Examining CO₂ and N₂O pollution and reduction from forestry application of pure and mixture forest

Greenhouse gases (GHGs) carbon dioxide (CO₂) and nitrous oxide (N₂O), contribute significantly to global warming, and they have increased substantially over the years. Reforestation is considered as an important forestry application for carbon sequestration and GHGs emission reduction, however, it remains unknown whether reforestation may instead produce too much CO₂ and N₂O contibuting to GHGs pollution. This study was performed to characterize and examine the CO₂ and N₂O emissions and their controlling factors in different species and types of pure and mixture forest used for reforestation. Five soil layers from pure forest Platycladus orientalis (PO), Robinia pseudoacacia (RP), and their mixed forest P-R in the Taihang mountains of central China were sampled and incubated aerobically for 11 days. The P-R soil showed lower CO₂ and N₂O production potentials than those of the PO soils (P < 0.01). The average reduction rate of cumulative CO₂ and N₂O was 31.63% and 14.07%, respectively. If the mixed planting pattern is implemented for reforestation, the annual CO₂ reduction amounts of China's plantation can be achieved at 8.79 million tonnes. With the increase of soil depths, cumulative CO₂ production in PO and RP soils decreased, whereas CO₂ and N₂O production in P-R soil did not show similar pattern. Soil particle size fraction was the main factor influencing GHGs emissions, and the clay fraction showed negative correlation with cumulative CO₂ and N₂O production. In summary, compared with PO pure artificial forests, the mixture plantation mode can not only reduce GHGs pollution but also improve soil fertility, which is conducive to sustainable management of artificial forests.