of beneficial bacteria (Bradyrhizobium) and harmful bacteria (Xanthobacteraceae) increased and decreased at 4 ml/L HA, respectively, while the bacterial and fungal network stability were enhanced. Structural equation model (SEM) revealed that the fresh weight of Sanqi and bacterial and fungal communities were the factors that directly affected the microbial network stability at moderate concentrations of HA. In conclusion, 4 ml/L of HA is beneficial for promoting Sanqi growth and soil quality. Our study provides a reference for increasing the yield of Sanqi and sustainable development of the Sanqi-pine agroforestry system.

QTL Mapping of Yield, Agronomic, and Nitrogen-Related Traits in Barley (Hordeum vulgare L.) under Low Nitrogen and Normal Nitrogen Treatments

Improving low nitrogen (LN) tolerance in barley (Hordeum vulgare L.) increases global barley yield and quality. In this study, a recombinant inbred line (RIL) population crossed between "Baudin × CN4079" was used to conduct field experiments on twenty traits of barley yield, agronomy, and nitrogen(N)-related traits under LN and normal nitrogen (NN) treatments for two years. This study identified seventeen QTL, comprising eight QTL expressed under both LN and NN treatments, eight LN-specific QTL, and one NN-specific QTL. The localized C2 cluster contained QTL controlling yield, agronomic, and N-related traits. Of the four novel QTL, the expression of the N-related QTL Qstna.sau-5H and Qnhi.sau-5H was unaffected by N treatment. Qtgw.sau-2H for thousand-grain weight, Qph.sau-3H for plant height, Qsl.sau-7H for spike length, and Qal.sau-7H for awn length were identified to be the four stable expression QTL. Correlation studies revealed a significant negative correlation between grain N content and harvest index (p < 0.01). These results are essential for barley marker-assisted selection (MAS) breeding.

Nitrogen fertilizer application rate affects the dynamic metabolism of nitrogen and carbohydrates in kernels of waxy maize

Introduction

Nitrogen (N) plays a pivotal role in the growth, development, and yield of maize. An optimal N application rate is crucial for enhancing N and carbohydrate (C) accumulation in waxy maize grains, which in turn synergistically improves grain weight.

Methods

A 2-year field experiment was conducted to evaluate the impact of different N application rates on two waxy maize varieties, Jinnuo20 (JN20) and Jindannuo41 (JDN41), during various grain filling stages. The applied N rates were 0 (N0), 120 (N1), 240 (N2), and 360 (N3) kg N ha-1.

Results

The study revealed that N application significantly influenced nitrogen accumulation, protein components (gliadin, albumin, globulin, and glutelin), carbohydrate contents (soluble sugars, amylose, and amylopectin), and activities of enzymes related to N and C metabolism in waxy maize grains. Notable varietal differences in these parameters were observed. In both varieties, the N2 treatment consistently resulted in the highest values for almost all measured traits compared to the other N treatments. Specifically, the N2 treatment yielded an average increase in grain dry matter of 21.78% for JN20 and 17.11% for JDN41 compared to N0. The application of N positively influenced the activities of enzymes involved in C and N metabolism, enhancing the biosynthesis of grain protein, amylose, and amylopectin while decreasing the accumulation of soluble sugars. This modulation of the C/N ratio in the grains directly contributed to an increase in grain dry weight.

Conclusion

Collectively, our findings underscore the critical role of N in regulating kernel N and C metabolism, thereby influencing dry matter accumulation in waxy maize grains during the grain filling stage.

Cadmium Minimization in Grains of Maize and Wheat Grown on Smelting-Impacted Land Ameliorated by Limestone

Cadmium (Cd) contamination in agricultural soils has emerged as a significant concern, particularly due to its potential impact on plant-based food. Soil pH reductions can exacerbate Cd mobility, leading to excessive accumulation in crops. While liming has been demonstrated as an effective method to mitigate Cd accumulation in rice grains in acid soils of southern China, its efficacy in remediating acid soils in northern China remains unclear. In this study, a multi-year field experiment was conducted on farmland impacted by zinc ore smelting at coordinates of 33.92° N 112.46° E to investigate the use of limestone for controlling Cd accumulation in wheat and maize grains. The results indicated that applying 7.5 t ha-1 of limestone significantly raised the soil pH from 4.5 to 6.8 as anticipated. Different rates of limestone application (2.25, 4.45, and 7.50 t ha-1) reduced Cd bioavailability in the soil by 20-54%, and Cd accumulation in wheat grains by 5-38% and maize grains by 21-63%, without yield penalty. The remediation effects were sustained for at least 27 months, highlighting limestone as a promising ameliorant for smelting-affected farmland in northern China.

The contribution of natural and anthropogenic causes to soil acidification rates under different fertilization practices and site conditions in southern China

Excessive application of mineral fertilizers has accelerated soil acidification in China, affecting crop production when the pH drops below a critical value. However, the contributions of natural soil acidification, induced by leaching of bicarbonate, and anthropogenic causes of soil acidification, induced by nitrogen (N) transformations and removal of base cations over acid anions, are not well quantified. In this study, we quantified soil acidification rates, in equivalents (eq) of acidity, by assessing the inputs and outputs of all major cations and anions, including calcium, magnesium, potassium, sodium, ammonium, nitrate, bicarbonate, sulphate, phosphate and chloride, for 13 long-term experimental sites in southern China. The acidification rates strongly varied among fertilizer treatments and with the addition of animal manure. Bicarbonate leaching was the dominant acid production process in calcareous soils (23 keq ha-1 yr-1) and in non-calcareous paddy soils (9.6 keq ha-1 yr-1), accounting for 80 % and 68 % of the total acid production rate, respectively. The calcareous soils were strongly buffered, and acidification led no or a limited decline in pH. In contrast, N transformations were the most important driver for soil acidification at one site with upland crops on a non-calcareous soil, accounting for 72 % of total acid production rate of 8.4 keq ha-1 yr-1. In this soil, the soil pH considerably decreased being accompanied by a substantial decline in exchangeable base cation. Reducing the N surplus decreased the acidification rate with 10 to 54 eq per kg N surplus with the lowest value occurring in paddy soils and the highest in the upland soil. The use of manure, containing base cations, partly mitigated the acidifying impact of N fertilizer inputs and crop removal, but enhanced phosphorus (P) accumulation. Combining mineral fertilizer, manure and lime in integrative management strategies can mitigate soil acidification and minimize N and P losses.

