INFLUENCE OF SOIL PHYSICAL AND CHEMICAL VARIABLES ON THE SPECIES COMPOSITION AND RICHNESS OF PLANTS IN THE ARID REGION OF TABUK, SAUDI ARABIA

摘要

The present study aims to investigate the effect of soil physical and chemical variables on the species richness and the floristic composition in four sites (Alwaz, Alqan, Sharma and Zetah) of Tabuk region in the Northwestern part of Arabian Peninsula. Only organic matter (OM), pH and calcium (Ca) showed significant differences (P < 0.05) amongst the four studied sites. Only magnesium and sodium were selected in the forward regression model and showed to be strong drivers of species richness of plants in Tabuk region (Adj-R~2 = 0.438, F2,13 = 6.85, P = 0.009). The multivariate analysis of canonical correspondence analysis (CCA ) was applied to reveal the effect of the physical and chemical variables on the species composition of the plants. The CCA classifies the plant species into three groups based on their preference to the environmental variables. The first group of plant species (Group 1) is characterised by positive preference to the chloride (Cl) and negative relationship with OM and pH. The second group (Group 2) is positively correlated with most of the soil variables such as OM, calcium (Ca), potassium (K), bicarbonate (HCO_3), electrical conductivity (EC), sulphate (SO_4) and sodium (Na). The third group (Group 3) has positive relationship with carbonate (CO_3) and negative relationship with EC and magnesium (Mg). The chloride, sodium, sulphate, EC and carbonate are the main environmental factors influencing the plant species composition in Tabuk region. The cluster analysis based on the Euclidian measure shows that Alqan and Zetah have closer species composition compared to Sharma.