荒漠区地表凋落物分解对季节性降水增加的响应

为探讨季节性降水增加对荒漠生态系统凋落物分解的影响,在古尔班通古特沙漠南缘,选择粗柄独尾草(Eremurus inderiensis)叶、尖喙牻牛儿苗(Erodium oxyrrhynchum)叶、尖喙牻牛儿苗茎、沙漠绢蒿(Seriphidium santolinum)茎4种凋落物样品,在2009-2011年研究了模拟季节降水增加(冬春增雪、夏季增水)和自然降水处理下凋落物的分解。持续2年的分解实验表明:(1)各组分凋落物的质量损失过程可以用负指数衰减方程较好地拟合(R20.90);经过637天的分解,各组分凋落物质量残留率在自然降水、冬春增雪、夏季增水处理下均无显著性差异(p0.05)。粗柄独尾草叶、尖喙牻牛儿苗叶、尖喙牻牛儿苗茎、沙漠绢蒿茎在自然降水处理下的质量残留率分别为40.59%、35.50%、36.00%和63.96%;(2)各组分凋落物的质量残留率与N残留率显著正相关,凋落物N的损失快于其质量损失,且初始N含量与分解速率显著正相关(r=0.60,p=0.038),C/N解释了71%的地面凋落物分解速率。研究表明,季节性的短暂降水增加对荒漠区地表凋落物分解没有显著影响,凋落物初始化学组成是预测荒漠区地表凋落物分解的重要因素。

Responses of surface litter decomposition to seasonal water addition in desert

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.