Transpiration of hazelnut (Corylus avellana L.) orchards in response to different climatic conditions and implications for water management

Plants are unquestionably at the basis of human life as they are directly or indirectly a source of food, but the agricultural sector accounts for more than 80% of water consumption. Agricultural production cannot ignore water supply to meet market demands, while it faces growing water shortages, droughts and heat waves. In this sense, it is paramount to manage water resources in a sustainable way by understanding the water responses of species to different climates. The European hazelnut is an expanding orchard tree, which has now established in all continents to answer the increasing demand for nuts from the food industry. Trees face the challenge of acclimating to new areas, while remaining productive. In this situation, still no precise knowledge exits about the average transpiration of hazelnut orchard under standard irrigation and thus about the real irrigation needs respect to its environment. The few studies on hazelnut water use are mainly leaf-based or hardly transferred to growers. This research focuses on three main topics in the perspective of providing useful reference for orchard managers set in different climatic contexts: I) to identify the pattern of transpiration response to different climates, irrigation and cultivars. II) To estimate the transpiration at the tree level and propose a realistic tool for growers to reintegrate water loss. III) Explore the links and limitations of transpiration activity and carbon gain processes. We set a long-term experiment across three growing seasons (from 2016 to 2019) on eight orchards in Chile, Australia, Italy, France and Republic of Georgia, involving two cultivars: Tonda Gentile delle Langhe and Tonda di Giffoni. We monitored in continuous the sap flow with Granier’s thermal dissipation probes (TDPs), the meteorological parameters and the soil water content. Tree biometrics and orchard features were recorded as well. TDPs were calibrated with a liquid flow meter applied to a potometric system. The transpiration responses showed to be linearly correlated to the vapor pressure deficit of the atmosphere (VPD) until 20hPa. The radiation intensity produced different responses in the two hemisphere, but cultivar and doubled irrigation had little impact. The calibration of TDPs lead to the correction of the Granier’s equation with parameters suitable for hazelnut. This, together with the estimation of the tree leaf area, allowed to derive a range of transpiration per unit of leaf (1-2.55 l m-2day-1). This is the basis for a water loss reintegration strategy by knowing the mean daily VPD. The link between transpiration and carbon assimilation was considered to highlight the interval of VPD at which the canopy conductance, and thus the potential carbon assimilation, is maximized. A conclusive ancillary study shows through the manipulation of C sources and sinks that the nut production depends on C previously stored in the stem showing that branches are not fully carbon autonomous.Le piante sono indiscutibilmente alla base della vita umana poiché sono direttamente o indirettamente fonte alimentare, ma il settore agricolo pesa per più dell’80% sul consumo di acqua. La produzione agricola non può prescindere dall’apporto idrico per raggiungere le richieste del mercato, mentre deve fronteggiare una crescente scarsità di acqua, eventi siccitosi e ondate di calore. In questo senso, diviene fondamentale gestire le risorse idriche in modo sostenibile comprendendo le risposte idriche delle specie ai diversi climi. Il nocciolo è un albero da frutto in grande espansione, che si è oggi affermato in tutti i continenti in risposta alla richiesta di nocciole da parte dell’industria alimentare. I noccioli debbono al contempo acclimatarsi alle nuove aree e rimanere produttivi. In questa situazione non c’è ancora una precisa conoscenza rispetto alla traspirazione media di noccioleti irrigati e quindi alle loro necessità irrigue calate nel contesto climatico. I pochi studi sull’ utilizzo dell’acqua nel nocciolo rimangono relativi alle dinamiche fogliari o sono difficili da trasferire agli agricoltori. Lo scopo di questa ricerca verte su tre scopi principali nella prospettiva di essere un riferimento per i gestori dei corileti che operano in diversi contesti climatici: I) Identificare la risposta traspirativa di piante adulte in diversi climi, irrigazioni e cultivar. II) Stimare la traspirazione al livello di albero e, sulla base di ciò, proporre un approccio realistico per reintegrare le perdite traspirative volto ai corilicoltori. III) Esplorare le connessioni e le limitazioni alla traspirazione e ai processi di acquisizione del carbonio. Si è installato un esperimento a lungo termine attraverso tre stagioni vegetative (2016-2019) in otto diversi corileti in Cile, Australia, Italia, Francia e Repubblica della Georgia, coinvolgendo due cultivar: Tonda Gentile delle Langhe and Tonda di Giffoni. Il flusso di linfa è stato monitorato con delle sonde a dissipazione termica di Granier (TDP). Sono stati misurati parametri meteorologici, contenuto idrico del suolo e parametri biometrici dei corileti. I TDP sono stati calibrati attraverso un misuratore di flusso e un approccio potometrico. Le risposte traspirative si sono dimostrate linearmente correlate con il deficit di pressione di vapore atmosferico (VPD) fino a circa 20 hPa. L’intensità di radiazione si è anche rivelata importante nel diversificare le risposte tra i due emisferi, ma la cultivar e le diverse strategie irrigue hanno avuto un effetto irrilevante nel diversificare le risposte traspirative. La calibrazione dei TDP ha condotto alla correzione dell’equazione di Granier con parametri adatti al nocciolo. Questo, insieme alla stima dell’area fogliare ha permesso di individuare un intervallo di traspirazione per unità di area fogliare (1-2.5 l m-2 giorno-1). Tale risposta è alla base di una strategia di reintegro delle perdite traspirative che utilizza il VPD medio come principale predittore della traspirazione totale giornaliera. Il legame tra traspirazione e assimilazione potenziale di carbonio è stato considerato per far emergere l’intervallo di VPD in cui la conduttanza di chioma è massimizzata, e quindi, anche il potenziale di assimilazione. Uno studio ancillare conclusivo mostra che per il riempimento delle nocciole la specie utilizza anche carboidrati precedentemente immagazzinati nel fusto oltre che a quelli forniti dalle foglie dell’anno