Biochar boosted high oleic peanut production with enhanced root development and biological N fixation by diazotrophs in a sand-loamy Primisol

Peanut yield and quality face significant threats due to climate change and soil degradation. The potential of biochar technology to address this challenge remains unanswered, though biochar is acknowledged for its capacity to enhance the soil microbial community and plant nitrogen (N) supply. A field study was conducted in 2021 on oil peanuts grown in a sand-loamy Primisol that received organic amendments at 20 Mg ha-1. The treatments consisted of biochar amendments derived from poultry manure (PB), rice husk (RB), and maize residue (MB), as well as manure compost (OM) amendment, compared to no organic amendment (CK). In 2022, during the second year after amendment, samples of bulk topsoil, rooted soil, and plants were collected at the peanut harvest. The analysis included the assessment of soil quality, peanut growth traits, microbial community, nifH gene abundance, and biological N fixation (BNF) rate. Compared to the CK, the OM treatment led to an 8 % increase in peanut kernel yield, but had no effect on kernel quality in terms of oil production. Conversely, both PB and MB treatments increased kernel yield by 10 %, whereas RB treatment showed no change in yield. Moreover, all biochar amendments significantly improved oilseed quality by 10-25 %, notably increasing the proportion of oleic acid by up to 70 %. Similarly, while OM amendment slightly decreased root development, all biochar treatments significantly enhanced root development by over 80 %. Furthermore, nodule number, fresh weight per plant, and the nifH gene abundance in rooted soil remained unchanged under OM and PB treatments but was significantly enhanced under RB and MB treatments compared to CK. Notably, all biochar amendments, excluding OM, increased the BNF rate and N-acetyl-glucosaminidase activity. These changes were attributed to alterations in soil aggregation, moisture retention, and phosphorus availability, which were influenced by the diverse physical and chemical properties of biochars. Overall, maize residue biochar contributed synergistically to enhancing soil fertility, peanut yield, and quality while also promoting increased root development, a shift in the diazotrophic community and BNF.

Strigolactones alleviate AlCl3 stress by vacuolar compartmentalization and cell wall blocking in apple

Poor management and excess fertilization of apple (Malus domestica Borkh.) orchards are causing increasingly serious soil acidification, resulting in Al toxicity and direct poisoning of roots. Strigolactones (SLs) are reported to be involved in plant responses to abiotic stress, but their role and mechanism under AlCl3 stress remain unknown. Here, we found that applying 1 μm GR24 (an SL analoge) significantly alleviated AlCl3 stress of M26 apple rootstock, mainly by blocking the movement of Al through cell wall and by vacuolar compartmentalization of Al. RNA-seq analysis identified the core transcription factor gene MdWRKY53, and overexpressing MdWRKY53 enhanced AlCl3 tolerance in transgenic apple plants through the same mechanism as GR24. Subsequently, we identified MdPMEI45 (encoding pectin methylesterase inhibitor) and MdALS3 (encoding an Al transporter) as downstream target genes of MdWRKY53 using chromatin immunoprecipitation followed by sequencing (ChIP-seq). GR24 enhanced the interaction between MdWRKY53 and the transcription factor MdTCP15, further increasing the binding of MdWRKY53 to the MdPMEI45 promoter and inducing MdPMEI45 expression to prevent Al from crossing cell wall. MdWRKY53 also bound to the promoter of MdALS3 and enhanced its transcription to compartmentalize Al in vacuoles under AlCl3 stress. We therefore identified two modules involved in alleviating AlCl3 stress in woody plant apple: the SL-WRKY+TCP-PMEI module required for excluding external Al by blocking the entry of Al3+ into cells and the SL-WRKY-ALS module allowing internal detoxification of Al through vacuolar compartmentalization. These findings lay a foundation for the practical application of SLs in agriculture.

Unraveling nitrogen loss in paddy soils: A study of anaerobic nitrogen transformation in response to various irrigation practice

Soil nitrogen (N) transformation processes, encompassing denitrification, anaerobic ammonium oxidation (anammox), and anaerobic ammonium oxidation coupled with iron reduction (Feammox), constitute the primary mechanisms of soil dinitrogen (N2) loss. Despite the significance of these processes, there is a notable gap in research regarding the assessment of managed fertilization and irrigation impacts on anaerobic N transformations in paddy soil, crucial for achieving sustainable soil fertility management. This study addressed the gap by investigating the contributions of soil denitrification, anammox, and Feammox to N2 loss in paddy soil across varying soil depths, employing different fertilization and irrigation practices by utilizing N stable isotope technique for comprehensive insights. The results showed that anaerobic N transformation processes decreased with increasing soil depth under alternate wetting and drying (AWD) irrigation, but increased with the increasing soil depth under conventional continuous flooding (CF) irrigation. The denitrification and anammox rates varied from 0.41 to 2.12 mg N kg-1 d-1 and 0.062-0.394 mg N kg-1 d-1, respectively, which accounted for 84.3-88.1% and 11.8-15.7% of the total soil N2 loss. Significant correlations were found among denitrification rate and anammox rate (r = 0.986, p < 0.01), Fe (Ⅲ) reduction rate and denitrification rate (r = 0.527, p < 0.05), and Fe(Ⅲ) reduction rate and anammox rate (r = 0.622, p < 0.05). Moreover, nitrogen loss was more pronounced in the surface layer of the paddy soil compared to the deep layer. The study revealed that denitrification predominantly contributed to N loss in the surface soil, while Feammox emerged as a significant N loss pathway at depths ranging from 20 to 40 cm, accounting for up to 26.1% of the N loss. It was concluded that fertilization, irrigation, and soil depth significantly influenced anaerobic N transformation processes. In addition, the CF irrigation practice is best option to reduce N loss under managed fertilization. Furthermore, the role of microbial communities and their response to varying soil depths, fertilization practices, and irrigation methods could enhance our understanding on nitrogen loss pathways should be explored in future study.

