Water vapor pressure deficit in Portugal and implications for the development of the invasive African citrus psyllid trioza erytreae

African citrus psyllid (Trioza erytreae (Del Guercio)) is a vector insect of the bacterium Candidatus Liberibacter africanus, the putative causal agent of Huanglongbing, the most devastating citrus disease in the world. The insect was found on the island of Madeira in 1994 and in mainland Portugal in 2015. Present in the north and center of the country, it is a threat to Algarve, the main citrus-producing region. Trioza erytreae eggs and first instar nymphs are sensitive to the combination of high temperatures and low relative humidity. Daily maximum air temperature and minimum relative humidity data from 18 weather stations were used to calculate the water vapor pressure deficit (vpd) from 2004 to 2018 at various locations. Based on the mean vpd and the number of unfavorable days (vpd < 34.5 and vpd < 56 mbar) of two time periods (February to May and June to September), less favorable zones for T. erytreae were identified. The zones with thermal and water conditions like those observed in the Castelo Branco and Portalegre (Center), Beja (Alentejo), Alte, and Norinha (Algarve) stations showed climatic restrictions to the development of eggs and first instar nymphs of African citrus psyllid. Effective control measures, such as the introduction and mass release of Tamarixia dryi (Waterson), a specific parasitoid, and chemical control are necessary in favorable periods for T. erytreae development, such as in spring and in areas with limited or no climate restrictions.info:eu-repo/semantics/publishedVersio

Stomatal behavior of different grapevine cultivars in response to soil water status and air water vapor pressure deficit

Aims: Genetic variability in grapevine cultivars may influence their strategy to cope with drought through stomatal regulation of transpiration rate. The aim of the present study was to evaluate the stomatal sensitivity of five cultivars (Ekigaïna, Grenache, Marselan, Mourvèdre, and Syrah) to soil water status and air water vapor pressure deficit (VPD). Methods and results: Leaf gas exchange and canopy light interception efficiency (εi) were evaluated through a wide range of predawn leaf water potential (ΨPD) measurements in a field experiment in Southern France. Additionally, greenhouse experiments were carried out to monitor stomatal response to increasing VPD levels. Ekigaïna showed a strong isohydric behavior with the highest decrease in leaf gas exchange in response to soil water stress and VPD. Mourvèdre and Grenache showed a similar but relatively less extreme behavior. These three cultivars showed a constant leaf water status during the day through stomatal regulation and a strong decrease in εi. In contrast, Syrah and Marselan displayed anisohydric behavior as they presented a less sensitive stomatal control. Both cultivars showed fluctuating midday leaf water potential and Marselan was the least affected in terms of εi. Conclusion: This study demonstrated that grape cultivars differed in their stomatal response to soil water deficit and VPD. For a given cultivar, a similar stomatal behavior was found in response to both ΨPD and VPD. Significance and impact of the results: Adaptation to drought and viticulture viability in hot and dry environments could be achieved by identifying and breeding cultivars with drought tolerance traits.Objectifs : La variabilité génétique existante chez les cépages de vigne peut affecter leur stratégie d’adaptation à la sécheresse en régulant la transpiration au travers de la fermeture des stomates. L’objectif du travail a été d’évaluer la sensibilité des stomates de cinq cultivars (Ekigaïna, Grenache, Marselan, Mourvèdre et Syrah) à la disponibilité en eau du sol et au déficit de pression de vapeur (VPD). Méthodes et résultats : Les échanges gazeux des feuilles et l’efficience d’interception du rayonnement (ei) ont été évalués dans une large gamme des valeurs de potentiel hydrique de base (yPD) en conditions de terrain dans le Sud de la France. En outre, une expérimentation complémentaire en serre a été réalisée pour analyser la réponse des stomates face à une augmentation du VPD. L’Ekigaïna a présenté un caractère ioshydrique très marqué avec la plus grande diminution des échanges gazeux en réponse au déficit hydrique du sol et au VPD. Le Mourvèdre et le Grenache ont présenté un comportement similaire bien que moins extrême que l’Ekigaïna. Ces trois cultivars ont montré un potentiel hydrique foliaire constant pendant la journée à cause d’une forte régulation stomatique et une diminution de ei. Par contre, le Syrah et le Marselan, ont montré un comportement anisohydrique avec un control stomatique moins sensible. Les deux cultivars ont présenté une diminution du potentiel hydrique foliaire à midi tandis que le Marselan a été le moins affecté en termes de ei. Conclusions : La présente étude montre que les cultivars présentent des différences dans leur réponse au déficit hydrique du sol et au VPD. Pour un cultivar donné, un comportement stomatique similaire a été observé en réponse au yPD et au VPD. Impacts et signification des résultats : L’adaptation à la sécheresse et la viabilité de la viticulture sur de climats chauds et secs pourrait être atteint par la sélection de cultivars avec de caractères de tolérance.EEA MendozaFil: Prieto, Jorge Alejandro. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Mendoza; Argentina.Fil: Lebon, Eric. Institut National de la Recherche Agronomique. Unité Mixte de Recherche Montpellier; FranciaFil: Ojeda, Hernan. Institut National de la Recherche Agronomique. Unité expérimentale de Pech Rouge; Franci

