Heterogeneity of soil salinity is a prominent environmental characteristic in the intertidal zone of estuaries,affecting the plant growth and the shift of biotic interactions in the salt marsh.This study aims to exami...Heterogeneity of soil salinity is a prominent environmental characteristic in the intertidal zone of estuaries,affecting the plant growth and the shift of biotic interactions in the salt marsh.This study aims to examine the interactive effects of a salinity gradient and salinity fluctuations on intraspecific interactions of a euhalophyte.We assessed the impact of daily fluctuating salinity on the outcome of intraspecific interactions by cultivating seeds of Suaeda salsa(Chenopodiaceae)in river sand.The experiment was conducted in a greenhouse with three treatments:daily salinity fluctuations(static and fluctuating salinity),a salinity gradient(200 and 400 mmol L^(−1))and three planting densities(1,2 and 4 plants/pot).First,height and biomass of plants were measured at both the start and end of the experiment.Then,the growth indexes and log response ratio of S.salsa were analyzed.The outcome of intraspecific interactions of S.salsa shifted from competition in low salinity to facilitation in high salinity,and high conspecific density strengthened the competition and facilitation intensities.Daily salinity fluctuation did not significantly affect the plant growth and the outcome of intraspecific interactions,but did have a significant influence on belowground biomass.Our results suggest that the stress-gradient hypothesis may apply to predicting the variation of the intraspecific relationship of a salt-tolerant species along a salinity gradient,and the magnitude of this variation is density dependent.These findings help us understand how individuals and populations of a euhalophyte species respond to the natural variation or human modification of salinity conditions.展开更多
Positive interactions are defined as non-trophic interactions where at least one of the interacting species is benefited in terms of fitness and the other remains unaffected.Nevertheless,the bidirectional feedbacks be...Positive interactions are defined as non-trophic interactions where at least one of the interacting species is benefited in terms of fitness and the other remains unaffected.Nevertheless,the bidirectional feedbacks between species may be positive,neutral or negative.Thus,if facilitated species induce negative effects on their‘nurses’,the assumed definition of positive interactions could be reconsidered.Methods We assessed if ecological interactions between cushions of Azorella madreporica and their facilitated species are positive.Specifically,we tested if cover of facilitated species has any costs for cushion plants from an ecophysiological perspective,and if these costs increase with the amount of cover of facilitated species.In addition,through pathway analysis and correlations,we assessed if cover and richness of facilitated species have a direct and/or indirect effect on the fitness of cushion plants.Important Findings We found that facilitated plant species induced a significant cost for their nurses(cushion plants),and this cost increases with cover of the facilitated species.Additionally,the facilitated species exert a strong direct negative effect on the cushion’s fitness and a moderate indirect negative cost evident through the nutrient status and physiological performance of cushion plants.We thus contribute evidence that positive interactions between high mountain cushion plants of central Chile and their‘facilitated’species may be an artifact more than a fact,especially when bidirectional effects are considered;contrasting with the majority of studies that document only one side of the interaction.展开更多
A considerable challenge in plant ecology is to understand how interactions,such as competition or facilitation,shape the spatial distribution of plants.The‘‘stress gradient hypothesis’’predicts that facilitation ...A considerable challenge in plant ecology is to understand how interactions,such as competition or facilitation,shape the spatial distribution of plants.The‘‘stress gradient hypothesis’’predicts that facilitation and competition will vary inversely across gradients of abiotic stress or consumer pressure.Surprisingly,few previous studies have explored how the balance between facilitation and competition affects spatial patterns along gradients of stress in a plant population based on field experiments.In order to investigate the effects of consumer pressure,facilitation,and competition on the spatial pattern of plant populations,we conducted a restoration succession series field experiment in the Inner Mongolian steppe in which sample sites of graded consumer pressure,specifically grazing stress,were established.We chose to examine the spatial patterns of Leymus chinensis,a dominant species in our experimental site.In order to test the‘‘stress gradient hypothesis,’’we applied the univariate O-ring statistic to analyze local neighborhood density at different spatial scales.We used the pair-correlation function to detect the characteristics of point patterns using complete spatial randomness,the Poisson cluster process,and the nested double-cluster process.We found that the local densities of L.chinensis were higher under high stress than lower stress environments.This demonstrated the‘‘stress gradient hypothesis’’in that facilitation and competition varied inversely across gradients of consumer pressure.However,we found nodifferences in the spatial patterns of L.chinensis based on complete spatial randomness when interactions shifted from facilitation to competition along gradients of consumer pressure.Furthermore,we detected the characteristics of point patterns using the Poisson cluster and nested doublecluster processes.The results showed the spatial patterns of L.chinensis to fit well with the nested double-cluster model under highly stressful conditions,while in lower stress environments they were best approximated by the Thomas process.Our results illustrate that a shift in interactions from facilitation to competition along gradients of consumer pressure can shape spatial patterns and that a combination of the Poisson cluster process and nested doublecluster process can detect spatial pattern characteristics which cannot be detected by complete spatial randomness.展开更多
基金the National Natural Science Foundation of China(U22A20558,32271588,32301317,32100304)the Beijing Natural Science Foundation(8232026)and the Beijing Government.
