Soil biochemical properties and microbial resilience in agroforestry systems: effects on wheat growth under controlled drought and flooding conditions

Effect of Drought on the Development of Deschampsia caespitosa (L.) and Selected Soil Parameters during a Three-Year Lysimetric Experiment

This work presents results from a field experiment which was focused on the impact of the drought period on microbial activities in rhizosphere and non-rhizosphere soil. To demonstrate the effect of drought, the pot experiment lasted from 2012 to 2015. Fifteen lysimeters (plastic containers) were prepared in our area of interest. These lysimeters were filled with the subsoil and topsoil from this area and divided into two groups. The first group consisted of two variants: V1 (control) and V2 (84 kg N/ha), which were not stressed by drought. The second group consisted of three variants, V3 (control), V4 (84 kg N/ha), and V5 (84 kg N/ha + 1.25 L lignohumate/ha), which were stressed by drought every year of the experiment for 30 days. Changes in the soil moisture content caused by drought significantly affect the growth of Deschampsia caespitosa L., the microbial activity, and the soil’s capacity to retain nutrients. The measured basal respiration and dehydrogenase activity values confirm the significant effect of drought on microbial activity. These values were demonstrably higher in the period before drought simulation by more than 60%. On the other hand, significant differences between microbial activities in the rhizosphere and non-rhizosphere soil were not found. We did not find a clear effect of drought on the formation of soil water repellency.

Soil Nematodes as the Silent Sufferers of Climate-Induced Toxicity: Analysing the Outcomes of Their Interactions with Climatic Stress Factors on Land Cover and Agricultural Production

Unsustainable anthropogenic activities over the last few decades have resulted in alterations of the global climate. It can be perceived through changes in the rainfall patterns and rise in mean annual temperatures. Climatic stress factors exert their effects on soil health mainly by modifying the soil microenvironments where the soil fauna reside. Among the members of soil fauna, the soil nematodes have been found to be sensitive to these stress factors primarily because of their low tolerance limits. Additionally, because of their higher and diverse trophic positions in the soil food web they can integrate the effects of many stress factors acting together. This is important because under natural conditions the climatic stress factors do not exert their effect individually. Rather, they interact amongst themselves and other abiotic stress factors in the soil to generate their impacts. Some of these interactions may be synergistic while others may be antagonistic. As such, it becomes very difficult to assess their impacts on soil health by simply analysing the physicochemical properties of soil. This makes soil nematodes outstanding candidates for studying the effects of climatic stress factors on soil biology. The knowledge obtained therefrom can be used to design sustainable agricultural practices because most of the conventional techniques aim at short-term benefits with complete disregard of soil biology. This can partly ensure food security in the coming decades for the expanding population. Moreover, understanding soil biology can help to preserve landscapes that have developed over long periods of climatic stability and belowground soil biota interactions.

Effects of Drought Stress and Rehydration on Physiological and Biochemical Properties of Four Oak Species in China

Quercus fabri Hance, Quercus serrata Thunb, Quercus acutissima Carruth, and Quercus variabilis BL are four Chinese oak species commonly used for forestation. To ensure the survival of seedlings, we first need to understand the differences in drought resistance of the four oak species at the seedling stage, and comprehensively evaluate their drought resistance capabilities. The four oak seedlings were divided into drought-rewatering treatment group and well watered samples (control group). For the seedlings of the drought-rewatering treatment group, drought stress lasting 31 days was used, and then re-watering for 5 days. The water parameters, osmotic solutes content, antioxidant enzyme activity and photosynthesis parameters of the seedlings in the two groups were measured every 5 days. Compared with the control group, the relative water content, water potential, net photosynthetic rate, transpiration rate, and stomatal conductance levels of the four oaks all showed a downward trend under continuous drought stress, and showed an upward trend after rehydration. The soluble protein, soluble sugar, proline, peroxidase, superoxide dismutase and catalase content of the four oaks increased first and then decreased under drought stress, and then increased after rehydration. The content of glycine betaine and malondialdehyde continued to increase, and gradually decreased after rehydration. The weight of each index was calculated by principal component analysis, and then the comprehensive evaluation of each index was carried out through the membership function method. The drought resistance levels of the four oak species were as follows: Q. serrata > Q. fabri > Q. variabilis > Q. acutissima.

