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

Abstract

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-yearold sessile oaks were 15 N labelled by spraying 15 NH 15 4 NO 3 : (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 15 N in leaves, twigs, phloem, xylem, fine roots, rhizospheric soil and microbial biomass was followed during two growing seasons. Results showed a significant incorporation of 15 N into the soiltree system; more than 30 % of the administered 15 N was recovered. Analysis of the partitioning clearly revealed that in autumn, roots' N reserves were formed from foliage 15 N (73 %) and to a lesser extent from soil 15 N (27 %). The following spring, 15 N used for the synthesis of new leaves came first from 15 N stored during the previous autumn, mainly from 15 N reserves formed from foliage (95 %). Thereafter, when leaves were fully expanded, 15 N uptake from the soil during the previous autumn and before budburst contributed to the formation of new leaves (60 %).

Below-ground nitrogen transfer from oak seedlings facilitates Molinia growth: 15N pulse-chase labelling

“…One explanation for this observation might be a greater soil N depletion by Molinia, leading to a higher demand for internal N remobilization in oak to sustain budburst and leaf development (Neilsen et al 2000;Bausenwein et al 2001). It has been shown that the level of N availability during bud break in oak is a critical factor affecting leaf C capture (Bazot et al 2016;Vernay et al 2016Vernay et al , 2018. Thus the magnitude of internal N recycling from roots might not depend only on limited soil inorganic N amounts but also on neighbour presence and neighbour identity (Welker et al 1991;Kaitaniemi et al 2018).…”

The Sensitivity of Vegetation Phenology to Extreme Climate Indices in the Loess Plateau, China

“…The reason for this result may be that vegetation needs its own stored carbohydrates and nutrients with one another growth and development, and that delay in vegetation EOS may cause a longer storage period in which to store more reserves [44,45]. These reserves can then be supplied to power shoot development and growth of vegetation in the second year, thus promoting the advance of vegetation SOS [46]. Of course, these explanations are only from the perspective of nutrition.…”

Thermo Condition Determines the Uptake of Autumn and Winter Applied Nitrogen and Subsequent Utilization in Spring Tea (Camellia sinensis L.)

“…The decreasing total N concentrations of young shoots from the first to the latest harvest, in contrast with the increasing N dff% at both sites reflected weakening support of N reserves, which progressively depleted (Table 3). The difference of shoot N dff% between application dates became smaller (Figure 5 and Table 3), likely suggesting the increasing ability of concurrent uptake in the late spring, and contribution to new spring growth with rising temperature [7,44]. The difference of young shoot N dff% among fertilization dates was closely associated with the GDD values between dates of fertilization and the first harvest (Figures 2 and 6).…”

“…The internal cycling of N reserves contributes a major proportion of N (up to 100%) to support the spring growth of trees, especially when the mineral N availability is low because of the slow mineralization rate under low temperature [6]. In deciduous trees, N reserves are built up by the re-translocation of nutrients in senescing leaves back to branches and roots and/or by absorption in autumn [7][8][9]. In evergreen trees, the N reserves are contributed from the previous absorption during active vegetative growth or the absorption from the soil during vegetative dormancy [10][11][12][13].…”