Ammonium, nitrate and glycine uptake of six Ecuadorian tropical montane forest tree species: an in situ pot experiment with saplings

作者：Wittich Baerbel; Homeier Juergen; Leuschner Christoph^*

来源：Journal of Tropical Ecology, 2015, 31(02): 139-152.

DOI：10.1017/S0266467414000650

• altitudinal gradient
• dual-labelled glycine
• Graffenrieda harlingii
• Hedyosmum purpurascens
• Hedyosmum sprucei
• Hedyosmum translucidum
• Myrcia sp nov.
• nitrogen uptake
• Pouteria torta
• N-15 tracer study

Not much is known about the nitrogen (N) uptake capacity and N-form preference of tropical trees. In a replicated labelling experiment with N-15-ammonium, N-15-nitrate and dual-labelled glycine applied to saplings of six tree species from southern Ecuadorian montane forests, we tested the hypotheses that (1) the saplings of tropical trees are capable of using organic N even though they are forming arbuscular mycorrhizas, and (2) with increasing altitude, tree saplings increasingly prefer ammonium and glycine over nitrate due to reduced nitrification and growing humus accumulation. Three- to 5-y-old saplings of two species each from 1000, 2000 and 3000 m asl were grown in pots inside the forest at their origin and labelled with non-fertilizing amounts of the three N forms; N-15 enrichment was detected 5 days after labelling in fine roots, coarse roots, shoots and leaves. The six species differed with respect to their N-form preference, but neither the abundance of ammonium and nitrate in the soil nor altitude (1000-3000 m asl) seemed to influence the preference. Two species (those with highest growth rate) preferred NH4+ over NO3-, while the other four species took up NO3- and NH4+ at similar rates when both N forms were equally available. After C-13-glycine addition, C-13 was significantly accumulated in the biomass of three species (all species with exclusively AM symbionts) but a convincing proof of the uptake of intact glycine molecules by these tropical montane forest trees was not obtained.

• 出版日期2015-3