Radiation and Drought Impact Residual Leaf Conductance in Two Oak Species With Implications for Water Use Models

Haiyan Qin,Faqrul Islam Chowdhury,Víctor Resco De Dios,Carles Arteaga,Ying Han,Yinan Yao,Elena Granda

doi:10.3389/fpls.2020.603581

Abstract

Stomatal closure is one of the earliest responses to water stress but residual water losses may continue through the cuticle and incomplete stomatal closure. Residual conductance (gres) plays a large role in determining time to mortality but we currently do not understand how do drought and shade interact to alter gres because the underlying drivers are largely unknown. Furthermore, gres may play an important role in models of water use, but the exact form in which gres should be incorporated into modeling schemes is currently being discussed. Here we report the results of a study where two different oak species were experimentally subjected to highly contrasting levels of drought (resulting in 0, 50 and 80% losses of hydraulic conductivity) and radiation (photosynthetic photon flux density at 1,500 μmol m–2 s–1 or 35–45 μmol m–2 s–1). We observed that the effects of radiation and drought were interactive and species-specific and gres correlated positively with concentrations of leaf non-structural carbohydrates and negatively with leaf nitrogen. We observed that different forms of measuring gres, based on either nocturnal conductance under high atmospheric water demand or on the water mass loss of detached leaves, exerted only a small influence on a model of stomatal conductance and also on a coupled leaf gas exchange model. Our results indicate that, while understanding the drivers of gres and the effects of different stressors may be important to better understand mortality, small differences in gres across treatments and measurements exert only a minor impact on stomatal models in two closely related species.

Highlights

Plant transpiration through stomatal pores and leaf cuticles dominates global evapotranspiration (Hetherington and Woodward, 2003)
We sought to test: (1) how do drought and shade interact to affect gres? and (2) what are some of the possible mechanisms underlying variation in gres across drought and shade treatments? Because gMLD is probably the most accepted method to measure residual conductance, here we focused on gMLD
The interaction between light and water was such that gMLD declined with drought in the sun treatment, but gMLD increased with drought in the shade from 3.1 at P50 to 5.0 mmol m−2 s−1 at P80)

Summary

Introduction

Plant transpiration through stomatal pores and leaf cuticles dominates global evapotranspiration (Hetherington and Woodward, 2003). As water stress intensifies under global warming, there is an increasing interest toward understanding ecological variation in residual leaf conductance (gres). Studies addressing ecological and physiological variation in the drivers of residual conductance are currently rare (Heredia-Guerrero et al, 2018). According to a recent review on this topic (Duursma et al, 2019), only 10 studies have addressed the effect of drought on gres and, from those, only 4 had been performed on trees. Multifactorial studies addressing ecological variation in residual conductance are much needed to understand its variation. The effects of residual conductance on mortality have been documented to be dramatic: time to mortality nearly doubles if gres declines from 4 to 2 mmol m−2 s−1 (Duursma et al, 2019)

Methods

Results

Conclusion