Effects of Nitrogen Addition on Plant Functional Traits in Freshwater Wetland of Sanjiang Plain,Northeast China

To clarify the responses of plant functional traits to nitrogen(N) enrichment, we investigated the whole-plant traits(plant height and aboveground biomass), leaf morphological(specific leaf area(SLA) and leaf dry mass content(LDMC)) and chemical traits(leaf N concentration(LNC) and leaf phosphorus(P) concentration(LPC)) of Deyeuxia angustifolia and Glyceria spiculosa following seven consecutive years of N addition at four rates(0 g N/(m2·yr), 6 g N/(m2·yr), 12 g N/(m2·yr) and 24 g N/(m2·yr)) in a freshwater marsh in the Sanjiang Plain, Northeast China. The results showed that, for both D. angustifolia and G. spiculosa, N addition generally increased plant height, leaf, stem and total aboveground biomass, but did not cause changes in SLA and LDMC. Moreover, increased N availability caused an increase in LNC, and did not affect LPC. Thus, N addition decreased leaf C∶N ratio, but caused an increase in leaf N∶P ratio, and did not affect leaf C∶P ratio. Our results suggest that, in the mid-term, elevated N loading does not alter leaf morphological traits, but causes substantial changes in whole-plant traits and leaf chemical traits in temperate freshwater wetlands. These may help to better understand the effects of N enrichment on plant functional traits and thus ecosystem structure and functioning in freshwater wetlands.

Intraspecific variations in fine root N and P and factors affecting their concentrations in Masson pine plantations across subtropical China

Fine roots(<2 mm)play vital roles in water and nutrient uptake.However,intraspecific variations in their chemical traits and their controlling mechanisms remain poorly understood at a regional scale.This study examined these intraspecific variations in fine roots in Masson pine(Pinus massoniana Lamb.)plantations across subtropical China and their responses to environmental factors.Root nitrogen(N)and phosphorus(P)concentrations and their mass ratios(N:P)ranged from 3.5 to 11.7 g kg^(-1),0.2 to0.9 g kg^(-1),and 7.8 to 51.6 g kg^(-1),respectively.These three chemical traits were significantly different between sites and in longitudinal patterns across subtropical China.Mean annual temperature was positively related to root N concentration but negatively related to root P concentration.There were significant,negative relationships between clay content and root P concentration and between pH and root N concentration.Available N had no significant relationship with root N concentration,while available P was a significantly positive relationship with root P concentration.The combined effects of altitude,climate(temperature and precipitation)and soil properties(pH,clay content,available N and P)explained 26%and 36%of the root N and P concentrations variations,respectively.These environmental variables had direct and indirect effects and exhibited disproportionate levels of total effects on root N and P concentrations.Root N and P concentrations explained 35%and 65%variations in their mass ratios,respectively.The results highlight different spatial patterns of chemical traits and various environmental controls on root N and P concentrations in these ecosystems.More cause-effect relationships of root chemical traits with abiotic and biotic factors are needed to understand nutrient uptake strategies and the mechanisms controlling intraspecific variations in plant traits.

Effects of Ecological Conditions of the Northeast of China on Protein，Oil and Protein＋ Oil Content in Soybean Seeds

Twenty five soybean strains of similar growth period were grown at eight locations simultanously in three northeast provinces of China.Most of the experimental sites differed markedly in temperature,precipitation, soil fertility and length of growing season.Protein and oil contents were detelmined to study the effects of ecological conditions on soybean chemical composition. The results showed that the average protein and protein + oil contents were higher at the south locations and lower at north locations, but there was no consistent variation for oil content,and there was no significant difference among most of the sites. Oil content of strains was highest when planted in Jiling. Combined analyses of variance indicated that there existed significant genotype,location and G×E interactions effects. F values of G×E interactions for all traits,although significant at 0.01 level of probability, were extremely smaller than those for location and genotype.This suggested that G×E interaction effects were relatively less important than both genotyp and location effects.Phenotypic correlations of the performance of genotypes,on single ehtry -basis,among eight locations were all positive for protein and protein+ oil and most of correlation coefficients were significant at 0.01 level of probability.This indicated that the relative performance of genotypes at each location was similar. In contrast,most of the correlation coefficients for oil content among the eight locations were not significant.Therefore,G×E interactions should be considered in breeding for high oil soybeans,as it may lead to the instability of genotypes and affect the rankings of genotypes when soybeans arc grown in diverse environments.

