Researchers from the Institute of Applied Ecology of the Chinese Academy of Sciences (CAS) have conducted an ecosystem-wide assessment of enhanced rock weathering (ERW) in forest plantations. Led by Dr. KANG Ronghua, they revealed how the application of finely ground silicate minerals influences soil carbon fluxes and tree growth in a larch plantation in northeastern China. 

Their findings were published in Forest Ecology and Management on Sept. 5.

ERW is a promising negative emission technology that removes atmospheric carbon dioxide (CO₂) by converting it into bicarbonate or carbonate minerals through chemical reactions between CO₂ and silicate rocks. While many previous studies have focused on inorganic carbon formation during this process, few have explored how ERW influences the overall carbon balance and biological processes at the forest ecosystem scale.

To investigate these effects, the researchers conducted a two-year field experiment in a Larix gmelinii (Dahurian larch) plantation located in the Changbai Mountain region of northeastern China. They applied wollastonite powder, a calcium silicate mineral, at three rates (0, 5, and 10 tons per hectare) and continuously monitored soil CO₂ fluxes, soil carbon composition, and tree growth indicators.

During the first year of the experiment, wollastonite application significantly reduced soil CO₂ emissions by about 16% compared to the control. The researchers attributed this reduction to the stabilization of soil organic carbon and the chemical conversion of CO₂ during silicate weathering. 

However, in the second year, soil CO₂ fluxes increased by approximately 5% in the treated plots relative to the control. The researchers hypothesized that this increase could be attributed to intensified root respiration, changes in soil pH, and more rapid decomposition of surface soil organic carbon, processes potentially induced by calcium ions released from wollastonite weathering. 

In addition to these soil effects, the researchers observed that trees in the treated plots displayed a non-significant increase in biomass. They speculated that, over extended periods, ERW might improve vegetation productivity, thus promoting greater carbon sequestration through enhanced plant growth.

These results demonstrate that assessing the carbon sequestration potential of ERW requires considering inorganic carbon formation, soil organic carbon dynamics and vegetation responses.

Responses of tree growth, litter production, and fine-root biomass to wollastonite application in the larch plantation (Image by SU Chenxia)