Responses of surface litter decomposition to seasonal water addition in desert
荒漠区地表凋落物分解对季节性降水增加的响应

Aims The decomposition of plant litter is a complex process mediated by biotic and abiotic factors. However, litter decomposition and its controlling factors are still controversial and unclear in arid and semi-arid ecosystems. In arid lands, precipitation has inconsistent effects on litter decomposition and nitrogen dynamics. Our objectives were to: (1) examine litter decomposition and nitrogen dynamics in litter with water additions at different seasons and (2) determine the factors critical to surface litter decomposition in arid lands. Methods We used the litter-bag method to investigate leaf decomposition of Eremurus inderiensis and Erodium oxyrrhynchum and stem decomposition of Erodium oxyrrhynchum and Seriphidium santolinum in China’s Gurbantunggut Desert. We placed litterbags filled with those litters on soil surface in October 2009. We added snow from December to March of the next year and water from June to August. Litterbags were collected in April, July and October of 2010 and in April and July of 2011. Mass loss, carbon, nitrogen and phosphorus content, and decomposition rates of litter were analyzed at each decomposition stage. In addition, soil water content at 0–10 cm soil depth was measured at 10-day intervals from April to November. Important findings The mass loss of different litters fit the exponential decay model (R2>0.90). After 637 days of decomposition, no significant differences were observed among natural precipitation, snow addition and water addition treatments, and the mass remaining for leaves of Eremurus inderiensis and Erodium oxyrrhynchum and stems of Erodium oxyrrhynchum and Seriphidium santolinum with natural precipitation were 40.59%, 35.50%, 36.00% and 63.96%, respectively. The mass remaining was positively related to nitrogen remaining, which meant the litter nitrogen loss was faster than mass loss. Correlation analysis showed that decay rates were positively related to initial nitrogen content and inversely related to initial C/N. Initial C/N could explain 71% of the variation in decomposition rate. Results suggest that water addition in different seasons will not promote decomposition of surface litters, and initial litter chemical composition is critical to surface litter decomposition in the Gurbantunggut Desert.