Effekte von Nährstoffgaben auf arbuskuläre Mykorrhizapilze in Süd-Ecuador
Zusammenfassung der Projektergebnisse
Within the DFG funded project „Responses of arbuscular mycorrhizal fungi to nutrient additions in Southern Ecuador”, which was part of the “Platform for Biodiversity and Ecosystem Monitoring and Research in South Ecuador”, we elucidated long-term effects of nitrogen (N) and phosphorus (P) additions on the abundance and diversity of arbuscular mycorrhizal fungi (AMF), its functional role in this special ecosystem, and also broadened current knowledge on nutrient limitations and demands of soil microbial organisms in tropical forests. The observed responses in AMF abundance to nutrient shifts were highly context dependent and affected by several parameters, e.g. tree species identity, soil nutrient status, elevation, the duration of nutrient additions and the AMF structure observed. Still, an overall detrimental effect of N additions was found, also supported by decreasing diversity, whereas P additions exerted partly positive effects. Beside shifts in abundance and richness, communities showed a significant shift following N and P inputs at different elevational sites. This community shift appeared to get more pronounced within the observed years, whereas shifts in AMF abundance were diminishing over time, pointing towards a highly resilient mycorrhizal interaction. Potentially, shifts in AMF species composition may compensate for detrimental effects on abundance by adaptations to changing conditions. Several pot experiments aiming to elucidate the effects of shifting communities and decreased AMF abundance failed, which may be an interesting hint that successful AMF colonization of tree seedlings requires an intact mycorrhizal network, as only found in soil surrounded by mother trees. Further experiments by mycorrhizal exclusion from soils revealed a potential role of AMF in NH4 uptake, and the positive effect of P additions might be explained by fungal P limitation in these nutrient poor soils: In a small-scale element addition experiment fungi showed increased demands for P, compared to the control and other elements, whereas N again showed negative impacts. To compare these fungal responses indicating P limitation in the tropical forest sampled here, we compared our results to other nutrient manipulation experiments in the tropics by meta-analytical methods. A global meta-analysis revealed primary P limitation of soil microbial organisms in tropical forests, while N limitation only was apparent in high montane areas characterized by younger soils. Interestingly, also other elements showed up as important limiting factors for certain microbial processes, though hardly considered in nutrient cycling models, e.g. molybdenum or zinc. Finally, in the study area we further looked at other elements, mostly sodium (Na) and potassium (K). As previously shown in other tropical sites with low oceanic inputs, litter decomposition rates in the lower montane site (1000m a.s.l.) proved to be Na limited, however, an involvement of fungi or microbes was precluded based on several field- and lab-based experiments. In future studies, it will be especially interesting to find further hints why AMF are the predominant mycorrhizal form in this tropical montane forest, which is characterized by slow decomposition rates and highly organic soils, a system typically rather characterized by ectomycorrhizae. Furthermore, the functional impacts of observed community shifts are still unknown and methodologically challenging, though such knowledge will provide relevant information for expected changes in future nutrient cycling.
Projektbezogene Publikationen (Auswahl)
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(2014) Nitrogen and phosphorus additions impact arbuscular mycorrhizal abundance and molecular diversity in a tropical montane forest. Global Change Biology 20: 3646–3659
Camenzind T, Hempel S, Homeier J, Horn S, Velescu A, Wilcke W and Rillig MC
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(2015) Above- and belowground linkages of a nitrogen and phosphorus co-limited tropical mountain pasture system – responses to nutrient enrichment. Plant and Soil 391: 333–352
Tischer A, Werisch M, Döbbelin F, Camenzind T, Rillig MC and Hamer U
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(2016) Increased nutrient depositions affect arbuscular mycorrhizal fungi in a tropical montane forest. In: Biodiversity hotspot tropical mountain forest. Eds: Bogner FX, Bendix J, Beck E. Naturaleza y Cultura Internacional, Loja, Ecuador
Camenzind, T, Suárez, JP, Rillig, MC
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(2016) Increases in soil aggregation following phosphorus additions in a tropical premontane forest are not driven by root and arbuscular mycorrhizal fungal abundances. Frontiers in Earth Sciences 3:89
Camenzind T, Papathanasiou HJ, Förster A, Dietrich K, Hertel D, Homeier J, Oelmann Y, Olsson PA, Suárez JP and Rillig MC
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(2016) Opposing effects of nitrogen versus phosphorus additions on mycorrhizal fungal abundance along an elevational gradient in tropical montane forests. Soil Biology & Biochemistry 94: 37-47
Camenzind T, Homeier J, Dietrich K, Hempel S, Hertel D, Krohn A, Leuschner C, Oelmann Y, Olsson PA, Suarez JP and Rillig MC
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(2017) Contrasting species responses to continued nitrogen and phosphorus addition in tropical montane forest tree seedlings. Biotropica
Cárate-Tandalla D, Camenzind T, Leuschner C and Homeier J
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(2017) Nutrient Enrichment Effects on Mycorrhizal Fungi in an Andean Tropical Montane Forest. Mycorrhiza 27: 311- 319
Delavaux CS, Camenzind T, Homeier J, Jiménez-Paz R, Ashton M, Queensborough SA
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(2018) Do fungi need salt licks? No evidence for fungal contribution to the Sodium Ecosystem Respiration Hypothesis based on lab and field experiments in Southern Ecuador. Fungal Ecology 32: 18-28
Camenzind T, Lehmberg J, Weimershaus P, Alvarez-Garrido L, Andrade Linares DR, Suarez JP and Rillig MC
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(2018) Nutrient limitation of soil microbial processes in tropical forests. Ecological Monographs 88: 4–21
Camenzind T, Hättenschwiler S, Treseder KK, Lehmann A and Rillig MC
