Effects of Lead and Water Stress on Soil Enzyme Activities from Two Plant Species

Through simulative methods, the influence on soil pH, the soil enzyme activities (urease, invertase and alkaline phosphatase) by the single and combined stress of water and lead were studied in a pot experiment. Five levels of Pb (0, 300, 500, 1000 and 2000 mg/kg soil) and four levels of water stress (soil relative water content (SRW), 100%, 80%, 60%, 40%) were applied. Sophora japonica and Platycladus orientalis were grown in soil-filled pots for pH and soil enzyme activities assays. The results showed that soil pH was affected by Pb and water deficiency. The addition of Pb and water stress caused soil alkalization in Platycladus orientalis, while acidification in Sophora japonica under water stress. Pb could stimulate the soil enzyme activities to some extent. The degree of influence on enzyme activities was related to plant species. Urease and invertase activities increased at 80% and 60% soil relative water content in P. orientalis and S. japonica. Interactions between Pb concentrations and water stress levels significantly impacted the three soil enzyme activities, synergism (ΔU<0) dominated the interaction in P. orientalis, while antagonism (ΔU>0) dominated the dominance for invertase and alkaline phosphatase in S. japonica.