Element cycling as driven by stoichiometric homeostasis of soil microorganisms

Response of ecological stoichiometry and homeostasis characteristic to nitrogen addition in Hippophae rhamnoides L

Nitrogen (N) in the atmosphere frequently affects plant growth, ecological stoichiometric equilibrium, and homeostasis stability. However, the effect of N addition application on the growth of Hippophae rhamnoides seedlings remains ambiguous. We investigated the effects of N addition on the ecological stoichiometry and homeostatic characteristics of H. rhamnoides seedlings. Greenhouse cultivation experiments were conducted at five N application levels: 0 kg ha-1 yr-1(CK), 100 kg ha-1 yr-1 (N10), 200 kg ha-1 yr-1 (N20), 400 kg ha-1 yr-1 (N40), 800 kg ha-1 yr-1 (N80). The results showed that pH and available phosphorus (AP) significantly decreased with increasing N, whereas soil C:P and N:P ratios significantly increased under the N40 and N80 treatments. The leaf C:N ratio significantly decreased with increasing N, whereas the N:P ratio increased. With N addition, the C:N ratio of plant stems and roots significantly decreased, whereas the C:P and N:P ratios significantly increased. N addition was significantly correlated with the ecological stoichiometry of plant leaves and soil properties (0.38 and 0.84, respectively). Homeostasis of the organs of H. rhamnoides seedlings exhibited an absolute steady state. The C, N, and C:P ratios of the roots exhibited insensitive states under the N40 treatment. N addition significantly modified both the soil ecological stoichiometry and the stoichiometry of H. rhamnoides seedlings. However, it did not demonstrate a pronounced negative effect on the homeostasis of H. rhamnoides seedlings. This study offers new insights into the ecological adaptation process of H. rhamnoides, particularly concerning its nutrient distribution, utilization strategies, and stability.

Biochar and wood vinegar altered the composition of inorganic phosphorus bacteria community in saline-alkali soils and promoted the bioavailability of phosphorus

As an important part of the ecosystem, saline-alkali soils are in urgent need of efficient and environmentally friendly soil conditioners. Biochar and wood vinegar are regarded as organic soil improvement and plant growth regulators to improve soil physicochemical properties and promote crop growth. However, the mechanism of how inorganic phosphorus bacteria increase phosphorus when biochar and wood vinegar applied to saline-alkali soils is not clear. Herein, the present study was designed to investigate the effects of biochar and wood vinegar with different rates on physicochemical properties of saline-alkali soils and inorganic phosphorus bacteria diversities and to discuss the mechanism of biochar and wood vinegar on available phosphorus by pot experiments. The application of biochar and wood vinegar exhibited an effect on the decrease in pH and salt contents and the increase in soil porosity, soil nutrients, and hundred-grain weight of rice. The 600 kg ha-1 biochar and 1800 kg ha-1 wood vinegar group showed the most significant increment in available phosphorus, alkaline phosphatase, acid phosphatase, and neutral phosphatase activities, with the increases of 49.24%, 40.35%, 48%, and 149%, respectively. The 600 kg ha-1 biochar and 1200 kg ha-1 wood vinegar group significantly enhanced microbial biomass phosphorus concentrations by 41.29%. Moreover, biochar and wood vinegar shifted inorganic phosphorus bacteria composition structure and promoted its diversities, more so at a higher rate of wood vinegar application. The dominant species of inorganic phosphorus bacteria were Proteobacteria, Gammaproteobacteria, Alphaproteobacteria, Pseudomonas, and Rhizobium in saline-alkali soils. The Alphaproteobacteria and Hydrogenophaga were the key microorganisms reducing pH and salt contents and increasing available phosphorus contents in saline-alkali soils. In conclusion, the application of biochar and wood vinegar was a useful strategy to improve saline-alkali soils.

Effect of conventional and biodegradable microplastics on the soil-soybean system: A perspective on rhizosphere microbial community and soil element cycling

As an exogenous carbon input, microplastics (MPs), especially biodegradable MPs, may significantly disrupt soil microbial communities and soil element cycling (CNPS cycling), but few studies have focused on this. Here, we focused on assessing the effects of conventional low-density polyethylene (LDPE), biodegradable polybutylene adipate terephthalate (PBAT), and polylactic acid (PLA) MPs on rhizosphere microbial communities and CNPS cycling in a soil-soybean system. The results showed that PBAT-MPs and PLA-MPs were more detrimental to soybean growth than LDPE-MPs, resulting in a reduction in shoot nitrogen (14.05% and 11.84%) and shoot biomass (33.80% and 28.09%) at the podding stage. In addition, dissolved organic carbon (DOC) increased by 20.91% and 66.59%, while nitrate nitrogen (NO3--N) significantly decreased by 56.91% and 69.65% in soils treated with PBAT-MPs and PLA-MPs, respectively. PBAT-MPs and PLA-MPs mainly enhanced copiotrophic bacteria (Proteobacteria) and suppressed oligotrophic bacteria (Verrucomicrobiota, Gemmatimonadota, etc.), increasing the abundance of CNPS cycling-related functional genes. LDPE-MPs tended to enrich oligotrophic bacteria (Verrucomicrobiota, etc.) and decrease the abundance of CNPS cycling-related functional genes. Correlation analysis revealed that MPs with different degradation properties selectively affected the composition and function of the bacterial community, resulting in changes in the availability of soil nutrients (especially NO3--N). Redundancy analysis further indicated that NO3--N was the primary constraining factor for soybean growth. This study provides a new perspective for revealing the underlying ecological effects of MPs on soil-plant systems.

Refining stoichiometric approaches to trace soil organic matter sources

In their Letter‐to‐Editor, Liu & Chen (2024) raised the importance and suitability of our recent stoichiometric approach to assess the contribution of plant residue (litter) and microbial sources to mineral‐associated organic matter (MAOM). We highly appreciate their Letter as well as the further suggestion and comments and offer two points of clarification. We call for staying aware of methodological benefits and limitations of each approach, and further develop and compare multiple methods to develop a clearer picture of where and to what extent MAOM is formed from direct vs. indirect (via the microbial funnel) plant inputs.

