Traits controlling shade tolerance in tropical montane trees.

Bonaventure Ntirugulirwa,Camille Ziegler,Donat Nsabimana,Elisée Bahati Ntawuhiganayo,Etienne Zibera,Félicien K Uwizeye,Göran Wallin,Johan Uddling,Mirindi E Dusenge

doi:10.1093/treephys/tpz119

Bonaventure Ntirugulirwa, Camille Ziegler + Show 7 more

Open Access

https://doi.org/10.1093/treephys/tpz119

Copy DOI

Abstract

Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among different tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with different degrees of shade tolerance, grown under three different radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these differences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspecific variation in shade tolerance of tropical montane trees is controlled by species differences in whole-plant biomass allocation strategy rather than by difference in physiological leaf traits determining leaf carbon balance at low radiation.

Highlights

Tropical forests host a high diversity of species and are extremely productive ecosystems, accounting for about onethird of global terrestrial gross primary production (Dirzo and Raven 2003, Lewis 2006, Beer et al 2010, Malhi et al 2013)
Our results suggest that interspeci c variation in shade tolerance of tropical montane trees is controlled by species di erences in wholeplant biomass allocation strategy (Figure 1) rather than by di erence in physiological leaf traits determining leaf carbon balance at low radiation (Figure 4)
Our results indicate that interspeci c variation in sun–shade leaf plasticity may markedly di er among physiological traits, but that shade tolerance is not the consequence of higher acclimation capacity of traits linked to leaf carbon balance at low radiation (i.e., Rd and light compensation point (LCP))

Summary

Introduction

Tropical forests host a high diversity of species and are extremely productive ecosystems, accounting for about onethird of global terrestrial gross primary production (Dirzo and Raven 2003, Lewis 2006, Beer et al 2010, Malhi et al 2013). Previous studies have often focused on either leaf physiological traits or whole-plant biomass allocation and structure (Valladares and Niinemets 2008) It remains unclear if there is a di erence in light acclimation capacity between shadetolerant (ST) and shade-intolerant (SI) tropical tree species, with con icting reports in the literature (Rozendaal et al 2006, Coste et al 2009, 2010, Houter and Pons 2014, Dusenge et al 2015). There is a need for new experimental studies exploring the contributions of di erent plant traits (i.e., leaf vs whole-plant level, and physiological vs structural) in controlling shade tolerance of tropical trees (Valladares and Niinemets 2008, Valladares et al 2016, Poorter et al 2019)

Objectives

Methods

Results

Discussion

Conclusion