Physiological And Ecological Properties Of Agriophyllum Squarrosum, A Pioneer Plant For Sand Control

Agriophyllum squarrosum Moq,an annual of Chenopodiaceae,is widely distributed in north China and the middle of Asia,with characteristics of endurance to drought,poor soil, and sand covering,as well as of adaptation to sandy soil.It is a pioneer plant in mobile sand areas and can accelerate the succession of vegetation in sandy areas.However,less attention has been paid to it.A little research has been done in the study on A.squarrosum,in particular its regulation mechanism of germination,competition and collaboration between species, response to unfavourable environment,and man-made promotion,which constrains the evaluation and utilization of it.Based on research into its biological and physiological properties,this paper reveals its properties of growth and its ecological role in vegetation succession,aiming to find basis for its ecological function.The Mingshazui of Gulang county,and the Xishawo of Minqin county,both are in the lower reaches of the Shiyang River,were selected as research sites.The Mingshazui of Gulang county is located at the south edge of the Tengger Desert with an annual rainfall of 170mm;the Xishawo of Minqin county lies in the southeast border of the Badanjiron Desert with a mean annual rainfall of 113mm;both being the wind-driven sand hardest hit areas in China.The research on its morphology,seed form and germination,photosynthesis,growth, community distribution and ecological defence,by means of a combination of field trial and lab test,an association of permanent site observation and investigation on a large scale,was conducted with man-made climatic chamber,Li-6200 photosyntometer,and wind meter and so on during 2004 to 2007.The main results were as follows:1.A plant of A.squarrosum is tower-shaped,ramified near the ground with more branches;the first group of side branches,totaling 2 pairs,is close to the ground with the longest length.The variation of its height is great.Its canopy,the first group of branches near the ground,root depth,root volume,length of the largest root all were increasing with its height;and were highly correlated positively with its height.There was a significant positive conic correlation between the above-ground biomass,under ground biomass,and total biomass;and its height respectively.There were not a significant correlation between the root/shoot ratio,lateral root number;and its height.Its basic morphologic features can be figured out by height measurement through the empirical equation.2.The biomass above-ground made up the largest proportion of the total biomass.As for the biomass above ground,the biomass the height of 10～20cm above ground was the greatest, the biomass of the heights of 0～10cm and 20～30cm above ground were the second,and the biomass of over 20cm above ground are decreasing.As to the biomass for different organs, the biomass for roots was the smallest,the biomass for taproots and lateral roots abated sharply with soil depth.The biomass for fruits was the greatest,and the quantities of the biomass for branches and leaves were similar with the same features:their biomasses near the ground were the greatest and decreasing from low part up to top.3.Its seeds are flat with a clear long and short diameter.The variation of the long and short diameters was 10%and the variance for different ecological regions or different years was extremely significant.The 1000 kernel weight of air-dried seeds ranged from 1.05g～1.652g and the variance for different ecological regions and different years was significant.The moisture content of its seeds was 7.08%～13.67%,the variance for different ecological regions and different years was significant.4.The natural germination rate of A.squarrosum was not high.In general,seeds 2cm deep in the soil could germinate and the maximum soil covering was 4cm.The germination rates of seeds in germination dish in different ecological regions Neiman,Shapotou,and Minqin were less than 10%at 25℃in doors while the germination rate at 25℃in darkness was severalfold higher,which suggested that the germination of A.squarrosum was suitable in darkness.In addition,sand covering,treatment with 49%of sulfuric acid,and rubbing could accelerate the germination significantly by a maximum of 50%.5.A.squarrosum germinates in the last 10 days of April or the first 10 days of May,is in its young seedling period in the middle of May to the early June,in its branching period in the middle of June to the early August,in its blossoming period in the middle of August to the early September,and in its maturing period in the middle of September to the early of October; then wilts and dies.It can delay germination or would not germinate all the year round,which is considered a protection to its development.6.The daily photosynthesis rate of A.squarrosum presented a 2-peak curve.The peak of its seasonal photosynthesis rate presented in July;the peak of seasonal TRANS presented in August with the ebb in September;the peak of its seasonal WUE presented in June with the ebb in September.The Pn of A.squarrosum was highly and positively correlated with QNTM, EAIR,and TRAN due to its characteristics and environmental elements. 7.The height and horizontal growth of A.squarrosum was quite different in mobile sand and flat sandy land respectively.The mean annual growth in mobile sand was greater than that in flat sandy land.Under the 2 site conditions,its height growth presented conic and its growing process consisted of 3 stages,i.e.a low growth in the early period,a fast growth in the middle period,and a slowing growth in the late period.Under the 2 site conditions,its accumulated height growths were S-shaped;the accumulated horizontal growth curve also presented S-shape in mobile sand and the accumulated horizontal growth curve in flat sandy land went like a log curve.8.There was an interspecific competition among communities of A.squarrosum and the number of its communities presented a conic with a stable number of communities in the early stage and a decreased quantity in the late stage due to individual expansion.However,it kept a high number of communities at large.9.The communities of A.squarrosum were distributed in patch mainly in windward foot to the middle of a mobile dune;and lest in top and leeward side of a dune.In addition it was distributed in the 2 wings of a mobile dune.It existed also in communities at a site.In other site conditions,where there was sandy lands in patch,there would be A.squarrosum distributed in communities10.Individual A.squarrosum could reduce wind speed.The wind speed curves at the same position were similar;the wind speed curve at 50cm behind an individual presented a conic;that at 2m behind an individual went like a line.Like a bare sandy land,the wind speed curve of communities went like an exponential function.The wind speed at 10cm in an A.squarrosum distributed area accounted for 4～20%of that in bare sand areas.A.squarrosum could not only reduce wind speed but bar mobile sand,accumulating stable sand drifts behind it.The sand accumulation behind an individual plant was correlated with the volume of the individual in a conic.The roughness of a typical community was up to 6.325cm compared with that of 0.0024cm at a bare sandy land and the sand transportation rate was reduced to 0.025 g/cm·10min from 143.58 g/cm·10min at a bare sand land,suggesting a good protection from it.The ecological protection of A.squarrosum resulted from its branch and leaves covering on ground,root holding the ground,and reducing wind speed by individuals and communities.