Physiological, morphological and allocational plasticity in understory deciduous trees: importance of plant size and light availability

Abstract

In a 4-year study, we investigated changes in leaf physiology, crown morphology and whole-tree biomass allocation in seedlings and saplings of shade-tolerant sugar maple (Acer saccharum Marsh.) and intermediate shade-tolerant yellow birch (Betula alleghaniensis Britt.) growing in natural understory light (0.5 to 35% of full sunlight) or in understory light reduced by 50% with shade nets to simulate the effect of gap closure. Leaf physiological parameters were mainly influenced by the light gradient, whereas crown morphological and whole-tree allocational parameters were mainly influenced by tree size. No single physiological, morphological or allocational trait was identified that could explain the difference in shade tolerance between the species. Yellow birch had higher growth rates, biomass allocation to branches and leaf physiological plasticity and lower crown morphological plasticity in unmodified understory light than sugar maple. Sugar maple did not display significant physiological plasticity, but showed variation with tree size in both crown morphology and whole-tree biomass allocation. When sugar maple was small, a greater proportion of whole-tree biomass was allocated to roots. However, physiological differences between the species decreased with decreasing light and most morphological and allocational differences tended to disappear with increasing tree size, suggesting that many species differences in shade-tolerance are expressed mainly during the seedling stage. Understory trees of both species survived for 4 years under shade nets, possibly because of higher plasticity when small and the use of stored reserves when taller.

Root architecture and allocation patterns of eight native tropical species with different successional status used in open-grown mixed plantations in Panama

“…Furthermore, both Delagrange et al (2004) and Claveau et al (2005) found that the effects of tree size varied according to the availability of resource, in this case light. In the present study, most allocational ratios were strongly influenced by tree size.…”

“…Efforts have also been made to relate architectural characteristics to ecological characteristics (Kohyama and Hotta 1990;Coomes and Grubb 1998). For example, it is well known that early-successional species tend to increase their allocation to height growth when growing in shade (Takahashi et al 2001;Sterck 1999;King et al 1997), while late-successional ones tend to reduce or even stop their height growth in order to maintain high LWR and LAR and minimise construction costs in light-limited environments (Takahashi et al 2001;Sterck 1999;King et al 1997;Delagrange et al 2004). Biomass allocation in trees thus appears to be relatively plastic.…”

“…Several recent papers have reported that tree size affects aboveground biomass distribution and the need to consider these effects when analysing such traits (Veneklaas and Poorter 1998;Menalled and Kelty 2001;Delagrange et al 2004). Furthermore, both Delagrange et al (2004) and Claveau et al (2005) found that the effects of tree size varied according to the availability of resource, in this case light.…”

“…Moreover, since most studies have been conducted with plants at the seedling stage (i.e. Kitajima 1994;Reich et al 1998;Paz 2003), and have shown that allocation patterns and morphology change with plant size (Delagrange et al 2004;Claveau et al 2005;Kneeshaw et al 2006), we sampled a range of tree heights within each species.…”

Révision du statut successionnel de l’érable à sucre (Acer saccharum)

“…For Crown H/D and all traits dealing with biomass partitioning in contrasting tree compartment, ANCOVA was performed using main stem length as the covariate. This procedure was used because recent studies have highlighted the importance of individual size or height in the variation of these parameters [12,16]; such analyses allowed us to determine if trait differences between light regimes were either light-or size-induced.…”