| Phosphorus(P)is one of vital life elements to the growth,development and evolution of organisms.Mineral P weathering and releasing?plant uptake and between-trophic transfer are important links in biogeochemical cycling,and strongly impact the ecosystem function.Due to strong weathering and leaching under high temperature and moisture levels,the Central Yunnan areas,which are located in subtropical China,are typically characterized as having P-deficient soils,which are lack of P,calcium(Ca)and magnesium(Mg)and enriched with iron(Fe)and aluminum(Al).Meanwhile,in this areas,lots of P-rich soils developed on natural P-rich ores and are surrounded by the dominant P-deficient soils.At these geological P-rich sites,soil P concentrations and other elements(e.g.,nitrogen(N)and Mg)are significantly increased,thus resulting significantly P-rich based elemental composition and stoichiometry in plants.Furthermore,long-term adaptation of plants to sites with these different soil nutrients may make them form nutrient resorption characteristics,chemical phenotype(e.g.,metabolome)and population genetic pattern based on differences in the nutrient supply.Therefore,this region become an ideal experimental location for studying how plants adapt to,and characteristics of plant element and metabolite content and genetic variation under,the geological P varying environments.Moreover,at these geological P-rich sites,mining and other human disturbance leads to severe degradation of vegetation and thus ecological restoration has become an important ecological environmental issue.However,there is still little in-depth study on the influence of the geological P-rich effects on plants,genetic differences of biological populations between the P-rich and P-deficient habitats,and mechanism of organisms in adapting to heterogeneous nutrient environments.Quercus variabilis,a Pan-Eastern-Asian deciduous oak,is a dominant tree species in the natural forest communities of the Central Yunnan and possesses very high timber,ecological,landscape and economic importance.Historically,the Central Yunnan area was heavily forested,and the Q.variabilis was the major dominant species,existing in pure stands,or mixtures with other tree species.But now the only natural forests and secondary forests of Q.variabilis are left as fragmented patches and located in remote mountainous areas,park and surrounding areas of villages.Therefore,there is important ecological and economic significance to study the characteristics,function and influence factors of the oak forest ecosystem,and to restore and construct the Q.variabilis and other oak forests.In this paper,the study area is located at the geological P-rich sites and the surrounding soil P-deficient sites in the Central Yunnan,and the study subjects are the natural Q.variabilis populations.The main research work are carried out as follows:1 Elemental stoichiometry of seeds of oak trees at soil P-rich and-deficient sitesSeeds are reproductive organs of plants,chemical composition of seeds are affected not only by the potential of site soil nutrient supply but also by plant biological characteristics.Q.variabilis and Q.acutissima are two oak tree species,have similar biological and ecological characteristics,and generally occur in mixed stands of each other.We investigated composition,stoichiometric variation and homeostasis of multiple elements(carbon(C),N,P,sulfur(S),potassium(K),Ca,Mg,Fe,manganese(Mn),zinc(Zn),copper(Cu),Al and sodium(Na))in the seeds of the two oak trees at soil P-deficient and-rich sites,and we wanted to understand the adaptive characteristics of the two oak trees under conditions with different soil nutrients.The study found that seed elemental stoichiometric traits of both Q.variabilis and Q.acutissima were strongly influenced by natural soil P variation,as well as by homeostatic regulation.Moreover,site types seemed have more effect on seed elemental stoichiometric variation than oak tree species.Based on the discriminant functional analysis,P,K,Mg and Mn had major contributions in distinguishing the differences of the seed elemental compositions between the P-deficient and P-rich sites,and the largest contribution was from seed P;moreover,K and Na had major contributions in distinguishing the differences of the seed elemental compositions between the two oak tree species.Most elemental stoichiometric traits were strict homeostasis in the oak tree seeds,but the seed P was one of the few elements that were non strict homeostasis in both Q.variabilis and Q.acutissima,showing strong adaptability of oak tree in their response to P variation.These findings reflect strong influences of geochemically based soil P-rich and-deficient effects on the elemental stoichiometry and compositions of plants,and highlight the importance of physiological regulations of nutritional needs in organisms.2 Leaf nutrient resorption stoichiometry of Quercus variabilis at soil P-rich and-deficient sitesNutrient resorption is an important strategy for plants to adapt to varying nutrient conditions.To understand the nutrient variability adaptation strategy of trees under conditions with contrasting geochemically based P soils,we determined leaf resorption efficiency and proficiency of 12 elements of two Q.variabilis populations growing at P-rich and-deficient sites and compared the patterns of leaf nutrient resorption stoichiometry.The differences of P resorption efficiency dominated the variation in nutrient resorption between the P-rich and-deficient sites.Q.variabilis exhibited a low P resorption efficiency and proficiency at the P-rich site and a high P resorption efficiency and proficiency at the P-deficient site.Both P resorption efficiency and proficiency strongly decreased with soil P content only and were positively related to the N:P and C:P ratios in green and senesced leaves.Moreover,resorption