High temperature effect on physiology, growth and flowering of Protea cv. Pink Ice.

Thesis (MScAgric)--Stellenbosch University, 2010.

ENGLISH ABSTRACT: As production areas expand to new, warmer areas, little information is available on the effect of high temperatures on the growth, physiology and flowering of Protea. In addition, high temperature effects on crops are becoming increasingly important as global temperatures rise. In this study, the influence of high temperature on Protea ‘Pink’ Ice was investigated. The expectation was that optimal and supra-optimal temperature regimes could be identified with respect to parameters of importance to commercial protea production. Firstly, a greenhouse-based experiment with potted plants subjected to five levels of warming with a temperature gradient ranging from ambient to ambient+3.1°C, was established with infra-red lamps. A field verification experiment with two treatments, ambient and ambient+2.9°C, was established in a commercial orchard. Leaf net CO2 assimilation rate (Amax) and dark respiration rate (Rd) acclimated to the temperature gradient on a leaf area-basis. However, on a leaf mass-basis Amax and Rd decreased at higher temperatures. Stomatal conductance (gs) remained approximately constant over the temperature gradient, but increased at higher temperatures on a mild spring day and decreased on hot days. On a seasonal basis, maximum Amax and gs values were reached during spring, whilst maximum Rd rates were achieved during mid-summer. Topt tracked seasonal temperatures closely. At higher temperatures spring budbreak advanced by 1-2 weeks in both the greenhouse and field verification experiments. Flowering took place on the spring flush at ambient temperature, but this bearing habit shifted to summer flushes at the high temperature treatments. In the field verification experiment inflorescences on warmed plants were harvested earlier compared to those at ambient temperatures, as warming was possibly more optimal in the field than in the greenhouse (greenhouse “ambient” being warmer than field “ambient”). In the second experiment conducted on a commercial farm, shoots bearing inflorescences which initiated on the autumn flush (April-May) were compared with shoots bearing inflorescences on the spring flush (August-September). Inflorescences initiated on the autumn flush, three months prior to those on the spring flush, were harvested one month earlier with a significantly higher final dry mass. When comparing the gas exchange capacity of the two systems, seasonal climatic changes was found to have a stronger controlling influence than the phenological stage of the shoot. For the third part of the study, vegetative and reproductive growth, physiology, gas exchange and carbohydrate trends were observed for one year in a commercial Protea ‘Pink Ice’ orchard. A threshold concentration of starch in mature leaves of the terminal flush, together with an estimated minimum stem diameter of 7.6 mm of a four- or five-flush shoot was suggested as a partial requirement for inflorescence initiation in Protea ‘Pink Ice’. The results of this study show that Protea ‘Pink Ice’ is well able to photosynthesise, grow and reproduce at temperatures 1-2°C higher than ambient. However, shifts towards weaker reproductive growth in favour of stronger vegetative growth under strong warming could have negative implications for commercial producers.

AFRIKAANSE OPSOMMING: Protea verbouing brei tans uit na nuwe, warmer produksie areas en daar is baie min inligting oor die effek van hoë temperatuur op die fenologie, groei, fisiologie en blominisiasie van Protea. Boonop word die impak van hoë temperature op gewasse toenemend belangrik as gevolg van aardverhitting. Tydens hierdie studie is die invloed van hoë temperature op Protea ‘Pink Ice’ ondersoek. Die verwagting was dat optimale en supra-optimale temperatuur grense geïdentifiseer kon word in terme van parameters wat belangrik is vir kommersiële proteaproduksie. Eerstens is twee jaar oue potplante in ‘n kweekhuis onderwerp aan ‘n temperatuur gradient van vyf verwarmings vlakke, van heersende temperatuur tot heersend+3.1°C, met behulp van infrarooi lampe. ‘n Boordbevestigings-eksperiment met twee temperatuur behandelings, heersende temperatuur en heersend+2.9°C, is opgerig op ‘n kommersiële protea plaas. Die tempo van netto CO2 vaslegging (Amax) en donker-respirasie tempo (Rd) het aangepas by die temperatuur gradiënt op ‘n blaar area-basis. Egter, indien uitgedruk op ‘n blaar massa-basis het Amax en Rd afgeneem by hoë temperature. Huidmondjie geleiding (gs) het ongeveer konstant gebly oor die gradiënt, maar het toegeneem by hoë temperature op gematigde lente dae en afgeneem op baie warm dae. Seisonale maksimum Amax en gs waardes is bereik tydens die lente maande, terwyl maksimum Rd waardes in die somer maande aangeteken is. Topt het die seisonale temperatuur neigings nageboots. By die hoë temperatuur behandelings van beide die kweekhuis en boordbevestigings-eksperimente het lente bot van die terminale groeistuwing 1-2 weke vroeër plaasgevind as by plante teen heersende temperature. Blominisiasie het hoofsaaklik plaasgevind op die lente groeistuwing by plante by heersende temperatuur, maar by hoë temperatuur behandelings het blominisiasie later, op somer groeistuwings plaasgevind. In die boordbevestigings-eksperiment is blomme vanaf die verhitte plante twee weke vroeër geoes in vergelyking met blomme afkomstig van plante sonder verhitting. Dit dui daarop dat die verwarming in die boord heel moontlik meer optimaal was as in die kweekhuis (kweekhuis “heersende temperatuur” was warmer as boord “heersende temperatuur”). ’n Tweede eksperiment is uitgevoer op ‘n kommersiële plaas, waar lote met blomme wat op die herfs-groeistuwing (April-Mei) inisieër het vergelyk is met lote waarvan die blomme op die lente-groeistuwing (Augustus-September) inisieër het. Blomme op die herfs-groeistuwing wat drie maande voor blomme op die lente groeistuwing inisieër het, is een maand vroeër geoes met ‘n verhoogde finale droëmassa. Wanneer gaswisseling van die twee sisteme vergelyk is, was dit bevind dat seisonale temperature ‘n groter beherende invloed op die gaswisseling patroon het as die fenologiese stadium van die loot. Vir die derde deel van die studie is vegetatiewe en reproduktiewe groei, fisiologie, gaswisseling en koolhidraat tendense waargeneem vir een jaar in ‘n kommersiële Protea ‘Pink Ice’ boord. ’n Drempelwaarde in die stysel konsentrasie van die volwasse blare van ’n vegetatiewe terminale groeistuwing, tesame met ’n minimum lootdikte van 7.6 mm by ’n vier- of vyf groeistuwingsloot word voorgestel as ’n gedeeltelike voorveiste vir blominisiasie by Protea ‘Pink Ice’. Die resultate van hierdie studie wys dat Protea ‘Pink Ice’ voldoende kan fotosinteer, groei en reproduseer by temperature 1-2°C hoër as heersend. Egter, ‘n verskuiwing na verlaagde reproduktiewe produksie kan voorkom, aangesien sterker vegetatiewe groei in lote bevoordeel word onder toestande van intense verwarming en dit mag negatiewe implikasies hê vir kommerisële produksie.

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