Stem and crown growth of Japanese larch and its hybrid F 1 grown in two soils and exposed to two free-air O 3 regimes

Abstract

Ozone (O₃) pollution and soil infertility may negatively affect boreal forests across the Northern Hemisphere. Impacts to economically and ecologically important larches (Larix sp., Pinacaeae) are particularly concerning. Using a free air O₃ enrichment (FACE) system, we investigated the effect of 2-year elevated O₃ exposure (≈66 nmol mol⁻¹) on Japanese larch (L. kaempferi) and its hybrid larch F₁ (L. gmelinii var. japonica × L. kaempferi) planted directly into either fertile brown forest soil (BF) or BF mixed with infertile volcanic ash soil (VA). Overall, photosynthetic pigmentation and the growth performance of the stem and crown were reduced in both taxa exposed to elevated O₃. Furthermore, hybrid larch, in both O₃ treatments, performed better than Japanese larch. This finding contradicts findings of prior experiments with potential experimental artifacts of O₃ exposure facilities and root restrictions. Elevated O₃ also disproportionately inhibited stem diameter growth and caused an imbalance in chlorophylls a/b and chlorophyll/carotenoid ratios. Hybrid and Japanese larches grown in BF and VA had a significantly lower drop of stem diameter over the run of stem height (from base to top) when exposed to elevated O₃, compared to ambient O₃. This finding indicates altered stem shape under elevated O₃. Among 11 response variables, there were no significant interactions between O₃ treatment and taxa. There was also no significant interaction of soil condition and taxa, suggesting that the two larches shared a similar response to O₃ and soil type. Understanding the performance of hybrid larch in relation to its parent species has ramifications for breeding success in a soil-degraded and O₃-polluted environment.

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