Global diurnal and nocturnal parameters of stomatal conductance in woody plants and major crops

Altres ajuts: LIFE+ project FO3REST, Grant/Award Number: LIFE10 ENV/FR/208; LIFE+ project MOTTLES, Grant/Award Number: LIFE15 ENV/IT/000183Aim: stomata regulate CO₂ uptake, water-vapour loss and uptake of gaseous pollutants. Jarvis-type models that apply multiple-constraint functions are commonly used to estimate stomatal conductance (gs), but most parameters for plant functional types (PFTs) have been estimated using limited information. We refined the data set of key components of the gs response to environmental factors in global PFTs. - Location: global. - Time period: data published in 1973-2015. - Major taxa studied: woody plants and major crops (rice, wheat and maize). - Methods: we reviewed 235 publications of field-observed gs for the parameterization of Jarvis-type models in global PFTs. The relationships between stomatal parameters and climatic factors [mean annual air temperature (MAT) and mean annual precipitation (MAP)] were assessed. - Results: we found that maximal stomatal conductance (gmax) in global woody plants was correlated with MAP rather than with MAT. The gmax of woody plants on average increased from 0.18 to 0.26 mol/m²/s with an increase in MAP from 0 to 2,000 mm. Models, however, can use a single gmax across major crops (0.44 mol/m²/s). We propose similar stomatal responses to light for C₃ crops and woody plants, but C₄ crops should use a higher light saturation point of gs. Stomatal sensitivity to vapour-pressure deficit (VPD) was similar across forest PFTs and crops, although desert shrubs had a relatively low sensitivity of stomata to VPD. The optimal temperature for gs increased by 1 °C for every 3.0 °C of MAT. Stomatal sensitivity to predawn water potential was reduced in hot and dry climate. The fraction of nighttime conductance to gmax (0.14 for forest trees, 0.28 for desert shrubs and 0.13 for crops) should be incorporated into the models. - Main conclusions: this analysis of global gs data provides a new summary of gs responses and will contribute to modelling studies for plant-atmosphere gas exchange and land-surface energy partitioning

Morpho-Physiological Responses of Three Italian Olive Tree (Olea europaea L.) Cultivars to Drought Stress

Water scarcity in agriculture can limit crop production and trigger the need for more effective water resource management. As a result, it is critical to identify new crop genotypes that are more drought tolerant and perform better under low irrigation or even rain-fed conditions. The olive tree is a high-value crop that is well adapted to dry Mediterranean conditions. However, different genotypes may have developed different mechanisms of tolerance to water stress. To investigate such mechanisms, we examined three Italian olive cultivars (‘Giarraffa’, ‘Leccino’, and ‘Maurino’) grown in a greenhouse under drought stress. We found that single genotypes responded differently to the drought, though not all parameters revealed significant differences. The first major difference among the cultivars was in transpiration: the lower stomatal density and stomatal conductance of ‘Giarraffa’ allow this cultivar to use water more conservatively. In parallel with the reduction in stomatal and mesophyll conductance, the drought-stressed group of ‘Giarraffa’ maintained the electron transport rate and effective efficiency levels of photosystem II similar to those of the control until the fourth week of stress. The fluorescence parameters revealed the earlier closure of reaction photosynthetic centres in ‘Leccino’. Finally, the higher rate of electrolyte leakage in ‘Maurino’ indicated a significant ions loss in this cultivar when it was subjected to the drought. Both water management under stress conditions and the effect of drought on photosynthesis make ‘Giarraffa’ interesting to researchers studying its use in breeding or water-saving programmes

Economic and Life Cycle Analysis of Passive and Active Monitoring of Ozone for Forest Protection

At forest sites, phytotoxic tropospheric ozone (O3) can be monitored with continuously operating, active monitors (AM) or passive, cumulative samplers (PM). For the first time, we present evidence that the sustainability of active monitoring is better than that of passive sensors, as the environmental, economic, and social costs are usually lower in the former than in the latter. By using data collected in the field, environmental, social, and economic costs were analyzed. The study considered monitoring sites at three distances from a control station in Italy (30, 400, and 750 km), two forest types (deciduous and Mediterranean evergreen), and three time windows (5, 10, and 20 years of monitoring). AM resulted in more convenience than PM, even after 5 years, in terms of O3 depletion, global warming, and photochemical O3 creation potential, suggesting that passive monitoring of ozone is not environmentally sustainable, especially for long time periods. AM led to savings ranging from a minimum of EUR 9650 in 5 years up to EUR 94,796 in 20 years in evergreen forests. The resulting social cost of PM was always higher than that of AM. The present evaluation will help in the decision process for the set-up of long-term forest monitoring sites dedicated to the protection of forests from O3

