Effects of sulfur dioxide on growth and net photosynthesis of six Japanese forest tree species grown under different nitrogen loads

摘要

We examined the growth and photosynthetic responses of Japanese forest tree species to sulfur dioxide (SO2) under different nitrogen (N) loads to soil. We grew Quercus serrata, Fagus crenata, Castanopsis sieboldii, Larix kaempferi, Pinus densiflora, and Cryptomeria japonica seedlings in Andisol supplemented with N as NH4NO3 solution at 0, 20, and 50 kg ha?1 year?1. Seedlings were exposed daily to charcoal-filtered air or SO2 at 10, 20, and 40 nl l?1 for two growing seasons. Except for C. japonica seedlings, exposure to SO2 at a relatively low concentration stimulated whole-plant growth, especially under a relatively high N load. The effects of N load on the negative impact of SO2 on whole-plant growth were synergistic in Q. serrata, F. crenata, C. sieboldii, and P. densiflora, counteractive in L. kaempferi, and additive in C. japonica. In Q. serrata, F. crenata, C. sieboldii, and P. densiflora seedlings, the different responses of whole-plant growth to SO2 among the N treatments were because of the effect of N load on the response of the net photosynthetic rate to SO2. L. kaempferi seedlings showed N load-induced tolerance of whole-plant growth to SO2. This was explained by the effect of N load on the responses of photosynthesis and development of assimilative organs to SO2. The different growth responses to SO2 among the N treatments were explained by the effects of N load on the SO2 uptake rate (evaluated by stomatal diffusive conductance) or the accumulated SO2 uptake (evaluated by foliar S concentration).