Self-organized Spatial Patterning In Intertidal Salt Marshes And Its Ecosystem Functioning

The spatial pattern formation is universal in natural ecosystems ranging from semiarid to tidal flats ecosystems.Scale-dependent feedback,the coupling of localrange positive feedback and long-range negative feedback,has been reported as the universal mechanism for the formation of regular spatial patterns.Theoretical and experimental studies have shown that spatial regular self-organized patterns have significant effects on ecosystem productivity,stability,resilience and vulnerability.However,the complexity of spatial patterns in nature is much diversity.Whether the mechanism,process and its ecosystem functioning of the formation of the regular patterns is suitable for explaining more complex spatial pattern still needs more exploration.Salt marshes are the most intense ecotone.With the increase of multiple stresses such as sea level rise,biological invasion,climate change,human activities and so on,the ecological function of salt marsh ecosystem is significantly affected,salt marsh protection and restoration is imminent.With the in-depth study of bioecomorphology,more studies emphasize the importance of the coupling effect among the elements of the salt marsh ecosystem.Based on the self-organization theory,the evolution or spatial response of the spatial pattern at the global scale is predicted from feedback at local scale,which provides a good perspective to explore the formation of the complex spatial pattern of the ecosystem and its ecosystem functioning.Through remote sensing image analysis,field transplantation experiments and mathematical models,this thesis explores the formation mechanism and ecological functions of some typical self-organizing spatial patterns in saltmarsh ecosystems,including vegetation patterns and ecogeomorphology patterns.We summarize the main conclusions as follows.(1)The shaping role of self-organization: linking vegetation patterning,palnt traits and ecosystem functioning.Using transplantation experiments in saltmarsh ecosystems dominated by Scirpus mariqueter in Chongming Dongtan Nature Reserve,we demonstrate that scale-dependent feedback is driving irregular spatial pattern formation of the vegetation.Field observations and experiments revealed that this self-organization process affects a range of plant traits,including shoot to root ratio,rhizome orientation,rhizome node number and rhizome length,as well as enhances vegetation productivity.Moreover,patchiness in self-organized saltmarsh vegetation can support a better micro-habitat for macro benthos,promoting their total abundance and spatial heterogeneity of species richness.Our results extend existing concepts of self-organization and its effects on productivity and biodiversity to the spatial irregular patterns that are observed in many systems.Our work also helps to link between the so-far largely unconnected fields of selforganization theory and trait-based,functional ecology.(2)Fairy circles imply high resilience of self-organized salt marshes and affect microbes biodiversity.Using field experiments conducted in Chongming Dongtan Nature Reserve and Nanhui Shoal,spatially explicit models and drone images,we tested two possible hypotheses concerning fairy circles patterning,including plant-sulfide feedback and plant-nutrient feedback.Field data shows significant nitrogen depletion in plant patches.Although field observations revealed a gradual buildup of sulfide in the ring centers,sulfide concentrations remained low,suggesting that sulfide buildup alone did not provide a reasonable explanation for the observed ring-type patterns in saltmarsh ecosystems.Model simulations provided a remarkable match between predicted fairy circles and the patterns observed in real-world marshes suggested that both nutrient depletion and sulfide accumulation could cause fairy circle patterning in diefferent salt marshes.These results suggest that the emergence of transient patterns(in terms of spots,circular patterns as well as concentric rings)could be used to identify the processes underlying pattern formation and to understand the ecological resilience of saltmarsh ecosystems to environmental stresses.In addition,fairy circles' patterning significantly improved the biodiversity of soil microorganisms in Scirpus mariquiter system,but have no effect on biodiversity of soil microorganisms in Spartina alterniflora salt marsh.(3)Skewness distribution of vegetation patch size in salt marsh verifies stress gradient hypothesis and indicate the presence of intraspecific facilitation.Through remote sensing image analysis of Chongming Dongtan Nature Reserve and Nanhui Shoal,this study reveals that the hump-shaped skewness distribution of vegetation patch size can be used to indicate the existence of intraspecific facilitation in the early development of salt marsh.Integrated with transplantation experiment and field observation,it is proved that the increase of vegetation density represents the most strong intraspecific facilitation under moderate flooding.In addition,making full use of mesoscale stress gradient hypothesis(SGH)and self-organization theory is helpful to improve the efficiency of salt marsh restoration.(4)Nonlocal entropy ratio and optimal of tidal channels.Based on remote sensing images analysis of Chongming Dongtan Nature Reserve,Saeftinghe and Schiermonnikoog,the dynamic optimality of the tidal channels indicated by the increase of non-local entropy ratio is increasing in the developing salt marshes.Compared with tidal channels in salt marsh coverd by different vegetation in Chongming Dongtan Nature Reserve,this research indicates that nonlocal entropy ratio of tidal channels have great correlation with the spatial distribution and species of salt marsh vegetation.In specifically,high above-and under-ground biomass is beneficial to the stability of tidal channels,and tidal channels in salt marshes with lower plant biomass and less sediment viscosity are more likely to achieve dynamic optimality.There is no obvious change trend in the nonlocal entropy ratio of the tidal channels in the degraded salt marshes in Venice Lagoon and Blackwater.However,under the pressure of sea level rise and sediment reduction,tidal channels with higher dynamic optimal may aggravate the degradation of salt marshes.Under the coupled effect of sea level rise and reduced sediment,more research need to focus on the contribution of tidal channels,including the dynamic optimality of the tidal channels and the high-efficiency tidal channels in degraded salt marshes,to degradation and maintenance of salt marshes.(5)Coupled effects of plant-crabs-wave interaction determine the scarp dynamics in salt marshes.Through remote sensing image analysis of Chongming Dongtan Nature Reserve,this research suggest that the presence of multiple scarps indicates the expansion of salt marshes.The dynamics of scarps in salt marshes have obvious quarterly and interannual dynamics.Generally speaking,the scarps move forward to the sea at the beginning of plant growth season,but retreats at the end of growth season.The interannual variation of the horizontal dynamics of scarps in salt marsh with higher biomass is tiny,but the horizontal stability of the scarps decreases due to lower plant biomass.Through the control experiment,it is proved that wave,palnt and crab behavior have great effect on the temporal and spatial dynamics of scarps.The presence of vegetation can stabilize the scarps,and crabs promote the collapse of scarps.When the above-and below-ground biomass of plant are both high,stability effect of vegetation is greater than the deconstruction of crabs,hence,scarps basically keep stable;However,when plant biomass is relatively lower,crab destroys scarps and promotes the seaward caving of falling plant under weak wave force;but promotes landward retreat under strong wave force.In salt marshes,multitude self-organization processes of biological,physical and chemical factors are involved in vegetation patterning and geomorphological patterning at varied temporal and spatial scales.As "engineer" of the salt marsh ecosystem,vegetation interacts with other elements of the system at different spatial and temporal scales,and produces a series of ecosystem functions,such as plant traits,primary productivity,macrobenthos' and microbes' biodiversity,stability and evolution of geomorphological patterns.Explaining vegetation spatial patterning and biogeomorphology patterning and their ecosystem functioning is essential to understand vulnerability and resilience of salt marshes to environmental stress,and provide theoretical support for salt marsh protection and restoration;Besides,it helps to broaden the framework of self-organization theory.