Diel and seasonal courses of ambient carbon dioxide concentration and their effect on productivity of the epilithic lichen Lecanora muralis in a temperate, suburban habitat

Abstract

Ambient CO 2 concentration (together with CO 2 exchange and microclimate) was recorded every 30 min for 15 months for Lecanora muralis growing in the Botanical Garden Wü rzburg (Germany, northern Bavaria), a habitat on the outskirts of the city. Annual mean CO 2 was around 17 ppm higher than the global average reported for the time of measurement (361 ppm; 1995/96), and daily values ranged from 317 to 490 ppm. Diel courses of CO 2 could be classified into three different types. Type A, when CO 2 levels rose overnight and then fell strongly to below global levels during the day, which predominated in the summer (about 75% of days); Type B, irregular diel courses occurred during all seasons with often very rapid changes apparently due to advective CO 2 transport; Type C, CO 2 concentration was typically almost stable at generally between c. 330 and 430 ppm which predominated in the winter (63% of days).Under controlled conditions, CO 2 saturation of net photosynthesis (NP) of L. muralis at optimal hydration and light occurred at around 1000 ppm. NP was also affected by low CO 2 at limiting light and thallus water contents. Based upon these data, we estimated the improvement of NP of L. muralis due to transient increase of ambient CO 2 (as compared with the global average) for one selected combination of environmental factors (nocturnal dew or frost). This combination is an important source of water for the lichen, resulting in 40% of its annual production and, especially in these situations, photosynthesis was increased by high ambient CO 2 in the early morning under prevailing Type A conditions. After dew activation, light compensation point of NP occurred at an average concentration of 413 ppm and diel maxima of NP at 402 ppm. This allows a rough estimate that the transiently elevated CO 2 increased the photosynthetic gain of the lichen after dew of 7%, or an improvement to its annual carbon balance of about 3%. Conditions, especially interrelationships between lichen hydration, light and CO 2 are so complex that we are not yet able to extend our estimates to other environmental situations of photosynthetic activity of L. muralis.

Water availability modifies tolerance to photo-oxidative pollutants in transplants of the lichen Flavoparmelia caperata

“…We can also argue that these two factors, which lead to the overall increase of oxidative stress, are sufficient to weaken or even eliminate the diaspores and young individuals eventually grown in periods of the year when the environmental conditions are more favorable. Finally, it should be kept in mind that the arid mesoclimate of urban environments would heavily reduce the length of the wet, metabolically active period that is a key factor for the total carbon gain of the lichen symbiosis, and thereby for thallus growth (Lange and Green 2008). This might be a further important reason, in addition to pollution, that explains the slow rate of lichen recolonization in urban environments.…”

Biocrusts in the Context of Global Change

“…Increased photosynthesis may allow for greater production of biomass, secondary osmoprotectants, and pigments (e.g., melanin, mycosporines) that could enhance stress tolerance relative to biocrusts under current ambient conditions. The effects of altered CO 2 concentrations would be strongly dependent upon biocrust moisture content and its effect on the diffusion of CO 2 (e.g., Lange 2002;Lange and Green 2008), and net photosynthesis responses observed under laboratory conditions may not translate into an observable effect on biocrust function or structure in the field. In addition, biocrust autotrophs may not consistently experience an increase in CO 2 when atmospheric CO 2 concentrations increase, as soil surface and soil atmosphere CO 2 concentrations can be much greater than that of the atmosphere (e.g., Pumpanen et al 2003).…”

Photosynthesis in chlorolichens: the influence of the habitat light regime

“…The results are reported in the last column of Table 1. Of course, the productive hydration periods for lichens are often early mornings during clear weather and rainy/cloudy weather (Lange and Green 2008). The total direct irradiation, however, represents an important stressor which moulds the photosynthetic apparatus and asks for efficient photoprotection mechanisms for energy dissipation (Veerman et al 2007).…”