| The essentiality of restoration of degraded ecosystem is community succession. Plantphysiological ecology is one of the research content of relation between ecosystem structureand function, playing important roles in the research of vegetation recovery of degradedecosystem. In order to understand the effect of Salix cheilophila plantation on the recoveryprocess of degraded ecosystem and adaptive characters of S. cheilophila plantation to localspecific high-cold climate condition in alpine sandy land, In this study, the physiological andecological characteristics of S. cheilophila vegetation were researched, includingphotosynthetic physiology, water physiology, leaf structure traits, community structure of S.cheilophila plantation, understory species diversity and soil physicochemical properties, themain results are as follows:(1) Four stand ages S. cheilophila showed different diurnal courses of gas exchange. Thediurnal fluctuations of net photosynthetic rate of37-and25-years-old S. cheilophila wererepresented by a bimodal curve, appearing the photosynthetic midday depression.11-and4-years-old S. cheilophila were represented by a unimodal curve. Pnand Trof11-and25-years-old S. cheilophila was significantly higher that of4-and37-years-old S. cheilophila,while WUEtof4-years-old S. cheilophila was significantly higher that of other three stand ageS. cheilophila. Light response parameters fitting and CO2response parameters fitting revealedthe initial quantum yield(α) of11-years-old S. cheilophila was significantly higher than that ofother three stand age S. cheilophila, and photosynthetic capacity (Amax) of11-and25-years-oldS. cheilophila were significantly higher than those of4-and37-years-old S. cheilophila,simultaneously, the dark respiratory rate(Rd) were significantly lower than that of4-and37-years-old S. cheilophila, indicating both of them have stronger photosynthetic and organicmatter accumulation ability. Meanwhile, the actual photochemical quantum efficiency (ΦPSⅡ)and photochemical quenching coefficient (qP) of11-and25-years-old S. cheilophila weresignificantly higher than that of4-years-old S. cheilophila, indicating both of them havestronger photosynthetic ability. Simultaneously, non-photochemical quenching coefficient(NPQ) of4-years-old S. cheilophila was significantly higher than that of other three stand age S.cheilophila, and NPQ of37-years-old S. cheilophila was significantly higher than that of11-years-old S. cheilophila, suggesting that there were a lot of light energy absorbed of4-and37-years-old S. cheilophila can not be used for photosynthesis, dissipating in the form of heat. The conclusion is that photosynthetic capacity of S. cheilophila shows significant changewith the increase of stand age. The photosynthetic capacity of11-and25-years-oldS.cheilophila is comparatively even higher, and the photosynthetic capacity and waterutilization efficiency of37-years-old S.cheilophila is decreasing obviously, which indicates thatthe plant of37-years-old S.cheilophila is in decline stage of growth and development.(2) The relative water deficit of four ages S. cheilophila had no significant difference. Thedaily mean value of water potential of37-years-old S. cheilophila was significantly lower thatof other three stand ages S. cheilophila, and the daily mean value of water potential of4-and11-years-old S. cheilophila was significantly lower that of25-years-old S. cheilophila, whichindicated that37-years-old S cheilophila suffers serious drought stress. The water losing rate of4-years-old S. cheilophila was significantly lower than that of other three stand ages S.cheilophila, and the water losing rate of25-years-old S. cheilophila was significantly lowerthat of11-year-old S. cheilophila, which indicated that4-and11-years-old S cheilophila havehigher drought resistance capability. Simultaneously, the SLA of4-years-old S. cheilophila wassignificantly lower that of other three stand ages S. cheilophila, implying the water useefficiency of4-years-old S. cheilophila is even higher. The Nmassof11-years-old S. cheilophilawas significantly higher that of other three stand ages S. cheilophila, and the Nmassof25-years-old S. cheilophila was significantly higher that of37-years-old S. cheilophila,implying photosynthetic capacity of11-and25-years-old S. cheilophila is even higher. ThePmassof11-years-old S. cheilophila was significantly higher that of25-and37-years-old S.cheilophila, and the Pmassof4-years-old S. cheilophila was significantly higher that of25-years-old S. cheilophila. The Nmass/Pmassof25-years-old S. cheilophila was significantlyhigher that of11-and25-years-old S. cheilophila, meanwhile, the average Nmass/Pmasswerebetween5.16and6.28, far below14, which revealed the productivity of S. cheilophila inGonghe basin is nitrogen limited. Correlation analysis indicated that the Nmassof four ages S.cheilophila was significantly positively correlated with Pmass, the Pmassof four ages S.cheilophila was highly significantly negatively correlated with Nmass/Pmass, the Pmassof fourages S. cheilophila was significantly negatively correlated with stand age, and the Nmass/Pmassoffour ages S. cheilophila was