Precipitation pulses and soil CO2 flux in a Sonoran Desert ecosystem
Precipitation pulses and soil CO2 flux in a Sonoran Desert ecosystem
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DOI：
10.1111/j.1365-2486.2006.01307.x
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发表时间：
2007-02
影响因子：
11.6
通讯作者：
R. Sponseller
中科院分区：
文献类型：
--
作者：
R. Sponseller
降水是干旱和半干旱生态系统中生物过程的主要驱动力。这些水有限系统中的土壤生态地球化学过程与偶发性降雨事件密切相关，微生物活动与降雨量和降雨时间之间的关系对整个系统的碳（C）平衡具有影响。在这里，风暴的大小和事件之间的时间脉冲土壤呼吸的影响进行了探讨，在上索诺兰沙漠生态系统。在现场实验性再润湿后，CO2流出量立即增加了30倍，但通常在48小时内恢复到背景水平。在48小时内，CO2的综合产量在2.5至19.3 g C m−2之间，灌木下的CO2产量大于间作空间。当水连续几天，后润湿损失的CO2只有一半大的初始通量，和第二个脉冲的大小随时间的连续事件之间的增加。土壤呼吸与表层土壤有机质含量的关系比与降雨量的关系更为密切。灌木下，率随风暴大小呈非线性增加，在约0.5厘米模拟风暴达到渐近线。这种非线性关系源于（1）在小时间尺度上表现出的微生物活性的资源限制，以及（2）在更深的土壤层中大大降低的处理速率。因此，超过风暴规模的某个阈值，增加土壤湿度的持续时间或深度对短期CO2损失的影响很小。此外，实验室复湿在很宽的范围内的土壤含水量表明，微生物活性和CO2流出降雨后，可能会进一步修改的路由和重新分配的水沿着山坡。最后，对长期降水数据的分析表明，该系统中一半的季风风暴足以引起土壤异养活动和C损失，但不足以引起沙漠灌木的自养活动和C积累。
Precipitation is a major driver of biological processes in arid and semiarid ecosystems. Soil biogeochemical processes in these water‐limited systems are closely linked to episodic rainfall events, and the relationship between microbial activity and the amount and timing of rainfall has implications for the whole‐system carbon (C) balance. Here, the influences of storm size and time between events on pulses of soil respiration were explored in an upper Sonoran Desert ecosystem. Immediately following experimental rewetting in the field, CO2 efflux increased up to 30‐fold, but generally returned to background levels within 48 h. CO2 production integrated over 48 h ranged from 2.5 to 19.3 g C m−2 and was greater beneath shrubs than in interplant spaces. When water was applied on sequential days, postwetting losses of CO2 were only half a large as initial fluxes, and the size of the second pulse increased with time between consecutive events. Soil respiration was more closely linked to the organic matter content of surface soils than to rainfall amount. Beneath shrubs, rates increased nonlinearly with storm size, reaching an asymptote at approximately 0.5 cm simulated storms. This nonlinear relationship stems from (1) resource limitation of microbial activity that is manifest at small time scales, and (2) greatly reduced process rates in deeper soil strata. Thus, beyond some threshold in storm size, increasing the duration or depth of soil moisture has little consequence for short‐term losses of CO2. In addition, laboratory rewetting across a broad range in soil water content suggest that microbial activity and CO2 efflux following rainfall may be further modified by the routing and redistribution of water along hillslopes. Finally, analysis of long‐term precipitation data suggests that half the monsoon storms in this system are sufficient to induce soil heterotrophic activity and C losses, but are not large enough to elicit autotrophic activity and C accrual by desert shrubs.