Temporal variation of microbial nutrient limitation in citrus plantations: Insights from soil enzyme stoichiometry

Soil enzyme carbon (C): nitrogen (N): phosphorous (P) stoichiometry and their vector model has been widely used to elucidate the balance between microbial nutrient requirements and soil nutrient availability. However, limited knowledge is available on the dynamics of soil enzyme stoichiometry and microbial nutrient limitation following afforestation, especially in the economic forest. In this study, the effects of citrus plantation on C: N: P stoichiometry were assessed through a comparative study between cropland and citrus plantations with varying durations of afforestation (i.e., 3, 15, 25, and 35 years). It was found that the C, N, and P contents in the soil (SOC, STN, and STP), microbial biomass (MBC, MBN, and MBP), as well as the activities of C-, N-, and P-acquiring enzymes (BG, NAG, and AP), were 1.02-2.51 times higher than those in cropland. Additionally, C, N, and P contents in soil and microbial biomass increased consistently with increasing afforestation time. While the activities of C-, N-, and P-acquiring enzymes increased from 3 years to 25 years and then significantly decreased. In addition to NAG: AP, the stoichiometry of C, N, and P in soil (SOC: STN, SOC: STP, and STN: STP) and microbial biomass (MBC: MBN, MBC: MBP, and MBN: MBP), along with BG: NAG, exhibited a decline of 7.69-27.38% compared to cropland. Moreover, the majority of the C: N: P stoichiometry in soil, microbial biomass, and enzymes consistently decreased with increasing afforestation time, except for SOC: STN and NAG: AP, which exhibited an opposite trend. Furthermore, a significant decrease in microbial carbon limitation and an increase in microbial nitrogen limitation were observed with increasing afforestation time. Collectively, the dynamic of microbial nutrient limitation was primarily influenced by the interaction between soil nutrients and edaphic factors. The findings suggest that with the increasing duration of citrus plantation, it is crucial to focus on nitrogen (N) fertilization while maintaining a delicate balance between fertilization strategies and soil acidity levels.

Interruption after Short-Term Nitrogen Additions Improves Ecological Stability of Larix olgensis Forest Soil by Affecting Bacterial Communities

Atmospheric nitrogen deposition can alter soil microbial communities and further impact the structure and function of forest ecosystems. However, most studies are focused on positive or negative effects after nitrogen addition, and few studies pay attention to its interruption. In order to investigate whether interruption after different levels of short-term N additions still benefit soil health, we conducted a 2-year interruption after a 4-year short-term nitrogen addition (10 and 20 kg N·hm-2·yr-1) experiment; then, we compared soil microbial diversity and structure and analyzed soil physicochemical properties and their correlations before and after the interruption in Larix olgensis forest soil in northeast China. The results showed that soil ecological stabilization of Larix olgensis forest further improved after the interruption compared to pre-interruption. The TN, C:P, N:P, and C:N:P ratios increased significantly regardless of the previous nitrogen addition concentration, and soil nutrient cycling was further promoted. The relative abundance of the original beneficial microbial taxa Gemmatimonas, Sphingomonas, and Pseudolabrys increased; new beneficial bacteria Ellin6067, Massilia, Solirubrobacter, and Bradyrhizobium appeared, and the species of beneficial soil microorganisms were further improved. The results of this study elucidated the dynamics of the bacterial community before and after the interruption of short-term nitrogen addition and could provide data support and a reference basis for forest ecosystem restoration strategies and management under the background of global nitrogen deposition.

Effects of nitrogen addition on rhizosphere priming: The role of stoichiometric imbalance

Nitrogen (N) input has a significant impact on the availability of carbon (C), nitrogen (N), and phosphorus (P) in the rhizosphere, leading to an imbalanced stoichiometry in microbial demands. This imbalance can result in energy or nutrient limitations, which, in turn, affect C dynamics during plant growth. However, the precise influence of N addition on the C:N:P imbalance ratio and its subsequent effects on rhizosphere priming effects (RPEs) remain unclear. To address this gap, we conducted a 75-day microcosm experiment, varying N addition rates (0, 150, 300 kg N ha-1), to examine how microbes regulate RPE by adapting to stoichiometry and maintaining homeostasis in response to N addition, using the 13C natural method. Our result showed that N input induced a stoichiometric imbalance in C:N:P, leading to P or C limitation for microbes during plant growth. Microbes responded by adjusting enzymatic stoichiometry and functional taxa to preserve homeostasis, thereby modifying the threshold element ratios (TERs) to cope with the C:N:P imbalance. Microbes adapted to the stoichiometric imbalance by reducing TER, which was attributed to a reduction in carbon use efficiency. Consequently, we observed higher RPE under P limitation, whereas the opposite trend was observed under C or N limitation. These results offer novel insights into the microbial regulation of RPE variation under different soil nutrient conditions and contribute to a better understanding of soil C dynamics.

Microbial successional pattern along a glacier retreat gradient from Byers Peninsula, Maritime Antarctica

The retreat of glaciers in Antarctica has increased in the last decades due to global climate change, influencing vegetation expansion, and soil physico-chemical and biological attributes. However, little is known about soil microbiology diversity in these periglacial landscapes. This study characterized and compared bacterial and fungal diversity using metabarcoding of soil samples from the Byers Peninsula, Maritime Antarctica. We identified bacterial and fungal communities by amplification of bacterial 16 S rRNA region V3-V4 and fungal internal transcribed spacer 1 (ITS1). We also applied 14C dating on soil organic matter (SOM) from six profiles. Physico-chemical analyses and attributes associated with SOM were evaluated. A total of 14,048 bacterial ASVs were obtained, and almost all samples had 50% of their sequences assigned to Actinobacteriota and Proteobacteria. Regarding the fungal community, Mortierellomycota, Ascomycota and Basidiomycota were the main phyla from 1619 ASVs. We found that soil age was more relevant than the distance from the glacier, with the oldest soil profile (late Holocene soil profile) hosting the highest bacterial and fungal diversity. The microbial indices of the fungal community were correlated with nutrient availability, soil reactivity and SOM composition, whereas the bacterial community was not correlated with any soil attribute. The bacterial diversity, richness, and evenness varied according to presence of permafrost and moisture regime. The fungal community richness in the surface horizon was not related to altitude, permafrost, or moisture regime. The soil moisture regime was crucial for the structure, high diversity and richness of the microbial community, specially to the bacterial community. Further studies should examine the relationship between microbial communities and environmental factors to better predict changes in this terrestrial ecosystem.

