合成氮肥对中国茶园土壤养分供应和活性氮流失的影响

茶树是我国广泛种植的一种高需氮经济植物。目前,尽管茶园生态系统中已开展了一些模拟氮肥施用的实验,但对于合成氮肥如何影响茶园土壤性质、养分供应及活性氮的流失仍缺乏全面的评估和量化。对2004—2016年间发表的相关研究数据进行整合分析,结果显示,施用合成氮肥导致我国茶园土壤p H平均降低0.20,使土壤总无机氮升高172%,对土壤有机碳、有效磷和钾离子浓度无影响。合成氮肥使土壤钙、镁离子浓度分别降低了23%和37%,铝离子浓度上升了近54%。同时,使土壤N_2O排放和无机氮淋溶分别增加292%和127%。总体上,大量施用合成氮肥加剧了我国茶园土壤酸化和养分元素的流失,增加了活性氮的流失,威胁着我国茶园生态环境的可持续发展。     

Response of ecosystem respiration to warming and grazing during the growing seasons in the alpine meadow on the Tibetan plateau

Intensive studies reveal that there is much uncertainty regarding how ecosystem and soil respiration will respond to warming and grazing, especially in the alpine meadow ecosystem. We conducted a first of its kind field-manipulative warming and grazing experiment in an alpine meadow on the Tibetan plateau to determine the effects of warming and grazing on ecosystem and soil respiration for 3-years, from 2006 to 2008. Generally, warming and grazing did not affect seasonal average ecosystem respiration (Re), and there was no interaction between grazing and warming. However, they significantly affected the Re early in the growing season and by the end of the growing season. Warming significantly increased seasonal average soil respiration (Rs) by 9.2%, whereas the difference mainly resulted from data gathered early in the growing season, before June 2007. Positive correlations between soil temperature and Re and Rs were observed, and soil temperature explained 63-83% of seasonal Re variations during the 3-year study and 19-34% of Rs variations in 2007. Seasonal Re in 2008 and Rs in 2007 were slightly negatively correlated to soil moisture, but interannual average Re decreased with a decrease in precipitation for all treatments. Warming and grazing reduced the Q₁₀ value of Re in 2007 and 2008 but did not affect the Q₁₀ value of Rs. The Q₁₀ values of Rs were much lower than the Q₁₀ values of Re in 2007. These results suggest that grazing may reduce the temperature sensitivity of Re and that Re was mainly controlled by soil temperature rather than moisture which varied with timescale in the alpine meadow.