Calibration of Granier-Type (TDP) Sap Flow Probes by a High Precision Electronic Potometer

Thermal dissipation probe (TDP) method (Granier, 1985) is widely used to estimate tree transpiration (i.e., the water evaporated from the leaves) because it is simple to build, easy to install, and relatively inexpensive. However, the universality of the original calibration has been questioned and, in many cases, proved to be inaccurate. Thus, when the TDP is used in a new species, specific tests should be carried out. Our aim was to propose a new method for improving the accuracy of TDP on trees in the field. Small hazelnut trees (diameter at breast height 5 cm) were used for the experiment. The response of TDP sensors was compared with a reference water uptake measured with an electronic potometer system provided with a high precision liquid flow meter. We equipped three stems where we measured the sap flow density, the sapwood area (by using fuchsine), the total tree water uptake (reference), and the main meteorological parameters during summer 2018. Results confirmed that the original Granier’s calibration underestimated the effective tree transpiration (relative error about −60%). We proposed a new equation for improving the measurement accuracy within an error of about 4%. The system proposed appeared an easier solution compared to potted trees and particularly suitable for orchards, thus contributing to improve the irrigation management worldwide

Does Education Equalize or Reproduce Inequality? Effects of College Degrees on Health Behaviors

Among U.S. adults, college degree earners live much healthier lives than those with less education, but we know little about why. This dissertation examines how, why, and for whom college degrees influence health behaviors, such as smoking, diet, exercising, maintaining of healthy weight status, and drinking. Theories posit that college degrees may exhibit: “transformative” effects if college degrees influence health behaviors independent of selection, “sorting” effects if health behavior advantages are due to selection, “conditional reproduction” if groups of historical advantage receive the greatest benefits, or “conditional equalizing” if groups of historical disadvantage have greater benefits. Three research questions characterize the study’s objectives: (1) Does education improve health behaviors or is the association spurious? (2) Does education have the same benefits for the health behaviors of all social groups? (3) If education does improve health behaviors, how does it do so? The National Longitudinal Study of Adolescent to Adult Health (Add Health) provides longitudinal data on education and health behaviors across adolescence and young adulthood for a cohort of individuals born 1977-1984. The methods include propensity score approaches to estimate causal effects and test for heterogeneity. This study affirms multiple functions of education: it sorts individuals, improves well-being, and stratifies the population into classes. Very little evidence supports the assertion that benefits of college degrees are conditional. College degrees improve health behaviors for all college graduates, leaving those without degrees lagging behind. A sociological understanding of why social groups engage in different behaviors can contribute to efforts in reducing social inequality and improving population health

Abbraccia la Natura: Alberi in bicicletta.

