Response of soil respiration to water and nitrogen addition and its influencing factors: a four-year field experiment in a temperate steppe

PurposeSoil respiration (Rs) plays a crucial role in the terrestrial carbon cycle. We attempted to investigate how changes in water and nitrogen affect the Rs of grassland ecosystems through biotic and abiotic factors under the context of global change.MethodsWe conducted a 4-year manipulative field experiment with a randomized complete block design in a 2 × 4 factorial consisting of two water addition levels and three nitrogen addition levels in a typical temperate grassland in China to explore the response of Rs to different water and nitrogen addition treatments in the growing season, and the potential factors controlling Rs were analyzed using structural equation modeling (SEM).ResultsWater addition significantly enhanced the cumulative Rs in all years. The precipitation during the months of vigorous plant growth (May to July) was an important factor in determining the average Rs during the growing season. Nitrogen addition alone had no significant impacts on Rs except for short-term positive effects caused by low nitrogen addition (25 kg N ha−1 yr−1) during the period after nitrogen application in the first year. Although soil microbes and plant roots contributed to Rs, the main factors controlling Rs were still temperature and soil moisture.ConclusionThese findings indicate that water addition could promote Rs in semiarid grassland ecosystems. Changes in environmental factors could control Rs by affecting soil microorganisms and plant roots activity.