Soil organic carbon dynamics jointly controlled by climate, carbon inputs, soil properties and soil carbon fractions

Abstract

Soil organic carbon (SOC) dynamics are regulated by the complex interplay of climatic, edaphic and biotic conditions. However, the interrelation of SOC and these drivers and their potential connection networks are rarely assessed quantitatively. Using observations of SOC dynamics with detailed soil properties from 90 field trials at 28 sites under different agroecosystems across the Australian cropping regions, we investigated the direct and indirect effects of climate, soil properties, carbon (C) inputs and soil C pools (a total of 17 variables) on SOC change rate (r , Mg C ha yr ). Among these variables, we found that the most influential variables on r were the average C input amount and annual precipitation, and the total SOC stock at the beginning of the trials. Overall, C inputs (including C input amount and pasture frequency in the crop rotation system) accounted for 27% of the relative influence on r , followed by climate 25% (including precipitation and temperature), soil C pools 24% (including pool size and composition) and soil properties (such as cation exchange capacity, clay content, bulk density) 24%. Path analysis identified a network of intercorrelations of climate, soil properties, C inputs and soil C pools in determining r . The direct correlation of r with climate was significantly weakened if removing the effects of soil properties and C pools, and vice versa. These results reveal the relative importance of climate, soil properties, C inputs and C pools and their complex interconnections in regulating SOC dynamics. Ignorance of the impact of changes in soil properties, C pool composition and C input (quantity and quality) on SOC dynamics is likely one of the main sources of uncertainty in SOC predictions from the process-based SOC models.

Proper estimate of residue input as condition for understanding drivers of soil carbon dynamics

“…In a recent paper, Luo, Feng, Luo, Baldock, and Wang () demonstrate that SOC dynamics in agricultural systems are mainly driven by, in order of importance, the amount and quality of C inputs to the soil from plant residues, climate, and soil properties including the amount and composition of soil C. While we concur with Luo et al. () that the average C input amount is the most influential variable on SOC change rate, their experimental set‐up did not enable its weight to be accurately quantified. They apply a path analysis and make use of an extensive data set that comprises detailed soil properties from 90 Australian field trials.…”

“…According to these data, the assumptions proposed would fit to potatoes, while Luo et al. () consider winter wheat and pasture. In addition, root‐derived C inputs are likely to contribute massively to soil C built‐up as they are more persistent in soil on a decadal time scale than inputs from aboveground tissue (Kätterer et al., ; Rasse, Rumpel, & Dignac, ).…”

“…Furthermore, the approach used by Luo et al. () does not account for differential C partitioning above and belowground in response to fertilization or management (Scott, Stewart, & Metherell, ). Plant C inputs and their effect on SOC might therefore have been strongly underestimated.…”

“…Luo et al. (), following Skjemstad and Spouncer (), account for site conditions by applying different HI's, but leave these HI's constant over time. Most likely however, the HI for cereal crops has changed during the duration of the study (mostly 1970–2000, though experiments of up to 82 years duration are included) due to plant breeding.…”

Effects of temperature, soil substrate, and microbial community on carbon mineralization across three climatically contrasting forest sites

“…This is consistent with previous findings that climate exerts dominant controls on SOM decomposition (Carvalhais et al., 2014; Kirschbaum, 2004; Sun et al., 2004). A recent synthesis by Luo, Feng, Luo, Baldock, and Wang (2017) showed that climate (precipitation and temperature) accounted for as much as 25% of the relative influence on SOC by various environmental, soil biotic, and abiotic factors. Within given temperatures, however, we found that soil substrate had much greater influence on the rate of soil C mineralization than microbial inoculum, suggesting the importance of soil quality in determining the soil C mineralization—possibly the microbial adaptation to the soil matrix.…”