Study On Leaf Ecological Stoichiometry Of Aquatic Plants In The Arid Zone Of The Northwest China

The arid zone of the Northwest China locates in the centre of Euroasia mainland(35-50°N,73-125°E),and it is far away from the sea which leads to its arid climate,shaping its unique characteristics in terrain,landform,climate as well as temporal and spatial variation of its water system,especially its development,feature and discrepancies in their distribution patterns.There are higher aquatic plants diversity in the zone due to diversity habitats such as permanent streams and rivers,natural swamps and lakes(both fresh and saline),man-made reservoirs,and irrigation channels which are generally favorable to the growth of aquatic plants.In this study,we chose the aquatic plants in the arid zone of northwest China to study the spatial pattern of foliar C%,N%,P%ecological stoichiometry of different life from aquatic plants,the correlationship between each element,and environmental factors.Also,Ranunculus natans C.A.Mey.(Ranunculaceae)was chosen to study that spatial patterns of leaf carbon,nitrogen stoichiometry and stable carbon isotope composition in the arid zone of northwest China.Our main results are as follows:(1)The carbon,nitrogen and phosphor content of aquatic plants in the arid zone of northwest China was 396.82 mg.g-1,23.21mg.g-1,1.46 mg.g-1,with an variable coefficient of 13.14%,46.56%,and 63.93%,respectively.C:N,C:P and N:P were 22.80,355.54,and 19.99,with an variable coefficient of 100.8%,64.65%and 93.35%,respectively.And C:N:P was 266:16:1.(2)Correlation analysis showed that there were significant positive correlation between C and N,C and N,C and P,C and C:N,C and C:P,C and N:P,C and C:N:P,N and P,N and N:P,C:N and C:P,C:N and C:N:P,C:P and N:P,C:P and C:N:P,N:P and C:N:P;and significant negative correlation between N and C:N,N and C:P,N and N:P,N and C:N:P,P and C:N,P and C:P,P and N:P,P and C:N:P,C:N and N:P.(3)There were significant differents in foliar C,N and P content among difference life froms.The floating-leaved plants had the highest C%(422.63mg.g-1)and N%(31.50mg.g-1),,while the lowest occurs in submergent plants(for C:360.04mg.g-1 and for N:22.12mg.g-1).For P%,the highest occurred in floating-leaved plants(2.18mg.g-1)and the lowest occured in free-floating plants(1.28mg.g-1).(4)Correlation analysis indicated that there were no significant correlation between C%and altitude,longitude,latitude,annual mean temperature or average annual rainfall.But N%showed significant negative correlation with longitude and significant positive correlation with altitude;A significant positive correlation was observed between P%and altitude,latitude,and average annual rainfall,while its correlation with annual mean temperature are negative.Our research showed that the discrepancy in their ecological stoichiometry characteristics may be influenced by their life form;the temperature affects the geographical distribution pattern of the ecological stoichiometry characteristics of aquatic plants in an direct or indirect way(by affecting species distribution);the discrepancy between the ecological stoichiometry characteristics of aquatic and land plants may be a reflection of the adaptive strategy of aquatic plants to water environment.(5)The average C%and N%of the leaves of R.natans in 26 sites of northwestern arid zone were 36.55%and 3.23%.ANOVA analysis showed that there was significant difference between N%and C:N of each sites.The linear-regression analysis showed that the temperature of water body did not correlate significantly with the C%,N%of the leaves,C:N,altitude,longitude and latitude.The result showed that C:N,N of the leaves of R.natans may mainly be influenced by its growth,development,metabolism and life history strategy.The significant influence of the temperature of water body to the N%of the leaves of R.natans showed that habitat temperature impacts the physiology of R.natans through the N%of leaves,which is an verification of temperature-plant physiology hypothesis.(6)The ?13C content of the leaves of R.natans in 26 sites of northwestern arid area was-25.5‰,ANOVA indicated that ?13C content among R.natans of each sites vary greatly.Correlation analysis showed that ?13C content was not remarkably correlated with C%,N%of leaves and C:N,but showed significant positive correlation with altitude and significant negative correlation with annual mean temperature and average annual rainfall.The analysis showed that it may be the stoma number or the stomatal aperture on the leaf surface of R.natans other than the photosynthetic efficiency correlated nutrient elements change that leads to the discrepancy between the ?13C content of the leaves of R.natans in different sites.