Organic material types have stronger effects on humic substances and
enzyme activities than soil types
Abstract
Organic materials are essential to increase soil organic carbon (SOC).
However, it is unclear whether C sequestration is primarily affected by
the form of organic materials or soil types. Wheat straw, tobacco straw,
and their derived biochars were added to acidic soil, saline soil and
calcareous soil in the same C concentration and incubated for 30, 90,
and 180 days, respectively. The contents of humic substances (HS), the
structural characteristic of SOC, and enzyme activities were
investigated. The results revealed that both biochar-C and crop straw-C
were mainly sequestered in humin (HU) across all soil types. Moreover,
humic acid (HA) levels increased in straw treatments but not in biochar
treatments. The cluster analysis and principal components analysis
showed that HU had a significantly positive correlation with SOC. The
aryl C of SOC increased in biochar treatments, while phenolic C and
O-alkyl C of SOC increased in straw treatments. A positive correlation
was found between aromatic C and SOC concentration, as well as between
polyphenol oxidase activity and O-alkyl C. The formation of O-alkyl C
was affected by polyphenol oxidase activity. These findings suggest that
the form of organic materials and microbial activity, rather than soil
types, influence the formation of HS and functional groups of SOC. Soil
amended with biochar can sequester more recalcitrant C while also
increasing the hydrophobicity of SOC.