Metabolic responses of Norway spruce (Picea abies) trees to long‐term forest management practices and acute (NH₄)₂SO₄ fertilization: transport of soluble non‐protein nitrogen compounds in xylem and phloem

Abstract

From laboratory experiments with seedlings and young trees of Norway spruce (Picea abies L. Karst.), a cycling pool of soluble non‐protein N compounds is thought to be indicative of the N‐nutritional status of trees. In order to test whether this assumption can be transferred to mature trees grown in the field, xylem sap and phloem exudate were collected from spruce trees in two remote forest stands: (1) a N‐limited stand (Villingen site), and (2) a stand where trees are sufficiently supplied with N from the soil (Schluchsee site). Trees at these sites were c. 80–100 (Villingen site) and c. 40–60 (Schluchsee site) yr old. In addition to untreated control areas, one entire watershed area at both sites was subjected to (NH2)2SO4 fertilization to the soil. In the xylem sap of the spruce roots at both sites Gln, Asp and Arg were the dominant total soluble non‐protein nitrogen (TSNN) compounds. In the xylem sap of the trunk and the twigs Arg was virtually absent and Gln plus Asp dominated TSNN. On average, TSNN in the xylem sap of trees at the Schluchsee site was 1·5–2‐fold higher than those at Villengen. Highest TSNN contents in the xylem sap were found during growth and development of current year tissues, while the lowest TSNN contents were found in summer. At the Villingen site (NH4)2SO4 fertilization caused an increase in the Gln content in the xylem sap of all tree sections analysed as well as an increase in the Arg content in the xylem sap of the roots. At the Schluchsee site only a small increase in TSNN contents of the xylem was observed, mostly in the xylem sap of the roots. In phloem exudates TSNN contents were much higher in trees on the Schluchsee than on the Villingen site. The seasonal pattern of TSNN in phloem exudates was similar to the seasonal pattern found in the xylem sap. During spring and early summer Gln was the predominant TSNN compound in phloem exudates, but during late summer and autumn Arg became predominant. At the Villingen site (NH4)2SO4 fertilization caused a significant increase in TSNN contents in phloem exudates of twigs and roots, but at Schluchsee an increase in TSNN was found only in phloem exudates of the roots. At both field sites Arg that was not transported to the shoot by xylem transport, was allocated from the leaves to the roots by phloem transport and was cycled within the root system by both xylem and phloem transport. From these results it is calculated that shoot‐to‐root signalling by long‐distance transport of amino compounds can also contribute to the regulation of N‐nutrition of mature spruce trees. Apparently, the internal cycling of individual N compounds within spruce trees differs considerably.

Fine Spatial Scale Variation of Soil Microbial Communities under European Beech and Norway Spruce

“…Spatial horizontal variations in bacterial community composition under beech and spruce, recorded in this study, might have been partly evoked by changes in root activities with respect to varying tree distances. N demand of spruce trees in summer and autumn is mainly met by uptake of N compounds from soil and subsequent transport of reduced N from the roots to the shoot via the transpiration stream (Weber et al, 1998). Due to a negative relationship between fine root biomass and tree distance (steep decrease of fine root biomass at tree distances >2 m) (Petritan et al, 2011), uptake of N compounds via roots might be more pronounced in soil located close to the analyzed coniferous tree trunks.…”

Exogenous supply of glutamine and active cytokinin to the roots reduces NO3–uptake rates in poplar

“…NH 3 fumigation of beech leaves with natural NH 3 concentrations (Gessler et al 1998c) resulted in amino acid enrichment in the exposed tissues in the same order of magnitude as observed in this study. Adult spruce grown in an N-over-saturated forest Gessler et al 1998b) showed up to fivefold higher phloem amino acid contents as compared to individuals from an N-poor environment (Weber et al 1998). In addition, Rennenberg & Gessler (1999) showed that the total amino acid and glutamine concentrations in the fine roots of adult beech at a given stand could differ by a factor of 5 between years.…”

Measurement of xylem sap amino acid concentrations in conjunction with whole tree transpiration estimates spring N remobilization by cherry (Prunus avium L.) trees

“…(Adams, Attiwell & Wang-Liang 1995), Actinidia deliciosa (Clark & Smith 1991), Vitis vinifera (Peuke 2000), Pinus spp. (Barnes 1963;Plassard, Bonafos & Touraine 2000) and Picea abies (Weber et al 1998). Asparagine was the predominant amino acid in Prunus dulcis (Youssefi, Brown & Weinbaum 2000), Malus domestica (Tromp & Ovaa 1985;Malaguti et al 2001) and Sorbus aucuparia (Prima Putra & Botton 1998).…”