Foliar δ13C and δ15N Response of Lodgepole Pine and Douglas-Fir Seedlings to Soil Compaction and Forest Floor Removal

Abstract

Abstract The effects of soil compaction, forest floor (FF) removal, and rehabilitation treatments on foliar δ13C and δ15N of lodgepole pine (Pinus contorta) and Douglas-fir (Pseudotsuga menziesii) were studied on a calcareous soil. Regardless of soil compaction, FF removal (which reduces soil water potential) resulted in less negative foliar δ13C values of lodgepole pine (from −25.9 to −23.4‰), whereas soil compaction effects on foliar δ13C were observed only within the FF intact treatment. This result and the more negative foliar δ13C with increasing seedling growth most likely reflected limitation on CO2 diffusion due to water stress caused by those treatments. However, foliar δ13C of Douglas-fir (range −25.0 ∼ −24.5‰) were not affected by the treatments, indicating less susceptibility to water stress. Soil compaction reduced NH4+-N concentrations in the FF (from 48.5 to 28.0) and NO3−-N concentrations in the FF (from 13.8 to 6.4) and mineral soil (from 4.3 to 2.1 mg kg−1), and FF removal tended to decrease NH4+-N concentrations in the mineral soil. Foliar δ15N of both species were not affected by soil compaction but were increased by the FF removal and rehabilitation treatments, indicating that the latter two treatments dramatically altered soil N dynamics. FOR. SCI. 51(6):546–555.