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Introduction. Optimising agricultural water use implies the combination of physiological, technological and engineering techniques, especially those for continuously monitoring the water status of plants subjected to deficit irrigation. A methodology to estimate water stress of young almond trees from thermal images was developed based on assessing the physiological status of almond crops under limited water-supply conditions. Materials and methods. Two irrigation treatments were tested during the maximum evapotranspirative demand period (214th to the 243rd day of the year) in an experimental almond [Prunus dulcis (Mill) D.A. Webb, cv. Guara] orchard: a low-frequency deficit irrigation (LFDI) treatment, irrigated according to the plant-water status, and a fully irrigated treatment (C100) at 100% of crop evapotranspiration. Daily canopy temperature at midday (TC) was measured with an infrared camera, together with standard measurements of stem-water potential (ΨStem) and stomatal conductance (gS). The time course of these parameters and their relationships were analysed. Results and discussion. The time course of the parameters studied showed highly significant correlations among the differentials of canopy-air temperature (ΔT), ΨStem and gS. The methodological protocol for analysing thermal images allowed a time saving in processing information and additionally offered the possibility of estimating the ΨStem and gS values. Conclusion. Our results confirm that infrared thermography is a suitable technique for assessing the crop-water status and can be used as an important step towards automated plant-water stress management in almond orchards. Introduction. Optimiser l’utilisation de l’eau en agriculture implique de combiner des techniques physiologiques, technologiques et d’ingénierie, en particulier celles qui permettent de surveiller en permanence l’état hydrique de plantes soumises à un déficit d’irrigation. Une méthodologie pour estimer le stress hydrique de jeunes amandiers à partir d’images thermiques a été développée sur la base de l’évaluation de l’état physiologique d’arbres placés en conditions d’alimentation en eau limitée. Matériel et méthodes. Deux traitements d’irrigation ont été testés au cours de la période de demande evapotranspirative maximale (214e au 243e jour de l’année) dans un dispositif expérimental en verger d’amandiers [Prunus dulcis (Mill.) D.A. Webb., cv. Guara] : un traitement avec une irrigation déficitaire à basse fréquence (LFDI), irrigué en fonction du statut hydrique des plants, et un traitement irrigué à 100 % de l’évapotranspiration des cultures (C100). La température quotidienne du couvert à midi (TC) a été mesurée à l’aide d’une caméra infrarouge, ainsi que des mesures standards du potentiel hydrique de la tige (ΨStem) et de la conductance stomatique (gS). L’évolution dans le temps de ces paramètres et leurs relations ont été analysées. Résultats et discussion. L’évolution dans le temps des paramètres mesurés et leurs relations ont mis en évidence des corrélations hautement significatives entre la différence de température canopie-air (ΔT), et les paramètres ΨStem, et gS. Le protocole méthodologique pour l’analyse des images thermiques a permis un gain de temps pour le traitement de l’information et a offert en plus la possibilité d’estimer les valeurs de ΨStem et de gS. Conclusion. Nos résultats confirment que la thermographie infrarouge est une technique appropriée pour l’évaluation de l’état hydrique des cultures et qu’elle peut être utilisée comme une technique adaptée à la gestion automatisée du stress hydrique des plants en vergers d’amandiers. Introducción. La optimización del uso del agua en la agricultura implica la combinación de técnicas fisiológicas, tecnológicas y de ingeniería, especialmente aquellas que permiten establecer un seguimiento en continuo del estado hídrico de plantas sometidas a riego deficitario. La metodología para estimar el estrés hídrico mediante el análisis de imágenes térmicas fue desarrollada a partir del seguimiento del estado fisiológico de un cultivo de almendros jóvenes bajo condiciones de aportes limitados de agua. Material y métodos. Se definieron dos tratamientos de riego durante el período de máxima demanda evapotranspirativa (214-243 día del año), en una parcela experimental de almendros [Prunus dulcis (Mill.) DA Webb., cv. Guara]: un tratamiento de riego deficitario de baja frecuencia (RDBF), que recibió dotaciones hídricas en función del estado hídrico del cultivo; y un tratamiento control (C100) que recibió el 100% de la demanda evapotranspirativa. Se realizaron medidas periódicas de la temperatura de la cubierta vegetal (TC) mediante una cámara de infrarrojos, junto con otras medidas tradicionalmente más usadas como son el potencial hídrico del tallo (ΨStem) y la conductancia estomática (gS). Se analizó la evolución temporal de los parámetros establecidos, así como las relaciones existentes entre ellos. Resultados y discusión. Se encontraron correlaciones altamente significativas en la evolución temporal de los parámetros estudiados. Por otra parte, la metodología empleada para al análisis y procesamiento de las imágenes térmicas permitió un ahorro importante de tiempo, ofreciéndonos además la posibilidad de realizar estimaciones significativas del potencial hídrico y la conductancia estomática. Conclusión. Los resultados obtenidos confirman que la termografía de infrarrojos es una técnica adecuada para evaluar el estado hídrico de los cultivos, y puede suponer un importante avance en la automatización del seguimiento del mismo en el cultivo de almendros.