Soil Organic Carbon in Alley Cropping Systems: A Meta-Analysis

Population growth and an increasing demand for food cause the intensification of agriculture leading to soil degradation and a decrease in the soil organic carbon (SOC) stock. Agroforestry systems such as alley cropping are gaining more and more attention as a practice to maintain and/or increase SOC in agroecosystems. The aim of this study was to add to the knowledge on SOC in alley cropping systems and to evaluate the contribution of introducing trees into agricultural landscapes by conducting a meta-analysis of the available data. The soil carbon (C) input will increase with time. Our findings suggest that a beneficial effect on SOC occurs after approximately a decade of alley cropping practice adoption. Furthermore, the effect of alley cropping is more beneficial in regions with lower initial SOC concentration compared to that in regions rich in SOC. Higher relative SOC is observed in the tropical region compared to that in the temperate climate zone. The establishment of alley cropping systems on agricultural land needs to consider several parameters such as alley width and tree species when designing such systems to achieve the highest possible tree and crop productivity while increasing SOC.

Tree rows in temperate agroforestry croplands alter the composition of soil bacterial communities

BACKGROUND

Tree-based intercropping (agroforestry) has been advocated to reduce adverse environmental impacts of conventional arable cropping. Modern agroforestry systems in the temperate zone are alley-cropping systems that combine rows of fast-growing trees with rows of arable crops. Soil microbial communities in these systems have been investigated intensively; however, molecular studies with high taxonomical resolution are scarce.

METHODS

Here, we assessed the effect of temperate agroforestry on the abundance, diversity and composition of soil bacterial communities at three paired poplar-based alley cropping and conventional monoculture cropland systems using real-time PCR and Illumina sequencing of bacterial 16S rRNA genes. Two of the three systems grew summer barley (Hordeum vulgare); one system grew maize (Zea mays) in the sampling year. To capture the spatial heterogeneity induced by the tree rows, soil samples in the agroforestry systems were collected along transects spanning from the centre of the tree rows to the centre of the agroforestry crop rows.

RESULTS

Tree rows of temperate agroforestry systems increased the abundance of soil bacteria while their alpha diversity remained largely unaffected. The composition of the bacterial communities in tree rows differed from those in arable land (crop rows of the agroforestry systems and conventional monoculture croplands). Several bacterial groups in soil showed strong association with either tree rows or arable land, revealing that the introduction of trees into arable land through agroforestry is accompanied by the introduction of a tree row-associated microbiome.

CONCLUSION

The presence of tree row-associated bacteria in agroforestry increases the overall microbial diversity of the system. We speculate that the increase in biodiversity is accompanied by functional diversification. Differences in plant-derived nutrients (root exudates and tree litter) and management practices (fertilization and tillage) likely account for the differences between bacterial communities of tree rows and arable land in agroforestry systems.

Home-field advantage in soil respiration and its resilience to drying and rewetting cycles

Climate change is expected to increase extreme weather events, such as more extreme drought and rainfall incidences, with consequences for ecosystem carbon (C) cycling. An understanding of how drying and rewetting (DRW) events affect microbe-mediated soil processes is therefore critical to the predictions of future climate. Here, a reciprocal-transplant experiment was conducted using two soils originated from distinct climate and agricultural managements to evaluate how soil biotic and abiotic properties regulate soil respiration and its resilience to simulated DRW cycles. We found that regardless of the DRW intensity, the effects of microbial community on soil respiration and its resilience to DRW cycles were dependent on soil type. Soil microbial communities yielded higher respiration rates and resilience in native than foreign soils under both one and four DRW cycles, supporting the "home-field advantage" hypothesis. Structural equation modeling demonstrated that soil pH and total C directly influenced soil respiration, but effects of soil abiotic properties on respiration resilience were mediated by microbial communities. Among microbial drivers, the microbial C utilization capacity (as characterized by community-level physiological profile, C-acquisition enzyme activities and microbial metabolic quotients) was the best predictor of respiration resilience to DRW cycles, followed by microbial biomass carbon/nitrogen ratio and microbial community composition. Our study suggests that soil microbial communities may have adapted to their historical conditions, which facilitates the resilience of soil respiration to changing environments, but this adaptation may accelerate C loss from soils facing increasingly variable climate.