Iniziazione ai corsi del dipartimento TESAF. per studenti delle Scuole superior

METEOROLOGICAL CONDITIONS FAVORING HIGH POLLEN CONCENTRATION IN HAZELNUT ORCHARDS

Understanding the importance of abiotic drivers in wind-pollinated species is a key issue to predict seed production. Researches on anemophilous species (e.g. olive, walnut, oak) highlighted the correlation between airborne pollen concentration and seed production. Moreover, recent phenological studies revealed the importance of humidity as a trigger for tree phenology. Despite the economic importance of Corylus avellana, few in-field studies on pollen dispersal have been produced on this species. Pollen concentration depends on pollen production and atmospheric stability at the lower layers of the atmosphere, i.e. low convective activity and low radiation). Thus, we tested the hypothesis that high air humidity and low wind velocity within the canopies favor high pollen concentration. To unravel these mechanisms, we monitored hazelnut reproductive phenology on 10 adult trees of C. avellana var. TGL in Piedmont (Italy), together with daily pollen concentrations, air and bud temperature, air humidity and wind, during winter 2016-2017. Our data set on meteorological parameters and daily pollen concentration of the five previous years indicates that pollen concentrations lasted on average 12 weeks from mid-December to mid-March involving multiple phenological phases from catkin elongation until its decay. The highest pollen concentration peaks always occurred with air vapor pressure deficit well below 5hPa and with no precipitation event. Also, catkins elongation resulted positively affected by higher absolute humidity between the 2nd and the 3rd phenological phase in 2016-2017. These findings disclose the importance of atmospheric stability within the canopy layer as explanatory parameters for hazelnut pollen emission

Transpiration decrease in shaded hazelnuts: a green light for experimenting new orchard structures

Global yields of cereals and fruit trees are projected to decrease as a consequence of the increasing air vapour pressure deficit (VPD) (Hsiao et al. 2019). VPD synthesize the effect of relative humidity and temperature of the air, which is unceasingly increasing due to anthropogenic global warming since 30 years of 0.2\ub0C (IPCC 2018). Mediterranean regions are among the most affected areas by this change. At the same time, VPD is one of the most significant parameter affecting plant physiology because it controls stomata aperture and carbon inflow into leaves. Long term exposure to high VPD leads to reduced growth (Sangin\ue9s de C\ue1rcer et al. 2018) and tree mortality even more than just high temperature rise (Eamus et al. 2013). Still, some food trees are more sensitive to high VPD than others are. Hazelnut (Corylus avellana L.) is one of these. Although it is a temperate forest species, it is cultivated since centuries for the nut production in the whole Europe. In recent years, its cultivated surface is rising significantly. Italy plans to reach 20.000 hectares of hazelnut orchards at national level. In the last years, the research on hazelnut eco-physiology highlighted the sensitivity of the species to VPD rise. Hazelnut resulted shade-tolerant, it barely stands wind (Baldwin et al. 2003), stomata closure occurs above 10hPa VPD thus reducing carbon assimilation. This leads to the hypothesis that decoupling hazelnut trees from the atmosphere prevents water loss in case of VPD rise. During summer 2019, we set an experimental study in the University of Padova (45\ub020\u201955\u2019\u2019N, 11\ub056\u201959\u2019\u2019E, 5 m a.s.l.) hazelnut orchard, located in Legnaro (PD), Italy. Three 12 years old hazelnuts were covered with a polypropylene net in mid-June, while three other net-free individuals served as a control. Trees were rain-fed for the entire growing season. In each treatment, we measured carbon assimilation (An), stomatal conductance (gs) and light saturation curve at leaf level with a porometer from DOY 203 to 262. In parallel, we installed in all trees TDP probes to measure the sap flow. Sap flow measurements, together with meteorological parameters and soil water content were recorded by a datalogger with a 15 minutes record frequency. Diurnal sap flow data and VPD were used to calculate the canopy conductance G in the two treatments with G = k*EL/VPD (mm s-1), where k=115.8+0.4226*T\ub0C (m3kPa\ub0C kg-1), EL= transpiration per unit of LAI (g m-2s-1) as described in Tang et al. (2006). At the leaf level, the light saturation curve showed that 48% of the CO2 assimilation was reached already at 100 \u3bcmol m-2s-1 of PAR and remained stable for PAR > 500 \u3bcmol m-2s-1, close to what found by Tombesi et al. (2015). The shading net did not change the response to light. Daily An resulted slightly higher in control respect to shaded treatment, especially between 7 and 8AM and between 3 and 5PM. The shading net provided 10% decrease in mean daily VPD compared to the control. This caused a decrease in the canopy transpiration per unit of leaf area (EL) of 13.9% (max 30.5%) in shaded compared to control treatment (0.024 and 0.028 g m-2s-1 respectively). The whole tree canopy conductance (i.e. gas exchange capacity) between the two treatments was 8% higher in control respect to shaded trees (0.16 2 and 0.14 mol m-2s-1 respectively). The cover net shifted the maximum G from 6 to 10hPa, but the response of G to VPD remained similar in the two treatments (Wilcoxon test, p>0.05). Even if the leaf carbon assimilation is negatively affected by shade only in the early morning and some afternoon hours, the relative gain in whole tree conductance remained lower in control respect to the amount of water saved by shading the trees. Indeed, it is possible to design agroforestry systems where hazelnut grows with other non-shade tolerant species (e.g. Populus spp.) as dominant trees. These partner trees can benefit from the water saved from the new hazelnut orchard layout, and on its turn, provide shelter from wind, heat waves or VPD increase in the long term. Still, more research is needed to include the effect of shade on nut yield, which is though difficult in hazelnut due to its alternate bearing of fruits. Still, this work suggests that hazelnut can tolerate the coexistence of dominant trees with water savings that might compensate carbon assimilation losses

