The exotic species may have played an important role in the decline due to niche overlap in the field. and can also be changed by environmental factors [7]C[14]. Nutrients, especially nitrogen, ARRY-438162 are an important factor that may affect plant interactions and succession of salt marsh communities [10], [12], [15], [16]. Nitrogen addition was found to change the relative abundance of and in a California salt marsh [17]. The interactions between and were facilitative in low nutrient conditions, but not in high nutrient conditions [4]. The ericoid species and were stronger competitors than the graminoid species and at high nutrient levels in peat bogs, but not at low nutrient conditions [18]. is a perennial salt marsh grass native in England [19], [20]. Invasions of in other countries or regions have caused great changes in local communities [21], [22]. was first introduced in coastal China in 1963 [23], [24], and grew to cover 36,000 ha by 1985 [25], [26]. In the past decade, however, large-scale decline of the species has been occurring in coastal China, and ARRY-438162 the cover has decreased to less than 50 ha [26], [27]. Due to the wide spread of in coastal China [23], the ecological range of is restricted to higher elevations where the native, rhizomatous species is abundant. Therefore, and currently possess overlapping ecological niches in the intertidal zone in China, and may compete strongly for space, nutrients and light. In this study, we aim to test the hypothesis that competition between and is one possible explanation for the on-going decline of in coastal China. Because interactions between species, especially between exotic and native species, often depend on environmental conditions [6], [28], and because nitrogen is one of the most important environment factors that limit the growth of salt marsh plants [17], [29], we also test whether nitrogen addition affects the interactions between and and whether the results can help explain the decline of in coastal China. Materials and Methods The species C. E Hubbard (cordgrass) is a rhizomatous perennial grass that spreads mainly by clonal growth [30]. The flowers occur in numerous, erect, dense panicles that consist of closely overlapping spikelets in two rows on one side of ARRY-438162 the rachis [31]. In Europe the flowers produce viable seeds through both self- and cross-pollination that is mainly by wind. However, seed production has changed significantly over years, especially in China [25]. Viable seed production has diminished [26] due to poor pollen quality and abnormal pollen tubes [32]. GREM1 The height of the plant has decreased from 100 cm to not more than 30 cm in coastal China. Linn. is trigonous stems and about 100 cm tall, with leafless sheaths below. The uppermost sheaths usually have a short lamina, and the glumes are between 3.4 and 4 mm. is characterized by two stigmas and nuts between 2.5 and 3 mm [33]. It occurs in different habitats in tidal wetlands that range from brackish to fresh water along the coast. Plant materials In April 2007, plants of and were collected from the same area of the marsh zone (12015E and 3342N) at Xinyang Harbor in Yancheng Nature Reserve in Jiangsu Province, China. The plants were carefully collected from the marsh and transplanted into big trays (length 75 cm, width 52 cm and height 41 cm) filled with a 30-cm-deep 11 (vv) mixture of sand and clay under greenhouse conditions. For each species, individual plants consisting of a single tiller with attached roots were separated from the plants in the trays. Uniformly sized ramets with a height of 12.60.5 cm (for (coded as SA2), (ii) only 2 individuals of (ST2), (iii) 4 individuals of (SA4), (iv) 4 individuals of (ST4), and (v) 2 individuals of and 2 individuals of (SA2+ST2). When the pot was planted with two individuals (treatments of SA2 and ST2), the two individuals were spaced 7.3 cm apart along a diameter of the pot. When the pot was planted with four individuals (treatments SA4, ST4 and SA2+ST2); two individuals were located along one diameter with 7.3 cm apart, and the other two were planted along its perpendicular diameter also with 7.3 cm apart. For SA2+ST2, the two individuals of the same species were planted along the same diameter. There were three nitrogen treatments, i.e., control (no added N), low nitrogen, and high nitrogen, imposed by hand-broadcasting a total.