Temperate Agroforestry Development: The Case of Québec and of France

This study sought to shed light on the political and organizational dynamics favoring the deployment of agroforestry in temperate environments. Development paths of agroforestry practices in Québec (Canada) and France were analyzed regarding five different issues: political status and recognition, regulation and financing, knowledge acquisition, knowledge transfer and training, development actors and implementation in the field. Scientific studies and results continue to accumulate concerning temperate agroforestry and its environmental benefits. Political recognition of the field appears to be stronger in France (and the EU), which makes state financial aid conditional upon the adoption of the practices. In Québec, only the Ministry of Agriculture provides limited support. It financially assists research at a moderate level, as well as the installation and maintenance of trees by participating farmers to perform specific functions, i.e., erosion control, water quality, and biodiversity. A large number of actors are active in France, where efforts are being made to improve consultation and to reduce redundancy. Stakeholders in Québec are linked to the broader agri-environment field and act partially through agroforestry, according to varying degrees of competency, creating a disparity between regions. Recognition at the highest level, i.e., training for councillors and advisors, greater flexibility in obtaining assistance, inclusion of a greater diversity of systems, and a structure that ensures promotion and consultation, would favour the further development of agroforestry in the industrialized nations of the temperate zone.

Agroforestry Benefits and Challenges for Adoption in Europe and Beyond

Soil degradation is a global concern, decreasing the soil’s ability to perform a multitude of functions. In Europe, one of the leading causes of soil degradation is unsustainable agricultural practices. Hence, there is a need to explore alternative production systems for enhanced agronomic productivity and environmental performance, such as agroforestry systems (AFS). Given this, the objective of the study is to enumerate the major benefits and challenges in the adoption of AFS. AFS can improve agronomic productivity, carbon sequestration, nutrient cycling, soil biodiversity, water retention, and pollination. Furthermore, they can reduce soil erosion and incidence of fire and provide recreational and cultural benefits. There are several challenges to the adoption and uptake of AFS in Europe, including high costs for implementation, lack of financial incentives, limited AFS product marketing, lack of education, awareness, and field demonstrations. Policies for financial incentives such as subsidies and payments for ecosystem services provided by AFS must be introduced or amended. Awareness of AFS products must be increased for consumers through appropriate marketing strategies, and landowners need more opportunities for education on how to successfully manage diverse, economically viable AFS. Finally, field-based evidence is required for informed decision-making by farmers, advisory services, and policy-making bodies.

Poplar Rows in Temperate Agroforestry Croplands Promote Bacteria, Fungi, and Denitrification Genes in Soils

Agroforestry, which is the integration of trees into monoculture cropland, can alter soil properties and nutrient cycling. Temperate agroforestry practices have been shown to affect soil microbial communities as indicated by changes in enzyme activities, substrate-induced respiration, and microbial biomass. Research exploring soil microbial communities in temperate agroforestry with the help of molecular tools which allow for the quantification of microbial taxa and selected genes is scarce. Here, we quantified 13 taxonomic groups of microorganisms and nine genes involved in N cycling (N₂ fixation, nitrification, and denitrification) in soils of three paired temperate agroforestry and conventional monoculture croplands using real-time PCR. The agroforestry croplands were poplar-based alley-cropping systems in which samples were collected in the tree rows as well as within the crop rows at three distances from the tree rows. The abundance of Acidobacteria, Actinobacteria, Alpha- and Gammaproteobacteria, Firmicutes, and Verrucomicrobia increased in the vicinity of poplar trees, which may be accounted for by the presence of persistent poplar roots as well as by the input of tree litter. The strongest population increase was observed for Basidiomycota, which was likely related to high soil moisture, the accumulation of tree litter, and the absence of tillage in the tree rows. Soil microorganisms carrying denitrification genes were more abundant in the tree rows than in the crop rows and monoculture systems, suggesting a greater potential for nitrate removal through denitrification, which may reduce nitrate leaching. Since microbial communities are involved in critical soil processes, we expect that the combination of real-time PCR with soil process measurements will greatly enhance insights into the microbial control of important soil functions in agroforestry systems.

Agroforestry systems and understory harvest management: the impact on growth and productivity of dual-purpose wheat

The objective of the study was to evaluate the growth and production efficiency of forage-grain dual-purpose wheat in two arrangements and four agroforestry systems (Intercrop-I and Intercrop-II), as well as to evaluate crop management for the wheat crops in two planting seasons (Crop Season I-2014 and Crop Season II-2015. The experiment was conducted in a randomized complete block design, factorial scheme 7x2x2, with seven cultivation systems Eucalyptus urophylla x Eucalyptus grandis Intercrop-II and Intercrop-I; Peltophorum dubium Intercrop-II and Intercrop-I; P. rigida Intercrop-I; S. parahyba Intercrop-I; a wheat monoculture with no tree species present; and two harvest management techniques (with and without harvesting of the forage species). Agroforestry systems generated shading for wheat plants, with a higher phyllochron and lower values of leaf area index of those individuals kept under trees with higher crown shading (non-deciduous trees) due to the lower transmissivity of solar radiation. The systems composed with Schizolobium parahyba in Intercrop-I and Parapiptadenia rigida in Intercrop-I provide a minor phyllochron to the wheat, resulting in a higher leaf area index and dry matter yield. Thus, the cultivation of tree species and dual-skilled agricultural crops, such as wheat, provides promising alternatives for the future use of land in tropical countries.

