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Species-specific variation of photosynthesis and mesophyll conductance to ozone and drought in three Mediterranean oaks.

ABSTRACT: Mesophyll conductance (g_mCO2 ) is one of the most important components in plant photosynthesis. Tropospheric ozone (O₃ ) and drought impair physiological processes, causing damage to photosynthetic systems. However, the combined effects of O₃ and drought on g_mCO2 are still largely unclear. We investigated leaf gas exchange during mid-summer in three Mediterranean oaks exposed to O₃ (ambient [35.2 nmol mol^-1 as daily mean]; 1.4 × ambient) and water treatments (WW [well-watered] and WD [water-deficit]). We also examined if leaf traits (leaf mass per area [LMA], foliar abscisic acid concentration [ABA]) could influence the diffusion of CO₂ inside a leaf. The combination of O₃ and WD significantly decreased net photosynthetic rate (P_N ) regardless of the species. The reduction of photosynthesis was associated with a decrease in g_mCO2 and stomatal conductance (g_sCO2 ) in evergreen Quercus ilex, while the two deciduous oaks (Q. pubescens, Q. robur) also showed a reduction of the maximum rate of carboxylation (V_cmax ) and maximum electron transport rate (J_max ) with decreased diffusive conductance parameters. The reduction of g_mCO2 was correlated with increased [ABA] in the three oaks, whereas there was a negative correlation between g_mCO2 with LMA in Q. pubescens. Interestingly, two deciduous oaks showed a weak or no significant correlation between g_sCO2 and ABA under high O₃ and WD due to impaired stomatal physiological behaviour, indicating that the reduction of P_N was related to g_mCO2 rather than g_sCO2 . The results suggest that g_mCO2 plays an important role in plant carbon gain under concurrent increases in the severity of drought and O₃ pollution.

SUBMITTER: Hoshika Y

PROVIDER: S-EPMC9303399 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background and aimsOaks are the foundation and dominant tree species of most Mediterranean forests. As climate models predict dramatic changes in the Mediterranean basin, a better understanding of the ecophysiology of seed persistence and germination in oaks could help define their regeneration niches. Tunisian oaks occupy distinct geographical areas, which differ in their rainfall and temperature regimes, and are thus a valuable model to investigate relationships between seed traits and species ecological requirements.MethodsSeed morphological traits, desiccation sensitivity level, lethal freezing temperature, embryonic axis and cotyledon sugar and lipid composition, and seed and acorn germination rates at various constant temperatures were measured in Quercus canariensis, Q. coccifera, Q. ilex and Q. suber, using seeds sampled in 22 Tunisian woodlands.Key resultsOnly faint differences were observed for desiccation sensitivity in the oak species studied. By contrast, the species differed significantly in sensitivity to freezing, germination rates at low temperature and base temperature. Quercus ilex and Q. canariensis, which occur at high elevations where frost events are frequent, showed the lowest freezing sensitivity. A significant correlation was found between hexose contents in the embryonic axis and freezing tolerance. Significant interspecific differences in the time for seeds to germinate and the time for the radicle to pierce the pericarp were observed. The ratio of pericarp mass to acorn mass differed significantly among the species and was negatively correlated with the acorn germination rate. Quercus coccifera, which is frequent in warm and arid environments, showed the highest acorn germination rate and synchrony.ConclusionsSeed lethal temperature, seed germination time at low temperatures, the ratio of pericarp mass to acorn mass and the embryonic axis hexose content appeared to be key functional traits that may influence the geographical ranges and ecological requirements of Mediterranean oaks in Tunisia.

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Species-specific variation of photosynthesis and mesophyll conductance to ozone and drought in three Mediterranean oaks.

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