Contrasting responses of soil inorganic carbon to afforestation in
acidic versus alkaline soils
Abstract
Afforestation has been suggested as an effective ecological engineering
approach for carbon sequestration and environmental benefits. However,
the impact of afforestation on soil inorganic carbon (SIC) is less clear
and sometimes controversial. Here, we conducted a field campaign, with
2346 soil profiles from 619 afforested plots and 163 control plots, to
investigate the relative and absolute changes of SIC between afforested
and corresponding control plots in northern China. We found positive
responses of SIC to afforestation in acidic soils, where afforestation
increased soil pH. In contrast, in alkaline soil, afforestation caused
soil acidification and thus negative SIC responses. Fitting a structure
equation model (SEM) confirmed that afforestation-induced soil pH change
(ΔpH) was the most significant factor regulated SIC responses to
afforestation. In particular, we observed stronger SIC sensitivity to pH
change in arid areas, where both soil pH and SIC stocks were high. Other
factors indirectly affected SIC responses to afforestation through
modulating soil pH and soil organic carbon (SOC) dynamics.
Afforestation-induced SIC changes also varied considerably among
different planted tree species and across different soil depths.
Specifically, in Pinus sylvestris var. mongholica,
Pinus tabuliformis and Populus spp. plantations, changes
of SIC were large enough to be comparable to that of SOC. Our finding
provides a data-based comprehensive understanding on the impact of
afforestation on SIC and its underlying mechanisms. With increased uses
of afforestation and reforestation as potential nature-based climate
solutions, decisions need to consider potential associated SIC changes,
especially in SIC-rich areas.