Leaf demography and the seasonal internal cycling of nitrogen in sycamore (Acer pseudoplatanus L.) seedlings in relation to nitrogen supply

Abstract

SUMMARYThe dynamics of tbe seasonal internal cycling of nitrogen (N) in Acer psexidoplatonus were studied in relation to N supply and leaf demography. Trees were grown in sand culture, and throughout 1988, supplied with either 1-0 mol N m"' (Low N) or 6-0 mol N m •' (High N), labelled with '-"'N to 5-0 atom %, in order to precondition their growth and capacity for N storage over the winter period. In 1989, the initial spring growth of leaves was independent of the current N supply at either 1-0 or 6-0 mol N n-i '', and depended only upon the N supplied in 1988. A net loss of '-''N from perennial tissues and recovery of '^N in the growing leaves confirmed that the current N supply had no eflect on the remobilization of N from winter stores in the roots and stem. After 22 May 1989, remobilization of stored N for leaf growtb bad ceased and leaf den-iography was influenced by the current N supply. Plants preconditioned to 6-0 mol N m'^ in 1988, but receiving only 1-0 mol N m"" in 1989, were unable to sustain previous leaf growth after 22 May and there was a decrease in leaf mass and area due to leaf abscission. In contrast, trees preconditioned with 1-0 mol N m~^ in 1988, hut receiving 6-0 mol N m"'' in 1989 greatly increased tbeir leaf growth after 22 May. This was a consequence ofthe stimulation by N uptake of growth of n-iany small leaves on axillary shoots at the base of the canopy. Although leaf number increased, mean area per leaf decreased.The trees were inefficient at withdrawing N from senescing leaves in botb years, allowing most of the N to fall from the tree witb tbe leaves. The spring remobilization of N, therefore, was dependent largely upon the direct uptake of N into the stem and roots, in late summer and autumn, for storage over the winter period. Tbe results are discussed in relation to leaf demography and the nitrogen use efficiency of deciduous trees.

Contribution of previous year's leaf N and soil N uptake to current year's leaf growth in sessile oak

“…This compartment could be defined as a storage compartment in young sessile oaks. Such an observation has been already reported for oaks of the same pole stand (Gilson et al, 2014), and similar findings were reported for field-grown adult peach trees by Tagliavini et al (1997), being typical of other young deciduous trees (Millard and Proe, 1991;Salaün et al, 2005;Tromp and Ovaa, 1979;Wendler and Millard, 1996). On this date (end of September), branches and coarse roots could also have contributed significantly to N storage, as previously described (Bazot et al, 2013).…”

Carbon and nitrogen winter storage and remobilisation during seasonal flush growth in two-year-old cork oak (Quercus suber L.) saplings

“…The experiment took place outdoors at the Instituto Superior de Agronomia (Lisbon, Portugal). Plants were regularly watered and, twice a week, fertilised with a complete nutrient solution (6 mol m -3 N in the form NH 4 NO 3 ) as detailed in [17]. Spring growth flush began in March and lasted until July 1997.…”

Use of stable isotopes to quantify nitrogen, potassium and magnesium dynamics in young Scots pine (Pinus sylvestris)

“…Each week, 1000 cm$ of nutrient solution containing 6n0, 1n33, 1n25, 0n75, 2n0 and 1n25 moles m −$ of N, P, K, Mg, Ca and S, respectively, with 20, 10, 5, 1 and 1 mmoles m −$ of Fe, Mn, B, Zn and Cu, respectively, was applied to each tree (Millard & Proe, 1991). Additional deionized water was applied as required during summer.…”