Responses Of Plant Functional Traits To Different Degrees Of Rocky Desertification

Karst landform is a comprehensive reflection of karst forms,which surface-and under-ground rocky morphology corroded by acidic water.The formation history of Karst landscape may be traced back to Early Paleozoic.From "Ice House" to "Green House","the early Cambrian bio-radiation" resulted in characteristic carbon isotopes shifting periods in ocean water.The process of life evolution became frequent,increasing carbon sedimentation in oceans.At last,carbonate rocky matrix was formed in this process.In Indo-Chinese epoch,Yangtze Platform uplifted from Paleo-Tethys Ocean which leaded to the extinction of Yangtze Platform.Affected by the geotectonic structural movement in Yanshanian period and Himalayan period,mass rock crevices was produced.The climate was warm and wet in southwest China grossly before glacier period,result in physico-chemical and biological action enhanced on bedrock by fissure water.Karst rocky desertification is a process of land degradation involving serious soil erosion,extensive exposure of basement rocks,drastic decrease in soil productivity,and the appearance of a desert-like landscape.And in essence,human activities contribute to this process result in ecosystem degradation in the end,which the ecosystem is reversal evolving.With the increasing degree of karst rocky desertification,soil mechanical composition became fragile,water losses and soil nutrient eluviations were increased,and vegetation coverage was reduced.In this process,degeneration of forests and the decrease of regional vegetation were alarming.High trees succeed by xerophilous vines,thorn bushes,coarse grass and succulent shrubs.Plants functional traits are the features(morphological,physiological,and phonological)of the represent ecological strategies and determine how plants respond to environment factor,affect other trophic levels and influence ecosystem properties.Variation in plant functional traits,and traits syndromes,has proven useful for taching many important ecological questions at range of scales,giving rise to a demand for standardized ways to measure ecologically meaning plant traits.So we measured plants functional traits to understand adaptive strategies of plants.In this study,plants functional traits were taken as study object,and Wushan County in Chongqing was taken as study region.We studied plants leaf functional traits and Arthraxon prionodes,Heteropogon contortus adaptive traits in different rocky desertification degrees of karst area.The main findings are shown as follows:(1)Soil physical and chemical properties were not harsher with the increased degree of karst rocky desertification.And instead soil water content,soil bulk density,soil nitrogen and soil phosphorus were increased in medium rocky desertification and strong rocky desertification.But compared with the nation's average of soil nitrogen and phosphorus,the soil nitrogen and phosphorus was lower.In all degrees rocky desertification,we also found 147 vascular plants including 4 arbors,66 shrubs,24 vines and 53 herbs.The tendency of degradation on vegetation was trees,trees and shrubs,shrubs,shrubs and grassland(or shrubs and grass and thin shrubs grass).And the munber of Rosaceae and Compositae species decreased greatly with the increased degree of karst rocky desertification,but the number of Gramineae species didn't change significantly.Then we analyzed plants life forms according to Raunkiaer's classification,and found that the major constituent was phanerophytes,geophytes followed proportion,which showed geophytes may be more adept environment.(2)In five degrees rocky desertification,145 vascular plants leaf functional traits were measured.The results showed that leaf thickness was increasing,specific leaf area and leaf area was reducing with the increased degree of karst rocky desertification,which were consistented with the global-scale plants functional properties changes under increasing drought stress.These change showed plants respond to drought stress in karst desertification region.There were no obvious changes in leaf tissue density and leaf dry matter content.Compare with the functional of trees and shrubs,vines,herbs,we found the functional of trees and shrubs was consistent with all plants changes in karst rocky desertification,but leaf area of vines was increased and herbs had not remarkable relationship.Coefficient of variation responded discrete degree of plants functional traits.With the increased degree of rocky desertification,the coefficient of variation of specific leaf area,leaf tissue density and leaf dry matter content were reduced.We also found the coefficient of variation of vines was highest level among tree and shrub?shurb?herb,so we argue the variation ability of vines were the strongest among tree and shrub?shurb?herb.(3)We analyzed the relationship of plants functional traits,combined with plant economics spectrum to come to the adaptive strategies of Arthraxon prionodes,Heteropogon contortus.Arthraxon prionodes increased leaf thickness,leaf dry matter content,specific root length,specific root density,specific root area,root ratio,nitrogen,nitrogen and phosphorus ratio,and reduced specific leaf area,root tissue density,stem ratio,carbon and nitrogen ratio,phosphorus to adapt the environment in different stages of rocky desertification.Heteropogon contortus increased leaf thickness,leaf area,leaf dry matter content,specific root length,specific root area,root ratio,nitrogen,nitrogen and phosphorus ratio,and reduced specific leaf area,root tissue density,stem ratio,leaf ratio,root diameter,carbon and nitrogen ratio,phosphorus to adapt the environment And these leaf functional changes armed at access to more light resources and those root functional changes armed to increase root absorption efficiency and root turnover or update.Then we analyzed the nitrogen and phosphorus of Arthraxon prionodes,Heteropogon contortus,we found the nitrogen and phosphorus of Arthraxon prionodes,Heteropogon contortus were lower than the nation's average,and the relationship of different organs was found(Arthraxon prionodes,leaf>root>stem.Heteropogon contortus,leaf>stem>root).But there was no obvious change in nitrogen and phosphorus among five degrees of rocky desertification.The nitrogen and phosphorus ratio was 10.598 in Arthraxon prionodes and 12.043 in Heteropogon contortus.So we suggest they all limited in nitrogen and phosphorus.At last,we compared with the plasticity index,the result showed the ability of plasticity of Arthraxon prionodes was stronger than Heteropogon contortus.Among all plants traits,the plasticity index of mass ratio was the smallest.So we suggest that in serious rocky desertification areas,Arthraxon prionodes and Heteropogon contortus may be are appropriate pioneer species to improve soil properties in karst desertification regions.And Heteropogon contortus was more appropriate than Arthraxon prionodes.