Responses of plant diversity and soil microorganism diversity to water and nitrogen additions in the Qinghai-Tibetan Plateau

Abstract

The Qinghai-Tibetan Plateau is experiencing significant nitrogen (N) deposition and increased precipitation. Although changes in N deposition and precipitation may cause changes in the composition and diversity of plants, the relationships between plant diversity and soil microbial diversity still has not been fully researched. Thus, we conducted a field simulation experiment in an alpine meadow that included three N and two water (W) addition levels, as well as their interactions. The abbreviations of all treatments are shown below: CK, control; W, added water; N5, added 5 g N m−2 yr−1; N10, added 10 g N m−2 yr−1; N5W, added N5 and W; N10W, added N10 and W. The dominant plant species belong to the Gramineae family and include Elymus dahuricus, Stipa capillata, Poa pratensis and Agropyron cristatum. One year later after N and water addition, the results indicated that soil pH decreased with N addition, and with a combination of N and W addition together. High rate of N addition significantly lowered plant diversity. For different plant functional groups, the relative abundance of grasses significantly increased, while the relative abundance of forbs significantly decreased under N10, N5W and N10W treatments. Under N10W treatment, the relative abundance of legumes was significantly reduced, while the relative abundance of cyperaceae was significantly increased. W and N interactions significantly decreased soil bacterial and fungal diversity. N addition showed an indirect effect on the fungal diversity by directly affecting plant productivity. Water addition showed an indirect effect on bacterial diversity by directly affecting plant diversity. Soil bacterial diversity showed a positive correlation with plant diversity, while soil fungal diversity had no significant correlation with plant diversity, but had a negative correlation with plant productivity. It also indicates that the strength of feedbacks between aboveground and belowground biodiversity will vary depending on which groups of soil biota are considered.