Increases in extremely large precipitation events (deluges) and shifts in seasonal patterns of water availability with climate change will both have important consequences for ecosystem function, particularly in water-limited regions. While previous work in the semi-arid shortgrass steppe of northeastern Colorado has demonstrated this ecosystem’s strong sensitivity to growing season deluges, our understanding of ecosystem responses to deluges during the dormant season is limited. Here, we imposed experimental 100 mm deluges (~ 30% of mean annual precipitation) in either September or October in a native C₄-dominated shortgrass steppe ecosystem to evaluate the impact of this post-growing season shift in water availability during the autumn and the following growing season. Soil moisture for both deluge treatments remained elevated compared with ambient levels through April as spring precipitation was atypically low. Despite overall low levels of productivity with spring drought, these deluges from the previous autumn increased aboveground net primary production (ANPP), primarily due to increases with C₄ grasses. C₃ ANPP was also enhanced, largely due to an increase in the annual C₃ grass, Vulpia octoflora, in the October deluge treatment. While spring precipitation has historically been the primary determinant of ecosystem function in this ecosystem, this combination of two climate extremes—an extremely wet autumn followed by a naturally-occurring spring drought—revealed the potential for meaningful carryover effects from autumn precipitation. With climate change increasing the likelihood of extremes during all seasons, experiments which create novel climatic conditions can provide new insight into the dynamics of ecosystem functioning in the future.

特大降水事件（洪水）的增加以及气候变化导致的可用水季节模式的变化都将对生态系统功能产生重要影响，特别是在水资源有限的地区。虽然之前在科罗拉多州东北部半干旱短草草原的研究表明该生态系统对生长季节洪水具有很强的敏感性，但我们对休眠季节生态系统对洪水响应的了解有限。在这里，我们在 9 月或 10 月在本地以 C₄ 为主的短草草原生态系统中实施了实验性 100 毫米洪水（约占年平均降水量的 30%）评估生长季节后的变化对秋季和接下来的生长季节可用水量的影响。由于春季降水量异常偏低，整个 4 月份，两次洪水处理的土壤湿度均高于环境水平。尽管春季干旱导致生产力水平总体较低，但去年秋季的洪水增加了地上净初级生产力 (ANPP)，这主要是由于 C₄草。 C₃ANPP 也有所增强，主要是由于年度 C₃Vulpia octoflora，十月洪水处理。虽然春季降水历来是该生态系统功能的主要决定因素，但两种极端气候的结合——极其潮湿的秋季和自然发生的春季干旱——揭示了秋季降水可能产生有意义的遗留影响。随着气候变化增加了所有季节出现极端事件的可能性，创造新的气候条件的实验可以为未来生态系统功能的动态提供新的见解。