Consequences of nocturnal water loss: a synthesis of regulating factors and implications for capacitance, embolism and use in models

Abstract

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.

The Relationship between Sap Flow Density and Environmental Factors in the Yangtze River Delta Region of China

“…Zeppel et al [49] used data from many ecosystems to examine the abiotic factors that may affect the S dn and found that S dn was higher in broad-leaved compared with needle-leaved plants and in tropical compared with temperate species. Our study also demonstrates that S dn accounted for 2.71%-12.56% (Q. acutissima) and 8.00%-24.29% (C. lanceolata) of the whole-day sap flow throughout the study period, respectively.…”

“…In our study, P ar and V pd explained the greatest amount of variation in daytime sap flow of Q. acutissima and C. lanceolata, respectively. In addition, V pd and soil water content (S wc ) were the abiotic drivers of nocturnal sap flow [49]. Causally, V pd is also used to determine whether S dn is related to either nocturnal transpiration or stem refilling [16,19,52,53].…”

A test of an optimal stomatal conductance scheme within the CABLE land surface model

“…Some authors suggest using nighttime stomatal conductance values (e.g. Zeppel et al, 2014). However, minimum stomatal conductance values measured during the day are considerably lower than measured nighttime values (Walden-Coleman et al, 2013).…”

Reduced nighttime transpiration is a relevant breeding target for high water-use efficiency in grapevine

“…First, night transpiration may lower leaf temperature by evaporative cooling, thereby decreasing carbon losses through dark respiration (42). Night water fluxes may otherwise have beneficial roles in nutrient transport (43) and O 2 supply to the xylem parenchyma (16,44). Incomplete stomatal closure at night may also accelerate photosynthesis resumption at sunrise (45), but this has not always been observed (46).…”