Minor contribution of leaf litter to N nutrition of beech (Fagus sylvatica) seedlings in a mountainous beech forest of Southern Germany

Ectomycorrhizal Communities on the Roots of Two Beech (Fagus sylvatica) Populations from Contrasting Climates Differ in Nitrogen Acquisition in a Common Environment

“…Microbial completion also was not relevant under N mass balance considerations due to the extremely low microbial activity in our soil system compared to that under field conditions (3 mg microbial N kg Ϫ1 dry soil in the experimental setting versus 100 to 300 mg microbial N kg Ϫ1 dry soil in Tuttlingen forest soil [30,34]). The finding that about 20% of the added 15 N was recovered in the soil microbial biomass and about 13% was recovered in the beech trees further supports the suggestion that microbial competition for N was relieved in our system because under field conditions, N uptake by microbial biomass was more than 1 order of magnitude greater than that by the microbial biomass of the young naturally regenerated beech trees (35).…”

“…In the rhizospheres of SW and NE trees, no evidence for differences in N cycling of the free-living microbes was found, suggesting that preculture of the SW and NE trees in the same substrate resulted in similar adjustments of microbial communities to the edaphic conditions. Under field conditions, soil microbes are significant competitors for N (34,35,52) and acquire soluble N faster than EMF (11). Here, however, the 15 N enrichment rates in microbes were similar (NE trees) or even lower (SW trees) than those in the corresponding ectomycorrhizal communities, a finding that does not support competition under our conditions.…”

“…The approach was based on the diffusion of NH 4 ϩ on acid filter traps prepared for isotope ratio mass spectrometry via detection of the increase in pH, after sequential conversion of all target N compounds in soil extracts to NH 4 ϩ , as described in detail in earlier studies (35). Determination of 15 N enrichment in the total extractable N of both unfumigated control soils and fumigated soils was based on alkaline persulfate oxidation of all N compounds to NO 3 Ϫ and subsequent NO 3 Ϫ reduction to NH 4 ϩ , as described previously (36).…”

“…Determination of 15 N enrichment in the total extractable N of both unfumigated control soils and fumigated soils was based on alkaline persulfate oxidation of all N compounds to NO 3 Ϫ and subsequent NO 3 Ϫ reduction to NH 4 ϩ , as described previously (36). The subsequent diffusion of NH 3 on acid filter traps enabled the quantification of 15 N enrichment in microbial biomass calculated from the difference in the N concentration and 15 N enrichment in TN between unfumigated control soils and fumigated soils (35). No correction factors were applied in order to obtain estimates of 15 N uptake into active microbial biomass (37).…”

Nitrogen Nutrition of Trees in Temperate Forests—The Significance of Nitrogen Availability in the Pedosphere and Atmosphere

“…Thus, ecosystem N fluxes and N redistribution almost entirely depend on ecosystem internal sources, in particular the decomposition of leaf and root litter as well as decaying microbial biomass and older soil organic matter [12,33]. Since the mean residence time of microbial biomass with a range between days and months [26,34,35] is significantly shorter than the lifespan of leaf and root litter [36][37][38], microbial biomass turnover is a major driver of N redistribution in N-limited ecosystems. However, our understanding of internal gross nitrogen turnover in N-limited forests is still fragmentary because available studies on the extremely dynamic gross nitrogen mineralization-immobilization turnover have been restricted to single or a few measurement dates.…”