Foliar uptake and release of inorganic nitrogen compounds in Pinus sylvestris L. and Picea abies (L.) Karst.

Abstract

SUMM.'^RVFoliar uptake and release of inorganic nitrogen compounds were studied by immersing current-year shoots of Scots pine {Pinus syhestris L.) and Norway spruce [Picea ahies (L.) Karst] in either NH^"-or NOg'-rain solutions at different N concentrations. The effects of N form, N concentration and tree species on ion influx and efflux were investigated.Spruce shoots absorbed NH^"^ from the external solution. Uptake apparently occurred by diffusion rather than by H"' or base cation exchange as commonly accepted, and increased iinearly with NH^"^ concentration in the external solution. In contrast, pine shoots released NH^* to the external solution. The different reactions of spruce and pine may refiect species differences in physical and chemical properties or differences in tissue N concentration. If the latter is the case, a tree's N status may determine whether the canopy acts as a source or sink for NH,', influencing deposition rates to the needle surface. The results show that where NHj* concentration on the needle surface exceeds 4 mg t"', foliar uptake may make a significant contribution to N status. In the absence of N'H^^-base cation exchange, atmospheric inputs of NH^"^ to the canopy appear unlikely to be directly responsible for the nutrient deficiencies typical of Dutch forest decline.Neither spruce or pine shoots were able to utilize NO^" in the external solution and generally released NO3". Adverse effects resulting from foliar accumulation of wet-deposited NO3" appear unlikely. However, higher NO3" concentrations and longer residence times than simulated in this experiment may result in foliar uptake of NOj" in the field.

Relative importance of macrophyte leaves for nitrogen uptake from flood water in tidal salt marshes

“…forest ecosystems (2 to 8%: Boyce et al 1996;up to 5%: Wilson & Tiley 1998). Similarly, as found for aquatic (Touchette & Burkholder 2000) and terrestrial (Wilson 1992, Peuke et al 1998, Ignatova & Dambrine 2000 angiosperms and marine algae (Lotze & Schramm 2000), we found that foliar uptake is generally higher for NH 4 + than for NO 3 -. A linear increase in the uptake rate (Figs.…”

“…Although leaching and the presence of epiphytic macroflora complicates interpretation of throughfall studies (Pearson & Stewardt 1993), it is also evident in terrestrial systems that foliar N-uptake is generally more efficient for NH 4 + than for NO 3 - (Wilson 1992, Peuke et al 1998, Ignatova & Dambrine 2000. In this study, we address the question as to the extent in which foliar uptake of nitrogen contributes to the nutrient demand of halophytic species that grow in the lowest areas of tidal salt marshes.…”

Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador

“…Deposition of NH 4 + likely stimulated nitrification and related isotope fractionation in the canopy. In tropical and temperate forests, ammonification of organic matter accumulated in the canopy and nitrification at leaf surfaces, respectively, have already been shown (Vance and Nadkarni 1990;Wilson 1992). The high abundance of epiphytes in the canopy and the high litterfall in our research area (Wilcke et al 2002) result in the accumulation of organic matter in the canopy that can be mineralized.…”

Canopy uptake of N deposition in spruce (Picea abies L. Karst) stands

“…Furthermore, the necessity of accurate deposition velocity models [8,9] and the need of scaling factors to relate measurements to forest canopy surfaces complicate this approach. Mineral N compounds in throughfall mainly originate from deposition [19], but the possibility of NH 4 + leaching from leaves has also been shown [28]. In remote or low polluted sites, several authors have found lower NH 4 + and NO 3 -fluxes in throughfall than in rain, suggesting uptake of the N by the canopy.…”