Thermography to explore plant-environment interactions

Review PaperStomatal regulation is a key determinant of plant photosynthesis and water relations, influencing plant survival, adaptation, and growth. Stomata sense the surrounding environment and respond rapidly to abiotic and biotic stresses. Stomatal conductance to water vapour (gs) and/or transpiration (E) are therefore valuable physiological parameters to be monitored in plant and agricultural sciences. However, leaf gas exchange measurements involve contact with leaves and often interfere with leaf functioning. Besides, they are time consuming and are limited by the sampling characteristics (e.g. sample size and/or the high number of samples required). Remote and rapid means to assess gs or E are thus particularly valuable for physiologists, agronomists, and ecologists. Transpiration influences the leaf energy balance and, consequently, leaf temperature (Tleaf). As a result, thermal imaging makes it possible to estimate or quantify gs and E. Thermal imaging has been successfully used in a wide range of conditions and with diverse plant species. The technique can be applied at different scales (e.g. from single seedlings/leaves through whole trees or field crops to regions), providing great potential to study plant–environment interactions and specific phenomena such as abnormal stomatal closure, genotypic variation in stress tolerance, and the impact of different management strategies on crop water status. Nevertheless, environmental variability (e.g. in light intensity, temperature, relative humidity, wind speed) affects the accuracy of thermal imaging measurements. This review presents and discusses the advantages of thermal imaging applications to plant science, agriculture, and ecology, as well as its limitations and possible approaches to minimize them, by highlighting examples from previous and ongoing researchinfo:eu-repo/semantics/publishedVersio

Suivi de l'évolution de la température du couvert végétal de deux variétés soumises a une irrigation déficitaire: un outil pour optimiser la géstion de l'eau ?

A better understanding of grapevine responses to drought and high air temperatures can help to optimize vineyard management to improve water use efficiency, yield and berry quality. Faster and robust field phenotyping tools are needed in modern precision viticulture, in particular in dry and hot regions such as the Mediterranean. Canopy temperature (Tc) is commonly used to monitor water stress in plants/crops and to characterize stomatal physiology in different woody species including Vitis vinifera. Thermography permits remote determination of leaf surface or canopy temperature in the field and also to assess the range and spatial distribution of temperature from different parts of the canopies. Our hypothesis is that grapevine genotypes may show different Tc patterns along the day due to different stomatal behaviour and heat dissipation strategies. We have monitored the diurnal and seasonal course of Tc in two grapevine genotypes, Aragonez (syn. Tempranillo) and Touriga Nacional subjected to deficit irrigation under typical Mediterranean climate conditions. Temperature measurements were complemented by determination of the diurnal course of leaf water potential (ψleaf) and leaf gas exchange. Measurements were done in two seasons (2013 and 2014) at different phenological stages: i) mid-June (green berry stage), ii) mid-July (veraison), iii) early August (early ripening) and iv) before harvest (late ripening). Correlations between Tc and minimal stomatal conductance will be presented for the two genotypes along the day. Results are discussed over the use of thermal imagery to derive information on genotype physiology in response to changing environmental conditions and to mild water stress induced by deficit irrigation. Strategies to optimize the use of thermal imaging in field conditions are also propose

Root functioning, tree water use and hydraulic redistribution in Quercus suber trees: a modeling approach based on root sap flow

Mediterranean evergreen oaks have to survive a long summer drought. Roots may play a relevant role under these conditions. We studied their structure and function in a mature Quercus suber L. tree in central Portugal. The root system was mapped till the lowest water table level (4.5 m depth). Xylem anatomy was analyzed in a vertical profile belowground. Sap flow was continuously monitored for 1.5 yrs in the stem and roots of this intensively studied tree (heat field deformation method) and in the stem of four trees (Granier method), in relation to environmental variables and predawn leaf water potential. The sources of water uptake were assessed by stable isotope analyses in summer. Results showed a dimorphic root system with a network of superficial roots linked to sinker roots, and a taproot diverting into tangles of deep fine roots submerged for long periods, with parenchyma aerenchyma. Transpiration was not restricted in summer due to root access to groundwater. The isotopic d18O signature of twig xylem water was similar to that of groundwater in the dry season. Two functional types of superficial roots were identified: shallow connected and deep connected roots. A modeling approach was built considering that each superficial root was linked to a sinker, with part of the root deep connected (between the stem and the sinker) and part shallow connected (between the sinker and topsoil). This conceptual framework simulated tree stem sap flow from root sap flow with a high efficiency (R2 = 0.85) in four plot trees. On an annual basis, soil water and groundwater contributions were 69.5% and 30.5% of stem flow, respectively. Annual hydraulic lift and hydraulic descent were 0.9% and 37.0% of stem flow, respectively. The trees maximize the exploitation of the environmental resources by using the topsoil water during most of the year, and groundwater together with hydraulic lift (nutrient supply) in the dry summer. This study shows that a dimorphic root system, with roots reaching groundwater, is an efficient strategy of Q. suber trees to cope with seasonal drought. Knowledge of the functional behavior of Q. suber trees under shallow water table conditions may contribute to the definition of better adapted management practices and to anticipate their responses to climate chang

