Serious grassland degradation is endangering the environment of the source regions of the Yangtze and Yellow Rivers (SRYYR). There is an urgent need to analyze and review the grassland resources, status of grassland degradation, factors causing grassland degradation, and measures for grassland protection and restoration so as to ensure sustainable development in the SRYYR. This review shows that: (1) The alpine meadow, one of the most important grassland types in the SRYYR, can be divided into four subtypes: typical alpine meadow, alpine swamp meadow, alpine steppe meadow and alpine shrub meadow. (2) There is approximately 357.13 × 104 ha degraded grassland in this area, which is 34.34% of the area of all the investigated grasslands in the SRYYR, and heavily degraded grasslands cover an area of 74.34 × 104 ha, approximately 20.82% of the degraded grasslands. (3) Alpine grassland degradation in the SRYYR follows the following sequence: non‐degraded grassland → lightly degraded grassland → moderately degraded grassland → heavily degraded grassland. (4) Grassland degradation in the SRYYR is caused by the integrated effect of anthropogenic and natural factors. The principal factors causing grassland degradation are thought to be long‐term overgrazing and the destruction by rodents that follows, and climate warming, which accelerates the grassland degradation process. (5) Some effective management practices (e.g. rodent and ruderal weed control, establishment of artificial grassland, rational management of grassland, and optimizing livestock structure) and integrated countermeasures for the restoration of degraded grasslands have been developed in the SRYYR.

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The photosynthetic characterization of Populus euphratica and their response to increasing groundwater depth and temperature were analyzed based on net photosynthetic rate (P N ), stomatal conductance (g s ), intercellular CO 2 concentration (C i ), transpiration rate (E), water use efficiency (WUE) and stomatal limitation (L s ) 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 (P max ), quantum yields (AQY), and dark respiration rates (R D ). 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 P N 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.

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