Seasonal dynamics of production, and nutrient accumulation and cycling by Phragmites asutralis (Cav.) Trin. ex Stuedel in a nutrient-enriched swamp in Inland Australia. II. Individual Shoots

Abstract

The seasonal dynamics of the growth of shoots of Pragmites australis, and the partitioning of dry matter and 12 mineral nutrients between shoot organs, were studied in a stand in a nutrient-enriched swamp in inland Australia. The stem accumulated over 75% of the total-shoot dry matter, the inflorescence less than 5%. About 26% of the shoot dry matter was redistributed to below-ground organs during senescence.

K and N were the most concentrated macronutrients in shoots, followed by Cl>> Ca > S > P > Mg > Na. Micronutrient concentrations were in the order Mn > Fe >> Zn > Cu. Concentrations of most nutrients and total amino compounds were higher in leaves than stems. Concentrations of N, P and K were highest in young shoots and decreased throughout the season, whereas concentrations of Ca, Cl, Fe, Mn and Na increased during the life of the shoot. There were gradients of concentration of some nutrients in the stem and leaves from the base to the top of the shoot. The top of the shoot had the highest concentrations of nutrients. Ca and Mn accumulated mainly in the large leaves from the middle of the shoot. The stem contained the major proportion of the quantity of most nutrients in living shoots; however, leaves had over 55% of the total shoot content of N, Ca and Mn. The inflorescence usually had less than 10% of the quantity of a nutrient in the shoot, but had over 20% of the N and 32% of the P in the shoot. N, P and K were redistributed from senescing shoots to below-ground organs with over 60% efficiency, and S, Mg, Zn and Cu with between 17 and 38% efficiency. There was negligible redistribution of Ca, C1, Na, Fe or Mn from either leaves or stems. Nutrients were redistributed to a greater extent from leaves than from stems. There were leaching losses of some nutrients from exposed senescing shoots, especially with K, C1 and Na. Nutrients were leached more readily from leaves than from stems. Leaching losses of N were low (c. 5%). Shoots from part of the reed-bed burnt the previous winter were smaller, had fewer leaves, and had lower concentrations of most nutrients than those from the unburnt part of the reed-bed.