Functional responses of two Mediterranean pine species in an ozone Free-Air Controlled Exposure (FACE) experiment

Abstract

Effects of the phytotoxic and widespread ozone (O3) pollution may be species specific, but knowledge on Mediterranean conifer responses to long-term realistic exposure is still limited. We examined responses regarding to photosynthesis, needle biochemical stress markers and carbon (C) and nitrogen (N) isotopes of two Mediterranean pine species (Pinus halepensis and P. pinea). Seedlings were grown in a Free-Air Controlled Exposure (FACE) experiment with three levels of O3 (ambient air, AA [38.7 ppb as daily average]; 1.5×AA; 2.0×AA) during the growing season (May to October, 2019). In P. halepensis, O3 caused a significant decrease in photosynthetic rate, which was mainly due to a reduction of both stomatal and mesophyll diffusion conductance to CO2. Isotopic analyses indicated a cumulative or memory effect of O3 exposure on this species, as the negative effects were highlighted only in the late growing season in associated with a reduced biochemical defense capacity. On the other hand, there was no clear effect of O3 on photosynthesis in P. pinea. However, this species showed an enhanced N allocation to leaves to compensate for reduced photosynthetic N use efficiency. We conclude that functional responses to O3 are different between the two species determining that P. halepensis with thin needles was relatively sensitive to O3 while P. pinea with thicker needles was more resistant due to a potentially low O3 load per unit mass of mesophyll cells, which may affect species-specific resilience in O3-polluted Mediterranean pine forests.

Allocation of Nutrients and Leaf Turnover Rate in Poplar under Ambient and Enriched Ozone Exposure and Soil Nutrient Manipulation

“…N is a constituent of amino acids, amides, proteins, nucleic acids, nucleotides, and coenzymes [39]. Our results confirmed that plants invest additional N to counteract the damage caused by elevated O 3 levels [40], although the increase was only in the leaves (e.g., +34.2 for 1.5 × AA and +23.7% for 2.0 × AA) and stems (e.g., +54.6% for 1.5 × AA and +48.5% for 2.0 × AA). As pointed out by Shang et al [41], alterations in N allocation in plant leaves in response to elevated O 3 can have significant ecological consequences, i.e., leaf litter decomposition.…”