No abstract

Initiation of new shoots originating from basal meristems of older shoots of Carex rostrata was studied in relation to the internal carbon/nitrogen balance. In a greenhouse experiment, individual shoots with a vigorous formation of a new shoot contained the highest concentrations of free amino acids (FAA) and the lowest concentrations of total nonstructural carbohydrates (TNC), resulting in a low TNC/FAA ratio. Thus shoots with high availability of nitrogenous compounds in relation to carbohydrates started growing a new shoot. The results suggest that TNC/FAA ratios could affect shoot densities. Field measurements supported this view: TNC/FAA ratios were lower in a mesotrophic site with a high density of shoots than in an oligotrophic site with a low density of shoots. Compared with roots, TNC/FAA ratios of shoots seemed to be more decisive both in the greenhouse experiment and in the field. In the greenhouse experiment, initiation of new shoots was measured in fragmented shoots of Carex having no intraclonal connections. Even if physiological integration was lacking due to fragmentation, shoot initiation was efficiently controlled in relation to the internal carbon/nitrogen balance.

Increased foliar N/K and N/Mg ratios are known to reduce the resistance of Pinus sylvestris to scleroderris canker caused by Gremmeniella ahietina. The aim of this work was to study how such changes in nutrient levels affect the growth of the pathogen in vitro. The mycelium of the pathogen was grown on artificial media adjusted to simulate the changes in inorganic N, K, Mg and Ca and free amino acid concentrations in the host with nutritional imbalance. Increased concentrations of K and Ca reduced the mycelial growth of the pathogen, whereas a modest increase in the concentration of inorganic N increased the growth. Tenfold concentrations (compared with normal host levels) of arginine and glutamic acid, and up to one hundred-fold concentrations of proline increased the mycelial growth. The results suggest, that nutrient imbalances may enhance the colonization of host tissues by G. ahietina.