Plant water-use strategy is considered to be a function of the complex interactions between species of different functional types and the prevailing environmental conditions. The functional type of a plant's root system is fundamental in determining the water-use strategy of desert shrubs and the physiological responses of the plant to an occasional rainfall event, or rain pulse. In this current study of Tamarix ramosissima Ledeb. Fl.Alt., Haloxylon ammodendron (C.A.Mey.) Bunge and Reaumuria soongorica (Pall.) Maxim., three dominant shrub species in the Gurbantonggut Desert (Central Asia), plant root systems were excavated in their native habitat to investigate their functional types and water-use strategies. We monitored leaf water potential, photosynthesis and transpiration rate during a 39-day interval between successive precipitation events during which time the upper soil water changed markedly. Plant apparent hydraulic conductance and water-use efficiency were calculated for the varying soil water conditions. Our results show that: 1) The three species of shrub belong to two functional groups: phreatophyte and nonphreatophyte; 2) The photosynthetic capacity and leaf-specific apparent hydraulic conductance of the three species was stable during the time that the water condition in the upper soil changed; 3) Transpiration, leaf water potential and water-use efficiency in Tamarix ramosissima Ledeb. Fl.Alt. were stable during the period of observation, but varied significantly for the other two species. Tamarix ramosissima Ledeb. Fl.Alt., as a phreatophyte, relies mostly on groundwater for survival; its physiological activity is not inhibited in any way by the deficiency in upper soil water. Non-phreatophyte Haloxylon ammodendron (C.A.Mey.) Bunge and Reaumuria soongorica (Pall.) Maxim. use precipitation-derived upper soil water for survival, and thus respond clearly to rain pulse events in terms of leaf water potential and transpiration. The observed similarity in leaf-specific photosynthesis capacity among all three species indicates that the two non-phreatophyte species are able to maintain normal photosynthesis within a wide range of plant water status. The observed stability in leaf-specific apparent hydraulic conductance indicates that the two non-phreatophyte species are able to maintain sufficient water supply to their foliage via, mostly likely, effective morphological adjustment at the scale of the individual plant.

As part of global climate change, variation in precipitation in arid ecosystems is leading to plant adaptation in wateruse strategies; significant interspecific differences in response will change the plant composition of desert communities. This integrated study on the ecophysiological and individual morphological scale investigated the response, acclimation and adaptation of two desert shrubs, with different water-use strategies, to variations in water conditions. The experiments were carried out on two native dominant desert shrubs, Tamarix ramosissima and Haloxylon ammodendron, under three precipitation treatments (natural, double and no precipitation, respectively), in their original habitats on the southern periphery of Gurbantonggut Desert, Central Asia, during the growing season in 2005. Changes in photosynthesis, transpiration, leaf water potential, water-use efficiency, above-ground biomass accumulation and root distribution of the two species were examined and compared under the contrasting precipitation treatments. There were significant interspecific differences in water-use strategy and maintenance of photosynthesis under variation in precipitation. For the phreatophyte T. ramosissima, physiological activity and biomass accumulation rely on the stable groundwater, which shields it from fluctuation in the water status of the upper soil layers caused by precipitation. For the nonphreatophyte H. ammodendron, efficient morphological adjustment, combined with strong stomatal control, contributes to its acclimation to variation in precipitation. On account of its positive responses to increased precipitation, H. ammodendron is predicted to succeed in interspecific competition in a future, moister habitat.

Aquaporins are membrane integral proteins responsible for the transmembrane transport of water and other small neutral molecules. Despite their well-acknowledged importance in water transport, their significance in gas transport processes remains unclear. Growing evidence points to the involvement of plant aquaporins in CO2 delivery for photosynthesis. The role of these channel proteins in the transport of O2 and other gases may also be more important than previously envisioned. In this study, we examined O2 permeability of various human, plant, and fungal aquaporins by co-expressing heterologous aquaporin and myoglobin in yeast. Two of the most promising O2-transporters (Homo sapiens AQP1 and Nicotiana tabacum PIP1;3) were confirmed to facilitate O2 transport in the spectrophotometric assay using yeast protoplasts. The over-expression of NtPIP1;3 in yeasts significantly increased their O2 uptake rates in suspension culture. In N. tabacum roots subjected to hypoxic hydroponic conditions, the transcript levels of the O2-transporting aquaporin NtPIP1;3 significantly increased after the seven-day hypoxia treatment, which was accompanied by the increase of ATP levels in the apical root segments. Our results suggest that the functional significance of aquaporin-mediated O2 transport and the possibility of controlling the rate of transmembrane O2 transport should be further explored.