Long-term egret (Egretta garzetta) habitation alters topsoil and subsoil phosphorus fractions and bacterial communities in coastal wetlands

The effects of egret habitation on soil ecological environment are poorly understood. In this study, we selected Metasequoia glyptostroboides and Ligustrum lucidum in the Hangzhou Bay wetland, where a large number of egrets nest annually in summer since 2008, to analyse the soil properties, P fractions, alkaline phosphatase (ALP) activity, and bacterial communities under egret habitation, and also to compare the seasonal dynamics of topsoil (0-10 cm) and subsoil (10-20 cm). We observed that decades of egret habitation caused soil acidification and increased soil nutrients, especially in May-August (summer). The total P (TP) accumulation was more rapid than that of soil organic C and total N. Calcium P (Ca-P) contributed the largest proportion to TP, accounting for approximately 61.46-91.15%. Egret habitation had the greatest effect on the relative proportion of iron-aluminium bound P ((Fe + Al)-P) in TP content, which increased from 1.21-2.34% (control) to 2.54-11.63% (egret habitation). Egret habitation decreased the alpha diversity index of bacterial communities but increased the soil ALP, indicating that egret effectively promoted the mineralisation of soil TP, while Olsen-P, organic P, (Fe + Al)-P, and Ca-P were strong predictors for dissimilarities of bacterial communities, suggesting that soil P is involved in soil bacterial community changes under egret habitation. The effect of egret habitation on soil gradually changed and weakened with an increase in soil depth. We conclude that egret habitation can alleviate P deficiency by increasing soil P supply capacity, but may accelerate P leaching and cause soil nutrient imbalance.

Automated summary

The effects of egret habitation on soil ecological environment were investigated in this study. The results showed that decades of egret habitation caused soil acidification and increased soil nutrients, especially in May-August. Egret habitation had a negative impact on the alpha diversity index of bacterial communities but increased the soil alkaline phosphatase activity. The study also found that soil phosphates were closely related to changes in soil bacterial communities. The effect of egret habitation on soil gradually weakened with an increase in soil depth.