Boosting the water productivity of world agriculture will be crucial in meeting the food needs in the future. Scientific research has led to improvements in agricultural productivity, but water constraints remain a problem.

We propose and test a classification of plant functional types for tropical trees based on demography, growth form, phenology, and moisture requirements, using data from a 50-ha forest dynamics plot in Panama. Correlations among demographic variables for individual species - mortality, growth, and the tendency to colonize light gaps - were strong, and a single principal component (PC) accounted for a large fraction of the demographic variability. Most species - shade-tolerants - were clustered at the low end of the PC axis (low growth, low mortality), while the rest were continuously distributed over a wide range. Three demographic guilds could be defined from scores on this axis: we call these pioneer, building phase, and shade-tolerant trees, following earlier terminology. Leaf lifetime correlated negatively with the demographic axis, and there was a weak relationship between demography and moisture-preference: no species with high demographic scores also had high moisture requirements. There was no significant relationship between deciduousness and the demographic axis, but deciduousness was negatively correlated with leaf lifetime and moisture index. Altogether, 11 different combinations of demographic variables, deciduousness, moisture needs, and growth form (canopy vs. understory species) were identified. We evaluated how these functional types changed in abundance between 1982 and 1995. Because of a recent run of dry years and long dry seasons, we predicted that deciduous species, canopy species, pioneers, and drought-tolerant species would be increasing at the expense of their counterparts. Only one aspect of this prediction was borne out: moisture-demanding species declined sharply in abundance relative to drought-tolerant species. Neither deciduousness nor growth form was associated with population change, and pioneer species declined in abundance more often than shade-tolerants. The overall structure of the forest - the density of deciduous, pioneer, and understory species - did not change much, but the decline of the moisture-demanding guild indicates that a change in composition is preceding a structural change.

