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A trait-based approach is adopted to understand the responses of the soil nematode food web following cover crops incorporated into the soil, i.e., afterlife effect of plant. We conducted an in situ microcosm experiment with two cover crops including leguminous Astragalus sinicus L. (A. sinicus), characterized by high nutrient content, and gramineous Lolium multiflorum Lam (L. multiflorum), characterized by high C and lignin content, representing the acquisitive and conservative side of the economic spectrum, respectively. Furthermore, two incorporation rates were set to represent low and high biomass production of cover crops that could be incorporated into the soil. Soil main microbial groups, nematode food web, and physicochemical properties were analyzed at weeks 4 and 18 after cover crops incorporated into the soil. Results showed that, regardless of time, cover crops affected the abundance and composition of the soil nematode food web. L. multiflorum supported higher nematode abundance and more complex nematode food web than A. sinicus, charactering with higher fungivore/bacterivore, predator/prey, maturity index, and structure index, particularly under the high incorporation rates. In addition, A. sinicus improved much more resource availability (mineral N and dissolved organic C) than L. multiflorum. Together, the quantity and quality of plant residues jointly drive soil food web structure, and a trait-based framework facilitates the mechanical understanding of afterlife effect of plant on soil ecosystems. [ABSTRACT FROM AUTHOR]

Soil fauna plays irreplaceable roles in delivering ecosystem functions in the face of climate change and human activities. Understanding how soil fauna-mediated processes change following environmental stresses is therefore critical to the maintenance of ecosystem services. This study assessed the soil functional capability, as measured by short-term decomposition of plant residues, subjected to simulated copper and heat stress in the presence, or absence, of enchytraeids (Enchytraeus florentinus) in an arable soil. Results showed that enchytraeid density decreased to 37%, 10%, and 5% of the initial density at the end of the experiment in the control, copper, and heat treatments, respectively. Soil functional capability increased in the presence of enchytraeids, but only in the stressed soils and not apparently in the controls. Fungal biomass was increased in the presence of enchytraeids particularly in the control soil. The enchytraeids did not affect water extractable organic C (WEOC) and total extractable N (TEN) in the control; however, they increased TEN in both stressed soils and WEOC in the copper stressed soil. We found that the enchytraeid effects on functional capability were positively related to the proportions of dead enchytraeids throughout the experiment duration. We infer that the contribution of enchytraeids to soil functional capability was mainly due to the after-life effects, most possibly through three potential mechanisms including (1) enhancement of microbial activity with resource contributed from their dead bodies, (2) through microhabitat improvement established before their death, and (3) microbiome composition changes derived from live or dead enchytraeids. We conclude by our case as an example that soil fauna could sustain key ecosystem functions under adverse conditions, highlighting the importance of soil biodiversity conservation in a changing world. [ABSTRACT FROM AUTHOR]

Two greenhouse experiments using soils from long-term field plots were carried out to test whether and how soil factors modulated by organic amendments feed back to rice plant growth and defense against an aboveground herbivore, the planthopper Nilaparvata lugens. Using factorial combinations of sterilized soil and soil inocula obtained from chemically amended plots (i.e., control treatment) or chemically plus organically amended plots (i.e., organic treatment), we disentangled the effects of biotic and abiotic soil properties on plant and planthopper performance. We found that, compared with abiotic soil properties, soil biological factors were the main drivers in regulating plant growth performance. Specifically, soil biota that are shaped by the organic treatment had high microbial abundance and diversity and enhanced rice plant tolerance (i.e., increasing plant total biomass) and resistance (i.e., decreasing amino acid and sugar concentrations) to planthoppers. Moreover, the organic treatment simultaneously increased plant growth and defense against planthoppers, which could be explained by high soil nutrient availability driven by soil biota. Our results demonstrate the importance of synergistic effects of soil biota and soil abiotic factors on plant growth and resistance to herbivory. These findings are important for better understanding the mechanisms and impacts of ecological intensification as well as the potential of steering soil communities to reduce the use of chemical fertilizers and pesticides and further optimize crop production. [ABSTRACT FROM AUTHOR]

Biochar application is perceived as a promising agricultural technology, but risk evaluation on the soil ecosystem has focused exclusively on soil microbes, whether microfood-web is likewise influenced by biochar remains unclear. We carried out a pot experiment planted with rapeseed for 2 years to test how biochar application (0, 20, 60 t ha−1), with or without nitrogen (N) fertilizer (0, 60, 120 t ha−1), affected soil microbes and microfauna (protists and nematodes). We observed that a high amount of biochar (60 t ha−1) increased crop productivity, microbial activity, and biomass carbon (C) and N, as well as the abundance of flagellates (protists), but decreased the abundances of bacterivorous, fungivorous, and herbivorous nematodes as well as the abundance of amoebae (protists). High biochar addition rates also shifted nematode community composition toward a fungivore dominance, and favored herbivores by decreasing the ratio of microbivorous to herbivorous nematodes. However, N fertilizer and its interaction with biochar generally had no effect on microbial activity and biomass as well as the abundance of protist and nematode. A structural equation model revealed that the effects of biochar on soil biota were largely direct, which might depend on biochar properties (e.g., pore size and alkalinity), whereas indirect effects, mediated by crop, soil pH, soil moisture, and polycyclic aromatic hydrocarbon (PAH) concentration, generally had no effect on soil biota. We conclude that biochar is a suitable soil amendment for increasing crop growth, but its detrimental effect on multitrophic levels of soil fauna calls for an identification of the optimal application rate and size fraction that could minimize potential negative effects on certain soil communities. [ABSTRACT FROM AUTHOR]

