Impacts of Soil Properties on Species Diversity and Structure in Alternanthera philoxeroides-Invaded and Native Plant Communities

Abstract

Soil properties can affect plant population dynamics and the coexistence of native and invasive plants, thus potentially affecting community structure and invasion trends. However, the different impacts of soil physicochemical properties on species diversity and structure in native and invaded plant communities remain unclear. In this study, we established a total of 30 Alternanthera philoxeroides-invaded plots and 30 control plots in an area at the geographical boundary between North and South China. We compared the differences in species composition between the invaded and native plant communities, and we then used the methods of regression analysis, redundancy analysis (RDA), and canonical correspondence analysis (CCA) to examine the impacts of soil physicochemical properties on four α-diversity indices and the species distribution of these two types of communities. We found that A. philoxeroides invasion increased the difference between the importance values of dominant plant species, and the invasion coverage had a negative relationship with the soil-available potassium (R² = 0.135; p = 0.046) and Patrick richness index (R² = 0.322; p < 0.001). In the native communities, the species diversity was determined with soil chemical properties, the Patrick richness index, the Simpson dominance index, and the Shannon-Wiener diversity index, which all decreased with the increase in soil pH value, available potassium, organic matter, and ammonium nitrogen. However, in the invaded communities, the species diversity was determined by soil physical properties; the Pielou evenness index increased with increasing non-capillary porosity but decreased with increasing capillary porosity. The determinants of species distribution in the native communities were soil porosity and nitrate nitrogen, while the determinants in the invaded communities were soil bulk density and available potassium. In addition, compared with the native communities, the clustering degree of species distribution in the invaded communities intensified. Our study indicates that species diversity and distribution have significant heterogeneous responses to soil physicochemical properties between A. philoxeroides-invaded and native plant communities. Thus, we need to intensify the monitoring of soil properties in invaded habitats and conduct biotic replacement strategies based on the heterogeneous responses of native and invaded communities to effectively prevent the biotic homogenization that is caused by plant invasions under environmental changes.

Keywords: Alternanthera philoxeroides; biological invasions; diversity index; habitat heterogeneity; plant community; species coexistence.

Figure 1

Terrestrial A. philoxeroides-invaded plant communities (A) and the studied species, A. philoxeroides (B), in Xinyang City, China (picture: Hao Wu).

Figure 2

Regression analysis between A. philoxeroides invasion coverage and soil factors (A) and species diversity index (B).

Figure 3

RDA ordination diagram of soil factors and species diversity index in control (A) and A. philoxeroides-invaded plant communities (B). Patrick, Simpson, Shannon, and Pielou represent the Patrick richness index, Simpson dominance index, Shannon–Wiener diversity index, and Pielou evenness index. Solid red vectors represent the 12 soil factors; hollow vectors represent 4 α-species diversity indices. Arrows indicate the direction of increase in variables from the RDA ordination center. The angle between each pair of variables represents their correlations; the smaller the angle, the greater the correlation.

Figure 4

Regression analysis between soil factors and species diversity index in control (A–E) and A. philoxeroides-invaded plant communities (F,G).

Figure 5

CCA ordination diagrams of dominant plant species in control (A) and A. philoxeroides-invaded plant communities (B) along soil property gradient. Red vectors represent the 12 soil factors. Solid dots represent the dominant plant species, and the locations represent their optimal distribution positions under multiple soil factor combinations. Arabic numbers are codes of dominant plant species, and their Latin names are shown in Table 1. Vertical distance between dots and vectors represents the influence degree of a certain soil factor on a certain species distribution; the shorter the vertical distance, the greater the influence degree.

Figure 6

Sampling plots of terrestrial A. philoxeroides-invaded plant communities along the geographical boundary between North and South China. Plot size: 5 × 5 m; transect size: 5 m; quadrat size: 0.5 × 0.5 m.