Photorespiration and drought-induced stomatal closure are two important physiological constraints that reduce carbon assimilation and productivity in C₃ forest trees under Mediterranean climatic conditions. Türkiye’s two dominant commercial pine species, Pinus brutia Ten. (Calabrian pine) and Pinus nigra J.F. Arnold subsp. pallasiana (Anatolian black pine), together cover approximately 8.15 million hectares. This study integrated published gas-exchange measurements, radiation-use efficiency estimates from MODIS, official forest inventory data, and dendrochronological growth records into a counterfactual accounting framework and propagated parameter uncertainty by Monte Carlo simulation (N = 40,000 draws). The two constraints jointly reduced weighted-mean net primary productivity (NPP) from a radiation-limited potential of 5.61 to an actual 3.46 Mg C ha⁻¹ yr⁻¹, a reduction of 37.9% (95% CI 32.2–43.4%). Decomposition shows that 47.7% of this loss is the obligate metabolic cost of C₃ carboxylation, which no silvicultural intervention can address, while 52.3%—20.1 of the 37.9 percentage points—is drought-attributable. Nationally, the deficit corresponds to 64.3 Mt CO₂ yr⁻¹ of forgone sequestration (47.8–81.2) and 34.4 Mm³ yr⁻¹ of forgone stemwood-volume equivalent (24.9–44.5), of which approximately 20.6 Mm³ would be merchantable, giving an annual economic deficit of USD 3.37 billion (2.40–6.48). Filtering the drought-attributable component for eligible area, recovery efficiency, additionality, leakage, and permanence yields approximately 1.0 Mt CO₂ yr⁻¹ of potentially issuable credits, fewer than two per cent of the headline figure. Eco-physiological suppression of this magnitude is currently invisible in national forest carbon accounting, and its recognition bears directly on dynamic baseline design and on the credibility of offsets generated from Mediterranean conifer forests.

Water availability is the primary environmental factor limiting plant establishment in arid and semi-arid ecosystems, and increasing drought-stress due to climate change is making forest restoration efforts in the Mediterranean basin increasingly critical. The Eastern Mediterranean region of Türkiye, particularly Kahramanmaraş Province, is characterized by increasingly severe drought stress resulting from low natural precipitation and rising temperatures under global warming. This study comparatively evaluates the ecophysiological responses of Ailanthus altissima (Mill.) Swingle and Crataegus orientalis Pall. ex M. Bieb., under adequate irrigation and drought-stress conditions. To determine plant water status, pre-dawn and midday leaf water potentials were measured, and leaf gas exchange was characterized by measuring net photosynthesis (A), stomatal conductance (gs), and transpiration rate (E); water-use efficiency (WUE) was then derived from these parameters as the ratio of net photosynthesis to transpiration (A/E). Both species sustained positive net photosynthesis under drought, although at rates significantly below those of the well-watered controls in the driest months, and both attained higher WUE than the controls in most months, with marked seasonal variation. However, significant differences in physiological adaptation strategies emerged between the species. Ailanthus altissima exhibited a water-saving strategy, restricting stomatal conductance to maintain a stable leaf water status, whereas Crataegus orientalis adopted a water-spending strategy, sustaining high leaf gas exchange while tolerating pronounced tissue dehydration. Modeling results, supported by spatial drought stress indices, have shown that both species have high adaptation potential in arid and semi-arid rehabilitation areas. The findings reveal that ecophysiological characteristics play a critical role in the selection of drought-tolerant woody species and provide a scientific basis for sustainable forest restoration under climate change.

Water availability is the primary environmental factor limiting plant settlement in arid and semi-arid ecosystems, and increasing drought stress due to climate change is making forest restoration efforts in the Mediterranean basin increasingly critical. The Eastern Mediterranean region of Turkey, particularly Kahramanmaraş Province, is characterized by increasingly severe drought stress resulting from low natural precipitation and rising temperatures under global warming. This study comparatively evaluates the ecophysiological responses of Ailanthus altissima (Mill.) Swingle and Crataegus orientalis Pall. ex M. Bieb. under adequate irrigation and drought-stress conditions. To determine plant water status, pre-dawn and midday leaf water potentials were measured; water use efficiency (WUE) was calculated using net photosynthesis rate, stomatal conductance, and transpiration parameters. Both species were able to maintain photosynthetic activity under drought conditions and showed higher WUE values compared to control conditions. However, significant differences in physiological adaptation strategies emerged between the species. Ailanthus altissima exhibited a water-spending strategy with rapid physiological adjustment, while Crataegus orientalis adopted a conservative water-saving strategy through pronounced stomatal regulation. Modeling results, supported by spatial drought stress indices, have shown that both species have high adaptation potential in arid and semi-arid rehabilitation areas. The findings reveal that ecophysiological characteristics play a critical role in the selection of drought-tolerant woody species and provide a scientific basis for sustainable forest restoration under climate change.

