Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA.
Glob Chang Biol. 2021 Mar;27(6):1157-1169. doi: 10.1111/gcb.15479. Epub 2020 Dec 23.
Climate change has intensified the hydrologic cycle globally, increasing the magnitude and frequency of large precipitation events, or deluges. Dryland ecosystems are expected to be particularly responsive to increases in deluge size, as their ecological processes are largely dependent on distinct soil moisture pulses. To better understand how increasing deluge size will affect ecosystem function, we conducted a field experiment in a native semiarid shortgrass steppe (Colorado, USA). We quantified ecological responses to a range of deluge sizes, from moderate to extreme, with the goal of identifying response patterns and thresholds beyond which ecological processes would not increase further (saturate). Using a replicated regression approach, we imposed single deluges that ranged in size from 20 to 120 mm (82.3rd to >99.9th percentile of historical event size) on undisturbed grassland plots. We quantified pre- and postdeluge responses in soil moisture, soil respiration, and canopy greenness, as well as leaf water potential, growth, and flowering of the dominant grass species (Bouteloua gracilis). We also measured end of season above- and belowground net primary production (ANPP, BNPP). As expected, this water-limited ecosystem responded strongly to the applied deluges, but surprisingly, most variables increased linearly with deluge size. We found little evidence for response thresholds within the range of deluge sizes imposed, at least during this dry year. Instead, response patterns reflected the linear increase in the duration of elevated soil moisture (2-22 days) with increasing event size. Flowering of B. gracilis and soil respiration responded particularly strongly to deluge size (14- and 4-fold increases, respectively), as did ANPP and BNPP (~60% increase for both). Overall, our results suggest that this semiarid grassland will respond positively and linearly to predicted increases in deluge size, and that event sizes may need to exceed historical magnitudes, or occur during wet years, before responses saturate.
气候变化在全球范围内加剧了水文循环，增加了大降水事件（或暴雨）的强度和频率。旱地生态系统预计将对暴雨规模的增加特别敏感，因为它们的生态过程在很大程度上依赖于独特的土壤湿度脉冲。为了更好地了解增加暴雨规模将如何影响生态系统功能，我们在美国科罗拉多州的一个原生半干旱短草草原（shortgrass steppe）进行了一项野外实验。我们量化了一系列暴雨规模（从中度到极端）对生态系统的响应，目的是确定生态过程不会进一步增加（饱和）的响应模式和阈值。我们使用复制回归方法，在未受干扰的草原斑块上施加大小从 20 到 120 毫米（历史事件大小的 82.3 百分位到>99.9 百分位）的单一暴雨。我们量化了雨后和雨后土壤水分、土壤呼吸和冠层绿色度以及优势草种（Bouteloua gracilis）的叶水势、生长和开花的响应，还测量了季末地上和地下净初级生产力（ANPP、BNPP）。正如预期的那样，这个水分限制的生态系统对应用的暴雨反应强烈，但令人惊讶的是，大多数变量与暴雨规模呈线性增加。我们在施加的暴雨规模范围内几乎没有发现响应阈值的证据，至少在这个干旱的年份是这样。相反，响应模式反映了随着事件规模的增加，土壤湿度升高的持续时间（2-22 天）呈线性增加。B. gracilis 的开花和土壤呼吸对暴雨规模的反应特别强烈（分别增加 14 倍和 4 倍），ANPP 和 BNPP 也是如此（两者都增加了约 60%）。总的来说，我们的结果表明，这个半干旱草原将对预测的暴雨规模增加做出积极和线性的响应，而且事件规模可能需要超过历史规模，或者在湿润年份发生，才能达到饱和。