Agroforestry and Biodiversity

Declining biodiversity (BD) is aecting food security, agricultural sustainability,and environmental quality. Agroforestry (AF) is recognized as a possible partial solution forBD conservation and improvement. This manuscript uses published peer-reviewed manuscripts,reviews, meta-analysis, and federal and state agency documents to evaluate relationships betweenAF and BD and how AF can be used to conserve BD. The review revealed that floral, faunal, and soilmicrobial diversity were significantly greater in AF as compared to monocropping, adjacent croplands, and within crop alleys and some forests. Among the soil organisms, arbuscular mycorrhizaefungi (AMF), bacteria, and enzyme activities were significantly greater in AF than crop and livestockpractices. Agroforestry also creates spatially concentrated high-density BD near trees due to favorablesoil-plant-water-microclimate conditions. The greater BD was attributed to heterogeneous vegetation,organic carbon, microclimate, soil conditions, and spatial distribution of trees. Dierences in BDbetween AF and other management types diminished with time. Evenly distributed leaves, litter,roots, dead/live biological material, and microclimate improve soil and microclimate in adjacentcrop and pasture areas as the system matures. Results of the study prove that integration of AFcan improve BD in agricultural lands. Selection of site suitable tree/shrub/grass-crop combinationscan be used to help address soil nutrient deficiencies or environmental conditions. Future studieswith standardized management protocols may be needed for all regions to further strengthen thesefindings and to develop AF establishment criteria for BD conservation and agricultural sustainability.

Impact of fruit-tree shade intensity on the growth, yield, and quality of intercropped wheat

Agroforestry is a common traditional practice in China-especially in the southern Xinjiang of Northwest China. However, the productivity of many agroforestry systems has been lower than expected in recent years, highlighting the need for an actionably deep mechanistic understanding of the competition between crops and trees. Here, three different fruit tree/wheat (jujube/wheat, apricot /wheat, and walnut /wheat) intercropping agroforestry systems were chosen to investigate influence of different fruit tree shade intensity on the growth, yield and quality of intercropping wheat. Compared to the monoculture wheat system, the mean daily shade intensity of the jujube-, apricot-, and walnut-based intercropping systems were, respectively, 23.2%, 57.5%, and 80.7% shade. The photosynthetic rate of wheat in the jujube-, apricot-, and walnut-based intercropping systems decreased by, respectively, 11.3%, 31.9%, and 36.2% compared to monoculture wheat, and the mean number of fertile florets per spike decreased by 26.4%, 37.4%, and 49.5%. Moreover, the apricot- and walnut-based intercropping systems deleteriously affected grain yield (constituent components spike number, grains per spike, and thousand grain weight) and decreased the total N, P, and K content of intercropping wheat. Tree shading intensity strongly enhanced the grain protein content, wet gluten content, dough development time, and dough stability time of wheat, but significantly decreased the softening degree. Strong negative linear correlations were observed between tree shade intensity and the number of fertile florets, grain yield related traits (including spike number, grains per spike, and thousand grain weight), nutrient content (N, P and K), and softening degree of wheat. In contrast, Daily shade intensity was positively linearly correlated with grain protein content, wet gluten content, dough development time, and dough stability time. We conclude that jujube-based intercropping systems can be practical in the region, as they do not decrease the yield and quality of intercropping wheat.

Soil Microbial Community Structure and Physicochemical Properties in Amomum tsaoko-based Agroforestry Systems in the Gaoligong Mountains, Southwest China