Soil quality and ecosystem multifunctionality after 13-year of organic and nitrogen fertilization

Organic and mineral fertilization increase crop productivity, but their combined effects on soil quality index (SQI) and ecosystem multifunctionality (EMF, defined as the capacity of soils to simultaneously provide multiple functions and services) are not clear. We conducted a 13-year field trial in North China Plain to examine how five maize-derived organic fertilizers (straw, manure, compost, biogas residue, and biochar) at equal C input rate (3.2 t C ha-1), with or without nitrogen (N) fertilization influenced topsoil (0-15 cm) physico-chemical properties, activities of enzymes responsible for carbon (C), N, and phosphorus (P) cycling, as well as SQI and soil EMF. Organic fertilizers with or without N increased SQI by 51-187 % and EMF by 31-351 % through the enhancement of soil physical (mean weight diameter of soil aggregates) and chemical properties (C, N, and P contents) as well as C, N, and P acquisition enzyme activities, albeit the biochar effects were of minor importance. N application increased EMF compared to soil without N. Soil quality increased with EMF. Random forest analysis revealed that microbial biomass C and N, available P, permanganate oxidizable C, dissolved organic C and N, mean weight diameter of aggregates, hot water extractable C, and electrical conductivity were the main contributions to soil EMF. We conclude that application of maize-derived organic fertilizers, especially compost and straw, with optimal N fertilization is a plausible strategy to increase SQI and EMF under a wheat/maize system.

Soil Acidification Can Be Improved under Different Long-Term Fertilization Regimes in a Sweetpotato-Wheat Rotation System

Soil acidification is a significant form of agricultural soil degradation, which is accelerated by irrational fertilizer application. Sweetpotato and wheat rotation has emerged as an important rotation system and an effective strategy to optimize nutrient cycling and enhance soil fertility in hilly areas, which is also a good option to improve soil acidification and raise soil quality. Studying the effects of different fertilization regimes on soil acidification provides crucial data for managing it effectively. An eight-year field experiment explored seven fertilizer treatments: without fertilization (CK), phosphorus (P) and potassium (K) fertilization (PK), nitrogen (N) and K fertilization (NK), NP fertilization (NP), NP with K chloride fertilization (NPK1), NP with K sulfate fertilization (NPK2), and NPK combined with organic fertilization (NPKM). This study focused on the soil acidity, buffering capacity, and related indicators. After eight years of continuous fertilization in the sweetpotato-wheat rotation, all the treatments accelerated the soil acidification. Notably, N fertilization reduced the soil pH by 1.30-1.84, whereas N-deficient soil showed minimal change. Organic fertilizer addition resulted in the slowest pH reduction among the N treatments. Both N-deficient (PK) and organic fertilizer addition (NPKM) significantly increased the soil cation exchange capacity (CEC) by 8.83% and 6.55%, respectively, compared to CK. Similar trends were observed for the soil-buffering capacity (pHBC). NPK2 increased the soil K+ content more effectively than NPK1. NPKM reduced the sodium and magnesium content compared to CK, with the highest magnesium content among the treatments at 1.60 cmol·kg-1. Regression tree analysis identified the N input and soil magnesium and calcium content as the primary factors influencing the pHBC changes. Structural equation modeling showed that the soil pH is mainly influenced by the soil ammonium N content and pHBC, with coefficients of -0.28 and 0.29, respectively. Changes in the soil pH in the sweetpotato-wheat rotation were primarily associated with the pHBC and N input, where the CEC content emerged as the main factor, modulated by magnesium and calcium. Long-term organic fertilization enhances the soil pHBC and CEC, slowing the magnesium reduction and mitigating soil acidification in agricultural settings.

Soil conditioner improves soil properties, regulates microbial communities, and increases yield and quality of Uncaria rhynchophylla

Uncaria rhynchophylla is an important traditional herbal medicine in China, and the yield and quality of Uncaria rhynchophylla can be improved by suitable soil conditioners because of changing the soil properties. In this paper, Uncaria rhynchophylla associated alkaloids and soil microbial  communities were investigated. The field experiment was set up with the following control group: (M1, no soil conditioner) and different soil conditioner treatment groups (M2, biomass ash; M3, water retention agent; M4, biochar; M5, lime powder and M6, malic acid). The results showed that M2 significantly increased the fresh and dry weight and the contents of isorhynchophylline, corynoxeine, isocorynoxeine, and total alkaloids. Acidobacteria, Proteobacteria, Actinobacteria, and Chloroflexi were major bacterial phyla. Correlation analysis showed that fresh and dry weight was significantly positively correlated with Acidobacteria, while alkali-hydrolyzable nitrogen, phosphatase activity, fresh and dry weight, corynoxeine, and isocorynoxeine were significantly negatively correlated with Chloroflexi. The application of soil conditioner M2 increased the abundance of Acidobacteria and decreased the abundance of Chloroflexi, which contributed to improving the soil nutrient content, yield, and quality of Uncaria rhynchophylla. In summary, biomass ash may be a better choice of soil conditioner in Uncaria rhynchophylla growing areas.

Quantifying the bioaccumulation and trophic transfer processes of heavy metals based on the food web: A case study from freshwater wetland in northeast China

The contamination of wetlands by heavy metals, exacerbated by agricultural activities, presents a threat to both organisms and humans. Heavy metals may undergo trophic transfer through the food web. However, the methods for quantifying the bioaccumulation and trophic transfer processes of heavy metals based on the food web remains unclear. In this study, we employed stable isotope technology to construct a quantitative oriental white stork's typical food web model under a more accurate scaled Δ15N framework. On this basis, the concentrations for heavy metal (Cu, Zn, Hg, Pb) were analyzed, we innovatively visualized the trophic transfer process of heavy metals across 13 nodes and 45 links and quantified the transfer flux based on the diet proportions and heavy metal concentrations of species, taking into account biomagnification effects and potential risks. Our findings revealed that as for Cu and Pb, the transfer flux level was consistent with diet proportion across most links. While Hg and Zn transfer flux level exceeded the corresponding diet proportion in the majority of links. In summary, Hg exhibited a significant biomagnification, whereas Cu, Zn, Pb experienced biodilution. The fish dietary health risk assessment for fish consumers showed that Hg, Pb posed certain risks. This research marks a significant step forward in the quantitative assessment of multi-link networks involving heavy metals within the food web.