Deciphering the dual role of bacterial communities in stabilizing rhizosphere priming effect under intra-annual change of growing seasons

The rhizosphere priming effect (RPE) is a widely observed phenomenon affecting carbon (C) turnover in plant-soil systems. While multiple cropping and seasonal changes can have significant impacts on RPE, the mechanisms driving these processes are complex and not yet fully understood. Here, we planted maize in paddy soil during two growing seasons having substantial temperature differences [May-August (warm season, 26.6 °C) and September-November (cool season, 23.1 °C)] within the same calendar year in southern China to examine how seasonal changes affect RPEs and soil C. We identified sources of C emissions by quantifying the natural abundance of 13C and determined microbial metabolic limitations or efficiency and functional genes related to C cycling using an enzyme-based biogeochemical equilibrium model and high-throughput quantitative PCR-based chip technology, respectively. Results showed that microbial metabolism was mainly limited by phosphorus in the warm season, but by C in the cool season, resulting in positive RPEs in both growing seasons, but no significant differences (9.02 vs. 6.27 mg C kg-1 soil day-1). The RPE intensity remained stable as temperature increased (warm season compared to a cool season), which can be largely explained by the simultaneous increase in the abundance of functional genes related to both C degradation and fixation. Our study highlights the simultaneous response and adaptation of microbial communities to seasonal changes and hence contributes to an understanding and prediction of microbially mediated soil C turnover under multiple cropping systems.

Long-Term Organic Fertilization Strengthens the Soil Phosphorus Cycle and Phosphorus Availability by Regulating the pqqC- and phoD-Harboring Bacterial Communities

The pqqC and phoD genes encode pyrroloquinoline quinone synthase and alkaline phosphomonoesterase (ALP), respectively. These genes play a crucial role in regulating the solubilization of inorganic phosphorus (Pi) and the mineralization of organic phosphorus (Po), making them valuable markers for P-mobilizing bacterial. However, there is limited understanding of how the interplay between soil P-mobilizing bacterial communities and abiotic factors influences P transformation and availability in the context of long-term fertilization scenarios. We used real-time polymerase chain reaction and high-throughput sequencing to explore the characteristics of soil P-mobilizing bacterial communities and their relationships with key physicochemical properties and P fractions under long-term fertilization scenarios. In a 38-year fertilization experiment, six fertilization treatments were selected. These treatments were sorted into three groups: the non-P-amended group, including no fertilization and mineral NK fertilizer; the sole mineral-P-amended group, including mineral NP and NPK fertilizer; and the organically amended group, including sole organic fertilizer and organic fertilizer plus mineral NPK fertilizer. The organically amended group significantly increased soil labile P (Ca2-P and enzyme-P) and Olsen-P content and proportion but decreased non-labile P (Ca10-P) proportion compared with the sole mineral-P-amended group, indicating enhanced P availability in the soil. Meanwhile, the organically amended group significantly increased soil ALP activity and pqqC and phoD gene abundances, indicating that organic fertilization promotes the activity and abundance of microorganisms involved in P mobilization processes. Interestingly, the organically amended group dramatically reshaped the community structure of P-mobilizing bacteria and increased the relative abundance of Acidiphilium, Panacagrimonas, Hansschlegelia, and Beijerinckia. These changes had a greater positive impact on ALP activity, labile P, and Olsen-P content compared to the abundance of P-mobilizing genes alone, indicating their importance in driving P mobilization processes. Structural equation modeling indicated that soil organic carbon and Po modulated the relationship between P-mobilizing bacterial communities and labile P and Olsen-P, highlighting the influence of SOC and Po on the functioning of P-mobilizing bacteria and their impact on P availability. Overall, our study demonstrates that organic fertilization has the potential to reshape the structure of P-mobilizing bacterial communities, leading to increased P mobilization and availability in the soil. These findings contribute to our understanding of the mechanisms underlying P cycling in agricultural systems and provide valuable insights for enhancing microbial P mobilization through organic fertilization.

Microbial fertilizer regulates C:N:P stoichiometry and alleviates phosphorus limitation in flue-cured tobacco planting soil

Fertilization can be optimized and managed during the flue-cured tobacco growing period by studying the response of soil and microbial biomass stoichiometric characteristics to fertilization. In this study, we investigated the effect of compound fertilizers combined with microbial fertilizer treatments on the stoichiometric characteristics of the rhizosphere soil and the limitations of microbial resources during the flue-cured tobacco growing period. The results indicated that soil and microbial C:N:P varied greatly with the growing period. The effect of sampling time was usually greater than that of fertilization treatment, and microbial C:N:P did not vary with the soil resource stoichiometric ratio. The microbial metabolism of the tobacco-growing soil was limited by phosphorus after extending the growing period, and phosphorus limitation gradually increased from the root extension to the maturation periods but decreased at harvest. The rhizosphere soil microbial nitrogen and phosphorus limitations were mainly affected by soil water content, soil pH, microbial biomass carbon, and the ratio of microbial biomass carbon to microbial biomass phosphorus. Applying microbial fertilizer reduced phosphorus limitation. Therefore, applying microbial fertilizer regulated the limitation of microbial resources by affecting the soil and microbial biomass C:N:P in flue-cured tobacco rhizosphere soils.

