Aims The volume of soil beyond a plant’s roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil.For this reason it has been hypothesized that the s...Aims The volume of soil beyond a plant’s roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil.For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility.We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition.In the first,the exchange of rhizosphere water and dissolved nutrients between two connected pots,each containing one plant,was manipulated by alternately raising and lowering the pots.In the second experiment,the roots systems of two competing plants were separated by partitions of differing porosity,thereby varying the plants’access to water and nutrients in the other plant's rhizosphere.In this second experiment,we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided,and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments,lower mobility reduced competitive effects on plant biomass and on relative growth rate(RGR),as hypothesized.In the second experiment,however,competition was more intense under high nutrient input,suggesting that low nutrient supply rates reduced the strength of the superior competitor.Competitive effects on RGR were only evident under the low water level,suggesting that under lower nutrient concentrations,competitive effects might be less pronounced.Taken together,our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.展开更多
Aims Plant community assembly in wetlands usually changes with eleva-tion gradients,which may be due to the direct effect of flooding and indirect effects such as changes in soil properties and competition.However,the...Aims Plant community assembly in wetlands usually changes with eleva-tion gradients,which may be due to the direct effect of flooding and indirect effects such as changes in soil properties and competition.However,the respective importance of each factor remains to be investigated.Methods We investigated patterns of plant diversity,community biomass and soil properties along an elevation gradient of a lakeshore meadow at Poyang Lake,China.Important Findings(i)With increasing elevation,species richness and Simpson diver-sity index decreased.Both aboveground biomass(AGB)and below-ground biomass(BGB)increased with elevation,however,the BGB/AGB ratio also increased,which suggests a significant effect of belowground competition.(ii)Soil N content and soil N:P ratio increased,whereas soil pH decreased with elevation.Other soil properties showed no significant response.(iii)Structural equa-tion modeling showed that variation of plant diversity was mainly explained by BGB.Thus,intensified belowground competition seems to be the primary mechanism causing lower plant diversity at higher elevations.(iv)These findings were further supported by the observed greater response ratio of N and P storage in plant commu-nities than the response ratio of soil N and P content to elevation,suggesting that soil nutrient limitation and belowground nutrient competition increased with elevation.Our study has important implications to wetland management and biodiversity conserva-tion under environmental change(e.g.changes in flooding regimes,eutrophication).展开更多
Background:Invasive species affect community dynamics and ecosystem functions,but the mechanisms of their impacts are poorly understood.Hypotheses on invasion impact range from Superior Competitor to Novel Function,fr...Background:Invasive species affect community dynamics and ecosystem functions,but the mechanisms of their impacts are poorly understood.Hypotheses on invasion impact range from Superior Competitor to Novel Function,from Enemy Escape to Microbial Mediation.In this study,we examined the effects of an urban tree invader,Acer platanoides(Norway maple,NM),on a mesic deciduous forest in contrast to its native congener Acer rubrum(red maple,RM)with a split-plot design experiment.A total of 720 maple seedlings were transplanted to 72 plots under 24 trees of three canopy types.The three experimental treatments were removal of resource competition at above-and belowground and removal of leaf-litter effect.Soil moisture and nitrogen-related microbial activities were followed for each plot.Results:We found that partial canopy removal increased canopy openness and light transmission to the forest floor,but to a greater extent under NM than under RM trees.NM seedlings were more shade tolerant than RM seedlings in height growth.During the reciprocal transplantation in the mixed forest,biomass accumulation of NM seedlings under RM trees were twice as much as under NM,while that of RM seedlings under NM trees was 23.5%less than under RM.Soil net nitrification and relative nitrification were significantly higher,but mineralization rate was much lower under NM than under RM trees,which would lead to faster N leaching and lower N availability in the soil.Plots with litter removal had significantly higher seedling mortality due to herbivory by the end of 2 years,especially for NM seedlings under NM trees.Trenching enhanced soil water availability but there was no difference among canopy types.Conclusions:Our results demonstrated that invasion of NM not only altered forest canopy structure but also changed herbivory rate for seedlings and N dynamics in the soils.NM seedlings were more shade tolerant under NM canopies than RM seedlings and were more protected by NM litter under NM canopies than under RM canopies.These altered biotic and abiotic environments will likely facilitate further invasion of NM in the forests,hence positive feedbacks,and make it an increasingly serious tree invader in North America.展开更多
基金Swiss National Science Foundation(31003A-112452).
