Soil nematode community and crop productivity in response to 5-year biochar and manure addition to yellow cinnamon soil

Plant Genotype Shapes the Soil Nematode Community in the Rhizosphere of Tomatoes with Different Resistance to Meloidognye incognita

Soil nematodes are considered indicators of soil quality due to their immediate responses to changes in the soil environment and plants. However, little is known about the effects of plant genotypes on the soil nematode community. To elucidate this, high-throughput sequencing and gas chromatography/mass spectrometry analysis was conducted to analyze the soil nematode community and the structure of root exudates in the rhizosphere of tomatoes with different resistance to Meloidognye incognita. The dominant soil nematode group in the soil of resistant tomatoes was Acrobeloides, while the soil nematode group in the rhizosphere of the susceptible and tolerant tomatoes was Meloidognye. Hierarchical clustering analysis and non-metric multidimensional scaling showed that the three soil nematode communities were clustered into three groups according to the resistance level of the tomato cultivars. The soil nematode community of the resistant tomatoes had a higher maturity index and a low plant-parasite index, Wasilewska index and disease index compared to the values of the susceptible and tolerant tomatoes. Redundancy analysis revealed that the disease index and root exudates were strongly related to the soil nematode community of three tomato cultivars. Taken together, the resistance of the tomato cultivars and root exudates jointly shapes the soil nematode community. This study provided a valuable contribution to understanding the mechanism of plant genotypes shaping the soil nematode community.

Meta-Analysis of the Effects of Biochar Application on the Diversity of Soil Bacteria and Fungi

Biochar is increasingly being used for soil improvement, but the effects on microbial diversity in soil are still ambiguous due to contrasting results reported in the literature. We conducted a meta-analysis to clarify the effect of biochar addition on soil bacterial and fungal diversity with an increase in Shannon or Chao1 index as the outcome. Different experimental setups, quantitative levels of biochar addition, various biochar source materials and preparation temperatures, and the effect of natural precipitation in field experiments were the investigated variables. From a total of 95 publications identified for analysis, 384 datasets for Shannon index and 277 datasets for Chao1 index were extracted that described the bacterial diversity in the soils, of which field experiments and locations in China dominated. The application of biochar in soil significantly increased the diversity of soil bacteria but it had no significant effect on the diversity of fungi. Of the different experimental setups, the largest increase in bacterial diversity was seen for field experiments, followed by pot experiments, but laboratory and greenhouse settings did not report a significant increase. In field experiments, natural precipitation had a strong effect, and biochar increased bacterial diversity most in humid conditions (mean annual precipitation, MAP > 800 mm), followed by semi-arid conditions (MAP 200–400 mm). Biochar prepared from herbaceous materials was more effective to increase bacterial diversity than other raw materials and the optimal pyrolysis temperature was 350–550 °C. Addition of biochar at various levels produced inconclusive data for Chao1 and Shannon indices, and its effect was less strong than that of the other assessed variables.

Characteristics of soil microbiota and organic carbon distribution in jackfruit plantation under different fertilization regimes

Manure amendment to improve soil organic carbon (SOC) content is an important strategy to sustain ecosystem health and crop production. Here, we utilize an 8-year field experiment to evaluate the impacts of organic and chemical fertilizers on SOC and its labile fractions as well as soil microbial and nematode communities in different soil depths of jackfruit (Artocarpus heterophyllus Lam.). Three treatments were designed in this study, including control with no amendment (CK), organic manure (OM), and chemical fertilizer (CF). Results showed that OM significantly increased the abundance of total nematodes, bacterivores, bacteria, and fungi as well as the value of nematode channel ratio (NCR) and maturity index (MI), but decreased plant-parasites and Shannon diversity (H′). Soil microbial and nematode communities in three soil depths were significantly altered by fertilizer application. Acidobacteria and Chloroflexi dominated the bacterial communities of OM soil, while Nitrospira was more prevalent in CF treatment. Organic manure application stimulated some functional groups of the bacterial community related to the C cycle and saprotroph-symbiotroph fungi, while some groups related to the nitrogen cycle, pathotroph-saprotroph-symbiotroph and pathotroph-saprotroph fungi were predominated in CF treatment. Furthermore, OM enhanced the soil pH, contents of total soil N, P, K, and SOC components, as well as jackfruit yield. Chemical fertilizers significantly affected available N, P, and K contents. The results of network analyses show that more significant co-occurrence relationships between SOC components and nematode feeding groups were found in CK and CF treatments. In contrast, SOC components were more related to microbial communities than to nematode in OM soils. Partial least-squares-path modeling (PLS-PM) revealed that fertilization had significant effects on jackfruit yield, which was composed of positive direct (73.6%) and indirect effects (fertilization → fungal community → yield). It was found that the long-term manure application strategy improves soil quality by increasing SOM, pH, and nutrient contents, and the increased microbivorous nematodes abundance enhanced the grazing pressure on microorganisms and concurrently promoted microbial-derived SOC turnover.

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.

Nematodes as Ghosts of Land Use Past: Elucidating the Roles of Soil Nematode Community Studies as Indicators of Soil Health and Land Management Practices

Soil health is a matter of growing concern because of its degradation due to unsustainable anthropogenic activities over the last few decades. It is maintained by interactions among the components of the soil food web commonly concentrated in the vicinity of the plant roots, called the rhizosphere. The soil food web is dominated by nematodes. They occupy various trophic positions because of their diverse feeding habits. The free-living forms are mainly dependent on soil bacteria and fungi for their nutrition, while the parasitic forms feed on plant roots. The population of these two groups is regulated by the activities of predatory nematodes which can be carnivorous or omnivorous. The soil nematodes thereby partake responsibilities in nutrient cycling, mineralization and decomposition pathways which, in turn, affects the aboveground productivity. This intricately connected food web structure is vulnerable to disturbances like increased soil salinity, acidity, nitrogen enrichment, tillage, crop rotations, fertilizers, pesticides, soil amendment techniques and heavy metal pollution. The effects are reflected by alterations in the abundance and diversity of soil nematodes belonging to various trophic groups. These alterations have been formulated into measurable indices like maturity index (MI), structure index (SI), enrichment index (EI) and channel index (CI). The faunal profile and metabolic footprints of soil nematodes are latest developments in the field of nematode community analyses. Though these indices cannot replace the conventional soil ecotoxicological assays, they can give added information about soil biology which can be utilized to design sustainable land use practices.

Effects of straw return and straw biochar on soil properties and crop growth: A review

Straw return is an effective method for disposing agricultural residues. It not only utilizes agricultural waste but also improves soil. In the current review, different crop straw and its characteristics were highlighted, and patterns of straw return were explored (including straw return, straw biochar return, and their combined with fertilizer return), as well as their environmental impacts were outlined. In addition, the effects of straw return and straw biochar amendment on soil properties [e.g., pH, soil organic carbon (SOC), soil nitrogen (N)/phosphorus (P)/potassium (K), soil enzyme activities, and soil microbes] were discussed. Information collected from this review proposed that straw return and straw biochar return or in combination with fertilizer is an applicable way for improving soil fertility and enhancing crop production. Straw return is beneficial to soil physicochemical properties and soil microbial features. The rice straw has positive impacts on crop growth. However, there are different climate types, soil types and crops in China, meaning that the future research need long-term experiment to assess the complex interactions among straw, soil, and plant eco-systems. Accordingly, this review aims to provide available information on the application of straw return in terms of different patterns of its to justify and to expand their effective promotion.