Articles | Volume 13, issue 11
Biogeosciences, 13, 3475–3484, 2016
https://doi.org/10.5194/bg-13-3475-2016
Biogeosciences, 13, 3475–3484, 2016
https://doi.org/10.5194/bg-13-3475-2016

Research article 15 Jun 2016

Research article | 15 Jun 2016

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

Stephane Bazot, Chantal Fresneau, Claire Damesin, and Laure Barthes Stephane Bazot et al.
  • Ecologie Systématique et Evolution, Univ-Paris-Sud, CNRS, AgroParisTech, Université Paris Saclay, rue du Doyen A. Guinier, Orsay, 91405, Orsay, France

Abstract. The origin of N which contributes to the synthesis of N reserves of in situ forest trees in autumn and to the growth of new organs the following spring is currently poorly documented. To characterize the metabolism of various possible N sources (plant N and soil N), six distinct 20-year-old sessile oaks were 15N labelled by spraying 15NH415NO3: (i) on leaves in May, to label the N pool remobilized in the autumn for synthesis of reserves, (ii) on soil in the autumn, to label the N pool taken up from soil and (iii) on soil at the beginning of the following spring, to label the N pool taken up from soil in the spring. The partitioning of 15N in leaves, twigs, phloem, xylem, fine roots, rhizospheric soil and microbial biomass was followed during two growing seasons. Results showed a significant incorporation of 15N into the soil–tree system; more than 30 % of the administered 15N was recovered. Analysis of the partitioning clearly revealed that in autumn, roots' N reserves were formed from foliage 15N (73 %) and to a lesser extent from soil 15N (27 %). The following spring, 15N used for the synthesis of new leaves came first from 15N stored during the previous autumn, mainly from 15N reserves formed from foliage (95 %). Thereafter, when leaves were fully expanded, 15N uptake from the soil during the previous autumn and before budburst contributed to the formation of new leaves (60 %).

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Short summary
The origin of N which contributes to N reserves of trees in autumn and to the growth of new organs the following spring is currently poorly documented. The metabolism of various possible N sources (plant and soil) was characterized in sessile oaks. Results revealed that in autumn, roots’ N reserves were formed from foliage N and to a lesser extent from soil N. The following spring, N used for the synthesis of new leaves came first from stored N and thereafter from N uptake from soil.
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