Nitrogen loading increases the ozone sensitivity of larch seedlings with higher sensitivity to nitrogen loading.

Larch (Larix sp.) tree is a critical species for the future afforestation in Northeast Asia. The impacts of elevated concentrations of ground-level ozone (O3) and nitrogen (N) deposition are raising concerns. However, knowledge of the combined effects of elevated O3 and N loading are still limited. We investigated whether nitrogen loading mitigates the negative impacts of ozone on two larch species: the Japanese larch (L. kaempferi) and its hybrid larch F1 (L. gmelinii var. japonica × L. kaempferi) or not. We used open-top cambers and compared responses of the larch seedlings. Results showed the N loading mitigated the negative effects of O3 on Japanese larch. However, in hybrid larch F1, N loading did not mitigate O3-induced inhibition of growth and photosynthetic capacity. Mitigation effect of N loading on negative O3 impacts may vary between the two Larix spp., Hybrid larch F1 could be more affected by the combined effects of O3 and N loading due to its higher growth response to N loading. Elevated O3 also reduced leaf nitrogen/phosphorus (N/P) ratio by elevated O3, with significant effects in hybrid larch F1, particularly under N loading. In the present study, leaf N/P ratio was utilized to validate the hypothesis that a positive effect of N loading may be observed if O3 does not induce P limitation in Larix spp. We demonstrated a potential leaf N/P ratio function, which could reflect responses to O3 and N loading in hybrid larch F1.

Stem and crown growth of Japanese larch and its hybrid F1 grown in two soils and exposed to two free-air O3 regimes.

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.

Growth and photosynthetic traits of hybrid larch F1 (Larix gmelinii var. japonica x L. kaempferi) under elevated CO2 concentration with low nutrient availability.

The hybrid larch F(1) (Larix gmelinii var. japonica × Larix kaempferi) is considered one of the most important tree species not only for timber production but also as an afforestation material for severe conditions such as infertile soil. To predict the ability of hybrid larch F(1) as an afforestation material under potential climates in the future, it is important to understand the response of hybrid larch F(1) to elevated CO(2) concentration ([CO(2)]) under low nutrient availability. Three-year-old seedlings of hybrid larch F(1) were grown under two different levels of [CO(2)], 360 (ambient) and 720 µmol mol(-1) (elevated), in combination with two different levels of nitrogen (N) supply (0 and 30 kg ha(-1)) for one growing season. Elevated [CO(2)] reduced the maximum rates of carboxylation and electron transport in the needles. Net photosynthetic rates at growth [CO(2)] (i.e., 360 and 720 µmol mol(-1) for ambient and elevated treatment, respectively) did not differ between the two CO(2) treatments. Reductions in N content and N use efficiency to perform photosynthetic functions owing to the deficiency of nutrients other than N, such as P and K, and/or increase in cell wall mass were considered factors of photosynthetic down-regulation under elevated [CO(2)], whereas stomatal closure little affected the photosynthetic down-regulation. Although we observed strong down-regulation of photosynthesis, the dry matter increase of hybrid larch F(1) seedlings was enhanced under elevated [CO(2)]. This is mainly attributable to the increase in the amount of needles on increasing the number of sylleptic branches. These results suggest that elevated CO(2) may increase the growth of hybrid larch F(1) even under low nutrient availability, and that this increase may be regulated by changes in both crown architecture and needle photosynthesis, which is mainly affected not by stomatal limitation but by biochemical limitation.

Prominent differences in leaf fatty acid composition in the F1 hybrid compared with parent trees Larix gmelinii var. japonica and L. kaempferi.

Fatty acid (FA) compositions in leaves were investigated for two families of F(1) hybrids of Larix gmelinii var. japonica x L. kaempferi (F(1)) and their parent clones. Twenty-one FAs, from C(12) to C(32), were found in the leaves of both adult trees and seedlings. The levels of 18:1/(18:2 + 18:3) increased in the order L. kaempferi, F(1), and L. gmelinii var. japonica, with significant differences between L. gmelinii var. japonica and F(1) in adult trees, but these differences were not found in the seedlings. Moreover, in the adult trees, the 18:1/(18:2 + 18:3) levels in the neutral phospholipid fraction and the SigmaC(18)/SigmaC(16), especially in the glycolipid fraction, showed significant differences among the three species. These characteristics are discussed from the viewpoint of lipid synthesis in the endoplasmic reticulum and chloroplasts, and of the activities and substrate specificities in sequential FA desaturation. Linear discriminant analysis suggested that the FA compositions are useable as an index in the identification of hybrid seedlings.