Long-term water stress and fertilization on Eucalyptus grandis trees: implications for growth, recovery and wood properties

• Ano de defesa: 2021
• Autor(a) principal: Legoas, Roger Chambi
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Climate change; Drought; Forest nutrition; Mudanças climáticas; NIRS; Nutrição florestal; Plasticidade do xilema; Resiliência das árvores; Seca; Tree resilience; Xylem plasticity
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/11/11150/tde-11022022-175353/

Eucalyptus plantations are already planted in - or expanding to - water-limited regions with a high risk of severe drought. In future drier climate including extreme events, the growth responses and xylem plasticity of trees to droughts, and the growth recovery ability following severe droughts emerge as a crucial for the sustainability of forest plantations. Also, since fertilizers such as potassium (K) are intensively used to achieve high productivity for Eucalyptus grandis in these regions, it is important to know the interactive effects of K fertilization and water availability over a full rotation, not only in productivity but also in wood properties, since they are determinants of the quality and yield of products. To address these concerns, two experimental plantations of E. grandis were set up in Itatinga, São Paulo, Brazil. (i) A 6-year experiment involving two levels of water regime: 37% throughfall reduction and undisturbed throughfall, and two levels of fertilization: K addition and non-K addition; and (ii) another 6-year experiment involving two levels of water regime: 80% throughfall reduction and undisturbed throughfall. In the first experiment, the main objectives were to evaluate the interactive effects of K fertilization, water availability, and age on basal area increment (BAI) and wood quality and test if K fertilization increases xylem plasticity in response to drought. The second experiment\'s main objective was to evaluate the growth recovery ability following 80% throughfall reduction. The study focused on the changes in basal area, stem radius, and total height measured by high-temporal resolution dendrometers and periodical surveys of trees. Xylem traits measured were wood density (WD), cell wall fraction (CWF), cell density (CDen), theoretical xylem specific hydraulic conductivity (Kst), vessel diameter (VD), vessel density (VDen), vessel area (VA), and vulnerability index (VI). Wood properties comprised heartwood proportion, fibers size, and wood density. The results show that K fertilization increased growth rate over the full rotation. However, these effects were highly dependent of water availability, increasing BAI by 3-fold in well-watered seasons but stopping growth in severe seasonal drought periods. The 37% throughfall reduction affected growth only in K-fertilized trees until 2.5 years after planting. K fertilization increased xylem traits plasticity. The 80% reduction in throughfall over 3 years significantly reduced tree growth rates by 73% in basal area and 95% in total height. However, under normal water availability following throughfall reduction, the basal area growth rate of water-stressed trees was 97% higher than that of the control trees while total height growth rate was only 8% higher. Despite the severe water stress, no tree mortality was observed. Trees recovered 51% of their basal area over the 31-month recovery period. In contrast, only 5% of total height was recovered. It demonstrates a great recovery ability of E. grandis trees in basal area growth. Regarding wood quality, K fertilization did not promote significant losses in wood quality, even under water stress over a complete rotation.