Differential responses of auto‐ and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe

Abstract

Abstract Evaluating how autotrophic (SR A ), heterotrophic (SR H ) and total soil respiration (SR TOT ) respond differently to changes of environmental factors is critical to get an understanding of ecosystem carbon (C) cycling and its feedback processes to climate change. A field experiment was conducted to examine the responses of SR A and SR H to water and nitrogen (N) addition in a temperate steppe in northern China during two hydrologically contrasting growing seasons. Water addition stimulated SR A and SR H in both years, and their increases were significantly greater in a dry year (2007) than in a wet year (2006). N addition increased SR A in 2006 but not in 2007, while it decreased SR H in both years, leading to a positive response of SR TOT in 2006 but a negative one in 2007. The different responses of SR A and SR H indicate that it will be uncertain to predict soil C storage if SR TOT is used instead of SR H to estimate variations in soil C storage. Overall, N addition is likely to enhance soil C storage, while the impacts of water addition are determined by its relative effects on carbon input (plant growth) and SR H . Antecedent water conditions played an important role in controlling responses of SR A , SR H and the consequent SR TOT to water and N addition. Our findings highlight the predominance of hydrological conditions in regulating the responses of C cycling to global change in the semiarid temperate steppe of northern China.