Calibration of Granier-Type (TDP) Sap Flow Probes by a High Precision Electronic Potometer

Thermal dissipation probe (TDP) method (Granier, 1985) is widely used to estimate tree transpiration (i.e., the water evaporated from the leaves) because it is simple to build, easy to install, and relatively inexpensive. However, the universality of the original calibration has been questioned and, in many cases, proved to be inaccurate. Thus, when the TDP is used in a new species, specific tests should be carried out. Our aim was to propose a new method for improving the accuracy of TDP on trees in the field. Small hazelnut trees (diameter at breast height 5 cm) were used for the experiment. The response of TDP sensors was compared with a reference water uptake measured with an electronic potometer system provided with a high precision liquid flow meter. We equipped three stems where we measured the sap flow density, the sapwood area (by using fuchsine), the total tree water uptake (reference), and the main meteorological parameters during summer 2018. Results confirmed that the original Granier’s calibration underestimated the effective tree transpiration (relative error about −60%). We proposed a new equation for improving the measurement accuracy within an error of about 4%. The system proposed appeared an easier solution compared to potted trees and particularly suitable for orchards, thus contributing to improve the irrigation management worldwide

Assessment of Canopy Conductance Responses to Vapor Pressure Deficit in Eight Hazelnut Orchards Across Continents

none4A remarkable increase in vapor pressure deficit (VPD) has been recorded in the last decades in relation to global warming. Higher VPD generally leads to stomatal closure and limitations to leaf carbon uptake. Assessing tree conductance responses to VPD is a key step for modeling plant performances and productivity under future environmental conditions, especially when trees are cultivated well outside their native range as for hazelnut (Corylus spp.). Our main aim is to assess the stand-level surface canopy conductance (Gsurf ) responses to VPD in hazelnut across different continents to provide a proxy for potential productivity. Tree sap flow (Fd) was measured by Thermal dissipation probes (TDP) probes (six per sites) in eight hazelnut orchards in France, Italy, Georgia, Australia, and Chile during three growing seasons since 2016, together with the main meteorological parameters. We extracted diurnal Fd to estimate the canopy conductance Gsurf.. In all the sites, the maximum Gsurf occurred at low values of VPD (on average 0.57 kPa) showing that hazelnut promptly avoids leaf dehydration and that maximum leaf gas exchange is limited at relatively low VPD (i.e., often less than 1 kPa). The sensitivity of the conductance vs. VPD (i.e., -dG/dlnVPD) resulted much lower (average m = −0.36) compared to other tree species, with little differences among sites. We identified a range of suboptimal VPD conditions for Gsurf maximization (Gsurf > 80% compared to maximum) in each site, named “VPD80,” which multiplied by the mean Gsurf might be used as a proxy for assessing the maximum gas exchange of the orchard with a specific management and site. Potential gas exchange appeared relatively constant in most of the sites except in France (much higher) and in the driest Australian site (much lower). This study assessed the sensitivity of hazelnut to VPD and proposed a simple proxy for predicting the potential gas exchange in different areas. Our results can be used for defining suitability maps based on average VPD conditions, thus facilitating correct identification of the potentially most productive sites.openPasqualotto, Gaia; Carraro, Vinicio; Suarez Huerta, Eloy; Anfodillo, TommasoPasqualotto, Gaia; Carraro, Vinicio; Suarez Huerta, Eloy; Anfodillo, Tommas