We conducted a microcosm experiment with soil being sterilized, reinoculated with native microbial community and subsequently manipulated the bacterivorous nematodes, including three treatments: without (CK) or with introducing one species of the two bacterivores characterized with different body size but similar c-p (colonizer-persister) value ( Rhabditis intermedia and Protorhabditis oxyuroides, accounted for 6 and 59% of bacterivores in initially undisturbed soil, respectively). We monitored the NO and CO emissions, soil properties, and especially quantified gross N transformation rates using N tracing technique after the 50 days incubation. No significant differences were observed on soil NH and NO concentrations between the CK and two bacterivores, but this was not the case for gross N transformation rates. In comparison to CK, R. intermedia did not affect soil N transformation rates, while P. oxyuroides significantly increased the rates of mineralization of organic N to NH , oxidation of NH to NO , immobilization of NO to organic N and dissimilatory NO reduction to NH . Furthermore, the mean residence time of NH and NO pool was greatly lowered by P. oxyuroides, suggesting it stimulated soil N turnover. Such stimulatory effect was unrelated to the changes in abundance of bacteria and ammonia-oxidizing bacteria (AOB). In contrast to CK, only P. oxyuroides significantly promoted soil NO and CO emissions. Noticeably, bacterivores increased the mineralization of recalcitrant organic N but decreased soil δC and δN values, in particular for P. oxyuroides. Combining trait-based approach and isotope-based analysis showed high potential in moving forward to a mechanistic understanding of bacterivore-mediated N cycling. [ABSTRACT FROM AUTHOR]

Insecticidal crystal (Cry) proteins produced by transgenic Bacillus thuringiensis (Bt) rice that enter the soil via root exudation and plant residues may be harmful to non-target soil organisms. We conducted a 3-year field investigation to determine if soil nematode abundance and diversity were affected by exposure to two transgenic Bt rice cultivars, compared to their non-transgenic near isolines. Near isolines were Kemingdao (KMD-Bt) expressing the single Cry1Ab gene and its non-Bt near isoline Xiushui-11 (XSD), as well as Huahui-1 (HH-Bt) expressing the fused Cry1Ab/Cry1Ac gene and its non-Bt near isoline Minghui-63 (MH). Nematode variables including community composition, abundance, trophic groups, and most of the common genera differed significantly between the rice cultivars. However, these nematode variables were similar under transgenic Bt rice and its non-Bt near isoline, although higher Shannon's index value and Pielou's index value were found in soils planted with Bt rice than the non-Bt near isoline. During this 3-year field study, gene modification (single Cry1Ab gene and fused Cry1Ab/Cry1Ac gene) supports a more uniform distribution of nematode species but had no effect on soil nematode abundance and community composition. We conclude that continuous cultivation of KMD-Bt and HH-Bt rice varieties for 3 years is not detrimental to soil nematode communities under field conditions. [ABSTRACT FROM AUTHOR]

In agricultural ecosystems, most crop cultivars are bred for pest resistance with the aim of resisting aboveground herbivores, but it is unclear if this resistance also affects abundance, composition, and activity of underground pests and content of soil labile pools. A fully factorial greenhouse experiment was carried out, using four rice cultivars with distinct resistance to shoot herbivore brown planthopper, Nilaparvata lugens, with and without rice root nematodes, Hirschmanniella spp., to test two hypotheses: (1) rice cultivars resistant to brown planthopper are more susceptible to rice root nematodes and (2) rice root nematodes of resistant cultivars cause greater modification of labile pools of rhizosphere soil than those of susceptible cultivars by inducing more leakage of plant metabolites. Nematode abundance, soluble sugar and soluble amino acid contents of plant, and microbial biomass C and N, dissolved organic C and N, and soluble sugar and amino acid contents of rhizosphere soil were analyzed. The abundance of rice root nematodes substantially increased under all rice cultivars following root nematode inoculation. Rice cultivar resistance to brown planthopper did not affect the numbers of rice root nematodes but decreased negative effects of nematodes on root growth, shoot soluble sugar and amino acid contents, and labile pools of rhizosphere soil, probably implying that integrated complex mechanisms other than only resource allocation were involved in rice resistance to aboveground and belowground herbivores. Our study will contribute to a better understanding of aboveground-belowground interactions and to the development of integrated pest managements by considering belowground ecosystem responses in crop systems. [ABSTRACT FROM AUTHOR]

The effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N transformations and composition of ammonia-oxidizing bacteria (AOB) communities was investigated at the centimeter scale in a microcosm experiment under laboratory conditions. After 28 days, samples were collected from soil treated with urea or urea and DMPP at increasing distance from the fertilizer zone; this distance ranged from 0 to 5 cm in both horizontal and vertical directions. The results showed that DMPP application significantly increased soil pH and NH-N and mineral N (NH-N, NO-N, and NO-N) concentrations but decreased (NO + NO)-N concentration, and such effect was decreased by increasing the distance from the fertilizer zone. Fingerprint profiles of denaturing gradient gel electrophoresis showed that the number of bands decreased by increasing the distance from the fertilizer zone due to decreasing NH-N concentrations in the urea treatment. Compared to urea applied alone, DMPP application increased NH-N concentrations and decreased AOB diversity from 0 to 3 cm but promoted diversity from 3 to 5 cm distance from the fertilizer zone. A phylogenetic analysis showed that AOB communities were dominated by Nitrosospira cluster 3. Therefore, the nitrification inhibitor DMPP modified the composition of AOB communities by increasing the distance from the fertilizer zone and this probably was related to the changes in soil pH and inorganic N concentration. [ABSTRACT FROM AUTHOR]