Toward an impact assessment of ozone on plant carbon fixation using a process-based plant growth model: A case study of Fagus crenata grown under different soil nutrient levels

An assessment of ozone risk for date palm suggests that phytotoxic ozone dose nonlinearly affects carbon gain

Tropospheric ozone (O3) is a significant phytotoxic air pollutant that has a negative impact on plant carbon gain. Although date palm (Phoenix dactylifera L.) is a globally important crop in arid or semi-arid regions, so far O3 risk assessment for this species has not been reported. This study estimated leaf- and plant-level photosynthetic CO2 uptake for understanding how elevated levels of O3 affects date palm biomass growth. Ozone risks to date palm plants were assessed based on exposure- (AOT40) or flux-based indices (Phytotoxic Ozone Dose, PODy, where y is a threshold of uptake). For this purpose, plants were exposed to three levels of O3 [ambient air, AA (45 ppb as daily average); 1.5 × AA; 2.0 × AA] for 92 days in an O3 Free-Air Controlled Exposure facility. According to the model simulations, the negative effects of O3 on plant-level net photosynthetic CO2 uptake were attributed to reduced gross photosynthetic carbon gain and increased respiratory carbon loss. Season-long O3 exposure and elevated temperatures promoted the negative O3 effect because of a further increase of respiratory carbon loss, which was caused by increased leaf temperature due to stomatal closure. POD1 nonlinearly affected the photosynthetic CO2 uptake, which was closely related to the variation of dry mass increment during the experiment. Although the dose-response relationship suggested that a low O3 dose (POD1 < 5.2 mmol m-2) may even positively affect photosynthetic CO2 uptake in date palms, stomatal O3 uptake at the current ambient O3 levels has potentially a negative impact on date palm growth. The results indicate 5.8 mmol m-2 POD1 or 21.1 ppm h AOT40 as critical levels corresponding to a 4% reduction of net CO2 uptake for date palm, suggesting that this species can be identified as a species moderately sensitive to O3.

Nitrogen addition changed the relationships of fine root respiration and biomass with key physiological traits in ozone-stressed poplars

Increasing ozone (O₃) and nitrogen (N) addition may have contradictory effects on plant photosynthesis and growth. However, it remains unclear whether these effects on aboveground parts further change the root resource management strategy and the relationships of fine root respiration and biomass with other physiological traits. In this study, an open-top chamber experiment was conducted to investigate the effects of O₃ alone and in combination with nitrogen (N) addition on root production and fine root respiration of poplar clone 107 (Populus × euramericana cv. '74/76'). Saplings were grown with (100 kg ha^-1 year^-1) or without (+0 kg ha^-1 year^-1) N addition under two O₃ regimes (non-filtered ambient air or non-filtered ambient air + 60 ppb of O₃). After about two to three months of treatment, elevated O₃ significantly decreased fine root biomass and starch content but increased fine root respiration, which occurred in tandem with inhibited leaf light-saturated photosynthetic rate (A_sat). Nitrogen addition did not change fine root respiration or biomass, neither did it alter the effect of elevated O₃ on the fine root traits. However, N addition weakened the relationships of fine root respiration and biomass with A_sat, fine root starch and N concentrations. No significant relationships of fine root biomass and respiration with soil mineralized N were observed under elevated O₃ or N addition. These results imply that changed relationships of plant fine root traits under global changes should be considered into earth system process models to project more accurately future carbon cycle.

Exogenous Ca2+ priming can improve peanut photosynthetic carbon fixation and pod yield under early sowing scenarios in the field

