Contrasting impacts of fertilization on topsoil and subsoil greenhouse gas fluxes in a thinned Chinese fir plantation

Qingyan Qiu; Chi Ding; Abubakari Said Mgelwa; Jiguang Feng; Mei Lei; Ziying Gan; Biao Zhu; Ya-Lin Hu

doi:10.1016/j.jenvman.2024.121055

Contrasting impacts of fertilization on topsoil and subsoil greenhouse gas fluxes in a thinned Chinese fir plantation

J Environ Manage. 2024 May 2:359:121055. doi: 10.1016/j.jenvman.2024.121055. Online ahead of print.

Authors

Qingyan Qiu¹, Chi Ding², Abubakari Said Mgelwa³, Jiguang Feng⁴, Mei Lei², Ziying Gan², Biao Zhu⁵, Ya-Lin Hu⁶

Affiliations

¹ College of Juncao Science and Ecology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China; College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
² College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, 350002, China.
³ College of Natural Resources Management & Tourism, Mwalimu Julius K. Nyerere University of Agriculture & Technology, P.O. Box 976, Musoma, Tanzania; CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China.
⁴ Institute of Ecology, College of Urban and Environmental Sciences, And Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China.
⁵ Institute of Ecology, College of Urban and Environmental Sciences, And Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China. Electronic address: biaozhu@pku.edu.cn.
⁶ College of Juncao Science and Ecology, Fujian Agriculture and Forestry University, Fuzhou, 350002, China; College of Forestry, Fujian Agriculture and Forestry University, Fuzhou, 350002, China. Electronic address: huyl@iae.ac.cn.

PMID: 38701585
DOI: 10.1016/j.jenvman.2024.121055

Abstract

Globally, forest soils are considered as important sources and sinks of greenhouse gases (GHGs). However, most studies on forest soil GHG fluxes are confined to the topsoils (above 20 cm soil depths), with only very limited information being available regarding these fluxes in the subsoils (below 20 cm soil depths), especially in managed forests. This limits deeper understanding of the relative contributions of different soil depths to GHG fluxes and global warming potential (GWP). Here, we used a concentration gradient-based method to comprehensively investigate the effects of thinning intensity (15% vs. 35%) and nutrient addition (no fertilizer vs. NPK fertilizers) on soil GHG fluxes from the 0-40 cm soil layers at 10 cm depth intervals in a Chinese fir (Cunninghamia lanceolata) plantation. Results showed that forest soils were the sources of CO₂ and N₂O, but the sinks of CH₄. Soil GHG fluxes decreased with increasing soil depth, with the 0-20 cm soil layers identified as the dominant producers of CO₂ and N₂O and consumers of CH₄. Thinning intensity did not significantly affect soil GHG fluxes. However, fertilization significantly increased CO₂ and N₂O emissions and CH₄ uptake at 0-20 cm soil layers, but decreased them at 20-40 cm soil layers. This is because fertilization alleviated microbial N limitation and decreased water filled pore space (WFPS) in topsoils, while it increased WFPS in subsoils, ultimately suggesting that soil WFPS and N availability (especially NH₄⁺-N) were the predominant regulators of GHG fluxes along soil profiles. Generally, there were positive interactive effects of thinning and fertilization on soil GHG fluxes. Moreover, the 35% thinning intensity without fertilization had the lowest GWP among all treatments. Overall, our results suggest that fertilization may not only cause depth-dependent effects on GHG fluxes within soil profiles, but also impede efforts to mitigate climate change by promoting GHG emissions in managed forest plantations.

Keywords: Chinese fir plantation; Fertilization; Greenhouse gases; Soil depths; Thinning; Water filled pore space.