A new look at water transport regulation in plants

Abstract

SummaryPlant function requires effective mechanisms to regulate water transport at a variety of scales. Here, we develop a new theoretical framework describing plant responses to drying soil, based on the relationship between midday and predawn leaf water potentials. The intercept of the relationship (Λ) characterizes the maximum transpiration rate per unit of hydraulic transport capacity, whereas the slope (r) measures the relative sensitivity of the transpiration rate and plant hydraulic conductance to declining water availability.This framework was applied to a newly compiled global database of leaf water potentials to estimate the values of Λ and r for 102 plant species.Our results show that our characterization of drought responses is largely consistent within species, and that the parameters Λ and r show meaningful associations with climate across species. Parameter r was ≤1 in most species, indicating a tight coordination between the gas and liquid phases of water transport, in which canopy transpiration tended to decline faster than hydraulic conductance during drought, thus reducing the pressure drop through the plant.The quantitative framework presented here offers a new way of characterizing water transport regulation in plants that can be used to assess their vulnerability to drought under current and future climatic conditions.

Comparative Drought Responses of Quercus ilex L. and Pinus sylvestris L. in a Montane Forest Undergoing a Vegetation Shift

“…The anisohydric behavior of Q. ilex observed here is at odds with the general view considering this species as isohydric [27], even in studies conducted in a nearby valley in the same study area [33,47]. Importantly, the iso-/anisohydric dichotomy does not account for differences in vulnerability to xylem embolism [12], nor for leaf traits involved in turgor regulation [65]. Given the current methodological controversy on the measurement of vulnerability to xylem embolism (e.g., [48,61]) we cannot be sure that the extremely high PLC values estimated here are real.…”

“…sylvestris showed a more isohydric behavior than Q. ilex trees. If we interpret the relationship between ΨPD and ΨMD (Figure 3) following the theoretical framework recently presented by Martínez-Vilalta et al [12], Q. ilex would be classified as strictly anisohydric and P. sylvestris as partially isohydric. Indeed, when SWC diminished and VPD increased during drought, Gs,md was more strongly reduced in P. sylvestris than in Q. ilex trees (Figure 4).…”

“…Furthermore, iso-/anisohydric behavior may vary within species as a function of environmental conditions [13]. In addition, the link between stomatal regulation and leaf water potential is likely to be more complex that previously realized, both because of the need to account for differences in the hydraulic properties of plants (e.g., the vulnerability to xylem embolism) [12] and because of the different mechanisms of stomatal closure across species [14]. A further complication in the study of plant responses to severe drought arises because water stress is triggered by both a reduction in soil moisture and an increase of the evaporative demand (vapor pressure deficit; VPD), and stomata regulation responds to both of them [15].…”

“…First of all, plants do not necessarily fall into either category, but rather stomatal regulation lies within a spectrum of stomatal sensitivity to water potential [11]. Hence, there is a wide range of stomatal responses to drought and these physiological responses are generally coordinated with the tree's hydraulic architecture [12]. Furthermore, iso-/anisohydric behavior may vary within species as a function of environmental conditions [13].…”

Water stress induced breakdown of carbon-water relations: indicators from diurnal FLUXNET patterns

“…Current estimates of isohydricity require repeated quantification of leaf water potential, which are currently restrained to the individual scale, i.e. from actual leaf measurements (Martínez-Vilalta et al, 2014) or to global scale, but only 0.5 degree resolution estimates from radar (Konings and Gentine, 2016). This limitation of large and small scales leaves a knowledge gap at the size of an eddy covariance footprint, hindering the study of ecosystem response to drought.…”