Is a drought a drought in grasslands? Productivity responses to different types of drought
Is a drought a drought in grasslands? Productivity responses to different types of drought
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DOI：
10.1007/s00442-020-04793-8
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发表时间：
2021-01-08
期刊：
影响因子：
2.7
通讯作者：
Knapp, Alan K.
中科院分区：
文献类型：
--
作者：
Carroll, Charles J. W.;Slette, Ingrid J.;Knapp, Alan K.
干旱的定义是降雨量明显低于正常水平，发生在降雨量低于平均水平或完全没有降水投入的时期，可限于一个季节，也可持续多年。草原通常对干旱非常敏感，但生态系统功能的损失程度可能会有很大的差异。我们假设，干旱发生方式的不同可能会导致这种差异。在四个原生大平原草原(三个C-4和一个C-3为主)上，我们连续四年实施干旱，方法是(1)在生长季(慢性干旱)期间将每次降雨事件减少66%，或(2)完全排除生长季较短时间段的降雨量(强烈干旱)。干旱处理在强度上相似，但在以下特征上有所不同：事件数量、事件大小和旱期长度。我们观察到干旱导致地上净初级生产力(ANPP)持续下降(28-37%)，仅在以C-4为主的草原上。总体而言，严重干旱比慢性干旱对ANPP的影响更大，几乎没有证据表明干旱持续时间改变了这种模式。相反，所有草原的地下净初级生产力都因干旱而减少(32-%)，在最中等程度的草原上，强干旱处理比长期干旱处理的净初级生产力减少得更多。我们的结论是，草地生产力对干旱的反应在这两种干旱类型之间没有明显的差异，但当存在差异时，强烈干旱一致地比慢性干旱更大地降低草地生产力的功能。
Drought, defined as a marked deficiency of precipitation relative to normal, occurs as periods of below-average precipitation or complete failure of precipitation inputs, and can be limited to a single season or prolonged over multiple years. Grasslands are typically quite sensitive to drought, but there can be substantial variability in the magnitude of loss of ecosystem function. We hypothesized that differences in how drought occurs may contribute to this variability. In four native Great Plains grasslands (three C-4- and one C-3-dominated) spanning a similar to 500-mm precipitation gradient, we imposed drought for four consecutive years by (1) reducing each rainfall event by 66% during the growing season (chronic drought) or (2) completely excluding rainfall during a shorter portion of the growing season (intense drought). The drought treatments were similar in magnitude but differed in the following characteristics: event number, event size and length of dry periods. We observed consistent drought-induced reductions (28-37%) in aboveground net primary production (ANPP) only in the C-4-dominated grasslands. In general, intense drought reduced ANPP more than chronic drought, with little evidence that drought duration altered this pattern. Conversely, belowground net primary production (BNPP) was reduced by drought in all grasslands (32-64%), with BNPP reductions greater in intense vs. chronic drought treatments in the most mesic grassland. We conclude that grassland productivity responses to drought did not strongly differ between these two types of drought, but when differences existed, intense drought consistently reduced function more than chronic drought.