Effects of non-uniform root zone salinity on water use, Na+ recirculation, and Na+ and H+ flux in cotton

A new split-root system was established through grafting to study cotton response to non-uniform salinity. Each root half was treated with either uniform (100/100 mM) or non-uniform NaCl concentrations (0/200 and 50/150 mM). In contrast to uniform control, non-uniform salinity treatment improved plant growth and water use, with more water absorbed from the non- and low salinity side. Non-uniform treatments decreased Na+ concentrations in leaves. The [Na+] in the ‘0’ side roots of the 0/200 treatment was significantly higher than that in either side of the 0/0 control, but greatly decreased when the ‘0’ side phloem was girdled, suggesting that the increased [Na+] in the ‘0’ side roots was possibly due to transportation of foliar Na+ to roots through phloem. Plants under non-uniform salinity extruded more Na+ from the root than those under uniform salinity. Root Na+ efflux in the low salinity side was greatly enhanced by the higher salinity side. NaCl-induced Na+ efflux and H+ influx were inhibited by amiloride and sodium orthovanadate, suggesting that root Na+ extrusion was probably due to active Na+/H+ antiport across the plasma membrane. Improved plant growth under non-uniform salinity was thus attributed to increased water use, reduced leaf Na+ concentration, transport of excessive foliar Na+ to the low salinity side, and enhanced Na+ efflux from the low salinity root

Ανάπτυξη συστήματος μείωσης της σχετικής υγρασίας στο θερμοκήπιο με τη χρήση αντλίας θερμότητας και υγροσκοπικών υλικών

