Abstract
Nitrogen deposition and uncertainty of precipitation are currently two of the most important ecological issues of global climate change in subtropical areas.To study the effects of nitrogen and precipitation on the eco-physiological traits and growth of subtropical trees,we set up a two-factorial experiment controlling the factors of precipitation and soil fertilization for the seedlings of Elaeocarpus glabripetalus,Liquidambar formosana,Schima superba and Cyclobalanopsis glauca for three years on Gutian Mountain in Zhejiang Province,China.Precipitation was set at three levels: natural precipitation(CK),increase of 30% natural precipitation and decrease of 30% natural precipitation.Soil fertilization was set at two levels: natural nitrogen and nitrogen addition of 10 g · m-2 · a-1NH4NO3.In general,the pH values in subtropical soil are low and the growth of most subtropical tree species may be limited by phosphorus deficiency in the soil not nitrogen availability,so we need to test if addition of nitrogen in soil will promote the eco-physiological traits and growth of the subtropical tree species.We also want to test how the interactive soil fertilization and precipitation changes affect the growth and photosynthetic traits in the four subtropical tree species.We periodically measured the seedlings' photosynthetic eco-physiological traits and their environmental growth factors for three years.The results showed that precipitation variation and nitrogen addition did have some effects on eco-physiological characteristics and total biomass across four tree species.We found that 10 g · m-2 · a-1 NH4NO3 nitrogen addition significantly improved the leaf chlorophyll synthesis(P0.05)and photosynthesis rate(P0.05)across the four subtropical tree seedlings.The addition of nitrogen also positively stimulated PSⅡ photochemical efficiency(Fv/Fm,PIABS)(P0.01)in the four subtropical tree seedlings.Addition of nitrogen significantly increased total biomass formation by more than 30%(P0.01).Hence,nitrogen addition would increase tree seedling photosynthesis ability and promote their growth in subtropical evergreen forest of Gutian Mountain.In contrast,we found that the effects of precipitation changes were less significant on the eco-physiological traits and total biomass for the four subtropical tree seedlings,Nevertheless,precipitation variations significantly influenced photosynthetic rate(P0.05),stomatal conduction and transpiration(P0.001) for some tree seedlings during the dry season of Gutian Mountain.Meanwhile,stomatal conduction was more sensitive to precipitation variations.The interactive effects of precipitation and nitrogen addition on the eco-physiological characteristics(excluding PIABS) and total biomass among the four tree species were not significant(P0.05).The differences in eco-physiological characteristics among the four tree species should attribute to their natural biological properties,while the difference in biomass among different tree species was due to the variations in precipitation change and nitrogen addition(P0.01)from this experiment.
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