Influence of soil redox potential on nitrogen uptake and growth of wetland Oak seedlings

Abstract

A study was conducted to determine ammonium nitrogen uptake by cherrybark oak and overcup oak as affected by soil redox conditions. Seedlings of the two species were grown in laboratory microcosms for 60 days in soil suspensions incubated at three separate Eh levels (+560, +340, and + 175 mV). In both species, uptake of added ¹⁵N labeled nitrogen (N) (NH₄Cl) and photosynthesis activity decreased with decreasing soil redox potentials. Net photosynthesis in cherrybark oak decreased by 72.9 and 100% in response to the +340 and + 175 mV treatments as compared to control plants, respectively. Similarly, net photosynthetic rates were reduced by 53.7 and 65.8% in overcup oak under + 340 and + 175 mV treatments, respectively. A significant correlation between net photosynthesis and leaf ¹⁵N content was found in cherrybark oak (r=0.866, P=0.01) but not in overcup oak (r=0.648, p>0.05). However, in overcup oak, the correlation between net photosynthesis and total leaf N content was significant (r=0.911, P=0.01). Maximum ¹⁵N uptake was measured at the highest soil redox level (+560 mV). Uptake of ¹⁵N in cherrybark oak decreased from a maximum of 1.83 mg under aerated (+560 mV) treatment to 0.11 mg under reduced conditions (+175 mV). Similarly, ¹⁵N uptake in overcup oak decreased from 2.37 mg under the + 560 mV treatment to 0.28 mg under + 175 mV treatment. Greater uptake of soil and fertilizer nitrogen was measured under the soil redox conditions in which adequate plant growth was recorded. Moderately reducing soil redox conditions (+340 and + 175 mV) adversely affected both plant nitrogen uptake and net photosynthetic activities of the two species.

Notes

Present address: Dept. of Biology, University of Memphis, Memphis, TN 38152.