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Epiphytic lichen responses to nitrogen deposition
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nitrogen (N) deposition has increased globally over the last 150 years and further increase is predicted for the future. Nitrogen is an important nutrient for lichens, involved in many processes in both photobiont and mycobiont.  However, N can be a stressor, causing many lichens and lichen communities to disappear with increased deposition. The objective of this thesis was to investigate the response of epiphytic lichens to increased N load. This was done by simulating an increased N deposition to lichens in a boreal forest with low background N, including both short term studies with transplanted lichens and long term studies of naturally established lichens. Alectoria sarmentosa was used as a model species for a N-sensitive lichens and Platismatia glauca as a relatively more N-tolerant lichen. Nitrogen deposition was simulated by daily spraying during the growing season with water and isotopically labeled ammonium nitrate (NH4NO3). In Paper I, I found that when N is supplied in realistic doses (equivalent to deposition of 0.6, 6, 12.5, 25 and 50 kg N ha-1), there were no significant differences in uptake of NO3- or NH4+ in either of the lichen species. The results in Paper II indicate that A. samentosa may be limited by phosphorous (P) and not N limited as expected. That study highlights the importance of P, when studying the effects of N deposition, since P can both mitigate and intensify the negative effects of N on epiphytic lichens. Paper III shows that four years of simulated N deposition caused an alteration of the epiphytic lichen community, since A. sarmentosa decreased in the highest N loads (25 and 50 kg ha-1 year-1), Bryoria spp. decreased to 12.5 kg N and higher loads and Hypogymnia physodes decreased over time for all treatments except in 12.5 kg ha-1, where it only decreased during the first treatment year and then increased after 2007.  The abundance of Platismatia glauca increased over time, independent of treatment. As hypothesized, responses to the treatments differed among species, reflecting their different N optima. In paper IV, the effects of N on carbon-based secondary compounds were studied. None of the studied species (P. glauca, A. sarmentosa, Lobaria scrobiculata and Xanthoria aureola) reduced their concentration of secondary compounds during the experimental period, but in P. glauca the concentration of all compounds were significantly lower in N treated thalli compared with control thalli. The results are consistent with a high degree of constitutive defence in three of the four studied lichens, and we conclude that all four studied lichens seem to have a robust chemical defence system despite considerable manipulation of the environmental conditions. However, we don't know if these lichens are able to keep up the high protection level over longer periods comprising a number of years when more new tissue is formed. In conclusion, long term experiments are necessary to understand lichen response to environmental changes.

Place, publisher, year, edition, pages
Umeå: Institutionen för ekologi, miljö och geovetenskap, Umeå universitet , 2011. , 25 p.
Keyword [en]
Lichens, air pollution, nitrogen deposition, phosphorus, growth, chlorophyll a, boreal forest, field experiment, irrigation, carbon based secondary compounds
Keyword [sv]
Lavar, luftföroreningar, alg, svamp, kväve, fosfor, skog
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-43751ISBN: 978-91-7459-232-0OAI: oai:DiVA.org:umu-43751DiVA: diva2:415773
Public defence
2011-06-01, Älgsalen, Uminova Science Park, Tvistevägen 48, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-05-11 Created: 2011-05-09 Last updated: 2011-05-11Bibliographically approved
List of papers
1. Responses of epiphytic lichens to an experimental whole-tree nitrogen-deposition gradient
Open this publication in new window or tab >>Responses of epiphytic lichens to an experimental whole-tree nitrogen-deposition gradient
2010 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 188, no 4, 1075-1084 p.Article in journal (Refereed) Published
Abstract [en]

• Here, we examined the responses of the epiphytic lichens Alectoria sarmentosa and Platismatia glauca to increased atmospheric nitrogen (N) deposition in an old-growth boreal spruce forest, to assess the sensitivity of these species to N and define their critical N load. • Nitrogen deposition was simulated by irrigating 15 trees over a 3 yr period with water and isotopically labeled NH(4) NO(3) , providing N loads ranging from ambient to 50 kg N ha(-1)  yr(-1) . • Thallus N concentration increased in both species with increasing N load, and uptake rates of both NH(4) (+) and NO(3) (-) were similar. Photobiont concentration increased linearly with increased N in both species, saturating in A. sarmentosa in the third year at the highest N loads (25 and 50 kg ha(-1 ) yr(-1) ). The simulated N deposition decreased the phosphorus (P) concentration in A. sarmentosa, and increased the N : P ratio in both species. • Significant responses in lichen chemistry were detected to inputs of 12.5 kg N ha(-1)  yr(-1) or higher, suggesting that resources other than N limit lichens at higher N loads. However, the data also suggest that N saturation may be cumulative over time, even at low N.

