Drier climate shifts leaf morphology in Amazonian trees

Abstract

The humid forests of Amazonia are experiencing longer and more intense dry seasons, which are predicted to intensify by the end of the 21st century. Although tree species often have long generation times, they may still have the capacity to rapidly respond to changing climatic conditions through adaptive phenotypic plasticity. We, therefore, predicted that Amazonian trees have shifted their leaf morphology in response to the recent drier climate. We tested this prediction by analysing historical herbarium specimens of six Amazonian tree species collected over a 60-year period and comparing changes in leaf morphology with historical precipitation data. Moreover, we explored spatial and temporal biases in herbarium specimens and accounted for their potentially confounding effect in our analysis. We found pronounced biases in herbarium specimens, with nearly 20% of specimens collected in close geographic proximity and around the 1975s. When accounting for such biases, our results indicate a trend of decreasing leaf size after the 1970s, which may have been spurred by an observed reduction in rainfall. Our findings support the hypothesis that (some) Amazonian trees have the capacity to adaptively change their leaf phenotypes in response to the recent drier climate. Nevertheless, the unavoidable spatial and temporal biases in herbarium specimens call for caution when generalizing our findings to all Amazonian trees.

Adaptation of Dryland Plants to a Changing Environment

“…Further analysis showed that the variation in leaf area could be better explained by phylogeny than by climatic factors, while the specific leaf area and leaf carbon-nitrogen ratio were mainly affected by climatic factors, demonstrating that the importance of phylogeny and climatic factors differs between different functional traits. Many studies have reported that plants adapt to drought conditions by adjusting leaf functional traits in various ways, such as the leaf dry matter content, specific leaf area, leaf carbon, nitrogen and phosphorus contents, and leaf stoichiometric ratio (Hameed et al, 2012;Stropp et al, 2017). In the present study, we found that plants in the Inner Mongolia grassland adapted to drought mainly by adjusting their leaf carbonnitrogen ratios, specific leaf area and leaf nitrogen contents ( Figure 5).…”

“…The characteristics of leaves are essential for the adaptation of plants to environmental change as leaves not only exhibit strong sensitivity and plasticity to spatial and temporal changes in the environment but can also improve the adaptability of plants through self-regulation (Picotte et al, 2009;. Therefore, the adaptation of plants to drought through the adjustment of leaf morphology has received much attention (Stropp et al, 2017).…”

Adaptation of Dominant Species to Drought in the Inner Mongolia Grassland – Species Level and Functional Type Level Analysis

“…Many studies have reported that plants adapt to drought conditions by adjusting leaf functional traits in various ways, such as the leaf dry matter content, specific leaf area, leaf carbon, nitrogen and phosphorus contents, and leaf stoichiometric ratio (Hameed et al, 2012; Stropp et al, 2017). In the present study, we found that plants in the Inner Mongolia grassland adapted to drought mainly by adjusting their leaf carbon-nitrogen ratios, specific leaf area and leaf nitrogen contents (Figure 5).…”

“…The characteristics of leaves are essential for the adaptation of plants to environmental change as leaves not only exhibit strong sensitivity and plasticity to spatial and temporal changes in the environment but can also improve the adaptability of plants through self-regulation (Picotte et al, 2009; Zhang et al, 2018). Therefore, the adaptation of plants to drought through the adjustment of leaf morphology has received much attention (Stropp et al, 2017).…”

“…Indeed, the leaves of some xerophytes become fleshy or even degenerate into rods. Such characteristics are conducive to reducing transpiration and promoting more effective heat dissipation (Bosabalidis and Kofidis, 2002; Stropp et al, 2017). In addition, plant leaves exhibit physiological and stoichiometric changes under drought conditions.…”