Ecological Stoichiometry Of Three Dioecious Tree Species

Due to the different reproduction costs,male and female plants may form sex specialization and their respective morphology,growth and spatial distribution under specific environmental conditions,which plays an important role in maintaining the structural and functional stability of forest ecosystems.Exploring the ecological stoichiometric characteristics of dioecious tree species is helpful to understand the distribution strategy of male and female plants and the differences in utilization between species,so as to enhance the understanding of the ecological stoichiometric distribution pattern of dioecious tree species and the adaptation mechanism to the environment.However,there are few studies on the ecological stoichiometry of dioecious adult trees growing in the field.In this study,adult trees of three dioecious tree species,Populus davidiana,Fraxinus mandshurica and Taxus cuspidata,which are grown in the natural conditions in the mountains of the eastern part of Northeast China,were selected as subjects.By measuring the ecological stoichiometric parameters of tissues and organs,leaf traits and soil parameters of male and female individuals of the three tree species,the differences in ecological stoichiometric characteristics of tissues and organs between male and female individuals of the three tree species,the differences in utilization among species and the relationship between elements were analyzed.The main results are as follows:(1)The needle parameters at each leaf age of T.cuspidata female were better than those of male plants,but there was no significant difference in the leaf traits parameters between male and female plants of P.davidiana and F.mandshurica.There was no significant difference in soil parameters between male and female plants of the three tree species,and the soil parameters of the same sex plants decreased with the increase of soil depth.(2)The effects of age,organ and their interaction on C,N and P contents and their ratios were greater than those of gender.The results showed that there were no significant differences in the contents of C,N,P and N:P in current needles,four-year-old needles,P and C:P in twoyear-old branches and C in three-year-old branches of T.cuspidata at the same age between male and female plants.Needles(or twigs)N vs.P showed a linear positive correlation(P < 0.05),which the former scaling exponent was significantly higher than 1 indicating that the P content increased faster than that of N in needles whereas the latter value approximated 1 indicating an isometric relationship in twig N vs.P.In addition,the scaling exponents between needle N(or P)and twig N(or P)were significantly less than 1(P < 0.05),and the value for the N was about half of that of P(P < 0.05).(3)Tree species,tissues and organs,and their interaction with sex had greater influence on the ecological stoichiometric parameters of the three tree species than gender.The differences of ecological stoichiometric parameters between gender of the three tree species were concentrated in twigs and roots,and the differences of parameters between sexes of P.davidiana were large,the contents of C,N and P of female were higher than those of male,while the ecological stoichiometric parameters between sexes of F.mandshurica and T.cuspidata were mostly similar.The differences of C,N,P content and their stoichiometric ratios in different tissues and organs of male and female plants of the three tree species were basically the same.There was a significant positive correlation between N and P contents in the tissues and organs of the three tree species.The contents of C,N(except leaves),P and C:N,C:P in tissues and organs of T.cuspidata were higher than those of P.davidiana and F.mandshurica,but the N:P was lower.The change rate of P content was lower than that of N content,which showed an allometric relationship(N and P showed an isometric relationship between the tissues of P.davidiana),and the allometric slope was significantly higher than 1(P < 0.05).In conclusion,there was no obvious sexual dimorphism in stoichiometric patterns among tissues and organs of the three tree species,and the differences in ecological stoichiometric characteristics among tissues and organs were closely related to their functional characteristics.There were differences in nutrient uptake and utilization strategies between deciduous broadleaved and evergreen coniferous.There was not synergistical relationship between N and P contents in needles,N(or P)contents in needles and branches,and N and P contents in various tissues and organs.Among the three species,only T.cuspidata was N limited to a certain extent.