Global change can easily cause the wetland ecosystem structure and function to be damaged by alien species. Former studies on Spartina alterniiora invasion only focused on the effect of aboveground communities, ignoring the potential regeneration of soil seed banks. Therefore, the study aimed to find the key resources that limit the S. alterniiora invasion and the regulation mechanism for S. alterniiora regeneration. Through investigating the S. alterniiora communities with different invasion stages, we studied the structure and composition of the aboveground communities and the soil seed banks, in response to the soil properties and water and nitrogen addition. The dominant competitive advantage of S. alterniiora was mainly affected by the aboveground biomass, which was regulated by soil NH4+-N and moisture content. Although the richness was same in the soil seed banks under the S. alterniiora communities with different coverage, S. alterniiora seeds maintained its specific competitive dominance. The niche breadth of S. alterniiora and the niche overlap between S. alterniiora and Tripolium pannonicum was the highest under low aboveground coverage. The soil seed bank germination experiments showed that the S. alterniiora density decreased when the soil nitrogen concentration exceeded 1 g/ kg, while the density of native species E. crusgalli and T. pannonicum decreased when the water depth above the soil surface exceeded 2 cm. The successful naturalization of S. alterniiora invasion regulated by nitrogen-water coupling is a bet-hedging of the niche and fitness differences between invasive and native species in the coastal salt marsh of eastern China.

Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. (Pampas grass) is a perennial grass native to temperate and subtropical regions of South America. The species was introduced to western Europe for ornamental purposes during the nineteenth century, where it has become naturalized in anthropogenic and natural habitats, especially in sandy, open, and disturbed areas. Female plants of C. selloana produce thousands of seeds that are dispersed over long distances by wind and germinate readily. Its invasive success is also attributed to its ability to adapt and tolerate a wide range of environmental conditions, such as high salinity levels, long droughts, and soil chemical pollution. Cortaderia selloana usually invades human-disturbed habitats where it encounters little competition with other plants and high resource availability. However, the species can invade natural habitats, especially those with high light availability, causing biodiversity loss and changes in ecosystem functioning (e.g. alteration of succession and nutrient dynamics). The species may cause negative socio-economic impacts by reducing productivity of tree plantations, causing respiratory allergies, and decreasing the recreational value of invaded areas. Control costs are high due to the extensive root system that C. selloana develops and the high resprouting ability following physical damage. Although herbicides are effective control measures, their use is not allowed or is undesirable in all situations where the plant occurs (e.g. near riverbanks, natural protected sites). No biological control agents have been released on C. selloana to date, but the planthopper Sacchasydne subandina and the gall midge Spanolepis selloanae are promising targets.

Gully erosion damages land resources and endangers human productivity and life, making it a key issue in global research on soil erosion nowadays. Gully headcut retreat (GHR) is the main form of gully erosion. Tiny concave features can be found in many retreating gully heads worldwide, and they are referred to as niche terrain in this study. To investigate the association between niche terrain and GHR, relevant research was reviewed on niches and stability analysis of gully heads with niches was modelled and analysed. Studies have shown that not all niches worldwide are identical due to regional differences in internal material-external environmental conditions. Special soil properties, joints, and cracks are the internal material conditions that lead to the formation of niche. External conditions include climate conditions, vegetation conditions, and topography. Water is the driving force for the formation of niche, while vegetation and topography are key factors. Niches can be regarded as the initial stage of GHR in areas where gully erosion is intense. In general, GHR is a composite cyclical process dominated by hydraulic erosion in the early stage and gravitational erosion in the late stage, including niche formation, inward concave formation, free face formation, overhanging soil collapse, and niche reformation. In this study, a model of gully head stability is applied, and it is found that the stability-based factor of safety decreases exponentially with increasing niche height and crack depth, increases exponentially with increasing niche angle, and decreases quadratically with increasing catchment slope. Summarizing the common characteristics of niche terrains worldwide can facilitate the study of the evolution of gully erosion globally. Niches can be regarded as the initial stage of gully head retreat. The mechanism of niches varies with regional internal material-external environmental conditions. Gully head retreat is a composite cycle process dominated by early hydraulic erosion and later gravity erosion. image