Chongming Dongtan Wetland Ecosystem Health Evaluation And Comparative Study Of Phragmites Australis And Spartina Alterniflora Invasion Of Photosynthetic Physiology

Ecosystem health is a newly emerged field with great potential, and the basis for ecosystem service and the new aim and new method of ecosystem management. It is an integrative science in the process of defining itself. It is a "mandated science" focusing on real-world problems, which requires systematic methods for diagnosis, prognosis, and rehabilitation of ecosystems and a more integrated understanding of the relationship between human health and ecosystem health. The vigor, organization and resilience of ecosystems are the core contents of ecosystem health concept. Wetland is a particular ecosystem between land and sea. It is one of the most important environment capitals. Wetland is considered as the kidney of earth because of huge function on water and element cycle. Wetland, which has tremendous food chains and various biology, is taken for the supermarket of biology.This paper systematically summarizes the research contents and progress, assessment methods and trends of ecosystem health since it was put forward. The assessment methods of indicator species, ecosystem function indicator and nature indicators system are adopted to evaluate wetland ecosystem health. According to the assessment cell of section, the paper evaluates each index and compositive index. It can provide scientific bases for both protection and use of wetland by disclosing the spatial distributing rules and analyzing the impact on environment brought because of exploiting. This research is scientific management of significance for the Chongming Dongtan wetland ecosystems, and provides some methods to the wetland ecosystem health evaluation of China.As a consequence of rapid globalization, greatly increased emphasis is being placed on research into the ecology of invasive plants. Since Spartina alterniflora was introduced into Chongming Dongtan in 1995, it has gradually occupied a large area of the Phragmites australis zone, and has became a threat to the intertidal vegetation. In this study, the photosynthetic characteristics of an invasive plant, Spartina alterniflora, and an indigenous plant, Phragmites australis, were measured during the growing season of 2004 by a Li-6400 Portable Photosynthesis (LI-COR inc, USA.) at Chongming Dongtan Nature Reserve, Shanghai, between 31°25'~-31°38'N and 121°50'~122°05'E. The results showed that: (1) Compared with the local plant Phragmites australis, the invasive plant Spartina alterniflora had a significantly higher apparent quantum yield (AQY) carboxylation efficiency (CE) and maximum net photosynthetic rate (Pnmax); (2) In the early growing season, the curves of net photosynthetic rate (Pn), leaf stomatal conductance (Gs) and transpiration rate (Tr) of Spartina alterniflora during mid-day displayed a "single-peak" pattern, which was generally consistent with the changes in light intensity and temperature. In contrast, Phragmites australis showed a distinct "noon-break" phenomenon after reaching the peak, which was not consistent with the changes in light intensity and temperature; (3)The net photosynthetic rate {Pn), leaf stomatal conductance (Gs) and transpiration rate (Tr) of Spartina altemiflora were higher than those of Phragmites australis during the measurement period. In particular, Spartina altemiflora had a stronger photosynthetic capability above PAR 1600 /miol/(m2-s); (4) These two plants had their own distinctive photosynthetic characteristics at different stages of the growing season. The average Pn for these two plants reached the maximum value in September, while the average Gs and Tr were the highest in May. In general, the photosynthetic parameters of Spartina altemiflora measured in May and September were significantly higher than those of Phragmites australis, while Phragmites australis exceeded Spartina altemiflora later in the growing season (November). The results from this study have important ecological implications in terms of the fast growth rate, high productivity and a strong competitive ability of the invasive plant Spartina altemiflora, which could provide a sound basis for formulating effective control measures on this species.