The Physiological Response Mechanism of Peanut Leaves under Al Stress

Aluminum (Al) toxicity in acidic soils can significantly reduce peanut yield. The physiological response of peanut leaves to Al poisoning stress still has not been fully explored. This research examined the influences of Al toxicity on peanut leaves by observing the leaf phenotype, scanning the leaf area and perimeter, and by measuring photosynthetic pigment content, physiological response indices, leaf hormone levels, and mineral element accumulation. Fluorescence quantitative RT-PCR (qPCR) was utilized to determine the relative transcript level of specific genes. The results indicated that Al toxicity hindered peanut leaf development, reducing their biomass, surface area, and perimeter, although the decrease in photosynthetic pigment content was minimal. Al toxicity notably affected the activity of antioxidative enzymes, proline content, and MDA (malondialdehyde) levels in the leaves. Additionally, Al poisoning resulted in the increased accumulation of iron (Fe), potassium (K), and Al in peanut leaves but reduced the levels of calcium (Ca), manganese (Mn), copper (Cu), zinc (Zn), and magnesium (Mg). There were significant changes in the content of hormones and the expression level of genes connected with hormones in peanut leaves. High Al concentrations may activate cellular defense mechanisms, enhancing antioxidative activity to mitigate excess reactive oxygen species (ROS) and affecting hormone-related gene expression, which may impede leaf biomass and development. This research aimed to elucidate the physiological response mechanisms of peanut leaves to Al poisoning stress, providing insights for breeding new varieties resistant to Al poisoning.

Soil organic matter and total nitrogen as key driving factors promoting the assessment of acid-base buffering characteristics in a tea (Camellia sinensis) plantation habitat

The issue of soil acidification in tea plantations has become a critical concern due to its potential impact on tea quality and plant health. Understanding the factors contributing to soil acidification is essential for implementing effective soil management strategies in tea-growing regions. In this study, a field study was conducted to investigate the effects of tea plantations on soil acidification and the associated acid-base buffering capacity (pHBC). We assessed acidification, pHBC, nutrient concentrations, and cation contents in the top 0-20 cm layer of soil across forty tea gardens of varying stand ages (0-5, 5-10, 10-20, and 20-40 years old) in Anji County, Zhejiang Province, China. The results revealed evident soil acidification due to tea plantation activities, with the lowest soil pH observed in tea gardens aged 10-20 and 20-40 years. Higher levels of soil organic matter (SOM), total nitrogen (TN), Olsen phosphorus (Olsen-P), available iron (Fe), and exchangeable hydrogen (H+) were notably recorded in 10-20 and 20-40 years old tea garden soils, suggesting an increased risk of soil acidification with prolonged tea cultivation. Furthermore, prolonged tea cultivation correlated with increased pHBC, which amplified with tea stand ages. The investigation of the relationship between soil pHBC and various parameters highlighted significant influences from soil pH, SOM, cation exchange capacity, TN, available potassium, Olsen-P, exchangeable acids (including H+ and aluminum), available Fe, and available zinc. Consequently, these findings underscore a substantial risk of soil acidification in tea gardens within the monitored region, with SOM and TN content being key driving factors influencing pHBC.

Pathways of soil organic carbon accumulation are related to microbial life history strategies in fertilized agroecosystems

Although the formation, turnover, and accumulation of soil organic carbon (SOC) are driven by different fertilizer inputs and their subsequent microbial-mediated transformation, the relationship between changes in plant-derived and microbial-derived components and soil microbial life history strategies under different fertilization regimes has not been well explored. In this study, the changes in microbial necromass carbon (MNC), lignin phenols, and glomalin-related soil protein (GRSP), as well as soil microbial life history strategy were determined in a 16-year field experiment in response to different fertilization regimes, including a no-fertilizer control (C), conventional chemical NPK fertilization (NPK), and partial substitutions of the NPK in chemical fertilizers with a low (30 %) or high (60 %) level of straw (0.3S and 0.6S) or cattle manure (0.3M and 0.6M). The results showed that total lignin phenol content and its contribution to SOC were significantly increased by 88.7 % and 74.2 %, respectively, in high-level straw substitution treatment as compared to chemical fertilization. Both high-level straw and cattle manure substitution increased MNC and total GRSP contents, but did not alter their contributions to SOC compared to chemical fertilization. In fertilized treatments, the high-level cattle manure substitution had the lowest and highest bacterial and fungal K/r ratio, respectively. Bacterial K/r ratio was an important factor in predicting bacterial necromass carbon content and there was a significant negative correlation between them. The ratio of ectomycorrhizal to saprotrophic fungi and fungal diversity were important factors for predicting lignin phenol and GRSP contents, respectively. In addition, the SEMs modeling indicated that straw substitution directly affected lignin phenol and MNC accumulation, whereas cattle manure substitution indirectly affected MNC accumulation by affecting microbial life history strategies. In conclusions, agricultural residues inputs support the formation of a multiple carbon pool of SOC compared to chemical fertilization; and microbial life history strategy is an important driver of SOC formation and affects SOC accumulation and stability in agroecosystems.

AcEXPA1, an α-expansin gene, participates in the aluminum tolerance of carpetgrass (Axonopus compressus) through root growth regulation

KEY MESSAGE

AcEXPA1, an aluminum (Al)-inducible expansin gene, is demonstrated to be involved in carpetgrass (Axonopus compressus) root elongation under Al toxicity through analyzing composite carpetgrass plants overexpressing AcEXPA1. Aluminum (Al) toxicity is a major mineral toxicity that limits plant productivity in acidic soils by inhibiting root growth. Carpetgrass (Axonopus compressus), a dominant warm-season turfgrass widely grown in acidic tropical soils, exhibits superior adaptability to Al toxicity. However, the mechanisms underlying its Al tolerance are largely unclear, and knowledge of the functional genes involved in Al detoxification in this turfgrass is limited. In this study, phenotypic variation in Al tolerance, as indicated by relative root elongation, was observed among seventeen carpetgrass genotypes. Al-responsive genes related to cell wall modification were identified in the roots of the Al-tolerant genotype 'A58' via transcriptome analysis. Among them, a gene encoding α-expansin was cloned and designated AcEXPA1 for functional characterization. Observed Al dose effects and temporal responses revealed that Al induced AcEXPA1 expression in carpetgrass roots. Subsequently, an efficient and convenient Agrobacterium rhizogenes-mediated transformation method was established to generate composite carpetgrass plants with transgenic hairy roots for investigating AcEXPA1 involvement in carpetgrass root growth under Al toxicity. AcEXPA1 was successfully overexpressed in the transgenic hairy roots, and AcEXPA1 overexpression enhanced Al tolerance in composite carpetgrass plants through a decrease in Al-induced root growth inhibition. Taken together, these findings suggest that AcEXPA1 contributes to Al tolerance in carpetgrass via root growth regulation.

