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

Abstract

summary During the vegetation period 1994, the nitrogen (N) composition and contents of leaves, xylem sap and phloem exudates of twigs from a coniferous (Picea abies (L.) and a deciduous (Fagus sylvatica L.) tree species were analysed at a field site (Höglwald, Germany) exposed to high loads of N. In April, total soluble non‐protein N (TSNN) in the xylem sap of twigs from spruce and beech reached a maximum of about 7.0 and 15.0 μmol ml−1, respectively, probably owing to remobilization of stored N. After bud break, TSNN in the xylem sap of both tree species decreased rapidly, to a minimum of c. 2.0 μmol ml−1 in July. Subsequently, TSNN increased two‐fold in the xylem sap of beech until September, but remained constant in the xylem sap of spruce at the low level observed in July. In both tree species, amides were the predominant TSNN compounds transported in the xylem. In xylem sap of beech. Gin, Asn and Arg were most abundant, together comparing more than 60% of TSNN. Gin and Asp, but not Arg, prevailed in the xylem sap of spruce, together comparing more than 50 % of TSNN. In addition, a number of other proteinogenic and non‐proteinogenic amino acids, and also nitrate and ammonium, were detected in small amounts in the xylem saps of both tree species. Remobilization of stored N during growth of the new flush resulted in a 4.5‐fold decrease of TSNN in previous year's needles from 9.1 μmol g−l f. wt in April to 2.0 μmol g−1 f. wt in May. This decrease was mainly attributed to Arg, the prevailing amino compound in needles of spruce. Subsequently, a 5.5‐fold increase was observed in July. High TSNN contents remained constant until September, Within current year's needles TSNN remained relatively constant during the entire vegetation period. In leaves of beech, TSNN amounted to c. 5.6 μmol g−1 f, wt from April to July and increased to 9.5 μmol g−1 f. wt in September. In April and May the predominant amino compounds in leaves of beech were Asn and Glu, in September they were Arg and Gin. Concomitant with the increase in Arg content of the leaves, its content in the phloem also increased, suggesting a transport of Arg from the senescencing leaves to storage tissues. Nitrate was found neither in needles nor in leaves, whereas ammonium amounted to up to 25 % of TSNN in both needles and leaves. In phloem exudates of twigs from beech, TSNN amounted to c. 34.0 μmol g−1 f. wt in April and decreased 10‐fold until May, during growth of the new flush. Subsequently, until September a threefold increase in TSNN was observed. In phloem exudates of twigs from spruce, TSNN decreased from 13.0 μmol g−1 f. wt in April to 4.8 μmol g−1 f. wt in May, By September, TSNN contents were doubled. In April, Arg was the prevailing amino acid in phloem exudates of beech. Concomitant with the decline in total TSNN the Arg content decreased. In September a significant increase in the Arg content was observed. In phloem exudates of spruce, Gin and Arg were the predominant N compounds in April and May. In July and September a decrease of the Gin conte...

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

“…A totally different situation was observed for beech which showed a seasonal maximum of TSNN in the root xylem and phloem before\during bud break with a subsequent decrease. A seasonal course of N contents similar to that in beech roots has previously been observed in above-ground parts of beech and spruce trees, with maximum N transport in xylem (Glavac & Jochheim, 1993 ;Dambrine et al, 1995 ;Schneider et al, 1996) and phloem immediately before and during bud break. The N supply of newly developing tissues of trees during spring can at least partly be met by remobilization of internal N sources from storage tissues (Millard & Proe, 1992 ;Millard, 1994).…”

Regulation of Sulfur Nutrition in Wild-Type and Transgenic Poplar Over-Expressing γ-Glutamylcysteine Synthetase in the Cytosol as Affected by Atmospheric H2S

“…The exuding xylem sap was collected in Eppendorf caps, frozen under liquid nitrogen, and stored until analysis at Ϫ80°C. Contamination with cellular compounds was measured by ATP analysis as described by Schneider et al (1996) and was less than 1%, as previously reported for other plant species.…”

Short-term natural δ<sup>13</sup>C and δ<sup>18</sup>O variations in pools and fluxes in a beech forest: the transfer of isotopic signal from recent photosynthates to soil respired CO<sub>2</sub>

“…Organic material transported with the phloem flow was extracted by phloem exudation technique as described by Schneider et al (1996) and Gessler et al (2004).…”