Plant Litter Chemical Characteristics Drive Decomposition in Subtropical Rangelands Under Prescribed Fire Management

Abstract

Rangelands used for cattle grazing in Florida are typically managed under prescribed fire to increase forage production and nutritive value while preventing shrub encroachment. Sustainability of extensively managed, low-input native rangelands is highly dependent on nutrient cycling through plant litter decomposition, which is often constrained by limited N availability. We evaluated the effect of prescribed fire (Unburned vs. Burned), N addition (0 vs. 180 kg N ha−1 yr−1), and species composition (Palmetto [Serenoa repens Bartr.] [100% saw-palmetto], Palmetto-Grass [50−50% mixture of saw-palmetto and grasses], and Grass [chalky bluestem, Andropogon capillipes Nash.; lopsided indiangrass, Sorghastrum secundum {Elliott} Nash]) on aboveground plant litter decomposition and N and P mineralization using field incubated litterbags over 224 d in a split-split plot design with three replicates. Litter disappearance followed a single exponential decay model (P ≤ 0.01) and was mainly driven by plant litter chemical characteristics. At the end of the 224-d incubation, remaining plant litter was less in Palmetto (62%) compared with other treatments (∼72%), possibly due to more favorable chemical characteristics associated with Palmetto treatment (43, 65, and 112 C:N ratio; and 15, 20, and 25 lignin:N ratio for Palmetto, Palmetto-Grass, and Grass, respectively). Remaining N was less (greater N mineralization) in Palmetto (79%) compared with Palmetto-Grass treatment (92%) but was not different from Grass (P ≥ 0.12, 86% remaining N). Greater lignin and proportion of N bound to fiber observed at the end of incubation suggested increased C and N recalcitrance as a result of decomposition. Nutrient inputs through ash or N addition suppressed litter net P and N mineralization. These results suggest litter quality, particularly N concentration and C:N and lignin:N ratios, are the main drivers in nutrient cycling through plant litter decomposition in Florida rangelands.