Greenhouse dehumidification is an essential part of the environmental control of the greenhouse. High relative humidity in the greenhouse causes the development of plant diseases, which cause significant qualitative and quantitative degradation on the production of greenhouse crops. The risk of plant infection against fungal diseases increases when there is available moisture on the surfaces of the plants. The relative humidity inside the greenhouse displays intense variability due to the uneven distribution of temperature, with increased likelihood of condensation on the plants. For this reason, humidity control is necessary. Humidity control, when it occurs with ventilation and simultaneously heating, increases the energy consumption. In greenhouses without heating system is not possible to control high humidity with ventilation and heating. To increase energy saving in heated greenhouses and to control the humidity in greenhouses without heating systems for reducing the relative humidity in the greenhouse are studied in this thesis. Initially, evapotranspiration of the greenhouse cultivation was calculated through a vapor balance model, based on losses of vapor of greenhouse through leaks in the external environment, condensation on the cover and removal by the dehumidification system. Thus, the requirements for greenhouse dehumidifying were determined using the above vapor balance to maintain the relative humidity up to the upper desirable setpoint. Three systems were manufactured and tested for the greenhouse dehumidification: a system of hygroscopic absorption, an air to air heat pump system and a hybrid system by the combination of heat pump and hygroscopic absorption. From the study of hygroscopic absorption system, was found, that the capacity to remove water vapor from greenhouse air is determined by the air temperature, air specific humidity and air flow rate through the system, as well as by the concentration and the temperature of the hygroscopic solution. If low cost regeneration of the hygroscopic solution is achievable then the operating cost is less that the cost of operating the heat pump system.Η αφύγρανση του θερμοκηπίου αποτελεί ένα ουσιαστικό μέρος του ελέγχου του περιβάλλοντος του θερμοκηπίου. Η υψηλή σχετική υγρασία στο θερμοκήπιο είναι μια αιτία ανάπτυξης των ασθενειών των φυτών η οποία προκαλεί σημαντική ποιοτική και ποσοτική υποβάθμιση της παραγωγής των θερμοκηπικών καλλιεργειών. Ο κίνδυνοςτης προσβολής των φυτών από μυκητολογικές ασθένει αυξάνεται όταν υπάρχει διαθέσιμη υγρασία στις επιφάνειες των φυτών. Η σχετική υγρασία μέσα στο θερμοκήπιο εμφανίζει έντονη παραλλακτικότητα εξαιτίας της ανομοιόμορφης κατανομής της θερμοκρασίας, με αυξημένη πιθανότητα εμφάνισης επιφανειακής συμπύκνωσης πάνω στα φυτά. Για το λόγο αυτό ο έλεγχος της υγρασίας είναι απαραίτητος. Ο έλεγχος της υγρασίας, όταν πραγματοποιείται με εξαερισμό και ταυτόχρονη θέρμανση, αυξάνει την κατανάλωση ενέργειας του θερμοκηπίου. Στα θερμοκήπια που δεν έχουν εγκατεστημένο κάποιο σύστημα θέρμανσης δεν είναι δυνατός ο έλεγχος της υψηλής υγρασίας με εξαερισμό και θέρμανση. Με στόχο τη μείωση, την εξοικονόμηση ενέργειας στα θερμαινόμενα θερμοκήπια αλλά και τη δυνατότητα ελέγχου της υγρασίας στα θερμοκήπια χωρίς συστήματα θέρμανσης, στη παρούσα διατριβή, μελετώνται συστήματα μείωσης της σχετικής υγρασίας στο θερμοκήπιο Πριν τη μελέτη των συστημάτων υπολογίστηκε η εξατμισοδιαπνοή θερμοκηπιακής καλλιέργειας, μέσω ενός μοντέλου ισορροπίας υδρατμών βασισμένο στις απώλειες υδρατμών του θερμοκηπίου, μέσω διαφυγών στο εξωτερικό περιβάλλον, συμπύκνωσης στην εσωτερική πλευρά του καλύμματος και απωλειών από το σύστημα αφύγρανσης. Έτσι, οι απαιτήσεις αφύγρανσης του θερμοκηπίου προσδιορίστηκαν μέσω του παραπάνω ισοζυγίου υδρατμών για διατήρηση της σχετικής υγρασίας μέχρις ανώτατου ορίου. Κατασκευάστηκαν και μελετήθηκαν τρία συστήματα για την αφύγρανση του θερμοκηπίου: σύστημα υγρσκοπικής απορρόφησης, σύστημα αντλίας θερμότητας αέρα-αέρα κι υβριδικό σύστημα με συνδυασμό αντλίας θερμότητας και υγροσκοπικής απορρόφησης. Από τη δοκιμή του συστήματος της υγροσκοπικής απορρόφησης, βρέθηκε ότι η ικανότητα του στην απομάκρυνση υδρατμών από τον αέρα του θερμοκηπίου καθορίζεται από τη θερμοκρασία και την ειδική υγρασία του αέρα, από το ρυθμό ροής του αέρα μέσα από το σύστημα, από την συγκέντρωση και τη θερμοκρασία του υγροσκοπικού διαλύματος. Αν μπορεί να εξασφαλιστεί χαμηλού κόστους αναγέννηση του υγροσκοπικού διαλύματος τότε το κόστος λειτουργίας είναι μικρότερο συγκριτικά με το κόστος λειτουργίας του συστήματος της αντλίας θερμότητας. Η αποτελεσματικότητα απομάκρυνσης υδρατμών από την αντλία θερμότητας αυξάνεται με την αύξηση της θερμοκρασίας του θερμοκηπίου για σταθερό επίπεδο σχετικής υγρασίας. Ο έλεγχος της σχετικής υγρασίας με τη χρήση αντλίας θερμότητας αέρα-αέρα αυξάνει την θερμοκρασία ενός μη θερμαινόμενου θερμοκηπίου μέχρι και κατά 2°C. Η λειτουργία των υβριδικών συστημάτων αυξάνει την αποτελεσματικότητα απομάκρυνσης υδρατμών από τον αέρα, όμως η τεχνολογική τους ανάπτυξη καθορίζεται από την πορεία ανάπτυξης των υγροσκοπικών συστημάτων μιας και τα συστήματα συμπίεσης ατμού έχουν ήδη τυποποιηθεί και παρουσιάζουν παγκόσμια εμπορική εξάπλωση. Για την ανάπτυξη ενός ολοκληρωμένου συστήματος αφύγρανσης του θερμοκηπίου με χρήση υγροσκοπικών υλικών απαιτείται ο σχεδιασμός και η διαστασιολόγηση ενός ηλιακού συλλέκτη, ο οποίος θα παράγει την απαιτούμενη ενέργεια για την αναγέννηση του υγροσκοπικού υλικού. Από την αξιολόγηση της επίδρασης του ελέγχου της σχετικής υγρασίας στην ανάπτυξη, την παραγωγή και ευαισθησία προσβολής από το βοτρύτη βγήκε το συμπέρασμα ότι, ο έλεγχος της υγρασίας στο θερμοκήπιο αυξάνει σημαντικά την παραγωγικότητα των καλλιεργειών και περιορίζει την ανάπτυξη μυκητολογικών ασθενειών όπως ο βοτρύτης. Συμπερασματικά, λαμβάνοντας υπόψη την παρούσα κατάσταση της τεχνολογικής προόδου, στη παρούσα χρονική στιγμή, η αφύγρανση του αέρα του θερμοκηπίου με τη χρήση αντλίας θερμότητας μπορεί να θεωρηθεί ως η πιο ενδεδειγμένη λύση για την αφύγρανση τόσο των μη θερμαινόμενων θερμοκηπίων όσο και για την αφύγρανση των θερμαινόμενων θερμοκηπίων. Η αύξηση του εισοδήματος, λόγω της βελτίωσης της απόδοσης των καλλιεργούμενων φυτών, με τον έλεγχο της υγρασίας, διευκολύνει την απόσβεση εγκατάστασης μιας αφυγραντικής αντλίας θερμότητας