Carbon exchange in a Caatinga area during an unusually drought year.

The objective of this study was to analyze the daily and seasonal variation of the carbon balance components in a caatinga area during an unusually drought year. Data were collected from a turbulent vortices covariance system installed at an area in Caatinga, in the region of Petrolina Municipality, State of Pernambuco, Brazil. Carbon dioxide flux data were collected in the year 2012, and the partitioning between gross primary productivity (GPP) and ecosystem respiration (Re). The vegetation cover index, weather elements and the soil water content were monitored. It was observed that the daily emissions of CO2 flux was dependent upon photosynthetically active radiation in the first days after rainfall events, being influenced by the water vapor pressure deficit with the reduction in the soil water content. The occurrence of up to 2 mm rainfall promoted peaks of Re after long periods of drought. The measured NEP was equal to 468.18 gC m-2 year-1. So, it is concluded that in years with severe drought, Caatinga may act as a source of carbon to the atmosphere

Hatching of Sod Webworm Eggs in Relation to Low and High Temperatures

Eggs of 12 species of sod webworm were exposed for various periods to temperatures of 0, 10, and 45°C. Hatchability was compared with control eggs kept at 25°C. Short exposures to any temperature did not significantly affect percent hatch. Prolonged exposure resulted in a significant decrease in hatchability for several species at 0° and for all species at 45°C. There was a significant difference in hatchability between the 3 generations of Crambus teterrellus (Zincken) and of Pediasia trisecta (Walker) at extreme temperatures. Populations of Agriphila ruricolella (Zeller), collected at 2 elevations, differed significantly in hatching percentage and developmental rate

Drought, mutualism breakdown, and landscape-scale degradation of seagrass beds

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Comparative measurements of carbon dioxide fluxes from two nearby towers in a central Amazonian rainforest: the Manaus LBA site

Forests around Manaus have staged the oldest and the longest forest-atmosphere CO2 exchange studies made anywhere in the Amazon. Since July 1999 the exchange of CO2, water, and energy, as well as weather variables, have been measured almost continuously over two forests, 11 km apart, in the Cuieiras reserve near Manaus, Brazil. This paper presents the sites and climatology of the region based upon the new data sets. The landscape consists of plateaus dissected by often waterlogged valleys, and the two sites differ in terms of the relative areas of those two landscape components represented in the tower footprints. The radiation and wind climate was similar to both towers. Generally, both the long-wave and short-wave radiation input was less in the wet than in the dry season. The energy balance closure was imperfect (on average 80%) in both towers, with little variation in energy partitioning between the wet and dry seasons; likely a result of anomalously high rainfall in the 1999 dry season. Fluxes of CO2 also showed little seasonal variation except for a slightly shorter daytime uptake duration and somewhat lower respiratory fluxes in the dry season. The net effect is one of lower daily net ecosystem exchange (NEE) in the dry season. The tower, which has less waterlogged valley areas in its footprint, measured a higher overall CO2 uptake rate. We found that on first sight, NEE is underestimated during calm nights, as was observed in many other tower sites before. However, a closer inspection of the diurnal variation of CO2 storage fluxes and NEE suggests that at least part of the nighttime deficits is recovered from either lateral influx of CO2 from valleys or outgassing of soil storage. Therefore there is a high uncertainty in the magnitude of nocturnal NEE, and consequently preliminary estimates of annual carbon uptake reflecting this range from 1 to 8 T ha-1 y-1, with an even higher upper range for the less waterlogged area. The high uptake rates are clearly unsustainable and call for further investigations into the integral carbon balance of Amazon landscapes

Comparison of two bidirectional atmosphere-surface exchange models for elemental mercury

