Dynamic characteristics of metal element content and return of Casuarina equisetifolia litter at different distances to the coastline

Aims Accurate estimation of the variation of nutrient cycling along environmental gradients within an ecosystem is important for assessing their ecological functions. The aim of this study is to explore the effects of different habitats on the metal element content and nutrient return dynamics of Casuarina equisetifolia.
Methods Taking the litter of C. equisetifolia in Chihu State-owned Protective Forest Farm of Huian, Fujian Province as the research object. Five distances named T₁, T₂, T₃, T₄ and T₅ respectively, were selected in order of near to far from the coastline, and the litter was collected to determine the metal element content.
Important findings We found that: 1) Different coastal distances had significant effects on the content and return of each element of C. equisetifolia litter. The element content and return from the forest edge zone to interior forest were linear. In order of near to far from the coastline, sodium (Na) content gradually decreases. Iron (Fe), copper (Cu), zinc (Zn) and manganese (Mn) increased since T₄, and their changing trend and amount of the return and content along the gradient were similar. 2) There were significant differences on the content of litter elements among different months. Litter Na, Fe, Cu, and Zn had similarities, and had lowest value in June and November. Litter Mn fluctuated after falling from February to April. The return amount was generally similar between litter Na and Cu, with peaks in May, August, and next January; Litter Mn, Fe, and Zn showed similar return amount, with peaks in May, August, and next January. 3) Na content in soils at different distances from the coastline decreased gradually, while other elements fluctuated and did not show significant difference along the gradient. 4) Litter Na and Fe were significantly positively correlated, and litter Na and Zn, Fe and Cu, and Fe and Zn were extremely significantly positively correlated, respectively. There was a positive correlation for the same element between soil and litter and the correlation was significant for Na and Cu. The difference in litter element was greatly affected by the difference in resorption rate during litter falling at different timing along the distance gradient. The temporal difference among different months was due to the requirements from plant life activity. The difference in the return of the element was related to the amount of litterfall and the content of elements in the litter.