GRAY CORRELATION ANALYSIS ON NUTRIENT ELEMENTS BETWEEN PHRAGMITES AUSTRALIS PLANT AND SOIL IN THE UPPER SHOAL OF JIUDUANSHA WETLAND,THE YANGTZE RIVER ESTUARY

Gray correlation analysis method was applied to analyze the relation of nutrient elements between Phragmites australis and soil at the Phragmites australis wetland in the upper shoal of Jiuduansha wetland,the Yangtze river estuary in order to understand the relations between the absorbing content of the nutrient elements in plant growth progress and the content of nutrient elements of soil in the wetland ecosystem in different periods of the growing season.The results indicated that the absorption of nutrient elements by Phragmites australis showed time-spatial distribution characteristics in the process of plant growth.Phragmites australis mainly absorbed N in the depth of 0～15cm,P and K in the depth of 15～40 cm in soil profile,while it absorbed less in depth of 40～60cm in the soil profile.Association degree of nu-trient elements between plant and soil was in the order of N KP in April;P K N in May,KP N in June to August;NKP in September to November;PNK in December respectively.The association degree of same nutrient element between the plant and soil also was not same in the different growth period of the plant.The closest relationship of the nutrient elements N,P,K between plant and soil occurred in September,December and June separately,and the closest relationship of the nutrient element between the plant and soil appeared in the upper layer of soil.The active period for migration,trans-formation and cycling of nutrient elements K,N,P occurred in June,September and December respectively,and the upper layer of soil was an important place for nutrient element activity.There was obvious difference in time and space for the growth of Phragmites australis to use nutrient elements K,N,P in the soil,and there was also difference for Phragmites australis to absorb nutrient elements K,N,P in different depth of soil in different growing periods of the plant.The orders of association degree of nutrient elements between different modular of underground part of Phragmites australis and soil were same,but those of association degree of nutrient elements between different modular of aboveground part of Phrag-mites australis and soil were different.