基金supported by the Fundamental Research Funds for the Central Non-Profit Research Institution of Chinese Academy of Forestry(CAFYBB2016SY034,key technologies of functional restoration and directional improvement of mudflat wetland)the National Key R&D Program of China(2017YFC0506200)the Research on the synchronicity of dichogamy in Scirpus planiculmis based on population clonal structure(NSFC31800348).
文摘Heterogeneity of soil salinity is a prominent environmental characteristic in the intertidal zone of estuaries,affecting the plant growth and the shift of biotic interactions in the salt marsh.This study aims to examine the interactive effects of a salinity gradient and salinity fluctuations on intraspecific interactions of a euhalophyte.We assessed the impact of daily fluctuating salinity on the outcome of intraspecific interactions by cultivating seeds of Suaeda salsa(Chenopodiaceae)in river sand.The experiment was conducted in a greenhouse with three treatments:daily salinity fluctuations(static and fluctuating salinity),a salinity gradient(200 and 400 mmol L^(−1))and three planting densities(1,2 and 4 plants/pot).First,height and biomass of plants were measured at both the start and end of the experiment.Then,the growth indexes and log response ratio of S.salsa were analyzed.The outcome of intraspecific interactions of S.salsa shifted from competition in low salinity to facilitation in high salinity,and high conspecific density strengthened the competition and facilitation intensities.Daily salinity fluctuation did not significantly affect the plant growth and the outcome of intraspecific interactions,but did have a significant influence on belowground biomass.Our results suggest that the stress-gradient hypothesis may apply to predicting the variation of the intraspecific relationship of a salt-tolerant species along a salinity gradient,and the magnitude of this variation is density dependent.These findings help us understand how individuals and populations of a euhalophyte species respond to the natural variation or human modification of salinity conditions.
基金funded by the Project of Scientific Monitoring of Sichuan Zoige Wetland National Nature Reserve and the Biodiversity Survey and Assessment Project of the Ministry of Ecology and Environment,People’s Republic of China(2019HJ2096001006).
文摘Positive interactions are defined as non-trophic interactions where at least one of the interacting species is benefited in terms of fitness and the other remains unaffected.Nevertheless,the bidirectional feedbacks between species may be positive,neutral or negative.Thus,if facilitated species induce negative effects on their‘nurses’,the assumed definition of positive interactions could be reconsidered.Methods We assessed if ecological interactions between cushions of Azorella madreporica and their facilitated species are positive.Specifically,we tested if cover of facilitated species has any costs for cushion plants from an ecophysiological perspective,and if these costs increase with the amount of cover of facilitated species.In addition,through pathway analysis and correlations,we assessed if cover and richness of facilitated species have a direct and/or indirect effect on the fitness of cushion plants.Important Findings We found that facilitated plant species induced a significant cost for their nurses(cushion plants),and this cost increases with cover of the facilitated species.Additionally,the facilitated species exert a strong direct negative effect on the cushion’s fitness and a moderate indirect negative cost evident through the nutrient status and physiological performance of cushion plants.We thus contribute evidence that positive interactions between high mountain cushion plants of central Chile and their‘facilitated’species may be an artifact more than a fact,especially when bidirectional effects are considered;contrasting with the majority of studies that document only one side of the interaction.
基金supported by the National Nat-ural Science Foundation of China(31160476)the National Key Basic Research Program of China(NKBRP)(2014CB138802,2010CB9 50602)the Natural Science Foundation of Inner Mongolia(2011MS0517)
文摘A considerable challenge in plant ecology is to understand how interactions,such as competition or facilitation,shape the spatial distribution of plants.The‘‘stress gradient hypothesis’’predicts that facilitation and competition will vary inversely across gradients of abiotic stress or consumer pressure.Surprisingly,few previous studies have explored how the balance between facilitation and competition affects spatial patterns along gradients of stress in a plant population based on field experiments.In order to investigate the effects of consumer pressure,facilitation,and competition on the spatial pattern of plant populations,we conducted a restoration succession series field experiment in the Inner Mongolian steppe in which sample sites of graded consumer pressure,specifically grazing stress,were established.We chose to examine the spatial patterns of Leymus chinensis,a dominant species in our experimental site.In order to test the‘‘stress gradient hypothesis,’’we applied the univariate O-ring statistic to analyze local neighborhood density at different spatial scales.We used the pair-correlation function to detect the characteristics of point patterns using complete spatial randomness,the Poisson cluster process,and the nested double-cluster process.We found that the local densities of L.chinensis were higher under high stress than lower stress environments.This demonstrated the‘‘stress gradient hypothesis’’in that facilitation and competition varied inversely across gradients of consumer pressure.However,we found nodifferences in the spatial patterns of L.chinensis based on complete spatial randomness when interactions shifted from facilitation to competition along gradients of consumer pressure.Furthermore,we detected the characteristics of point patterns using the Poisson cluster and nested doublecluster processes.The results showed the spatial patterns of L.chinensis to fit well with the nested double-cluster model under highly stressful conditions,while in lower stress environments they were best approximated by the Thomas process.Our results illustrate that a shift in interactions from facilitation to competition along gradients of consumer pressure can shape spatial patterns and that a combination of the Poisson cluster process and nested doublecluster process can detect spatial pattern characteristics which cannot be detected by complete spatial randomness.
