Bamboo climatic tolerances are decoupled from leaf functional traits across an Andean elevation gradient

Abstract

Widespread changes in temperature and precipitation patterns present plant species with new and combined stresses that affect their performance and distribution. Functional traits are indicators of plant resource use–acquisition strategies and thus they are commonly used to understand the geographic distributions of plant species and species' potential responses to climate change. To date, most studies have targeted a few easy‐to‐measure leaf traits even though other traits, such as climatic tolerances, could provide valuable information directly related with species' current and future distributions. Here, we measured both leaf functional traits and indices of physiological tolerance to heat (T50) and drought (cell membrane stability) in 28 woody bamboo populations from 22 narrow‐ranged species along a > 3000 m elevation gradient in the southern Peruvian Andes. We found that bamboo leaf functional traits remain fairly constant with a combination indicative of an acquisitive strategy (low leaf mass area and high nitrogen per mass) along the elevation gradient, despite drastic changes in environment and fast species turnover. Heat and drought tolerances of bamboos varied widely along the gradient and were negatively correlated to each other. Drought tolerance of bamboo populations was positively related with elevation and with precipitation seasonality while heat tolerance decreased at higher, colder elevations. When analyzed for individuals within each species or for individuals within each elevation, the two metrics of climatic tolerances did not show a consistent relationship, contrasting with the expectation of a potential tradeoff between heat and drought tolerance. We also found that the measured leaf functional traits were not good predictors of climatic tolerances. Our results illustrate the diversity and complexity of the relationships between functional strategies and environmental gradients and highlight the limitations of using basic (i.e. ‘soft') leaf traits to understand plant distributions and climatic tolerances.

Variation in leaf carbon economics, energy balance, and heat tolerance traits highlights differing timescales of adaptation and acclimation

“…Contrary to recent hypotheses that physiological heat tolerance is coordinated with carbon economics (Knight & Ackerly, 2003;Sastry & Barua, 2017;Fadrique et al, 2022) and energy balance (Slot et al, 2021) traits, we observed that photosynthetic heat tolerance traits were orthogonal to carbon economics and energy balance traits. Although we observed remarkable variation in photosynthetic heat tolerance in our common garden (c. 40 to 51°C), this variation was not explained by phylogenetic structure.…”

“…1b; Knight & Ackerly, 2003; Sastry et al ., 2018). However, support for this hypothesis is mixed, with some studies finding a positive association between heat tolerance and LMA (Knight & Ackerly, 2003; Sastry & Barua, 2017; Sastry et al ., 2018; Slot et al ., 2021; Li et al ., 2022) and others finding no such relationship (O'Sullivan et al ., 2017; Fadrique et al ., 2022; Münchinger et al ., 2023).…”

“…A negative relationship between τ and heat tolerance would be consistent with selection acting primarily via energy balance, whereas a positive relationship between LMA and heat tolerance would be consistent with selection acting primarily via carbon economics. However, tests of these predictions are often limited in taxonomic breadth, and/or use trait data collected across climate gradients that introduce acclimation and trait filtering as potentially confounding variables (Knight & Ackerly, 2003; Michaletz et al ., 2016; Sastry & Barua, 2017; Slot et al ., 2021; Fadrique et al ., 2022).…”

Variation in the Drought Tolerance of Tropical Understory Plant Communities across an Extreme Elevation and Precipitation Gradient

“…The SL has previously been used in laboratory and agricultural assays, but only a few very recent studies have used it to assess the drought tolerance of plants in the field. This is surprising, given that SL has many advantages that make it particularly well suited for studying the patterns of plant drought tolerances in biodiverse communities and in remote settings [ 59 , 60 ]. Specifically, the protocol is easy to follow and standardize, large numbers of treatments can be performed relatively quickly, the equipment needed for the experiments have a low-cost relative to other physiological measures of drought tolerance, and the measurements can be made in areas with little or no existing infrastructure (e.g., measuring SL does not require electricity or compressed gases and uses only distilled water and polyethylene glycol).…”

“…Twelve hours after boiling, we took a second conductivity measurement (C 2 ). We calculated the relative solute leakage (%) as (C 1 − C 0 )/(C 2 − C 0 ) × 100 [ 59 , 60 ]. Higher SL values indicate greater cytorrhysis when exposed to desiccating conditions and thus a lower relative leaf drought tolerance.…”