| The problem of rock desertification has seriously restricted the ecological and economic development in karst region,so carrying out ecological restoration is the core task of managing karst rock desertification.Carbon is the basis of all life on land,nitrogen is an important nutrient for vegetation restoration,and calcium is a key element in the karst power cycle during the ecological restoration of karstic desertification management.Therefore,it is necessary not only to focus on the carbon and nitrogen nutrients in the soil,but also to enhance the attention to the rich element calcium during the vegetation ecological restoration in the karst region.This study takes plant-soil calcium cycling as the main line of research to explore the distribution of calcium elements in the ecological restoration of rocky desertification and its relationship with carbon and nitrogen elements,to reveal the distribution characteristics of calcium elements in plants,to describe the adaptation of Zanthoxylum bungeamun var.dintanensis growth to calcium-rich karst soil environment,and to explore the change of carbon,nitrogen and calcium in plant-soil during the rock desertification restoration.It aims to provide a scientific basis for the restoration of degraded karstic desertification ecosystems and basic information for calcium cycle research.The main research achievements are as follows:1.The organic carbon,total nitrogen and total calcium contents of the soil under the Zanthoxylum bungeamun var.dintanensis ranged from 21 ～ 55 g/kg,8.4 ～ 12 g/kg and 40 ～ 59 g/kg,all of which were higher in the surface soil from0 to 10 cm.The total carbon content of Zanthoxylum bungeamun var.dintanensis plant was 404 ～ 431 g/kg,and the content in each part was ranked as branch >leaf > root > litter.Total nitrogen content ranged from 26 ～ 43 g/kg,with the highest content in root,followed by leaf,with significant differences among Zanthoxylum bungeamun parts.The total calcium content ranged from 4.1 to 43g/kg,and show the distribution rule of litter> leaf > root > branch in the Zanthoxylum bungeamun var.dintanensis.2.With the increase of years of cultivation of the Zanthoxylum bungeamun var.dintanensis,the carbon and nitrogen content of soil,root and litter were increased,the total carbon content of leaf was decreased,while the total nitrogen content of leaf was increased then decreased.The total calcium content in soil and leaf were increased,the total calcium content in root and litter was increased and then decreased;there were no significant change in carbon,nitrogen and calcium content in branch.The imbalance among carbon,nitrogen and calcium elements,as well as the delayed response of the physiological regulation function of calcium caused by long-term cultivation of Zanthoxylum bungeamun may be another reason for it growth decline.3.Soil calcium content of exchange,acid-soluble and water-soluble calcium were 1.99 g/kg,0.34 g/kg and 0.29 g/kg,which were strongly influenced by soil moisture,total phosphorus and total magnesium.Principal component analysis showde that calcium,like carbon,nitrogen and phosphorus,dominated soil quality in karst ecosystems.4.The leaf of Zanthoxylum bungeamun var.dintanensis had higher content of calcium pectate,water soluble calcium,calcium phosphate and calcium carbonate,while the root had more calcium oxalate and the branch had less calcium in all forms.It is indicated that the Zanthoxylum bungeamun var.dintanensis enhances the rigidity of the cell wall by strengthening the bond between the cell tissues of the leaves and the stability of the cell membrane,while the excess calcium that was not transported to the above-ground part of the plant in time is digested at the root,thus adapted to the calcium-rich environment.The diversity of calcium storage in various parts of the Zanthoxylum planispinum var.dintanensis during long-term adaptive evolution may be the reason why Zanthoxylum planispinum can grow better in highcalcium environments.5.The calcium content of Zanthoxylum planispinum var.dintanensis was closely related to the levels of water-soluble calcium,exchangeable calcium and acid-soluble calcium in soil,but not significantly related to the soil total calcium,which indicated that the soil carbon and nitrogen nutrient content and effective calcium level were the dominant factors for the calcium content of Zanthoxylum planispinum.Soil total nitrogen had a promoting effect on calcium pectate,calcium oxalate,calcium nitrate and calcium chloride in Zanthoxylum planispinum var.dintanensis,which indicated that the increase of soil nitrogen level can enhance the adaptation of Zanthoxylum planispinum var.dintanensis to high calcium environment.There was a significant negative correlation between leaf total carbon and leaf total calcium,and a significant positive correlation between leaf total nitrogen and total calcium in Zanthoxylum planispinum,which indicating that Zanthoxylum planispinum has developed a low carbon-high calcium leaf building strategy under the harsh environment of drought;Calcium affects plant photosynthesis and plant growth and development by influencing carbon allocation,nitrogen effectiveness. |
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