Woody species variations in biomass allocation, photosynthetic wue and carbon isotope composition under natural drought condition in Mongolia

Water is one of the most limiting environmental factors for successful rehabilitation in Mongolia. In this study, variations in biomass allocation, water use efficiency (WUE) and carbon isotope composition of fi ve woody species (Caragana arborescens Lam., Hippophae rhamnoides L., Larix sibirica Ledeb., Pinus sylvestris L. and Ulmus pumila L.) seedlings were investigated in an open field nursery. There are diverse responses of species under drought conditions. Hardwood species, U. pumila, showed the lowest photosynthetic WUE and carbon isotope composition among fi ve species but demonstrated superior morphological response in terms of root weight ratio (0.49±0.02) and root biomass allocation compared to other species (p<0.01). Conifer species, L. sibirica and P. sylvestris, showed higher photosynthetic WUE (4.52 and 3.59 μmol CO₂/mmol H₂O in July and 7.66 and 6.86 μmol CO₂/mmol H₂O in August, respectively) than other species with lower transpiration rate relative to photosynthesis (p<0.05). However, shrub species, H. rhamnoides, exhibited higher carbon isotope composition (-26.5±0.3 δ¹³C) and demonstrated high potential competitiveness than tree species under drought condition (p<0.001). It is concluded in this study that all the studied species showed diverse responses under drought condition owing to their specifi c morphological, physiological and genetic characteristics. Although the results of ranking species were different when measuring various parameters, WUE which was measured by photosynthetic parameters may not be a representative of the overall WUE. Also, carbon isotope composition has several conceptual and logistic advantages to monitor plants' drought tolerance. In line with this, H. rhamnoides and L. sibirica are the most recommended species for rehabilitating arid areas in Mongolia.