Free-air carbon dioxide(CO_(2))enrichment(FACE)experiments provide an opportunity to test models of heat and water flow under novel,controlled situations and eventually allow use of these models for hypothesis evaluat...Free-air carbon dioxide(CO_(2))enrichment(FACE)experiments provide an opportunity to test models of heat and water flow under novel,controlled situations and eventually allow use of these models for hypothesis evaluation.This study assesses whether the United States Department of Agriculture SHAW(Simultaneous Heat and Water)numerical model of vertical one-dimensional soil water flow across the soil-plant-atmosphere continuum is able to adequately represent and explain the effects of increasing atmospheric CO_(2) on soil moisture dynamics in temperate grasslands.Observations in a FACE experiment,the Bio CON(Biodiversity,CO_(2),and Nitrogen)experiment,in Minnesota,USA,were compared with results of vertical soil moisture distribution.Three scenarios represented by different plots were assessed:bare,vegetated with ambient CO_(2),and similarly vegetated with high CO_(2).From the simulations,the bare plot soil was generally the wettest,followed by a drier high-CO_(2) vegetated plot,and the ambient CO_(2) plot was the driest.The SHAW simulations adequately reproduced the expected behavior and showed that vegetation and atmospheric CO_(2) concentration significantly affected soil moisture dynamics.The differences in modeled soil moisture amongst the plots were largely due to transpiration,which was low with high CO_(2).However,the modeled soil moisture only modestly reproduced the observations.Thus,while SHAW is able to replicate and help broadly explain soil moisture dynamics in a FACE experiment,its application for point-and time-specific simulations of soil moisture needs further scrutiny.The typical design of a FACE experiment makes the experimental observations challenging to model with a one-dimensional distributed model.In addition,FACE instrumentation and monitoring will need improvement in order to be a useful platform for robust model testing.Only after this can we recommend that models such as SHAW are adequate for process interpretation of datasets from FACE experiments or for hypothesis testing.展开更多
Aims The Gap Partitioning Hypothesis(GPH)posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests,allowing trees with contrasting strategies to coexist along resource g...Aims The Gap Partitioning Hypothesis(GPH)posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests,allowing trees with contrasting strategies to coexist along resource gradients.Few studies have examined gap partitioning of temperate,ground-layer vascular plants.We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin,USA,as a model system to test whether the GPH extends to the relatively species-rich ground layer.Methods We used a well-replicated experimental approach that included a gap opening gradient(five gap sizes,6,10,20,30 and 46 m diameter,and undisturbed reference areas),a within-gap location gradient(gap edge to center),and a temporal gradient(0,2,6 and 13 years after gap creation).The data were observations of ground-layer plant abundance,published plant traits,and a modeled index of understory light environments.We ordinated the plant abundance data and evaluated the relationships of composition,traits and light environment by gap size,location along the forest-gap transect and time,with several approaches such as correlations,descriptive statistics,non-parametric tests of group differences and indicator species importance values.Important Findings Ground-layer plant composition and traits differed across gap sizes,within-gap locations and over time.Gaps of all sizes differed in composition from undisturbed areas,and all pair-wise combinations of gap size also differed in composition,except the 6 m from the 10-m gaps.Large gaps(46 m)also displayed within-gap compositional gradients from gap edge to center locations.Compositional differences in gap size were evident 2 years after gap creation and,contrary to our hypotheses,remained different over the 13-year period,even in gaps with crown closure.In contrast to the neutral theory,species functional traits and microenvironmental conditions were related to variation in ground-layer composition.Species with smaller seeds,lower shade tolerance,later bloom times,shorter stature and longer leaves were associated with higher light,more central gap locations,larger gap sizes and greater time since gap creation.The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community.展开更多
Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes.Abiotic site characteristics may also affect a site’s susceptibility to invasion...Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes.Abiotic site characteristics may also affect a site’s susceptibility to invasion.We quantified resident plant species richness,phylogenetic diversity and several abiotic site characteristics for 24 oak forests in Minnesota,USA,to assess their impact on the abundance of a widespread,introduced terrestrial plant species,common buckthorn(Rhamnus cathartica L.).Specifically,we asked(1)whether resident species richness and phylogenetic diversity affected the abundance of R.cathartica and(2)what site characteristics explained the overall abundance of R.cathartica.Methods Our survey included 24 oak-dominated stands in Minnesota’s deciduous forests.In each stand,we identified all species in 16 plots.We also measured a series of environmental site characteristics,including canopy openness(a proxy for light availability),percent bare soil,soil pH,percent sand,an index of propagule availability,duff layer thickness(a proxy for earthworm activity),an index of insolation and slope.For all species present in at least one site,we estimated a community phylogeny.We combined all sitelevel characteristics,including phylogenetic diversity of the resident plant species,in a multiple regression model to examine site-level drivers of community invasibility.Important Findings Results indicate that sites with higher overall plant phylogenetic diversity harbor less R.cathartica,even though native species richness was not significantly related to R.cathartica abundance.Regression analyses indicated that,in addition to resident species phylogenetic diversity,the most important predictors of R.cathartica abundance were canopy openness and the amount of bare soil,both positively related to the abundance of the invader.By combining the effects of abiotic site characteristics and resident species phylogenetic diversity in a model that predicted the abundance of R.cathartica,we were able to simultaneously account for a wide range of factors that might influence invasibility.Overall,our results suggest that management strategies aimed at reducing disturbances that lead to increased bare soil and light levels may be more successful if they also maximize phylogenetic diversity of the resident plant community.展开更多
Aims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species.Warming-induced plant range expansions could partly depen...Aims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species.Warming-induced plant range expansions could partly depend on how warming modifies relationships with soil biota that promote plant growth,such as by mineralizing nutri-ents.Here,we grew two pairs of congeneric herbaceous plants spe-cies together in soil with a 5-year warming history(ambient,+1.7℃,+3.4℃)and related their performances to plant-beneficial soil biota.Methods Each plant pair belonged to either the mid-latitude temperate climate or the higher latitude southern boreal climate.Warmed soils were extracted from a chamberless heating experiment at two field sites in the temperate-boreal ecotone of North America.To isolate poten-tial effects of different soil warming histories,air temperature for the greenhouse experiment was identical across soils.We hypothesized that soil with a 5-year warming history in the field would enhance the performance of temperate plant species more than boreal plant species and expected improved plant performances to have positive associations with plant growth-promoting soil biota(microbial-feeding nematodes and arbuscular mycorrhizal fungi).Important Findings Our main hypothesis was partly confirmed as only one temperate spe-cies performed better in soil with warming history than in soil with his-tory of ambient temperature.Further,this effect was restricted to the site with higher soil water content in the growing season of the sampling year(prior to soil collection).One of the boreal species performed con-sistently worse in previously warmed soil,whereas the other species showed neutral responses to soil warming history.We found a positive correlation between the density of microbial-feeding nematodes and the performance of one of the temperate species in previously wetter soils,but this correlation was negative at the site with previously drier soil.We found no significant correlations between the performance of the other temperate species as well as the two boreal species and any of the studied soil biota.Our results indicate that soil warming can modify the relation between certain plant species and microbial-feeding nematodes in given soil edaphic conditions,which might be important for plant performance in the temperate-boreal ecotone.展开更多
基金supported by the National Science Foundation(NSF)Long-Term Ecological Research(LTER)grants(Nos.DEB-0620652,DEB-1234162,and DEB-1831944)Long-Term Research in Environmental Biology(LTREB)grants(Nos.DEB1242531 and DEB-1753859)+2 种基金Biological Integration Institutes grant(No.NSF-DBI-2021898)supported by the Geology Foundation at The University of Texas at Austinsupported by an Ivanhoe Foundation Fellowship。
