Data from: Precipitation and environmental constraints on three aspects of flowering in three dominant tallgrass species

Flower production can comprise up to 70% of aboveground primary production in grasslands. Yet we know relatively little about how the environment and timing of rainfall determine flower productivity. Evidence suggests that deficits or additions of rainfall during phenlologically relevant periods (i.e. growth, storage, initiation of flowering, and reproduction) can determine flower production in grasslands.
We used long-term data from the Konza Prairie LTER to test how fire, soil topography, and precipitation amounts during four phenologically relevant periods of the growing season constrain three aspects of flowering in three dominant C4 grass species. Specifically, we examined the probability of flowering, flowering stalk density, and individual flowering stalk biomass for Andropogon gerardii, Schizachyrium scoparium and Sorghastrum nutans.
We found that each of the three species responded to the amount of precipitation during phenologically relevant periods in unique ways. All aspects of A. gerardii flowering were sensitive to precipitation during the flowering stalk elongation period (June 20 – Aug 3). The probability of S. nutans flowering was partly determined by precipitation during the rapid growth phase (April 21 – June 4), whereas flowering stalk density of this species depended on rainfall during flowering stalk elongation (June 20 – Aug 3). In contrast, all aspects of flowering of S. scoparium were relatively independent of rainfall during any period.
Our results demonstrate that three functionally similar, codominant C4 grass species respond differently to phenologically relevant precipitation periods. As a result, drought during any phenological window during the growing season can adversely impact biomass and flowering production of grasslands via species-specific reductions in flowering stalk density and biomass.

草原生态系统中，开花生物量可占地上初级生产力的70%之多。然而，目前我们对环境条件与降雨时序如何调控开花生产力的认知仍较为有限。已有研究表明，在与物候相关的关键时段（即生长、贮藏、开花启动与生殖阶段），降雨的盈亏均可显著影响草原的开花量。

本研究依托康扎草原长期生态研究站点（Konza Prairie LTER）的长期监测数据，旨在探究火干扰、土壤地形以及生长季内四个物候关键时段的降水量，如何制约三种优势C4草本（C4 grass）的三个开花性状。具体而言，我们分别针对大须芒草（Andropogon gerardii）、小须芒草（Schizachyrium scoparium）以及拟高粱（Sorghastrum nutans），检测了其开花概率、花茎密度以及单花茎生物量三个指标。

研究结果显示，三种C4草本对物候关键时段降水量的响应模式各有独特性。大须芒草的所有开花性状均对花茎伸长期（6月20日至8月3日）的降水量变化极为敏感。拟高粱的开花概率部分受快速生长期（4月21日至6月4日）的降水量调控，而其花茎密度则取决于花茎伸长期（6月20日至8月3日）的降雨情况。与之形成鲜明对比的是，小须芒草的所有开花性状均与任意时段的降水量无显著关联。

本研究结果表明，尽管三种C4草本在功能上相似且同为群落优势种，但其对物候关键时段降水量的响应却存在显著差异。由此可见，生长季内任意物候窗口发生的干旱，均可通过物种特异性地降低花茎密度与单花茎生物量，对草原的生物量及开花产出产生负面影响。