Structural and functional processes during water vapour uptake and desiccation in selected lichens with green algal photobionts

Scheidegger, Christoph; Schroeter, B.; Frey, Beat

doi:10.1007/bf00202663

Cited by 82 publications

(64 citation statements)

References 38 publications

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“…Cells with thicker walls, such as the endodermis and pericycle cells, resist distortion by the negative turgor, and the metastable water may vaporize, forming a cavitation (arrowheads, Fig. 5d) as predicted by Oertli (1993) and observed by cryo-microscopy in water-stressed lichens (Scheidegger et al 1995). Such cavitations were seen rarely in the maize roots, and not at all at RWC > 0·30.…”

Section: Cell Collapse and Negative Turgormentioning

confidence: 59%

Responses of maize roots to drying – limits of viability

Facette

McCully

Canny

1999

Plant Cell & Environment

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Turgid pieces of mature maize roots were dried in air and progressive changes in their relative water content (RWC) determined. Viability was tested by reproducibility of the drying curves after dehydration to successively lower RWCs. After reaching a chosen RWC, the pieces were rehydrated (approximately 2 h), and a 2nd and 3rd dehydration curve measured. Each drying curve was characterized by two parameters (a scale parameter l l, and a shape parameter b b) of a survivorship function, which is a linear function of time. The parameter l l is more informative, and does not change in successive dehydrations for RWC > > 0·4, suggesting no irreversible damage to the roots. Damage and death were indicated by divergences of l l in successive dehydrations to RWC = = 0·35-0·15. Cryo-analytical microscopy confirmed these data while indicating specifically death of 50 and 100% of cortical cells at RWC 0·30 and 0·15, respectively, and survival of 50% or more of sieve tubes, pericycle and vascular parenchyma cells at root RWC as low as 0·15. This pattern of stelar cell survival may allow roots to preserve their capacity for renewal of axial conductivity and branch root development following periods of severe water stress.

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Section: Cell Collapse and Negative Turgormentioning

confidence: 59%

Responses of maize roots to drying – limits of viability

Facette

McCully

Canny

1999

Plant Cell & Environment

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“…As discussed in section III.2, lichen productivity is strongly dependent on thallus water content (WC), but the extent varies depending on photobiont species Scheidegger et al, 1995 ;Sundberg et al, 1997b), species morphology (Lange et al, 1993) and habitat preferences (Bewley, 1979). Typically, lichens contain 1-3 g of water g −" d. wt at maximal hydration (Blum, 1973 ;Rundel, 1988), whereas gelatinous lichens can contain 20-30 g of water g −" d. wt when external water films are included (Lange et al, 1993).…”

Section: Water Relationsmentioning

confidence: 99%

“…In lichens with green algal photobionts, photosynthesis can be recovered if the thallus is allowed to equilibrate with air with a water potential above approx. k10 MPa Scheidegger et al, 1995). However, this generally requires equilibration periods of up to 30-60 h. Also, even if 20-30% of maximal photosynthesis can be achieved in this way, the addition of liquid water might still be required for all cells to become turgid and for the lichen to attain maximal photosynthetic activity (Scheidegger et al, 1995).…”

Section: Water Relationsmentioning

confidence: 99%

“…k10 MPa Scheidegger et al, 1995). However, this generally requires equilibration periods of up to 30-60 h. Also, even if 20-30% of maximal photosynthesis can be achieved in this way, the addition of liquid water might still be required for all cells to become turgid and for the lichen to attain maximal photosynthetic activity (Scheidegger et al, 1995). By contrast, when liquid water is provided, green algal lichens with Trebouxia photobionts can induce 75-80% of maximal photosynthetic electron transport and CO # fixation activity within 10 min, with complete induction after 30 min (Fig.…”

Section: Water Relationsmentioning

confidence: 99%

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Tansley Review No. 117

Palmqvist

2000

New Phytologist

220

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Lichens are nutritionally specialized fungi (the mycobiont component) that derive carbon and in some cases nitrogen from algal or cyanobacterial photobionts. The mycobiont and photobiont live together in an integrated thallus, but they lack specific tissue for the transport of metabolites and resources between them. Carbon is acquired through photosynthesis in the photobiont, which is active when the lichen is wet and exposed to light. Lichen photosynthesis is limited primarily by water, light and nitrogen, but can also be constrained by slow diffusion of CO # within the wet thallus. The assimilated carbon is exported from photobiont to mycobiont, which also predominates in terms of biomass, and apparently regulates the size of the photobiont population. It has therefore generally been assumed that most of the carbon is used for growth and maintenance of the fungal hyphae. However, the extent of photobiont respiration in relation to mycobiont respiration has seldom been quantified ; neither do we know the pool sizes of various carbon sinks within lichens. Owing to this lack of fundamental data we do not know whether, or how, carbohydrate resources are regulated to maintain an optimal balance between energy input and expenditures in these symbiotic organisms. This review summarizes data on growth, carbon gain and carbon expenditures in lichens, with particular emphasis on factors determining the photosynthetic capacity of their photobionts. An attempt is made to introduce an economic analysis of lichen growth processes, a view that has often been adopted in studies of higher plants. Areas in which more data are needed for the construction of a model on ' lichen resource allocation patterns ' are discussed.

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“…On long timescales, weathering rates of silicates control atmospheric CO 2 concentration and thus have a large influence on global climate. The work of Schwartzmann and Volk (1989) shows, for example, that without biotic enhancement of weathering in the course of evolution, atmospheric CO 2 would have remained at a high level. The surface temperature associated with this CO 2 level would probably have been too high for complex life to evolve.…”

Section: Introductionmentioning

confidence: 99%

Estimating global carbon uptake by lichens and bryophytes with a process-based model

et al. 2013

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Abstract. Lichens and bryophytes are abundant globally and they may even form the dominant autotrophs in (sub)polar ecosystems, in deserts and at high altitudes. Moreover, they can be found in large amounts as epiphytes in old-growth forests. Here, we present the first process-based model which estimates the net carbon uptake by these organisms at the global scale, thus assessing their significance for biogeochemical cycles. The model uses gridded climate data and key properties of the habitat (e.g. disturbance intervals) to predict processes which control net carbon uptake, namely photosynthesis, respiration, water uptake and evaporation. It relies on equations used in many dynamical vegetation models, which are combined with concepts specific to lichens and bryophytes, such as poikilohydry or the effect of water content on CO 2 diffusivity. To incorporate the great functional variation of lichens and bryophytes at the global scale, the model parameters are characterised by broad ranges of possible values instead of a single, globally uniform value. The predicted terrestrial net uptake of 0.34 to 3.3 Gt yr −1 of carbon and global patterns of productivity are in accordance with empirically-derived estimates. Considering that the assimilated carbon can be invested in processes such as weathering or nitrogen fixation, lichens and bryophytes may play a significant role in biogeochemical cycles.

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Structural and functional processes during water vapour uptake and desiccation in selected lichens with green algal photobionts

Cited by 82 publications

References 38 publications

Responses of maize roots to drying – limits of viability

Responses of maize roots to drying – limits of viability

Tansley Review No. 117

Estimating global carbon uptake by lichens and bryophytes with a process-based model

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