Peach orchard evapotranspiration in a sandy soil: comparison between eddy covariance measurements and estimates by the FAO 56 approach

The evapotranspiration from a 3 to 4 years old drip irrigated peach orchard, located in central Portugal, was measured using the eddy covariance technique during two irrigation seasons, allowing the determination of crop coefficients. These crop coefficient values differed from those tabled in FAO Irrigation and Drainage Paper 56. In order to improve evapotranspiration estimates obtained from FAO tabled crop coefficients, a dual crop coefficient methodology was adopted, following the same guidelines. This approach includes a separation between the plant and soil components of the crop coefficient as well as an adjustment for the sparse nature of the vegetation. Soil evaporation was measured with microlysimeters and compared with soil evaporation estimates obtained by the FAO 56 approach. The FAO 56 method, using the dual crop coefficient methodology, was also found to overestimate crop evapotranspiration. During 2 consecutive years, measured and estimated crop coefficients were around 0.5 and 0.7, respectively. The estimated and measured soil evaporation components of the crop coefficient were similar. Therefore, the overestimation in evapotranspiration seems to result from an incorrect estimate of the plant transpiration component of the crop coefficient. A modified parameter to estimate plant transpiration for young, yet attaining full production, drip irrigated orchards is proposed based on field measurements. The method decreases the value of basal crop coefficient for fully developed vegetation. As a result, estimates of evapotranspiration were greatly improved. Therefore, the new approach seems adequate to estimate basal crop coefficients for orchards attaining maturity established on sandy soils and possibly for other sparse crops under drip irrigation conditionsinfo:eu-repo/semantics/publishedVersio

Green roof design techniques to improve water use under Mediterranean conditions

Green roof typology can vary depending on buildings structure, climate conditions, substrate, and plants used. In regions with hot and dry summers, such as the Mediterranean region, irrigation plays an essential role, as the highest temperatures occur during the driest period of the year. Irrigation might reduce the heat island effect and improve the cooling of buildings during this period, however, the added cost of maintenance operations and additional energy consumption could outrun the benefits provided by the project. Moreover, in situations where water is scarce or primarily channelled to other uses (e.g., domestic, agriculture or industry) during drought occurrence, it is advisable to implement green roof projects with the lowest use of water possible. The objective of the present work is to investigate solutions to optimize water use in green roofs under Mediterranean conditions, such as those of southern Europe. Two case studies are presented for Portugal, and potential techniques to reduce irrigation requirements in green roofs were tested. These addressed the use of native plant species, including the extreme type of a non-irrigated green roof (Biocrust roof) and techniques for plant installation. Plant drought tolerance was found to be an advantage in green roofs under these climatic conditions and, for the species studied, aesthetic value could be maintained when irrigation decreasedinfo:eu-repo/semantics/publishedVersio

Selecting potential moss species for green roofs in the Mediterranean Basin

Green roofs are important infrastructures to address the e ects of climate change in urban areas. However, most studies and applications have been done in cooler and wetter regions of the northern hemisphere. Climate change will lead to more extreme weather events, such as increased drought and decreased precipitation with intense flash rain events. Increase desertification is expected especially in the Mediterranean Basin, where in summer, radiation and temperature are high and water is scarce. Therefore, while vascular plants increase water consumption in green roofs during warmer periods, mosses present themselves as potential candidates due to their poikilohydric nature, responding to the environmental availability of water, completely drying out and recovering upon rehydration. Although criteria for the selection of vascular plants adapted to the Mediterranean and suitable for green roofs have been developed, no information is available regarding the selection of mosses based on scientific criteria. Here we propose selection criteria for moss species based on ecological preferences according to Ellenberg’s values and help to define moss traits suitable for a nonirrigated, nature-based green roof that tolerates the Mediterranean climate. The main result is a table of potential candidate mosses that can be either used as standalone or in conjunction with vascular plants to decrease water usage and/or manage stormwater through an easily applicable selection methodology. For green roof practitioners, we proposed that acrocarpous mosses exhibiting turf/cushion life forms and colonist or perennial life strategies best fit the requirements for such a green infrastructure in extreme climate regions with scarce water resourcesinfo:eu-repo/semantics/publishedVersio

Evapotranspiration and crop coefficients for a super intensive olive orchard. An application of SIMDualKc and METRIC models using ground and satellite observations

The estimation of crop evapotranspiration (ETc) from the reference evapotranspiration (ETo) and a standard crop coefficient (Kc) in olive orchards requires that the latter be adjusted to planting density and height. The use of the dual Kc approach may be the best solution because the basal crop coefficient Kcb represents plant transpiration and the evaporation coefficient reproduces the soil coverage conditions and the frequency of wettings. To support related computations for a super intensive olive orchard, the model SIMDualKc was adopted because it uses the dual Kc approach. Alternatively, to consider the physical characteristics of the vegetation, the satellite-based surface energy balance model METRIC™ – Mapping EvapoTranspiration at high Resolution using Internalized Calibration – was used to estimate ETc and to derive crop coefficients. Both approaches were compared in this study. SIMDualKc model was calibrated and validated using sap-flow measurements of the transpiration for 2011 and 2012. In addition, eddy covariance estimation of ETc was also used. In the current study, METRIC™ was applied to Landsat images from 2011 to 2012. Adaptations for incomplete cover woody crops were required to parameterize METRIC. It was observed that ETc obtained from both approaches was similar and that crop coefficients derived from both models showed similar patterns throughout the year. Although the two models use distinct approaches, their results are comparable and they are complementary in spatial and temporal scalesinfo:eu-repo/semantics/publishedVersio

