Fate of nitrogen released from 15N-labeled litter in European beech forests

Abstract

The decomposition and fate of 15N-labeled beech litter was monitored in three European beech (Fagus sylvatica L.) forests (Aubure, France; Ebrach, Germany; and Collelongo, Italy) for 3 years. Circular plots around single beech trees were isolated from roots of neighboring trees by soil trenching, and annual litterfall was replaced by 15N-labeled litter. Nitrogen was continuously released from the decomposing litter. However, over a 2-year period, this release was balanced by the incorporation of exogenous N. Released N accumulated mainly at the soil surface and in the topsoil. Microbial biomass remained almost constant during the experiment at all sites except for considerably lower values at Ebrach. The 15N enrichment of the microbial biomass increased strongly during the first year and then remained stable. The 15N released from the decomposing litter was rapidly detected in roots and leaves of the beech trees, increasing regularly and linearly over the course of the experiment. The uptake of litter-released 15N by the trees was reduced under conditions that reduced tree growth. Under these conditions, leaves and fine roots were the dominant N sinks, and little N was allocated to other plant parts. By contrast, N uptake and N allocation from leaves to stem and bark tissues increased when tree growth was enhanced. Budgets for 15N showed that 2 to 4% of litter-released N was incorporated into the trees, about 35% remained in the litter and about 50% reached the topsoil.

Competition for nitrogen between trees in a mixed-species plantation in the Solomon Islands

“…Teak and flueggea allocated a higher proportion of the applied 15 N to their foliage, followed by the root, stem and branch, indicating allocation of N to the growing tissues for growth. The large N allocation to leaves is consistent with results found in other forest ecosystems (Zeller et al 2001;Bloomfield et al 2014) and reflects N investment in photosynthesis. However, when expressed in mass units, the highest 15 N content was found in stems and roots for both teak and flueggea at both ages, which indicates higher biomass allocation to their stems as TN concentration was lowest in the stem and branch (Buchmann et al 1996).…”

“…The lowest amounts of TN were found in the stem for both species at both ages. A lower concentration of TN in tree stem was also reported by Blumfield and Xu (2006) in hoop pine seedling stem and Zeller et al (2001) in European beech. Changing amounts of TN in flueggea components over time may indicate prioritisation and allocation of N in the 4-year plots for canopy development for photosynthesis requirements (Zeller et al 2001).…”

“…A lower concentration of TN in tree stem was also reported by Blumfield and Xu (2006) in hoop pine seedling stem and Zeller et al (2001) in European beech. Changing amounts of TN in flueggea components over time may indicate prioritisation and allocation of N in the 4-year plots for canopy development for photosynthesis requirements (Zeller et al 2001). Although TN concentrations among the components were different (data not shown), these differences were masked when expressed in mass units due to the differences in dry biomass between tree components.…”

Changes in epilithic diatom communities and periphytic biomass downstream of a reservoir on a Mediterranean river (Calabria region, S Italy)

“…In August, the increase in average temperature stimulates microbial reproduction and metabolism (Abelho et al, 2005), which causes both nitrogen incorporation in microbial biomass and a reduction in water nitrate concentration. In November, the increase in CPOM due to litter deposition coincides with a general increase in NO 3 -levels, suggesting that the accumulation and decomposition of biodegradable organic matter results in an excess of mineral nitrogen in relation to microbial requests (Zeller et al, 2001). Due to the prevailing igneous and metamorphic nature of the rocks of the Mucone watershed, PO 4 3-concentrations are low.…”

Density fractions versus size separates: does physical fractionation isolate functional soil compartments?

“…Ebrach and in February 2000 at Fougères, undecomposed litters were removed and replaced by the labeled beech leaves in an amount equal to the respective mean annual leaf litter input and covered with a 2-cm mesh nylon net (Zeller et al, 2001). Twelve years (November 2007) and eight years (January 2008) after tracer application, labeled and control soils were collected at Ebrach and Fougères, respectively.…”