Combining cover cropping with deficit irrigation in a Mediterranean low vigor vineyard

Available at ScienceDirectThe aim of this research was to test the effects of vineyard soil management practices combined with deficit irrigation strategies on the performance of the grapevine (Vitisvinifera L.) red variety Tempranillo. Two soil management practices (soil tillage – ST and permanent resident vegetation – RV) were combined with three deficit irrigation treatments (regulated deficit irrigation – RDI, partial rootzone drying – PRD and conventional sustained deficit irrigation – DI) during two growing cycles. Compared to ST, RV reduced soil water content during spring, inducing a significant reduction in vine vegetative growth, yield and must titratable acidity. The effects of irrigation treatments were not much pronounced. Only in the second season RDI showed a significant reduction on vine vegetative growth, yield and must titratable acidity as compared to PRD and DI whose results were similar to one another. In a dry area such as ours and a low vigor vineyard, the combination of resident vegetation with deficit irrigation treatments should be carefully considered as it can reduce yield without any benefits to grape quality. In this site the conventional deficit irrigation should be preferred to RDI and PRD as it is technically the simplest deficit irrigation strategy and has enabled an efficient control of vegetative growth without negative impact on yield and berry composition as compared to the other irrigation treatment

Cork oak physiological responses to manipulated water availability in a Mediterranean woodland

tThis study details the physiological responses of cork oak (Quercus suber L.) to manipulated water inputs.Treatments named as dry, ambient and wet, which received 80, 100 and 120% of the annual precipitation,respectively, were applied to a Mediterranean woodland in southern Portugal. Tree ecophysiology andgrowth were monitored from 2003 to 2005.The impacts of the water manipulation were primarily observed in tree transpiration, especially dur-ing summer drought. Rainfall exclusion reduced the annual stand canopy transpiration by 10% over the2-year study period, while irrigation increased it by 11%. The accumulated tree transpiration matchedprecipitation in spring 2004 and 2005 at the stand level, suggesting that cork oak trees rely on precip-itation water sources during the peak of the growing season. However, during the summer droughts,groundwater was the main water source for trees.Despite the significant differences in soil water content and tree transpiration, no treatment effectscould be detected in leaf water potential and leaf gas exchange, except for a single event after spring irri-gations in the very dry year 2005. These irrigations were intentionally delayed to reduce dry spell durationduring the peak of tree growing season. They resulted in an acute positive physiological response of treesfrom the wet treatment one week after the last irrigation event leading to a 32% raise of stem diame-ter increment the following months. Our results suggest that in a semi-arid environment precipitationchanges in spring (amount and timing) have a stronger impact on cork oak physiology and growth thanan overall change in the total annual precipitation.The extreme drought of 2005 had a negative impact on tree growth. The annual increment of treetrunk diameter in the ambient and dry treatments was reduced, while it increased for trees from the wettreatment. Water shortage also significantly reduced leaf area. The latter dropped by 10.4% in responseto the extreme drought of 2005 in trees from the ambient treatment. The reduction was less pronouncedin trees of the wet treatment (−7.6%), and more pronounced in trees of the dry treatment (−14.7%).Cork oak showed high resiliency to inter-annual precipitation variability. The annual accumulated treetranspiration, the minimum midday leaf water potential and the absolute amount of groundwater usedinfo:eu-repo/semantics/publishedVersio