Conversion from temperate secondary forests into plantations (Larix spp.): Impact on belowground carbon and nutrient pools in northeastern China

Conversions from natural broad-leaved forests into conifer plantations have been increasing over the past half century worldwide, especially in China. However, the impacts of plantation afforestation on macronutrient and micronutrient pools combined with litter, soil, and roots have not been well quantified. We compared macronutrient and micronutrient pools in litter, fine roots, and at 0- to 80-cm soil depths of paired secondary forests and larch plantations. The results showed that compared with natural forest soils, plantation soils exhibited lower concentrations and stocks of C, as well as lower fine root biomass at 0- to 10-cm depth. In contrast, the K, Fe, Mn, and Cu pools in the larch plantations were greater by 27-44% for the 20- to 40-cm depth. Furthermore, soil N, P, Ca, and Mg pools and stoichiometry of C/N/P in litter, soil, and fine roots did not differ significantly in the larch plantation relative to secondary forests. These results suggest that the conversion from secondary forests to larch plantations only decreases soil C pools but does not lead to reductions in other nutrient pools. Our results also showed that there were less C and nutrients in roots and more C and nutrients accumulated in litter of larch plantations compared with secondary forests. In conclusion, converting secondary forests to larch plantations changed the vertical distribution of C and nutrient pools in litter, soil, and root. The results suggest that C and nutrient pools in soils should be considered at levels below 40 cm in depth when evaluating C and nutrient change with afforestation.