Soluble N compounds in trees exposed to high loads of N: a comparison between the roots of Norway spruce (Picea abies) and beech (Fagus sylvatica) trees grown under field conditions

Abstract

During the growing session of 1995, the total soluble non‐protein nitrogen (TSNN) composition and contents of mycorrhizal fine roots, xylem sap and phloem exudates of roots from a coniferous (Picea abies L.(Karst)) and a deciduous (Fagus sylvatica L.) tree species were analysed at a field site (‘Höglwald’, Germany) exposed to high loads of N. In April, TSNN in fine roots of spruce and beech trees amounted to 16 μmol N g−1 f. wt and 23·3 μmol N g−1 f. wt, respectively. It decreased to 9·2 μmol N g−1 f. wt and 18·1 μmol N g−1 f. wt, respectively, after bud break in June. The seasonal maximum of TSNN in fine roots of spruce was observed in July (32·7 μmol N g−1 f. wt) followed by a decline of c. 30% until the end of the growing season in September. TSNN in fine roots of beech trees showed a further decline between June and July, when its seasonal minimum was determined (15·6 μmol N g−1 f. wt), and increased to c. 29 μmol N g−1 f. wt until September. In spruce roots Gln and Arg were the most abundant TSNN compounds during the entire growing season. In roots of beech Asn played an important role alongside Gln and Arg, especially in April, when it was the most abundant TSNN compound. Other proteinogenic and non‐proteinogenic N compounds comprised c. 20–30% of TSNN. Nitrate made up <1%, and ammonium <7% of TSNN in the fine roots of both species. In April, TSNN in the xylem sap of roots of spruce and beech trees amounted to 3·4 and 8·6 μmol N ml−1, respectively. In roots of spruce trees xylem sap TSNN increased after bud break up to 12·7 μmol N ml−1 in July. At the end of the growing season TSNN had declined again to 3·9 μmol N ml−1. TSNN in the root xylem sap of beech trees decreased after bud break until July (2·4 μmol N ml−1 in July) followed by a slight increase until September (2·9 μmol N ml−1). Arg, Gln and Asp were the most abundant TSNN compounds in the xylem sap of spruce trees contributing together c. 90% to TSNN. The same TSNN compounds prevailed in the root xylem sap of beech trees in April and July, whereas in June and September Asp was replaced by Asn comprising 57% of TSNN in June. In addition to the N compounds mentioned above, a number of other proteinogenic and non‐proteinogenic amino compounds were found in root xylem sap of both species. In either species, nitrate and ammonium were present in small amounts, contributing <1% and <4% to TSNN, respectively. Apparently, inorganic N taken up by the mycorrhizal roots is mainly assimilated in root tissues or by the mycorrhiza and N uptake by the roots is largely adapted to the assimilatory capacity of this organ. In phloem exudates of spruce roots, TSNN amounted to 10·7 μmol N g−1 f. wt in April, increased in June to 23·4 μmol N g−1 f. wt and decreased again until September to a seasonal minimum of 4·8 μmol N g−1 f. wt. In contrast to spruce, TSNN content in phloem exudates of beech roots showed a seasonal maximum (c. 20 μmol N g−1 f. wt) in April with a subsequent decrease in June after bud break (c. 2 μmol N g−1 f. wt). A fourfold increase in July was foll...

Nitrogen Nutrition of Trees in Temperate Forests—The Significance of Nitrogen Availability in the Pedosphere and Atmosphere

“…In contrast to the influx of atmospheric N, N uptake from pedospheric/ hydrospheric sources can at least be partially controlled (see below) and can be down-regulated to the extent that atmospheric N contributes to N nutrition [54,57,58]. If high rates of N deposition result in N over-nutrition [29], this is often indicated by extremely high amounts of the N-rich amino acid arginine in phloem and xylem sap [54,59].…”

“…Thus, the cycling plant N pool mediates swift N supply of any part of the plant throughout the year. The size of this cycling plant N pool may change depending on N nutrition, and this pool may even be used for N storage, particularly in the form of arginine, an amino acid with high N content [59]. Mobilization of N from this storage pool may provide N faster than the mobilization from storage proteins in bark and wood [70,71]; therefore, it may be of particular significance to meet N requirements in response to environmental changes.…”

NH3 and NO2 fluxes between beech trees and the atmosphere – correlation with climatic and physiological parameters

“…The gas-exchange equipment was installed in the crown by means of scaffolding. Elemental analyses of the leaves showed no nutrient deficiencies or imbalances (Rothe, 1998), while leaves and phloem of twigs contained high amounts of soluble arginine (Geßler et al, 1998c), indicating excessive N supply (Na$ sholm & Ericson, 1989). Since the site is between the urban regions of Munich and Augsburg, and is surrounded by intensively used agricultural land to which liquid manure from pig and cattle farming is applied , the forest ecosystem is exposed to large loads of ammonium and nitrate from wash-out and rain-out processes (Kreutzer, 1995).…”

“…The experiments were performed with the whole shoot, excluding the hypocotyl, of 12-wk-old potted beech seedlings (Geßler et al, 1998c). The influence of c NH $ or c NO # , PPFR, T and rh on J NH $ and J NO # , respectively, was tested by varying one of these parameters while the others were kept constant at defined standard levels.…”

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

“…Nevertheless, seasonal N cycling is a determinant of plant fitness in perennials, particularly long-lived perennials such as forest trees (Cooke and Weih, 2005). In early spring, trees' nitrogen demand for growth can be satisfied either by uptake of external sources such as ammonium, nitrate and organic N available from the soil (Gessler et al, 1998a) or by remobilization of internal stores (Bazot et al, 2013;Coleman and Chen, 1993;Cooke and Weih, 2005;El Zein et al, 2011b;Gilson et al, 2014;Millard, 1996;Taylor, 1967). In many species, N remobilization for growth in spring occurs before utilization of N taken up by roots, typically during the 20-30 days before the roots actively take up N. These species include deciduous species, such as Quercus petraea (El Zein et al, 2011a), Malus domestica (Guak et al, 2003;Neilsen et al, 2001), Populus trichocharpa (Millard et al, 2006), Prunus avium (Grassi et al, 2003), Pyrus communis (Tagliavini et al, 1997) and Sorbus aucuparia ; marcescent/evergreen species, such as Nothofagus fusca (Stephens et al, 2001) and coniferous evergreens, such as Picea sitchensis (Millard and Proe, 1993).…”