Abstract
The aim of this study was to evaluate the use of leaf color pattern to analyze leaf nutrient concentrations in Eucalyptus and to establish relationships between color patterns and leaf nutrient concentrations. The study was carried out in Eucalyptus stands at 25 months old using three leaves from the lower of tree crowns classified into five color patterns of Munsell color charts for plant tissues. The principal component analyses and the self-organizing maps were used to aid in the classification of samples in leaf color patterns. Subsequently, the k-means cluster algorithm was performed. In principal component analysis, the 7.5 GY 8/8 leaf color pattern stood out from the others and it was mainly influenced by nitrogen, phosphorous, copper, and potassium concentrations. The samples of 7.5 GY 8/4 leaf color pattern did not present a great nitrogen, phosphorous, sulfur, copper and potassium concentrations as the 7.5 GY 8/8 neither a great manganese, calcium, boron, zinc and iron concentrations as others leaf color patterns. The self-organizing map provides a greater proximity between the 7.5 GY 8/8 and 7.5 GY 8/4 leaf color patterns and the others leaf color patterns were randomly distributed in the U-matrix. Although the k-means algorithm presented two clusters in both analyses, the self-organizing map presented a slight superiority than principal component analysis. Using leaf color patterns was possible to infer about leaf nutrient concentrations in Eucalyptus. Both methods were able to distinguish only the healthy leaves 7.5 GY 8/8 from those whose were in the leaf senescence process.
Highlights
The Eucalyptus, a relevant tree for Brazilian timber production, contributed R$ 71.1 billion to the country’s gross domestic product in 2016 (Ibá 2017)
The leaf senescence process in crown basal leaves begins with the canopy closure
The leaf senescence is a process of leaf cell disruption with traits and ions mobilization released during the process (Thomas and Stoddart 1980; Maillard et al 2015)
Summary
The Eucalyptus, a relevant tree for Brazilian timber production, contributed R$ 71.1 billion to the country’s gross domestic product in 2016 (Ibá 2017). These species undergo different development and growth stages during its stand growing season. The canopy closure and nutrients cycling start and, along with fertilizations previously carried out, are enough to ensure production until the stem cutting with approximately seven years old. The leaf senescence process in crown basal leaves begins with the canopy closure. Leaf nutrients with greater mobility in phloem are translocate from senescent leaves to young tissues in plants (Himelblau and Amasino 2001; Avice and Etienne 2014). Protein and chlorophyll concentrations decrease in senescent leaves causing leaf yellowing (Hörtensteiner and Krãutler 2011)
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