Harnessing cold-resilient and calcium-enriched peanut production technology are crucial for high-yielding peanut cultivation in high-latitude areas. However, there is limited field data about how exogenous calcium (Ca²⁺) application would improve peanut growth resilience during exposure to chilling stress at early sowing (ES). To help address this problem, a two-year field study was conducted to assess the effects of exogenous foliar Ca²⁺ application on photosynthetic carbon fixation and pod yield in peanuts under different sowing scenarios. We measured plant growth indexes, leaf photosynthetic gas exchange, photosystems activities, and yield in peanuts. It was indicated that ES chilling stress at the peanut seedling stage led to the reduction of Pn, g_s, Tr, Ls, WUE, respectively, and the excessive accumulation of non-structural carbohydrates in leaves, which eventually induced a chilling-dependent feedback inhibition of photosynthesis due mainly to weaken growth/sink demand. While exogenous Ca²⁺ foliar application improved the export of nonstructural carbohydrates, and photosynthetic capacity, meanwhile activated cyclic electron flow, thereby enhancing growth and biomass accumulation in peanut seedlings undergoing ES chilling stress. Furthermore, ES combined with exogenous Ca²⁺ application can significantly enhance plant chilling resistance and peanut yield ultimately in the field. In summary, the above results demonstrated that exogenous foliar Ca²⁺ application restored the ES-linked feedback inhibition of photosynthesis, enhancing the growth/sink demand and the yield of peanuts.

Ozone modelling and mapping for risk assessment: An overview of different approaches for human and ecosystems health

Tropospheric ozone (O₃) is one of the most concernedair pollutants dueto its widespread impacts on land vegetated ecosystems and human health. Ozone is also the third greenhouse gas for radiative forcing. Consequently, it should be carefully and continuously monitored to estimate its potential adverse impacts especially inthose regions where concentrations are high. Continuous large-scale O₃ concentrations measurement is crucial but may be unfeasible because of economic and practical limitations; therefore, quantifying the real impact of O₃over large areas is currently an open challenge. Thus, one of the final objectives of O₃ modelling is to reproduce maps of continuous concentrations (both spatially and temporally) and risk assessment for human and ecosystem health. We here reviewedthe most relevant approaches used for O₃ modelling and mapping starting from the simplest geo-statistical approaches andincreasing in complexity up to simulations embedded into the global/regional circulation models and pro and cons of each mode are highlighted. The analysis showed that a simpler approach (mostly statistical models) is suitable for mappingO₃concentrationsat the local scale, where enough O₃concentration data are available. The associated error in mapping can be reduced by using more complex methodologies, based on co-variables. The models available at the regional or global level are used depending on the needed resolution and the domain where they are applied to. Increasing the resolution corresponds to an increase in the prediction but only up to a certain limit. However, with any approach, the ensemble models should be preferred.

Seed-borne fungal endophytes constrain reproductive success of host plants under ozone pollution

Tropospheric ozone is among the global change factors that pose a threat to plants and microorganisms. Symbiotic microorganisms can assist plants to cope with stress, but their role in the tolerance of plants to ozone is poorly understood. Here, we subjected endophyte-symbiotic and non-symbiotic plants of Lolium multiflorum, an annual species widely distributed in temperate grasslands, to high and low (i.e., charcoal-filtered air) ozone levels at vegetative and reproductive phases. Exposure to high ozone reduced leaf photochemical efficiency and greenness in both symbiotic and non-symbiotic plants. However, ozone-induced oxidative damage at biochemical level (i.e., lipid peroxidation) was mostly detected in symbiotic plants. Ozone exposure at the vegetative phase did not affect the reproductive investment in seeds, indicating full recovery from stress. Ozone exposure at the reproductive phase reduced biomass and seed production only in symbiotic plants indicating a symbiont-associated cost. At low ozone, endophyte-symbiotic plants showed a steeper slope in the relationship between seed number and seed weight (i.e., a number-weight trade-off) compared to non-symbiotic plants. However, when plants were treated at the reproductive phase, ozone increased the imbalance between seed number and seed weight in both endophyte-symbiotic and non-symbiotic plants. Plants with endophytes at the reproductive stage produced fewer seeds, which were not compensated by increased seed weight. Thus, fungal mycelium growing within ovaries or ozone-induced antioxidant systems may result in costs that finally depress the fitness of plants. Despite ozone pollution could destabilize plant-endophyte mutualisms and render them dysfunctional, other endophyte-mediated benefits (e.g., resistance to herbivory, tolerance to drought) could over-compensate these losses and explain the high incidence of the symbiosis in nature.