Plant traits related to leaf decomposition processes in arid ecosystems of northern Patagonia

Aims Plants play an important role in ecosystem processes.Functional meaning of trait variation in wide environmental gradients is well known but is scarcely known across narrow gradients.We analyze the variation of morphological,physical and chemical traits of dom-inant plant species and the potential rates of dry mass loss and N release/immobilization during senesced leaf decomposition of these species across a narrow aridity gradient,and to identify indicative traits useful to set species functional groups sharing decomposition patterns.Methods We analyzed the variation of morphological,physical and chemical traits(specific leaf area,seed mass,N and soluble phenols in green and senesced leaves,plant height)in dominant plant species at 12 sites across an aridity gradient in northern Patagonia,Argentina.We collected senesced leaves of each plant species at each site and used them to estimate the poten-tial rates of dry mass loss and N release/immobilization from decomposing senesced leaves in a microcosm experiment.We analyzed the variation of plant traits and decomposition rates across the aridity gradient.We grouped plants species accord-ing to growth forms(perennial grasses,deciduous shrubs,ever-green shrubs)and different combinations of morpho-physical and chemical traits of green and senesced leaves and compared the potential rates of dry mass loss and N release/immobiliza-tion during leaf decomposition among these groups delimited by each grouping criteria.Important Findings Plant traits did not vary across the aridity gradient.The potential rate of dry mass loss was positively related to aridity,while the potential rate of N release/immobilization did not vary across the gradient.Grouping species by separately morpho-physical and chemical traits resulted in a large overlapping in mean values of decomposition rates among groups.In contrast,plant groupings based on growth forms and those including all morpho-physical and chemical traits of green or senesced leaves yielded groups with differentiated rates of decomposition processes.The two latter groupings clustered spe-cies from more than one growth form indicating some overlapping in the rates of decomposition processes among species of different growth forms.Among traits,N concentration in senesced leaves and plant height explained the highest variation in decomposition rates being positively related to potential rates of dry mass loss and N release/immobilization.We concluded that plant groupings based on morpho-physical and chemical traits of either green or senesced leaves may be more powerful to differentiate functional species groups sharing decomposition patterns than the growth form group-ing.Moreover,plant height and N concentration in senesced leaves may be considered relevant synthetic functional traits in relation to decomposition processes in narrow aridity gradients.

Leaf trait variation captures climate differences but differs with species irrespective of functional group

Aims To clarify whether variation in leaf traits with climate differs with scale,i.e.across species and within a species,and to detect whether plant functional group affects species-specific response.Methods Leaf dry matter content(LDMC),specific leaf area(SLA),mass-and area-based leaf N(N_(mass),N_(area))and leaf P concentrations(P_(mass),P_(area))and leaf chlorophyll concentration(SPAD)were measured for 92 woody plant species in two botanical gardens in China.The two gardens share plant species in common but differ in climate.Leaf trait variation between the two gardens was examined via mean comparison at three scales:all species together,species grouped into plant functional groups and within a species.A meta-analysis was performed to summarize the species-specific responses.Important Findings At the scale of all species together,LDMC,SLA,P_(mass) and N_(mass) were significantly lower in the dry-cold habitat than in the wet-warm one,whereas N_(area) and SPAD showed an inverse pattern,indicating a significant environmental effect.The meta-analysis showed that the above-mentioned patterns persisted for SLA,N_(area) and SPAD but not for the other variables at the species-specific scale,indicating that intraspecific variation affects the overall pattern of LDMC,P_(mass) and N_(mass) and P_(area).In terms of species-specific response,posi-tive,negative or nonsignificant patterns were observed among the 92 species.Contrary to our prediction,species-specific responses within a functional group were not statistically more similar than those among functional groups.Our results indicated that leaf trait variation captured climatic difference yet species-specific responses were quite diverse irrespective of plant functional group,providing new insights for interpreting trait variability with climate.