Zeppel M J B, Lewis J D, Phillips N G, Tissue D T
Macquarie University, Sydney, NSW 2109, Australia
Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, NSW 2753, Australia Louis Calder Center-Biological Field Station and Department of Biological Sciences, Fordham University, Armonk, NY 10504, USA.
Tree Physiol. 2014 Oct;34(10):1047-55. doi: 10.1093/treephys/tpu089.
Total daily water use is a key factor influencing the growth of many terrestrial plants, and reflects both day-time and nocturnal water fluxes. However, while nocturnal sap flow (En) and stomatal conductance (gs,n) have been reported across a range of species, ecosystems and microclimatic conditions, the regulation of these fluxes remains poorly understood. Here, we present a framework describing the role of abiotic and biotic factors in regulating En and gs,n highlighting recent developments in this field. Across ecosystems, En and gs,n generally increased with increasing soil water content and vapor pressure deficit, but the interactive effects of these factors and the potential roles of wind speed and other abiotic factors remain unclear. On average, gs,n and En are higher in broad-leaved compared with needle-leaved plants, in C3 compared with C4 plants, and in tropical compared with temperate species. We discuss the impacts of leaf age, elevated [CO2] and refilling of capacitance on night-time water loss, and how nocturnal gs,n may be included in vegetation models. Younger leaves may have higher gs,n than older leaves. Embolism refilling and recharge of capacitance may affect sap flow such that total plant water loss at night may be less than estimated solely from En measurements. Our estimates of gs,n for typical plant functional types, based on the published literature, suggest that nocturnal water loss may be a significant fraction (10-25%) of total daily water loss. Counter-intuitively, elevated [CO2] may increase nocturnal water loss. Assumptions in process-based ecophysiological models and dynamic global vegetation models that gs is zero when solar radiation is zero are likely to be incorrect. Consequently, failure to adequately consider nocturnal water loss may lead to substantial under-estimation of total plant water use and inaccurate estimation of ecosystem level water balance.
每日总用水量是影响许多陆生植物生长的关键因素，反映了白天和夜间的水分通量。然而，尽管已报道了一系列物种、生态系统和微气候条件下的夜间液流（En）和气孔导度（gs,n），但对这些通量的调节仍知之甚少。在此，我们提出一个框架，描述非生物和生物因素在调节En和gs,n中的作用，突出该领域的最新进展。在不同生态系统中，En和gs,n通常随土壤含水量和水汽压差的增加而增加，但这些因素的交互作用以及风速和其他非生物因素的潜在作用仍不清楚。平均而言，与针叶植物相比，阔叶植物的gs,n和En更高；与C4植物相比，C3植物的更高；与温带物种相比，热带物种的更高。我们讨论了叶龄、[CO2]升高和电容再填充对夜间水分损失的影响，以及夜间gs,n如何纳入植被模型。较年轻的叶片可能比较老的叶片具有更高的gs,n。栓塞再填充和电容充电可能影响液流，使得夜间植物总失水量可能小于仅根据En测量所估计的量。我们基于已发表文献对典型植物功能类型的gs,n估计表明，夜间水分损失可能占每日总水分损失的很大一部分（10 - 25%）。与直觉相反，[CO2]升高可能增加夜间水分损失。基于过程的生态生理模型和动态全球植被模型中太阳辐射为零时gs为零的假设可能是不正确的。因此，未能充分考虑夜间水分损失可能导致对植物总用水量的大幅低估以及对生态系统水平水分平衡的不准确估计。