significantly positively correlated with stand age.The conclusion is that water physiological status and leaf structure type traits of S.cheilophila shows significant change with the increase of stand age. The water physiologicalstatus of11-years-old S.chelophila is better, and drought resistance capability is stronger, andthe photosynthetic capacity reflected by leaf traits is higher. The drought-resistant ability of11-years-old S.chelophila is weaker, but the photosynthetic capacity reflected by leaf traits is the highest.4-years-old S.chelophila reveals stonger drought-resistant ability and waterutilization efficiency through its own adjustment of physiology and leaf traits under worsewater condition. The drought-resistant ability of37-years-old S.chelophila decreasesignificantly as well as photosynthetic capacity reflected by leaf traits, which indicates that theplant of37-years-old S.cheilophila is in decline stage of growth and development.(3) The species of the important value were different in four understory vegetation of S.cheilophila. Leymus decalinus was the dominant species in understory vegetation of differentstand ages of S. cheilophila, which indicated that L. decalinus has strong adaptability. With theincrease of age, some annual species in drifting or semi-drifting sandy land graduallydisappeared from the community, and shrub and subshrub began to appear in the undergrowthvegetation community, implying the structure of undergrowth vegetation community tended tobe stable. During the process of succession, the important value of one perennials species wassignificantly higher than that of annuals, which indicated that perennial plants played animportant role in maintenance of community function. Both aboveground biomass andcoverage of understory communities presented increasing-decreasing-increasing trend in theprocess of vegetation restoration. Simultaneously, the species richness, species diversity,evenness and ecological dominance index of undergrowth vegetation community increasedwith progress of succession, which indicated that structure tended to be stable and ecosystemfunction also strengthened constantly. In early-middle period of vegetation restoration, due tothe poor stability of the soil substrate, low soil nutrients and the competition and shading ofupper Salix cheilophila, the restorative course for understory species diversity were relativelyslow, and primary productivity and coverage of vegetation aslo be in low level. Therefore, inorder to promote development of forest stands and understory species diversity, a selectivecutting for upper layer of S. cheilophila plantation should be carried out in the middle stage ofsuccession. Meanwhile, upper layer of S. cheilophila plantation was in a state of decline in thelater stage of succession, stumping and rejuvenating treatments should be done to improvestability and ecological function of forest stands.The conclusion is that community structure and understoryapecies diversity of S.cheilophila shows significant change. With the increase of stand age of S. cheilophila, thestructure of undergrowth vegetation community tend to be stable, and diversity of species areincreasing, and ecosystem function improve steadly.(4) With the growth of S. cheilophila plantation, soil water content of010cm increasedgradually, while soil water content of1020cm primarily decreased and then increased, therangeability of010cm soil water content was obviously higher than1020cm soil water content. The soil silt, organic matter, TOC and TN content of010cm and1020cm soil layerincreased with the restoration period of S. cheilophila plantation, and the increase amplitudeand the content presented decreasing trend in vertical direction. Simultaneously, soil sandcontent and pH of010cm and1020cm soil layer decreased with ages increasing of S.cheilophila plantation, and the falling range presented decreasing trend, and the content wastending to rise in vertical direction. The Soil pH was highly significantly negatively correlatedwith TOC and TN. TOC was highly significantly positively correlated with TN. Soil sand(10.05mm) content was highly significantly negatively correlated with organic matter, TOC,and TN content. Soil silt (0.050.002mm) content was highly significantly positivelycorrelated with organic matter, TOC, and TN content. In research area, it could be predicted foraccumulated quantitative relation of organic matter, TOC, TN because of soil particlescomposition by linear equation, which provided scientific basis to estimate soil carbon sink inthe process of S. cheilophila plantation vegetation restoration.The conclusion is that characteristic parameters of forest soil of S. cheilophila showssignificant change. With the increase of stand age of S. cheilophila, the physicochemicalproerty of surface soil layer improved gradually. The increase of the content of silt and thedecrease of the content of sand grains led jointly the fining of soil texture in surface soil layer,the fining of soil texture was accompanied with the soil environment improved and the fixedexisting effect of organic carbon and nitrogen.
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