Tree allometry responses to competition and complementarity in mixed-species plantations of Betula alnoides

Tree allometry plays a crucial role in tree survival,stability,and timber quantity and quality of mixed-species plantations.However,the responses of tree allometry to resource utilisation within the framework of interspecific competition and complementarity remain poorly understood.Taking into consideration strong-and weakspace competition(SC and WC),as well as N_(2)-fixing and non-N_(2)-fixing tree species(FN and nFN),a mixedspecies planting trial was conducted for Betula alnoides,a pioneer tree species,which was separately mixed with Acacia melanoxylon(SC+FN),Erythrophleum fordii(WC+FN),Eucalyptus cloeziana(SC+nFN)and Pinus kesiya var.langbianensis(WC+nFN)in southern China.Six years after planting,tree growth,total nitrogen(N)and carbon(C)contents,and the natural abundances of^(15)N and^(13)C in the leaves were measured for each species,and the mycorrhizal colonisation rates of B.alnoides were investigated under each treatment.Allometric variations and their relationships with space competition and nutrient-related factors were analyzed.The results showed a consistent effect of space competition on the height-diameter relationship of B.alnoides in mixtures with FN or nFN.The tree height growth of B.alnoides was significantly promoted under high space competition,and growth in diameter at breast height(DBH),tree height and crown size were all expedited in mixtures with FN.The symbiotic relationship between ectomycorrhizal fungi and B.alnoides was significantly influenced by both space competition and N_(2) fixation by the accompanying tree species,whereas such significant effects were absent for arbuscular mycorrhizal fungi.Furthermore,high space competition significantly decreased the water use efficiency(WUE)of B.alnoides,and its N use efficiency(NUE)was much lower in the FN mixtures.Structural equation modeling further demonstrated that the stem allometry of B.alnoides was affected by its NUE and WUE via changes in its height growth,and crown allometry was influenced by the mycorrhizal symbiotic relationship.Our findings provide new insights into the mechanisms driving tree allometric responses to above-and belowground resource competition and complementarity in mixed-species plantations,which are instructive for the establishment of mixed-species plantations.

Mixed-ownership Reform:Private Firms’Role in Targeted Poverty Alleviation-A Perspective on Resource Complementarity and Check&Balance

Targeted poverty alleviation(TPA)serves as a winning formula for fighting poverty and has generated valuable experiences for achieving common prosperity.The mixed-ownership reform has enhanced corporate economic performance.However,further testing is required to assess whether enterprises contribute to the improvement of distribution by participating in TPA.Taking A-share-listed private enterprises between 2016 and 2021 as research samples,we conducted an investigation into the extent and manner in which the mixed-ownership reform contributes to TPA.Our research reveals that a higher proportion of state capital equity participation is correlated with a greater level of private enterprises’contribution to TPA.This indicates that the mixed-ownership reform is beneficial for prompting private enterprises to shoulder responsibilities for building a society of common prosperity.As shown by the mechanism test,state capital equity participation encourages private enterprises to contribute to TPA primarily by alleviating corporate financing constraints through the resource complementarity effect.In contrast,the check&balance effect of promoting corporate poverty alleviation by mitigating the principal-agent problem has not yet been significantly demonstrated.Regarding the poverty alleviation model,state capital equity participation prompts private enterprises to contribute to TPA through industrial development,educational investment,and environmental protection,emphasizing a combination of providing external assistance and cultivating endogenous development capacity.In terms of TPA regions,state capital equity participation plays a significant role in supporting economically less-developed regions,regions with high unemployment rates,and central and western regions.This paper provides new empirical evidence for deepening mixed-ownership reforms and advancing common prosperity.

Can root trait diversity explain complementarity effects in a grassland biodiversity experiment?

Aims The positive relationship between plant biodiversity and com-munity productivity is well established.However,our knowledge about the mechanisms underlying these positive biodiversity effects is still limited.One of the main hypotheses is that com-plementarity in resource uptake is responsible for the positive biodiversity effects:plant species differ in resource uptake strat-egy,which results in a more complete exploitation of the avail-able resources in space and time when plant species are growing together.Recent studies suggest that functional diversity of the community,i.e.the diversity in functional characteristics(‘traits’)among species,rather than species richness per se,is important for positive biodiversity effects.However,experimental evidence for specific trait combinations underlying resource complemen-tarity is scarce.As the root system is responsible for the uptake of nutrients and water,we hypothesize that diversity in root traits may underlie complementary resource use and contribute to the biodiversity effects.Methods In a common garden experiment,16 grassland species were grown in monoculture,4-species mixtures differing in root trait diversity and 16-species mixtures.The 4-species mixtures were designed to cover a gradient in average rooting depth.Above-ground biomass was cut after one growing season and used as a proxy for plant productivity to calculate biodiversity effects.Important Findings Overall,plant mixtures showed a significant increase in biomass and complementarity effects,but this varied greatly between com-munities.However,diversity in root traits(measured in a separate greenhouse experiment and based on literature)could not explain this variation in complementarity effects.Instead,complementa-rity effects were strongly affected by the presence and competitive interactions of two particular species.The large variation in comple-mentarity effects and significant effect of two species emphasizes the importance of community composition for positive biodiversity effects.Future research should focus on identifying the traits asso-ciated with the key role of particular species for complementarity effects.This may increase our understanding of the links between functional trait composition and biodiversity effects as well as the relative importance of resource complementarity and other underly-ing mechanisms for the positive biodiversity effects.