efficiency ratios of both N:P and C:P were positively associated with soil P.These results revealed that plants might employ energy-efficient strategies to meet their nutrient needs,P-limiting characteristics of plant production at the P-deficient site,and a possible limiting-element control pattern of P resorption.Hence,these results consistently show the importance of leaf P resorption of trees in adapting to sites with varying soil P content.3 Metabolomics and ionomics characterization of Quercus variabilis at soil P-rich and-deficient sitesTo understand how in situ woody plants metabolically adapt to contrasting geochemically based P soils,we investigated the foliar metabolomics and ionomics of two Q.variabilis populations,respectively growing at geological P-rich and P-deficient sites.Principal component analysis and orthogonal projections to latent structures discriminant analysis indicated that the two Q.variabilis populations were distinguished by foliar metabolome and ionome,with major contributions from 25 identified metabolites(primarily as sugars,amino acids and organic acids)and 4 chemical elements(P,S,Fe,and Zn);and orthophosphate contributed most to the variations in the metabolomes of Q.variabilis between the two P-type sites.Orthophosphate was correlated with leaf P,while leaf P was significantly influenced only by soil resident P at the P-rich site,which demonstrated the potent effects of soil-enriched P on the variations in the ionomes and metabolomes of the two Q.variabilis populations.Furthermore,the metabolic pathway analysis using MetaboAnalyst indicated four critical metabolic pathways:galactose metabolism,amino sugar and nucleotide sugar metabolism,glyoxylate and dicarboxylate metabolism,fructose and mannose metabolism.These findings suggest that the two Q.variabilis populations growing at P-rich and P-deficient sites have formed differential metabolite and element compositions and correlations,and this may be related to the formation of the edaphic ecotypes and growth status adapted to the localized soil nutrient environments.4 Genetic variation and differentiation of Quercus variabilis populations at soil P-rich and-deficient sitesExploring influence of geochemically based varying environments on the genetic variation of natural woody plants has important significance for understanding the adaptive evolution of plants.In this experiment,we took advantage of next-generation sequencing methods(double digest restriction site associated DNA sequencing(ddRAD-seq))to investigate the genetic variation of 8 natural Q.variabilis populations growing at geologically derived soil P-rich and-deficient sites.Results are as follows:1)4 Q.variabilis populations growing at P-rich sites generally had lower genetic diversity than those at P-deficient sites,and there was significantly negative correlation between the genetic diversity and soil P only(p<0.05).2)The overall degree of genetic differentiation among Q.variabilis was low at the genome scale with average pairwise Fst=0.047(ranged 0.028 to 0.073).3)The majority of genetic variation occurred within populations(95.76%),and that genetic variation among populations constituted 2.27%,among two P-type sites constituted 1.97%.Moreover,significant genetic divergence(p<0.0001)was found between the two site-type populations at the P-rich and-deficient sites,although the degree of genetic differentiation was rather low(Fst=0.025).4)The genetic distances between the populations significantly correlated with the geographical distances,showing the effect of geographical isolation among the Q.variabilis populations.However,Pairwise Fst statistics,PCA,phylogenetic tree and Structure model clustering analysis showed that Q.variabilis populations were structured into three clusters based on soil P variation,and the degree of genetic differentiation was the most highest between populations from sites with the greatest difference in soil P.5)The selection signal analysis found that genes embedded in selected regions for populations at P-rich site and P-deficient site were involved in different functions.Moreover,some candidate genes were annotated as transcription factors and some involved in protein synthesis and degradation,and might have roles in regulating Q.variabilis responses to P availability and other environmental stresses.These results suggest that P plays an important role in regulating the genetic diversity of Q.variabilis populations and there is a significant correlation between variation of soil P content and population genetic structure of Q.variabilis at the P-rich and-deficient sites;moreover,soil P content may be an important selective force and may cause adaptive genetic differentiation between Q.variabilis populations at sites with significant differences in soil P.In conclusion,compared with the generally subtropical soil P-deficient sites,the geologically derived soil P-rich sites not only significantly influence the nutrient and nutrient resorption stoichiometry,element and metabolite composition of Q.variabilis,but also make Q.variabilis populations form genetic variations closely related to the soil P content.Analyzing the influences of geologically based P-rich and-deficient effects on Q.variabilis by using ecological stoichiometry,metabolomics and ionomics,and population genetics,providing new methods in studying plant adaptive mechanism in the subtropics.These results enhance our understanding of strategies and mechanisms of woody plants in adapting to heterogeneous nutrient environments,adaptation evolutionary mechanism in plants,and the characteristics and possible ecological consequences of organism in response to anthropogenic P-loading,and also provide theoretical basis for establishing the vegetation eco-system's restoration measures in the abandoned phosphorus mining area. |
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