Browsing by Author "Nevhungwili, Mashudu Lucy"

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    Cambial responsiveness in four eucalypt varieties to onset of drought as well as spring conditions
    (Stellenbosch : Stellenbosch University, 2024-02) Nevhungwili, Mashudu Lucy; Drew, David Michael; Eckert, Michelle; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT:Xylogenesis is a highly dynamic and seasonal process resulting from variations in cell production by the meristem (vascular cambium). This process results in the formation of secondary xylem and phloem cells within the period of active wood formation, leading to increased stem radius. This study explored secondary wood formation amongst four Eucalyptus varieties (Eucalyptus grandis, Eucalyptus grandis x nitens, Eucalyptus grandis x urophylla and Eucalyptus urophylla)in response to change in environmental conditions. It focussed on two study periods (an induced drought and spring period)in order to see how sensitive the varieties are to drought along with the responsiveness of the varieties to change in growth conditions during spring. To answer these questions, two-year old trees growing in an uncontrolled environment with Mediterranean climate were monitored during drought induced (March) and spring growth (August-September) seasons of 2022. Repeated wood core sampling, together with diameter change measurements, were carried out twice a week during drought induced period and once a week during spring period. Environmental data was obtained from a weather station placed adjacent to the trees. From the selected trees wood samples were extracted using a Trephor corer in a descending spiral pattern. Microcores were cut, stained, and fixed in the laboratory to produce anatomical sections, which were then observed under both Brightfield and Fluorescence microscopic imagery. The developing zone width (cambial and expanding cells zone) along with the cells in two stages of xylogenesis (cell division and differentiation) were analysed using QuPath. The results of the drought induced period showed that irrigation suspension had the greatest effect on wood formation in all studied varieties. Trees experiencing stress showed a decreased cell production as drought progressed, indicating ceased cambial activity, resulting to narrower developing zone contributing to a decreased tree size. After temporal irrigation during this period, varieties showed recovery which was observed in both stem radius and cell production. The response in the developing zone was however delayed in Eucalyptus grandis x urophylla and Eucalyptus urophylla. The response to irrigation application showed that the cambium of trees was in an eco-dormancy stage before irrigation application. The results on irrigated trees during spring period showed an active cambium during late-winter to early spring with no spring start up evident. Rainfall during this season did not show noticeable effects on wood formation across all varieties. The response of the varieties showed different maximum temperatures for wood formation during spring period. Eucalyptus urophylla showed to be sensitive to daily temperatures of above 16°C, while other varieties were sensitive to temperatures above 17°C. Results from this study lead to the conclusion that secondary wood formation in Eucalyptus varieties growing in the Mediterranean climate is controlled by how favorable the environment is.