Effects Of Biophysical Constraints,biotic Factors,climate And Phylogeny On Forest Plants Allometries Across Northeast China

Allometric scaling laws are not only a hot topic of theoretical ecology,but also practically important for the estimation of forest carbon sinks and community dynamic monitoring in a rapid changing world.While several allometric models based on biophysical constraints have been proposed,they can not well explain why allometric exponents changes significantly with climate,phylogeny and other biotic factors.In this study,we sampled forest plants at the organ,individual and community levels along latitude and altitude gradients in Northeast China to test whether theoretical allometric models can predict allometric relationships,and to examine how allometric relationships were modulated by abiotic and biotic factors.Then,we used data across China to test whether our findings in Northeast China could be extended to borader scales.We aim to answer the following questions:1)How allometric exponents are affected by climate,biotic factors,disturbance and phylogeny?What are the differences of these effects among allometries at different levels,life forms and forest types?2)Whether exsiting theoretical models can predict plant allometric exponents at different levels from organ to community?Why a number of observations deviate from theory predictions?Our major findings are as follows(1)Existing biophysical models based on assumptions at individual level are not suitable to describe leaf allometric relationships,while the modified model(PES)of metabolic scaling theory(MST)can well predict leaf allometries,which has considered the construction of leaf vascular networks.Leaf allometric exponents are only weakly affected by life forms,climate and taxa,while allometric constants are significantly affected(2)Empirical allometric exponents of trees support the predictions of metabolic scaling theory at late successional stage.Trees at an earlier successional stage reveal greater deviations These deviations may be caused by ecological processes not yet considered in MST,including light competition,demography dynamics and successional status.Climate has indirect effect on allometry through these biotic factors.(3)Two biophysical models could not predict the allometries of forest shrubs,while geometric similarity model and the MST for small plants gained supports.Both climate and phylogeny only affects allometric exponents very weakly,suggesting that there are be strong biophysical constraints on shrub allometries.(4)The theoretical models of small plants can well predict the exponents of herbs at the vegetative period.However,the exponents of herbs at reproductive period deviated significantly from theoretical predictions.Allometric exponents of understory herbs are closer to theoretical predictions than herbs under disturbed forest environment.Climate and phylogeny have very weak effect on herb allometries,suggesting that there are also strong biophysical constraints on herb allometries.MSTs can roughly predict allometric exponents of herbs,but failed for herbs at the reproductive period and in disturbed forests.(5)The allometric relationships of trees,shrubs and herbs in steady-state forest conform to the theoretical models for large and small plants,respectively.Both shrub and herb data support the predicted exponents of allometric models for small plants,despite that shrubs are woody plants while herbs are not.The influence of climate and phylogeny is more significant on large individuals such as trees,while allometries of small plants such as shrubs and herbs are weakly affected.These results suggest that the finite size effect is more important for plant allometries than being a woody plant.(6)An allometric relationship at the community level,the scaling of tree size distribution,also changes with forest succession,and only supports the prediction of MST model at late successional stage.Biotic factors such as recruitment limitation may be responsible for the greater deviation of allometric exponent from MST prediction at earlier successional stages.(7)Tree allometric relationships across China support our findings in Northeast China,that allometric exponents change across successional series and only support MST predictions at late successional stage.Allometric exponents for plantations are located between the exponents of primary forest and early successional natural forests,and are mainly affected by biotic factors.These difference between plantations and natural forests highlight the significant influence of forest management on allometric scalings.Biomass allocation of conifers' roots and stems are affected by climate and biotic factors,while that of leaf biomass is not affected.However,the exponents of roots and stems biomass with DBH for broadleaf trees are significantly affected by taxonomic groups,while that of leaf is mediumly affected by climate and biotic factors.Our results reconcile the discrepance between theoretical allometric model and the observations that allometries changes systematically with environmental gradients,phylogeny and biotic factors.We showed that metabolic scaling theory can be used to predict allometric relationships in primary forests,but should be improved to depict the allometric relationships in secondary forest.Our studies suggest that successional status,competition and recruitment limitation may be critical for allometries in secondary forests,and should be considered in future theoretical models to develop an unified allometric theory for primary,secondary and planted forests.