A dose-response relationship for marketable yield reduction of two lettuce (Lactuca sativa L.) cultivars exposed to tropospheric ozone in Southern Europe

From kitchen to crop: The efficacy and safety of the microbial consortium treated dishwasher wastewater for the Zero Mile system

A microbial consortium, based on the functional integration of photosynthetic and heterotrophic microorganisms, is the core of the Zero Mile System. This system is designed for reusing and upcycling household greywaters, a still untapped water resource. The previous challenges of dishwasher wastewater bioremediation demonstrated the capability of an ad hoc consortium (including a photosynthetic cyanobacterium and three heterotrophic bacterial isolates from dishwasher wastewater) to reclaim the wastewater at small/medium scale. In this study the wastewater treatment demonstrated to be effective in nutrient recycling and upcycling at a larger scale, i.e. 4 L (in three replicates to treat the total amount of wastewater discharged by the dishwasher), by removing high percentage of N and P from the wastewater (70% nitrogen, 50% phosphorous, respectively). Again, the reclaimed wastewater successfully fertilized lettuce plants both indoor (in the Zero Mile System demonstrator) and outdoor (in open field). Plants showed a significant higher biomass productivity in fresh weight compared to control plants and comparable or better values of the pigments and quality indices (e.g., soluble solids, total phenols, total flavonoids). Furthermore, the safety of the reclaimed wastewater is demonstrated by the analysis of the metabolic/ecologically relevant functions of the microbial communities in both untreated and treated wastewater. Colonizers were mainly organic matter degraders and bacteria involved in nitrogen cycling. The human related genera are quite few and no pathogens or potential microbiological contaminants of water bodies (as E. coli), were found. Hence, the utilization of treated dishwasher wastewater does not imply biological risks to agricultural products, soil, or groundwater.

Novel ozone flux metrics incorporating the detoxification process in the apoplast: An application to Chinese winter wheat

A modified Ball-Berry-Leuning model of stomatal conductance was applied to data from fully open-air ozone (O₃)-enrichment experiments with winter wheat (Triticum aestivum L.). The O₃ fluxes reaching both surface of cell wall (F_cw) and plasmalemma (F_pl) were estimated considering apoplastic ascorbate, a major scavenger of O₃. The difference (D) between F_cw and F_pl was defined as detoxification capacity of O₃ by reaction with ascorbate in the leaf apoplast (ASC_apo). The accumulated stomatal O₃ flux above D nmol O₃ m^-2 s^-1 (AF_stD) and the accumulated F_pl (AF_pl) were calculated over the optimal integration period covering the whole reproductive development of wheat, and used to derive O₃AF_stD yield-response relationships in comparison with POD_Y (phytotoxic O₃ dose above a threshold of Y nmol m^-2 s^-1) and AOT40 (accumulated O₃ dose over a threshold of 40 ppb). There was a good agreement between the observed and modeled values of ASC_apo and stomatal conductance. AF_stD and AF_pl performed better than POD_Y and AOT40 in terms of R² and intercept. However, the AF_stD metric was more suitable for assessing grain yield loss due to lower sensitivity of the regression slope to variations in the input parameters, compared with AF_pl. The average critical level (CL) of four cultivars for 5% grain-yield reduction was 1.53 mmol m^-2 using POD₆ and 2.81 mmol m^-2 using AF_stD, with the latter being well above the POD₆-derived value for European cultivars (1.3 mmol m^-2). The minimum hourly averaged O₃ concentration contributed to CLs was below 20 ppb according to AF_stD, a value that is lower than that suggested by POD₆ (≈27 ppb). O₃ flux-response relationships and CLs on the basis of quantified detoxification capacity shall facilitate the understanding of the different degrees of susceptibility to O₃ among species or cultivars, and improve the assessments of O₃ impacts on plants.