文摘Free-air carbon dioxide(CO_(2))enrichment(FACE)experiments provide an opportunity to test models of heat and water flow under novel,controlled situations and eventually allow use of these models for hypothesis evaluation.This study assesses whether the United States Department of Agriculture SHAW(Simultaneous Heat and Water)numerical model of vertical one-dimensional soil water flow across the soil-plant-atmosphere continuum is able to adequately represent and explain the effects of increasing atmospheric CO_(2) on soil moisture dynamics in temperate grasslands.Observations in a FACE experiment,the Bio CON(Biodiversity,CO_(2),and Nitrogen)experiment,in Minnesota,USA,were compared with results of vertical soil moisture distribution.Three scenarios represented by different plots were assessed:bare,vegetated with ambient CO_(2),and similarly vegetated with high CO_(2).From the simulations,the bare plot soil was generally the wettest,followed by a drier high-CO_(2) vegetated plot,and the ambient CO_(2) plot was the driest.The SHAW simulations adequately reproduced the expected behavior and showed that vegetation and atmospheric CO_(2) concentration significantly affected soil moisture dynamics.The differences in modeled soil moisture amongst the plots were largely due to transpiration,which was low with high CO_(2).However,the modeled soil moisture only modestly reproduced the observations.Thus,while SHAW is able to replicate and help broadly explain soil moisture dynamics in a FACE experiment,its application for point-and time-specific simulations of soil moisture needs further scrutiny.The typical design of a FACE experiment makes the experimental observations challenging to model with a one-dimensional distributed model.In addition,FACE instrumentation and monitoring will need improvement in order to be a useful platform for robust model testing.Only after this can we recommend that models such as SHAW are adequate for process interpretation of datasets from FACE experiments or for hypothesis testing.
文摘Aims The Gap Partitioning Hypothesis(GPH)posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests,allowing trees with contrasting strategies to coexist along resource gradients.Few studies have examined gap partitioning of temperate,ground-layer vascular plants.We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin,USA,as a model system to test whether the GPH extends to the relatively species-rich ground layer.Methods We used a well-replicated experimental approach that included a gap opening gradient(five gap sizes,6,10,20,30 and 46 m diameter,and undisturbed reference areas),a within-gap location gradient(gap edge to center),and a temporal gradient(0,2,6 and 13 years after gap creation).The data were observations of ground-layer plant abundance,published plant traits,and a modeled index of understory light environments.We ordinated the plant abundance data and evaluated the relationships of composition,traits and light environment by gap size,location along the forest-gap transect and time,with several approaches such as correlations,descriptive statistics,non-parametric tests of group differences and indicator species importance values.Important Findings Ground-layer plant composition and traits differed across gap sizes,within-gap locations and over time.Gaps of all sizes differed in composition from undisturbed areas,and all pair-wise combinations of gap size also differed in composition,except the 6 m from the 10-m gaps.Large gaps(46 m)also displayed within-gap compositional gradients from gap edge to center locations.Compositional differences in gap size were evident 2 years after gap creation and,contrary to our hypotheses,remained different over the 13-year period,even in gaps with crown closure.In contrast to the neutral theory,species functional traits and microenvironmental conditions were related to variation in ground-layer composition.Species with smaller seeds,lower shade tolerance,later bloom times,shorter stature and longer leaves were associated with higher light,more central gap locations,larger gap sizes and greater time since gap creation.The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community.
基金Legislative-Citizen Commission on Minnesota Resources(M.L.2010,Chp.362,Sec.2,Subd.6c‘Healthy Forests to Resist Invasion’,to P.B.R.)Integrative Graduate Education and Research Traineeship:Risk Analysis for Introduced Species and Genotypes(NSF DGE-0653827)+2 种基金University of Minnesota Graduate School Fellowshipthe Hubachek Wilderness Research Foundationthe Dayton Fund of the Bell Museum of Natural History.
