Ecofisiologia de árvores na fase juvenil em resposta à adubação mineral e sazonalidade da precipitação em uma floresta nativa na Amazônia Central
Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objectiv...
| Autor principal: | Magalhães, Nilvanda dos Santos |
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| Grau: | Tese |
| Idioma: | por |
| Publicado em: |
Instituto Nacional de Pesquisas da Amazônia – INPA
2020
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| Acesso em linha: |
https://repositorio.inpa.gov.br/handle/1/4952 http://lattes.cnpq.br/5752676372195234 |
| Resumo: |
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Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to investigate how photosynthetic rates, growth of tree saplings and leaf nutrient content respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. It was also studied the relationships between leaf nutrients contents, photosynthetic rates and growth of saplings in the understory of the forest. The study was conducted at the Tropical Forestry Experimental Station (ZF2 reserve), of the (National Institute for Research in the Amazon). We used five species at the juvenile stage, with up to 3 m tall. We assessed the effect of adding 75 g per plant of a slow-release fertilizer (containing 15% N, 9% P, 12% K, 1% Mg, 2.3% S and micronutrients). The control was unfertilized plants. In the fertilized treatment, the total amount of fertilizer was equally split into five applications (Dec 2010, Mar, June, Sept and Dec of 2011; i.e. 15 g per plant on each occasion). We determined plant growth from 2010 to 2012 and gas exchange (Light saturated photosynthesis (Amax) and photosynthetic capacity of the leaf (Apot), stomatal conductance (gs), maximum carboxylation velocity of Rubisco (Vc-max) and maximum rate of electron transport (Jmax), leaf contents of nitrogen (N), phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg), leaf area index (LAI), soil water content, predawn leaf water potential (Ψleaf) and leaf traits (thickness and specific leaf area - SLA) in the wet and dry season of 2012. Rainfall seasonality led to variations in soil moisture (51% in the dry season to 67% in the rainy season and Ψleaf (-0.26 Mpa in the dry period) to -0.13 MPa in the rainy season), but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings, gs-max, Vcmax e Jmax declined with increases in LAI of the forest canopy. Likewise, the decline in water content in the soil during the dry season and the addition of nutrients had no effect on the leaf contents of N, P, K, Ca and Mg, leaf thickness and SLA. With the exception of the annual relative growth rate (RGR), Apot on a mass basis was responsive to variation in leaf nutrient contents (p>0,05). The lack of an effect of rainfall
seasonality on photosynthetic rates, growth of saplings and leaf nutrient contents may be due to the fact that during the studied period the dry season was not so strong as to reduce soil moisture to levels that could negatively affect carbon assimilation and other leaf traits of examined species. It was also shown that photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Finally it was concluded that although the Amazonian soils are poor in nutrients, photosynthesis and sapling growth in the forest understory will not be limited by the availability of mineral nutrients in the soil. |