Effects of long-term vegetation cover changes on the organic carbon fractions in soil aggregates of mollisols

doi:10.17521/cjpe.2019.0028

Abstract

Abstract:

Aims Soil aggregate is the main habitat for decomposition and transformation of soil organic carbon (SOC) and is important to regulate SOC sequestration. The mechanisms of the stability of SOC fractions may vary among different aggregate sizes. The aims of this study were to explore the characteristics of SOC “fractionation” in soil aggregates, and to reveal the mechanisms of carbon (C) sequestration in soil aggregates of mollisols after 31-year changes in vegetation cover.
Methods A long-term field experiment with different vegetation cover (grassland, farmland and bareland) was established in National Observation Station of Hailun Agro-ecosystem System. Soil aggregate fractionation, the density and humus fractionation within different aggregate sizes were further carried out.
Important findings The results showed that after 31 years of land cover change, the surface SOC and total nitrogen (TN) contents in grassland with higher C inputs increased significantly with time, while the SOC and TN contents decreased significantly in bareland, but with no statistical significance in farmland. The 2-0.25 mm (include 2 mm, the same below) aggregates was the excellent fraction for SOC sequestration under all three land cover. The stability of soil aggregate was in the order of: grassland > farmland > bareland. The mass proportion of soil aggregate and its associated content were highest in grassland, while the proportion of microaggregate and its carbon allocation rate were lowest in grassland. However, due to the lower C inputs in farmland and bareland, the distribution of aggregates was in the order of microaggregate > macroaggregate > silt-clay fraction under these two types of land cover, and organic carbon (OC) content was highest in microaggregates. Different vegetation cover changed the C “fractionation” of density and humus fractions in aggregates. Compared with farmland and bareland soils, OC contents in light fractions in >2 mm and 2-0.25 mm aggregates were higher in grassland, and the OC contents in furic acid, humic acid and humin were highest in 2-0.25 mm aggregates in grassland, while the humus OC accumulated in microaggregates in farmland and bareland. Our results indicated that the plant-derived C entered macroaggregates first, and long-term grass cover enhanced free and light C fractions in macroaggregate, which consequently improved the stability of soil aggregates and enhanced the “fractionation” effects of large aggregates on the humus fractions. Our results revealed the characteristics of carbon sequestration in soil aggregates under different vegetation cover.

Key words: vegetation cover, water-stable aggregates, soil organic carbon, density fraction, humus

LI Na, ZHANG Yi-He, HAN Xiao-Zeng, YOU Meng-Yang, HAO Xiang-Xiang. Effects of long-term vegetation cover changes on the organic carbon fractions in soil aggregates of mollisols[J]. Chin J Plant Ecol, 2019, 43(7): 624-634.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2019.0028

https://www.plant-ecology.com/EN/Y2019/V43/I7/624

Figures/Tables 6

Fig. 1 Contents of soil organic carbon and total nitrogen in initial soil and soils under different vegetation covers (mean ± SD). Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers. BL, bareland; FL, farmland; GL, grassland.

Fig. 2 Distribution of soil aggregates and mean weight diameter (MWD) of aggregates under different vegetation covers (mean ± SD). Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers.

Fig. 3 Contents of organic carbon in soil aggregates fractions under different vegetation covers (mean ± SD). Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers.

Fig. 4 Organic carbon contents in different density fractions of aggregates under different vegetation covers (mean ± SD). Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers.

Fig. 5 Contents of organic carbon in humic substances and humification index in bulk soil under different vegetation covers (mean ± SD). FA, fulvic acid; HA, humic acid; HU, humin. Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers.

Fig. 6 Contents of organic carbon in soil aggregates under different vegetation covers (mean ± SD). Different lowercase letters above the bar differ at 0.05 levels among different vegetation covers.

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