How soil biodiversity and related ecosystem functions respond to temporal and spatial changes in precipitation is still an open question. Non-plant-parasitic soil nematodes depend directly upon soil water availability for movement, and therefore they may be highly vulnerable to changes in precipitation. Non-parasitic nematodes are one of the most diverse metazoan taxa in terrestrial ecosystems and are a major player in global soil carbon cycling through their role in organic matter decomposition. In fact, the nematode carbon footprint conveys additional information on the biomass, metabolic activity and magnitude of carbon flow in soil food-webs and provides an effective method for monitoring resource availability and estimating the contribution of nematodes to ecosystem functioning. We experimentally reduced and increased growing-season precipitation for 2 years in field plots at arid, semiarid, and mesic grasslands and assessed precipitation controls on non-parasitic nematode genera diversity and community carbon footprint estimated through open access data on biomass and metabolic activity of nematode genera. We tested predictions that nematode diversity and carbon footprint would consistently increase with temporal increases in precipitation at dry, but not wetter grasslands, because of increased predation of dominant species with more precipitation in mesic environments.
Results/Conclusions
Changes in annual precipitation affected both nematode generic diversity (p<0.01, r2=0.25) and evenness (p<0.001, r2=0.47) across all sites, but the mechanism behind these temporal responses appears to differ for arid and mesic grasslands. In arid and semiarid conditions, there was a loss of drought-adapted rare taxa with increasing precipitation, whereas in mesic conditions increases in the population of predaceous taxa with increasing precipitation may have caused the observed reductions in colonizer taxa and yielded the negative precipitation–diversity relationship. Our results also revealed a negative relationship among spatial changes in precipitation and nematode genera evenness (p<0.05, r2=0.47). The effects of temporal changes in precipitation on nematode respiration, production, and biomass carbon were all dependent on local long-term precipitation (significant spatial*temporal precipitation interaction; prespiration=0.05, r2respiration=0.53, pproduction<0.001, r2production=0.90, pbiomass<0.01, r2biomass=0.73). At the mesic site, nematode respiration, production, and biomass C decreased at a rate of –1.39, –0.63, and –7x10-4 µg C respectively for each 1-mm increase in received precipitation. At the arid site, respiration, production, and biomass C increased at 0.16, 0.01, and 6x10-5 µg C respectively for each 1-mm increase in received precipitation. Our results indicate that effects of precipitation on soil nematode communities will have contrasting functional implications to soil carbon cycling from arid to mesic grasslands.