Modelling the Seasonal Nitrogen Partitioning in Young Sycamore (Acer pseudoplatanus) Trees in Relation to Nitrogen Supply

A model of nitrogen partitioning during the seasonal growthof sycamore (Acer pseudoplatanus) seedlings was developed andtested against data from trees grown with two contrasting levelsof nitrogen supply. The model considered each tissue type (roots,trunk, stems and leaves) as sources and sinks for nitrogen andused flow equations to simulate the dynamics of nitrogen partitioningduring a growing season, with increases in tissue dry matteras driving force variables. Withdrawal of nitrogen from leavesduring senescence was allocated back to other tissues assuminga linear decrease in leaf mass. The model was fitted to data from trees grown in sand culturewith 6·0 molN m^-3 (high N) supplied with the irrigation.Model parameters thus determined were used to predict nitrogenpartitioning in trees grown with 1·0 molN m^-3 (low N)in the same year, and for trees from both treatments given eitherhigh or low N during a second year. The model accurately predictedthe nitrogen content of roots and leaves and gave small errorsin the amount of nitrogen partitioned to stems. In contrast,the nitrogen content of the trunks were over-estimated due toa failure to simulate the decreased in nitrogen content foundat the start of the growing season. The ability of the modelto simulate nitrogen partitioning by changes in tissue dry matterin trees of varying size and nitrogen status is discussed andpossible modifications to model partitioning of trunk nitrogenmore accurately suggested.Copyright 1993, 1999 Academic Press Modelling, nitrogen partitioning, ¹⁵N supply, Acer pseudoplatanus (sycamore), young seedlings