Chacteristics And Correlation Of Vegetation And Soil At The Boundary Of Forest-Grass Landscape In Weibei Loess Plateau

Landscape boundary is an important component of landscape and often plays indispensable roles in regulating ecological flows. By field investigation and experimental work , the gradient distribution and variation of microclimatic element, vegetation composiyion,soil water,soil nutrients were analyzed,through which the correlations of plants to soil factors were described.The main results were summarized as following:Ⅰ.By cluster analysis, the 25 sites were divided into 3 types of landscape: forest, grassland and forest- grassland boundary. The influential range of boundary on speciesdiversity was about 20m,ranging from 14m in forest to 6m in grassland.The main communities in the three types of landscape were"Roegneria ciliaris(Trin.)Nevski.+ Festuca ovina L","Deschampsis caespitosa (L)Beauv.+ Festuca ovina L."and"Festuca ovina L.+Leymus secalinus(Georgi)Tzvel.".Ⅱ. Simpson Index,Shannon-Wiener Index,Margalef Index and Pielou Index for the three types of landscape appeared consistent in variations,with highest number for forest,followed by that of grassland and boundary respectively.III.Soil water at the horizontal dimension across the sample plot appears most in content in grassland,then in landscape boundary followed by forest. Across the soil profiles of grassland and forest, 0-210cm depth can be divided into four layers: rapid change layer, active layer, sub-active layer and relatively stable layer. Landscape boundary only has three layers observed: rapid layer, active layer and sub-active layer. Seasonal variations of soil water are significant and higher at early phase and last phase of growth. Three stages of soil water variation have been observed: relatively stable stage ( March—May), exhaustion stage ( June—July) and recovery stage (August—October).IV. Soil nutrients across the horizontal and vertical dimensions of sample plot were significantly different. On the horizontal dimension, highest OM goes to landscape boundary, followed by forest and grassland respectively. TN and AN contents were not significantly different between forest and boundary but significantly different compared to grassland. In the sub-surface layer, OM, TN and AN were not significantly distributed across the horizontal level of sample plot. TP, AP TK and AK of same soil layer with grassland, boundary and forest were not significantly different in contents but in the vertical direction for grassland, boundary and forest, OM, TN, AN, AP and AK in surface layer were all higher than those in sub-surface layer, significant difference indeed. Only with grassland and boundary, TP in surface layer was higher than that in sub-surface layer. PH value with surface layer was higher than that of sub-surface layer but significantly different among grassland. TK contents were not significantly different among layers.V. Temperatures were increasing along grassland-boundary-forest gradients, with temperature difference amounting to 1.59℃. A reverse variation happened to relative humidity, with a interior-exterior difference of 0.77%. Soil temperature tendency was following the order of grassland>boundary >forest.VI. Correlation analysis revealed that in grassland, the indices of phyto-biodiversity were correlated with AN and TN; in forest, indices of speciesdiversity were significantly correlated with soil water; and in forest-grassland boundary, indices of speciesdiversity were significantly correlated with soil water, AP, TP and TK.