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 C₄- and one C₃-dominated) spanning a ~ 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 C₄-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.

干旱被定义为相对于正常降水量明显不足，表现为降水量低于平均水平或降水输入完全失效的时期，并且可能仅限于单个季节或持续多年。草原通常对干旱非常敏感，但生态系统功能丧失的程度可能存在很大差异。我们假设干旱发生方式的差异可能导致这种可变性。在四个原生大平原草原（三个 C ₄ - 和一个 C ₃-主导）跨越约 500 毫米的降水梯度，我们通过（1）在生长季节（慢性干旱）期间将每次降雨事件减少 66% 或（2）在较短的时间内完全排除降雨，从而连续四年施加干旱生长季节（严重干旱）。干旱处理在幅度上相似，但在以下特征上有所不同：事件数量、事件规模和干旱期长度。我们仅在 C ₄——以草原为主。一般来说，严重干旱比慢性干旱更能降低 ANPP，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（32-64％）的地下净初级生产（BNPP）都因干旱而减少，在最中等草原的强烈干旱与慢性干旱处理中，BNPP的减少幅度更大。我们得出的结论是，草地生产力对干旱的反应在这两种干旱之间没有很大差异，但是当存在差异时，强烈干旱始终比慢性干旱更能降低功能。