Effect of Individual Trees on the Soil Respiration in Forest Ecosystems under Industrial Pollution

Abstract

The effect of individual trees on soil and litter respiration in forests polluted with heavy metals from copper smelter emissions was investigated for the first time. We tested the hypothesis that polluted sites exhibit a d-ecrease in the portion of spatial variance of soil respiration associated with the distance to the tree trunk compared to the background area. The study was conducted in the southern taiga spruce-fir and birch forests exposed to long-term pollution from the Middle Ural Copper Smelter in Revda City, Sverdlovsk region, Russia. Measurement points were placed near spruce and birch trees at different distances from the tree trunk (tree-base site, middle of the crown projection, and canopy gap), and total CO2 emission, litter respiration, litter contribution to soil respiration, litter-specific respiratory activity, and litter stock were measured at each point. In the background area, soil respiration decreased from the tree trunk to the canopy gap. The hypothesis was partially confirmed, as the variance portion associated with distance to tree trunks decreased in spruce forests with increasing pollution but did not change in birch forests. A change in spruce forests was due to a decline in litter-specific respiratory activity, while litter stock was considerably higher in the tree-base site than in the canopy gap. It is proposed to locate measurement points in the middle of the crown projection, at a sufficient distance from tree trunks and outside the canopy gaps, to minimize bias in soil respiration estimates.