Ultraviolet Radiation Management in Greenhouse to Improve Red Lettuce Quality and Yield

The intensity of ultraviolet (UV) radiation affects the yield and quality of red lettuce. The current study aimed to develop a UV management system in a greenhouse to achieve high yield and quality in red lettuce production. The study consisted of two experiments. In the first experiment, the effects of the different UV transparencies of the plastic materials covering the greenhouse on plant growth and the concentration of antioxidants in red lettuce were studied. For this purpose, two greenhouses were covered with polyethene of different transparencies to UV radiation. One greenhouse was covered with a common type of polyethene transparent in a large spectrum of UV radiation (UV-open), while the second greenhouse was covered with polyethene untransparent to ultraviolet radiation (UV-block). The plants were grown in a deep flotation hydroponic system. At the end of the cultivation, plant growth measurements, leaf colour measurements, and the determination of antioxidant components’ concentration were carried out. Red lettuce plants harvested 42 days after planting had an average head weight 42% greater in the UV-block greenhouse compared to plants grown in the UV-open greenhouse. However, the red leaf colour of plants in the UV-block greenhouse lagged significantly compared to that in the UV-open greenhouse. Moreover, the total phenolic content, the total flavonoid content, and the antioxidant capacity of the lettuce leaves in the UV-block greenhouse were significantly lower compared to the corresponding values of the plants in the UV-open greenhouse. During the second experiment, a new cultivation system of red lettuce, which combined a UV-block polyethene film as a greenhouse cover and a pre-harvested supplemental UV light, was tested. For this purpose, various doses of supplemental UV lighting were tested in the UV-block greenhouse for ten days prior to harvest. From these tests, it emerged that applying supplemental UV lighting with a dose of 425 kJ m−2 d−1 for ten days before harvest produces red lettuces of the same quality as those produced in a UV-open greenhouse. This technique of growing red lettuce increases its yield by 30% without a negative effect on the quality of the product

Effects of infrared radiation (IR) on growth parameters of eggplant cultivation and greenhouse energy efficiency

Greenhouses are an exceptionally energy consuming sector of rural production with important contribution in the environmental imprint. This is because they are complex and sophisticated productive systems of intensive exploitation and require optimal management of radiation, heating and cooling. Energy consumption for greenhouse heating represents a serious concern for greenhouse operators throughout Europe that is further aggravated by the present oil price. An alternative method of heating the plants in a greenhouse is the use of infrared (IR) radiation. Infrared radiation heating systems possess the advantage of high directional control and focused compensation of energy losses, appropriate for creating local temperature conditions in thermally unprotected spaces like greenhouses. The advantages of infrared heating are verified and demonstrated in an experimental greenhouse with eggplant cultivation. The objective of this research is to investigate the effect of infrared radiation on growth parameters of eggplant. Extensive experimental results are presented from a full cultivation period inside two identical, small scale experimental greenhouses, with IR and forced air heating system, correspondingly, in South-West of Peloponnese, Greece. Eggplant (Solanum melongena L.) is used as the test crop for a three months’ period. The design, energy performance and plant growth results from the two greenhouses are presented, regarding the effect of IR heating to the cultivated plant. The produced data include solar radiation, relative humidity, and greenhouse indoor air temperature and plant growth. Results are compared to conventional cultivation. The implementation of an IR heating system in a greenhouse for eggplants production had satisfactory results, establishing a smooth distribution of the temperature at the canopy, while inside greenhouse air temperature was maintained at lower values than in the conventionally heated greenhouse. Quantitative results on plant growth and yield have been collected, and the favourable conditions resulted in better plant growth than in the conventionally heated greenhouse. © 2020 International Society for Horticultural Science. All rights reserved

