Summary The spatiotemporal dynamics of, and interspecific differences in, the acquisition of litter‐derived nitrogen (N) by natural assemblages of ectomycorrhizal root tips are poorly understood. Small cylindrical mesh bags containing 15N‐labelled beech (Fagus sylvatica) leaf litter that permit hyphal but not root ingrowth were inserted vertically into the top soil layer of an old‐growth beech forest. The lateral transfer of 15N into the circumjacent soil, roots, microbes and ectomycorrhizas was measured during an 18‐month exposure period. Ectomycorrhial fungi (EMF) showed large interspecific variation in the temporal pattern and extent of 15N accumulation. Initially, when N was mainly available from the leachate, microbes were more efficient at N immobilization than the majority of EMF, but distinct fungal species also showed significant 15N accumulation. During later phases, the enrichment of 15N in Tomentella badia was higher than in microbes and other EMF species. Roots and soil accumulated 15N with a large delay compared with microbes and EMF. Because approximately half of the studied fungal species had direct access to N from leaf litter and the remainder to N from leached compounds, we suggest that EMF diversity facilitates the N utilization of the host by capturing N originating from early‐released solutes and late degradation products from a recalcitrant source.

European beech forests growing on marginal calcareous soils have been proposed to be vulnerable to decreased soil water availability. This could result in a large-scale loss of ecological services and economical value in a changing climate. In order to evaluate the potential consequences of this drought-sensitivity, we investigated potential species range shifts for European beech forests on calcareous soil in the 21st century by statistical species range distribution modelling for present day and projected future climate conditions. We found a dramatic decline by 78% until 2080. Still the physiological or biogeochemical mechanisms underlying the drought sensitivity of European beech are largely unknown. Drought sensitivity of beech is commonly attributed to plant physiological constraints. Furthermore, it has also been proposed that reduced soil water availability could promote nitrogen (N) limitation of European beech due to impaired microbial N cycling in soil, but this hypothesis has not yet been tested. Hence we investigated the influence of simulated climate change (increased temperatures, reduced soil water availability) on soil gross microbial N turnover and plant N uptake in the beech-soil interface of a typical mountainous beech forest stocking on calcareous soil in SW Germany. For this purpose, triple 15N isotope labelling of intact beech seedling-soil-microbe systems was combined with a space-for-time climate change experiment. We found that nitrate was the dominant N source for beech natural regeneration. Reduced soil water content caused a persistent decline of ammonia oxidizing bacteria and therefore, a massive attenuation of gross nitrification rates and nitrate availability in the soil. Consequently, nitrate and total N uptake of beech seedlings were strongly reduced so that impaired growth of beech seedlings was observed already after one year of exposure to simulated climatic change. We conclude that the N cycle in this ecosystem and here specifically nitrification is vulnerable to reduced water availability, which can directly lead to nutritional limitations of beech seedlings. This tight link between reduced water availability, drought stress for nitrifiers, decreased gross nitrification rates and nitrate availability and finally nitrate uptake by beech seedlings could represent the Achilles’ heel for beech under climate change stresses.

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N O, NO and N ) and N leaching after a high-intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha year for N , from 1.1 to 1.9 kg N ha year for NO and from 0.05 to 0.2 kg N ha year for N O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha year of minor importance for the postfire N mass balance. N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N -N), 2.7% (NO-N) and 5.0% (N O-N) of the direct fire combustion losses of the respective N gas species.

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