| As an important sand-fixing pioneer,Salix gordejevii is widely distributed in Otingdag sandy land,Horqin sandy land and Hulunbeier sandy land,plays an important role in vegetation restoration and reconstruction.With the two mixed ways of ecological experiment in wild areas and laboratory,This paper systematically researched the ecological adaptability of S.gordejevii in different sites in Otingdag sandy land.We discussed the heterogeneity of the sites,revealed the dynamics and allometric relationships of the cluster branches population,and the adaptive mechanism of resources allocation,morphological anatomy and physiological ecology of S.gordejevii.The main results and conclusion obtained as follows:(1)The spatial heterogeneity of soil and vegetation in different stands of S.gordejevii showed that it had the high ecological adaptability.The soil surface temperature(0?20cm)of the different sites decreased in the order of moving sandy land>semi-fixed sandy land>fixed sandy land>dune slack.The vertical temperature difference and soil water content in the layers of 0?120cm were opposite.The soil particle-size distribution in different sites and the layers were consists of fine sand(100?250?m)and medium sand(250?500?m),and the total proportion of them were more than 81.86%,decreased in the order of moving sandy land>semi-fixed sandy land>dune slack>fixed sandy land.With the improvement of vegetation status in different sites,the soil were fine granulated.The pH were no significant change at different sites.The organic matter,total nitrogen and total phosphorus in fixed sandy land and dune slack were larger than those in semi-fixed sandy land and mobile sandy land,which changed significantly between the layers in dune slack.The special life history strategy played an important role in vegetation restoration in Otingdag sandy land.The communities of semi-fixed sandy land had the higher stability,and the fixed sandy land showed a poor stability to need to be renewed with a danger of potential degradation.(2)Analysis of the age structure and quantity dynamic of population showed that,the branches population of S.gordejevii on the mobile sandy land was in the period of growing,branches on semi-fixed sand and dune-lowland were in the period of stabilization,and branches on fixed sand were in a recession.The decline of the number of sprouting branches and young branches viability were the main reasons for the problem of the population development and renewal.(3)The analysis of the allometric relationship between the branch height growth and the basal diameter growth showed that there was an allometric growth in mobile sandy land and dune-lowland,the allometric values(a)were 1.270 and 0.519,and the growth rate of the former branch was greater than that of the basal diameter.The growth rate of the latter was less than that of the base diameter.The semi-fixed sand and fixed sand were isometry,and the height growth rate was equal to the basal diameter growth rate.The plants in mobile sandy land tended to have a high longitudinal growth rate to achieve rapidly larger photosynthetic organs and reproductive organs occuping more space,capturing light resources,and expanding the range of seed dispersal.With the site conditions changing,they in dune slack tended to have a high radial growth rate to resist the twist deformation caused by weight,to keep upright,to minimize the obstacle of resources transmission.The plants in semi-fixed sandy land and fixed sandy land to adapt to the middle.(4)The biomass of shoots,leaves and branches of S.gordejevii increased gradually with the increase of water gradient,and the proportion of biomass distribution of branches increased gradually,and the proportion of stems and leaves biomass was gradually decreased.Analysis on allometric growth of different components biomass showed that the biomass of shoot-stem was equal to the growth rate,that was the biomass accumulation rate was equal,which was independent of the site types.The growth relationships between in other modulars were related to site types.The cumulative rate of leaf biomass was the main regulator of biomass allocation strategy.It had a large accumulation rate in mobile sandy land,and reduced relatively in semi-fixed sand and fixed sand.The minimum rate in dune slack.The biomass accumulation rates of branch and stem were increased in fixed sand and dune slack to balance the accumulation rate of leaf biomass decreasing.There was a significant negative correlation between the size and number of twigs in different sites of S.gordejevii,that was,the increasing or decreasing rate of leaf size was larger than the decreasing or increasing rate of leaf number in twigs.In the case of a certain leafing intensity,the plants in mobile sandy land and dune slack had a larger single leaf dry weight or leaf area than the semi-fixed sand and fixed sandy land.(5)There were a significant difference in morphological and anatomical structures of different order roots.Their first and second order roots had only primary growth.The fourth and the fifth order roots had secondary growth.Some of the third order roots had primary growth.The primary xylem was triarch or tetrarch.Through dissection,diameter and root sequence synthesis method,S.gordejevii fine root was defined that the first 3 level roots have not formed continuous cork layer and their diameter less than 0.7 mm while less than the fine roots of the wet medium plants of S.microstachya var.bordensis(2 mm).When moisture decreases,fine root showed shallow-distribution,and weaken speed was fast.On the contrary,it was the same.The S.gordejevii catheter was given priority to reticulate vessels with both end walls with one tail and a tail in one wall.Its ends of vessel elements with alternate pitting had simple perforation plates.There were significant differences between the length,diameter and end wall slope angle of xylem vessels in the root of S.gordejevii and S.microstachya var.bordensis.The diameter,of root vessel elements of the former was wider and the end wall slope angle of those was smaller than the latter's,which showed the evolutionary features.However,the length of root vessel elements of the former was longer which showed the primitive feature.There were no significant differences between the length,diameter and end wall slope angle of xylem vessels in the stem of S.gordejevii and S.microstachya var.bordensis.The arid environment was more suitable for S.gordejevii to grow due to the higher water transmitting ability than S.microstachya var.bordensis.Leaf epidermal micromorphology had a significant difference on different site types.The leaf epidermal micromorphology and leaf function of S.gordejevii had a trade-off.(6)The diurnal change of photosynthetic characteristic of S.gordejevii had obvious difference between different site types.Pn of semi-fixed and fixed sandy lands showed unobvious bimodal pattern,dune-lowland showed significant bimodal pattern,andflowing sand showed single peak.Pn change of semi-fixed sand was mainly affected by non-stoma factors while Pn of other sites were affected by stoma and non-stoma together.S.gordejevii Tr all showed unimodal type.The order of daily mean value of Tr was:dune-lowland>flowing sand>fixed sand>semi-fixed sand.There existed a optimal strategy of water use that was low Gs with high Tr.The order of WUE was:semi-fixed sand>flowing sand>fixed sand>dune-lowland.There was no significant difference in the content of soluble sugar and soluble protein in the leaves of different oriental plants,while the flow of S.gordejevii accumulated a large amount of Pro,which had protective effect and improved the adaptability of osmotic stress to a certain extent.POD was affected by environmental stresses strongly,and SOD and CAT played a key role in active oxygen removal.S.gordejevii was under environmental stress or aged and death phase on fixed sand.Due to the protection of their own protective enzyme activity,MDA did not cause the membrane lipid peroxidation.But long-term imbalance of antioxidant enzyme system and MDA accumulation would lead to the decline and the risk of death.Above all,S.gordejevii has the special strategies of resource allocation,cluster branches allometry,physiological ecology,to ensure self-renewal of their population,so as to adapt to the sand environment,take the appropriate tending management measures(such as stubble etc)can maintain the population stability and avoid S.gordejevii brush death. |
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