Influence of tree internal nitrogen reserves on the response of beech (Fagus sylvatica) trees to elevated atmospheric carbon dioxide concentration

Abstract

We examined the influence of plant internal nitrogen (N) reserves on the response of 3-year-old beech (Fagus sylvatica L.) trees to elevated atmospheric CO2 concentration ([CO2]) in a dual 15N and 13C long-term labeling experiment. Trees were grown on sand and received either no N nutrition (-N treatment) or 4 mM N (+N treatment) for 1 year. The -N and +N pretreated trees were then placed in growth chambers and grown in 350 (ambient) or 700 ppm (elevated) of a 13CO2 atmosphere for 24 weeks. In all treatments, trees were supplied with 4 mM 15N during the experiment. Irrespective of tree N reserves, elevated [CO2] increased cumulative carbon (C) uptake by about 30% at Week 24 compared with that for trees in the ambient treatment. Elevated [CO2] also caused a shift in C allocation to belowground compartments, which was more pronounced in -N trees than in +N trees. In +N trees, belowground allocation of new C at Week 24 was 67% in ambient [CO2] compared with 70% in elevated [CO2]. The corresponding values for -N trees were 70 and 79%. The increase in C allocation in response to elevated [CO2] was most evident as an increase in belowground respiration; however, specific root respiration was unaffected by the CO2 or N treatments. Although elevated [CO2] increased root growth and belowground respiration, it had no effect on N uptake at Week 24. As a result of increased C uptake, N concentrations were decreased in trees in the elevated [CO2] treatment compared with trees in the ambient treatment in both N treatments. Partitioning of new N uptake was unaffected by elevated [CO2] in +N trees. In -N trees, however, N allocation to the stem decreased in response to elevated [CO2] and N allocation to fine roots increased, suggesting a reduction in the formation of N reserves in response to elevated [CO2]. We conclude that the response of beech trees to elevated [CO2] is affected by internal N status and that elevated [CO2] may influence the ability of the trees to form N reserves.

Partitioning of remobilised N in young beech (Fagus sylvatica L.) is not affected by elevated [CO2]

“…Carbon uptake during the experiment was significantly increased under elevated [CO 2 ], as was indicated by the increase in RSA of new C in the elevated treatment by 27% from 30.5 ± 2.8 under ambient to 38.6 ± 5.7% under elevated [CO 2 ], which is comparable to results we obtained earlier [6].…”

“…In an earlier study this was also found for the partitioning and amount of new N uptake although the partitioning of new C to roots and root respiration was increased under elevated [CO 2 ] as compared to ambient [6]. In this latter study, we could also show that no increased N store formation was observed under elevated [CO 2 ].…”

“…The partitioning describes the proportion of the labelled element in a given plant organ relative to the total labelled element in the whole plant [3,6].…”

“…Generally, tissue N concentration in trees under elevated [CO 2 ] tends to decrease [2], indicating that store formation is not increased under elevated [CO 2 ]. It has been shown, that N stores formation in beech (Fagus sylvatica L.) was not increased under elevated [CO 2 ], but might even be decreased under unfavourable conditions [6].…”

Do trees use reserve or newly assimilated carbon for their defense reactions? A 13C labeling approach with young Scots pines inoculated with a bark-beetle-associated fungus (Ophiostoma brunneo ciliatum)

“…Labeling trees with a stable carbon isotope ( 13 C) is a powerful tool to follow dynamics of newly assimilated and of stored C [3,19]. We report here on an experiment aiming at quantifying the relative contribution of the two available sources of carbon (assimilation, storage) in supplying the induced-reaction zones of three-year-old Scots pines.…”