Contrasting effects of thinning on soil CO2 emission and above- and belowground carbon regime under a subtropical Chinese fir plantation

Dong Wang; Xinli Chen; H Y H Chen; Olusanya Abiodun Olatunji; Qingwei Guan

doi:10.1016/j.scitotenv.2019.06.417

Contrasting effects of thinning on soil CO₂ emission and above- and belowground carbon regime under a subtropical Chinese fir plantation

Sci Total Environ. 2019 Nov 10:690:361-369. doi: 10.1016/j.scitotenv.2019.06.417. Epub 2019 Jun 26.

Authors

Dong Wang¹, Xinli Chen², H Y H Chen², Olusanya Abiodun Olatunji³, Qingwei Guan⁴

Affiliations

¹ Department of Ecology, College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037, China; College of Environmental Science and Engineering, China West Normal University, Nanchong 637000, China; Institute of Environmental Science, China West Normal University, Nanchong 637000, China.
² Faculty of Natural Resources Management, Lakehead University, 955 Oliver Rd., Thunder Bay, ON P7 B 5E1, Canada.
³ Key Laboratory of Mountain Ecological Restoration and Bioresource Utilization & Ecological Restoration Biodiversity Conservation Key Laboratory of Sichuan Province, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China.
⁴ Department of Ecology, College of Biology and the Environment, Nanjing Forestry University, Nanjing 210037, China. Electronic address: guanjapan999@163.com.

PMID: 31299570
DOI: 10.1016/j.scitotenv.2019.06.417

Abstract

Thinning plays a major role in forest soil carbon cycling. However, the mechanisms governing soil C fluxes, i.e., C input through litterfall and fine root (FR) production and C output through soil heterotrophic respiration (R_h), remain unclear. To fill this gap, we quantified the C fluxes in the topsoil layer (0-20 cm) by measuring litterfall, FR production and total soil respiration (R_s) (R_a (autotrophic respiration) and R_h) at three thinning intensities (control; low-intensity thinning: extraction of 30% of individual trees; high-intensity thinning (HIT): extraction of 70% of individual trees) in a 26-year-old Chinese fir plantation in southern China. In the control plots, the total C input (110 g C m^-2 year^-1) via litterfall (59 g C m^-2 year^-1) and FR production (51 g C m^-2 year^-1) was much lower than the C output via R_h (518 g C m^-2 year^-1). This finding demonstrated that the soil is a C source (407 g C m^-2 year^-1). Furthermore, the C source increased with increasing thinning intensity, particularly under HIT, due to the decreased litterfall return and increased soil CO₂ emissions through R_h; this increase occurred despite the increased C input from FR production. In addition, the C output via R_s significantly increased by 42% under HIT due to the stimulation of R_a and R_h. Consequently, thinning reduced the topsoil C pool by 7-8%. Redundancy analysis indicated that the soil C fluxes following thinning were driven by increased FR mortality, understory plant biomass and diversity, and microbial biomass carbon (MBC). Overall, our results indicate that heavy thinning increases soil C loss by increasing soil CO₂ emissions and decreasing litterfall return, even under substantially increased FR production. This finding suggests that thinning practices should consider the trade-off between soil C inputs and outputs to reduce the impact of thinning on forest soil carbon sequestration.

Keywords: Fine roots; Litterfall; Soil carbon balance; Soil respiration; Thinning intensity.

MeSH terms

Agriculture
Air Pollutants / analysis*
Carbon / analysis
Carbon Cycle
Carbon Dioxide / analysis*
Carbon Sequestration
China
Cunninghamia
Forestry
Forests
Soil
Trees

Substances

Air Pollutants
Soil
Carbon Dioxide
Carbon