Abstract
Soil respiration (Rs) is an important source of atmospheric CO2 flux and is sensitive to changes in soil nutrient and water contents. Despite extensive studies on the effects of enhanced atmospheric nitrogen (N) deposition and changes in precipitation (P) on Rs, few studies have taken into account the effects of interactions between these factors on Rs of alpine grasslands. To address these questions, we investigated the effects of N addition (10 g N m−2 yr−1), changes in precipitation (±50% precipitation), and their interaction on soil respiration and its components, including heterotrophic respiration (Rh) and autotrophic respiration (Ra),in a Tibetan alpine steppe during three consecutive growing seasons. We found that Rs differed in its response to N addition and precipitation regimes. Specifically, decreased precipitation led to a significant reduction in Rs during the last two years, whereas N addition minimally impacted Rs. Another important finding was that soil respiration components differed in their response to N addition and precipitation regimes. Nitrogen addition significantly enhanced Ra, whereas Rh was not altered in response to N addition. By contrast, the precipitation regime led to marked changes in Rh, but exhibited marginally significant effects on Ra. Therefore, our findings highlighted that soil respiration differed in its response to N addition and precipitation regimes mainly due to the different responses of soil respiration components to these factors. Therefore, carbon dynamics should take soil respiration components into account under global change scenarios.
Highlights
As the second-largest carbon (C) flux, soil respiration (Rs) plays a critical role in the regulation of C cycling in terrestrial ecosystems
We conducted a field precipitation and N manipulative experiment in an alpine steppe, and we aimed to investigate the responses of soil respiration and its components to precipitation changes and N additions
We found that the addition of and altered precipitation had differential effects on soil respiration in a Tibetan alpine steppe plateau (Fig. 6)
Summary
As the second-largest carbon (C) flux, soil respiration (Rs) plays a critical role in the regulation of C cycling in terrestrial ecosystems. The effects of N availability on Rs were generally evaluated in previous studies, but the responses of these processes on the interaction of N additions and precipitation changes remain limited, in this semi-arid grassland. More extreme precipitation events and drought are predicted to occur in the future[26], and such changes will likely significantly affect the soil moisture and Rs. compared with drought, few studies have evaluated the influence of heavy precipitation on Rs27–29. The Bucket Model predicts that the primary productivity and Rs in arid lands is increased by the increased precipitation variability[34] To date, it remains unknown how precipitation changes affect soil respiration in cold and dry environments, such as the Tibetan alpine steppe. Few studies have concentrated on the influence of precipitation changes and N addition on Rs in alpine steppe
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