Spatial Variation Characters And Environmental Response Of Soil Organic Carbon In Protective Forests Of Casuarina Equisetifolia L. And Pinus Elliotii E.

Casuarina equisetifolia L.and Pinus elliotii E.are 2 popular protection forest populations in southeast coasts.In the study,the diameter-class structure of Casuarina equisetifolia L.and Pinus elliotii E.were investigated by plots investigation,stand inventory,soil sampling.The stand characteristics of the 2 coastal protection forests were analyzed based on widely used theoretical growth equations including population life table,survival analysis and probability density function.The soil physical traits,nutrient contents and topsoil carbon flux of the two stands were determined by pH meter,carbon flux analyzer and element analyzer and geostatistics,principal component analysis and canonical correlation analysis were applied in the discussion of spatial distribution and variation characteristics in order to explore the correlation between different variables.The results showed that:1.The southeastern coastal Casuarina equisetifolia L.populations had 2 mortality peaks,which included very high mortality at the beginning of growth followed by constant mortality later,with the IV age class as dividing part of population survival curve.The survival curve trends to the type of Deevey-II.The fundamental fluctuation was not obvious in the natural regeneration of Casuarina equisetifolia L.populations but there was apparent bottleneck effect in the growth of seedlings.In the growth fitting of DBH and tree height of Pinus elliotii E.,Logistics equation was recommended with maximum relation value R?0.9618?and minimum surplus square sum?96.599?and Weibull was the second best.The fitting model of DBH and tree height of southeastern coastal Pinus elliotii E.populations could be applied to other protection forest types.2.The physical and chemical characteristics of soils reflect the soil leanness of coastal protection forests.The max moisture contents were in soil layer B,with 3.50%of Casuarina equisetifolia L.and 4.49%of Pinus elliotii E.The soil bulk density in vertical soil layers of the 2 stands was close while the soil general porosity density of Pinus elliotii E.was a little higher than that of Casuarina equisetifolia L.The soil pH values of the 2 stands were low,indicating the acidity traits.The minimum pH averages of the 2 stands both appeared in soil layer A,with 4.01 of Casuarina equisetifolia L.with insignificant vertical differences and 4.59 of Pinus elliotii E.with significant differences.Horizontal spatial analysis showed that the related layer models of the variables of the 2 stands were different in the fitting model types of physical trait variables in soil layers A,B and C,from which the exponential model was primary followed by linear sill model of Casuarina equisetifolia L.and the linear sill model was primary followed by Gauss model of Pinus elliotii E.There was insignificant overall correlation in soil pH values and significant overall correlation in general porosity.The pH values and moisture rates of soil layer B were obviously different with the other layers mainly because the root distribution and secretion of the 2 stands probably affected the water intakes,water contents and pH valuesSome index of soil nutrients were extremely low in coastal protection forests.The maximum averages of total N,total P,available N,available P and available K in the soil layers of Casuarina equisetifolia L.were 1.53g.kg^-1,13.72 g.kg^-1,39.66mg.kg^-1,0.34mg.kg^-1 and 63.81 g.kg^-1 and those of Pinus elliotii E.were 1.26g.kg^-1,19.41 g.kg^-1,36.67mg.kg^-1,0.30mg.kg^-1 and 132.06kg^-1 respectively.Although total K contents were comparatively high,with 64.42 g.kg^-1 of Casuarina equisetifolia L.and 69.64 g.kg^-1 of Pinus elliotii E,the available K still lacked in coastal protection forest soils due to the difficulty in absorption by plants.The topsoil C contents of the 2 stands were much higher than the other layers,with the averages of 120.12 g.kg^-1 and 111.72g.kg^-1 respectively.The organic C contents of the 2 stands were low with the averages less than 5g.kg^-1 from which the organic C contents of Pinus elliotii E.were lower than those of Casuarina equisetifolia L.There was significant difference between soil layers and stands and the structure of Pinus elliotii E.was better than that of Casuarina equisetifolia L.The averages of topsoil carbon flux were close,with 1.194umol.m-2.s^-1 and 1.191 umol.m-2.s^-1 respectively of the 2 stands.In horizontal spatial distribution,semi variance function,Moran's I exponential and Kriging values showed that the sampling scale was reasonable and there was insignificant spatial differences in soil pH values and physical traits of coastal protection forests.The optimum fitting equations of total elements?total N,P and K?and available elements?available N,P and K?presented no obvious regulations,from which there was insignificant difference of the stands in the former and difference in available N and P in the latter.Significant differences existed in organic C horizontal distribution of the stands and spatial self-correlation of topsoil in Pinus elliotii E.stand was more obvious than that of Casuarina equisetifolia L.The Kriging values of variables of various layers were mainly patch distributed,with several parts layer-distributed or uniform-distributed.3.There was no significant correlation between soil organic C,soil physical characteristics?bulk density,general porosity and moisture content rate?,soil chemical characteristics?pH values and nutrients?and soil C flux.However,principal component analysis showed that primary components?physical characteristics?and secondary components?chemical characteristics and C contents?existed in the 2 stands and canonical correlation analysis showed that there was certain correlation between the variables of soil layer A in Casuarina equisetifolia L.and soil layer A and C in Pinus elliotii E.Further researches will be conducted on the monthly,seasonal and yearly changes of variables.The soils of coastal protection forests are low in nutrients and organic C contents,which lead to the slow growth of protection forests and organic matter accumulation.Although there is no obvious correlation between organic C contents and a single factor,a certain correlation presents between the grouped variables in the comprehensive soil system and the grouped components are likely to vary with soil layers,stands and seasons.Multi-response Analysis showed that the low containment of SOC and other nutrients were a common phenomenon in the soil of coastal forests.In addition,with the deepening of soil,the deficiency became more serious.The structure of coastal protection forests is comparatively simple,so relevant researches can be conducted in the investigation scale.