Effects of exposure and vegetation type on organic matter stock in the soils of subalpine meadows in the Eastern Carpathians

Abstract

Slope exposure is a rarely considered factor in studies on organic matter sequestration in soil. This process depends on climate conditions and other factors. Our hypothesis assumes that soils with a northern exposure in the northern hemisphere should have a larger organic matter stock than soils with the opposite exposure as a side effect of weaker insolation. Moreover, the stock of organic matter should vary with vegetation type. The main objectives of the presented study were to examine the variation of soil organic carbon (SOC) stock and nitrogen (N) stock in soils on slopes with opposite exposure (NNE and SSW) under different vegetation types (tall-grass communities vs. Vaccinium thickets). The study area was found in the Połonina Caryńska subalpine meadow area situated in the Western Bieszczady Mountains in southeastern Poland. The mean values of SOC and N stock were significantly (p≤0.003) higher for soils with an SSW exposure (74.8 and 6.5Mgha−1, respectively) in comparison with an NNE exposure (61.3 and 5.2Mgha−1, respectively). Thus, the lower decomposition rate of organic matter in soils due to lower insolation on north-facing slopes did not result in higher organic matter stock in the soil. This is likely due to two factors: (1) high humidity together with severe and long winters throughout the studied area and (2) higher insolation on south-facing slopes. The higher mean values of both SOC and N stock were deemed significant (p≤0.007) when determined under tall-grass vegetation (69.9 and 6.1Mgha−1, respectively) versus Vaccinium thickets (66.2 and 5.2Mgha−1, respectively), regardless of exposure. Higher SOC stock and N stock in soils under tall-grasses can be explained by the higher organic matter input that these communities supply to soils every year in comparison with Vaccinium. C/N ratios calculated for the analyzed soils did not reflect any differences with respect to slope exposure or vegetation type (p<0.5).