Wood ash application for crop production, amelioration of soil acidity and contaminated environments

Agriculture is vital to human life and economic development even though it may have a detrimental influence on soil quality. Agricultural activities can deteriorate the soil quality, endangers the ecosystem health and functioning, food safety, and human health. To resolve the problem of soil degradation, alternative soil conditioners such as wood ash are being explored for their potential to improve soil-plant systems. This study provides an overview of the production, properties, and effects of wood ash on soil properties, crop productivity, and environmental remediation. A comprehensive search of relevant databases was conducted in order to locate and assess original research publications on the use of wood ash in agricultural and environmental management. According to the findings, wood ash, a byproduct of burning wood, may improve the structure, water-holding capacity, nutrient availability, and buffering capacity of soil as well as other physico-chemical, and biological attributes of soil. Wood ash has also been shown to increase agricultural crop yields and help with the remediation of polluted regions. Wood ash treatment, however, has been linked to several adverse effects, such as increased trace element concentrations and altered microbial activity. The examination found that wood ash could be a promising material to be used as soil conditioner and an alternative supply of nutrients for agricultural soils, while, wood ash contributes to soil improvement and environmental remediation, highlighting its potential as a sustainable solution for addressing soil degradation and promoting environmental sustainability in agricultural systems.

Physiological and molecular mechanisms of plant-root responses to iron toxicity

The chemical form and physiological activity of iron (Fe) in soil are dependent on soil pH and redox potential (Eh), and Fe levels in soils are frequently elevated to the point of causing Fe toxicity in plants, with inhibition of normal physiological activities and of growth and development. In this review, we describe how iron toxicity triggers important physiological changes, including nitric-oxide (NO)-mediated potassium (K+) efflux at the tips of roots and accumulation of reactive oxygen species (ROS) and reactive nitrogen (RNS) in roots, resulting in physiological stress. We focus on the root system, as the first point of contact with Fe in soil, and describe the key processes engaged in Fe transport, distribution, binding, and other mechanisms that are drawn upon to defend against high-Fe stress. We describe the root-system regulation of key physiological processes and of morphological development through signaling substances such as ethylene, auxin, reactive oxygen species, and nitric oxide, and discuss gene-expression responses under high Fe. We especially focus on studies on the physiological and molecular mechanisms in rice and Arabidopsis under high Fe, hoping to provide a valuable theoretical basis for improving the ability of crop roots to adapt to soil Fe toxicity.

Distinct effects of canopy vs understory and organic vs inorganic N deposition on root resource acquisition strategies of subtropical Moso bamboo plants

Atmospheric nitrogen (N) deposition inevitably alters soil nutrient status, subsequently prompting plants to modify their root morphology (i.e., adopting a do-it-yourself strategy), mycorrhizal symbioses (i.e., outsourcing strategy), and root exudation (i.e., nutrient-mining strategy) linking with resource acquisition. However, how N deposition influences the integrated pattern of these resource-acquisition strategies remains unclear. Furthermore, most studies in forest ecosystems have focused on understory N and inorganic N deposition, neglecting canopy-associated processes (e.g., N interception and assimilation) and the impacts of organic N on root functional traits. In this study, we compared the effects of canopy vs understory, organic vs inorganic N deposition on eight root functional traits of Moso bamboo plants. Our results showed that N deposition significantly decreased arbuscular mycorrhizal fungi (AMF) colonization, altered root exudation rate and root foraging traits (branching intensity, specific root area, and length), but did not influence root tissue density and N concentration. Moreover, the impacts of N deposition on root functional traits varied significantly with deposition approach (canopy vs. understory), form (organic vs. inorganic), and their interaction, showing variations in both intensity and direction (positive/negative). Furthermore, specific root area and length were positively correlated with AMF colonization under canopy N deposition and root exudation rate in understory N deposition. Root trait variation under understory N deposition, but not under canopy N deposition, was classified into the collaboration gradient and the conservation gradient. These findings imply that coordination of nutrient-acquisition strategies dependent on N deposition approach. Overall, this study provides a holistic understanding of the impacts of N deposition on root resource-acquisition strategies. Our results indicate that the evaluation of N deposition on fine roots in forest ecosystems might be biased if N is added understory.

Nitrogen management indicators for sustainable crop production in an intensive potato system under drip irrigation

Reliable nitrogen (N) fertilizer management indicators are essential for improving crop yields and minimizing environmental impacts for sustainable production. The objectives of this study were to assess the importance of major N management indicators (NMIs) for higher yield with low risks of environmental pollution in an intensive potato system under drip irrigation. Six drip-irrigated field experiments with no N application (Control), farmer practice (FP), and optimized N management (OM) based on N-balance, soil mineral N (Nmin), and target yield were conducted from 2018 to 2020 in Inner Mongolia, China. The response of NMIs to potato yield and yield-based environment impact indices (EIY) was evaluated by the random forest algorithm. The N input, N losses from N leaching, ammonia (NH3) volatilization, nitrous oxide (N2O) emission, N use efficiency (NUE), N surplus, and soil residual N after harvest were obtained to identify the best NMIs for high yield and minimal ecological impact. The N management practices in field experimental sites affected the importance of the order of NMIs on potato yield and EIY. The NUE and N leaching were identified as the highest importance scores and the most essential controlling variables to potato yield and EIY, respectively. The integrated NUE and N leaching indicator played a vital role in improving potato yield and reducing ecological impact. The OM treatment achieved 46.0%, 63.6%, and 64.6% lower in N application rate, N surplus, and reactive N loss, and 62.4% higher in NUE than the FP treatment while achieving equal potato yields, respectively. Those key NMIs can guide farmers in understanding their practice short comes to achieve both high productivity and environmental sustainability in intensive potato production systems under drip irrigation.

