Physiological drought responses improve predictions of live fuel moisture dynamics in a Mediterranean forest.

The moisture content of live fuels is an important determinant of forest flammability. Current approaches for modelling live fuel moisture content typically focus on the use of drought indices. However, these have mixed success partly because of species-specific differences in drought responses. Here we seek to understand the physiological mechanisms driving changes in live fuel moisture content, and to investigate the potential for incorporating plant physiological traits into live fuel moisture models. We measured the dynamics of leaf moisture content, access to water resources (through stable isotope analyses) and physiological traits (including leaf water potential, stomatal conductance, and cellular osmotic and elastic adjustments) across a fire season in a Mediterranean mixed forest in Catalonia, NE Spain. We found that differences in both seasonal variation and minimum values of live fuel moisture content were a function of access to water resources and plant physiological traits. Specifically, those species with the lowest minimum moisture content and largest seasonal variation in moisture (Cistus albidus: 49–137% and Rosmarinus officinalis: 47–144%) were most reliant on shallow soil water and had the lowest values of predawn leaf water potential. Species with the smallest variation in live fuel moisture content (Pinus nigra: 96–116% and Quercus ilex: 56–91%) exhibited isohydric behaviour (little variation in midday leaf water potential, and relatively tight regulation of stomata in response to soil drying). Of the traits measured, predawn leaf water potential provided the strongest predictor of live fuel moisture content (R2 = 0.63, AIC = 249), outperforming two commonly used drought indices (both with R2 = 0.49, AIC = 258). This is the first study to explicitly link fuel moisture with plant physiology and our findings demonstrate the potential and importance of incorporating ecophysiological plant traits to investigating seasonal changes in fuel moisture and, more broadly, forest flammability.This study was made possible thanks to the collaboration of and the staff from the Natural Park of Poblet, P Sopeña, and the technical staff from MedForLab. This study was funded by the Spanish Government (RYC-2012-10970, AGL2015-69151-R). R. H. Nolan was supported with funding from the New South Wales Office of Environment and Heritage, via the Bushfire Risk Management Research Hub. We benefitted from critical comments from J Voltas, JM Moreno and L Serrano and instrument loans from R Savín

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 x 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

Landscape gradient of autumn photosynthetic decline in Abies sachalinensis seedlings

Understanding what environmental factors are genetically linked to a phenological event is critical for predicting responses to climate change. Photosynthetic phenology often varies among a species of evergreen conifers due to local adaptation. However, few empirical studies have revealed relevant relationships between climatic factors in provenance environments and photosynthetic phenology. This study evaluated the effects of environmental conditions of the growing site and seed source provenance on the seasonal changes in maximal photochemical quantum yield of photosystem II (F-v/F-m) in a common garden experiment with 2-year-old seedlings of Sakhalin fir (Abies sachalinensis), a representative species with local adaptation, from four seed source provenances. A logistic model was constructed to explain the seasonal variation of F-v/F-m from July to October and the relationships between the estimated model parameters and representative factors featuring provenance environments were evaluated. The landscape gradient of the detected model parameters responsible for the provenance environments was visualized in a map of the distribution area. The lowest temperature was the most plausible factor in the growing environment to explain the seasonal changes of F-v/F-m. Among the representative meteorological factors of provenance environments, the lowest temperatures in July showed significant relationships with two model parameters, explaining the lower limit of F-v/F-m and the higher sensitivity of autumn F-v/F-m decline. The estimated spatial maps of model parameters consistently showed that the higher the lowest temperature in July in the provenance environment, the lower the F-v/F-m in October and the greater the decrease in the autumn F-v/F-m decline. Therefore, the lowest summer temperature could be associated with the local adaptation of autumn photosynthetic phenology in A. sachalinensis

Leaf defense capacity of Japanese elm (Ulmus davidiana var. japonica) seedlings subjected to a nitrogen loading and insect herbivore dynamics in a free air ozone-enriched environment

Japanese elm (Ulmus davidiana var. japonica) is a native species in cool-temperate forests in Japan. We investigated growth, physiological reactions, and leaf defense capacity of Japanese elm seedlings under nitrogen (N) loading (45.3 kg N ha⁻¹ year⁻¹) and seasonal insect dynamics in a free-air ozone (O₃)-enriched environment (about 54.5 nmol O₃ mol⁻¹) over a growing season. Higher leaf N content and lower condensed tannin content in the presence of N loading and lower condensed tannin content in elevated O₃ were observed, suggesting that both N loading and elevated O₃ decreased the leaf defense capacity and that N loading further enhanced the leaf quality as food resource of insect herbivores. Two major herbivores were observed on the plants, elm leaf beetle (Pyrrhalta maculicollis) and elm sawfly (Arge captiva). The peak number of observed insects was decreased by N loading. Visible foliar injury caused by N loading might directly induce the reduction of number of the observed elm sawfly individuals. While elevated O₃ slightly suppressed the chemical defense capacity, significantly lower number of elm leaf beetle was observed in elevated O₃. We conclude that N loading and elevated O₃ can alter not only the leaf defense capacity of Japanese elm seedlings but also the dynamics of elm leaf beetle and sawfly herbivores

