Nitrogen distribution in young Norway spruce (Picea abies) trees as affected by pedospheric nitrogen supply

Abstract

In numerous locations in Europe spruce trees are exposed to high loads of nitrogen. The present study was performed to characterize the distribution of nitrogen compounds under these conditions. For this purpose Norway spruce (Picea abies [L.] Karst.) trees were cultivated under close‐to‐natural conditions of a forest understory in soil from an apparently nitrogen‐limited field site in the Black Forest either with, or without supplementation of nitrogen as ammonium nitrate. After 11 and 20 months, growth, total nitrogen contents of the biomass, and total soluble non‐proteinogenic nitrogen compounds (TSNN, i.e. nitrate, ammonium, soluble proteinogenic and non‐proteinogenic amino compounds) in needles, xylem sap and phloem exudate were analysed. After 20 months of growth, N‐fertilization had slightly enhanced the biomass of current‐, but not of 1‐year‐old shoots. At both harvests, total N‐content of 1‐year‐old needles was increased by N‐fertilization, whereas current‐year needles were not significantly affected. By contrast, TSNN was elevated by N‐fertilization in both current‐year and 1‐year‐old needles. The increase in TSNN was mainly attributed to an accumulation of arginine. Xylem sap analysis showed that the increase in TSNN of the needles was a consequence of enhanced nitrogen assimilation of the roots rather than the shoot. Since also TSNN in phloem exudates was enhanced, it appears that N‐fertilization elevates the cycling pool of amino compounds in young Norway spruce trees. However, this pool seems to be subject to metabolic interconversion, since mainly glutamine and aspartate are transported in the xylem from the roots to the shoot, but arginine accumulated in the needles and the phloem.

Consequences of high loads of nitrogen for spruce (Picea abies) and beech (Fagus sylvatica) forests

“…If xylem and phloem transport constitute part of a cycling pool of organic N, metabolic interconversion of amino compounds is required in the roots and the needles in autumn, since in the xylem Gln and Asp are the main forms transported, whereas in the phloem Arg is predominant . Similar conclusions were drawn from experiments with young spruce trees exposed to different levels of N nutrition under controlled environmental conditions (Stoermer et al, 1997).…”

The role of sulphur compounds for breeding success of Ips typographus L. (Col., Scolytidae) on Norway Spruce (Picea abies [L.] Karst.)

“…Arginine is the most abundant N compound in trees and makes up 60–85% of the total soluble non‐protein N during the entire growing season (G ESSLER et al., 1998a). It is accumulated in needles and phloem exudates in spruce stems and roots (S TOERMER et al., 1997). The arginine content in this study amounted to 56% of the total soluble non‐protein N at felling and declined to 27% after 8 weeks.…”

Physiological significance of pedospheric nitric oxide for root growth, development and organismic interactions

“…In roots, however, nitrate reductase activity is usually low, except for numerous forest tree species that can reduce nitrate predominantly in the roots (Hu et al, 2020). The latter is not only indicated by high root nitrate reductase activity, but also by the lack of appreciable amounts on nitrate in the xylem sap of conifers and deciduous trees (see for example Schneider et al, 1996;Stoermer, Seith, Hanemann, George, & Rennenberg, 1997). However, up to now, data on the generation of NO by nitrate reductase in roots of trees are not available.…”