Reducing Soil-Emitted Nitrous Acid as a Feasible Strategy for Tackling Ozone Pollution

Severe ozone (O3) pollution has been a major air quality issue and affects environmental sustainability in China. Conventional mitigation strategies focusing on reducing volatile organic compounds and nitrogen oxides (NOx) remain complex and challenging. Here, through field flux measurements and laboratory simulations, we observe substantial nitrous acid (HONO) emissions (FHONO) enhanced by nitrogen fertilizer application at an agricultural site. The observed FHONO significantly improves model performance in predicting atmospheric HONO and leads to regional O3 increases by 37%. We also demonstrate the significant potential of nitrification inhibitors in reducing emissions of reactive nitrogen, including HONO and NOx, by as much as 90%, as well as greenhouse gases like nitrous oxide by up to 60%. Our findings introduce a feasible concept for mitigating O3 pollution: reducing soil HONO emissions. Hence, this study has important implications for policy decisions related to the control of O3 pollution and climate change.

Low levels of Al stimulate the aboveground growth of Davidia involucrata saplings

Davidia involucrata is a woody perennial and the only living species in the Genus Davidia. It is native to southern China where it holds cultural and scientific importance. However, D. involucrata is now an endangered species and its natural range includes low pH soils which are increasingly impacted by acid rain, nitrogen deposition and imbalanced nutrient cycling. The combination of these stresses also poses the additional risk of aluminum (Al) toxicity. Since the responses of D. involucrata to low pH and aluminum toxicity have not been investigated previously, a hydroponic experiment was conducted to examine the growth of one year old D. involucrata saplings after 50 d growth in a range of pH and Al conditions. Plant biomass, morphology, antioxidant enzyme activity, mineral concentrations and plant ecological strategy were compared at pH 5.8 and pH 4.0 without added Al (AlCl3) and in 0.1, 0.2 and 0.5 mM Al at pH 4.0. Our results showed that compared with pH 5.8, pH 4.0 (without added Al) not only inhibited root and shoot growth but also limited accumulation of nitrogen (N) and phosphorus (P) in leaves of D. involucrate. However, low Al concentrations (0.1 and 0.2 mM Al) at pH 4.0 partially restored the aboveground growth and leaf N concentrations, suggesting an alleviation of H+ toxicity by low Al concentrations. Compared with low Al concentrations, 0.5 mM Al treatment decreased plant growth and concentrations of N, P, and magnesium (Mg) in the leaves, which demonstrated the toxicity of high Al concentration. The results based on plant ecological strategy showed that D. involucrate decreased the competitiveness and favored its stress tolerance as pH changed from 5.8 to 4.0. Meanwhile, the competitiveness and stress tolerance of D. involucrata increased and decreased at low Al concentrations, respectively, and decreased and increased at high Al concentration, respectively. These trade-offs in ecological strategy were consistent with the responses of growth and antioxidant enzyme activity, reflecting a sensitive adaptation of D. involucrata to acid and Al stresses, which may aid in sustaining population dynamics. These findings are meaningful for understanding the population dynamics of D. involucrata in response to aluminum toxicity in acid soils.

Promoting sustainable smallholder farming via multistakeholder collaboration

Transforming smallholder farms is critical to global food security and environmental sustainability. The science and technology backyard (STB) platform has proved to be a viable approach in China. However, STB has traditionally focused on empowering smallholder farmers by transferring knowledge, and wide-scale adoption of more sustainable practices and technologies remains a challenge. Here, we report on a long-term project focused on technology scale-up for smallholder farmers by expanding and upgrading the original STB platform (STB 2.0). We created a formalized and standardized process by which to engage and collaborate with farmers, including integrating their feedback via equal dialogues in the process of designing and promoting technologies. Based on 288 site-year of field trials in three regions in the North China Plain over 5 y, we find that technologies cocreated through this process were more easily accepted by farmers and increased their crop yields and nitrogen factor productivity by 7.2% and 28.1% in wheat production and by 11.4% and 27.0% in maize production, respectively. In promoting these technologies more broadly, we created a "one-stop" multistakeholder program involving local government agencies, enterprises, universities, and farmers. The program was shown to be much more effective than the traditional extension methods applied at the STB, yielding substantial environmental and economic benefits. Our study contributes an important case study for technology scale-up for smallholder agriculture. The STB 2.0 platform being explored emphasizes equal dialogue with farmers, multistakeholder collaboration, and long-term investment. These lessons may provide value for the global smallholder research and practitioners.

Identification, management and pecuniary impact of major carbon footprint contributor in potato production system of north-west India

Assessment of carbon footprint of a crop is an important component of sustainable crop production, as it helps in framing effectual and viable crop management strategies to minimize ecosystem tampering. Thus, in present investigation carbon footprint of potato production system in different agro-climatic zones viz. undulating plain zone, central plain zone and western plain zone of North-west India were estimated, and compared with the recommended practices of these zones. The carbon footprint was higher in undulating plain zone followed by central plain zone and western plain zone with values being 343, 296 and 220 kg CO2 eq./t tuber yield (TY), sequentially, whereas same were 198 kg CO2 eq./t tuber yield (TY) in case of recommended practices. The social cost of carbon (SCC), that represents economic damage from the CO2 emissions, was also estimated. The integrated net economic balance (net return from yield - SCC) was also better in case of recommended practices. The major sources of emission from potato production system were fertilizer (NPK) application (42 %), irrigation (20 %), seed (14 %), fertilizer production (13 %) and energy use (excluding Irrigation) (5 %). Top most in the list of carbon footprint contributors was fertilizer application which was due to imbalanced application of these, and for getting the clear picture of this imbalance as well as its impact, a new and exclusive index- Relative Imbalance Fertilization Index (RIFIcf) was developed and tested. Carbon footprints were also related to tuber yield and an empirical model was developed that can be used to predict tuber yield on the basis of carbon footprint of potato production system. An increase in tuber yield with increasing carbon footprint was noticed, which became somewhat static at higher emissions. The findings of this investigation provide a clear picture of quantitative GHG emissions due to imbalanced inputs that can be plummeted to some extent if already existing recommendations are followed.