Afforestation assessments in Mediterranean karst regions often focus on vegetation and soil carbon, paying less attention to microbial activity. We examined the surface soil properties of a four-site Cedrus libani chronosequence in southern Turkey. In October 2024, topsoil (0–10 cm deep) was sampled at one degraded reference site and three plantation sites aged approximately 9, 14 and 24 years (15 samples were taken from each site). The afforested sites generally exhibited higher levels of soil organic carbon, total nitrogen, aggregate stability and microbial biomass carbon (MBC). Mean MBC ranged from 288 to 536 mg C kg⁻¹ at afforested sites versus 180 mg C kg⁻¹ at the reference site. Basal respiration was lower (0.30–0.36 versus 0.96 µg CO₂-C g⁻¹ h⁻¹), as was biomass-specific respiration (qCO₂: 0.54–1.39 versus 5.41 mg CO₂-C g⁻¹ MBC h⁻¹). The microbial quotient did not differ significantly. The pooled MBC–respiration association was weak, whereas the site-adjusted association was positive. Multivariate patterns and the non-monotonic ordering of sites highlighted edaphic heterogeneity. As plantation age was completely confounded with site identity, these single-campaign observations cannot establish causal temporal effects. Nevertheless, integrating structural, chemical and microbial indicators provides complementary information for characterizing soil conditions across these karst sites.

Photorespiration constrains net carbon gain in C3 plants by competing with carboxylation at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). Quantifying this flux requires kinetic models that accurately describe the CO2 and light dependence of assimilation across diverse species and temperatures. Here I perform a meta-analysis of published A-Cc and A-PAR curves from eleven species-temperature combinations spanning six crop species - Nicotiana tabacum, Glycine max, Triticum aestivum, Arabidopsis thaliana, Helianthus annuus and Gossypium hirsutum ̶ and three temperate forest tree species ̶ European beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), and silver birch (Betula pendula Roth) ̶ over a temperature range of 22-35°C. I fit the Farquhar-von Caemmerer-Berry (FvCB) model to each dataset using nonlinear least-squares optimization with Bernacchi temperature-response functions and extract maximum carboxylation rates (Vcmax), maximum electron transport rates (Jmax), day respiration (Rd), and CO2 compensation points (Γ*). Fitted Vcmax ranged from 137.5 to 244.4 µmol m⁻² s⁻¹ across all species, with forest species spanning the upper half of the range (178.6-244.4 µmol m⁻² s⁻¹) and silver birch showing the highest Vcmax of any species in the dataset, consistent with published reports for temperate broadleaf trees. Model fits were excellent across all A-Cc curves (R² = 0.957-0.994, RMSE = 0.65-2.44 µmol m⁻² s⁻¹) and satisfactory for A-PAR curves (R² = 0.80-0.97). Photorespiratory CO2 release (Rp) at pre-industrial CO2 (Cc ≈ 280 µbar) accounted for 18-26% of gross assimilation, and 14-21% at current ambient CO2 (Cc ≈ 420 µbar), with no systematic difference between crop and forest species at the same temperature, confirming that the Γ*/CcTo our knowledge, this is the first meta-analysis to apply a single, consistently parameterized FvCB framework to both crop and temperate forest tree species and to compare their photorespiratory flux on a common basis. Ratio rather than species identity is the primary determinant of photorespiratory fraction. These results validate the FvCB framework across a taxonomically diverse C3 species set and provide a consolidated parameterization for canopy-scale and Earth system modelling.

Türkiye holds the world's largest natural stands of Lebanon cedar (Cedrus libani A. Rich.) and extensive Crimean juniper forest (Juniperus excelsa M. Bieb.), together 884,361 ha of closed, drought-exposed forest. Both assimilate at needle water potentials near −3.0 MPa, yet lose some of their potential assimilation to photorespiration and stomatal closure under water deficit. A literature-parameterized scenario model relaxes both constraints against a radiation-limited ceiling. Zonal photorespiratory and stomatal input fractions of potential gross primary production (GPP) are 8%–16% and 14%–28%; after coupling, the model removes 13%–23% and 12%–23%. Together, these reduce weighted-mean net primary productivity from 3.29 to 2.14 Mg C ha⁻¹ yr⁻¹, a 34.9% reduction in potential GPP (Monte Carlo interval 31.7%–37.3%, conditional on the elicitation). Of that loss, 37%–45% is obligate photorespiration beyond management reach, depending on how the jointly caused interaction is assigned; the obligate share falls along the aridity gradient. Whether the loss becomes forgone wood is a separate question: radial growth in these species is confined to a narrow climatic window that does not coincide with peak assimilation. Under complete source control, the estate forgoes 1.5 million m³ and 3.7 million Mg CO₂ annually, worth US$ 0.21 billion; under complete sink control, none.