Key Laboratory of National Forestry Administration on Forest Resources Conservation and Ecological Safety in the Upper Reaches of the Yangtze River, College of Forestry, Sichuan Agricultural University, Chengdu, China.
PLoS One. 2022 Feb 4;17(2):e0262961. doi: 10.1371/journal.pone.0262961. eCollection 2022.
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.
耕地转换为林地被认为是减缓气候变化的有效措施之一。然而，由于缺乏不同转换类型土壤有机碳（SOC）矿化的比较信息，干旱地区耕地转换为林地或草地对土壤 CO2 排放的影响尚不清楚。通过实验室培养，测量了耕地（FL）、撂荒地（AL）和不同年龄（包括 8、15、20 和 28 年）花椒种植园 0-100cm 土层中的土壤有机碳（SOC）矿化。通过双指数模型估算了不同土地利用类型和土层中快库（Cf）和慢库（Cs）的大小和分解率。结果表明：1）耕地转换增加了累积 CO2-C 释放（Cmin）和 SOC 矿化效率，AL 中的这些指标高于花椒种植园。0-100cm 土壤的 Cmin 和 SOC 矿化效率随花椒种植园年龄的增加而增加。Cmin 和 SOC 矿化效率均随土壤深度的增加而降低；2）耕地转换为花椒种植园和 AL 后，土壤 Cf 和 Cs 均增加。同一土层的 Cs 随花椒种植园年龄的增加而增加，Cf 随花椒种植园年龄的增加呈“V”型。Cf 和 Cs 随所有土地利用类型中土壤深度的增加而降低；3）耕地转换分别增加了所有土层 Cf（k1）的分解率 0.008-0.143 d-1 和花椒种植园和 AL 中的 0.082-0.148 d-1。0-20cm 土层的 k1明显高于其他土层，而 FL 转换和土壤深度对 Cs（k2）的分解率没有影响；4）初始土壤化学性质和酶活性影响 SOC 矿化，特别是总有机氮（TON）、SOC、易氧化有机碳（EOC）和微生物生物量碳（MBC）的浓度。这表明耕地向花椒种植园和 AL 的转换增加了 SOC 矿化，特别是在较深的土壤中，并随着年龄的增长而增加。考虑到植物-土壤系统的潜在碳固存，耕地向花椒种植园的转换是最佳措施。