Introduction. Plant water stress indicators have become valuable for moving towards deficit irrigation strategies and saving water. In this case evapotranspiration (ET) is below its maximum value for the crop and stage (ETc), and a stress coefficient (Ks) is applied to obtain actual ET (ETa). Predawn leaf water potential (Yp) can be related to relative transpiration (RT), the ratio between transpiration of a stressed plot (T) and transpiration of a well-irrigated plot (Tm). Estimating RT from Yp allows calculating ETa for determination of irrigation amounts, if deficit irrigation practices are used, as RT corresponds approximately to Ks. Materials and methods. RT and Yp were measured with the aim of establishing a relationship to estimate RT under moderate water stress for irrigation scheduling, in a peach orchard in south Portugal. RT was calculated using sap flow measurements (heat balance method) in two plots, one well-irrigated (daily drip irrigation amounts calculated for Tm) and another temporarily without irrigation. Results and discussion. A high correlation was found between RT and Yp, allowing the estimation of RT for the studied conditions. Significant differences regarding the relationship RT-Y p obtained for another peach orchard in the same region and similar soil conditions were found for Yp in the range between –0.11 and –0.45 MPa. The results suggest that the differences resulted from the different irrigation systems: drip and micro-sprinkling, as they determine different temporal and spatial water distribution and therefore different geometry of root systems. A formerly proposed equation to estimate RT from Yp with a general form for different fruit tree species was tested, proving to be adequate within some limits: when RT is lowered to 0.7, the error was below 9%. The threshold value RT = 0.7 was considered a minimum as it was successfully tested in deficit irrigation practices for peach orchards. Introduction. Les indicateurs du stress hydrique végétal sont devenus précieux pour conduire des stratégies d’irrigation en cas de déficit et économiser l’eau. Dans ce cas, l’évapotranspiration (ET) est inférieure à sa valeur maximale pour la culture et pour le stade (ETc), et un coefficient de contrainte (Ks) s’applique pour obtenir la valeur réelle de ET (ETr). Le potentiel hydrique foliaire de base (Yp) peut être lié à la transpiration relative (RT), rapport entre la transpiration d’une parcelle stressée (T) et la transpiration d’une parcelle bien irriguée (Tm). L’estimation de RT à partir de Yp permet de calculer l’ETr pour déterminer les doses d’irrigation, si une irrigation en conditions de déficit est appliquée, puisque RT correspond approximativement à Ks. Matériel et méthodes. RT et Yp ont été mesurés afin d’établir une relation pour estimer RT sous un stress hydrique modéré pour programmer l’irrigation dans un verger de pêchers dans le sud du Portugal. RT a été calculé à partir de la mesure du flux de sève (bilan thermique) dans deux parcelles, l’une bien irriguée (quantités d’irrigation journalière au goutte-à-goutte calculées pour Tm) et une autre temporairement non irriguée. Résultats et discussion. Une forte corrélation a été observée entre RT et Yp, ce qui a permis d’estimer RT dans les conditions étudiées. Des différences importantes concernant la relation RT-Yp obtenue pour un autre verger de pêchers de la même région, disposant de conditions pédologiques similaires, ont été trouvées pour Yp compris entre –0,11 MPa et –0,45 MPa. Les résultats suggèrent que ces différences ont résulté des différents systèmes d’irrigation utilisés : goutte-à-goutte ou microasperseurs, puisque ceux-ci déterminent la distribution spatiale et temporelle de l’eau dans le sol et donc la géométrie différente du système racinaire. Une équation précédemment proposée pour estimer RT à partir Yp, avec une forme générale pour les différentes espèces d’arbres fruitiers, a été testée et s’avère suffisante dans certaines limites : jusqu’à RT = 0,7, l’erreur s’est révélée inférieure à 9 %. La valeur de seuil RT = 0,7 a été considérée comme un minimum, car elle a été testée avec succès lors de l’utilisation d’irrigation en conditions de déficit pour les vergers de pêchers. Introducción. Los indicadores del estrés hídrico vegetal se han vuelto esenciales para llevar a cabo estrategias de irrigación en caso de déficit y de ahorro de agua. En este caso, la evapotranspiración (ET) es inferior a su valor máximo para el cultivo y para la fase (ETc), y se aplica un coeficiente de tensión (Ks) para obtener el valor real de ET (ETr). El potencial hídrico de base foliar (Yp) puede estar unido a la transpiración relativa (RT), relación entre la transpiración de una parcela estresada (T) y la transpiración de una parcela bien irrigada (Tm). La estimación de RT a partir de Yp permite calcular la ETr para determinar las dosis de irrigación, si se aplica una irrigación en condiciones de déficit, dado que RT corresponde aproximadamente a Ks. Material y métodos. RT y Yp se midieron con el fin de establecer una relación para estimar RT bajo un estrés hídrico moderado, para programar la irrigación en un vergel de melocotoneros en el sur de Portugal. Se calculó RT a partir de la medida del flujo de savia (balance térmico) en dos parcelas, una bien irrigada (cantidades de irrigación diaria por goteo calculadas para Tm) y otra temporalmente no irrigada. Resultados y discusión. Se observó una fuerte correlación entre RT y Yp, lo que permitió estimar RT en condiciones estudiadas. Se encontraron importantes diferencias en cuanto a la relación RT-Y p obtenida para otro vergel de melocotoneros de la misma región, que dispusiera de condiciones pedológicas similares, para Yp comprendido entre –0,11 MPa y –0,45 MPa. Los resultados sugieren que dichas diferencias resultaron de diferentes sistemas de irrigación empleados: goteo o microaspersores, ya que éstos determinan la distribución espacial y temporal del agua en el suelo, y, por lo tanto, la diferente geometría del sistema radicular. Se testeó una ecuación anteriormente propuesta para estimar RT a partir Yp, con una forma general para las diferentes especies de árboles frutales, y resulta suficiente con ciertos límites: hasta RT = 0,7, el error resultó ser inferior al 9 %. El valor de aceptabilidad RT = 0,7 se consideró como un mínimo, ya que se testeó exitosamente durante la utilización de irrigación en condiciones de déficit para los vergeles de melocotoneros.

