Abstract
Farmland conversion to forest is considered to be one of the effective measures to mitigate climate change. However, the impact of farmland conversion to forest land or grassland on soil CO2 emission in arid areas is unclear due to the lack of comparative information on soil organic carbon (SOC) mineralization of different conversion types. The SOC mineralization in 0–100 cm soil layer in farmland (FL), abandoned land (AL) and different ages (including 8, 15, 20 and 28 years) of Zanthoxylum bungeanum plantations were measured by laboratory incubation. The size and decomposition rate of fast pool (Cf) and slow pool (Cs) in different land-use types and soil layers were estimated by double exponential model. The results showed that: 1) Farmland conversion increased the cumulative CO2-C release (Cmin) and SOC mineralization efficiency, and those indexes in AL were higher than that in Z. bungeanum plantations. The Cmin and SOC mineralization efficiency of 0–100 cm soil increased with the ages of Z. bungeanum plantation. Both Cmin and SOC mineralization efficiency decreased with the increase of soil depth; 2) Both soil Cf and Cs increased after farmland converted to Z. bungeanum plantations and AL. The Cs in the same soil layer increased with the ages of Z. bungeanum plantation, and the Cf showed a “V” type with the increased ages of Z. bungeanum plantation. The Cf and Cs decreased with the increase of soil depth in all land-use types; 3) Farmland conversion increased the decomposition rate of Cf (k1) in all soil layer by 0.008–0.143 d−1 and 0.082–0.148 d−1 in Z. bungeanum plantations and AL, respectively. The k1 was obviously higher in the 0−20 cm soil layer than that in other soil layers, while the decomposition rate of Cs (k2) was not affected by FL conversion and soil depth; and 4) The initial soil chemical properties and enzyme activity affected SOC mineralization, especially the concentrations of total organic nitrogen (TON), SOC, easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC). It indicated that the conversion of farmland to Z. bungeanum plantations and AL increases SOC mineralization, especially in deeper soils, and it increased with the ages. The conversion of farmland to Z. bungeanum plantation is the optimal measure when the potential C sequestration of plant-soil system were taken in consideration.
Highlights
The soil is the largest carbon (C) pool in terrestrial ecosystem, it stores about 1.5 × 1015 kg C [1, 2]
The CO2 emission of same soil layer increased with the ages of Z. bungeanum plantation in each stage of the whole incubation period, and in which the soil CO2 emissions of all land-use types decreased with the increase of soil depth
The SOC mineralization efficiency of the same soil layer among different types was the highest in AL and the lowest in FL (Fig 2B). Both Cmin and SOC mineralization efficiency increased with the ages of Z. bungeanum plantation in all soil layer, and decreased with the increasing soil depth in all land-use types
Summary
The soil is the largest carbon (C) pool in terrestrial ecosystem, it stores about 1.5 × 1015 kg C [1, 2]. Small losses or sequestration in such a huge soil C pool will significantly change the soilatmosphere C cycle and cause global climate change [3,4,5]. SOC mineralization is the main output flux of CO2 from soil to atmosphere, so it may be the key to regulate soil C pool, atmospheric CO2 concentration and global C cycle [6]. Farmland conversion would change the SOC mineralization matrix, and microbial and soil properties, which could significantly impact on the SOC mineralization process, and making the direction and degree of change in SOC mineralization uncertain [16, 17]. The quantitative study of SOC mineralization and its driving factors after farmland conversion has become a hot spot in terrestrial ecosystem research
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