Diurnal Variation in Transport and Use of Intracellular Leaf Water and Related Photosynthesis in Three Karst Plants

Except for transpired water, the intracellular water stored in leaves accounts for only 1–3% of the water absorbed by roots. Understanding water transport and use, as well as the related photosynthetic response, helps with determining plant water status and improving the revegetation efficiency in fragile karst habitats. In this study, we conducted experiments on 8 year old naturally growing plants of <i>Coriaria nepalensis</i> Wall., <i>Broussonetia papyrifera</i> (L.) Vent., and <i>Elaeocarpus decipiens</i> Hemsl. in karst areas. We determined the diurnal variations in leaf electrophysiology, water potential, gas exchange, and chlorophyll fluorescence parameters. The results indicated that <i>C. nepalensis</i> plants maintained a high photosynthetic rate, with a high root water uptake ability and leaf intracellular water-holding capacity (LIWHC). The stomata quickly closed to conserve water within cells and protect the photosynthetic structure. <i>B. papyrifera</i> maintained stable intracellular water transport rate (LIWTR), and the photosynthetic efficiency was increased with increasing intracellular water-use efficiency (LIWUE). <i>B. papyrifera</i> also maintained its photosynthesis by efficiently using the transpired water when the LIWHC was increased. The inter- and intracellular water in the leaves of <i>E. decipiens</i> remained stable, which could be attributed to the leathery leaves and its high water-holding capacity. The photosynthesis of <i>E. decipiens</i> was low and stable. Compared with the high photosynthesis, high transpiration, and low instantaneous water-use efficiency (WUE_i) pattern in <i>C. nepalensis</i> plants, <i>E. decipiens</i> plants exhibited low photosynthesis, low transpiration, and low WUE_i, whereas <i>B. papyrifera</i> plants presented high photosynthesis, low transpiration, and high WUE_i. Plants in karst regions change their transport and use of intracellular leaf water to regulate the photosynthetic performance, which differs among different plant species.