Effects of seasonal drought on net carbon dioxide exchange from a woody-plant-encroached semiarid grassland
Effects of seasonal drought on net carbon dioxide exchange from a woody-plant-encroached semiarid grassland
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DOI：
10.1029/2008jg000900
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发表时间：
2009-12
影响因子：
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通讯作者：
R. Scott;G. D. Jenerette;D. Potts;T. Huxman
中科院分区：
文献类型：
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作者：
R. Scott;G. D. Jenerette;D. Potts;T. Huxman
[1]北美中部和南部温暖沙漠地区的年降水量在气候上分布在夏季和冬季之间，其间有两个显著的干旱期。我们使用来自涡旋协方差的能量和二氧化碳(CO2)通量，以及美国亚利桑那州南部半干旱稀树草原的标准气象和土壤湿度测量，以更好地了解暖季或冷季干旱对这些双峰强迫缺水地区生态系统二氧化碳交换的影响。在过去的100年里，这片历史悠久的草原被当地的沼泽树(Prosopis velutina Woot.)侵占，变成了稀树草原。在2004-2007年的4个观测年中，年降水量(P)均低于平均水平，但季风(7-9月)P均高于和低于平均水平，而冷季(12-3月)P始终不同程度地低于平均水平。该生态系统是大气中二氧化碳的净来源，范围为14~95gCm�2yr�1，其强度随降水量的减少而增大。当降雨量在分布和数量上最接近长期平均值时，生态系统基本上是碳中性的。夏季干旱导致碳损失增加，主要原因是生长季节缩短，以及该季节后期光合作用收益超过呼吸损失的时间长度。严重的冷季干旱导致春季碳吸收减少，夏季呼吸似乎增强，导致最大的年度净碳损失。
[1] Annual precipitation in the central and southern warm-desert region of North America is distributed climatologically between summer and winter periods with two prominent dry periods between them. We used energy and carbon dioxide (CO2) fluxes from eddy covariance along with standard meteorological and soil moisture measurements at a semiarid savanna in southern Arizona, United States, to better understand the consequences of warm or cool season drought on ecosystem CO2 exchange in these bimodally forced water-limited regions. Over the last 100 years, this historic grassland has converted to a savanna by the encroachment of the native mesquite tree (Prosopis velutina Woot.). During each of the 4 years of observation (2004–2007), annual precipitation (P) was below average, but monsoon (July–September) P was both above and below average while cool-season (December–March) P was always less than average by varying degrees. The ecosystem was a net source of CO2 to the atmosphere, ranging from 14 to 95 g C m � 2 yr � 1 with the strength of the source increasing with decreasing precipitation. When the rainfall was closest to the long-term average in its distribution and amount, the ecosystem was essentially carbon neutral. Summer drought resulted in increased carbon losses due mainly to a shortening of the growing season and the length of time later in the season when photosynthetic gain exceeds respiration loss. Severe cool season drought led to decreased spring carbon uptake and seemingly enhanced summer respiration, resulting in conditions that led to the greatest annual net carbon loss.