Drought-induced embolism in current-year shoots of two Mediterranean evergreen oaks

threatened by the increasing water deficits related to climate change. To contribute to the understanding of the capacity of these oaks to withstand severe drought we assessed the vulnerability to xylem embolism and the anatomical traits in current-year shoots. Data were collected in mature trees at two sites, in central/ coastal and southern/inland Portugal. In situ safety margins to hydraulic failure were evaluated from long-term predawn and midday leaf water potential records. Results showed that xylem vulnerability to embolism was similar in Q. ilex and Q. suber. The 50% loss in hydraulic conductivity (Wxyl,50PLC) was observed at xylem water potentials of 2.9 and 3.2 MPa in shoots of Q. suber and Q. ilex, respectively. Values of mean vessel diameter of Q. suber shoots at both sites suggest an intra-species adaptation to the local water availability, with larger vessels at the more mesic site. In situ hydraulic safety margins observed in shoots showed that, even during the driest periods, both oaks lived comfortably above the most critical embolism thresholds. However, the hydraulic safety margins were narrower in the driest site. Results are relevant to the understanding of survival, growth, and functional behaviour of evergreen oaks in Mediterranean climates, under recurrent/seasonal drought condition

Evapotranspiration from a Mediterranean evergreen oak savannah: The role of trees and pasture

Mediterranean evergreen oak woodlands of southern Portugal (montados) are savannah-type ecosystems with a widely sparse tree cover, over extensive grassland. Therefore, ecosystem water fluxes derive from two quite differentiated sources: the trees and the pasture. Partitioning of fluxes according to these different sources is necessary to quantify overall ecosystem water losses as well as to improve knowledge on its functional behaviour. In southern Iberia, these woodlands are subjected to recurrent droughts. Therefore, reaction/resilience to water stress becomes an essential feature of vegetation on these ecosystems. Long-term tree transpiration was recorded for 6 years from a sample of holm oak (Quercus ilex ssp. rotundifolia) trees, using the Granier sap flow method. Ecosystem transpiration was measured by the eddy covariance technique for an 11-month period (February to December 2005), partly coincident with a drought year. Pasture transpiration was estimated as the difference between ecosystem (eddy covariance) and tree (sap flow) transpiration. Pasture transpiration stopped during the summer, when the surface soil dried up. In the other seasons, pasture transpiration showed a strong dependence on rainfall occurrence and on top soil water. Conversely, trees were able to maintain transpiration throughout the summer due to the deep root access to groundwater. Q. ilex trees showed a high resilience to both seasonal and annual drought. Tree transpiration represented more than half of ecosystem transpiration, in spite of the low tree density (30 trees ha 1) and crown cover fraction (21%). Tree evapotranspiration was dominated by transpiration (76%), and interception loss represented only 24% of overall tree evaporatio

Response of intensive and super-intensive olive grove to two different irrigation regimens: physiological parameters, production and quality

Olive grove irrigation has substantially increased in the past years on the region of Alentejo (southern Portugal). The correct determination of the plant water requirements is one of the key factors on the orchard management. This work evaluates the response of two varieties of Olea europaea, Cobrançosa in an intensive grove (hereafter named FEA) and Arbequina in a hedgerow orchard (hereafter named OSul), subject to two water regimes, the one usually practiced by the farmer (emitters with flow rate 1.6 or 2.3 l h-1 on FEA or OSul, respectively) and an excessive water supply on FEA or a deficit irrigation in OSul. The main water relation parameters, chlorophyll content and spectral emission were determined on adult and young leaves, at solar mid-day, three times over the year, spring, late summer and winter 2011. In October, fruits were harvested and total production, oil content and quality were assessed. The results show that in the intensive grove of Cobrançosa (FEA), water supply above the one practiced by the farmer did not improve fruit production neither oil content or quality. There were also no significant differences between the water relation parameters of plants subject to the two irrigation regimes. As to the hedgerow orchard of Arbequina (OSul), deficit irrigation induced lower production and also lower leaf water content, lower water potential and lower stomatal conductance at the end of summer and winter, although oil content and quality remained similar. Chlorophyll content and vegetation indexes were only occasionally affected by the irrigation regime. In both olive groves and irrigation regimes, oil quality was not affected, always attaining the characteristics of an extra virgin olive oil. This research continues in 2012

Nota introdutória

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Scheduling peach orchard irrigation in water stress conditions: use of relative transpiration and predawn leaf water potential

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

Optimising Artificial Moss Growth for Environmental Studies in the Mediterranean Area

Bryophytes are poikilohydric organisms that play a key role in ecosystems, while some of them are also resistant to drought and environmental disturbances but present a slow growth rate. Moss culture in the laboratory can be a very useful tool for ecological restoration or the development of urban green spaces (roof and wall) in the Mediterranean region. Therefore, we aim to: (i) determine the optimal culture conditions for the growth of four moss species present in the Mediterranean climate, such as Bryum argenteum, Hypnum cupressiforme, Tortella nitida, and Tortella squarrosa; (ii) study the optimal growth conditions of the invasive moss Campylopus introflexus to find out if it can be a threat to native species. Photoperiod does not seem to cause any recognisable pattern in moss growth. However, temperature produces more linear but slower growth at 15 C than at 20 and 25 C. In addition, the lower temperature produced faster maximum cover values within 5–8 weeks, with at least 60% of the culture area covered. The study concludes that the culture of moss artificially in the organic gardening substrate without fertilisers is feasible and could be of great help for further use in environmental projects to restore degraded ecosystems or to facilitate urban green spaces in the Mediterranean area. Moreover, this study concludes that C. introflexus could successfully occupy the niche of other native moss species, especially in degraded areas, in a future global change scenario.info:eu-repo/semantics/publishedVersio