Soil geochemistry as a driver of soil organic matter composition: insights from a soil chronosequence

[摘要] A central question in carbon research is howstabilization mechanisms in soil change over time with soil development andhow this is reflected in qualitative changes in soil organic matter (SOM).To address this matter, we assessed the influence of soil geochemistry onbulk SOM composition along a soil chronosequence in California, USA, spanning3 million years. This was done by combining data on soil mineralogy andtexture from previous studies with additional measurements on total carbon(C), stable isotope values ( δ 13 C and δ 15 N), andspectral information derived from diffuse reflectance infraredFourier transform spectroscopy (DRIFTS). To assess qualitative shifts inbulk SOM, we analysed the peak areas of simple plant-derived (S-POM),complex plant-derived (C-POM), and predominantly microbial-derived organic matter (OM; MOM) and their changes in abundance across soils with several millenniato millions of years of weathering and soil development. We observed thatSOM became increasingly stabilized and microbial-derived (lower C : N ratio,increasing δ 13 C and δ 15 N) as soil weatheringprogressed. Peak areas of S-POM (i.e. aliphatic root exudates) did notchange over time, while peak areas of C-POM (lignin) and MOM (components ofmicrobial cell walls (amides, quinones, and ketones)) increased over timeand depth and were closely related to clay content and pedogenic ironoxides. Hence, our study suggests that with progressing soil development,SOM composition co-varied with changes in the mineral matrix. Our studyindicates that structurally more complex OM compounds (C-POM, MOM) play anincreasingly important role in soil carbon stabilization mechanisms as themineral soil matrix becomes increasingly weathered.

[学科分类] 大气科学