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Resource aquisition and allocation in lichens
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lichens are fascinating symbiotic systems, where a fungus and a unicellular alga, most often green (bipartite green algal lichens; 90% of all lichens), or a fi lamentous cyanobacterium (bipartite cyanobacterial lichens; 10% of all lichens) form a new entity (a thallus) appearing as a new and integrated organism: in about 500 lichens the fungus is associated with both a cyanobacterium and an alga (tripartite lichens). In the thallus, the lichen bionts function both as individual organisms, and as a symbiont partner. Hence, in lichens, the participating partners must both be able to receive and acquire resources from the other partner(s) in a controlled way.

Lichens are particularly successful in harsh terrestrial environments. In part this is related to their poikilohydric nature and subsequent ability to repeatedly become desiccated and hydrated. Metabolic activity, i.e. photosynthesis, respiration, and for cyanobacterial lichens N2-fixation, is limited to periods when the thallus is suffi ciently hydrated. Mineral nutrients are mainly acquired from dry or wet deposition directly on the thallus. Taken together it then appears that lichens are to a large extent passively controlled by their environment, making their control over resource allocation and acquisition particularly challenging.

The aim of this thesis was to investigate resource acquisition and allocation processes in different lichens, and to see how these respond to changes in resource availability. This was done by following lichen growth in the fi eld during manipulation of water, light, and nutrient supply, and by assessing the responses of both the integrated thallus as well as the individual bionts. As a fi rst step, resource allocation and acquisition was investigated for a broad range of lichens aiming to determine the magnitude of metabolic variation across lichens. Seventy-fi ve lichen species were selected to cover as broad a spectrum as possible regarding taxonomy, morphology, habitat, and nitrogen requirements. The lichens had invested their nitrogen resources so that photosynthetic capacity matched respiratory carbon demand around a similar equilibrium across the contrasting species. Regulation of lichen growth was investigated in another study, using the two tripartite species Nephroma arcticum and Peltigera aphthosa, emphasizing the contribution of both internal and external factors. The empirical growth models for the two lichens were similar, showing that weight gain is to a higher extent dependent on those external factors that regulate their photosynthesis, whilst area gain is more controlled by internal factors, such as their nitrogen metabolism. This might be inferred from another study of the same species, where nitrogen manipulations resulted in an undisturbed weight gain, a similar resource allocation pattern between the bionts, but a distorted area gain.

Aiming to investigate lichen nitrogen relations even further, lichens’ capacities to assimilate combined nitrogen in the form of ammonium, nitrate and amino acids were assessed using 14 contrasting boreal species. All these had the capacity to assimilate all the three nitrogen forms, with ammonium absorption being more passive, and nitrate uptake being low in bipartite cyanobacterial lichens. Differences in uptake capacities between species were more correlated to photobiont than to morphology or substrate preferences. Finally, to investigate intra-specifi c plasticity in relation to altered nutrient supply, resource investments between photo- and mycobiont were investigated in the two bipartite green algal lichens Hypogymnia physodes and and Platismatia glauca in a low and a high nutrient environ- in a low and a high nutrient environ- ment. In both species, more of the resources had been directed to the photobiont in the high nutrient environment also increasing their overall carbon status. Taken together, my studies indicate that in spite of the apparent passive environmental control on lichen metabolism, these symbiotic organisms are able to both optimize and control their resource acquisition and allocation processes.

Place, publisher, year, edition, pages
2003. , 57 p.
Keyword [en]
Ecology, Amino acid, Arginine, carbohydrates, chlorophyll, ergosterol, microclimate, Lichen growth, nitrogen stress, photosynthesis, proteins, respiration, Symbiosis (lichen), nitrogene uptake
Keyword [sv]
Ekologi
National Category
Ecology
Research subject
Ecological Botany
Identifiers
URN: urn:nbn:se:umu:diva-115ISBN: 91-7305-496-8 (print)OAI: oai:DiVA.org:umu-115DiVA: diva2:140381
Public defence
2003-10-17, KB3B1, KBC-huset, Umeå, 10:00
Opponent
Available from: 2003-10-02 Created: 2003-10-02Bibliographically approved
List of papers
1. CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones.
Open this publication in new window or tab >>CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones.
Show others...
2002 (English)In: Oecologia, ISSN 0029-8549, Vol. 133, 295-306 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2398 (URN)
Available from: 2003-10-02 Created: 2003-10-02 Last updated: 2010-03-23Bibliographically approved
2. Growth in two foliose tripartite lichens Nephroma arcticum and Peltigera aphthosa: empirical modelling of external versus internal factors
Open this publication in new window or tab >>Growth in two foliose tripartite lichens Nephroma arcticum and Peltigera aphthosa: empirical modelling of external versus internal factors
2003 (English)In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 17, no 6, 821-831 p.Article in journal (Refereed) Published
Abstract [en]

1 To assess how internal and external factors contribute to lichen growth, light, water and nutrient supplies were manipulated during 3 months in the field for the lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Concomitant measures of weight and area gain, microclimatic conditions and investments in photobiont vs mycobiont tissue were also conducted.

2 In both lichens ≈80% of the variation in weight gain was explained by a linear regression model including light received during wet active periods, chlorophyll a concentration and area gain. All three parameters had a positive effect on weight gain.

3 About 80% of the variation in area gain was explained by a model including variation in weight gain, initial thallus specific weight, ergosterol and chitin concentration. The model was identical for the two lichens, with a positive effect of weight gain and thallus specific weight and a negative effect of ergosterol and chitin.

4 Peltigera aphthosa grew faster than N. arcticum when exposed to the same environmental conditions. This could be explained by its higher chlorophyll a to ergosterol ratio, and a greater water-holding capacity prolonging the active time in light.

Keyword
Chitin, chlorophyll, ergosterol, microclimate, symbiosis
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-2399 (URN)10.1046/j.0269-8463.2003.00804.x (DOI)
Available from: 2003-10-02 Created: 2003-10-02 Last updated: 2017-12-14Bibliographically approved
3. Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress
Open this publication in new window or tab >>Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress
2002 (English)In: New Phytologist, ISSN 0028-646X, Vol. 153, no 2, 307-315 p.Article in journal (Refereed) Published
Abstract [en]

 

  • The lichens were irrigated with different N forms, enriched in 15N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m−2. Nitrogen deprivation was induced by removing the nitrogen-fixing cephalodia.

  • The lichens took up 11–134 mg N m−2 of the added N, corresponding to 1–4% of their total thallus N. Uptake was 4 times higher for NH4+ than for NO3, and the highest 15N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species.

  • It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.

Identifiers
urn:nbn:se:umu:diva-2400 (URN)10.1046/j.0028-646X.2001.00321.x (DOI)
Available from: 2003-10-02 Created: 2003-10-02 Last updated: 2010-03-23Bibliographically approved
4. Carbon and nitrogen distribution in the green algal lichens Hypogymnia physodes and and Platismatia glauca in relation to nutrient supply.
Open this publication in new window or tab >>Carbon and nitrogen distribution in the green algal lichens Hypogymnia physodes and and Platismatia glauca in relation to nutrient supply.
2003 (English)In: Planta, ISSN 0032-0935, Vol. 217, no 1, 41-48 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-2401 (URN)
Available from: 2003-10-02 Created: 2003-10-02 Last updated: 2010-03-23Bibliographically approved
5. Organic and inorganic nitrogen uptake in lichens.
Open this publication in new window or tab >>Organic and inorganic nitrogen uptake in lichens.
In: Planta, ISSN 0032-0935Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-2402 (URN)
Available from: 2003-10-02 Created: 2003-10-02Bibliographically approved

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