VARIATION IN THE δ13C VALUE OF TYPICAL PLANTS OF LOESS PLATEAU OVER THE LAST 70 YEARS Application of Discriminant Analysis in Distinguishing Plant Photosynthetic Types-A Case Study in Northeast China Transect (NECT) Area Photosynthetic Characteristics of Dendrobium williamsonii and D. longicornu Ecological effect of photorespiration of plants under environmental stress Photorespiration of C4 Plants The Distribution of Stomata and Photosynthetic Pathway in Leaves