2021 Volume 20 Issue 1 Pages 1-12
In the understory of an evergreen forest, how leaf traits and light availability affect whole-plant carbon balance is less investigated. We predicted that variety of leaf traits can contribute to maintain whole-plant carbon balance positive in a shaded understory, and tested it in a subtropical forest in Japan, where typhoon disturbance is relatively frequently occurred. We estimated the potential net assimilation rate (NAR) of understory sites, including typhoon-disturbed sites, by measuring photosynthetic active photon flux density (PPFD). Then, for understory saplings we applied our original ‘leaf relative growth rate’ (RGRleaf) method to simulate the whole-plant carbon balance according to its relation to leaf mass per area (LMA), leaf lifespan (LL), net assimilation rate (NAR), and leaf partitioning rate (LP). RGRleaf > 0 indicates positive growth. Under the fully closed canopy the potential NAR was estimated to be < 50 g glucose m-2 yr-1, where most species were predicted to have a negative RGRleaf. However, with a better NAR of the site which had likely experienced a past typhoon attack, most species would have positive RGRleaf. With those low-level NAR, neither LMA nor LL had significant relationships to RGRleaf. There, saplings’ LMA and LL showed positive relationship, but LMA tended to be smaller relative to LL compared to known global trend. With higher-level NAR, it is predicted that having smaller LMA and LL is advantageous to have large RGRleaf. We concluded that balance of the leaf traits is important to maintain positive whole plant carbon balance in the low light understory, and then, various leaf traits were valid for growth in a low light understory. The moderate shade environment brought by typhoon disturbances may help to exist species with various leaf traits.
