The response of stomatal conductance to seasonal drought in tropical forests

Abstract

Stomata regulate CO2 uptake for photosynthesis and water loss through transpiration. The approaches used to represent stomatal conductance (gs) in models vary. In particular, current understanding of drivers of the variation in a key parameter in those models, the slope parameter (i.e. a measure of intrinsic plant water‐use‐efficiency), is still limited, particularly in the tropics. Here we collected diurnal measurements of leaf gas exchange and leaf water potential (Ψleaf), and a suite of plant traits from the upper canopy of 15 tropical trees in two contrasting Panamanian forests throughout the dry season of the 2016 El Niño. The plant traits included wood density, leaf‐mass‐per‐area (LMA), leaf carboxylation capacity (Vc,max), leaf water content, the degree of isohydry, and predawn Ψleaf. We first investigated how the choice of four commonly used leaf‐level gs models with and without the inclusion of Ψleaf as an additional predictor variable influence the ability to predict gs, and then explored the abiotic (i.e. month, site‐month interaction) and biotic (i.e. tree‐species‐specific characteristics) drivers of slope parameter variation. Our results show that the inclusion of Ψleaf did not improve model performance and that the models that represent the response of gs to vapor pressure deficit performed better than corresponding models that respond to relative humidity. Within each gs model, we found large variation in the slope parameter, and this variation was attributable to the biotic driver, rather than abiotic drivers. We further investigated potential relationships between the slope parameter and the six available plant traits mentioned above, and found that only one trait, LMA, had a significant correlation with the slope parameter (R2 = 0.66, n = 15), highlighting a potential path towards improved model parameterization. This study advances understanding of gs dynamics over seasonal drought, and identifies a practical, trait‐based approach to improve modeling of carbon and water exchange in tropical forests.

Low predictability of energy balance traits and leaf temperature metrics in desert, montane and alpine plant communities

“…The species in this study thus independently vary their energy balance traits and their other traits, without strong trade-offs being necessary. This result contrasts with some of the linkages hypothesized or observed between energy balance and functional traits in prior studies (Falster & Westoby, 2003;Ollinger et al, 2008;Wu et al, 2020) and has several possible explanations.…”

“…We hypothesized such a linkage, as recent studies have demonstrated linkages between energy balance traits and functional traits, potentially supporting coordination along the well-known fast-slow continuum of leaf and plant economics (Reich, 2014). For example, stomatal conductance model parameters have been linked to LMA (Wu et al, 2020) and other stoichiometric traits (Hasper et al, 2017; ( Kröber, Plath, Heklau, & Bruelheide, 2015), while stomatal ratio has been linked to growth form (Muir, 2018). Strong relationships have been identified between leaf size and angle and photosynthetic rates (Falster & Westoby, 2003), and various relationships have been found between leaf economic traits and leaf albedo (Bartlett, Ollinger, Hollinger, Wicklein, & Richardson, 2011;Ollinger et al, 2008).…”

Drought tolerance inBrassica napusis accompanied with enhanced antioxidative protection, photosynthetic and hormonal regulation at seedling stage

“…This response is mainly associated with decreased stomatal conductance (Gs), more CO 2 uptake to maintain the photosynthetic efficiency to sustain plant growth and development. Many predictions about future global environmental changes involve the increase in severity and frequency of drought stress (Wu et al, 2020). Clearly, a robust assessment about the soil water availability and its impact on ecological processes is urgently required, engineering and breeding more efficient and drought stress tolerant crop cultivars are becoming very important (Qamar et al, 2020).…”

Agrometeorological models to forecast açaí (Euterpe oleracea Mart.) yield in the Eastern Amazon

“…(a)), indicating that the açaí stems could have been experiencing thermal stress during the period of these maximums. In C3 plants such as the açaí palm photorespiration rates can be as dynamic as those for photosynthesis, being altered by light, carbon dioxide (CO 2 ) concentration, and air temperature . Therefore, photorespiration rates increase with an increase in light intensity and temperature .…”