Interaction between nematodes and bacteria enhances soil carbon sequestration under organic material amendments

The process of carbon (C) sequestration plays an important role in soil fertility and productivity, yet most studies have focused on the individual role of the bacterial community. However, an in-depth mechanistic understanding of how soil nematodes interact with the bacterial community to regulate soil C accumulation is still lacking. We conducted a 10-year field experiment to explore the nematode and bacterial communities and determine the influence of nematode-bacteria interactions on C mineralization, microbial metabolic quotient (qCO₂), and carbon use efficiency (CUE) under the organic material amendments, including chemical fertilizers with straw (NS), chemical fertilizers with straw and pig manure (NSM), and chemical fertilizer with straw biochar (NB). Here, our results showed the abundance of bacterial and nematode communities was significantly higher under NS, NSM, and NB treatments than under chemical fertilizers (N) treatment, with the highest abundance under the NSM treatment. The enrichment index and functional dispersion index were significantly higher under NSM treatment than under N, NS, and NB treatments, while the channel index followed the opposite pattern. Structural equation modeling indicated that the potential predation pressure induced by nematodes may improve bacterial abundance, with positive cascading effects on C sequestration. Collectively, our study highlights the functional importance of nematode-microorganism interactions in mediating C dynamics under organic material amendments.

Effects of different fertilization methods on Lolium multiflorum Lam. growth and bacterial community in waste slag

Waste slag has low nutrient content, so it has insufficient nutrient cycling and transformation in the soil ecosystem. There are few studies on the application of oligotrophic phosphate-solubilizing bacteria and phosphate (P) fertilizer to improve the properties of waste slags. In this study, three oligotrophic bacterial strains with P solubilizing activity, namely, Bacillus subtilis 2C (7.23 μg/mL), Bacillus subtilis 6C (4.07 μg/mL), and Bacillus safensis 2N (5.05 μg/mL), were isolated from waste slags. In the pot experiment, compared with no application of P fertilizer, inoculation of Bacillus subtilis 2C with a 50% recommended dose of P fertilizer significantly increased the available phosphorus (AP), total phosphorus (TP), and total nitrogen (TN) in slag by 33.16%, 76.70%, and 233.33%, respectively. The N, P uptake and fresh weight of Lolium multiflorum Lam. were significantly improved by 114.15%, 139.02%, and 100%, respectively. The analysis of the bacterial community showed that the application of P fertilizer decreased the diversity and richness of the bacterial community, and with the addition of phosphorus fertilizer and Bacillus subtilis 2C, the bacterial community in the slag developed towards eutrophication. Redundancy analysis (RDA) showed that the TP content in the slag was significantly correlated with the bacterial community (P = 0.001, < 0.01), followed by the TN content. This study on different P fertilizer application methods can provide some basic ideas for improving the performance of waste slag.

How arbuscular mycorrhizal fungi drives herbaceous plants' C: N: P stoichiometry? A meta-analysis

Plant element stoichiometry is fundamental for preserving growth-related terrestrial ecosystem structures and functions. However, effects of arbuscular mycorrhizal fungi (AMF) on herbaceous plant element stoichiometry (carbon (C), nitrogen (N), and phosphorus (P)) remain unclear. In this study, we aimed at evaluating the potential effects of AMF on herbaceous plant C, N and P concentration and their C:N:P stoichiometry worldwide through a quantitative meta-analysis. We observed that AMF reduced C:P and N:P ratios in the shoot of plants by 35.83 % and 54.23 %, respectively, and in plant root organs by 36.24 % and 46.35 %, respectively. Conversely, C:N ratios increased in roots by 6.61 %. The negative effect of AMF on N:P and C:P ratios in plant shoots and root organs is mainly attributed to the plant benefits in P and N concentrations. AMF impact on plant C:N:P stoichiometry depends on fungal and plant functional group identities and soil nutrient availability. Our results suggest that plant functional group identity affects plant nutrient concentration, which, in turn, controls herbaceous plant C:N:P stoichiometry. Overall, we emphasize the importance of abiotic and biotic environmental factors in changing AMF effects on plant element stoichiometry. Therefore, clarifying the relationship between AMF and herbaceous plant C:N:P stoichiometry will improve our understanding of herbaceous plant stoichiometric variations in terrestrial ecosystems.

Latitudinal shifts of soil microbial biomass seasonality

Soil microbes ultimately drive the mineralization of soil organic carbon and thus ecosystem functions. We compiled a dataset of the seasonality of microbial biomass carbon (MBC) and developed a semi-mechanistic model to map monthly MBC across the globe. MBC exhibits an equatorially symmetric seasonality between the Northern and Southern Hemispheres. In the Northern Hemisphere, MBC peaks in autumn and is minimal in spring at low latitudes (<25°N), peaks in the spring and is minimal in autumn at mid-latitudes (25°N to 50°N), while peaks in autumn and is minimal in spring at high latitudes (>50°N). This latitudinal shift of MBC seasonality is attributed to an interaction of soil temperature, soil moisture, and substrate availability. The MBC seasonality is inconsistent with patterns of heterotrophic respiration, indicating that MBC as a proxy for microbial activity is inappropriate at this resolution. This study highlights the need to explicitly represent microbial physiology in microbial models. The interactive controls of environments and substrate on microbial seasonality provide insights for better representing microbial mechanisms in simulating ecosystem functions at the seasonal scale.

Three-dimensional mapping of carbon, nitrogen, and phosphorus in soil microbial biomass and their stoichiometry at the global scale

Soil microbial biomass and microbial stoichiometric ratios are important for understanding carbon and nutrient cycling in terrestrial ecosystems. Here, we compiled data from 12245 observations of soil microbial biomass from 1626 published studies to map global patterns of microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and their stoichiometry using a random forest model. Concentrations of MBC, MBN, and MBP were most closely linked to soil organic carbon, while climatic factors were most important for stoichiometry in microbial biomass ratios. Modeled seasonal MBC concentrations peaked in summer in tundra and in boreal forests, but in autumn in subtropical and in tropical biomes. The global mean MBC/MBN, MBC/MBP, and MBN/MBP ratios were estimated to be 10, 48, and 6.7, respectively, at 0-30 cm soil depth. The highest concentrations, stocks, and microbial C/N/P ratios were found at high latitudes in tundra and boreal forests, probably due to the higher soil organic matter content, greater fungal abundance, and lower nutrient availability in colder than in warmer biomes. At 30-100 cm soil depth, concentrations of MBC, MBN, and MBP were highest in temperate forests. The MBC/MBP ratio showed greater flexibility at the global scale than did the MBC/MBN ratio, possibly reflecting physiological adaptations and microbial community shifts with latitude. The results of this study are important for understanding C, N, and P cycling at the global scale, as well as for developing soil C-cycling models including soil microbial C, N, and P as important parameters.

