Influence of tree species on carbon, nitrogen, and phosphorus stocks and stoichiometry under different soil regeneration scenarios on reclaimed and afforested mine and post-fire forest sites

Abstract

In this work, we present the effects of Scots pine (Pinus sylvestris L.), common birch (Betula pendula Roth), and black alder (Alnus glutinosa Gaertn.) on the carbon (Cstock), nitrogen (Nstock), and phosphorus (Pstock) stocks and stoichiometry in the uppermost soil horizons (Oi + Oe, 0–5 cm) on afforested post-mining sand-pit and post-fire forest sites. These results were compared to those for undisturbed forest sites under the same tree species. The Cstock and Nstock of the post-fire soils were similar to those of the undisturbed soils, but lower for the reclaimed mine site. Notably, tree species affected the distribution of Cstock between the organic and mineral horizons. Compared to the other tree species, pine was characterized by a higher Cstock in the Oi + Oe horizons of the post-mining and undisturbed soils. In the 0–5-cm soil horizons, the highest Cstock values were detected under alder at the post-mining site and under birch and alder at the undisturbed site. For all of the studied sites, the C:N ratios in the litter horizons occurred in the following order: alder < birch < pine. This trend was only reflected in the mineral horizons of the undisturbed sites, which indicates the very temporary impact of organic matter on the disturbed sites. The C:P and N:P ratios in the mineral soil horizons were higher for the post-fire site than the post-mining and undisturbed sites, which may indicate a P limitation for the given content of C and N. Black alder, as a N-fixer, can increase the C:P and N:P ratios in nutrient-poor, sandy soils after disturbance in comparison with the other studied tree species, especially in post-fire soils. The uppermost mineral soil horizons under alder were characterized by higher C:P and N:P ratios than the soils under pine on the post-mining site and under the other tree species on the post-fire site. The N:P ratios in the litter horizons under alder on the disturbed sites were higher than for the other tree species, while this was not true for the undisturbed soils where alder grew under nutrient-optimal conditions. This suggests that the phytomelioration influence of N-fixers on degraded and nutrient-poor soils, may be inhibited by P limitation.