Soil respiration response to nitrogen fertilization experiment in tropical grassland

Abstract

We examined the response of soil respiration (SR) to nitrogen (N) input using a manipulation experiment in a tropical grassland. Studying the influence of N-input on the SR is important under sustainable agricultural strategies and future climate change. The response of SR is expected to vary in each ecosystem; therefore, manipulation experiments in many ecosystems and subsequent synthesis can be a significant strategy for climate change mitigation and adaptation. We hypothesized that the higher levels of N-input suppress the SR by reducing soil-C, species diversity, and biomass of the roots and microbes. For this study, seventy-two 1 × 1–m experimental plots (equally divided into six N-levels; each with 12 replicates) were established in 2013 on the campus of the Banaras Hindu University, India. On monthly basis, six levels of N (0, 30, 60, 90, 120, and 150 kg N ha−1 year−1) were applied to the plots. Soil and vegetation data were collected for 3 years and analyzed using statistical methods. The SR (mg m−2 h−1) ranged between 156 and 197 and significantly varied across the N-inputs. Analysis revealed 85 kg N ha−1 year−1 input is needed for the maximum SR because of higher contents of microbial biomass, soil-C, plant diversity, root biomass, and fast decomposition of the litters. The N-input beyond 85 kg ha−1 year−1 inhibited the SR due to N-induced soil acidification to the microbes and plants. We conclude that the SR of the tropical grassland ecosystem is synergistically governed by the N-input-modulated indirect effects of the soil and vegetation traits. © 2022 The Ecological Society of Japan.