Ethylenediurea (EDU) effects on hybrid larch saplings exposed to ambient or elevated ozone over three growing seasons

Ground-level ozone (O3) pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production, thus indicating a need for forestry interventions to mediate O3 effects. We treated hybrid larch (Larix gmelinii var. japonica × L. kaempferi) saplings grown in nutrient-poor soils with 0 or 400 mg L−1 water solutions of the antiozonant ethylenediurea (EDU0, EDU400) and exposed them to ambient O3 (AOZ; 08:00 − 18:00 ≈ 30 nmol mol−1) or elevated O3 (EOZ; 08:00 − 18:00 ≈ 60 nmol mol−1) over three growing seasons. We found that EDU400 protected saplings against most effects of EOZ, which included extensive visible foliar injury, premature senescence, decreased photosynthetic pigment contents and altered balance between pigments, suppressed gas exchange and biomass production, and impaired leaf litter decay. While EOZ had limited effects on plant growth (suppressed stem diameter), it decreased the total number of buds per plant, an effect that was not observed in the first growing season. These results indicate that responses to EOZ might have implications to plant competitiveness, in the long term, as a result of decreased potential for vegetative growth. However, when buds were standardized per unit of branches biomass, EOZ significantly increased the number of buds per unit of biomass, suggesting a potentially increased investment to bud development, in an effort to enhance growth potential and competitiveness in the next growing season. EDU400 minimized most of these effects of EOZ, significantly enhancing plant health under O3-induced stress. The effect of EDU was attributed mainly to a biochemical mode of action. Therefore, hybrid larch, which is superior to its parents, can be significantly improved by EDU under long-term elevated O3 exposure, providing a perspective for enhancing afforestation practices.

X-ray microdensitometry for assessing the resistance of hybrid larch to fungus Coniophora puteana

X-ray microdensitometry was performed on small wood samples after fungal exposure to assess wood density loss and its variability within a hybrid larch population. Microdensitometry was applied to thin wood slices obtained from increment cores collected from standing trees before and after 4 weeks of exposure to Coniophora puteana fungus. Density loss rates were measured and compared to mass loss percentages calculated on wood blocks following a 16-week decay test according to CEN TS 15083-1 (2005). The relationship between the standard mass loss and the density loss percentages was weak. Several explanations for the results are presented in this work, and methodological improvements are suggested to achieve a more accurate comparison. The proposed screening test has several advantages over the current standard method, as it is less invasive for the tree, less time consuming, and is therefore better suited for genetic studies and breeding. As predicted, due to extractive content variation and fungus behaviour, density loss after 4 w was more important in earlywood than in latewood and in inner heartwood than in outer heartwood. The new method also better determined the differences in decay among trees within the larch population than the standard method at 16 w.

Evaluating Soil–Root Interaction of Hybrid Larch Seedlings Planted under Soil Compaction and Nitrogen Loading

Although compacted soil can be recovered through root development of planted seedlings, the relationship between root morphologies and soil physical properties remain unclear. We investigated the impacts of soil compaction on planted hybrid larch F1 (Larix gmelinii var. japonica×L. kaempferi, hereafter F1) seedlings with/without N loading. We assumed that N loading might increase the fine root proportion of F1 seedlings under soil compaction, resulting in less effects of root development on soil recovery. We established experimental site with different levels of soil compaction and N loading, where two-year-old F1 seedlings were planted. We used a hardness change index (HCI) to quantify a degree of soil hardness change at each depth. We evaluated root morphological responses to soil compaction and N loading, focusing on ectomycorrhizal symbiosis. High soil hardness reduced the total dry mass of F1 seedlings by more than 30%. Significant positive correlations were found between HCI and root proportion, which indicated that F1 seedling could enhance soil recovery via root development. The reduction of fine root density and its proportion due to soil compaction was observed, while these responses were contrasting under N loading. Nevertheless, the relationships between HCI and root proportion were not changed by N loading. The relative abundance of the larch-specific ectomycorrhizal fungi under soil compaction was increased by N loading. We concluded that the root development of F1 seedling accelerates soil recovery, where N loading could induce root morphological changes under soil compaction, resulting in the persistent relationship between root development and soil recovery.

Survival rate and shoot growth of grafted Dahurian larch (Larix gmelinii var. japonica): a comparison between Japanese larch (L. kaempferi) and F1hybrid larch (L. gmelinii var. japonica × L. kaempferi) rootstocks

We grafted scions of Dahurian larch (Larix gmelinii var. japonica) onto Japanese larch (L. kaempferi) and F1 hybrid larch (L. gmeli­nii var. japonica × L. kaempferi) rootstocks and examined root­stock-scion compatibility by assessing the survival rate (SR) in two independent experiments. Scion overgrowth on the root­stock was not observed. SR was not significantly different among rootstocks due to large interquartile ranges (IQR) among clones within a rootstock type. Results suggested that the SR was more dependent on the clonal characteristics of the scion than on the growth vigor of the rootstock. Shoot elonga­tion of grafts on F1 hybrid rootstock was superior to that of grafts on Japanese larch rootstock. Selection of an appropriate combination of scion and rootstock may improve the SR of grafted Dahurian larch and shorten the cultivation period.