Impacts of ethylenediurea (EDU) soil drench and foliar spray in Salix sachalinensis protection against O3-induced injury

It is widely accepted that elevated levels of surface ozone(O-3) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O-3-caused phytotoxicity. Among other questions, the one still open is: which EDU application method is more appropriate for treating fast-growing tree species. The main aims of this study were: (i) to test if chronic exposure of Salix sachalinensis plants to 200-400 mg EDU L-1, the usually applied range for protection against O-3 phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O-3 on S. sachalinensis; (iii) to assess the efficacy of two methods (i.e. soil drench and foliar spray) of EDU application to plants; (iv) to investigate the appropriate concentration of EDU to protect against elevated O-3-induced damage in S. sachalinensis; and (v) to compare the two methods of EDU application in terms of effectiveness and EDU consumption. Current-year cuttings grown in infertile soil free from organic matter were exposed either to low ambient O-3 (AOZ, 10-h approximate to 283 nmol mol(-1)) or to elevated O-3 (EOZ, 10-h approximate to 65.8 nmol mol(-1)) levels during daylight hours. Over the growing season, plants were treated every nine days with 200 mL soil drench of 0, 200 or 400 mg.EDU L-1 or with foliar spray of 0, 200 or 400 mg EDU L-1 (in two separate experiments). We found that EDU per se had no effects on plants exposed to AOZ. EOZ practically significantly injured S. sachalinensis plants, and the impact was indifferent between the experiments. EDU did not protect plants against EOZ impact when applied as soil drench but it did protect them when applied as 200-400 mg.L-1 foliar spray. We conclude that EDU may be. more effective against O-3 phytotoxicity to fast-growing species when applied as a spray than when applied as a drench. Key message: Soil-drenched EDU was ineffective in protecting willow plants against O-3-induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200 mg L-1. (C) 2016 Elsevier B.V. All rights reserved

Developing Ozone Risk Assessment for Larch Species

Ozone (O-3) risk assessment for the protection of forests requires species-specific critical levels (CLs), based on either O-3 concentrations (AOT40) or stomatal uptake (PODY) accumulation over the growing season. Larch (Larix sp.) is a genus with O-3-susceptible species, widely distributed in the northern hemisphere and with global economic importance. We analyzed published and unpublished data of Japanese larch (Larix kaempferi) and its hybrid F-1 (Larix gmelinii var. japonica x L. kaempferi) stomatal responses for developing a parameterization of stomatal conductance model and estimating PODY-based CLs with two Y thresholds, that is, 0 and 1 nmol m(-2) s(-1) projected leaf area (PLA). In parallel, we estimated AOT40-based CLs. The results show that the AOT40-based CLs for a 2% and 4% biomass loss in Japanese larch were 5.79 and 11.59 ppm h, that is, higher than those in hybrid larch F-1 (2.18 and 4.36 ppm h AOT40), suggesting a higher O-3 susceptibility of the hybrid. However, the use of PODY reconciled the species-specific differences, because the CLs were similar, that is, 9.40 and 12.00 mmol m(-2) POD0 and 2.21 and 4.31 mmol m(-2) POD1 in Japanese larch versus 10.44 and 12.38 mmol m(-2) POD0 and 2.45 and 4.19 mmol m(-2) POD1 in the hybrid, for 2% and 4% biomass loss, respectively. Overall, the CLs were lower than those in other forest species, which suggests a relatively high susceptibility of these larches. These results will inform environmental policy-makers and modelers about larch susceptibility to O-3

Effects of soil compaction on the seedlings growth and ectomycorrhizal fungal community in hybrid larch

Soil physical composition is one of the fundamental factors regulating plant growth as well as soil microbes. For the rising expectation to optimize techniques of forestry machinery for sustainable forest managements in Japan, it is essential to assess the effects of soil compaction caused by machinery running on seedlings of afforestation tree species. Since most afforestation tree species interact with soil microbes, such as the symbiosis with ectomycorrhizal fungi, the effects of soil compaction would extend to the relationship between these microbes and planted seedlings. We evaluated the effects of soil compaction on growth and ectomycorrhizal fungi in hybrid larch seedlings. The experimental site was established with no compacted and compacted plots in the Sapporo experimental forest site of Hokkaido University, where two-year-old seedlings were planted. At compacted plots, the surface hardness was 25 kg cm-2 and the bulk density was 1.1 g cm-3. Height growth of seedlings was significantly suppressed, and the dry weight was decreased 50% at compacted plots than that of seedlings grown at uncompacted plots. The dominant group of associated ectomycorrhizal fungi was changed by soil compaction. Our data showed that the effect of soil compaction can suppress growth of seedlings and shape the specific ectomycorrhizal fungal community