Leaf age dependent changes in within-canopy variation in leaf functional traits: a meta-analysis

Abstract

Within-canopy variation in leaf structural and photosynthetic characteristics is a major means by which whole canopy photosynthesis is maximized at given total canopy nitrogen. As key acclimatory modifications, leaf nitrogen content (N A ) and photosynthetic capacity (A A ) per unit area increase with increasing light availability in the canopy and these increases are associated with increases in leaf dry mass per unit area (M A ) and/or nitrogen content per dry mass and/or allocation. However, leaf functional characteristics change with increasing leaf age during leaf development and aging, but the importance of these alterations for within-canopy trait gradients is unknown. I conducted a meta-analysis based on 71 canopies that were sampled at different time periods or, in evergreens, included measurements for different-aged leaves to understand how within-canopy variations in leaf traits (trait plasticity) depend on leaf age. The analysis demonstrated that in evergreen woody species, M A and N A plasticity decreased with increasing leaf age, but the change in A A plasticity was less suggesting a certain re-acclimation of A A to altered light. In deciduous woody species, M A and N A gradients in flush-type species increased during leaf development and were almost invariable through the rest of the season, while in continuously leaf-forming species, trait gradients increased constantly with increasing leaf age. In forbs, N A plasticity increased, while in grasses, N A plasticity decreased with increasing leaf age, reflecting life form differences in age-dependent changes in light availability and in nitrogen resorption for growth of generative organs. Although more work is needed to improve the coverage of age-dependent plasticity changes in some plant life forms, I argue that the agedependent variation in trait plasticity uncovered in this study is large enough to warrant incorporation in simulations of canopy photosynthesis through the growing period.

Global leaf trait estimates biased due to plasticity in the shade

“…Leaf trait acclimation to integrated light has been reported to stabilize about 30-60 days after leaf formation in both woody and herbaceous canopies 21,22 , but age-dependent modifications are possible for some plant growth forms 23 and such modifications can further alter the correlative relationships within the leaf economics spectrum 24 . In particular, in evergreen woody species, M a and N a plasticity has been reported to decrease with increasing leaf age, with limited changes in A a plasticity 23 .…”

“…In particular, in evergreen woody species, M a and N a plasticity has been reported to decrease with increasing leaf age, with limited changes in A a plasticity 23 . In forbs, N a plasticity increased, whereas in grasses, N a plasticity decreased with increasing leaf age, potentially reflecting life form differences in age-dependent changes in light availability.…”

“…In forbs, N a plasticity increased, whereas in grasses, N a plasticity decreased with increasing leaf age, potentially reflecting life form differences in age-dependent changes in light availability. Unfortunately, there are very few studies that use replicate sampling when reporting age effects 23 , which makes it difficult to distinguish between exceptional and characteristic responses, and this thus limits the generality of the conclusions that can be drawn. In addition, only a few studies have looked at a suite of relevant functional traits simultaneously, which complicates inference about the structural, chemical and physiological coordination of canopy functioning due to agedriven changes in plasticity.…”

“…In addition, only a few studies have looked at a suite of relevant functional traits simultaneously, which complicates inference about the structural, chemical and physiological coordination of canopy functioning due to agedriven changes in plasticity. Although a full characterization of age-driven trait plasticity remains elusive 23 , current evidence suggests that both light and age effects should be considered in the analysis of leaf trait values.…”

Spatio-temporal variations in photosynthesis

“…Comprehensive understanding of these processes may be the most difficult N-body problem in this research field. Niinemets (2016) tackled this problem bravely to find out trends in the complicated situations by meta-analyzing the relevant papers, most of which only fragmentally related to the problem. Iwaki (1959), one of the students of Monsi applied the Monsi and Saeki approach to analyze an interspecific competition.…”