Photosynthetic performance of two poplar species in shelterbelt under water‐saving irrigation in arid northwest China

Understanding the physiology of plants in arid regions under changed water availability is critical to projecting the future of arid ecosystems. A water‐saving irrigation has been implemented in an ecological shelter forest of an agricultural reclamation area located in the arid desert region in northwestern Dzungaria Basin in Xinjiang, China. In order to understand the effects of changed irrigation on trees, two poplar species (Populus euphratica and P. russkii) growing in the shelterbelt were selected, and their photosynthetic performance was contrasted by measuring their photosynthetic gas exchange and photochemical parameters under water‐saving irrigation and traditional extensive flood irrigation. Results showed that reduced water availability during water‐saving irrigation had a moderate but not significant impact on the photosynthesis of the two poplar species. Populus russkii was more sensitive to changed irrigation than P. euphratica, and the latter showed a relatively higher water‐deficit resistance and a better photosynthetic performance under water‐saving irrigation. Populus russkii exhibited higher capability of non‐photochemical quenching by thermal dissipation of excess excitation energy at both irrigation modes making it capable of maintaining excess energy better than P. euphratica. Thermal dissipation on excess energy and increased photo‐respiration rate at water‐saving irrigation together provided photo protection in P. euphratica. Both species can maintain normal function of the photosystem at water‐saving irrigation. The declined photosynthetic performance of the two species at water‐saving irrigation could be attributed to photo protection but not to photo inhibition. All this together suggested that the water‐saving irrigation implemented by a manager on the shelterbelt could be feasible.