Testing allometric scaling relationships in plant roots

Background:Metabolic scaling theory predicts that plant productivity and biomass are both size-dependent.However,this theory has not yet been tested in plant roots.Methods:In this study,we tested how metabolic scaling occurs in plants using a comprehensive plant root dataset made up of 1016 observations from natural habitats.We generated metabolic scaling exponents by logtransformation of root productivity versus biomass.Results:Results showed that the metabolic scaling exponents of fine root(<2mm in diameter)productivity versus biomass were close to 1.0 for all ecosystem types and functional groups.Scaling exponents decreased in coarse roots(>2mm in diameter).Conclusions:We found isometric metabolic scaling in fine roots,a metabolically active organ similar to seedlings or saplings.Our findings also indicate a shift in metabolic scaling during plant development.Overall,our study supports the absence of any unified single constant scaling exponent for metabolism-biomass relationships in terrestrial plants,especially for forests with woody species.

N and P resorption as functions of the needle age class in two conifer trees

Aims Given the importance of resorption in nutrient conservations,nu-trient resorption should change with leaf age if resorption depends on nutrient content,and if nutrient content changes with leaf age.However,no study has addressed this issue.Methods Here,we measured N and P concentrations of needles of different ages in two woody evergreen conifer species-white spruce(Picea glauca Voss.)and balsam fir(Abies balsamea Mill.)-to determine the effects of needle aging on nutrient resorption.Important Findings For both species,N and P concentrations were higher in newer needles than in older needles.Nutrient resorption efficiency,i.e.percentage of nutrients resorbed during senescence,also declined significantly with needle age from 73 to 22%in these two evergreen conifer species.The difference in nutrient resorp-tion between old and young needles may be attributed to the size of N and P sink tissues,which is likely to decrease with needle age.These results suggest that needle age affects the extent of N and P resorption in these two evergreen conifer species.