Responses Of Soil Nematode Community To Changing Climate And Carbon Input Pathway

Since the Industrial Revolution, human activities have resulted in atmospheric enrichment of greenhouse gases, climate warming, changing precipitation regimes, and nitrogen(N) deposition, which can profoundly impact terrestrial ecosystems. Soil nematodes are one of the dominant componenst in soil food web and play an important role in biogeochemical cycles. However, the composition and structure of soil nematode community under climate change are still unclear.This study used four manipulative experiments to examine the impacts of climate warming, changing precipitation, N addition and changing C inputs on soil nematode population density and community structure. The first experiment examined the impacts of climate warming and water addition on soil nematode community. The second one showed the effects of water and N addition on soil nematode community in an old-field grassland of North China Plain. The third one illustrated the responses of soil nematode to multi-level N fertilizer addition in winter wheat field of North China Plain. The last one compared the differential influences of plant C input parthways on soil nematode. The key findings showed as follows:1. Warming had limited influence on soil nematodes in the temperate grassland of northern China.However, increased precipitation significantly stimulated nematode total abundance and bacterivore proportion. The relative abundance of omnivores-predators was significantly decreased by increased precipitation. Across the 2 years, elevated precipitation enhanced the relative abundance of Rhabditis spp,Plectus spp, Tylecholaimus spp and Tylenchus spp, whereas suppressed those of Nygolaimun spp,Axonchium spp and Eudorylaimus spp. Comparing with the control treatment, warming slightly increased the relative abundance of Labronema spp and Axonchium spp, but resulted in a decrease in the relative abundance of Nyglaimus spp. There were no interactive effects of warming and increased precipitation on the abundance of soil nematodes.2. Water addition significantly increased soil nematode abundance and generic richness, but had no effects on the relative abundance of different trophic groups in an old-field grassland of North China Plain.Nitrogen addition had little effect on nematode abundance, but reduced their generic richness, and significantly altered community structure by promoting the abundance of bacterivores and suppressing that of fungivores and omnivores- predators. The changes in nematode community structure could have been attributed to the changes in soil p H, whereas nematode population size was predominantly influenced by resource availability.3. In the winter wheat field of North China Plain, total nematode abundance reached the highest values at the shooting stage of wheat, and was significantly increased by fertilization. On the contrary, the nematode generic richness decreased with increasing level of N fertilizer. The relative abundance of bacterivores showed minor changes among different fertilization treatments whereas that of fungivores was suppressed by the N4 treatment. Plant parasites were most abundant under the N2 treatment. The relative abundance of omnivores-predators declined with increasing level of N fertilizer. The results indicate that trophic groups have distinctive responses to different levels of N fertilization and N fertilization may induce an abundant but simple nematode community in the winter wheat field of North China Plain. Our findings also highlight the potential of adequate N application to reduce plant parasites and control agriculture pests.4. Plant removal significantly decreased soil resource availability(i.e. SOC and TN) and soil p H, and subsequently altered nematode abundance and trophic structure. The nematode abundance and generic richness were decreased by 73.09% and 17.98%, respectively, by plant removal. Plant removal enhanced the relative abundance of bacterivores, but reduced those of plant parasites and omnivores-predators. Litter addition increased nematode abundance by 37.88%. Litter removal decreased the nematode generic richness by 9.39%. There were significantly interactive effects of plant removal and litter manipulations on the total nematode abundance and genus richness. Our observations suggest that the effects of belowground C input on soil nematodes are greater than those of the aboveground C input. The impacts of litter on soil nematode community could be mediated by living plants.5. Positive dependences of soil respiration on soil nematode abundance and generic richness indicate that the potential contribution of soil microfauna to soil respiration should be considered when assessing the C dynamic of semiarid grassland ecosystems.