Competitive patterns of N partitioning between plants and microorganisms in intact plant-soil-systems
Final Report Abstract
In this project, the effects of simulated climate change on nitrogen (N) cycling and its partitioning between plants and soil microorganisms in typical beech forests of Germany were investigated. For this purpose, we deployed a method for triple isotope labeling of intact beech-soil mesocosms for simultaneous quantification of all major N turnover processes in the plant-soilmicrobe system. This enriched stable isotope approach was combined with a space for time climate change experiment, i. e. mesocosms were transferred from N exposure (cool moist microclimate, control) to S exposure (warm-dry model climate for climate change conditions). The realistic N turnover rates gained from this experiment revealed very large mineralization and nitrification rates, which governed soil inorganic N availability. Furthermore, nitrate was found to be the dominant N source for beech seedlings due to strong competition for ammonium by free living microorganisms. Climate change (increased temperature, reduced water availability in the growing season) resulted in an unexpectedly strong and rapid deceleration of soil microbial N turnover. In this context, the most pronounced effect was a five-fold decline in gross nitrification rates. Consequently, also soil nitrate availability declined. Beech was found to be unable to compensate this nutritional deficiency via increased uptake of ammonium or amino acids, since microbial competition remained strong also under climate change conditions. Consequently, nitrate as well as total N uptake by beech strongly declined under simulated climate change conditions. Already after two growing seasons, this resulted in decreased performance of beech with reduced growth, N content and biomass. The nutritional limitation under climate change stresses was enhanced due to the surprisingly low importance of leaf litter for beech N nutrition, as could be revealed in a set of experiments with 15N enriched leaf litter. Furthermore, the extremely shallow soil with underlying bedrock does not allow to access N sources in deeper soil layers. Consequently, impaired N cycling may be a major stressor limiting the competitive performance of beech on marginal soil in a changing climate. The detailed process understanding gained in this project due to the close cooperation with the involved groups also provides pointers to mitigation options to sustain the economical value and ecosystem services of beech forests on marginal soil in the 21st century. While N fertilization or mixing with more deep rooting tree species to increase soil water content may be sufficient at moderate drought, it may be necessary to replace beech at extremely dry sites by trees with higher N use efficiency.
Publications
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2011 Competition for nitrogen between adult European beech and its offspring is reduced by avoidance strategy. Forest Ecology and Management, 262, 105-114
Simon J, Dannenmann M, Gasche R, Holst J, Mayer H, Papen H, and Rennenberg H
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2013. Preferential use of root litter compared to leaf litter by beech seedlings and soil microorganisms. Plant and Soil 368, 519-534
Guo C, Dannenmann M, Gasche R, Zeller B, Papen H, Polle A, Rennenberg H, and Simon J
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2013: Interspecific temporal and spatial differences for the acquisition of litter-derived nitrogen of ectomycorrhizal fungal assemblages. New Phytologist, 199, 520-528
Pena R, Tejedor J, Zeller B, Dannenmann M, and Polle A
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2013: Minor contribution of leaf litter to N nutrition of beech (Fagus sylvatica) seedlings in a mountainous beech forest of Southern Germany. Plant and Soil 369, 657-668
Guo C, Simon J, Gasche R, Naumann PS, Bimüller C, Pena R, Polle A, Kögel-Knabner I, Zeller B, Rennenberg H, and Dannenmann M
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2013: Rapid transfer of 15N from labeled beech leaf litter to functional soil organic matter fractions in a Rendzic Leptosol. Soil Biology & Biochemistry, 58, 323-331
Bimüller C, Naumann PS, Buegger F, Dannenmann M, Zeller B, Von Lützow M, and Kögel-Knabner I
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2014: Prolonged summer droughts retard soil N processing and stabilization in organo-mineral fractions. Soil Biology & Biochemistry 68, 241-251
Bimüller C, Dannenmann M, Tejedor J, Von Lützow M, Buegger F, Meier R, Haug S, Schroll R, and Kögel-Knabner I
