Response of long-, medium- and short-term processes of the carbon budget to overgrazing-induced crusts in the Tibetan Plateau
Response of long-, medium- and short-term processes of the carbon budget to overgrazing-induced crusts in the Tibetan Plateau
复制标题
DOI：
10.1007/s10533-011-9632-9
复制
发表时间：
2012-11
期刊：
影响因子：
4
通讯作者：
Sebastian Unteregelsbacher;S. Hafner;G. Guggenberger;G. Miehe;Xingliang Xu;Jianquan Liu;Y. Kuzyakov
中科院分区：
文献类型：
--
作者：
Sebastian Unteregelsbacher;S. Hafner;G. Guggenberger;G. Miehe;Xingliang Xu;Jianquan Liu;Y. Kuzyakov
青藏高原的嵩草牧场是世界上最大的高山草原生态系统。这些牧场在过去的几千年游牧畜牧业中保持稳定。然而，畜群密度的大幅增加促进了过度放牧，对植被和土壤的影响尚不清楚，特别是对碳（C）、养分和水的循环。无植被斑块的死根垫覆盖的蓝绿藻和甲壳地衣（结壳）是常见的overgrazedKobresiapastures，但其对碳周转过程的影响是完全未知的。我们测试的假设，结皮强烈影响C循环通过检查：（一）长期C股票测量土壤有机质含量;（二）中期C股票死根;（三）最近的C通量分析活根和CO2流出;（四）快速分解的根分泌物。高达7.5倍，地上和地下的生物量少1.9倍，发现在地壳补丁，反映了一个小得多的C输入到土壤中相比，非crustKobresiapatches。一个较低的C输入最初改变了长期的C股票下地壳在上根垫层。活根和CO2排放量之间的线性回归表明，根贡献了23%的总CO2在非结皮地区（平均7 - 8月5.4克C m − 2天− 1）和18%在结皮（5.1克C m − 2天− 1）。为了确定土壤中快速周转过程的差异，我们添加了13 C标记的葡萄糖，甘氨酸和乙酸，代表三种主要的根系分泌物。葡萄糖（0.7天-1）、甘氨酸（1.5天-1）和乙酸（1.2天-1）的分解率在结壳和非结壳下没有差别。然而，更多的13 C，仍然在土壤中的结壳，反映不完全分解的分泌物和根吸收。这表明，地壳斑块减少中期的C周转率响应低得多的C输入。非常高的13 C量回收的植物从非结壳地区以及2倍以下的吸收结壳下的根表明，非常密集的根是有效的竞争对手与微生物的可溶性有机物。总之，过度放牧引起的甲壳地衣和蓝藻结皮的C循环改变与强烈减少C输入和中期C周转减少。
TheKobresiapastures of the Tibetan Plateau represent the world’s largest alpine grassland ecosystem. These pastures remained stable during the last millennia of nomadic animal husbandry. However, strongly increased herds’ density has promoted overgrazing, with unclear consequences for vegetation and soils, particularly for cycles of carbon (C), nutrients and water. Vegetation-free patches of dead root-mat covered by blue-green algae and crustose lichens (crusts) are common in overgrazedKobresiapastures, but their effect on C turnover processes is completely unknown. We tested the hypothesis that the crusts strongly affect the C cycle by examining: (i) the long-term C stock measured as soil organic matter content; (ii) medium-term C stock as dead roots; (iii) recent C fluxes analyzed as living roots and CO2efflux; and (iv) fast decomposition of root exudates. Up to 7.5 times less aboveground and 1.9 times less belowground living biomass were found in crust patches, reflecting a much smaller C input to soil as compared with the non-crustKobresiapatches. A lower C input initially changed the long-term C stock under crusts in the upper root-mat horizon. Linear regression between living roots and CO2efflux showed that roots contributed 23% to total CO2under non-crust areas (mean July–August 5.4 g C m−2day−1) and 18% under crusts (5.1 g C m−2day−1). To identify differences in the fast turnover processes in soil, we added13C labeled glucose, glycine and acetic acid, representing the three main groups of root exudates. The decomposition rates of glucose (0.7 day−1), glycine (1.5 day−1) and acetic acid (1.2 day−1) did not differ under crusts and non-crusts. More13C, however, remained in soil under crusts, reflecting less complete decomposition of exudates and less root uptake. This shows that the crust patches decrease the rates of medium-term C turnover in response to the much lower C input. Very high13C amounts recovered in plants from non-crust areas as well as the two times lower uptake by roots under crusts indicate that very dense roots are efficient competitors with microorganisms for soluble organics. In conclusion, the altered C cycle in the overgrazing-induced crustose lichens and blue-green algae crusts is connected with strongly decreased C input and reduced medium-term C turnover.