This study compared two bidirectional atmosphere-surface exchange models by Wang et al. (2014) and Wright & Zhang (2015) for one monitoring site in the state of Georgia in the United States of evergreen needleleaf forest and deciduous broadleaf forest in summer and winter. Input data includes observed GEM concentrations and simulated meteorological data from June 2010 to September 2010 and from December 2010 to March 2011. For evergreen needleleaf forest in summer, the net emission flux estimated by Wang’s model was greater than that by Wright & Zhang’s (0.5 pg m-2s-1 vs. 0.18 pg m-2s-1). For deciduous broadleaf forest in summer, the net emission flux predicted by Wang’s model was smaller than that by Wright & Zhang’s (0.1 pg m-2s-1 vs. 0.29 pg m-2s-1). However, regardless of land cover in winter, the net flux produced by Wang’s model was emission flux (0.21 pg m-2s-1 for evergreen needleleaf forest and 0.18 pg m-2s-1 for deciduous broadleaf forest) while that simulated by Wright & Zhang’s model was deposition flux (0.59 pg m-2s-1 for evergreen needleleaf forest and 0.49 pg m-2s-1 for deciduous broadleaf forest). Additionally, stomata resistance, in-canopy aerodynamic resistance, stomata emission velocity, GEM compensation point concentration in stomata, GEM compensation point concentration in soil, stomata emission flux, soil emission flux, and net flux had large differences (≥100%) between the two models. The dominant factors resulting in these differences were identified. Wright & Zhang’s model is more appropriate for simulating GEM exchange flux in winter when a net deposition flux is expected

Calcium physiology of sweet cherry fruits

Key message: Xylem functionality is the primary determinant of the Ca relations of developing sweet cherry. Calcium influx is positively related to transpiration and decreases as xylem functionality is progressively lost during development. Abstract: Fruit calcium (Ca) may be associated with susceptibility to rain cracking in sweet cherry but little background information is available on the fruits’ Ca relations. The objectives of the study were to identify the key determinants of the Ca content in developing sweet cherry fruit. The masses of Ca and K in the flesh (mg per fruit) increased continuously through to maturity. However, their dry mass ratios [mg per g dry mass (DM)] decreased continuously. The decrease in Ca/dry mass ratio was to about 30% of the transition stage II/III value, and for K to about 55%. These decreases occurred in all cultivars investigated. Moreover, the Ca mass per fruit and the Ca/dry mass ratio were normally distributed and wide ranging; the maximum recorded values were about twice the minimum ones. Within a fruit, the Ca/dry mass ratio was two to three times higher in the stem end than in the stylar scar end. Fruit held under low relative humidity (26.2%) contained more Ca per fruit and had a higher Ca/dry mass ratio compared with fruit held under high humidity (91.6%). There was a positive relationship between Ca mass per fruit and cumulative transpiration. Our results indicate xylem functionality is the primary determinant of the Ca relations of sweet cherry fruit. © 2020, The Author(s)

Light stress-induced chloroplast movement and midday depression of photosynthesis in sorghum leaves

Plants are exposed to high light intensity, high leaf temperatures and high air-to-leaf water vapor pressure deficit (ALVPD) during the day. These environmental stresses cause stomatal closure and photoinhibitory damage, leading to midday depression of photosynthesis. Chloroplast positioning is essential for the efficient operation of photosynthesis. However, chloroplast behavior before, during, and even after the midday depression of photosynthesis remains unknown. We investigated changes in the intracellular positioning of chloroplasts and photosynthetic traits under a diurnal pattern of light. Sorghum leaves were exposed to a 12-h regime of light mimicking the natural light environment, with constant leaf temperature and ALVPD. Net photosynthetic rate (Pn) showed a diurnal pattern, and midday depression in Pn was observed at 3.8 h of irradiation. Depression in Pn was attributed to stomatal limitation because the decrease in Pn was in accordance with the decrease in stomatal conductance. The maximum efficiency of photosystem II decreased with the increase in light intensity and remained low after 12 h of irradiation. Bundle sheath chloroplasts swelled after 8 h of irradiation, representing the accumulation of starch. Conversely, mesophyll chloroplasts exhibited avoidance response after 4 h of irradiation, and the avoidance position was maintained during the remainder of the daytime. These data suggest that chloroplasts are subject to light stress during and after the midday depression of photosynthesis. The intensity of natural light is excessive for most of the day and this light stress induces chloroplast avoidance response and depression of photosynthesis