Table

Time Required by Different Poikilohydrous Autotrophs to Resume Photosynthetic Activity (Net Photosynthesis) after Rehydration with Water Vapor (>90% Relative Humidity) or with Liquid Water

Species

Parmelia hypoleucina Cladonia portentosa Caloplaca regalis Lobaria pulmonaria Hypnum cupressiforme Tortula ruralis Exormotheca holstii Polypodium virginianum Craterostigma plantagineum Selaginella lepidophylla Ramonda serbica Myrothamnus flabellifolius Xerophyta scabrida

Water Source

Time

Water vapor

<1 h

Water vapor

6 h

Water vapor

24 h

Liquid

<30 sa

Water vapor

12 h

Liquid

90 min

Liquid

2 ha

Liquid

6 hb

Liquid

15 hb

Liquid

24 hb

Liquid

24 h

Liquid

c. 40 h

Liquid

Lange and Kilian 1985 Lange and Kilian 1985 Lange and Kilian 1985 Scheidegger et al. 1997 Lange 1969 Scott and Oliver 1994 Hellwege et al. 1994 Reynolds and Bewley 1993 Bernachia et al. 1969 Eickmeier 1979 Markowska et al. 1997 Sherwin and Farrar 1996 Tuba et al. 1993b a Chlorophyll a fluorescence positive. b Chloroplasts reconstituted.

cells were shriveled and the fungal hyphae cavitated because of the low water content of the thallus. At a given low water potential, different lichen species exhibited different fractions of collapsed photobiont cells and different photosynthetic rates (Figure 2.6). It has therefore

FIGURE 2.6 Amount of photobionts (open bars, heavily collapsed; hatched bars, partially folded; solid bars, globular) and water content (solid circles, % dry weight) of thalli of the lichens Ramalina maciformis (top) and Pseudevernia furfuracea (bottom) at an equilibrium with water potentials between -30 and -2.7 MPa. (After Scheidegger, C., Schroeter, B., and Frey, B., Planta, 197, 399, 1995.)

FIGURE 2.6 Amount of photobionts (open bars, heavily collapsed; hatched bars, partially folded; solid bars, globular) and water content (solid circles, % dry weight) of thalli of the lichens Ramalina maciformis (top) and Pseudevernia furfuracea (bottom) at an equilibrium with water potentials between -30 and -2.7 MPa. (After Scheidegger, C., Schroeter, B., and Frey, B., Planta, 197, 399, 1995.)

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