Ecological stoichiometry, salt ions and homeostasis characteristics of different types of halophytes and soils

Studying eco-stoichiometric and salt ions characteristics of halophytes and soils is helpful to understand the distribution mechanism of nutrients and salts in halophytes and their adaptation strategies to salinized habitats. In this study, three different types of halophytes (Phragmites communis-salt repellent, Suaeda salsa-salt accumulating, and Aeluropus sinensis- salt secreting) and soils were selected to analyze the differences and correlations of C, N, P stoichiometry and salt accumulation. Results showed that: (1) the total nitrogen (TN) and total phosphorus (TP) contents of the three halophytes' leaves were significantly higher than those of the roots and stems, and the C: N ratios were contrary to the difference mentioned above. The growth of P. communis and S. salsa was mainly limited by P, whereas A. sinensis was limited by both N and P. S. salsa had a stronger absorption capacity for Na⁺ and Mg²⁺ than P. communis and A. sinensis. The interrelationship between salt ions and C, N and P ecological stoichiometry of halophyte organs was influenced by the type of halophytes. (2) The TC, TN, and N: P contents of the three halophyte communities in the surface soil (0-20 cm) were significantly higher than the other soil layers, while P did not differ significantly among soil layers. The planting of different halophytes affected the TC, TN, C: N, N: P values and the content of seven ions in the surface soil. SO₄ ^2-was positively correlated with soil TC, TN, N:P, and Na⁺ were positively correlated with soil TC in three halophytes. (3) The P. communis TC and A. sinensis TN contents were negatively correlated with soil TC, TN, C: P, and N: P, whereas TC contents of S. salsa were positively correlated with the aforementioned soil indicators. The P. communis and A. sinensis TC contents were negatively correlated with soil K⁺, while this correlation was opposite between S. salsa and soil. (4) The homeostasis of C, N, and P elements in all three halophytes showed that C > N > P, the homeostasis was strongest in A. sinensis and weakest in S. salsa. The results provide a theoretical basis for the restoration of saline land in the Yellow River Delta.

Plant Interaction Patterns Shape the Soil Microbial Community and Nutrient Cycling in Different Intercropping Scenarios of Aromatic Plant Species

Intercropping systems improve the soil nutrient cycle through microbial community activity and then land productivity. However, their interactions mechanism underlying that the mixed aromatic plant species intercropping regulate the soil microbiome and nutrient cycling on the perennial woody orchard is still uncovered. We designed treatments with 0, 1, and 3 aromatic plant species intercropped in two scenarios of clean tillage (T model, T1, T2, and T4) and natural grass (G model, G1, G2, and G4) in apple orchards, and investigated intercrops effects at the branch growing stage (BGS) and fruit development stage (FDS), respectively. Compared with T model, G model in FDS increased alpha diversity of bacterial community and Shannon index fungal community, the relative abundance of dominant taxa, such as Acidobacteria and Actinobacteria, and also the numbers of up and down-regulated OTUs, the most of indices of co-occurrence network in both bacterial and fungal community, and then improved invertase activity and available nitrogen content. Relative to G1, G2 and G4 reduced diversity bacterial community in FDS, the relative abundance of dominant taxa, the most of indices of co-occurrence network, and then improved soil invertase activity and total phosphorus content in soil. Moreover, Shannon index of fungal community, the altered number of OTUs and the most indices of co-occurrence network were higher in G4 than those in G2 in FDS. These changes above in FDS were more markedly than those in BGS, suggesting that chemical diversity of litter from mixed species of aromatic plants in natural grass scenario led to diversity, complexity, and stability of soil microbial community and then nutrient cycling. It provided a novel highlight and method to modulate biocenosis and then improve the soil nutrient cycling.

Soil microbial stoichiometry and community structure responses to long-term natural forest conversion to plantations in a subtropical region

Soil microbial stoichiometry reflects carbon (C) and nutrient (e.g., nitrogen (N) and phosphorus (P)) elemental balances under land-use change (LUC). However, how soil microbial community (SMC) structure and stoichiometry respond to long-term LUC in forests is still unclear. Here, we investigated three 36-year-old typical plantations, Cryptomeria fortunei, Metasequoia glyptostroboides, and Cunninghamia lanceolata, and the natural forest to assess their soil microbial stoichiometry and SMC structure. Three plots (30×30 m²) were randomly set in each forest site. In each plot of every forest site, soil samples of three depths (0-10, 10-30, and 30-60 cm) were collected. Dissolved organic C, N, and P (abbreviated as DOC, DON, and DOP, respectively) and environmental factors were measured. We also detected microbial biomass C, N, and P as well as SMC structure. The results showed that the soil microbial C:N:P stoichiometry had a strong or strict homeostasis regardless of soil depth and exhibited decoupling from the SMC structure at each depth. The SMC structure across forest types was mainly driven by mean annual soil temperature (MAST) and DOC at 0-10 cm depth, by soil water content and MAST at 10-30 cm depth, and by DOC to DOP ratio at 30-60 cm depth. Thus, SMC structure could be jointly regulated by available resources and environment. These results suggest that the C dynamics in forests tend to gain resilience or re-equilibrium over more than three decades after forest conversion. These findings highlight the importance of reforested plantations forest management for sustaining soil C over a long term.

