Soil pH determines microbial utilization strategy for straw-derived hydrophilic and hydrophobic fractions in a Ferralsol

Abstract Lime is commonly used to neutralize acidic soil in practical farmland management. This study aimed to examine the effect of soil pH change by liming in acidic soil on the mineralization and microbial assimilation of 13 C-labelled maize straw-derived hydrophilic and hydrophobic fractions in a 60-d incubation experiment. Our results showed a higher cumulative mineralization of hydrophilic fraction in acidic (34.5%) than neutralized Ferralsol (22.3%), related to lower microbial substrate use efficiency under low soil pH. The cumulative mineralization of hydrophobic fraction was similar between acidic and neutralized Ferralsol. Soil pH affected substrate (hydrophilic and hydrophobic fractions) utilization by actinomycetes and bacteria, but not fungi. The utilization of hydrophilic fraction followed the order: bacteria (57–68%) > actinomycetes (10–19%) > fungi (4.2–5.5%). In contrast, utilization of hydrophobic fraction was the highest for fungi (24–38%), followed by bacteria (21–29%) and actinomycetes (3.2–15%). Actinomycetes showed a greater preference for hydrophilic fraction in neutralized than acidic Ferralsol; bacteria preferred to utilize hydrophilic fraction in both soils, while fungi favored hydrophobic fraction. Also, various substrate uses were found in specific phospholipid fatty acids, which showed that some individual species harbor particular organic C metabolization strategies. In conclusion, soil pH regulates the mineralization of hydrophilic fraction and variously determines the preferential utilization of hydrophilic and hydrophobic fractions by fungi, bacteria, and actinomycetes. Graphical Abstract