Function of mycorrhiza in the competition for water and nitrogen
Final Report Abstract
Beech (Fagus sylvatica L.) is an ecologically and economically important tree species in the temperate forests in Central Europe. Because these forests are often confined to nutrientlimited soils, beech competes with soil organisms for the available nitrogen. It has been hypothesized that under warmer and drier climatic conditions reduced soil water availability promotes nitrogen N limitation of European beech due to impaired microbial N cycling in soil. Ectomycorrhizas link soil and plant nutrient exchange and, therefore, play a crucial role in nutrient cycling and plant nutrition. The goal of this proposal was to investigate the function of ectomycorrhizal (EM) fungal species in their communities for nitrogen acquisition of beech and to understand how these functions are affected by drought. 15N labelling was used to investigate N uptake of beech plants and ectomycorrhizas under field und controlled conditions to explore relationships between EM 15N enrichment and plant N uptake. The field sites were located in beech forests in the low mountain range of the Swabian Alb on a moist north-east facing slope (NE) and a warm, dry south-west facing slope (SW). Field studies with 15N-labelled litter to which fungal hyphae had access, but not the tree roots revealed strong interspecific differences of EM species in the accumulation of 15N from degrading beech leaves. By mesh bag removal experiments we demonstrated that Tomentella badia, Humaria hemisphaerica, and a Cortinariaceae species had direct access to litter-derived N, whereas other species, mainly of the contact and short distance type acquired N from their surroundings, probably in form of released solutes. Similarly, in greenhouse experiments EM fungi in ectomycorrhizal assemblages of young beech trees showed strong interspecific differences for 15NH4+ accumulation. Moreover, we demonstrated that the ability for N acquisition increased in some fungal species, e.g. in Tuber rufum, in response to drought, while it decreased in response to shade in most fungi studied. Modeling approaches supported that the specific enrichment of 15N in ectomycorrhizas can be employed as a proxy for the net N flux through the root tips. These findings underline that the composition of the ectomycorrhizal assemblages are crucial for N delivery to the plant. Indeed, ectomycorrhizal communities together with associated microbes of a SW site resulted in stronger N uptake and plant translocation compared to an assemblage from NE. This finding was unexpected because the SW beech trees suffered stronger stress than the NE beeches. Our data suggest that under unstressed conditions and in absence of profound bacterial competition, the SW ectomycorrhizal community was more efficient for N acquisition than the NE assemblage. When young beech trees from the NE site in intact soil cores were exposed to the SW site for two seasons and challenged by drought stress, the N supply declined significantly. However, this decline was mainly caused by an interruption of the bacterial N cycle, and probably not by failure of ectomycorrhizal functions. Göttinger Tageblatt 26.10.2013 Erfolg durch Vielfalt (http://www.goettingertageblatt.de/Nachrichten/Wissen/Wissen-vor-Ort/Baumphysiologie-Uni-Goettingen-Mykorrhizapilze-bei-Trockenstress-Vorteilhaft) Hessische/Niedersächische Allgemeine 2.11.2013: Forstwissenschaftler: Viele Pilze machen Baum stark. (http://www.hna.de/lokales/goettingen/forstwissenschaftler-vielepilze-machen-baum-stark-3197287.html) Filmbeitrag in der ARD (2012): http://www.ardmediathek.de/das-erste/w-wiewissen/pilze-der-unterwelt?documentId=11135930
Publications
- (2012) Fagirhiza inflata + Fagus sylvatica. In: Descriptions of Ectomycorrhizae (eds.: Agerer R., Danielson RM., Egli S, Ingleby K, Luoma D, Treu R.) 13: 39-42
Leberecht M, Polle, Agerer R
- (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
(See online at https://doi.org/10.1016/j.envexpbot.2012.11.005) - (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, Polle A
(See online at https://doi.org/10.1111/nph.12272) - (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 CJ, Simon J, Gasche R, Naumann PS, Bimüller C, Pena R, Polle A, Kögel- Knabner I, Zeller B, Rennenberg H, Dannenmann M
(See online at https://doi.org/10.1007/s11104-013-1603-6) - (2013) Preferential use of root litter compared to leaf litter by beech seedlings and soil microorganisms. Plant and Soil 368: 519-534
Guo CJ, Dannenmann M, Gasche R, Zeller B, Papen H, Polle A, Rennenberg H, Simon J
(See online at https://doi.org/10.1007/s11104-012-1521-z) - (2014) Attributing functions to ectomycorrhizal fungal identities in assemblages for nitrogen acquisition under stress. The ISME Journal, 8: 321-330
Pena R, Polle A
(See online at https://doi.org/10.1038/ismej.2013.158)
