Temperate rainforest lichens in New Zealand: high thallus water content can severely limit photosynthetic CO2 exchange

Abstract

CO exchange rate in relation to thallus water content (WC, % of dry weight) was determined for 22 species of lichens, mainly members of the genera Pseudocyphellaria and Sticta, from a temperate rainforest, Urewere National Park, New Zealand. All data were obtained in the field, either using a standard technique in which the lichens were initially wetted (soaked or sprayed, then shaken) and allowed to slowly dry, or from periodic measurements on samples that were continuously exposed in their natural habitat. A wide range of WC was found, with species varying from 357 to 3360% for maximal WC in the field, and from 86 to 1300% for optimal WC for photosynthesis. Maximal WC for lichens, wetted by the standard technique, were almost always much less than the field maxima, due to the presence of water on the thalli. The relationships between CO exchange rate and WC could be divided into four response types based on the presence, and degree, of depression of photosynthesis at high WC. Type A lichens showed no depression, and Type B only a little at maximal WC. Type C had a very large depression and, at the highest WC, CO release could occur even in the light. Photosynthetic depression commenced soon after optimal WC was reached. Type D lichens showed a similar depression but the response curve had an inflection so that net photosynthesis was low but almost constant, and never negative, at higher WC. There was little apparent relationship between lichen genus or photobiont type and the response type. It was shown that high WC does limit photosynthetic CO uptake under natural conditions. Lichens, taken directly from the field and allowed to dry under controlled conditions, had net photosynthesis rates that were initially strongly inhibited but rose to an optimum, before declining at low WC. The limiting effects of high WC were clearly shown when, under similar light conditions, severe photosynthetic depression followed a brief, midday, rain storm. Over the whole measuring period the lichens were rarely at their optimal WC for photosynthesis, being mostly too wet or, occasionally, too dry. Photosynthetic performance by the lichens exposed in the field was similar to that expected from the relationship between the photosynthetic rate and WC established by the standard procedure.

Recovery of chlorophyll fluorescence and CO2 exchange in lichen soil crusts after rehydration

“…The positive value means the respiration was stronger than photosynthesis, and the negative value means CO 2 assimilation occurred. As for cyanolichen, it was reported that net photosynthesis was severely depressed by both too low and too high water contents [25,27]. But a seemingly conflicting result was found in LSCs in the present study.…”

Fluorescent Fingerprints of Endolithic Phototrophic Cyanobacteria Living within Halite Rocks in the Atacama Desert

“…It is significant that activation of PSII in the halite cyanobacteria did not occur until liquid water was produced through deliquescence (8) and/or water vapor condensed within the nanopores of halite (9). Hence, it seems that photosynthesis in cyanobacteria can only be activated in the presence of liquid water (50). All these factors can cause different viability states of the cells.…”

Carbonic anhydrase(s) associated with lichens: in vivo activities, possible locations and putative roles

“…Most lichens seem to have an optimal WC for photosynthesis, for net CO^ uptake may be depressed when the WC is too high (Lange et al, 1994). This depression has been shown to result from high COd iffusion resistance through a water-saturated fungal matrix (Cowan, Lange & Green, 1993), but the relati\-e inhibition of net photosynthesis at supraoptimal WC varies between species (Lange et al, 1994).…”

“…Most lichens seem to have an optimal WC for photosynthesis, for net CO^ uptake may be depressed when the WC is too high (Lange et al, 1994). This depression has been shown to result from high COd iffusion resistance through a water-saturated fungal matrix (Cowan, Lange & Green, 1993), but the relati\-e inhibition of net photosynthesis at supraoptimal WC varies between species (Lange et al, 1994). Several features of the lichens might explain these different responses, including variations in the gross morphology of the lichen thallus, production of water-repellent substances by some mycobionts and differences in the organization of the mycohiontphotobiont interface.…”

“…The operation of a CCM in the photobiont might also affect the relative inhibition of net photosynthesis at high WCs as one can assume that photobionts with a CCM can create a steeper CO2 concentration gradient through tbe fungal matrix and thus enhance the CO^ diffusion rate. However, it has not been possible to find any key factor which can alone explain the various types of responses, and there are probably several and perhaps different mechanisms hy which particular lichen copes with high water contents (Lange et al, 1994). Yet, there is one additional factor tbat might affect the relative inhibition of photosynthesis at high WCs in licbens that has so far not been taken into consideration.…”