Abstract
Leaf area is one of the most important biophysical characteristics of a plant, as it determines how much photosynthetic radiation is intercepted so that the photosynthesis can occur. The presented research aim was to generate numerical indicators of leaf area and to study the behavior of black wattle (Acacia mearnsii De Wild.) throughout a plantation cycle (7 years), relating them with environmental variables. The study was conducted in commercial stands located in agroecological regions with high densities of black wattle plantations in the state of Rio Grande do Sul, Brazil. The leaf area was obtained by measuring leaf biomass and leaf area with an integrator (3000 Canopy Analyser, Li-Cor). Leaf area was found to be strongly related to leaf biomass, and is not influenced by planting site, but rather by stand age. Values ​​of individual leaf area vary depending on stand age and plantation area. The leaf area is related to soil properties and particularly with the phosphorus content. It is also related to meteorological conditions, most notably accumulated solar radiation. The obtained model, which involves global accumulated solar radiation, phosphorus and clay content, adequately explain variations in leaf area. Key words: Global solar radiation, phosphorus, leaf biomass, black wattle, plantation cycle.
Highlights
Black wattle (Acacia mearnsii De Wild.) is a commonly occurring tree species today in the state of Rio Grande do Sul, and stands of the species rank among the most widely planted in the region behind the generaEucalyptus and Pinus
Among planting sites in 5 and 7 year old stands were observed (Table 2 - simple effects), and those stands established in Piratini had the highest mean leaf area values. These results suggest that when mean values of leaf area are used, one must consider planting location and stand age
Leaf area was strongly related to dry leaf weight
Summary
Black wattle (Acacia mearnsii De Wild.) is a commonly occurring tree species today in the state of Rio Grande do Sul, and stands of the species rank among the most widely planted in the region behind the generaEucalyptus and Pinus. Leaf area is a variable indicator of productivity because plant growth (when soil nutrition, water availability and temperature are not limiting factors) depends on the amount of photosynthetically active radiation intercepted and the utilization efficiency of this energy during photosynthesis for biomass production (Monteith, 1977). Generating numerical indicators of leaf area with the purpose to address these points will allow further studies to be conducted relating leaf area to yield (either in timber, volume or biomass) of certain species. The present study sought to analyze leaf area in stands of black wattle (Acacia mearnsii De Wild.) for the duration of the plantation cycle; and with the following hypothesis to be tested: Leaf area in plantations of black wattle can be evaluated as a function of the climatic and soil variables
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