Contrasts in growth and nitrogen nutrition of species in the Cupressaceae and Pinaceae in response to calcium
2014
Hawkins, B. J. | Robbins, S.
BACKGROUND AND AIMS: Cupressaceae species thrive on calcareous soils and accumulate calcium (Ca) in their tissues. High nitrification rates occur in soils under these species, and many prefer nitrate (NO₃) as a nitrogen (N) source. We tested the hypothesis that high levels of available Ca enhance NO₃uptake to a greater degree in Cupressaceae than Pinaceae using seedlings of Thuja plicata and Callitropsis (Chamaecyparis) nootkatensis compared with Pseudotsgua menziesii and Tsuga heterophylla. METHODS: Seedling growth and long-term N uptake were measured in a 2 × 2 factorial experiment supplying Ca and NO₃at 50 μM (low) or 1,000 μM (high). Short-term measures of Ca²⁺, NO₃⁻and NH₄⁺net flux in seedling roots were made in the same four test solutions using microelectrodes. RESULTS: In T. plicata, C. nootkatensis and P. menziesii, 50 μmol Ca²⁺supply resulted in greater growth and N content than 1,000 μmol Ca²⁺. Short-term NO₃⁻uptake was greater in the low Ca treatment for T. plicata, and P. menziesii, but the high Ca treatment for T. heterophylla. Ca treatment had no significant effect on net NO₃⁻flux in C. nootkatensis. With high Ca, significant net Ca²⁺efflux was observed from P. menziesii and T. heterophylla roots, but Ca²⁺uptake occurred in C. nootkatensis. CONCLUSIONS: Ca did not enhance NO₃uptake in Cupressaceae species under the conditions tested, and the apparent preference for calcareous soils in these species may be associated, instead, with mechanisms of Ca tolerance.
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