Increasing soil carbon stocks in eight permanent forest plots in China

Jianxiao Zhu,Chuankuan Wang,Shuqing Zhao,Peng Li,Guohua Liu,Zhang Zhou,Jiangling Zhu,Guoyi Zhou,Xueyang Hu,Jingyun Fang,Yude Pan,Zhiyao Tang,Yide Li,Richard A Birdsey,Chengjun Ji,Lai Jiang,Chengyang Zheng

doi:10.5194/bg-17-715-2020

Abstract

Abstract. Forest soils represent a major stock of organic carbon (C) in the terrestrial biosphere, but the dynamics of soil organic C (SOC) stock are poorly quantified, largely due to lack of direct field measurements. In this study, we investigated the 20-year changes in SOC stocks in eight permanent forest plots, which represent boreal (1998–2014), temperate (1992–2012), subtropical (1987–2008), and tropical forest biomes (1992–2012) across China. SOC contents increased significantly from the 1990s to the 2010s, mostly in the upper 0–20 cm soil depth, and soil bulk densities do not change significantly during the same period. As a result, the averaged SOC stocks increased significantly from 125.2±85.2 Mg C ha−1 in the 1990s to 133.6±83.1 Mg C ha−1 in the 2010s across the forest plots, with a mean increase of 127.2–907.5 kg C ha−1 yr−1. This SOC accumulation resulted primarily from increasing leaf litter and fallen logs, which accounts 3.6 %–16.3 % of above-ground net primary production. Our findings provided direct evidence that China's forest soils have been acting as significant C sinks, although their strength varies in forests with different climates.

Highlights

Terrestrial ecosystems have absorbed approximately 30 % of the carbon dioxide (CO2) emitted from human activity since the beginning of the industrial era (IPCC, 2013)
soil organic C (SOC) stocks were investigated in eight permanent forest plots in four forest sites from northern to southern China over two periods: the 1990s and 2010s
The temperate pine plantation experienced the largest increase in SOC stock in the top 20 cm depth (630.8 ± 111.2 kg C ha−1 yr−1)

Summary

Introduction

Terrestrial ecosystems have absorbed approximately 30 % of the carbon dioxide (CO2) emitted from human activity since the beginning of the industrial era (IPCC, 2013). Forests have contributed more than half of these carbon (C) fluxes of terrestrial ecosystems (Pan et al, 2011). Since soils contain a huge C stock in forest ecosystems, even a slight change in this stock will induce a considerable feedback to atmospheric CO2 concentrations (Lal, 2004; Luo et al, 2011). Accurate assessment of the changes in soil organic carbon (SOC) is critical to understanding how forest soils will respond to global climate change. Previous efforts have estimated the changes in regional SOC stocks with indirect approaches, such as regional assessments (Yang et al, 2014) and model simulations It is difficult to capture the SOC change with short-term measurements (Smith, 2004) because the soil C pool typically has a longer turnover time and higher spatial variability compared to the vegetation C pool (Schrumpf et al, 2011; Canadell and Schulze, 2014).

Methods

Results

Discussion

Conclusion