Foliar nutrient and carbohydrate in Aralia elata can be modified by understory light quality in forests with different structures at Northeast China

Many non-wood forest product (NWFP) plants are shade-obligate species, but current understanding about their foliar response to understory spectrum is quite scarce. To monitor understory light condition at large scale faces significant obstacles from heavy canopy shade and high cost of sensors arrangement. Therefore, we employed a novel methodology to meter the relative light ratio between plots under canopy and in the open-air. In this study, a number of 34 plots of natural Aralia elata populations were investigated for forest structure across six types of forests at Northeast China. Light properties of relative intensity, photosynthetic photon flux rate (PPFD), spectra in red, green, and blue wavelengths, and relative ratio of red/green, red/blue, and green/blue were measured at the height of 1.3m. Leaves of A. elata were collected to determined concentrations of nitrogen (N), phosphorus (P), starch, and soluble sugars. We found that relative blue light ratio was different among forest-types, but it had little further effect on leaf traits in A. elata. Instead, higher ratios of relative green light and green/blue depressed leaf P concentration. Increases in PPFD and light intensity promoted leaf N and P concentrations, respectively. The red/green ratio had adverse relationships with leaf P and starch concentrations in A. elata. In conclusion, due to the variation understory light condition, sites with low canopy density would benefit leaf N concentration and those with larger canopies can promote leaf starch accumulation in A. elata.