Soil respiration and organic matter decomposition dynamics respond to legacy fertilizer and weed control treatments in loblolly pine stands

Abstract

Most studies examining how forest soil carbon (C) cycling responds to silvicultural treatments are restricted to a single rotation, with the legacy effects of past management practices being relatively unstudied. Here, we examined soil respiration and organic matter decomposition dynamics (important proxies for C dynamics), climate, and nutrient cycling in a second rotation, 2-year-old loblolly pine (Pinus taeda L.) plantation in north Florida. Carryover (C-) effects of the previous rotation's control (CC), fertilizer (CF), weed control (CW), and combined fertilizer and weed control (CFW) treatments were examined for residual effects on soil respiration (Rs), heterotrophic respiration (Rh), and substrate decomposition potential. Repeated measurements were made over 13 months. The mean Rs for both the CF (4.56 μmol CO2 m−2 s−1) and CFW (4.49 μmol CO2 m−2 s−1) treatments were increased by 29% and 27%, respectively, compared to the CC (3.53 μmol CO2 m−2 s−1) treatment. The Rh in the CW (2.97 μmol CO2 m−2 s−1) was significantly lower compared to the CF (4.02 μmol CO2 m−2 s−1) and CFW (3.66 μmol CO2 m−2 s−1) treatments, despite having warmer soil temperatures than the CF treatment, and no differences in soil moisture contents. Soil temperature and Mehlich III soil extractable manganese (Mn) concentrations (0–10 cm) were the only variables that explained variation in Rh. Decomposition rates for a common substrate were also lower in the CW compared to the CF, treatment (p = 0.027), potentially because the removal of understory plants in the CW treatment affected both microclimate and Mn cycling compared to the CF treatment where understory plants were retained and micronutrients were added as fertilizers. Overall, forest management affected organic matter cycling after replanting and 12 years after the last treatment in the previous rotation, suggesting that long-term studies are needed to understand the effects of silvicultural practices on ecosystem C cycling.