Effects of Plum Plantation Ages on Soil Organic 2 Carbon Mineralization in The Karst Rocky 3 Desertification Ecosystem of Southwest China 4

: Soil organic carbon (SOC) mineralization is closely related to carbon source or sink of terrestrial ecosystem. Understanding soil organic carbon (SOC) mineralization under plum 15 plantation is essential for improving our understanding of SOC responses to land-use change in 16 karst rocky desertification ecosystem. In this study, 2-y, 5-y and 20-y plum plantations and adjacent 17 woodland were sampled and a 90-day incubation experiment was conducted to investigate the effect of plum plantation with different years on SOC mineralization in subtropical China. Results 19 showed that: (1) there was no significant difference in SOC content between different planting years, 20 but there were significant differences in accumulative SOC mineralization (C t ) and potential SOC 21 mineralization (C 0 ); (2) the dynamics of the SOC mineralization was a good fit to a first-order kinetic 22 model. Both C 0 and C t in calcareous soil of this study was several to ten folds lower than that in 23 other soils, indicating that SOC in karst region has higher stability. (3) Correlation analysis revealed 24 that both C t and C 0 was significantly correlated with soil calcium (Ca) and C/N, indicating the 25 important role of Ca and C/N in SOC mineralization in karst rocky desertification area.


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The study area is a hilly and middle-low mountain landform. Its parent material is 77 Carboniferous limestone. Karst soil is sparse and drought-prone. Because of long-term human 78 activities, natural vegetation is destroyed and large areas of steep slopes are reclaimed, resulting in 79 surface rock bareness, coupled with thin soil layer, shallow bedrock exposure, storm erosion, and a 80 large number of rock gradually exposed after soil erosion. Severe rocky desertification occurs (Figure 81 S1).

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Each soil sample (100 g dry) including three repeats was placed in a 1000 ml incubation jar 108 ( Figure S2). The soil moisture content was adjusted to 60% of field capacity prior to incubation. All 109 samples were pre-incubated at 20 °C for seven days to minimize the burst of respiration due to 110 wetting the dry soils [9]. Then, a 50 ml beaker containing 10 ml of 0.1 mol/L NaOH solution was 111 placed at the bottom of the incubation jar, sealed and capped, and incubated in a 20 o C thermostat in Ltd., Nanjing, China); SOC was determined using the K2Cr2O7-H2SO4 volumetric dilution heating 120 method; total nitrogen was determined using the Kjeldahl procedure [14]; total potassium (TK) 121 concentration was determined with the HF-HClO4 flame photometric method; and total phosphorus 122 (TP) was measured using HClO4-H2SO4 digestion followed by a Mo-Sb colorimetric assay [1]; soil 123 calcium (Ca) was extracted by HNO3-HF-HClO4 and analyzed by Inductively Coupled Plasma-

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Atomic Emission Spectrometry (ICP-AES). Three replicates were performed for each soil sample.

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The mineralization of SOC was calculated by the following formula (1).

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The half turnover period was calculated by the formula (3).

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Soil organic carbon mineralization rate decreased with incubation time (Figure 2), and accorded 160 with logarithmic function y=a+bln(x) (

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According to the decline rate of SOC mineralization (Figure 2), it can be divided into three stages.

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The first stage (2-14 days) was the early stage of the incubation. The rate of CO2 production decreased 167 rapidly from the peak (2 days) and changed greatly. There was no significant difference in 168 mineralization rate of SOC among three planting years, but it was significantly lower than CK. The

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second stage (14-62 days) was the medium stage of the incubation, and the rate of CO2 production 170 was in a slow decline to a stable stage. The SOC mineralization rate of CK is higher than that in the 171 three planting years. At the last stage (62-90 days), the SOC mineralization rate of CK began to be 172 lower than that of soils with different planting years and the difference was significant.   Table 3). The values of k for different soil depths showed the same trend with C0.

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With plum plantation ages, soil potential mineralized carbon pool decreased, but soil potential 195 mineralized carbon pool increased slightly after 20 years of restoration, but the difference was not 196 significant between 5-y and 20-y plum plantations (p>0.05).   235 Table 4. Correlations between the carbon parameters and soil property factors.

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Supplementary Materials: Figure S1: Rocky desertification in the study area, Figure S2: