Ecology, Evolution and Organismal Biology
Journal or Book Title
Oxisols are the dominant soil type in humid tropical and subtropical regions and are subjected to both drying–rewetting (DRW) cycles and fluctuating oxygen (O2) availability driven by warm temperatures and abundant rainfall in surface layers. Drying-rewetting cycles and O2 fluctuations may critically affect the microbial transformation of plant litter and subsequent stabilization as mineral-associated organic carbon (MAOC), but experimental data are still limited. We examined the impacts of DRW cycles, and variable O2 regimes with constant moisture, on carbon (C) and iron (Fe) dynamics in a degraded Oxisol (under long-term fallow) with added plant residues. In laboratory incubations (> 3 months), both DRW cycling and fluctuating O2 availability induced a flush of respiration and a temporary increase in microbial biomass C (MBC) following soil rewetting or O2 exposure, although MBC was consistently suppressed in these treatments relative to the control (60 % water holding capacity under constantly aerobic condition). Consequently, DRW cycles significantly increased but O2 fluctuations significantly decreased cumulative C mineralization relative to the control. Concentrations of short-range-ordered Fe oxides peaked immediately after litter addition and decreased five-fold during the remainder of the experiment. Mineral-associated C (defined as the chemically dispersed < 53 m soil fraction) increased 42-64% relative to initial values but was significantly lower under DRW cycling and fluctuating O2 relative to the control. Correspondingly, these treatments had greater fine particulate organic C (53 – 250 m), despite increased CO2 production under DRW cycling. Our data indicate the potential for rapid and significant accrual of MAOC in a degraded Oxisol, but environmental factors such as DRW cycling and fluctuating O2 can inhibit the conversion of plant litter to MAOC— possibly by suppressing microbial biomass formation and/or microbial transformations of organic matter.
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Ye, Chenglong; Hall, Steven J.; and Hu, Shuijin, "Controls on mineral-associated organic matter formation in a degraded Oxisol" (2019). Ecology, Evolution and Organismal Biology Publications. 326.