The relationship between relative growth rate and whole-plant C:N:P stoichiometry in plant seedlings grown under nutrient-enriched conditions

Aims Recent theories indicate that N is more in demand for plant growth than P;therefore,N concentration and N:C and N:P ratios are predicted to be positively correlated with relative growth rate(RGR)in plants under nutrient-enriched conditions.This prediction was tested in this study.Methods We examined the whole-plant concentrations of C,N and P and RGR,as well as the relationship between RGR and the concentrations and the ratios of N:C,P:C and N:P,for different harvest stages(the days after seed germination)of the seedlings of seven shrub species and four herbaceous species grown in N and P non-limiting conditions.The relationships among plant size,nutrient concentrations and ratios were subsequently determined.Important Findings RGR was positively correlated with N concentration and the ratios of N:PandN:C when the data were pooled for all species and for each shrub species,but not for individual herbaceous species.However,the relationship between RGR and P concentration and P:C was not significantly correlated for either shrubs or herbs.The variation of N among harvest stages and species was much greater than that of P,and the variation in N:P ratio was determined primarily by changes in N concentration.The shrub species differed from the herbaceous species in their N and P concentrations,nutrient ratios and in intraspecific relationships between RGR and nutrient ratios.These differences possibly reflect differences in the capacity for P storage and biomass allocation patterns.In general,our data support recent theoretical predictions regarding the relationship between RGR and C:N:P stoichiometry,but they also show that species with different life forms differ in the relationships among RGR and C:N:P stoichimetries.

Linking species performance to community structure as affected by UV-B radiation:an attenuation experiment

Aims UV-B radiation is known to affect plant physiology and growth rate in ways that can influence community species composition and structure.Nevertheless,comparatively little is known about how UV-B radiation induced changes in the performance of individual species cascades to affect overall community properties.Because foliage leaves are primarily responsible for photosynthesis and carbon gain and are the major organ that senses and responds to UV-B radiation,we hypothesized that,under reduced UV-B radia-tion,species with larger leaf areas per plant would manifest higher growth rates and hence tend to improve their community status compared to species with smaller leaf areas per plant in herba-ceous plant communities.Methods We tested this hypothesis by examining plant traits(leaf area per plant and plant height),plant growth rate(aboveground biomass per plant and plant biomass per area)and community status(spe-cies within-community relative biomass)for 19 common species in a two-year field experiment in an alpine meadow on Tibetan Plateau.Important findings Aboveground biomass per plant,as well as per area,progressively increased in a 39%reduced(relative to ambient)UV-B treatment dur-ing the experimental period.At the second year,11 out of 19 species significantly or marginally significantly increased their plant height,leaf area per plant and aboveground biomass per plant.No species was negatively affected by reducing UV-B.As hypothesized,the increase in aboveground biomass per plant increased with increasing leaf area per plant,as indicated by cross-species regression analysis.Moreover,the change in species within-community status increased with increasing leaf area per plant.Our study demonstrates that UV-B radiation has differential effects on plant growth rate across species and hence significantly affects species composition and plant commu-nity structure.We suggest that UV-B radiation is an ecological factor structuring plant communities particularly in alpine and polar areas.

Ecogeographical variation of 12 morphological traits within Pinus tabulaeformis: the effects of environmental factors and demographic histories

Aims More data are needed about how genetic variation(GV)and envi-ronmental factors influence phenotypic variation within the natural populations of long-lived species with broad geographic distribu-tions.To fill this gap,we examined the correlations among envi-ronmental factors and phenotypic variation within and among 13 natural populations of Pinus tabulaeformis consisting of four demo-graphically distinct groups within the entire distributional range.Methods Using the Akaike’s information Criterion(AiC)model,we measured 12 morphological traits and constructed alternative candidate models for the relationships between each morphological trait and key climatic variables and genetic groups.We then compared the AiC weight for each candidate model to identify the best approximating model for ecogeographical variation of P.tabulaeformis.The partitioning of vari-ance was assessed subsequently by evaluating the independent vari-ables of the selected best models using partial redundancy analysis.Important Findings Significant phenotypic variation of the morphological traits was observed both within individual populations and among populations.Variation partition analyses showed that most of the phenotypic variation was co-determined by both GV and climatic factors.GV accounted for the largest proportion of reproductive trait variation,whereas local key climatic factors(i.e.actual evapotranspiration,AET)accounted for the largest proportion of phenotypic variation in the remaining investigated traits.Our results indicate that both genetic divergence and key environmental factors affect the phenotypic variation observed among populations of this species,and that reproductive and vegetative traits adaptively respond differently with respect to local environmental conditions.This partitioning of factors can inform those making predictions about phenotypic variation in response to future changes in climatic conditions(particularly those affecting AET).