文摘Aims The volume of soil beyond a plant’s roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil.For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility.We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition.In the first,the exchange of rhizosphere water and dissolved nutrients between two connected pots,each containing one plant,was manipulated by alternately raising and lowering the pots.In the second experiment,the roots systems of two competing plants were separated by partitions of differing porosity,thereby varying the plants’access to water and nutrients in the other plant's rhizosphere.In this second experiment,we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided,and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments,lower mobility reduced competitive effects on plant biomass and on relative growth rate(RGR),as hypothesized.In the second experiment,however,competition was more intense under high nutrient input,suggesting that low nutrient supply rates reduced the strength of the superior competitor.Competitive effects on RGR were only evident under the low water level,suggesting that under lower nutrient concentrations,competitive effects might be less pronounced.Taken together,our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.
基金This work was supported by National Natural Science Foundation of China(31600369,31260107)China Postdoctoral Science Foundation(2016M590315)+2 种基金Key Laboratory of Poyang Lake Environment and Resource Utilization,Ministry of Education(PYH2015-09)Key Laboratory of Watershed Ecology and Geographical Environment Monitoring,NASG(WE2015009)Guangxi Key Laboratory of Water Engineering Materials and Structures,Guangxi institute of Water Resources Research(GXHRI-WEMS-2018-4).
文摘Aims Plant community assembly in wetlands usually changes with eleva-tion gradients,which may be due to the direct effect of flooding and indirect effects such as changes in soil properties and competition.However,the respective importance of each factor remains to be investigated.Methods We investigated patterns of plant diversity,community biomass and soil properties along an elevation gradient of a lakeshore meadow at Poyang Lake,China.Important Findings(i)With increasing elevation,species richness and Simpson diver-sity index decreased.Both aboveground biomass(AGB)and below-ground biomass(BGB)increased with elevation,however,the BGB/AGB ratio also increased,which suggests a significant effect of belowground competition.(ii)Soil N content and soil N:P ratio increased,whereas soil pH decreased with elevation.Other soil properties showed no significant response.(iii)Structural equa-tion modeling showed that variation of plant diversity was mainly explained by BGB.Thus,intensified belowground competition seems to be the primary mechanism causing lower plant diversity at higher elevations.(iv)These findings were further supported by the observed greater response ratio of N and P storage in plant commu-nities than the response ratio of soil N and P content to elevation,suggesting that soil nutrient limitation and belowground nutrient competition increased with elevation.Our study has important implications to wetland management and biodiversity conserva-tion under environmental change(e.g.changes in flooding regimes,eutrophication).
基金WF received funding for the field study from Sigma Xi,Association of Women in Sciences and International Society of ArboricultureWF is currently supported by NSF 18-600 Program(ID:1921773)National Natural Science Foundation of China Major International Joint Research Project(ID:81620108010).
文摘Background:Invasive species affect community dynamics and ecosystem functions,but the mechanisms of their impacts are poorly understood.Hypotheses on invasion impact range from Superior Competitor to Novel Function,from Enemy Escape to Microbial Mediation.In this study,we examined the effects of an urban tree invader,Acer platanoides(Norway maple,NM),on a mesic deciduous forest in contrast to its native congener Acer rubrum(red maple,RM)with a split-plot design experiment.A total of 720 maple seedlings were transplanted to 72 plots under 24 trees of three canopy types.The three experimental treatments were removal of resource competition at above-and belowground and removal of leaf-litter effect.Soil moisture and nitrogen-related microbial activities were followed for each plot.Results:We found that partial canopy removal increased canopy openness and light transmission to the forest floor,but to a greater extent under NM than under RM trees.NM seedlings were more shade tolerant than RM seedlings in height growth.During the reciprocal transplantation in the mixed forest,biomass accumulation of NM seedlings under RM trees were twice as much as under NM,while that of RM seedlings under NM trees was 23.5%less than under RM.Soil net nitrification and relative nitrification were significantly higher,but mineralization rate was much lower under NM than under RM trees,which would lead to faster N leaching and lower N availability in the soil.Plots with litter removal had significantly higher seedling mortality due to herbivory by the end of 2 years,especially for NM seedlings under NM trees.Trenching enhanced soil water availability but there was no difference among canopy types.Conclusions:Our results demonstrated that invasion of NM not only altered forest canopy structure but also changed herbivory rate for seedlings and N dynamics in the soils.NM seedlings were more shade tolerant under NM canopies than RM seedlings and were more protected by NM litter under NM canopies than under RM canopies.These altered biotic and abiotic environments will likely facilitate further invasion of NM in the forests,hence positive feedbacks,and make it an increasingly serious tree invader in North America.