Linking soil organic carbon stock to microbial stoichiometry, carbon sequestration and microenvironment under long-term forest conversion

Forest conversion can drastically impact carbon (C) and nutrient processes and microbial stoichiometry, which will modify soil organic C (SOC) stock. However, SOC stock dynamics and its underlying mechanisms induced by long-term forest conversion remain unclear. Three well-protected plantations converted from natural forests for 36 years were compared, i.e., Cryptomeria fortunei (CF), Metasequoia glyptostroboides (MG) and Cunninghamia lanceolata (CL), with a natural forest (NF) as a control. SOC stock size and stability across three soil depths (0-10, 10-30 and 30-60 cm) were examined with aggregate-based method. Forest floors and fine roots were treated as C and nutrient inputs while soil respiration (Rs) was treated as C output. Soil microbial biomass C, nitrogen and phosphorus were measured to calculate microbial stoichiometry, as well as microenvironment and soil physicochemical properties. The relationships between SOC stock (size and stability) and these factors were explored using structural equation model. The results showed that microbial stoichiometry had strong or strict homeostasis at each soil depth. At 0-10 cm soil deep, SOC stock size varied with tree species (following the rank of CL > NF ≈ CF > MG) but its stability increased in all forest conversion types, regulated by forest floor quantity and quality associated with Rs; at 10-30 cm soil deep, the SOC stock sizes decreased in CF and MG, but SOC stock stability increased in MG, jointly driven by fine root quality and microenvironment; at 30-60 cm soil deep, SOC stock size decreased but its stability increased in MG, whereas both its size and stability had few changes in CF or CL, modified by soil physicochemical property associated with microbial stoichiometry and Rs. Overall, the effects of microbial stoichiometry and microenvironment on SOC stock were not pronounced. Thus, SOC stock size changed with soil depth and tree species but its stability tended to be steady at all depths varying with tree species. These results suggest that SOC stock size and stability are mainly determined by self-regulation process of forest ecosystems over more than three-decade after forest conversion, which will help us more accurately assess C sequestration strategies regarding long-term forest conversion.

Shift of microbial turnover time and metabolic efficiency strongly regulates rhizosphere priming effect under nitrogen fertilization in paddy soil

Microbial turnover and the decomposition of soil organic matter can be stimulated by living roots in a phenomenon known as the rhizosphere priming effect (RPE). Both the microbial turnover time (MTT) and metabolic efficiency are closely related to RPE. However, changes in MTT, metabolic efficiency and RPE in response to nitrogen (N) fertilization at different levels and the associations between these factors during plant growth are unknown. The effects of N fertilization at different levels (0, 150 and 300 kg N ha^-1) on RPE and the underlying mechanisms were investigated in maize (Zea mays L.) grown in paddy soil using a ¹³Carbon (C) natural abundance method. The RPE varied from -1.49 to 15.93 mg C kg^-1 soil day^-1, with significant effects at different levels of N fertilization, growth stages and interactions between these factors. Nitrogen fertilization reduced microbial C:N imbalance and soil pH. During the plant growth periods, the RPE was initially low because the microbes preferentially utilized plant-derived C, but later increased due to trade-offs between microbial N acquisition and acidity stress alleviation under N fertilization. The soil microbes altered their MTT and metabolic efficiency with changes in the microbial community structure to maintain stoichiometric homeostasis and adapt to acidity stress. RPE was lowest whereas MTT and metabolic efficiency were highest with N fertilization at 150 kg N ha^-1. Changes in MTT and metabolic efficiency explained 84.5% of the variations in the RPE, and the latter had greater impact (55.8%) than the former (28.7%). Changes in MTT and metabolic efficiency to cope with microbial resource acquisition and acidity stress under N fertilization represent an important pathway for RPE regulation in paddy soil. These findings highlight the significance of MTT and metabolic efficiency in RPE regulation for optimization of the N fertilization level to mitigate soil C losses.

Land use intensification destabilizes stream microbial biodiversity and decreases metabolic efficiency

Urbanization and agricultural intensification can transform landscapes. Changes in land-use can lead to increases in storm runoff and nutrient loadings which can impair the health and function of stream ecosystems. Microorganisms are an integral component of stream ecosystems. Due to the sensitivity of microorganisms to perturbations, changes in hydrology and water chemistry may alter microbial activity and structure. These shifts in microbial community dynamics may alter stream metabolism and water quality, potentially impacting higher trophic levels. Here we examine the effects of land-use and associated changes in water chemistry on sediment microbial communities by studying the West Run Watershed (WRW) a mixed-land-use system in West Virginia, USA. Streams were sampled throughout the growing season at six sites within the WRW spanning different levels of land use intensification. The proportion of land impacted by agricultural and urban development was positively correlated with temporal variation in stream sediment microbial community composition (adj R² = 0.65), suggesting development can destabilize microbial communities. Moreover, streams in developed watersheds had an increased metabolic quotient (20-50% higher), this indicates that microorganisms have greater respiration per unit biomass and signifies reduced metabolic efficiency. Further, our results suggest that land use associated changes in water chemistry alter microbial function both directly and indirectly via changes in microbial community composition and biomass. Taken together our results suggest that highly developed watersheds with elevated conductivity, metal ion concentration, and pH impose stress on microbial communities resulting in reduced microbial efficiency and elevated respiration.

Effects of Different Ages of Robinia pseudoacacia Plantations on Soil Physiochemical Properties and Microbial Communities

