Abstract
The exotic species Spartina anglica, introduced from Europe in 1963, has been experiencing a decline in the past decade in coastal China, but the reasons for the decline are still not clear. It is hypothesized that competition with the native species Scirpus triqueter may have played an important role in the decline due to niche overlap in the field. We measured biomass, leaf number and area, asexual reproduction and relative neighborhood effect (RNE) of the two species in both monoculture and mixture under three nitrogen levels (control, low and high). S. anglica showed significantly lower biomass accumulation, leaf number and asexual reproduction in mixture than in monoculture. The inter- and intra-specific RNE of S. anglica were all positive, and the inter-specific RNE was significantly higher than the intra-specific RNE in the control. For S. triqueter, inter- and intra-specific RNE were negative at the high nitrogen level but positive in the control and at the low nitrogen level. This indicates that S. triqueter exerted an asymmetric competitive advantage over S. anglica in the control and low nitrogen conditions; however, S. anglica facilitated growth of S. triqueter in high nitrogen conditions. Nitrogen level changed the interactions between the two species because S. triqueter better tolerated low nitrogen. Since S. anglica is increasingly confined to upper, more nitrogen-limited marsh areas in coastal China, increased competition from S. triqueter may help explain its decline.
Highlights
Salt marsh communities are often characterized by elevational gradients [1,2]
Nitrogen addition was found to change the relative abundance of Spartina foliosa and Salicornia bigelovii in a California salt marsh [17]
Biomass Total biomass, shoot mass and root mass of S. anglica in SA2 were significantly higher in the low nitrogen treatment than in the high nitrogen treatment (Fig. 1A–C; Table 1A)
Summary
Salt marsh communities are often characterized by elevational gradients [1,2]. Such patterns often result from trade-offs between plant competitive ability and tolerance of stresses such as flooding, salinity and low nitrogen [3,4,5,6]. Interactions between plants can strongly affect community structure and can be changed by environmental factors [7,8,9,10,11,12,13,14]. Especially nitrogen, are an important factor that may affect plant interactions and succession of salt marsh communities [10,12,15,16]. The ericoid species Calluna vulgaris and Vaccinium oxycoccus were stronger competitors than the graminoid species Eriophorum vaginatum and Rhynchospora alba at high nutrient levels in peat bogs, but not at low nutrient conditions [18]
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