Effects of Manipulating Water and Temperature on Soil Nematode Communities of Heterogeneous Karst Habitats in Southwest China

ABSTRACT: Global climates are rapidly changing and future climates are predicted to be characterized by extreme climatic events, especially prolonged drought and hot weather. In this study, we explored the effects of manipulated low and high soil water availability and soil temperature on soil food webs (as indicated by soil nematode communities) from contrasting soil habitats. Soils were collected from a relatively arid karst mountain peak, a relatively moist karst piedmont, and a mixed soil of these two was also tested. The results showed that water availability was the primary factor influencing the soil food web. Soil food web structures were mature under low water availability in mountain peak soils and under high water availability in piedmont soils. In the mountain peak soils, high water availability decreased the maturity index and structure index of soil nematodes, which was mainly due to marked increase in the absolute and relative abundances of low trophic level organisms (i.e., bacterivores and fungivores). In the Piedmont soils, high water supply increased the maturity index and structure index of soil nematodes, which mainly due to the increases in the absolute and relative abundances of higher trophic level nematodes, such as omnivores and predators. However, the nematode maturity index and structure index showed no significant response to variations in water availability when soils from the mountain peak and piedmont were mixed and cultured together. Although the overall effect of temperature on the soil nematode community was weaker than that of water availability, temperature exerted significant context-dependent effects. Particularly, moderate temperatures increased fungivorous nematode abundance under drought conditions in mountain peak soils but decreased it under moist conditions in piedmont soils. Notably, plant-parasitic nematodes showed no significant response to either soil moisture or temperature treatments across all soil types, indicating a high degree of stability in this trophic group under short-term fluctuations in water and temperature. Our results suggest that changes in precipitation may have stronger effects on soil nematode communities than increases in temperature. However, the interaction between temperature and moisture should not be overlooked, as it can shape nematode community composition in habitat-specific ways. In addition, drought-tolerant soil organisms may be available for improving the resistance of soil food webs to prolonged drought under climate change conditions.