| Carex tussock wetlands are typical wetlands with a series of ecological functions including carbon sequestration,habitat provision and biodiversity support.Hydrological conditions play an important role in the formation and evolution of the Carex tussock wetlands,determining the plant community succession and distribution,and the health and stability of ecosystem.Due to the influence of the climate change and human activities(industrial and agricultural development and utilization),hydrological conditions in wetlands have changed.In recent years,Carex tussock wetlands have been degraded in Northeast China,and even died over a large area,indicating a serious threat to their existence.In this thesis,Northeast China is taken as the research object,combining with multi-disciplinary theories and methods of physical geography,ecology,hydrology,botany,and pedology,the effects of hydrological changes on wetland distribution pattern evolution,plant community composition and structure,decomposition and input of organic matter and vegetation-soil carbon storage were studied by data collection,remote sensing image interpretation,field sampling investigation and laboratory simulation analysis.The distribution pattern,ecosystem community structure and carbon sequestration function of Carex tussock wetland under different hydrological conditions was clarified.The response mechanism of Carex tussock wetland ecosystem to hydrological changes was revealed from the three aspects of landscape,structure and function.This research provided a multi-angle and multi-level scientific basis for wetland protection and restoration based on hydrological regulation.It also has an important reference value for ecological restoration and conservation of typical swamps in Northeast China.The main conclusions were as follows:1.Hydrological conditions were the main driving factors for the evolution of landscape pattern of Carex tussock wetland,and had an importance impact on the growth and development of Carex tussocks.From 2010 to 2018,the temporal and spatial distribution pattern of restored Carex tussock wetland significantly changed.The area of tussock wetland was increased by about 722 m2 with an increasing rate of48.13%,and the total area of restored tussock wetland reached 2222 m2.The patch boundary and centroid expanded 29.91 m and migrated 5.9 m to the low-lying southwest respectively,where is more boggy with higher soil water content and water level.Additionally,the increasing Development and Weight of Curve Boundary indicated that the shape and boundary of a patch tended to be complex,thus enhancing landscape heterogeneity.It was necessary to adjust the hummock distance(54.22?117.89 cm)and density(1.89?3.08 ind/m2)to create a suitable living space and maintain the long-term health and stability of Carex tussock during the restoration and protection of Carex tussock wetland.In addition,it was suggested that water replenishment measures should be carried out in the arid area in spring to appropriately increase soil water content and water level,thus promoting the growth and development of Carex tussocks and accelerate the recovery of Carex population.2.Hydrological conditions influenced the species composition,community structure,diversity,and productivity of Carex tussock wetland.A total of 52 species of wetland plants,belonging to 21 families and 39 genera,were recorded in the field survey.The abundance of mesophytes including Beckmannia syzigachne,Echinochloa crus-galli,and Setaria viridis was significantly higher in dry area(D).Species richness,Shannon-Wiener index,Simpson index and Pielou evenness index of Carex schmidtii community were significantly lower,and the community dominance index and productivity were significantly higher in WD and W than D.The dominant position of C.schmidtii was more prominent under seasonally flooded(WD)and long-term flooded(W)conditions,but excessive water(long-term flooding)led to a decrease in the C.schmidtii community dominance.The C.schmidtii biomass in the hummock regions was the main source of community productivity.Drought led to a loss of the dominant position of C.schmidtii and a decrease in community productivity.The overall productivity of C.schmidtii community under different hydrological conditions was as follows:W(1186.43±304.47 g/m2)>WD(858.96±119.85 g/m2)>D(500.67±92.01 g/m2).3.Hydrological changes had a significant effect on litter decomposition,CO2release rate and amount of organic matter decomposition in Carex tussock wetland.Wetting(W0)and frequent dry-wet alternations(WD10,WD15)promoted litter decomposition.The cumulative release of CO2 increased initially and then decreased with the increase of soil water content.The highest CO2 release amount from organic matter decomposition was 5280.91 m L/kg with soil water content of 60%,whereas extreme humidity and drought inhibited the decomposition of soil organic matter.The decomposition of soil organic matter was well coordinated with the fluctuation in water level.With the gradual drying and wetting process of water level,the CO2release amount rose and fall periodically.Compared with long-term drought(FP0,SWC=30%)and long-term flooding(FP0,SWC=150%),the periodic fluctuation in water level promoted the decomposition of soil organic matter.4.There were significant differences in the total organic carbon storage in Carex tussock wetland under different hydrological conditions.Seasonally flooded plots exhibited the highest carbon storage of 9806.08±349.48 g C/m2,followed by long-term flooded plots at 8204.697±943.31 g C/m2,and the lowest was in drought plots at 6451.34±347.60 g C/m2.In Carex tussock wetland,soil carbon storage was the main contributor to ecosystem carbon storage(57.4%?83.1%),followed by hummock carbon storage(13.6%?36.5%),and plants exhibit a low contribution to ecosystem carbon storage.The significant decrease in hummock carbon storage in drought conditions was the main reason of the significantly lower carbon storage in D than in WD and W.Water conditions changed the distribution pattern of carbon storage in Carex tussock wetland ecosystem,with drought leading to a decrease in the proportion of hummock carbon storage and an increase in the proportion of soil carbon storage.5.The current and future(2050s and 2070s)potential distribution patterns of Carex tussocks in Northeast China were predicted using the maximum entropy(Max Ent)model.The results showed that the current highly suitable habitats of Carex tussock is about 5.7×104 km2,concentrated in Sanjiang Plain,Changbai Mountains and along the rivers in the Songnen Plain,and sporadically distributed in Da Hinggan Mountains.The organic carbon storage was about 428 Tg in the current highly suitable habitats.Under the future climate scenario,the potential suitable area of Carex tussock wetland was relatively stable,and the lost and expanded habitats mainly occurred in high latitudes and high elevations such as Da Hinggan Mountains,Xiao Hinggan Mountains and Changbai Mountains.By 2050s,the organic carbon storage of Carex tussock wetland under different climate scenarios was 441 Tg(RCP2.6),459 Tg(RCP4.5)and 381 Tg(RCP8.5),respectively.And by 2070s,the organic carbon storage of Carex tussock wetland under different climate scenarios was 360 Tg(RCP2.6),375 Tg(RCP4.5)and 393 Tg(RCP8.5),respectively.Compared with the current situation,the organic carbon storage of Carex tussock wetland decreased by 35?68 Tg in 2070s under the future climate scenario. |
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