Ionic balance and organic acids in western redcedar, western hemlock, and Douglas-fir seedlings grown in low- and high-N soils

Seedlings of western redcedar (Thuja plicata Donn ex. D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were transplanted into soils with low and high levels of available NO3 – (and total N). Current-year foliage was sampled after 10 weeks to determine the effect of N availability on foliar cation–anion balance (C–A) and the concentrations of low molecular weight organic acids of the three species. Carboxylate concentrations were estimated by using the difference between sums of cations and anions (C–A): 750 mequiv.·kg–1 for western redcedar, 351 mequiv.·kg–1 for western hemlock, and 266 mequiv.·kg–1 for Douglas-fir. Quinic acid was a primary constituent, accounting for 40% of the total for western redcedar and 75% for western hemlock and Douglas-fir. Oxalic acid was present in greatest concentration in the foliage of western redcedar (65 mequiv.·kg–1) but was a minor constituent in western hemlock and Douglas-fir. The quantified acids accounted for only 15% of the C–A of western redcedar but >80% of the C–A of western hemlock and Douglas-fir. A considerable portion of the C–A balance not accounted for in redcedar may be associated with the accumulation of CaCO3. Litterfall deposition of CaCO3 may lead to the consumption of H+ ions and enrichment of exchangeable soil Ca in the rooting zone of long-lived western redcedar trees. No statistically significant differences among the soils were detected with regard to C–A or the concentration of organic acids