Physiological responses of young eucalyptus grandis × eucalyptus urophylla plants to soil moisture and vapor pressure deficit variables, and kaolin particle film application as a water stress mitigator
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Data
2025-03-21
Autores
Gibson, Elbya Leão
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Universidade Federal do Espírito Santo
Resumo
Eucalyptus is the most extensively cultivated forest species on the planet, with a total area of 25 million hectares planted. Brazil is the world's foremost producer, with 7.6 million hectares under cultivation. Among the hybrids, Eucalyptus grandis × Eucalyptus urophylla (I144) is especially prominent due to its rapid growth, robust resistance to fungal diseases, adaptability and high density. However, climate change can have a severe impact on Eucalyptus production, making it essential to look for alternatives to mitigate the impacts of water restrictions and increasingly frequent temperature rises. The present thesis is thus structured in three chapters. The aim of Chapter I was to assess the ecophysiological responses of Eucalyptus grandis × Eucalyptus urophylla plants grown at different levels of water availability, in order to identify the level at which water limitation begins to affect plant growth. The plants were grown for 30 days in 12-litre pots with commercial substrate and watered daily to keep the water in the substrate close to the maximum water retention capacity (MWRC). Subsequent to this initial period, the plants were subjected to five levels of water availability: 100%, 80%, 60%, 40%, and 20% of the MWRC. The analyses encompassed measurements of leaf water potential (leaf), leaf gas exchange, branch hydraulic conductivity (Ks) and growth. The results obtained demonstrate that the critical threshold for the growth of young Eucalyptus grandis × Eucalyptus urophylla plants is between 40% and 60% of the MWRC. Below this range, the plants exhibited signs of water stress, which compromised their growth and development. The aim of Chapter II was to examine the responses of young Eucalyptus grandis × Eucalyptus urophylla plants to different vapor pressure deficits (VPD) under conditions of water restriction. Plants of the Eucalyptus grandis × Eucalyptus urophylla clone were grown for 75 days in pots (60 litres) containing commercial substrate, with daily watering. The plants were then exposed to two distinct environments: I) high atmospheric demand (HAD) - high maximum VPD (5.8 kPa) and II) low atmospheric demand (LAD) - low maximum VPD (3.2 kPa) and two levels of soil water availability (control and stressed). Ecophysiological analyses included measurements of leaf, leaf gas exchange, photosystem II quantum efficiency (Fv/Fm) and Ks. The results obtained suggest that high atmospheric demand exacerbates the negative effects of water stress, impairing plant hydraulic efficiency and gas exchange. Hydraulic efficiency was reduced by 28% in the HAD treatment compared to the LAD treatment under water deficit, and CO2 assimilation was reduced by 10%. The aim of Chapter III was to assess the effects of foliar application of kaolin in mitigating the negative effects of water restriction on young Eucalyptus grandis × Eucalyptus urophylla plants. Plants were grown for 75 days in pots (60 litres) containing commercial substrate, with daily watering. The plants were then subjected to three treatments: 70% of MWRC (control), progressive reduction of water availability (Stress) and progressive reduction of water availability with kaolin application (Stress + KL). Ecophysiological analyses included measurements of reflected solar radiation, leaf temperature, leaf gas exchange, leaf, Fv/Fm and Ks. The results obtained from this study demonstrate that the foliar application of kaolin constitutes an effective strategy for mitigating the adverse effects of water stress in Eucalyptus grandis × Eucalyptus urophylla clones, particularly during the initial days of water restriction.
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Restrição hídrica , Espécies arbóreas , Demanda atmosférica , Fotoprotetor foliar , Relações hídricas , Assimilação de CO2