Data from: Afforestation mitigates soil nitrogen limitation by enhancing mineralization and lowering denitrification in central China

Afforestation has profoundly altered soil nitrogen (N) transformation,
particularly the key processes governing soil organic N and inorganic N
dynamics, which determine soil N availability. However, the divergences in
soil N transformation and the main influencing factors following different
afforestation types have not been systematically clarified. Here, we
examined soil net N mineralization rate (NMR), net nitrification rate
(NNR), and potential denitrification rate (PDR) at 144 paired sampling
sites by comparing different afforestation types (initial land use types
and tree species) in central China. Afforestation significantly enhanced
soil NMR, but lowered NNR and PDR, respectively, compared to
non-afforested lands. Soil NMR and PDR responses to afforestation from
cropland were more sensitive than those from shrubland. Notably, broadleaf
afforestation (i.e., Quercus variabilis) had a stronger effect on altering
NMR compared to coniferous afforestation (i.e., Platycladus orientalis)
from cropland. These variations in soil NMR and NNR responses were
primarily attributed to soil properties [e.g., soil organic nitrogen
(SON), soil organic carbon (SOC), C: N ratio] across both non-afforested
and afforested lands, whereas the main influencing factor for PDR shifted
from microbial traits in non-afforested lands to soil properties in
afforested lands. Although higher SON contents promoted soil NMR in
afforested lands, significantly higher microbial biomass N in the
afforested lands compared to non-afforested lands suggested intensified
microbial inorganic N assimilation, which consequently constrained NNR and
PDR relative to non-afforested lands, further avoiding N loss and N
limitation. Our findings emphasized that afforestation types divergently
influenced soil net N transformation rates with overall impacts on
alleviating possible soil N constraints, thereby providing a theoretical
basis for the regulation of soil N cycling under future afforestation and
forest management.