Invasive Spartina strengthens soil resilience in wetlands of the east-central China coast

Introducing nonnative species as a restoration strategy has been widely implemented to rehabilitate coastal ecosystems. Nonnative species becomes an important factor influencing soil physicochemical patterns. Although these effects have been explored individually, the comprehensive examination of soil physicochemical attributes that indicate possible processes of coastal soil resilience or degradation induced by nonnative species has been less emphasized. To expand such understanding, we used a space-for-time substitution methodology to capture characteristics of soil physicochemical attributes and plant productivity in space and time, and further, we used a structural equation model (SEM) to evaluate a set of hypotheses about positive effects of plant invasion (Spartina alterniflora) on soil resilience in terms of soil degradation processes (fertility, salinization, acidification, alkalization, structure, and erosion) in the east-central China coast. SEM analyses revealed 3 aspects of soil degradation that appear to be improved by the exotic S.alterniflora: (a) fertility, (b) desalinization, and (c) erosion resistance. SEM also presented that soil alkalization had occurred with the invasion, indicating the possible decreased capacity of soil against degradation. Although soil became more alkaline, these findings highlight that in the absence of native species, the nonnative species has an overall positive effect on soil resilience against degradation. The connections between nonnative species and soil degradation observed in SEM verified the hypothesized causal relationship, suggesting the significant role nonnative species plays in maintaining soil resilience in regions without native species.