Acidification of European croplands by nitrogen fertilization: Consequences for carbonate losses, and soil health

Soil acidification is an ongoing problem in intensively cultivated croplands due to inefficient and excessive nitrogen (N) fertilization. We collected high-resolution data comprising 19,969 topsoil (0-20 cm) samples from the Land Use and Coverage Area frame Survey (LUCAS) of the European commission in 2009 to assess the impact of N fertilization on buffering substances such as carbonates and base cations. We have only considered the impacts of mineral fertilizers from the total added N, and a N use efficiency of 60 %. Nitrogen fertilization adds annually 6.1 × 107 kmol H+ to European croplands, leading to annual loss of 6.1 × 109 kg CaCO3. Assuming similar acidification during the next 50 years, soil carbonates will be completely removed from 3.4 × 106 ha of European croplands. In carbonate-free soils, annual loss of 2.1 × 107 kmol of basic cations will lead to strong acidification of at least 2.6 million ha of European croplands within the next 50 years. Inorganic carbon and basic cation losses at such rapid scale tremendously drop the nutrient status and production potential of croplands. Soil liming to ameliorate acidity increases pH only temporarily and with additional financial and environmental costs. Only the direct loss of soil carbonate stocks and compensation of carbonate-related CO2 correspond to about 1.5 % of the proposed budget of the European commission for 2023. Thus, controlling and decreasing soil acidification is crucial to avoid degradation of agricultural soils, which can be done by adopting best management practices and increasing nutrient use efficiency. Regular screening or monitoring of carbonate and base cations contents, especially for soils, where the carbonate stocks are at critical levels, are urgently necessary.

Thresholds of Nitrogen and Phosphorus Input Substantially Alter Arbuscular Mycorrhizal Fungal Communities and Wheat Yield in Dryland Farmland

Arbuscular mycorrhizal (AM) fungi are essential for preserving the multifunctionality of ecosystems. The nitrogen (N)/phosphorus (P) threshold that causes notable variations in the AM fungus community of the soil and plant productivity is still unclear. Herein, a long-term (18 years) field experiment with five N and five P fertilizer levels was conducted to investigate the change patterns of soil AM fungus, multifunctionality, and wheat yield. High-N and -P fertilizer inputs did not considerably increase the wheat yield. In the AM fungal network, a statistically significant positive correlation was observed between ecosystem multifunctionality and the biodiversity of two primary ecological clusters (N: Module #0 and P: Module #3). Furthermore, fertilizer input thresholds for N (92-160 kg ha-1) and P (78-100 kg ha-1) significantly altered the AM fungal community, soil characteristics, and plant productivity. Our study provided a basis for reduced N and P fertilizer application and sustainable agricultural development from the aspect of soil AM fungi.

Enhancing soil health to minimize cadmium accumulation in agro-products: the role of microorganisms, organic matter, and nutrients

Agro-products accumulate Cd from the soil and are the main source of Cd in humans. Their use must therefore be minimized using effective strategies. Large soil beds containing low-to-moderate Cd-contamination are used to produce agro-products in many developing countries to keep up with the demand of their large populations. Improving the health of Cd-contaminated soils could be a cost-effective method for minimizing Cd accumulation in crops. In this review, the latest knowledge on the physiological and molecular mechanisms of Cd uptake and translocation in crops is presented, providing a basis for developing advanced technologies for producing Cd-safe agro-products. Inoculation of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi, application of organic matter, essential nutrients, beneficial elements, regulation of soil pH, and water management are efficient techniques used to decrease soil Cd bioavailability and inhibiting the uptake and accumulation of Cd in crops. In combination, these strategies for improving soil health are environmentally friendly and practical for reducing Cd accumulation in crops grown in lightly to moderately Cd-contaminated soil.

Intercropping fruit trees in tea plantation improves soil properties and the formation of tea quality components

Intercropping has been recommended as a beneficial cropping practice for improving soil characteristic and tea quality. However, there is limited research on the effects of intercropping fruit trees on soil chemical properties, soil aggregate structure, and tea quality components. In this study, intercropping fruit trees, specifically loquats and citrus, had a significant impact on the total available nutrients, AMN, and AP in soil. During spring and autumn seasons, the soil large-macroaggregates (>2 mm) proportion increased by 5.93% and 19.03%, as well as 29.23% and 19.14%, respectively, when intercropping loquats and citrus. Similarly, intercropping waxberry resulted in a highest small-macroaggregates (0.25 mm-2 mm) proportion at 54.89% and 77.32%. Soil aggregate stability parameters of the R0.25, MWD, and GMD were generally considered better soil aggregate stability indicators, and significantly improved in intercropping systems. Intercropping waxberry with higher values for those aggregate stability parameters and lower D values, showed a better soil aggregate distribution, while intercropping loquats and citrus at higher levels of AMN and AP in different soil aggregate sizes. As the soil aggregate sizes increased, the AMN and AP contents gradually decreased. Furthermore, the enhanced levels of amino acids were observed under loquat, waxberry, and citrus intercropping in spring, which increased by 27.98%, 27.35%, and 26.21%, respectively. The contents of tea polyphenol and caffeine were lower under loquat and citrus intercropping in spring. These findings indicated that intercropping fruit trees, specifically loquat and citrus, have immense potential in promoting the green and sustainable development of tea plantations.