Amomum tsaoko is cultivated in forests of tropical and subtropical regions of China, and the planting area is expanding gradually. However, little attention has been paid to the impact of A. tsaoko cultivation on the soil characteristics of the regions. We analyzed the effects of the A. tsaoko-forest agroforestry system (AFs) on the composition of soil microbial communities with increasing stand ages. We also compared the soil physicochemical properties, microbial biomass, and phospholipid fatty acid (PLFA) composition between native forest (NF) and AFs. The results showed that the level of total carbon, nitrogen, and organic matter dramatically dropped in AFs with increasing stand ages. pH affected other soil properties and showed close correlation to total carbon (P = 0.0057), total nitrogen (P = 0.0146), organic matter (P = 0.0075), hydrolyzable nitrogen (P = 0.0085), available phosphorus (P < 0.0001), and available potassium (P = 0.0031). PLFAs of bacteria (F = 4.650, P = 0.037), gram-positive bacteria (F = 6.640, P = 0.015), anaerobe (F = 5.672, P = 0.022), and total PLFA (F = 4.349, P = 0.043) were significantly affected by different treatments, with the greatest value for NF treatment, and least value for AF5. However, the microbial biomass declined during the initial 5 years of cultivation, but it reached the previous level after more than 10 years of cultivation. Our research suggests that AFs is a profitable land-use practice in the Gaoligong Mountains and that AFs showed a recovering trend of the soil nutrient condition with increasing stand ages. However, the severe loss of nitrogen in the soil of AFs requires additional nitrogen during cultivation to restore it to pre-cultivation levels.

Rubber and plantain intercropping: Effects of different planting densities on soil characteristics

Two field experiments were conducted at Ellembelle and Jomoro districts in the Western region of Ghana where rubber cultivation is a predominant farming activity. The objective of the study was to assess the effect of rubber and plantain intercropping systems on selected soil properties. The experiment was arranged in a randomized complete block design (RCBD) with 3 replications. The treatments were the sole crop rubber (R), sole crop plantain (P) and three intercrop systems comprising an additive series of plantain: one row of plantain to one row of rubber (PR), two rows of plantain to one row of rubber (PPR) and three rows of plantain to one row of rubber (PPPR). Generally, agroforestry systems improved the soil hydraulic properties considerably, with the highest cumulative infiltration rates of 5.16 and 8.68 cm/min observed under the PPPR systems at the Ellembelle and Jomoro sites, respectively. Microbial biomass C (C_mic), N (N_mic) and P (P_mic) was significantly improved (P < 0.05) under the agroforestry than the monocrop systems. The C_mic, N_mic and P_mic values were highest under the PPPR system at both Ellembelle (C_mic, = 139.9 mg/kg; N_mic = 36.26 mg/kg and P_mic = 87.6 mg/kg) and Jomoro (C_mic = 78.7 mg/kg; N_mic = 80.3 mg/kg and P_mic = 3.45 mg/kg) sites.

Extreme rainfall affects assembly of the root-associated fungal community

Global warming is resulting in increased frequency of weather extremes. Root-associated fungi play important roles in terrestrial biogeochemical cycling processes, but the way in which they are affected by extreme weather is unclear. Here, we performed long-term field monitoring of the root-associated fungus community of a short rotation coppice willow plantation, and compared community dynamics before and after a once in 100 yr rainfall event that occurred in the UK in 2012. Monitoring of the root-associated fungi was performed over a 3-yr period by metabarcoding the fungal internal transcribed spacer (ITS) region. Repeated soil testing and continuous climatic monitoring supplemented community data, and the relative effects of environmental and temporal variation were determined on the root-associated fungal community. Soil saturation and surface water were recorded throughout the early growing season of 2012, following extreme rainfall. This was associated with a crash in the richness and relative abundance of ectomycorrhizal fungi, with each declining by over 50%. Richness and relative abundance of saprophytes and pathogens increased. We conclude that extreme rainfall events may be important yet overlooked determinants of root-associated fungal community assembly. Given the integral role of ectomycorrhizal fungi in biogeochemical cycles, these events may have considerable impacts upon the functioning of terrestrial ecosystems.

The response of the soil microbial food web to extreme rainfall under different plant systems

An agroforestry experiment was conducted that involved four planting systems: monoculture of the focal species Zanthoxylum bungeanum and mixed cultures of Z. bungeanum and Capsicum annuum, Z. bungeanum and Medicago sativa and Z. bungeanum and Glycine max. Soil microbial food web (microorganisms and nematodes) was investigated under manipulated extreme rainfall in the four planting systems to assess whether presence of neighbor species alleviated the magnitude of extreme rainfall on nutrient uptake of the focal species by increasing the stability of soil food web. Our results indicate that in the focal species and G. max mixed culture, leaf nitrogen contents of the focal species were higher than in the monoculture and in the other mixed cultures under extreme rainfall. This result was mainly due to the significant increase under extreme rainfall of G. max species root biomass, resulting in enhanced microbial resistance and subsequent net nitrogen mineralization rate and leaf nitrogen uptake for the focal species. Differences in functional traits of neighbors had additive effects and led to a marked divergence of soil food-web resistance and nutrient uptake of the focal species. Climate change can indirectly alleviate focal species via its influence on their neighbors.