Effect of drought stress on apparent resource utilization efficiency of Quercus mongolica Comparison of potential yield and resource utilization efficiency of main food crops in three provinces of Northeast China under climate change. Study on the multiple crops cultivation model in two years taking watermelon and peanut as the main crops Differences in clonal growth between female and male plants of Rhus typhina Linn. and their diurnal changes in photosynthesis and chlorophyll fluorescence