Comparative leaf growth strategies in response to low-water and low-light availability: variation in leaf physiology underlies variation in leaf mass per area in Populus tremuloides

Abstract

Developmental phenotypic plasticity can allow plants to buffer the effects of abiotic and biotic environmental stressors. Therefore, it is vital to improve our understanding of how phenotypic plasticity in ecological functional traits is coordinated with variation in physiological performance in plants. To identify coordinated leaf responses to low-water (LW) versus low-light (LL) availability, we measured leaf mass per area (LMA), leaf anatomical characteristics and leaf gas exchange of juvenile Populus tremuloides Michx. trees. Spongy mesophyll tissue surface area (Asmes/A) was correlated with intrinsic water-use efficiency (WUEi: photosynthesis, (Aarea)/stomatal conductance (gs)). Under LW availability, these changes occurred at the cost of greater leaf tissue density and reduced expansive growth, as leaves were denser but were only 20% the final area of control leaves, resulting in elevated LMA and elevated WUEi. Low light resulted in reduced palisade mesophyll surface area (Apmes/A) while spongy mesophyll surface area was maintained (Asmes/A), with no changes to WUEi. These leaf morphological changes may be a plastic strategy to increase laminar light capture while maintaining WUEi. With reduced density and thickness, however, leaves were 50% the area of control leaves, ultimately resulting in reduced LMA. Our results illustrate that P. tremuloides saplings partially maintain physiological function in response to water and light limitation by inducing developmental plasticity in LMA with underlying anatomical changes. We discuss additional implications of these results in the context of developmental plasticity, growth trade-offs and the ecological impacts of climate change.

Within‐species patterns challenge our understanding of the leaf economics spectrum

“…; Baird et al . ), the average within‐species explanatory power of environmental variables in natural plots is similar to the trait–environment relationships found between species across multiple biomes: stronger for temperature than precipitation but weak overall (Moles et al . ; Maire et al .…”

“…For example leaf thickness, mesophyll cell size/number and mesophyll air space jointly determine LMA, yet respond differently to abiotic stresses (Baird et al . ). Broad application of functional traits will require a mechanistic understanding of the environmental causes and physiological consequences of variation in these underlying attributes.…”

Disentangling the effects of photosynthetically active radiation and red to far-red ratio on plant photosynthesis under canopy shading: a simulation study using a functional–structural plant model

“…Reductions in PAR, on the one hand, directly decrease plant photosynthesis due to reductions in light as a resource. On the other hand, reductions in PAR induce plastic responses such as decreasing leaf photosynthetic capacity and respiration rate, changing leaf anatomy, increasing leaf photosynthetic nitrogen, increasing specific leaf area and increasing the fraction of assimilates partitioned to the leaf ( Gulmon and Chu, 1981 ; Lichtenthaler et al ., 1981 ; Walters et al ., 1993 ; Evans and Poorter, 2001 ; Baird et al ., 2017 ). Reductions in R:FR mostly induce plastic responses of plant morphogenesis, including increased elongation of hypocotyls, internodes, petioles, leaf sheaths and blades, increased leaf inclination angle, reduced branching and tillering, and early flowering ( Franklin, 2008 ; Casal, 2012 ; Pierik and De Wit, 2014 ).…”

Photochemical Efficiency and Oxidative Metabolism of Tree Species during Acclimation to High and Low Irradiance

“…As the light supply can be very heterogeneous, the plants, more specifically their leaves, must exhibit great flexibility of physiological responses to cope with light fluctuations. Given the spatial and seasonal changes in the availability of primary resources, plants with low physiological flexibility would likely be constrained in their ability to survive in changing environments [ 1 , 2 , 3 ].…”