Spatial heterogeneity of subsoil organic carbon turnover times in forest ecosystems across China

<p>Soil organic carbon turnover time (&#964;, year) is an important indicator of soil carbon stability and sequestration capacity. However, our understanding of the spatial heterogeneity of subsoil &#964; still was poorly qualified over a large scale, even though subsoil organic carbon below 0.2 m accounts for the majority of total soil organic carbon. We compiled a dataset that consisted of 630 observations in subsoil (0.2 - 1 m) from published literatures to investigate the spatial heterogeneity of subsoil &#964; (defined as the ratio of soil carbon stock and net primary production) and explore its main environmental drivers using structural equation modelling (SEM) in forest ecosystems across China.<strong> </strong>Results indicated that mean (&#177; standard deviation) subsoil &#964; was 72.4 &#177; 68.6 years with a large variability ranging from 2.3 to 896.2 years. Subsoil &#964; varied significantly with forest types that mean subsoil &#964; was the longest in deciduous broadleaf forest (82.9 &#177; 68.7 years), followed by evergreen needleleaf forest (77.6 &#177; 60.8 years), deciduous needleleaf forest (75.3 &#177; 78.6 years) and needleleaf and broadleaf mixed forest (71.3 &#177; 80.9 years), while the shortest &#964; in evergreen broadleaf forest (59.9 &#177; 40.7 years). SEM suggested that soil environment was the most important factor in predicting subsoil &#964;. However, the dominant driver differed with forest types, i.e. soil environment for evergreen broadleaf forest and climate for evergreen needleleaf forest. This study highlights the different dominant controlling factors in subsoil &#964; and improve our understanding of biogeographic variations of subsoil &#964;. These findings are essential to better understand (and reduce uncertainty) in biogeochemical models of subsoil carbon dynamics at regional scales.</p>