Assessment of soil nematode diversity based on different taxonomic levels and functional groups

Although soil nematode diversity has been used as an indicator of habitat characteristics and environmental change,the diversity of entire soil nematode communities has not been comprehensively evaluated at different taxonomic levels,or for different functional groups,or at a fine taxonomic level within functional groups.In this study,two taxonomic diversity indices,the Shannon-Wiener index(H′)and Simpson index(l),were used to evaluate the following:1)nematode diversity at different taxonomic levels for the whole community,2)nematode diversity of different functional groups,and 3)nematode generic diversity of functional groups in the following four land-use types:forage land,cropland,secondary forest,and grassshrubland.The results showed that significant differences in nematode diversity among landuse types were detected by assessment at the order level but not at the family or genus level.The results also showed that significant differences in nematode diversity were better revealed by assessment of trophic groups rather than cp groups.The generic diversities(H′)of omnivorous nematodes and cp3 nematodes also significantly differed among land-use types.Our results indicate that diversity at a high taxonomic level(i.e.,order)may be a more useful indicator than diversity at a low taxonomic level(i.e.,family or genus)of differences among land-use types.In addition,the functional group diversity(i.e.,trophic group,cp group,and the combination of these two groups)for the whole community and the taxonomic diversity within functional groups were useful indicators of differences among land-use types.

Plant species coexistence alleviates the impacts of lead on Zea mays L.

Whether plant coexistence can reduce the impacts of lead （Pb） on crops in agroecosystems has not been well understood. We conducted a factorial experiment to investigate the effects of weeds coexisting with maize （Zea mays L.） on Pb accumulation in maize and soil microbes at two Pb levels （ambient and 300 mg/kg）. Elevated Pb tended to increase the Pb concentration in maize and decreased soil microbial activity （indicated by the average well color development, AWCD）, functional group diversity, as well as arbuscular mycorrhizal （AM） colonization and vesicle number of maize. Compared to the monoculture, weeds coexisting with maize reduced the Pb concentrations in the root, leaf, sheath and stem of maize at both seedling and mature stages. In maize-weed mixtures, soil microbial activity and functional group diversity tended to increase for both Pb treatments relative to the monoculture. Furthermore, principal component analysis revealed that the soil microbial community structure changed with the introduction of weeds. The highest Pb accumulation in weeds occurred for the elevated Pb treatment in a three species mixture. The results suggest that multiple plant species coexistence could reduce lead accumulation in crop plants and alleviate the negative impacts on soil microbes in polluted land, thereby highlighting the significance of plant diversity in agroecosystems.