| Karst ecosystems are special and fragile ecosystems.With the climate change at global scale,how to protect the existing plant community,prevent the degradation of plant community,build a healthy and stable plant community and improve the ecosystem function of plant community in karst areas are crucial issues in forestry and ecology.In this study,we investigated the species composition,species diversity,functional traits,phylogeny diversity,aboveground carbon storage(AGC)and environmental factors of natural forests in karst and non-karst areas along elevation profiles(800 m,1200 m,1600 m and 2000 m)in Dawei Mountain.Through the redundancy analysis,variation partitioning analysis,zero models,multiple linear regressions and structural equation models,we explored the relative effects of environmental factors on species diversities,functional traits,phylogenetic and functional structure and AGC.Finally,we explored the community assembly mechanisms and the drivers of AGC to better maintain biodiversity and provide scientific basis for vegetation restoration and combat rocky desertification in karst areas.The main results and conclusions are as follows:(1)Through comparing the plant species composition and species diversity in karst and non-karst areas along elevation profiles,there were 243 species in 93 families and 186 genera in karst areas,201 species in85 families and 144 genera in non-karst areas,and 89 species in 65 families and 82 genera in both karst areas and non-karst areas.The effect of elevation on the compositions of trees,shrubs and herbs was greater than that of lithology type,while the effect of elevation on the compositions of soil bacteria and fungi was less than that of lithology type.With the increase of elevation,only the diversity of herbs in karst areas increased significantly(P<0.01),and the species diversities of trees,shrubs,herbs,soil bacteria and fungi in non-karst areas increased significantly(P<0.05).The species diversities of trees,shrubs,herbs,soil bacteria and fungi in karst areas were higher than that in non-karst areas.Elevation and lithology type significantly(P<0.001)affected the species diversities of trees,shrubs,herbs,soil bacteria and fungi.The annual rainfall,soil p H,soil organic carbon,calcium and magnesium were the major drivers of plant species diversities in karst areas.The annual rainfall,soil available potassium,total potassium and soil organic carbon were the major drivers of plant species diversities in non-karst areas.(2)Through comparing the leaf functional traits of all trees(152 species)in karst and non-karst areas along elevation gradients,the community-weighted mean leaf calcium concentration in karst areas(8.15-13.82 g/kg)was more than twice that in non-karst areas(3.01-5.89 g/kg)at each elevation,and the leaf nitrogen concentration in karst areas was also significantly higher than that in non-karst areas at each elevation.With the increase of elevation in karst areas,the leaf thickness(LT),the ratio of leaf nitrogen and phosphorus(N:P),leaf calcium,magnesium,aluminum and sodium concentrations increased significantly,while leaf carbon,phosphorus and zinc contents decreased significantly.With the increase of elevation in non-karst areas,the specific leaf area(SLA),N:P,leaf potassium,copper,aluminum and nickel concentration decreased significantly,while the leaf dry matter concentration(LDMC),LT,leaf carbon and phosphorus concentration increased significantly.With the increase of elevation,leaf functional traits changed from acquisitive traits to conservative traits.The economic spectrum of leaf functional traits was different at the individual and community levels.At the individual and community levels,the trade-off strategies of LDMC,LT,SLA,leaf nitrogen,phosphorus,potassium and magnesium concentration were same,while the trade-off strategies of leaf carbon,calcium,iron,copper,zinc,aluminum,sodium,manganese and nickel concentration were different at the individual and community levels.The main environmental factors affecting leaf functional traits in karst area were annual rainfall,soil p H,soil organic carbon,total nitrogen,total phosphorus,ammonium nitrogen,available phosphorus,total potassium,calcium,magnesium,copper and manganese.The main environmental factors affecting leaf functional traits in non-karst areas were annual rainfall,soil p H value,soil organic carbon,total nitrogen,total phosphorus,available phosphorus,total potassium,available potassium and nickel concentration.(3)Through comparing the phylogenetic structure and functional structure in karst areas and non-karst areas along elevation profiles,the phylogenetic diversity of karst areas increased significantly with the increase of elevation,and there were no significant patterns in non-karst area.The phylogenetic diversity of karst area is higher than that of non-karst area.The phylogenetic structure is over-dispersion in karst areas,and under-dispersion in non-karst areas.The LMA,leaf calcium and potassium concentrations had significant phylogenetic signals.The functional diversity of karst areas was higher than that of non-karst area,and the mean pair-wise functional distance and nearest neighbor functional distance in karst areas were less than zero.The functional structure is over-dispersion in karst areas,while the functional structure in-non karst areas was under-dispersion,which were consistent with the conclusion based on the phylogenetic structure.Community assembly in karst areas was dominated by competition exclusion among species,while it was dominated by environmental filtration in non-karst areas.Average annual rainfall,soil p H value,soil organic carbon and calcium were the environmental factors that affected the community assembly in karst areas.Average annual rainfall,soil p H value,soil organic carbon and available phosphorus were the environmental factors affecting the community assembly in non-karst areas.(4)Through comparing the AGC in karst areas and non-karst areas along elevation profiles,the distribution range of AGC in karst areas was 22.18-206.7 t/hm~2,and that in non-karst area was 21.72-288.61t/hm~2.With the increase of elevation,the AGC in karst and non-karst areas decreased significantly as a whole(P<0.05).Elevation significantly affected the AGC(P<0.01),and lithology type had no significant effect on the AGC.The most important drivers of AGC was diameter at breast height(DBH)diversity(P<0.001,β=0.47),followed by the variation of LDMC(P=0.009,β=-0.27)and leaf nitrogen concentration(P=0.011,β=-0.25)Elevation indirectly decreased the AGC via the DBH diversity(P=0.002).Complex stand structural diversity and species with conservative leaf nitrogen concentration improved the AGC.Both the niche complementarity effects and mass ratio effects affected the AGC,and niche complementarity effect was more important than mass ratio effect.In conclusion,the species diversity,phylogenetic diversity and functional diversity of karst areas were higher than those of non-karst areas,but there was no significant difference in AGC between karst areas and non-karst areas.The important adaptive strategy of plants in karst area are high calcium in leaves,and the competition exclusion among species dominated the community assembly in karst areas.Complex stand structure and plants with conservative nitrogen concentration could improve the AGC.These results could provide scientific basis for ecological restoration and accurately improve the forest quality in karst areas. |
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