Effects Of Biodiversity On Fine Root Production In Subtropical Forests

The relationship between biodiversity and ecosystem functions is the frontier and hotspot of modern ecology.Increased biodiversity is conducive to improving ecosystem functions,ecosystem services and stability.At present,the mechanism of aboveground overyielding is relatively clear,mainly including selection effects and complementary effects.However,the research on the relationship between biodiversity and belowground ecological process and its influence mechanism is still lacking.There are two main reasons for this:(1)it is difficult to identify the tree species,and there is no effective method to study the structure of the belowground plant community;(2)the spatial heterogeneity of soil moisture,nutrients and texture is strong,which makes the plant belowground structure more complicated than the aboveground structure.Therefore,the identification technology of fine root(diameter less than 2 mm)tree species,and the study of the composition and spatial distribution of fine roots are extremely important for analyzing the relationship between biodiversity and belowground ecological processes.In this study,we selected three typical subtropical secondary forests(coniferous and broadleaved mixed forest,broadleaved forest,and evergreen broadleaved forest)in Dashanchong Forest Park in Changsha County,Hunan Province,China.In a tree diversity gradient in subtropical forests ranging from 1 to 12 tree species,we identified the species identity of fine roots(?2 mm in diameter)using a molecular method to unveil tree species composition and relative proportion of fine roots,and analytical selection effects(tree species)and complementarity effects(spatial distribution,nutrient utilization)on belowground production.The main results are listed as followed:(1)We established a method for identifying fine roots of tree species.As for the 6 dominate tree species,we developed 6 specific-primers and using qPCR method to identify the tree species,and predict the relative proportion fine roots of each tree species.As for more tree species,we also developed a universal primer-marking method.Firstly,we compared trnL(UAA)introns and rbcLa DNA fragments of 58 common tree species and confirmed that rbcLa are more suitable for subtropical forests.The universal primer-marking method has been proved that it can correctly detect the diversity of belowground tree species in the wild subtropical forest and the relative proportion of each tree species.(2)We explored the relationship between biodiversity index and fine root biomass.Specifically,we selected 4 biodiversity index(species richness,functional diversity,community-weighted means and phylogenetic diversity)and found that species richness is the best predictor of predicting changes in fine root biomass,which is inconsistent with previous aboveground studies,indicating that species richness is more important in explaining belowground processes than the other three(p=0.004).Community-weighted means is significant related to fine root biomass(p=0.032),but functional diversity is insignificant related to fine root biomass(p>0.05),indicating that mass-ratio hypotheses is better than niche-complementarity hypotheses for explaining the belowground subtropical forests.(3)We explored the mechanism of diversity affects frne root biomass.We found that only surface fine root biomass increased with increasing species richness(p=0.003),a result consistent with the phenomenon of "overyeilding".The specific results of our belowground mechanisms are not consistent with the vertical ecological complementation hypothesis.Instead,we found that the growth of plants in nutrient-rich soil layers showed a strong symmetric root-proliferation strategy.We also found that fine root overyielding depends on the interaction between biodiversity and stand density(p=0.038),suggesting that stand density and biofeedback should be considered as important drivers of belowground biomass in different subtropical forests.(4)We explored the mechanism of diversity affects the annual production fine roots.We found that in surface and deep soil layer,the annual production of fine roots both increased with the increase of species richness,which also indicates the phenomenon of "overyeilding".In addition,with the increase of species richness,the higher annual fine root production and the dominant species(selection effect)are significantly correlated in the forests with rich biodiversity.And we found that the growth of fine root in the nutrient-rich soil layer also showed a significant asymmetric root-proliferation strategy.And more importantly,we have found that soil phosphorus(P)limitations may be beneficial to enhance the selection effect.In addition to this,we also found that the annual production of fine roots depends on the interaction between species richness and stand density(p=0.011),which shows a negative density effect.Fine root biomas variation is inconsistent with annual fine root production.The phenomenon of fine root biomass "o very eilding" only appeared in surface layer,and root showed a symmetric root-proliferation strategy.In contrast,The phenomenon of annual fine root production "overyeilding" appeared in surface and deep layers,and root showed an asymmetric root-proliferation strategy.Furthermore,fine root biomass depends on the interaction between species richnes and stand density.But annual fine root production depends on the interaction between species richnes,stand density and soil phosphorus.