19The moisture content of live fuels is an important determinant of forest flammability. Current 20 approaches for modelling live fuel moisture content typically focus on the use of drought 21 indices. However, these have mixed success partly because of species-specific differences in 22 drought responses. Here we seek to understand the physiological mechanisms driving 23 changes in live fuel moisture content, and to investigate the potential for incorporating plant 24 physiological traits into live fuel moisture models. We measured the dynamics of leaf 25 moisture content, access to water resources (through stable isotope analyses) and 26 physiological traits (including leaf water potential, stomatal conductance, and cellular 27 osmotic and elastic adjustments) across a fire season in a Mediterranean mixed forest in 28 Catalonia, NE Spain. We found that differences in both seasonal variation and minimum 29 values of live fuel moisture content were a function of access to water resources and plant 30 physiological traits. Specifically, those species with the lowest minimum moisture content 31 and largest seasonal variation in moisture (Cistus albidus: 49-137 % and Rosmarinus 32 officinalis: 47-144 %) were most reliant on shallow soil water and had the lowest values of 33 predawn leaf water potential. Species with the smallest variation in live fuel moisture content 34 (Pinus nigra: 96-116 % and Quercus ilex: 56-91 %) exhibited isohydric behaviour (little 35 variation in midday leaf water potential, and relatively tight regulation of stomata in response 36 to soil drying). Of the traits measured, predawn leaf water potential provided the strongest 37 predictor of live fuel moisture content (R 2 = 0.63, AIC = 249), outperforming two commonly 38 used drought indices (both with R 2 = 0.49, AIC = 258). This is the first study to explicitly link 39 fuel moisture with plant physiology and our findings demonstrate the potential and 40 importance of incorporating ecophysiological plant traits to investigating seasonal changes in 41 fuel moisture and, more broadly, forest flammability.42 43 65LFMC. An eco-physiological approach to investigating LFMC dynamics may overcome 66 these limitations and lead to improved modelling (Jolly and Johnson, 2018). 67There are at least three different but mutually inter-related physiological processes 68 that might explain why leaf moisture varies differentially across species. One of them is 69 access to water resources, a function of rooting patterns and water availability in the soil 70 profile that, in turn, appears to be related to the post-fire regeneration strategy. For example, 71 species that can resprout following high intensity fire typically have greater allocation to 72 roots and deeper root systems than species lacking this capacity (Bell et al., 1996; Verdu, 73 2000). As a consequence, resprouting species often maintain greater water supply to foliage 74 during dry periods than obligate seeding species (which are fire-killed but regenerate via 75 seed) (Saura-Mas and...

It is widely accepted that elevated levels of surface ozone (O) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O-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 200-400mgEDUL, the usually applied range for protection against O phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O 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-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 (AOZ, 10-h≈28.3nmolmol) or to elevated O (EOZ, 10-h≈65.8nmolmol) levels during daylight hours. Over the growing season, plants were treated every nine days with 200mL soil drench of 0, 200 or 400mgEDUL or with foliar spray of 0, 200 or 400mgEDUL (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 200-400mgL foliar spray. We conclude that EDU may be more effective against O phytotoxicity to fast-growing species when applied as a spray than when applied as a drench. Keymessage: Soil-drenched EDU was ineffective in protecting willow plants against O-induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200mgL.

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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 yr -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 under 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.

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