Distribution of organic carbon fractions in soil aggregates in Chinese fir plantations with different stand ages

Abstract

Background Revealing the variations in soil aggregate-related organic carbon (OC) and labile organic carbon (LOC) fractions in a chronosequence of Chinese fir plantations plays an important role in better understanding the impact of soil carbon sink or source on the Chinese fir plantation ecosystem. In this study, soil samples in a depth of 0–20 cm were collected from Chinese fir plantations at different stand ages (0, 9, 17, and 26 years old) in Guangxi, China. With the optimal moisture sieving method adopted, the soil aggregates of 4 different sizes were obtained, including > 2-mm, 2–1-mm, 1–0.25-mm, and < 0.25-mm aggregates. Soil OC and LOC fractions were measured in the aggregates of different sizes. The LOC fractions included readily oxidizable carbon (ROC), particulate organic carbon (POC), microbial biomass carbon (MBC), water-soluble organic carbon (WOC), and mineralized organic carbon (MOC). Results Soil aggregate stability, as indicated by the mean weight diameter (MWD), was the highest in the 17-year-old Chinese fir plantations and was significantly positively related (p < 0.05) to the concentrations of OC and LOC fractions (except for the ROC and MOC), with the POC in particular. As for all stand ages of Chinese fir plantations, the concentrations of soil OC and LOC fractions were significantly increased as the aggregate size decreased. Consequently, there were more OC and LOC fractions distributed in the < 0.25-mm aggregates. During the stand development, the concentrations of soil OC and LOC fractions first increased and then decreased, with the highest levels detected in the 17-year-old Chinese fir plantations, indicating that the 17-year-old Chinese fir plantations were conducive to the accumulation of soil OC and LOC fractions. Conclusion After 17 years of planting, promoted soil carbon (especially for the POC) accumulation contributes significantly to enhancing soil aggregate stability for the Chinese fir plantations in Guangxi, China.

Dynamics of soil aggregate‐related C‐N‐P stoichiometric characteristics with stand age and soil depth in Chinese fir plantations

“…Regardless of the Chinese fir‐plantation age, the proportions of larger aggregates (namely, >2 and 1–2 mm fractions) significantly declined with increasing soil deepness, but the proportions of smaller aggregates (namely, 0.25–1 and <0.25 mm fractions ) visibly increased (Figure 2), which was attributed to the surface cumulation of soil C org (He et al, 2021). Soil C org is the important binding agent for soil aggregation, which could provide cementing agents to facilitate the formation of larger aggregates (Al‐Kaisi et al, 2014).…”

Characteristics of Soil Organic Carbon Fractions and Stability along a Chronosequence of Cryptomeria japonica var. sinensis Plantation in the Rainy Area of Western China

“…In August 2020, we selected seven stand ages (6,12,23,27,32,46, 52 a) of C. japonica plantations based on the stand age classification standard of China [14,16]. There were three 20 m × 20 m plots chosen in each stand age forest community.…”

“…Stand age is one of the main characteristics of forest growth and development and is closely related to SOC fractions. Firstly, forest growth and development can regulate SOC by affecting stand structure, understory vegetation diversity, and soil properties [13,14]. Secondly, stand-age-associated changes in canopy conditions, stand structure, and understory vegetation could affect litter residue and root exudate, which could in turn affect soil microbial biomass, enzyme activity, and soil physicochemical properties, further leading to changes in SOC accumulation and fractions [15,16].…”

“…Thus, the balance between carbon input (e.g., above-and belowground litter) and output (e.g., soil respiration) determines SOC fractions [1,8,11,15,16]. Although a number of studies have reported SOC over stand ages, the stand-age-caused patterns in forest SOC are still highly controversial [13][14][15][16][17]. For example, Meta et al (2015) showed that SOC increased with increasing stand age [17], but other studies found that SOC decreased first and then increased with increasing stand age [14,16].…”

“…Although a number of studies have reported SOC over stand ages, the stand-age-caused patterns in forest SOC are still highly controversial [13][14][15][16][17]. For example, Meta et al (2015) showed that SOC increased with increasing stand age [17], but other studies found that SOC decreased first and then increased with increasing stand age [14,16]. Meanwhile, how different carbon components (labile carbon vs. recalcitrant carbon) respond to stand age in forest ecosystems remains poorly understood.…”