| The vegetation of Stone Forest Karst was seriously damaged by human in thelast century and the ecosystem degradation, after being protected by the human andnatural restoration, the vegetation in different succession stages appeared. This thesisfrom the point of plant community and individual vegetation in different successionstages responsed to the environmental gradient,and combined with stable isotopetechnique and plant physiological ecology method to explore different environmentalhabitats of plant competition for moisture and utilization strategy in Karst.By using stable isotope to analyze the vegetation of Ba River Stone Forest Karstat different succession stages, the conclusions are as follows:1The Source of Plants’ Water Utilization(1) The study area plant xylem water δ18O values are mainly distributed between-6.218‰~-11.28‰, different successional rank kind would use different watersources, the virgin forest mainly use the20~110cm depth of soil water, the secondaryforest use of0~20cm soil water and epikarst water for secondary forest, plantationhas the highest percentage of water absorption of0~55cm soil water, however, shrubis mainly absorbed0~55cm soil water and epikarst water. The soil water has thelargest contribution, but the epikarst water is indispensable to the vegetation watersupply.(2) Plant xylem water δD and δ18O values are significantly different in season.During the dry season,for the virgin forest, the water comes mainly from the50~110cm soil water and Epikarst water, the rainy season from20~110cm soil water,this shows that it had a certain adaptability to the karst; Regardless of season,secondary forest trends to use0~20cm soil water and Epikarst water; In dry season,plantation water utilization sources are more diversified, during the rainy season,itmainly use of0~20cm of soil water, if plant water (nutrient) competition is intense, itwill not conducive to the vegetation during the dry period.(3)By the affected of level and seasonal succession, different plants or the same plant in different period will appear different response to the moisture factor changes.The roots of the plants according to water conditions will choose the more easilyavailable, stable, adequate water to meet plant growth’s require water, so the waterutilization strategy has a different degree of plasticity.2The Efficiency of Plants’ Water Utilization(1)According to the research area geographical position, vegetationcharacteristics and δ13C, it is concluded that the area is for C3plants. Plant leavesδ13C in the study area are mainly distributed in the range of30.307‰~25.401‰, andthe average value is28.148‰per thousand.(2) Due to the effect of canopy density, soil nutrient and other factors, differentsuccession stage of plant leaves δ13C values exist the following order: Virgin forest>Ssecondary forest> Plantation, but no obvious difference for secondary forest andplantation, water utilization efficiency (WUE) of plant: WUEV> WUES> WUEP, thisshows that virgin forest has the highest plant water utilization efficiency,and strongdrought resistance.(3) Plant leaves δ13C values have greater differences in season. Plant cell growactively in the rainy season, in order to meet the leaves grow, it requires a lot oforganic matter,that will cause the intracellular CO2concentration in the "hunger"state, plant leaves δ13C values trend to be a positive value; During dry season, plantleaves grow completely, internal physiological and metabolic functions trend to becomplete, physiological and biochemical mechanism are more perfect, δ13C values ofplant leaves is low, thus presents the WUErainy season> WUEdry season.(4)For the difference of environmental habitat, the same plants or different plantspecies leaves has big changes in the δ13C values. Different plants plant leaves δ13Cvalues increase with the increase of moisture, this shows that these plants can makefull use of water resources as far as possible when the water supply sufficientabsorption utilization, this is the main model in the study area. However, due to thedifference of survival environment, similar plants obtain soil nutrients and moisture isdifferent, the δ13C values are also different.3Mechanisms of Plants’ Water UtilizationAccording to the difference of time and space in the water utilization strategy of plant, In ecological construction the species should have selection and matching,avoid excesses interspecific competition, especially elected diversification of watersources or deep roots absorbent of plants to adapt the lack of surface water, andwithout excessive absorption epikarst water. In the dry season virgin forest plantleaves δ13C values show that plant drought resistance ability is stronger, but theYunnan pine forest plant leaves δ13C values are conducive to rapid forest vegetation,therefore drought-resistant ability of virgin forest and grow faster in the river basin ofYunnan pine forest areas play an important role in the management of rockydesertification and vegetation restoration. |
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