Altered energy dynamics of multitrophic groups modify the patterns of soil CO2 emissions in planted forest

Soil microbes and fauna as key components of belowground food webs play important roles in energy flux and carbon cycling in terrestrial ecosystems. However, it remains unclear whether forestry management regimes alter the energetic structure of soil food webs and thereby reshape the patterns of soil CO2 emissions in planted forest. Here, we tested the effects of legume (Cassia alata) addition, understory removal, understory removal with legume addition and all plants removal on energy fluxes through soil food webs and soil CO2 flux in the wet and dry seasons. We show that soil heterotrophic respiration contributed 36.9–57.8% of total CO2 flux in the soil. In the dry season, C. alata addition increased soil heterotrophic respiration by 24.6% and 57.3%, respectively, when compared with the control and understory removal treatment. Compared with the understory removal treatment, the total energy flux across the whole food web increased with legume addition (i.e., C. alata addition and understory removal with C. alata addition). Legume addition supported a high proportion of energy flux through herbivorous nematodes, whereas understory vegetation removal supported a high proportion of energy flux through microbivorous nematodes. Less energy fluxes were transferred from basal resources to fungivorous mites and collembolans compared with microbivorous and herbivorous nematodes. The total soil CO2 flux was positively correlated with metabolic rates of herbivorous and omnivorous-predatory nematodes, and energy fluxes through multitrophic groups. Taken together, legume addition and understory vegetation removal modify the patterns of soil CO2 emissions via changing nematode metabolic rates and re-shaping the energetic structure of soil food webs.