Stable Carbon And Nitrogen Isotopes Of Casuarina Equisetifolia And Pinus Elliottii Plantation In Coastal Sandy Land

In the sandy land on the southeastern coast of our province,nitrogen and phosphorus nutrient deficiencies and seasonal drought are one of the key factors restricting the growth of forest trees,which seriously affects the nutrient cycling of tree species and their ecological benefits.Steady carbon and nitrogen isotopes have been widely used in biogeochemical research as an effective means.Carbon and nitrogen isotopes as natural tracers provide important tools for the study of ecological problems such as carbon and nitrogen cycle efficiency,nitrogen saturation,photosynthesis efficiency,and water use efficiency in the artificial forests of the coastal sandy land,such as Casuarina equisetifolia and Pinus elliottii.The Casuarina equisetifolia and Pinus elliottii artificial forests constructed in the spring of 2003 in the Changle Dahu State-owned Protective Forest Farm(N:25°96';E:119°68')were studied.Determination of Carbon and Nitrogen Contents and Nitrogen Stable Isotope Ratios(?15N)in the Surface Soils of Two Plantations and different leaf ages(new leaves and old leaves of the year)were determined.Statistical methods were used to study the correlations between stable carbon and nitrogen isotope ratios(?13C,?15N)and the seasonal dynamics of chlorophyll fluorescence parameters,water use efficiency,and soil carbon and nitrogen contents of the two plant species.The main findings are as follows:(1)The carbon and nitrogen contents of the surface soil of Casuarina equisetifolia were 4.415 g/kg and 0.457 g/kg,respectively.The soil carbon and nitrogen contents of Pinus elliottii were 2.462 g/kg and 0.372 g/kg,respectively.The carbon and nitrogen contents of Casuarina equisetifolia were higher than that of Pinus elliottii,and the carbon and nitrogen conversion ability of Casuarina equisetifolia was stronger than that of Pinus elliottii.(2)The stable nitrogen isotope ratio of the new leaves in the current year ranged from-3.98‰ to-4.82‰,which was larger than the range of stable isotope ratio in the old leaves of-4.29‰ to-5.32‰;the new leaf nitrogen of Casuarina was stable in the current year.The isotope ratio ranged from-2.239‰ to-3.573‰,which was larger than the range of stable isotope ratio of old leaves of Casuarina equiserii ranged from-3.99‰ to-4.946‰.(3)The data showed that the C,N content and stable carbon-nitrogen isotope ratio of surface soil of Casuarina equisetifolia were higher than that of Pinus elliottii;that is,Casuarina equisetifolia was better than S.glauca in the coastal sandy land.(4)The water use efficiency of Casuarina equisetifolia and Pinus elliottii leaves showed a positive correlation with the ?13C value.(5)The annual chlorophyll fluorescence of Casuarina equisetifolia changes a lot,and the maximum extent of changes in summer,but in terms of light energy conversion efficiency,the spring and winter seasons reach the peak,the fall is the lowest,and the potential energy activity in spring peaks.In terms of parameters Fm,summer>spring>winter>fall;in terms of parameter Fo,summer>fall>winter>spring;in Fv,summer>spring>winter>autumn.In terms of parameters Fm,summer pine>spring>autumn>winter;in parameters Fo,summer>autumn>winter>spring;in terms of Fv,summer>winter>spring>autumn.