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Purpose: Roots bridge aboveground and belowground systems, and play a pivotal role in structuring root-associated organisms via influencing food resources and habitat conditions. Most studies focused on the relationships between plant identity and root-associated organisms, however, little is known about how root traits affect nematode communities within the rhizosphere. Methods: We investigated the relationships between root traits of four plant species and nematode abundance, community structure and trophic complexity in an ex-arable field. Results: While the relative abundance of herbivores was negatively associated with specific root length (SRL), specific root area (SRA), root length density (RLD) and root C: N ratio, free-living nematodes were positively affected by these traits, implying a multifaceted effect of root traits on root-associated organisms. Importantly, we found that finer root systems promoted the complexity of rhizosphere nematode community, by increasing the relative abundance of high trophic-level nematodes (i.e., omnivores and predators) and enhancing nematode diversity. Conclusions: Our findings suggest that root traits could comprehensively shape soil community structure and interactions, and provide new insights into soil biodiversity conservation and functional maintenance. [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]

The small subunit ribosomal gene (SSU rDNA) is used in both environmental and phylogenetic studies of nematodes. However, currently described SSU rDNA primers near to the 5′ end of the gene show mismatches with a number of different nematode sequences. Here a new SSU rDNA 5′ forward primer, Nem_SSU_F74, is designed from existing database sequences and its performance compared with a previously described forward primer, SSU_F04, by sequencing from nematode assemblage DNA, in combination with a previously described reverse primer. DNA was extracted from three nematode assemblages isolated from arable soil and, in total, six clone libraries were created: three amplified with established forward primer SSU_F04 and three with the novel primer Nem_SSU_F74. Ninety six clones were sequenced from each library. Nem_SSU_F74 libraries yielded a higher number of nematode sequences than SSU_F04 libraries, and a greater number of nematode taxa were found using the novel forward primer. The most abundant sequences were common to libraries created with either forward primer. Data from a morphological survey of the same samples revealed that biomass was more closely related to molecular analysis than simple counts of nematodes. For all but one nematode order (Aphelenchida), percentage assemblage composition was not significantly different between biomass and sequences obtained with the novel forward primer Nem_SSU_F74. [ABSTRACT FROM AUTHOR]

The long-term (18 years) effects of re-vegetating eroded soil on soil microbial biomass, community structure and diversity were investigated in a forest soil derived from Quaternary clay in the Red Soil Ecological Experimental Station of the Chinese Academy of Sciences. Large areas of land in this region of China have been subjected to severe soil erosion, characterised by the removal of the fertile surface soil and even the exposure of parental rock in some areas due to a combination of deforestation and heavy rainfall. The effects of planting eroded or uneroded soil with Pinus massoniana, Cinnamomum camphora or Lespedeza bicolor on the soil microbial community and chemical properties were assessed. Total soil microbial community DNA was extracted and bacterial 16 S rRNA gene fragments were amplified by PCR and analysed by terminal restriction fragment length polymorphism (T-RFLP). Microbial biomass carbon (Cmic) was measured by chloroform fumigation-extraction. Following the restoration there were significant increases in both Cmic and bacterial diversity (Shannon index), and significant changes in bacterial community structure. Erosion factors were significant only in minor dimensions suggesting that the restoration had been largely successful in terms of bacterial community structure. Compared with uneroded soil, Cmic recovered in L. bicolor and P. massoniana restored eroded plots and was significantly greater under these tree species than C. camphora, although soils in C. camphora restored plots displayed the highest bacterial diversity. The recovery of microbial biomass and diversity in the eroded plots was, to large extent, accompanied by the development of the same bacterial community structure as in the uneroded plots with erosion having relatively little effect on bacterial community structure. [ABSTRACT FROM AUTHOR]