Robinia pseudoacacia is widely planted on the Loess Plateau as a strong drought-tolerant and salt-tolerant species for vegetation restoration. However, this mode of pure plantation has triggered great concern over the soil ecosystem. The aim of this study was to explore the effects of the plantation on soil physiochemical properties, soil microorganisms, and the relationship between them in Robinia pseudoacacia plantations of different ages. Four different ages of Robinia pseudoacacia stands, including 10-year-old, 15-year-old, 25-year-old, and 40-year-old (abbreviated as Y10, Y15, Y25, and Y40, respectively) were selected, and 20 soil physicochemical and biological indicators were determined. The variation in soil microbial biomass was influenced by sampling depth, and consistent with the variations in TN (soil total nitrogen) and SOC (soil organic carbon) during 25 years’ artificial forestation. Soil moisture increased significantly at Y15 and then decreased at Y40 but other soil properties remained relatively stable. The contents of phosphor lipid fatty acid (PLFA) of different microbial groups followed the order of B (Bacteria) > G− (Gram-negative) > G+ (Gram-positive) > A (Actinomycetes) > F (Fungi). The ratios of F/B (Fungi to Bacteria) and Sat/Mono (Saturated PLFAs to Monosaturated PLFAs) of different ages of plantations showed a similar trend, i.e., declined first, then rose, and declined again. The ratios of Cy/Pre (Cyclopropyl PLFAs to Precursor PLFAs) and G+/G− (Gram-positive to Gram-negative) of the soil of all ages of plantations showed a trend of slow growth and a trend of rapid growth, respectively. Redundancy analysis showed that the contents of individual PLFAs and total PLFA were positively correlated with SOC and TN, but variations of soil PLFA ratios mostly depended on other soil properties. After artificial forestation, the ratios of F/B and Sat/Mono were lower than before forestation, while the ratio of Cy/Pre varied with different soil layers. The ratio of G+/G− increased with the increase in afforestation time, peaking at the 25th year. The contents of individual PLFAs and total PLFA may be sensitive indicators of SOC and TN within 25 years’ plantation. Lower ratio of F/B and higher G+/G− suggest that the sustainability of the ecosystem is weaker and the fertility of the soil is lower after plantation of Robinia pseudoacacia.

Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus

Despite the fact that phosphorus (P) is critical for plant biomass production in many ecosystems, the implications of soil organic carbon (OC) sequestration for the P cycle have hardly been discussed yet. Thus, the aims of this study are, first, to synthesize results about the relationship between C and P in soil organic matter (SOM) and organic matter inputs to soils, second, to review processes that affect the C:P ratio of SOM, and third, to discuss implications of OC storage in terrestrial ecosystems for P sequestration. The study shows that the storage of OC in mineral soils leads to the sequestration of large amounts of organic phosphorus (OP) since SOM in mineral soils is very rich in P. The reasons for the strong enrichment of OP with respect to OC in soils are the mineralization of OC and the formation of microbial necromass that is P-rich as well as the strong sorption of OP to mineral surfaces that prevents OP mineralization. In particular, the formation of mineral-associated SOM that is favorable for storing OC in soil over decadal to centennial timescales sequesters large amounts of OP. Storage of 1,000 kg C in the clay size fraction in the topsoils of croplands sequesters 13.1 kg P. In contrast, the OC:OP ratios of wood and of peatlands are much larger than the ones in cropland soils. Thus, storage of C in wood in peatlands sequesters much less P than the storage of OC in mineral soils. In order to increase the C stocks in terrestrial ecosystems and to lock up as little P as possible, it would be more reasonable to protect and restore peatlands and to produce and preserve wood than to store OC in mineral soils.

Potential utilization of terrestrially derived dissolved organic matter by aquatic microbial communities in saline lakes

Lakes receive large amounts of terrestrially derived dissolved organic matter (tDOM). However, little is known about how aquatic microbial communities interact with tDOM in lakes. Here, by performing microcosm experiments we investigated how microbial community responded to tDOM influx in six Tibetan lakes of different salinities (ranging from 1 to 358 g/l). In response to tDOM addition, microbial biomass increased while dissolved organic carbon (DOC) decreased. The amount of DOC decrease did not show any significant correlation with salinity. However, salinity influenced tDOM transformation, i.e., microbial communities from higher salinity lakes exhibited a stronger ability to utilize tDOM of high carbon numbers than those from lower salinity. Abundant taxa and copiotrophs were actively involved in tDOM transformation, suggesting their vital roles in lacustrine carbon cycle. Network analysis indicated that 66 operational taxonomic units (OTUs, affiliated with Alphaproteobacteria, Actinobacteria, Bacteroidia, Bacilli,  Gammaproteobacteria, Halobacteria, Planctomycetacia, Rhodothermia, and Verrucomicrobiae) were associated with degradation of CHO compounds, while four bacterial OTUs (affiliated with Actinobacteria, Alphaproteobacteria, Bacteroidia and Gammaproteobacteria) were highly associated with the degradation of CHOS compounds. Network analysis further revealed that tDOM transformation may be a synergestic process, involving cooperation among multiple species. In summary, our study provides new insights into a microbial role in transforming tDOM in saline lakes and has important implications for understanding the carbon cycle in aquatic environments.

Interactions of nitrogen and phosphorus cycling promote P acquisition and explain synergistic plant-growth responses

Plant growth is often co-limited by nitrogen (N) and phosphorus (P). Plants might use one element to acquire another (i.e., trading N for P and P for N), which potentially explains synergistic growth responses to NP addition. We studied a 66-yr-old grassland experiment in South Africa that consists of four levels of N addition with and without P addition. We investigated the response of aboveground net primary production (ANPP) to N and P addition over the last 66 yr. Further, we tested whether phosphatase activity and plant P uptake depend on N availability, and vice versa, whether non-symbiotic N₂ fixation and plant N uptake depend on P availability. We expected that the interaction of both elements promote processes of nutrient acquisition and contribute to synergistic plant growth effects in response to NP addition. We found synergistic N and P co-limitation of ANPP for the period from 1951 to 2017 but the response to N and P addition diminished over time. In 2017, aboveground P stocks, relative rRNA operon abundance of arbuscular mycorrhizal fungi, and soil organic P storage increased with N fertilization rate when N was added with P compared to the treatment in which only N was added. Further, N addition increased phosphatase activity, which indicates that plants used N to acquire P from organic sources. In contrast, aboveground N stocks and non-symbiotic N₂ fixation did not change significantly due to P addition. Taken together, our results indicate that trading N for P likely contributes to synergistic plant-growth response. Plants used added N to mobilize and take up P from organic sources, inducing stronger recycling of P and making the plant community less sensitive to external nutrient inputs. The latter could explain why indications of synergistic co-limitation diminished over time, which is usually overlooked in short-term nutrient addition experiments.

