Data from: Drivers of nocturnal water flux in a tallgrass prairie

1. Nocturnal transpiration can impact water balance from the local community to earth-atmosphere fluxes. However, the dynamics and drivers of nocturnal transpiration among coexisting plant functional groups in herbaceous ecosystems are unknown. 2. Here, we addressed the following questions: (1) How do nocturnal (Enight) and diurnal (Eday) transpiration vary among coexisting grasses, forbs, and shrubs in a tallgrass prairie? (2) What environmental variables drive Enight and do these differ from the drivers of Eday? (3) Is Enight associated with daytime physiological processes? 3. We measured diurnal and nocturnal leaf gas exchange on perennial grass, forb, and woody species in a North American tallgrass prairie. Measurements were made periodically across two growing seasons (May-August 2014-2015) on three C4 grasses (Andropogon gerardii, Sorghastrum nutans, and Panicum virgatum), two C3 forbs (Vernonia baldwinii and Solidago canadensis), one C3 sub-shrub (Amorpha canescens) and two C3 shrubs (Cornus drummondii and Rhus glabra). 4. By extending our study to multiple functional groups we were able to make several key observations: (1) Enight was variable among co-occurring plant functional groups, with the highest rates occurring in C4 grasses, (2) Enight and Eday exhibited different responses to vapor pressure deficit and other environmental drivers, and (3) rates of Enight were strongly related to predawn leaf water potential for grasses and woody species, and likely modulated by small-scale changes in soil moisture availability. 5. Our results provide novel insight into an often-overlooked portion of ecosystem water balance. Considering the high rates of Enight observed in C4 grasses, as well as the widespread global occurrence of C4 grasses, nocturnal water loss might constitute a greater proportion of global evapotranspiration than previously estimated. Additionally, future predictions of nocturnal water loss may be complicated by stomatal behavior that differs between during the day and at night. Finally, these data suggest a water-use strategy by C4 grasses wherein the high rates of Enight occurring during wet periods may confer a competitive advantage to maximize resource consumption during periods of availability.夜间蒸腾作用可影响从局域群落到地气通量的水分平衡。然而，草本生态系统中共存植物功能群间的夜间蒸腾动态及其驱动因子仍尚不明确。本研究于北美高草草原开展，在2014-2015年两个生长季（5-8月）周期性测量了多年生禾草、杂类草及木本物种的日间与夜间叶片气体交换。研究对象包括3种C4禾草（须芒草*Andropogon gerardii*、拟高粱*Sorghastrum nutans*、柳枝稷*Panicum virgatum*）、2种C3杂类草（*Vernonia baldwinii*、加拿大一枝黄花*Solidago canadensis*）、1种C3亚灌木（灰毛紫穗槐*Amorpha canescens*）与2种C3灌木（康多鼠刺*Cornus drummondii*、盐肤木*Rhus glabra*）。研究探讨了三个核心问题：一是共存的禾草、杂类草与灌木的夜间蒸腾（Enight）与日间蒸腾（Eday）速率存在何种差异；二是驱动夜间蒸腾的环境变量与日间蒸腾的驱动因子是否存在不同；三是夜间蒸腾是否与日间生理过程相关。研究结果显示：夜间蒸腾速率在不同植物功能群间存在显著差异，C4禾草的夜间蒸腾速率最高；夜间蒸腾与日间蒸腾对水汽压亏缺等环境因子的响应模式存在明显分异；禾草与木本物种的夜间蒸腾速率与黎明前叶片水势紧密相关，且受土壤水分可利用性的小幅调控。本研究为生态系统水分平衡中常被忽视的夜间水分损失环节提供了全新认知：鉴于C4禾草在全球广泛分布且夜间蒸腾速率较高，夜间水分损失在全球总蒸散量中的占比可能高于此前估算值。同时，日间与夜间气孔行为的差异将增加未来夜间水分损失预测的复杂性，而C4禾草在湿润时期的高夜间蒸腾速率，可帮助其在资源可利用期最大化资源摄取，从而获得竞争优势。