Abstract
AbstractSoil respiration, Rs, is strongly controlled by water availability in semiarid grasslands. However, how Rs is affected by precipitation change (either as rainfall or as snowfall) especially under increasing nitrogen (N) deposition has been uncertain. A manipulative experiment to investigate the responses of growing season Rs to changes in spring snowfall or summer rainfall with or without N addition was conducted in the semiarid temperate steppe of China during three hydrologically contrasting years. Our results showed that both spring snow addition and summer water addition significantly increased Rs by increasing soil moisture. The effect of spring snow addition only occurred in years with both relatively lower natural snowfall and later snowmelt time. Summer water addition showed a much stronger effect on Rs by increasing plant root growth and microbial activities, but the magnitude also largely depended on the possible legacy effect of previous year precipitation. Our results indicated that precipitation increase in the form of snowfall had weaker effects than that in the form of rainfall as the former only accounted for less than 30% of total precipitation. Compared with other ecosystem processes, Rs was less responsible for increase in N deposition as it did not increase root productivity and microbial activities in the soils. Our results provided field data constraints for modeling the ecosystem carbon balance under the future global change scenarios in semiarid grasslands.
Highlights
Soil respiration, Rs, is considered one of the largest fluxes in global terrestrial carbon (C) cycle, and a small change in the magnitude of Rs could have a significant impact on the atmospheric CO2 concentration (Schlesinger and Andrews 2000)
Responses of soil temperature and moisture to water and N addition. Both spring snow addition and summer water addition showed significant effects either on soil temperature or on moisture, but the effects varied across different years
Averaged across growing seasons, spring snow addition showed no significant effects on soil temperature during the three study years (Fig. 1a, c, e, Table 2)
Summary
Rs, is considered one of the largest fluxes in global terrestrial carbon (C) cycle, and a small change in the magnitude of Rs could have a significant impact on the atmospheric CO2 concentration (Schlesinger and Andrews 2000). As productivity in dryland areas, similar to many other terrestrial ecosystems, is limited by the coupling availability of nitrogen (N) and water (Wang et al 2015), changes in N deposition and precipitation regimes will inevitably affect Rs owing to changes in C supply for roots, microbial activities, and eventually ecosystem C cycle (Yan et al 2010). In areas where N is the limiting factor for plant growth, N addition might increase Rs, but in tropical and other regions with older severely weathered soils, where nitrogen may not be the most limiting nutrient, the opposite effect might occur (Janssens et al 2010)
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