Response Of Productivity And Water Use Efficiency Of Mongolian Pine Shelter Forest To Climate Change

The plant growth in different regions is affected by different factors owing to the difference of climate.In this study,Mongolian pines（Pinus sylvestris var.Mongolia）,the main afforestation tree species in the Three-North area of China,was selected as the research object.The ring width of Ringwood（RW）,Early wood（EW）and Late wood（LW）in different regions were measured by tree chronology method to calculate the basal area increment（BAI）and net primary productivity（NPP）.The chronology of Mongolian pine was established.The intrinsic water use efficiency（i WUE）was calculated with the stable carbon isotope ratio(δ¹³C).We analyzed the differences in radial growth,NPP and i WUE of Mongolian pine in different regions and their response mechanism to climate change.The aim is to provide basic data for the management and construction of Mongolian pines shelter forest in the Three-North area of China.The main conclusions of this manuscript were as follows:（1）In the Three-North area of China,the variation of the width of RW,EW and LW and BAI of Mongolian pines was basically the same at the same sample location,and the variation trends in different sites were obviously different.The annual BAI was in a linear increase trend of Mongolian pines plantations in Mu Us and Zhanggutai and a stable state of the natural Mongolian pines forest in Hailar,while the growth of BAIs decreased in the later stage of the other sample plots.The BAIs were decreased obviously year by year in Fujia and Ertai,indicated the stand declined.（2）The radial growth of Mongolian pines was significantly positively correlated with monthly mean precipitation,monthly relative humidity,standardized precipitation evaporation index（SPEI）and minimum temperature,and negatively correlated with monthly maximum temperature.The radial growth was negatively correlated with the monthly mean temperature in Hailar and Zhanggutai,but the opposite was found in Mu Us,no relationships were found at other sites.The radial growth was positively correlated with the monthly maximum temperature in Ertai,not correlated with the monthly minimum temperature in Hailar,Heishui and Saihanba.RW of Mongolian pine was mainly affected by annual mean precipitation and annual mean temperature,EW was greatly affected by annual mean precipitation,while LW was significantly affected by annual mean temperature,annual minimum temperature and annual maximum temperature.（3）The biomass and NPP of Mongolian pines in natural forest were significantly higher than those in plantations,and two indices of Mongolian pines plantations decreased along the direction from Mu Us to Heishui.The main climatic factors affecting NPP of Mongolian pines gradually changed from monthly temperature and humidity to monthly precipitation,then to monthly humidity and precipitation in Mu Us-Heishui-Hailar lines.The annual relative humidity and mean precipitation had significant impacts on NPP of Mongolian pines in Mu Us and Hailar.NPP was limited by the annual maximum temperature and the annual minimum temperature in Fujia,Zhanggutai and Saihanba,while was constraind by the annual minimum temperature in Ertai and Heishui.（4）Along the direction from Mu Us-Heishui-Hailar,i WUEs were low in the middle and high on both sides,indicated a trend of decreasing at the beginning and then increasing.i WUEs were the highest in Ertai and Heishui,followed by Mu Us,Zhanggutai and Fujia,and those of Hailar and Saihanba were the lowest.Except for Mu Us,i WUEs of Mongolian pines were positively correlated with monthly mean temperature and maximum temperature,negatively correlated with monthly mean precipitation,relative humidity,SPEI and minimum temperature.The relationships between i WUEs with monthly mean temperature and relative humidity of Mu Us were consistent with other sample plots,the other relationships were the opposite.Temperature had the major impact on i WUE of Mongolian pines,while precipitation had little effect.The relative humidity had a significant effect on i WUE in Mu Us and Hailar.The results indicated that the main factors were different for the width of RW,EW and LW in different sample locations.