Net ecosystem productivity of Panjin Phragmites australis wetland during 1971 to 2020 and its impact factors.

Coastal estuarine wetland ecosystem has strong ability for carbon (C) storage and sequestration. Accurate assessment of C sequestration and its environmental impact factors is the basis of scientific protection and mana-gement of coastal estuarine wetlands. Taking the Panjin reed (Phragmites australis) wetland as the object, we used terrestrial ecosystem model, together with Mann-Kendall mutation test, statistical analysis methods, and scenario simulation experiment, to analyze the temporal characteristics, stability, changing trend of net ecosystem production (NEP) of wetlands and the contribution rate of environmental impact factors to NEP during 1971 to 2020. The results showed that the annual average NEP of Panjin reed wetland was 415.51 g C·m-2·a-1 during 1971 to 2020, with a steady increase rate of 1.7 g C·m-2·a-1, which would still have a continuous increasing trend in the future. The annual average NEP in spring, summer, autumn, and winter was 33.95, 418.05, -18.71, and -17.78 g C·m-2·a-1, with an increase rate of 0.35, 1.26, 0.14 and -0.06 g C·m-2·a-1, respectively. In the future, NEP would show an increasing trend in both spring and summer, but a declining trend in both autumn and winter. The contribution rates of environmental impact factors to NEP of Panjin reed wetland depended on temporal scale. At the interannual scale, the contribution rate of precipitation was the highest (37.1%), followed by CO2 (28.4%), air temperature (25.1%) and photosynthetically active radiation (9.4%). Precipitation mainly affected NEP in both spring and autumn with the contribution rates of 49.5% and 38.8%, while CO2 concentration (36.9%) and air temperature (-86.7%) were dominant in summer and winter, respectively.

[Temporal and spatial variations of net primary productivity (NPP) and its climate driving effect in the Qinghai-Tibet Plateau, China from 2000 to 2020]. / 2000­2020å¹´é’è—é«˜åŽŸæ¤è¢«å‡€åˆçº§ç”Ÿäº§åŠ›æ—¶ç©ºå˜åŒ–åŠå ¶æ°”å€™é©±åŠ¨ä½œç”¨.

Qinghai-Tibet Plateau is a "climate change laboratory" for China and the world. Driven by climate change, net primary productivity (NPP) in the Qinghai-Tibet Plateau has significant variations. Using the data of normalized difference vegetation index, digital elevation, annual precipitation, and annual temperature, we explored the temporal and spatial variation characteristics of NPP and its correlation with climate factors on the Qinghai Tibet Plateau from 2000 to 2020. The results showed that NPP of the Qinghai-Tibet Plateau increased significantly from 2000 to 2020, with an increase rate of 1.67 g C·m-2·a-1. The NPP was significantly positively correlated with temperature and precipitation. The climate trend of warming and wetting was an important driving force to promote the significant increase of NPP. The increases of NPP would continue if the climate become warmer and wetter.

Photosynthetically physiological mechanism of Stipa krylovii withered and yellow phenology response to precipitation under the background of warming.

We examined the photosynthetically physiological mechanism of Stipa krylovii response to warming and precipitation changes, based on an experiment with the treatments of warming by infrared radiator and precipitation treatments by irrigation water. Under the warming background, precipi-tation was the main influencing factor of the withered and yellow phenology. Increasing precipitation postponed the occurrence time of both the beginning and the peak of the withered and yellow phenology, and prolonged the duration of the withered and yellow phenology. The effect of decreasing precipitation on prolonging the duration of the withered and yellow phenology was much stronger. Under the background of warming, the changes of precipitation markedly affected the physiological and ecological characteristics of the withered and yellow phenology, with the effect being the most significant at the beginning of the withered and yellow phenology. The net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), and the maximum ribulose 1,5-bisphosphate (RuBP) carboxylation rate (Vc max), RuBP regeneration capacity (Jmax) were positively correlated with precipitation. Results of the pathway analysis showed that the photosynthetically physiological mechanism of withered and yellow phenology of S. krylovii would be different under different conditions of precipitation and temperature. Under the current environmental condition, Jmax was the main influencing factor of the withered and yellow phenology, and Vc max was the main limiting factor. Under the scenarios of warm and dry climate and warm and wet climate, Vc max become the main influencing factor of the withered and yellow phenology. Jmax would be the main limiting factor in the warm and dry climate conditions, and there would be no limiting factor in the warm and wet climate conditions. Our findings indicated that the withered and yellow phenological changes of S. krylovii depend on the photosynthetical capacity limitation resulted from meteorological conditions.