Strategic roadmap to assess forest vulnerability under air pollution and climate change

Although it is an integral part of global change, most of the research addressing the effects of climate change on forests have overlooked the role of environmental pollution. Similarly, most studies investigating the effects of air pollutants on forests have generally neglected the impacts of climate change. We review the current knowledge on combined air pollution and climate change effects on global forest ecosystems and identify several key research priorities as a roadmap for the future. Specifically, we recommend (1) the establishment of much denser array of monitoring sites, particularly in the South Hemisphere; (2) further integration of ground and satellite monitoring; (3) generation of flux-based standards and critical levels taking into account the sensitivity of dominant forest tree species; (4) long-term monitoring of N, S, P cycles and base cations deposition together at global scale; (5) intensification of experimental studies, addressing the combined effects of different abiotic factors on forests by assuring a better representation of taxonomic and functional diversity across the similar to 73,000 tree species on Earth; (6) more experimental focus on phenomics and genomics; (7) improved knowledge on key processes regulating the dynamics of radionuclides in forest systems; and (8) development of models integrating air pollution and climate change data from long-term monitoring programs.</p

Photosynthetic responses of Monarch birch seedlings to differing timings of free air ozone fumigation

To study the effects of different periods of ozone (O-3) fumigation on photosynthesis in leaves of the Monarch birch (Betula maximowicziana), we undertook free air O-3 fumigation to Monarch birch seedlings at a concentration of 60 nmol mol(-1) during daytime. Plants were exposed to O-3 at early, late or both periods in the growing season. The light-saturated net photosynthetic rate (A (sat)) in July and August was reduced by O-3 exposure through a reduction in the maximum rate of carboxylation (V (c,max)). In early September, on the other hand, despite a reduction in V (c,max), A (sat) was not reduced by O-3 due to a counteracting increase in the stomatal conductance. Through the experiment, there was no difference in sensitivity to O-3 between maturing and matured leaves. We analyzed the relationship between A (sat), V (c,max) and accumulated stomatal O-3 flux (AF(st)). Whereas V (c,max) decreased with increasing AF(st), the correlation between A (sat) and AF(st) was weak because the response of stomatal conductance to O-3 was affected by season. We conclude photosynthetic response of Monarch birch to O-3 exposure changes with season. This is due to the inconstant stomatal response to O-3 but not due to the respose of biochemical assimilation capacity in chloroplasts

Ecophysiological Responses of Northern Birch Forests to the Changing Atmospheric CO2and O3Concentrations

ABSTRACT:The effects on birch (Betula spp.) of elevated carbon dioxide (CO2) and ozone (O3), which are both increasing in the troposphere, are surveyed in detail based on the literature. Birches establish themselves in the open field after disturbances, and then become dominant trees in temperate or boreal forests. Ecophysiological approaches include the measurement of photosynthesis, biomass, growth, and survival of seedlings and trees. Elevated CO2 levels give rise to a net enhancement of the growth of birch trees, whereas high O3 generally reduces growth. Although the effects of the two are opposed, there is also an interactive effect. Basic physiological responses of the single genus Betula to CO2 and O3 are set out, and some data are summarized regarding ecological interactions between trees, or between trees and other organisms

Ozone-induced stomatal sluggishness develops progressively in Siebold's beech (Fagus crenata)

We investigated the effects of ozone and leaf senescence on steady-state stomatal conductance and stomatal response to light variation. Measurements were carried out in a free-air ozone exposure experiment on a representative deciduous broadleaved tree species in Japan (Fagus crenata). Both steady-state and dynamic stomatal response to light variation varied intrinsically with season due to leaf senescence. Ozone induced the decrease in steady-state leaf gas exchange and the sluggish stomatal closure progressively. These findings suggest that ozone reduces the ability of plants to adapt to a fluctuating light environment under natural conditions, and therefore impairs plant growth and ability to control water loss