Place, publisher, year, edition, pages
Wiley, 2010
Keyword
15N-labeled ammonium nitrate, Alectoria sarmentosa, Chla, critical load, lichen sensitivity, phosphorus, latismatia glauca, simulated nitrogen deposition
Identifiers
urn:nbn:se:umu:diva-37620 (URN)10.1111/j.1469-8137.2010.03426.x (DOI)000284074900016 ()20731782 (PubMedID)
Available from: 2010-11-10 Created: 2010-11-10 Last updated: 2016-05-20Bibliographically approved
2. Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses
Open this publication in new window or tab >>Lichen responses to nitrogen and phosphorus additions can be explained by the different symbiont responses
2011 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 191, no 3, 795-805 p.Article in journal (Refereed) Published
Abstract [en]

Responses to simulated nitrogen (N) deposition with or without added phosphorus (P) were investigated for three contrasting lichen species – the N-sensitive Alectoria sarmentosa, the more N-tolerant Platismatia glauca and the N2-fixing Lobaria pulmonaria– in a field experiment.

To examine whether nutrient limitation differed between the photobiont and the mycobiont within the lichen, the biomass responses of the respective bionts were estimated.

The lichenized algal cells were generally N-limited, because N-stimulated algal growth in all three species. The mycobiont was P-limited in one species (A. sarmentosa), but the growth response of the mycobionts was complex, as fungal growth is also dependent on a reliable carbon export from the photobiont, which may have been the reason for the decrease of the mycobiont with N addition in P. glauca.

Our findings showed that P availability was an important factor when studying effects of N deposition, as P supply can both mitigate and intensify the negative effects of N on epiphytic lichens.

Place, publisher, year, edition, pages
Wiley, 2011
Keyword
chlorophyll a, epiphytic lichens, fertilization experiment, growth rate, nitrogen deposition, nutrient limitation, phosphorus, symbiosis
National Category
Botany
Identifiers
urn:nbn:se:umu:diva-43772 (URN)10.1111/j.1469-8137.2011.03739.x (DOI)
Available from: 2011-05-09 Created: 2011-05-09 Last updated: 2016-05-20Bibliographically approved
3. Nitrogen drives lichen community changes through the different species responses
Open this publication in new window or tab >>Nitrogen drives lichen community changes through the different species responses
(English)Manuscript (preprint) (Other academic)
Research subject
Ecological Botany
Identifiers
urn:nbn:se:umu:diva-43773 (URN)
Available from: 2011-05-09 Created: 2011-05-09 Last updated: 2011-05-11
4. Defensive compound concentration in boreal lichens in response to simulated nitrogen deposition
Open this publication in new window or tab >>Defensive compound concentration in boreal lichens in response to simulated nitrogen deposition
2009 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 15, no 9, 2247-2260 p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen (N) deposition is expected to increase in northwestern Europe the next 50–100 years. The effects of higher N availability on lichens will presumably depend on their capacity to acquire carbon (C), that is, of the timing and duration of the wet and active state. If lichens respond like plants, their C and N status may affect their concentration of carbon-based secondary compounds (CBSCs), and thus their defence against herbivores, detrimental radiation, pathogens and parasites. In the present study we have manipulated N availability and timing and duration of the metabolically active state by spraying lichen transplants in an old spruce forest with rainwater or rainwater with added N corresponding to 50 kg N ha−1 yr−1. The spraying was applied either at night, in the morning or at noon to also investigate the effect of timing and duration of the active state. Concentrations of N, chlorophyll a (Chl a) and CBSCs were measured before and after one summer's spraying of 10 thalli in each of four different lichen species; Alectoria sarmentosa, Lobaria scrobiculata, Platismatia glauca, and Xanthoria aureola. The added N was readily taken up by all the lichen species. A. sarmentosa, P. glauca, and X. aureola increased their Chl a concentration in response to increased N, while L. scrobiculata increased Chl a in response to increased active time. None of the studied species reduced their concentration of secondary compounds during the experimental period, but in P. glauca the concentration of all compounds were significantly lower in N-treated thalli compared with those that got only rainwater. The results are consistent with a high degree of constitutive defence in three of four species, and we conclude that all the investigated lichens seem to have rather robust chemical defence systems despite considerable manipulation of the environmental conditions.

Place, publisher, year, edition, pages
Wiley, 2009
Keyword
Alectoria sarmentosa, CBSCs, lichens, Lobaria scobiculata, nitrogen deposition, platismatia glauca, precipitation, xanthoria aureola
Identifiers
urn:nbn:se:umu:diva-40355 (URN)10.1111/j.1365-2486.2009.01853.x (DOI)
Available from: 2011-02-22 Created: 2011-02-22 Last updated: 2011-05-11Bibliographically approved

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