Temporal And Spatial Variation In Atmospheric Nitrogen And Phosphorus Deposition In Four Forest Types In Different Climatic Regions

Nitrogen?N?and phosphorus?P?are two important elements in controlling ecological structure and functioning.The input of N and P from the atmospheric deposition to land and ocean is of great importance in regulating the biogeochemical cycles of terrestrial and aquatic ecosystems.As the increasing intensities of anthropogenic activities,such as the combustion of fossil fuels,the application of fertilizers and increasing mining activities,the substantial input of reactive N and P makes them critical components of biogeochemical cycles in terrestrial ecosystems.The spatial and temporal variation of N and P deposition associated with anthropogenic activities has imposed tremendous impact on nutrient cycling in forests.A better understanding of the temporal and spatial pattern of N and P deposition in different four types can advance our current knowledge about the cycling and interaction of N and P in forest ecosystems,how to maintain their capacity of sequester carbon and reduce the loss of nutrient from leaching.We measured the N and P deposition from atmosphere and throughfall and investigated their spatiotemporal variations with ion-exchange resin at Baotianman warm-temperate deciduous broad-leaved forest,Tianmushan subtropical evergreen broad-leaved forest,Huitong subtropical Chinese fir plantation and Jianfengling tropical mountain rainforest.The main results are shown as follows:?1?The annual flux of dissolved organic N deposition were 27.58±1.80,17.09±2.37,15.60±1.12 and 15.08±1.43 kg ha^-1 yr^-1 at Baotianman,Tianmushan,Huitong and Jianfengling,respectively,with a decreasing trend from north to south of China.?2?NH₄⁺-N was the dominant N form and the ratio between NO₃^--N ranged from 1.67 to7.57 across four sites,indicating that N deposition in the investigated sites was more affected by the volatilization of fertilizers and excrements of animal during agriculture management and less affected by the emissions from industrial development.?3?The deposition of dissolved inorganic N was higher in the non-growing season than the growing season at Baotianman and Tianmushan,which might be related to the intensive power consumption and generation in winter.Besides,the cleaning effect of precipitation on suspended particle in the air can lead to the decrease in deposition,therefore,the less precipitation over the non-growing season than the growing season might contribute to the low precipitation in the former.In contrast,the deposition of dissolved inorganic N was higher in the growing season than the non-growing season at Huitong and Jianfengling,which might be due to the high ammonia volatilization during the spring-sowing period after intensive fertilization,or the increased activity of nitrification and denitrification due to elevated temperature in the growing season.?4?The annual flux of P deposition were 1.51±0.11,0.56±0.07,1.34±0.12 and 0.16±0.01 kg ha^-1 yr^-1 at Baotianman,Tianmushan,Huitong and Jianfengling,respectively,with the remarkable impact of surrounding‘hot spot'of large cities.The P deposition was greater in the non-growing season than the growing season,which may be controlled by the long-distance transportation in the spring and winter due to stronger winds in the non-growing season or the enhanced P deposition with in situ fugitive dust.?5?Atmospheric N deposition was greater than the throughfall at Baotianman,Tianmushan and Huiting,indicating the strong interception of tree canopy on N.Besides,the uptake for N by the leaves might further decreasing N content in the throughfall.?6?Atmospheric P deposition was lower than the through at Baotianman,Tianmushan and Jianfengling,indicating the critical role of canopy leaching in P biogeochemical cycling in forest ecosystems.Due to the small P content in the precipitation as well as the smaller P content in the coniferous needles than the broad leaves,the limited leaching effect lead to the comparable P deposition in the atmosphere and throughfall.?7?The ratio between N and P were 18.3±0.5,30.7±3.5,11.7±2.4 and 91.9±9.7 at Baotianman,Tianmushan,Huitong and Jianfengling,respectively,suggesting that the external nutrient input from atmospheric deposition at Jianfengling and Huitong was limited by P and N,respectively,and the deposition in Baotianman and Tianmushan were also short of P in a relative manner.?8?The ratios between N and P in the throughfall were substantially lower than in the atmospheric deposition,indicating the stronger interception of N than P by the canopy that leaded to the decreased N:P ratio in the throughfall.To summarize,although the fertilization effect of increased N deposition and CO2concentration may enhance plant growth and carbon sequestration,the unbalanced P input may lead to P limitation that in turn constrain their facilitation.A systematic approach by considering the interaction between N and P from the perspective of ecological stoichiometry will benefit the management of forest resources and sustainable development.