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

Abstract

Atmospheric air pollutants such as acid rain and O 3 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, O 3 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 O 3 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 O 3 concentrations. A decreased content of P, Ca and Mg in secondary needles was also found with increasing O 3 concentration. Neither SAR chemistry (N-to-S ratios) or the interaction of SAR chemistry and O 3 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 O 3 when S application through simulated acid rain was higher (7-to-3, S-to-N). The inhibitory effects appeared at 160 nl O 3 l −1 for acid phosphatase and 240 nl O 3 l −1 for arylsulfatase. Dehydrogenase activity was not affected by either O 3 or SAR chemistry.