Ozone Response of Leaf Physiological and Stomatal Characteristics in Brassica juncea L. at Supraoptimal Temperatures

Plants are affected by the features of their surrounding environment, such as climate change and air pollution caused by anthropogenic activities. In particular, agricultural production is highly sensitive to environmental characteristics. Since no environmental factor is independent, the interactive effects of these factors on plants are essential for agricultural production. In this context, the interactive effects of ozone (O3) and supraoptimal temperatures remain unclear. Here, we investigated the physiological and stomatal characteristics of leaf mustard (Brassica juncea L.) in the presence of charcoal-filtered (target concentration, 10 ppb) and elevated (target concentration, 120 ppb) O3 concentrations and/or optimal (22/20 °C day/night) and supraoptimal temperatures (27/25 °C). Regarding physiological characteristics, the maximum rate of electron transport and triose phosphate use significantly decreased in the presence of elevated O3 at a supraoptimal temperature (OT conditions) compared with those in the presence of elevated O3 at an optimal temperature (O conditions). Total chlorophyll content was also significantly affected by supraoptimal temperature and elevated O3. The chlorophyll a/b ratio significantly reduced under OT conditions compared to C condition at 7 days after the beginning of exposure (DAE). Regarding stomatal characteristics, there was no significant difference in stomatal pore area between O and OT conditions, but stomatal density under OT conditions was significantly increased compared with that under O conditions. At 14 DAE, the levels of superoxide (O2-), which is a reactive oxygen species, were significantly increased under OT conditions compared with those under O conditions. Furthermore, leaf weight was significantly reduced under OT conditions compared with that under O conditions. Collectively, these results indicate that temperature is a key driver of the O3 response of B. juncea via changes in leaf physiological and stomatal characteristics.

Ozone exposure- and flux-yield response relationships for maize

A stomatal ozone (O₃) flux-response relationship for relative yield of maize was established by parameterizing a Jarvis stomatal conductance model. For the function (f_VPD) describing the limitation of stomatal conductance by vapor pressure deficit (VPD, kPa), cumulative VPD during daylight hours was superior to hourly VPD. The latter function is proposed as a methodological improvement of this multiplicative model when stomatal conductance peaks during the morning and it is reduced later as it is the case of maize in this experiment. The model agreed relatively well with the measured stomatal conductance (R² = 0.63). Based on the comparison of R² values of the response functions, POD₆ (Phytotoxic Ozone Dose over an hourly threshold 6 nmol m^-2 s^-1) and AOT40 (accumulated hourly O₃ concentrations over a threshold of 40 ppb) performed similarly. The critical levels based on POD₆ and AOT40 for 5% reduction in maize yield were 1.17 mmol m^-2 PLA and 8.70 ppm h, respectively. In comparison with other important crops, the ranking of sensitivity of maize strongly differed depending on the O₃ metric used, AOT40 or POD₆. The newly proposed response functions are relevant for O₃ risk assessment for this crop in Asia.

Interactive effects of changing stratospheric ozone and climate on tropospheric composition and air quality, and the consequences for human and ecosystem health

The composition of the air we breathe is determined by emissions, weather, and photochemical transformations induced by solar UV radiation. Photochemical reactions of many emitted chemical compounds can generate important (secondary) pollutants including ground-level ozone (O₃) and some particulate matter, known to be detrimental to human health and ecosystems. Poor air quality is the major environmental cause of premature deaths globally, and even a small decrease in air quality can translate into a large increase in the number of deaths. In many regions of the globe, changes in emissions of pollutants have caused significant changes in air quality. Short-term variability in the weather as well as long-term climatic trends can affect ground-level pollution through several mechanisms. These include large-scale changes in the transport of O₃ from the stratosphere to the troposphere, winds, clouds, and patterns of precipitation. Long-term trends in UV radiation, particularly related to the depletion and recovery of stratospheric ozone, are also expected to result in changes in air quality as well as the self-cleaning capacity of the global atmosphere. The increased use of substitutes for ozone-depleting substances, in response to the Montreal Protocol, does not currently pose a significant risk to the environment. This includes both the direct emissions of substitutes during use and their atmospheric degradation products (e.g. trifluoroacetic acid, TFA).