An approach to the use of plants for monitoring soil conditions in wetlands in arid areas

The soil environment is a key factor affecting the distribution of plant communities. The soil environments of many arid wetland areas are deteriorating. The present study investigated plant-soil relationships in an arid wetland region (along the middle reaches of Heihe River, Northwest China). The main objective was to establish an approach to use plants as bioindicators of soil conditions. With such an approach, environmental changes inferred from plant observations can be monitored, facilitating the prevention of negative environmental impacts and the improvement of environmental management. Collection of vegetation data and soil sampling was conducted at a total of 87 plots from 27 stations in the study area from July to August 2017. The vegetation data included plant community type and the abundance, height, and coverage of each species. The soil characteristics included salinity (SA), pH, water content (WC), bulk density (BD), soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP) and available potassium (AK). A total of 13 main plant community types were identified by detrended correspondence analysis. The soil physicochemical properties varied among the different plant communities. Multivariate analysis showed that the vegetation variables were closely related to SA, pH and WC. The quantitative plant-soil relationships was also established to aid the management of the wetlands. Based on the established relationships, an expansion of Calamagrostis spp. would suggest a decrease in soil SA, a replacement of Inula japonica with Equisetum ramosissimum would indicate an increase in soil pH, and an expansion of Tamarix spp. would suggest increases in soil SA and pH. Our results support the use of plants as soil bioindicators of disturbance and the approach of quantitative plant-soil relationship to improve the environmental management of wetland ecosystems in arid areas.