《Table 4 Summary of the R2, explained deviance and P values in all sub-models using the generalized

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《"Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem,China"》

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Note:a represents that the soil depth interval of 110–170 cm was selected to describe the best relationship between changes in soil p H and SIC；b represents that the soil depth interval of 10–70 cm was selected to describe the best relationship between c

Given the different distribution patterns of changes in soil p H and soil carbon content，we investigated whether there are significant relationships between changes in soil p H and soil carbon content at different soil depths by comparing their explained deviance and significance value in the sub-models of GAM.The full model comparison is listed in Table 4.The results show that SOC content and SIC content showed different responses to the changes in soil p H.For the optimal relationship between changes in soil p H and SOC content，the changes in soil p H at the0–80 cm soil depth explained 51.3%of the changes in SOC content（P=0.006；Fig.3）.In contrast，the changes in soil p H at the 100–180 cm soil depth only explained 12.3%of the changes in SOC content（P=0.310）.The optimal relationship between changes in soil p H and SIC content was found at the 100–180 cm soil depth（Fig.3）.The changes in soil p H at this depth explained 16.1%of the changes in SIC content（P=0.015）.In contrast，the changes in soil p H at the 0–80 cm soil depth only explained 5.5%of the changes in SIC content（P=0.488）.These results imply that in calcareous soils，soil acidification will mainly regulate the SOC dynamics in the root layer and the SIC dynamics in the deep soil layer.Furthermore，two piecewise trends for the relationship between soil acidification and SOC dynamics were found.Specifically，when the soil p H decreased by more than 0.2 units，the SOC content would increase significantly；and when the soil p H decreased by less than 0.2 units，the SOC content would decrease profoundly.For the SIC dynamics，this relationship suggests a nearly linear decline in SIC content with soil acidification.