In carbonate-rich soils with plants, CO2 emissions from the rhizosphere may come from as many as three sources, i.e., root-derived respiration, decomposition of soil organic carbon (SOC), and dissolution of soil inorganic carbon (SIC), so partitioning of CO2 emissions by source is important to accurately quantify the rhizosphere effect (RE). Because of limited methods for three-source partitioning of soil CO2, how living roots affect SOC and SIC release (RE) has not yet been clarified, and this urgently needs to be evaluated. In this study, the RE of summer maize and winter wheat on SOC decomposition and SIC dissolution were investigated at three phenological stages in pot experiments with the aid of 13CO2 pulse labeling combined with 13C natural abundance techniques. We found that the contribution of SIC dissolution to CO2 emissions from unplanted soils ranged from 25% to 44%. As crop growth progressed, the maize rhizosphere effect on SOC- and SIC-derived CO2 emissions increased from 14% and 74% at the elongation stage to 84% and 268% at the grain filling stage compared to that in unplanted soils, respectively, while the wheat rhizosphere effect on SOC- and SIC-derived CO2 emissions increased from 51% and 34% at the elongation stage to 77% and 76% at the grain filling stage. We concluded that the rhizosphere effects increased SOC and SIC release over the entire growing season of maize (by 54% for SOC and 159% for SIC) and wheat (by 64% and 49%) compared to that in unplanted soils, indicating that ignoring SIC dissolution in carbonate-rich soils with plants will result in overestimation of SOC decomposition.

中文翻译：

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玉米和小麦的根际效应增加了富碳酸盐土壤中土壤有机碳和无机碳的释放：三源13C分配研究

在植物丰富的碳酸盐土壤中，根际的CO2排放可能来自三种来源，即根源呼吸，土壤有机碳分解（SOC）和土壤无机碳溶解（SIC），因此进行了分配。排放源的CO2排放量对于准确定量根际效应（RE）至关重要。由于用于土壤CO2的三源分配的方法有限，因此尚不清楚活根如何影响SOC和SIC释放（RE），因此迫切需要对此进行评估。在这项研究中，借助13CO2脉冲标记结合13C自然丰度技术，在盆栽试验的三个物候阶段研究了夏玉米和冬小麦的RE对SOC分解和SIC溶解的影响。我们发现SIC溶解对未种植土壤的CO2排放的贡献范围为25％至44％。随着作物生长的增长，玉米根际对SOC和SIC产生的CO2排放的影响，从拉长期的14％和74％增加到了灌浆期的84％和268％，而未种植的土壤分别为84％和268％。小麦根际对SOC和SIC产生的CO2排放的影响从伸长期的51％和34％增加到了籽粒灌浆期的77％和76％。我们得出的结论是，与未种植的土壤相比，根际效应增加了整个玉米（SOC分别为54％和SIC 159％）和小麦（分别为64％和49％）的SOC和SIC释放，表明无视SIC在植物富含碳酸盐的土壤中的溶解将导致高估SOC分解。