| The causes of widespread forest mortality in the context of global climate change are a current research hotspot.It is speculated that the difficulty of maintaining carbon-water balance in trees is the main factor of poor growth and even death of trees.To explore the dynamic distribution and storage characteristics of nonstructural carbohydrates（NSC）within trees under different moisture conditions can help to understand their adaptation mechanism to the environment.In this study,the seasonal dynamics and allocation characteristics of NSC and its components（soluble sugar and starch）in each organ（leaves,branches,stem and roots）of Quercus mongolica forest under three different drought gradients（shady slope,half sunny slope and sunny slope）in 2021 growing season were analyzed and compared with the environmental factors in the Sai Han Wu La Forest Ecological Station.The main results of the study are as follows:（1）The potential evapotranspiration of Quercus mongolica forest under the three drought gradients during the growing season（From May 1 to September 30）gradually increased along the drought gradient（shady slope:701.86mm;half sunny slope:770.12mm;sunny slope:901.05mm）,the soil moisture and nutrient contents were significantly different,and the mean monthly soil moisture content decreased along the drought gradients in the growing season（shady slope:31.89%;half sunny slope:26.25%;sunny slope:24.21%）;The contents of soil organic carbon and total nitrogen showed the same trend,while total phosphorus content showed less difference among the three gradients.The stand density of Quercus mongolica forest increased gradually along the drought gradient,while the total biomass of Quercus mongolica forest and the aboveground biomass of shrub and grass decreased gradually along the drought gradient.（2）Drought caused an increase in Quercus mongolica NSC concentrations,where for each organ,leaves and roots were more sensitive to drought,with leaf(shady slope:166.14mg·g-1;half sunny slope:199.63mg·g-1;sunny slope:228.46mg·g-1)and root(shady slope:199.19mg·g-1;half sunny slope:203.17mg·g-1;sunny slope:228.32mg·g-1),the NSC concentrations of Quercus mongolica branches were significantly reduced by drought,while the trunk NSC concentrations did not change significantly between the different drought gradients.In addition,the contents of soluble sugar,starch and total NSC in all organs of the three gradients showed a seasonal dynamic trend of consumption in the early growing season and accumulation in the late growing season.（3）The total NSC reserves of Quercus mongolica at the individual and stand levels,the individual and stand NSC reserves of Quercus mongolica in all three gradients gradually decreased along the drought gradient.At the level of each organ,the NSC and its component reserves of all three gradients were trunk>root>branch>leaf.For the relative accumulation of NSC in each organ during the growing season,the accumulation of branches in shady slope was the highest,while the accumulation of roots in half sunny slope and sunny slope was the highest.（4）The differences in soluble sugar,starch and total NSC contents of whole plant and each organ in Quercus mongolica under the three drought gradients were significantly affected by changes in soil water,and not significantly affected by soil N and P.Among them,the contents of NSC and its components in branches and trunks were positively proportional to the changes of soil water content,while the changes of NSC and its components in leaves and roots were inversely proportional to soil water content.In summary,water is a key limiting factor for Quercus mongolica growth in this region,and drought will promote Quercus mongolica NSC to preferentially supply to"source-sink"organs to enhance the ability to resist drought stress and induce trees to allocate more energy to storage organs such as roots to increase resilience rather than preferential growth in dry climates. |
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