Objective This paper aims to reveal the spatial distribution pattern and the cause of formation of the natural plant ecosystem carbon storage in the semi-arid area of temperate Nenjiang River of Taihu National Wetland Park of Northeastern China along the lakeshore to the highland environmental gradient, and to provide a scientific basis for the long term carbon sink management of natural vegetation in the temperate semi-arid area of China.
Method The ecosystem carbon storage (vegetation carbon storage and soil carbon storage), net primary productivity (NPP), annual net carbon sequestration (ANCS) and related environmental factors (water level, total nitrogen and total phosphorus, etc.) of eight plant communities, i.e. Typha angustifolia wetland (XYP), Typha minima wetland (XP), Phragmites australis wetland (L), tussock wetland (C), Calamagrostis epigeios meadow (F), wet Leymus chinensis grassland (S), dry Leymus chinensis grassland (H), sand dune Ulmus pumila sparse forest (Y) distributed along the lakeshore to the highland environmental gradient were simultaneously determined by relative growth equation and carbon/nitrogen analyzer method, so as to reveal its spatial differentiation law and its formation mechanism.
Result (1) The vegetation carbon storage (0.98−27.86 t/ha) showed a downward and then ascending tendency along the lakeshore to the highland environmental gradient (Y > L, XYP, XP > C, F, S, H), and herbaceous carbon storage (0.30−8.11 t/ha) showed a stepwise decreasing trend (L, XYP, XP > C, F, S > H, Y). (2) The soil carbon storage (38.49−321.72 t/ha) showed a stepwise decreasing trend along the lakeshore to the highland environmental gradient, and there were obvious horizontal spaces (XYP, XP were the highest at all soil layers; L, C were higher at most soil layers; F, S, H only was higher at the surface layer; Y was the lowest at all soil layers) and vertical space (XYP, XP, L decreased with soil depth; F, S, H at middle and upper soil layers decreased; C and Y were similar at all layers) differentiation regularity. (3) Ecosystem carbon storage (66.35−329.94 t/ha) also showed a stepwise decreasing trend along the lakeshore to the highland environmental gradient, and its distribution pattern was mostly dominated by soil carbon storage (95.43%−99.04%), only Y soil carbon storage accounted for low proportion (58.2%); (4) The NPP (2.11−16.28 t/(ha·year)) and ANCS (0.68−7.00 t/(ha·year)) of vegetation showed a decreasing trend along the lakeshore to the highland environmental gradient (XYP, XP and L were significantly higher than the other five communities by 0.3−9.3 times), and the ANCS of L and XYP was higher than the average carbon sequestration of vegetation in China and the world by 10.6%−70.7%; (5) Ecosystem carbon stocks and annual net carbon sequestration of vegetation of plant communities in permanently flooded habitat in the lower part of the environmental gradient were controlled by water level; plant communities in seasonally flooded habitat in the middle environment gradient were controlled by SOM, TN, TP and AK; plant communities in arid habitats in the upper environmental gradient were controlled by SOM and AP.
Conclusion Therefore, the spatial heterogeneity of water and nutrient redistribution caused by the micro-topography controls the distribution of plant communities and their carbon sinks along the lakeshore to the highland environmental gradient in the Nenjiang River of Taihu National Wetland Park of China, so the integrity of such environmental gradients should be protected.