The Significance of Nitrogen Uptake and Metabolism by Beech Roots for the Competition for Nitrogen in the Rhizosphere
Final Report Abstract
In the present project the consequences of climate change on beech forests on calcareous soil were addressed in microcosm experiments under controlled and by comparison of opposing stands on two slopes differing in explosion with special emphasis on nitrogen nutrition of beech. Relatively cold and wet NE exposition was taken as a control, relatively warm and dry SW exposition as a model of future climate. Genetic analyses of the population structure on the two slopes revealed differences between old growth trees, but not of natural regeneration. This result indicates differences in selection processes during stand development between the two slopes that did not yet result in changes of germplasm, but are likely to mediate such changes in future. The exchange of monoliths with beech natural regeneration between the two slopes revealed that nitrogen nutrition of the saplings is rapidly impaired by the warm and dry climate on the slope with SW exposition with immediate consequences for biomass accumulation. Integration with the results of the other participants of the research package PAK 538 suggests that the changes in tree nitrogen nutrition are a consequence of the disturbance of the ecosystem nitrogen cycle with nitrification and, hence, nitrate availability to the trees as an achilles´ heel. This conclusion is supported by experiments in microcosms under controlled conditions that clearly showed a strong negative effect of drought on nitrogen acquisition from both root and shoot litter and its incorporation into microbial and plant biomass. In this context, root litter was a superior nitrogen source compared to leaf litter and microbial biomass was by far a stronger nitrogen sink than beech plants. These results show the high significance of microbial processes of N acquisition in the ecosystem nitrogen cycle and its vulnerability to climate change. Since preferential nitrogen acquisition of natural regeneration of beech took place in spring, that of old growth beech trees in fall, a direct transfer of the present results with natural regeneration to old growth tress does not seem to be appropriate. However, reduced growth of old growth beech on the SW compared to the NE slope subsequent to periods of drought has previously been reported. The significance of nitrogen nutrition for this reduction has so far not been elucidated. From the present results, it appears that long-tern analyses of nitrogen availability in the soil with special emphasis on nitrate could provide an answer to this question of high economic impact. Despite this restriction results of this project indicate the need to replace beech at sites on calcareous soils particular prone to drought (e.g. at southern exposition) by tree species less susceptible to water limitation. Inter-planting sycamore maple into beech forests may not be an appropriate choice in this context because of the reduced competitiveness of sycamore maple for nitrogen at low light availability.
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, Rennenberg H
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(2012): Natural regeneration of Fagus sylvatica L. adapts with maturation to warmer and drier microclimatic conditions. Forest Ecology and Management 275: 60-67
Bilela S, Dounavi A, Fussi B, Konnert M, Holst J, Mayer H, Rennenberg H, Simon J
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(2013) Ectomycorrhiza affect architecture and nitrogen partitioning of beech (Fagus sylvatica L.) seedlings under shade and drought. Environmental and Experimental Botany 87: 207-217
Pena R, Simon J, Rennenberg H, 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, Dannenmann M
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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, Simon J
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(2014): Competition for nitrogen between European beech and sycamore maple shifts in favour of beech with decreasing light availability. Tree Physiology 34: 49-60
Simon J, Li X, Rennenberg H
