Impacts Of Nitrogen Fertilize And Understory Removal On Water Use Efficiency In A Chinese Fir Plantation

In recent decades,the proportion of forest plantation in our country is growing.One of the most concerned points in forestation is to quantify the influence of forestation expansion on regional water resources.In particular in the context of global climate change,how to manage the artificial forest scientifically and utilize the water resources more efficiently has become a very important research direction of the forest management.In order to provide basic data for the scientific evaluation of water consumption of artificial forests,in this study,we selected the representative Chinese Fir Plantation in subtropical area to investigate the main and interactive effects of nitrogen addition and understory clipping.Transpiration was measured at leaf-,single wood-and stand-levels and soil water evaporation was also determined.The following results were obtained through 1 years of monitoring?July 2016-June 2015?,:?1?The understory clipping treatment has no significant effect on leaf conductance have a significant impact,however,nitrogen fertilizer treatment and nitrogen fertilizer and removal of shrub and grass composite measures the leaf stomatal conductance increased by 56.74% and 55.29%,reached a significant level?P<0.05?..?2?Nitrogen addition and the combination of nitrogen and understory clipping significantly enhanced the chlorophyll content by 14.8% and 16.3%,respectively.However,understory clipping treatment did not affect the chlorophyll content.?3?When the understory vegetation was removed,the soil evaporation was significantly increased by 58.51%.The combination of nitrogen and understory clipping significantly increased soil evaporation by 68.50%,compared to the control treatment significantly;After applying fertilizer soil evaporation decreased compared to the control,but did not reach significant level.?4?Sap flow velocity was ranked as following :summer>spring>autumn> winter.In spring winter,various management measures have no significant impact on the liquid flow rate of the day.In the autumn,understory clipping measures will significantly reduce the sap flow velocity and the compound?fertilization and understory clipping?measures will significantly reduce sap flow velocity in the autumn rainy day.The application of nitrogen fertilizer in summer will make the sap flow velocity rate significantly higher than other treatments,especially in sunny days.The annual transpiration of Cunninghamia lanceolata under different treatments was calculated as follows: no fertilization and understory clipping measures 368.53 mm,understory clipping measures 342.25 mm,application of nitrogen fertilizer measures 397.21 mm,fertilization and understory clipping measures 368.44 mm.?5?The water use efficiency of different management measures of Chinese fir experimental plots was: No understory clipping and no nitrogen addition measures 4.83x10^-3m³/m³?wood/water?,understory clipping measures 4.82x10^-3m³/m³?wood /water?,nitrogen addition measures 4.91x10^-3m³/m³?wood/water?,nitrogen addition and understory clipping measures 4.86x10^-3m³/m³?wood/water?.Through the analysis,nitrogen fertilizer measures can improve the water use efficiency of Chinese fir,understory clipping and nitrogen fertilizer measures measures will reduce the water use efficiency.In actully Chinese fir plantation production activities can be considered to retain its understory vegetation and to avoid the summer of nitrogen fertilizer to improve the water use efficiency of Chinese fir production.