Acidic deposition effects on above- and belowground wood biomass and nutrient status in a young hardwood forest.

摘要

The impact of acid deposition on forest productivity has been studied extensively during the past 30 years. Mixed results abound due to variations in forest age, species composition, land use history, climate, and different experimental procedures. However, most results suggest alterations in productivity and nutrient status as a result of elevated acid deposition. The Long-Term Soil Productivity (LTSP) site in the Fernow Experimental Forest served as the study site; it was initiated with the purpose of observing the impact of forest management and air quality on biomass production and nutrient cycling (Adams et al. 2004). In its entirety, this experiment specifically examines the effect of acidification on above- and belowground wood productivity as well as the nutrient relations within those pools. Three treatments were replicated in four blocks, in which all naturally regenerated after whole-tree harvesting in 1996. The treatments included a control (WT), ammonium sulfate additions at two times the annual ambient rate (WT+NS), and ammonium sulfate additions (two times ambient) plus dolomitic lime additions that was added at two times the rate of calcium and magnesium export to local stream waters (WT+NS+CA). The liming treatment was implemented to test ameliorative effects on acidified soil conditions. The first study estimated forest productivity, expressed as total aboveground wood biomass and included stem and branch weight of standing live trees, among the three treatments ten years after stand regeneration and treatment initiation. Total aboveground wood biomass was compared among three treatments. Additionally, future stand productivity was estimated for a subsequent 70 years using growth projection simulator SILVAH. Total aboveground wood biomass at ten years was not significantly different among treatments (ANOVA: F = 1.20, p = 0.33, n = 9). Projected aboveground wood biomass estimated the WT+NS+CA treatment may increase 34 percent by forest age 80. The second study involved macro- and micronutrient analysis of stem wood tissue from each treatment in five of the most abundant species. These species included yellow-poplar, red maple, sweet birch, black cherry, and pin cherry; northern red oak was also examined. Results suggest altered (though not significantly so) wood concentrations of K, Ca, and Zn in the WT treatment compared to the WT+NS and WT+NS+CA treatments. The data also indicated possible signs of nutrient stress in the WT+NS treatment due to lower wood Ca:Mn and higher N:P nutrient ratios compared to the WT and WT+NS+CA treatment. The third study was carried out to understand the effects of simulated acidic deposition and additions of dolomitic lime on belowground fine root (≤ 2mm) biomass and nutrient levels. Differences in fine root biomass and nutrient content were observed in these plots due to significant block*treatment interactions (ANOVA: F=5.27, p0.05, n=9). Compared to the WT+NS treatment in block III, fine root nitrogen and phosphorus content was significantly lower in the WT and WT+NS treatments in block II and the WT and WT+NS+CA treatments in block IV.