文摘Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes.Abiotic site characteristics may also affect a site’s susceptibility to invasion.We quantified resident plant species richness,phylogenetic diversity and several abiotic site characteristics for 24 oak forests in Minnesota,USA,to assess their impact on the abundance of a widespread,introduced terrestrial plant species,common buckthorn(Rhamnus cathartica L.).Specifically,we asked(1)whether resident species richness and phylogenetic diversity affected the abundance of R.cathartica and(2)what site characteristics explained the overall abundance of R.cathartica.Methods Our survey included 24 oak-dominated stands in Minnesota’s deciduous forests.In each stand,we identified all species in 16 plots.We also measured a series of environmental site characteristics,including canopy openness(a proxy for light availability),percent bare soil,soil pH,percent sand,an index of propagule availability,duff layer thickness(a proxy for earthworm activity),an index of insolation and slope.For all species present in at least one site,we estimated a community phylogeny.We combined all sitelevel characteristics,including phylogenetic diversity of the resident plant species,in a multiple regression model to examine site-level drivers of community invasibility.Important Findings Results indicate that sites with higher overall plant phylogenetic diversity harbor less R.cathartica,even though native species richness was not significantly related to R.cathartica abundance.Regression analyses indicated that,in addition to resident species phylogenetic diversity,the most important predictors of R.cathartica abundance were canopy openness and the amount of bare soil,both positively related to the abundance of the invader.By combining the effects of abiotic site characteristics and resident species phylogenetic diversity in a model that predicted the abundance of R.cathartica,we were able to simultaneously account for a wide range of factors that might influence invasibility.Overall,our results suggest that management strategies aimed at reducing disturbances that lead to increased bare soil and light levels may be more successful if they also maximize phylogenetic diversity of the resident plant community.
基金German Research Foundation(DFG)in the frame of the Emmy Noether research group(Ei 862/2)German Centre for Integrative Biodiversity Research(iDiv)Halle-Jena-Leipzig,funded by the German Research Foundation(FZT 118)+1 种基金the US Department of Energy(DE-FG02-07ER64456)the College of Food,Agricultural and Natural Resource Sciences(CFANS)at the University of Minnesota.
文摘Aims Climate warming raises the probability of range expansions of warm-adapted temperate species into areas currently dominated by cold-adapted boreal species.Warming-induced plant range expansions could partly depend on how warming modifies relationships with soil biota that promote plant growth,such as by mineralizing nutri-ents.Here,we grew two pairs of congeneric herbaceous plants spe-cies together in soil with a 5-year warming history(ambient,+1.7℃,+3.4℃)and related their performances to plant-beneficial soil biota.Methods Each plant pair belonged to either the mid-latitude temperate climate or the higher latitude southern boreal climate.Warmed soils were extracted from a chamberless heating experiment at two field sites in the temperate-boreal ecotone of North America.To isolate poten-tial effects of different soil warming histories,air temperature for the greenhouse experiment was identical across soils.We hypothesized that soil with a 5-year warming history in the field would enhance the performance of temperate plant species more than boreal plant species and expected improved plant performances to have positive associations with plant growth-promoting soil biota(microbial-feeding nematodes and arbuscular mycorrhizal fungi).Important Findings Our main hypothesis was partly confirmed as only one temperate spe-cies performed better in soil with warming history than in soil with his-tory of ambient temperature.Further,this effect was restricted to the site with higher soil water content in the growing season of the sampling year(prior to soil collection).One of the boreal species performed con-sistently worse in previously warmed soil,whereas the other species showed neutral responses to soil warming history.We found a positive correlation between the density of microbial-feeding nematodes and the performance of one of the temperate species in previously wetter soils,but this correlation was negative at the site with previously drier soil.We found no significant correlations between the performance of the other temperate species as well as the two boreal species and any of the studied soil biota.Our results indicate that soil warming can modify the relation between certain plant species and microbial-feeding nematodes in given soil edaphic conditions,which might be important for plant performance in the temperate-boreal ecotone.