Dynamics of soil microbial C:N:P stoichiometry and its driving mechanisms following natural vegetation restoration after farmland abandonment

Vegetation restoration after farmland abandonment has increased greatly and is commonly used to improve soil fertility and ecosystem service. Knowledge of soil community-level elemental homeostasis following natural vegetation restoration is specially limited for the abandoned farmlands. This study examined the changes in soil microbial biomass stoichiometry and homeostasis with a chronosequence of 3, 8, 13, 18, 23 and 30 years following natural vegetation restoration since farmland abandonment on the Loess Plateau, China. Vegetation communities, soil properties, microbial communities, and enzyme activities were analyzed to study the drivers on soil microbial C:N:P stoichiometry. The results showed that soil microbial biomass C: N ratios had little change following natural vegetation restoration since farmland abandonment, natural vegetation >23 years had significantly enhanced the microbial biomass C:P and N:P ratios by 26.1%-133.9% and 31.7%-67.4%, respectively. However, microbial biomass C:N, C:P and N:P ratios were constrained following natural vegetation restoration. Vegetation restoration for 30 years enhanced urease and alkaline phosphatase activities by 125.4% and 42.9%, respectively, which showed synchronous changes with N and P contents in microbial biomass. Soil fungi, urease and alkaline phosphatase were the drivers to the changes in microbial C:N:P stoichiometry. The results suggest that long-term vegetation restoration (>23 years) will aggravate microbial P limitation, however, soil microorganism maintained the homeostatic regulation of stoichiometric ratios to mitigate P limitation. Fungi played a strong role in shaping microbial community-level elemental homeostasis and nutrient cycling through releasing N-converting and P-converting enzymes into soil following natural vegetation restoration.

Relationships between feeding and microbial faeces indices in dairy cows at different milk yield levels

A study was carried out to gain quantitative information on the diet-dependent faecal microbial biomass of dairy cows, especially on the biomass fractions of fungi, Gram-positive (G+) and Gram-negative (G-) bacteria. Groups of high-yield, low-yield and non-lactating cows were investigated at four different farms. A mean faecal microbial biomass C (MBC) concentration of 33.5 mg g-1 DM was obtained by the chloroform fumigation extraction method. This is similar to a mean microbial C concentration of 31.8 mg g-1 DM, which is the sum of bacterial C and fungal C, estimated by cell-wall derived muramic acid (MurN) and fungal glucosamine (GlcN), respectively. However, the response of these two approaches to the feeding regime was contradictory, due to feeding effects on the conversion values. The higher neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations in the non-lactating group led to higher (P < 0.05) concentrations of cellulose and lignin in their faeces in comparison with the lactating cows. This change in faecal chemical composition in the non-lactating group was accompanied by usually higher ratios of G+/G- phospholipid fatty acids (PLFA), ergosterol/MBC and fungal C/bacterial C. Although bacteria dominate the faecal microbial biomass, fungi contribute a considerable mean percentage of roughly 20% to the faecal microbiome, according to PLFA and amino sugar data, which requires more attention in the future. Near-infra red spectroscopic estimates of organic N and C fractions of cow faeces were able to model microbial biomarkers successfully, which might be useful in the future to predict its N2O emission potential and fertilizer value.

C:N:P stoichiometry of rhizosphere soils differed significantly among overstory trees and understory shrubs in plantations in subtropical China

Rhizosphere soil C:N:P stoichiometry is useful for identifying the linkage of plant species and soil nutrients, which can be particularly helpful for understory vegetation management of forest ecosystems. There has been limited research on rhizosphere soil stoichiometry, especially for co-existing overstory and understory plant species. We investigated the bulk and rhizosphere soil C:N:P stoichiometry of dominant overstory trees and understory shrubs (Adinandra millettii, Eurya muricata, and Loropetalum chinense) in Pinus massoniana Lamb., Pinus elliottii Engelm., and Cunninghamia lanceolata (Lamb.) Hook. plantations in subtropical China. Rhizosphere soil C, N, and P concentrations and ratios increased significantly compared with bulk soil, and those of overstory trees were higher than those of understory shrubs with the exception of L. chinense. Rhizosphere soil C:N, C:P, and N:P of L. chinense were not significantly different with those of overstory trees but were higher than those of A. millettii and E. muricata. Soil pH significantly influenced the profiles produced by soil C, N, and P concentrations and their stoichiometries. This study indicated that the difference in nutrient status between overstory trees and understory shrubs was related to shrub species, in which soil pH was the dominant driving factor. Understory shrub species should be considered in plantation management to reduce resource competition among species.

Carbon:Nitrogen:Phosphorus Stoichiometry in Fungi: A Meta-Analysis

Surveys of carbon:nitrogen:phosphorus ratios are available now for major groups of biota and for various aquatic and terrestrial biomes. However, while fungi play an important role in nutrient cycling in ecosystems, relatively little is known about their C:N:P stoichiometry and how it varies across taxonomic groups, functional guilds, and environmental conditions. Here we present the first systematic compilation of C:N:P data for fungi including four phyla (Ascomycota, Basidiomycota, Glomeromycota, and Zygomycota). The C, N, and P contents (percent of dry mass) of fungal biomass varied from 38 to 57%, 0.23 to 15%, and 0.040 to 5.5%, respectively. Median C:N:P stoichiometry for fungi was 250:16:1 (molar), remarkably similar to the canonical Redfield values. However, we found extremely broad variation in fungal C:N:P ratios around the central tendencies in C:N:P ratios. Lower C:P and N:P ratios were found in Ascomycota fungi than in Basidiomycota fungi while significantly lower C:N ratios (p < 0.05) and higher N:P ratios (p < 0.01) were found in ectomycorrhizal fungi than in saprotrophs. Furthermore, several fungal stoichiometric ratios were strongly correlated with geographic and abiotic environmental factors, especially latitude, precipitation, and temperature. The results have implications for understanding the roles that fungi play in function in symbioses and in soil nutrient cycling. Further work is needed on the effects of actual in situ growth conditions of fungal growth on stoichiometry in the mycelium.