Loblolly pine needle nutrient and soil enzyme activity as influenced by ozone and acid rain chemistry

Atmospheric air pollutants such as acid rain and O3 are present throughout the Southeastern U.S.A. and are known to suppress tree growth and crop productivity. Precipitation chemistry has shown changes in the ratio of N and S compounds in recent years. A greenhouse study was conducted using continuous stirred reactor chambers to determine the effects of simulated acid rain (SAR) chemistry, O3 and their interaction on loblolly pine seedling biomass, loblolly pine secondary needly nutrient content and soil enzyme activities. The seedlings were exposed to 0, 80, 160, 240 or 320 nl O3 l−1 at SAR pH 4.3 with two ratios of N-to-S (7N-to-3S and 3N-to-7S) for 11 wk. The secondary needle and root biomass were significantly suppressed by increasing O3 concentrations. A decreased content of P, Ca and Mg in secondary needles was also found with increasing O3 concentration. Neither SAR chemistry (N-to-S ratios) or the interaction of SAR chemistry and O3 had significant effects on loblolly pine seedling biomass. Acid phosphatase and arylsulfatase activities were dependent on SAR chemistry. The activity of soil acid phosphatase and arylsulfatase was inhibited by O3 when S application through simulated acid rain was higher (7-to-3, S-to-N). The inhibitory effects appeared at 160 nl O3 l−1 for acid phosphatase and 240 nl O3 l−1 for arylsulfatase. Dehydrogenase activity was not affected by either O3 or SAR chemistry.