Effects of infrared radiation (IR) on growth parameters of eggplant cultivation and greenhouse energy efficiency

Greenhouses are an exceptionally energy consuming sector of rural production with important contribution in the environmental imprint. This is because they are complex and sophisticated productive systems of intensive exploitation and require optimal management of radiation, heating and cooling. Energy consumption for greenhouse heating represents a serious concern for greenhouse operators throughout Europe that is further aggravated by the present oil price. An alternative method of heating the plants in a greenhouse is the use of infrared (IR) radiation. Infrared radiation heating systems possess the advantage of high directional control and focused compensation of energy losses, appropriate for creating local temperature conditions in thermally unprotected spaces like greenhouses. The advantages of infrared heating are verified and demonstrated in an experimental greenhouse with eggplant cultivation. The objective of this research is to investigate the effect of infrared radiation on growth parameters of eggplant. Extensive experimental results are presented from a full cultivation period inside two identical, small scale experimental greenhouses, with IR and forced air heating system, correspondingly, in South-West of Peloponnese, Greece. Eggplant (Solanum melongena L.) is used as the test crop for a three months’ period. The design, energy performance and plant growth results from the two greenhouses are presented, regarding the effect of IR heating to the cultivated plant. The produced data include solar radiation, relative humidity, and greenhouse indoor air temperature and plant growth. Results are compared to conventional cultivation. The implementation of an IR heating system in a greenhouse for eggplants production had satisfactory results, establishing a smooth distribution of the temperature at the canopy, while inside greenhouse air temperature was maintained at lower values than in the conventionally heated greenhouse. Quantitative results on plant growth and yield have been collected, and the favourable conditions resulted in better plant growth than in the conventionally heated greenhouse. © 2020 International Society for Horticultural Science. All rights reserved

Response to non-uniform salinity in the root zone of the halophyte Atriplex nummularia: growth, photosynthesis, water relations and tissue ion concentrations

Background and Aims Soil salinity is often heterogeneous, yet the physiology of halophytes has typically been studied with uniform salinity treatments. An evaluation was made of the growth, net photosynthesis, water use, water relations and tissue ions in the halophytic shrub Atriplex nummularia in response to non-uniform NaCl concentrations in a split-root system. Methods Atriplex nummularia was grown in a split-root system for 21 d, with either the same or two different NaCl concentrations (ranging from 10 to 670 mm), in aerated nutrient solution bathing each root half. Key Results Non-uniform salinity, with high NaCl in one root half (up to 670 mm) and 10 mm in the other half, had no effect on shoot ethanol-insoluble dry mass, net photosynthesis or shoot pre-dawn water potential. In contrast, a modest effect occurred for leaf osmotic potential (up to 30 % more solutes compared with uniform 10 mm NaCl treatment). With non-uniform NaCl concentrations (10/670 mm), 90 % of water was absorbed from the low salinity side, and the reduction in water use from the high salinity side caused whole-plant water use to decrease by about 30 %; there was no compensatory water uptake from the low salinity side. Leaf Na+ and Cl− concentrations were 1·9- to 2·3-fold higher in the uniform 670 mm treatment than in the 10/670 mm treatment, whereas leaf K+ concentrations were 1·2- to 2·0-fold higher in the non-uniform treatment. Conclusions Atriplex nummularia with one root half in 10 mm NaCl maintained net photosynthesis, shoot growth and shoot water potential even when the other root half was exposed to 670 mm NaCl, a concentration that inhibits growth by 65 % when uniform in the root zone. Given the likelihood of non-uniform salinity in many field situations, this situation would presumably benefit halophyte growth and physiology in saline environments