Functional trait trade-offs for the tropical montane rain forest species responding to light from simulating experiments.

Peili Mao,Hongbo Shao,Junbao Yu,Runguo Zang

doi:10.1155/2014/649031

Abstract

Differences among tropical tree species in survival and growth to light play a key role in plant competition and community composition. Two canopy species with contrasting functional traits dominating early and late successional stages, respectively, in a tropical montane rain forest of Hainan Island, China, were selected in a pot experiment under 4 levels of light intensity (full, 50%, 30%, and 10%) in order to explore the adaptive strategies of tropical trees to light conditions. Under each light intensity level, the pioneer species, Endospermum chinense (Euphorbiaceae), had higher relative growth rate (RGR), stem mass ratio (SMR), specific leaf area (SLA), and morphological plasticity while the shade tolerant climax species, Parakmeria lotungensis (Magnoliaceae), had higher root mass ratio (RMR) and leaf mass ratio (LMR). RGR of both species was positively related to SMR and SLA under each light level but was negatively correlated with RMR under lower light (30% and 10% full light). The climax species increased its survival by a conservative resource use strategy through increasing leaf defense and root biomass investment at the expense of growth rate in low light. In contrast, the pioneer increased its growth by an exploitative resource use strategy through increasing leaf photosynthetic capacity and stem biomass investment at the expense of survival under low light. There was a trade-off between growth and survival for species under different light conditions. Our study suggests that tree species in the tropical rainforest adopt different strategies in stands of different successional stages. Species in the earlier successional stages have functional traits more advantageous to grow faster in the high light conditions, whereas species in the late successional stages have traits more favorable to survive in the low light conditions.

Highlights

In tropical rain forests, light is the most important limiting resource for tree seedling establishment, growth, and survival [1,2,3,4,5]
The objectives of the study were to explore the following questions: (1) whether light intensity had any significant influence on the performance of tree species in terms of growth and morphological traits, (2) whether the ecological adaptation strategies to light for the two tree species differed significantly, (3) whether irradiance-elicited morphological plasticity differed among the two species, and (4) whether there were any trade-offs between growth and survival related traits under different light conditions
relative growth rate (RGR) in 100% was similar to that in 50% full light (P > 0.05), and they were significantly higher than that in 10% full light (P < 0.01)

Summary

Introduction

In tropical rain forests, light is the most important limiting resource for tree seedling establishment, growth, and survival [1,2,3,4,5]. Two important hypotheses for species’ shade tolerance have been proposed: carbon gain hypothesis [11] and stress tolerance hypothesis [12]. Carbon gain hypothesis defines shade tolerance as the maximization of net carbon gain together with the minimization of respiration costs for maintenance. Carbon gain hypothesis has been challenged by some studies on tropical tree seedlings that have not found growth ranking reversals of different shade tolerance species in high and low light [12,13,14]. Stress tolerance hypothesis thought of shade tolerance as maximization of the resistance to biotic and abiotic stresses in low light. Some new researches agreed with this hypothesis in recent years [13,14,15,16,17]

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Conclusion