Precipitation events and long-term nitrogen addition synergistically stimulate heterotrophic respiration in a semi-arid meadow steppe

Abstract

Variation in precipitation event size and nitrogen deposition are important global change factors, which have the potential to affect soil respiration and its components, especially in water- and nitrogen-limited semi-arid ecosystems. However, interactive effects of precipitation events and nitrogen input on soil respiration and its components remain largely unknown. We conducted a mesocosm simulation experiment to examine responses of soil respiration and its components, heterotrophic respiration and autotrophic respiration, to changes in precipitation event size (0, 5, 10, 20, and 50 mm; July 2020) and long-term nitrogen addition (0 and 10 g m⁻² yr⁻¹; since 2011). The precipitation events triggered the pulsing release of soil respiration and its components, but heterotrophic respiration and autotrophic respiration had different response thresholds, response times, and flux magnitude. The precipitation events significantly stimulated the cumulative soil respiration and its components, among which the cumulative soil respiration and heterotrophic respiration increased quadratically, and the cumulative autotrophic respiration increased linearly, with the increase in precipitation event size. The nitrogen addition suppressed the rates of soil respiration and heterotrophic respiration before the precipitation events but improved the net increment of cumulative soil respiration and heterotrophic respiration after the precipitation events. The precipitation events and long-term nitrogen addition synergistically stimulated the cumulative soil respiration and heterotrophic respiration but had no synergistic effect on the cumulative autotrophic respiration. Precipitation events and nitrogen addition increased soil moisture and dissolved inorganic nitrogen, enhancing microbial biomass and activity, which in turn drove cumulative soil respiration and heterotrophic respiration, and by increasing plant biomass, promoted cumulative autotrophic respiration. Overall, our results highlight the importance of the interactive effects of precipitation events and long-term nitrogen addition on soil respiration and heterotrophic respiration, suggesting that such interactions should be considered to accurately assess and predict carbon budget in future global change scenarios.