In the tropics, the water potential of a region cannot be adequately assessed from precipitation alone due to the seasonal character of rainfall and even more so owing to the changing climate scenario. It is therefore necessary that in any agro-climatological program, there must be a clear understanding of the actual amount of water that evaporates and transpires (AET), and the amount of water that would evaporate and transpire if water were always readily available (PET). This could be done through the method of the water balance. The present work examines the water budget of parts of the Imo river basin and its implications for improved crop production through supplementary irrigation schedules. It was observed, that the study area is already facing moisture-stress. This is because even during rainy months supplementary irrigation is required to compensate for the occasionally moisture deficit due to increased evapotranspiration. The study showed that cultivation of maize, rice and tomatoes can be carried out on an all-year round basis under a scientific irrigation scheme. Thus the study provided farmers with guideline on the period and quantity of water required for supplementary irrigation, a development which will prevents wilting of plants before the application of needed water.

While the cultivated olive tree (Olea europaea L.) is known to be sclerophyllous and effective at tolerating drought, little is known of its short-term water-use dynamics for most studies have been based on longer-term, water-balance information. We present here, for the first time, heat-pulse measurements of the sap flux measured not only within the semi-trunk of an olive tree, but also within a root excavated close to the stump. One tree in the olive grove near Seville in Spain had regularly received basin irrigation during the summer, whereas the other, growing on this deep silt loam, had been without water for over 3 months. Following a flood irrigation of 730 L to a dyked area around the tree, the regularly-irrigated olive maintained a transpiration rate of 1.65 mm³ mm⁻² d⁻¹, on a leaf area basis, for only 3 days following the irrigation. This rate was maintained for a total consumption of 110 L. It then began again to limit its rate of water use with transpiration falling below that predicted for well-watered conditions by the Penman-Monteith equation. The flow of sap in the near-surface root dropped concomitantly. Meanwhile the unirrigated tree was using water at just 0.78 mm d⁻¹. Yet following an irrigation of 870 L it only lifted its consumption to 1.12 mm d⁻¹, on a leaf area basis. Neither did it recover its leaf water potential following this wetting because of an inability to refill cavitated vessels. These data again show olive to be a parsimonious and cautious consumer of soil water.

In this study we observed an important interrelationship between the ability of Hordeum spontaneum C. Koch (Poaceae) seeds to germinate after a small rainfall in winter and the dehydration tolerance of young seedlings after one, two or three weeks in dry conditions. In winter, local ecotypes of H. spontaneum started to germinate after only 10 mm of 'rain', when temperatures were mild, daily evaporation rates were low, and soil water content was 5.8%. In summer, however, germination was not triggered until at least 50 mm of 'rain' was received, at higher temperatures, evaporation rates and soil water content. The 'point of no return' is the earliest stage of germination or after germination at which dehydration will cause the death of the seedling and it depends on the duration in a dry environment, root length before desiccation and on the ecotype. Seedlings were stored in dry conditions for one, two or three weks and then rewetted. A higher percentage of seedlings which had developed roots of 5-20 mm long before desiccation, developed adventitious roots than that of seedlings with roots 1-4 or 40-50 mm long before desiccation. The strategy of regulating germination according to different amounts of rainfall, depending on the season, and seedling drought tolerance, are important survival adaptations in arid and semi-arid regions. These adaptations may enable the young seedlings to overcome drought periods between rainfalls.[PUBLICATION ABSTRACT]

Pima cotton (Gossypium barbadense L. cv S-6) exhibits foliar injury and yield reduction at ambient concentrations of O3. We tested the hypotheses that O3 reduces the allocation of biomass to the root system, and that this disrupted carbohydrate allocation impairs root hydraulic capacity relative to transpiring leaf area. Both hypotheses are supported, even though leaf area development is itself reduced by O3. Seedlings were grown in pots in greenhouse fumigation chambers and exposed from planting to sinusoidal O3 profiles with peak concentrations of 0, 0.1, 0.2, and 0.3 microliters L-1 (12-h averages of 0, 0.037, 0.074, and 0.111 microliters L-1). At 8 weeks after planting, stem basal diameter, leaf area, and total plant dry weight decreased by 61, 83, and 88%, whereas root/shoot dry weight ratio declined from 0.16 to 0.09 g/g. Hydraulic conductance decreased per plant by 85%, and per unit leaf area by 35%. Conductance of all organs declined per plant, but only root conductance declined per leaf area by 41%. Root resistance increased from 69 to 82% of whole plant resistance, a functional consequence of reduced carbon allocation to roots. Stomatal conductance declined with root hydraulic conductance, protecting short-term leaf water status. Reduced root hydraulic efficiency may mediate O3 injury to whole plants by reducing shoot gas exchange and biomass productivity through the inhibition of water and nutrient acquisition.