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Seasonal variation in the nutrient composition of mountain birch leaves.
Ruuhola, Teija*,1, Ossipov, Vladimir2, Lempa, Kyösti3, Haukioja, Erkki4, 1 University of Turku, Turku, -, Finland2 University of Turku, Turku, -, Finland3 University of Turku, Turku, -, Finland4 University of Turku, Turku, -, Finland
ABSTRACT- In ecological studies, plant nutritive value for herbivores is often described by its total nitrogen or protein content although the nutritive value of proteins is strongly depended on the amino acid composition of plant proteins that differs considerably from the amino acid composition of animal proteins. Herbivore growth may depend on the paucity of only some essential amino acids that may restrict herbivore growth. In this study, we examined seasonal variation of the concentration of individual amino acids, both free and protein-bound, in mountain birch leaves. Both free and protein-bound amino acids steeply decreased along the leaf maturation, but within free amino acids this was due to some nonessential amino acids (Asp, Asn, Glu, Gln, Pro, Ala) only; essential free amino acids stayed at a low level all the time. In general, individual amino acids decreased at different rates, profoundly changing the ratios among different amino acids. Among free amino acids, the relative levels of several essential amino acids (Lys, Ile, Phe, His, Leu, Val) increased at the expense of non-essential amino acids. On the other hand, among protein-bound amino acids the relative levels of three essential amino acids, Phe, Ile, Arg and Lys, decreased in early season that might further decrease the nutritive value of maturing birch leaves.
KEY WORDS: mountain birch, amino acids, nutrients, herbivory