Cellular Cd2+ fluxes in roots confirm increased Cd availability to rice (Oryza sativa L.) induced by soil acidifications

Soil acidifications become one of the main causes restricting the sustainable development of agriculture and causing issues of agricultural product safety. In order to explore the effect of different acidification on soil cadmium (Cd) availability, soil pot culture and hydroponic (soil potting solution extraction) were applied, and non-invasive micro-test technique (NMT) was combined. Here three different soil acidification processes were simulated, including direct acidification by adding sulfuric acid (AP1), acid rain acidification (AP2) by adding artificial simulated acid rain and excessive fertilization acidification by adding (NH4)2SO4 (AP3). The results showed that for direct acidification (AP1), DTPA-Cd concentration in field soils in Liaoning (S1) and Zhejiang (S2) increased by 0.167 - 0.217 mg/kg and 0.181 - 0.346 mg/kg, respectively, compared with control group. When soil pH decreased by 0.45 units in S1, the Cd content of rice stems, leaves and roots increased by 0.48 to 6.04 mg/kg and 2.58 to 12.84 mg/kg, respectively, When the pH value of soil S1 and S2 decreased by 0.20 units, the average velocity of Cd2+ at 200 µm increased by 10.03 - 33.11 pmol/cm2/sec and 21.33 -52.86 pmol/cm2/sec, respectively, and followed the order of AP3 > AP2 > AP1. In summary, different acidification measures would improve the effectiveness of Cd, under the same pH reduction condition, fertilization acidification increased Cd availability most significantly.

Maize functional requirements drive the selection of rhizobacteria under long-term fertilization practices

Rhizosphere microbiomes are pivotal for crop fitness, but the principles underlying microbial assembly during root-soil interactions across soils with different nutrient statuses remain elusive. We examined the microbiomes in the rhizosphere and bulk soils of maize plants grown under six long-term (≥ 29 yr) fertilization experiments in three soil types across middle temperate to subtropical zones. The assembly of rhizosphere microbial communities was primarily driven by deterministic processes. Plant selection interacted with soil types and fertilization regimes to shape the structure and function of rhizosphere microbiomes. Predictive functional profiling showed that, to adapt to nutrient-deficient conditions, maize recruited more rhizobacteria involved in nutrient availability from bulk soil, although these functions were performed by different species. Metagenomic analyses confirmed that the number of significantly enriched Kyoto Encyclopedia of Genes and Genomes Orthology functional categories in the rhizosphere microbial community was significantly higher without fertilization than with fertilization. Notably, some key genes involved in carbon, nitrogen, and phosphorus cycling and purine metabolism were dominantly enriched in the rhizosphere soil without fertilizer input. In conclusion, our results show that maize selects microbes at the root-soil interface based on microbial functional traits beneficial to its own performance, rather than selecting particular species.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11-129.44%, 32.58-173.73%, and 90.98-347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0-40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

Size, distribution, and vulnerability of the global soil inorganic carbon

Global estimates of the size, distribution, and vulnerability of soil inorganic carbon (SIC) remain largely unquantified. By compiling 223,593 field-based measurements and developing machine-learning models, we report that global soils store 2305 ± 636 (±1 SD) billion tonnes of carbon as SIC over the top 2-meter depth. Under future scenarios, soil acidification associated with nitrogen additions to terrestrial ecosystems will reduce global SIC (0.3 meters) up to 23 billion tonnes of carbon over the next 30 years, with India and China being the most affected. Our synthesis of present-day land-water carbon inventories and inland-water carbonate chemistry reveals that at least 1.13 ± 0.33 billion tonnes of inorganic carbon is lost to inland-waters through soils annually, resulting in large but overlooked impacts on atmospheric and hydrospheric carbon dynamics.

Climate controls on nitrate dynamics and gross nitrogen cycling response to nitrogen deposition in global forest soils

Understanding the patterns and controls regulating nitrogen (N) transformation and its response to N enrichment is critical to re-evaluating soil N limitation or availability and its environmental consequences. Nevertheless, how climatic conditions affect nitrate dynamics and the response of gross N cycling rates to N enrichment in forest soils is still only rudimentarily known. Through collecting and analyzing 4426-single and 769-paired observations from 231 15N labeling studies, we found that nitrification capacity [the ratio of gross autotrophic nitrification (GAN) to gross N mineralization (GNM)] was significantly lower in tropical/subtropical (19%) than in temperate (68%) forest soils, mainly due to the higher GNM and lower GAN in tropical/subtropical regions resulting from low C/N ratio and high precipitation, respectively. However, nitrate retention capacity [the ratio of dissimilatory nitrate reduction to ammonium (DNRA) plus gross nitrate immobilization (INO3) to gross nitrification] was significantly higher in tropical/subtropical (86%) than in temperate (54%) forest soils, mainly due to the higher precipitation and GNM of tropical/subtropical regions, which stimulated DNRA and INO3. As a result, the ratio of GAN to ammonium immobilization (INH4) was significantly higher in temperate than in tropical/subtropical soils. Climatic rather than edaphic factors control heterotrophic nitrification rate (GHN) in forest soils. GHN significantly increased with increasing temperature in temperate regions and with decreasing precipitation in tropical/subtropical regions. In temperate forest soils, gross N transformation rates were insensitive to N enrichment. In tropical/subtropical forests, however, N enrichment significantly stimulated GNM, GAN and GAN to INH4 ratio, but inhibited INH4 and INO3 due to reduced microbial biomass and pH. We propose that temperate forest soils have higher nitrification capacity and lower nitrate retention capacity, implying a higher potential risk of N losses. However, tropical/subtropical forest systems shift from a conservative to a leaky N-cycling system in response to N enrichment.

Nutrient-induced acidification modulates soil biodiversity-function relationships

Nutrient enrichment is a major global change component that often disrupts the relationship between aboveground biodiversity and ecosystem functions by promoting species dominance, altering trophic interactions, and reducing ecosystem stability. Emerging evidence indicates that nutrient enrichment also reduces soil biodiversity and weakens the relationship between belowground biodiversity and ecosystem functions, but the underlying mechanisms remain largely unclear. Here, we explore the effects of nutrient enrichment on soil properties, soil biodiversity, and multiple ecosystem functions through a 13-year field experiment. We show that soil acidification induced by nutrient enrichment, rather than changes in mineral nutrient and carbon (C) availability, is the primary factor negatively affecting the relationship between soil diversity and ecosystem multifunctionality. Nitrogen and phosphorus additions significantly reduce soil pH, diversity of bacteria, fungi and nematodes, as well as an array of ecosystem functions related to C and nutrient cycling. Effects of nutrient enrichment on microbial diversity also have negative consequences at higher trophic levels on the diversity of microbivorous nematodes. These results indicate that nutrient-induced acidification can cascade up its impacts along the soil food webs and influence ecosystem functioning, providing novel insight into the mechanisms through which nutrient enrichment influences soil community and ecosystem properties.