Honghua Zhou

Photosynthesis of Populus euphratica in relation to groundwater depths and high temperature in arid environment, northwest China

The photosynthetic characterization of Populus euphratica and their response to increasing groundwater depth and temperature were analyzed based on net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE) and stomatal limitation (Ls) measured by a portable gas-exchange system (LI-6400) in the lower reaches of the Tarim River. Light-response curves were constructed to obtain light-compensation and light-saturation points (LCP and LSP), maximum photosynthetic rates (Pmax), quantum yields (AQY), and dark respiration rates (RD). The growth condition of P. euphratica, soil moisture, and groundwater depth in the plots were analyzed by field investigation. The results showed that the growth condition and photosynthetic characterization of P. euphratica were closely related to groundwater depth. The rational groundwater depth for the normal growth and photosynthesis was 3–5 m, the stress groundwater depth for mild drought was more than 5 m, for moderate drought was more than 6 m, for severe drought was more than 7 m. However, P. euphratica could keep normal growth through a strong drought resistance depended on the stomatal limitation and osmotic adjustment when it faced mild or moderate drought stress, respectively, at a normal temperature (25°C). High temperature (40°C) significantly reduced PN and drought stress exacerbated the damage of high temperature to the photosynthesis. Moreover, P. euphratica would prioritize the resistance of high temperature when it encountered the interaction between heat shock and water deficit through the stomata open unequally to improve the transpiration of leaves to dissipate overheating at the cost of low WUE, and then resist water stress through the osmotic adjustment or the stomatal limitation.

Implications of climate change for water management of an arid inland lake in Northwest China

Abstract To evaluate potential effects of climate change on the water budget of Bosten Lake, the largest inland freshwater lake in China, we evaluated trends and step change points between 1980 and 2011 in evaporation, air temperature, and precipitation. Significant increases in air temperature accelerated glacier melt, increasing flow in the Kaidu River, which ultimately discharges into Bosten Lake. The increased inflow resulted in increased lake water depth and 10% greater water surface area. Increased surface area along with higher temperatures led to increased lake evapotranspiration. If glaciers continue to recede and snowpacks continue to decline with projected warmer temperatures under climate change, inflows to Bosten Lake will decrease substantially in the future, with critical implications for long-term water resource management. Our calculations suggest that the water surface area of Bosten Lake should be maintained >963.14 km2 to maintain low lake water salinity (total dissolved solids: TDS ≤ 1.5 g/L), 3-year and 5-year means for annual net inflows to Bosten Lake must be approximately 21.80 × 108 m3 and 23.50 × 108 m3, respectively, and Kaidu River mean runoff must be approximately 35.83 × 108 m3 to maintain that surface area while supplying 14.42 × 108 m3/yr of water to meet public water demand in the Kongqi Basin. Water should only be diverted from Bosten Lake to the lower Tarim River for ecological restoration in years when Kaidu River annual runoff is >35.83 × 108 m3. To minimize evaporation loss, water diversions from Bosten Lake should occur between May and September.

Experimental study on water transport observations of desert riparian forests in the lower reaches of the Tarim River in China

Studying the water use processes of desert riparian vegetation in arid regions and analyzing the response and adaptation strategies of plants to drought stress are of great significance for developing ecological restoration measures. Based on field monitoring and test analyses of physiological ecological indicators of dominant species (Populus euphratica and Tamarix chinensis) in the desert riparian forest in the lower reaches of the Tarim River, the water relations of P. euphratica and T. chinensis under drought stress are discussed and some water use strategies put forward. The results show that (1) concerning plant water uptake, desert riparian forests depend mainly on groundwater to survive under long-term water stress. (2) Concerning plant water distribution, the survival of P. euphratica and nearby shallow root plants is mainly due to the hydraulic lift and water redistribution of P. euphratica under drought stress. (3) Concerning plant water transport, P. euphratica sustains the survival of competitive and advantageous branches by improving their ability to acquire water while restraining the growth of inferior branches. (4) Concerning plant transpiration, the sap flow curves of daily variations of P. euphratica and T. chinensis were wide-peak sin and narrower-peak respectively. T. chinensis has better environmental adaptability.