Interactive effect of leaf age and ozone on mesophyll conductance in Siebold's beech

Mesophyll conductance (G(m)) is one of the most important factors determining photosynthesis. Tropospheric ozone (O-3) is known to accelerate leaf senescence and causes a decline of photosynthetic activity in leaves. However, the effects of age-related variation of O-3 on G(m) have not been well investigated, and we, therefore, analysed leaf gas exchange data in a free-air O-3 exposure experiment on Siebold's beech with two levels (ambient and elevated O-3: 28 and 62 nmol mol(-1) as daylight average, respectively). In addition, we examined whether O-3-induced changes on leaf morphology (leaf mass per area, leaf density and leaf thickness) may affect CO2 diffusion inside leaves. We found that O-3 damaged the photosynthetic biochemistry progressively during the growing season. The G(m) was associated with a reduced photosynthesis in O-3-fumigated Siebold's beech in August. The O-3-induced reduction of G(m) was negatively correlated with leaf density, which was increased by elevated O-3, suggesting that the reduction of G(m) was accompanied by changes in the physical structure of mesophyll cells. On the other hand, in October, the O-3-induced decrease of G(m) was diminished because G(m) decreased due to leaf senescence regardless of O-3 treatment. The reduction of photosynthesis in senescent leaves after O-3 exposure was mainly due to a decrease of maximum carboxylation rate (V-cmax) and/or maximum electron transport rate (J(max)) rather than diffusive limitations to CO2 transport such as G(m). A leaf agexO(3) interaction of photosynthetic response will be a key for modelling photosynthesis in O-3-polluted environments

Effects of ozone-induced stomatal closure on ozone uptake and its changes due to leaf age in sun and shade leaves of Siebold's beech

An estimation of stomatal ozone uptake for the assessment of ozone risks in forest trees can be modified by ozone-induced stomatal closure. We thus examined a seasonal course of stomatal conductance in sun and shade leaves of Siebold's beech native to northern Japan (Fagus crenata) grown under free-air ozone exposure. A performance of multiplicative stomatal conductance model was also tested, when considering ozone-induced stomatal closure into the model. Ozone caused stomatal closure in both sun and shade leaves (20% and 30-40% reduction of stomatal conductance in sun and shade leaves, respectively) during early summer. However, in autumn, stomatal closure was diminished regardless of canopy positions (approximately 7% and 6% reduction of stomatal conductance in sun and shade leaves, respectively). When observed seasonal course of stomatal closure was taken into account in stomatal conductance model, the model provided a good agreement with measurements even under conditions of elevated ozone. As a result, ozone-induced stomatal closure limited stomatal ozone uptake by 11% and 17% in sun and shade leaves of Siebold's beech, respectively. In addition, stomatal ozone uptake in shade leaves under elevated ozone was much less than that in sun leaves (35% of the value in sun leaves), indicating better avoidance of ozone stress in shade leaves. Our results suggest that a loss of ozone-induced stomatal closure after ozone exposure in the late growing season should be considered in modeling stomatal ozone uptake for the assessment of ozone impacts on Siebold's beech

Modeling of Stomatal Conductance for Estimating Ozone Uptake of Fagus crenata Under Experimentally Enhanced Free-air Ozone Exposure

We examined a performance of the multiplicative stomatal conductance model to estimate the stomatal ozone uptake for Fagus crenata. Parameterization of the model was carried out by in-situ measurements in a free-air ozone exposure experiment. The model performed fairly well under ambient conditions, with low ozone concentration. However, the model overestimated stomatal conductance under enhanced ozone condition due to ozone-induced stomatal closure. A revised model that included a parameter representing ozone-induced stomatal closure showed better estimation of ozone uptake. Neglecting ozone-induced stomatal closure induced a 20 % overestimation of the stomatal uptake of ozone. The ozone-induced stomatal closure was closely related to stomatal ozone uptake, rather than AOT40 (accumulated concentrations of ozone exceeding 40 nmol mol^[-1]). Our results suggest that ozone-induced stomatal closure should be implemented to stomatal conductance model for estimating ozone uptake for F. crenata and the implementation will contribute to adequate risk assessments of ozone impacts on F. crenata forests in Japan