Quantifying determinants of ozone detoxification by apoplastic ascorbate in peach (Prunus persica) leaves using a model of ozone transport and reaction.

Ascorbate in leaf apoplast (ASCapo ) reacts with ozone (O3 ) and thereby reduces O3 flux reaching plasmalemma (Fpl ). Some studies have shown significant protection of cells from O3 by ASCapo , while others have questioned its efficacy. Hypothesizing that the protection by ASCapo depends on other variables, we quantified determinants of O3 detoxification with a model of O3 transport and reaction in apoplast. The model determines ascorbic acid concentration in apoplast (AAapo ) using measured values of O3 concentration (co ), leaf tissue ascorbic acid concentration (AAleaf ), cell wall thickness (L3 ), apoplastic pH (pHapo ), and stomatal conductance (Gsw ). We compared the measured and model-estimated AAapo in leaves of peach (Prunus persica) grown in open-top chambers under non-filtered air (NF) and elevated (EO3 : NF + 80 ppb) O3 concentrations. The estimated AAapo in individual leaves agreed well with the measured values (R2  = .91). Analyses of the simulation results yielded the following findings: (a) The efficacy of O3 reduction with ASCapo as quantified by fractional reduction (ϕ3 ) of O3 flux at the surface of plasmalemma (Fpl ) was lowered from 70% in NF to 40% in EO3 due to the reduction of L3 . The EO3 reduced AAapo , but the lower Gsw and L3 in EO3 increased AAapo resulting in no significant change in AAapo due to EO3 . ϕ3 can be calculated with measured values of AAapo and L3 , and Fpl can be estimated with the measurement-based ϕ3 . (b) When c0 is increased, Fpl increased curvilinearly with the increase of Fst : nominal O3 flux via stomatal diffusion, exhibiting apparent threshold on Fst . The deviation of Fpl from Fst became greater when L3 , pHapo , and AAleaf were increased. The quantification of ϕ3 and Fpl using leaf traits shall facilitate the understanding of the mechanisms of differential plant sensitivity to O3 and improve quantification of the O3 impacts on plants.

Ozone changes the linear relationship between photosynthesis and stomatal conductance and decreases water use efficiency in rice.

Ozone is an important air pollutant that affects growth, transpiration, and water use efficiency (WUE) in plants. Integrated models of photosynthesis (An) and stomatal conductance (Gs) (An-Gs) are useful tools to consistently assess the impacts of ozone on plant growth, transpiration, and WUE. However, there is no information on how to incorporate the influence of ozone into An-Gs integrated models for crops. We focused on the Ball-Woodrow-Berry (BWB) relationship, which is a key equation in An-Gs integrated models, and aimed to address the following questions: (i) how does ozone change the BWB relationship for crops?; (ii) are there any difference in the changes in the BWB relationship among cultivars?, and (iii) how do the changes in the BWB relationship increase or decrease WUE for crops? We grew four rice cultivars in a field under ambient or Free-Air Concentration Enrichment (FACE) of ozone in China and measured An and Gs using a portable photosynthesis analyzer. We simulated WUE in individual leaves during the ripening period under different BWB relationships. The results showed that ozone significantly changed the BWB relationship only for the most sensitive cultivar, which showed an increase in the intercept of the BWB relationship under FACE conditions. These results imply that changes in the BWB relationship are related to the ozone sensitivity of the cultivar. Simulations of an An-Gs integrated model showed that increases in the intercept of the BWB relationship from 0.01 to 0.1 mol(H2O) m-2 s-1 indicated decreases in WUE by 22%. Since a reduction in WUE indicates increases in water demand per unit of crop growth, air pollution from ozone could be a critical issue in regions where agricultural water is limited, such as in rainfed paddy fields.

Causes of variation among rice models in yield response to CO2 examined with Free-Air CO2 Enrichment and growth chamber experiments.

The CO2 fertilization effect is a major source of uncertainty in crop models for future yield forecasts, but coordinated efforts to determine the mechanisms of this uncertainty have been lacking. Here, we studied causes of uncertainty among 16 crop models in predicting rice yield in response to elevated [CO2] (E-[CO2]) by comparison to free-air CO2 enrichment (FACE) and chamber experiments. The model ensemble reproduced the experimental results well. However, yield prediction in response to E-[CO2] varied significantly among the rice models. The variation was not random: models that overestimated at one experiment simulated greater yield enhancements at the others. The variation was not associated with model structure or magnitude of photosynthetic response to E-[CO2] but was significantly associated with the predictions of leaf area. This suggests that modelled secondary effects of E-[CO2] on morphological development, primarily leaf area, are the sources of model uncertainty. Rice morphological development is conservative to carbon acquisition. Uncertainty will be reduced by incorporating this conservative nature of the morphological response to E-[CO2] into the models. Nitrogen levels, particularly under limited situations, make the prediction more uncertain. Improving models to account for [CO2] × N interactions is necessary to better evaluate management practices under climate change.

Adaptation pathways of global wheat production: Importance of strategic adaptation to climate change.

Agricultural adaptation is necessary to reduce the negative impacts of climate change on crop yields and to maintain food production. However, few studies have assessed the course of adaptation along with the progress of climate change in each of the current major food producing countries. Adaptation pathways, which describe the temporal sequences of adaptations, are helpful for illustrating the timing and intensity of the adaptation required. Here we present adaptation pathways in the current major wheat-producing countries, based on sequential introduction of the minimum adaptation measures necessary to maintain current wheat yields through the 21st century. We considered two adaptation options: (i) expanding irrigation infrastructure; and (ii) switching crop varieties and developing new heat-tolerant varieties. We find that the adaptation pathways differ markedly among the countries. The adaptation pathways are sensitive to both the climate model uncertainty and natural variability of the climate system, and the degree of sensitivity differs among countries. Finally, the negative impacts of climate change could be moderated by implementing adaptations steadily according to forecasts of the necessary future adaptations, as compared to missing the appropriate timing to implement adaptations.

Observational constraints indicate risk of drying in the Amazon basin.

Climate warming due to human activities will be accompanied by hydrological cycle changes. Economies, societies and ecosystems in South America are vulnerable to such water resource changes. Hence, water resource impact assessments for South America, and corresponding adaptation and mitigation policies, have attracted increased attention. However, substantial uncertainties remain in the current water resource assessments that are based on multiple coupled Atmosphere Ocean General Circulation models. This uncertainty varies from significant wetting to catastrophic drying. By applying a statistical method, we characterized the uncertainty and identified global-scale metrics for measuring the reliability of water resource assessments in South America. Here, we show that, although the ensemble mean assessment suggested wetting across most of South America, the observational constraints indicate a higher probability of drying in the Amazon basin. Thus, over-reliance on the consensus of models can lead to inappropriate decision making.