Tansley Review No. 117

Abstract

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.

Photosynthesis in chlorolichens: the influence of the habitat light regime

“…1b). This result strongly supports the observation of Palmqvist (2000) that Table 1 in function of chlorophyll a content (a), potential solar irradiation (b), and eutrophication (c). R Spearman's R rank correlation; r Pearson's r correlation in lichens carbon and nitrogen are strictly connected: high light availability apparently induces these organisms to invest more nitrogen (when available), towards selected components of the photosynthetic apparatus (Rubisco, ATPase, Cyt f, see Hikosaka and Terashima 1995) in order to achieve a more efficient use of the energy input.…”

“…Interestingly, the maximum rate of Pg (Pg max) was always higher in S-exposed than in N-exposed populations of the same lichen, from 1.12 (F. caperata) to 1.74 times (X. calcicola), on both area and weight basis. In agreement with previous results (Tretiach and Carpanelli 1992;Palmqvist 2000;Palmqvist et al 2002), the CO 2 fixation increases with the Chl a content of samples (Fig. 1a).…”

“…The main aim of this work was to understand whether the photosynthetic features of lichens from light contrasting habitats are well differentiated as in ''sun'' and ''shade'' leaves of vascular plants, as contrasting results have been reported in the past (Green et al 1997;Hill and Woolhouse 1966;Kershaw 1985;Palmqvist 2000;Pintado et al 1997;Tretiach and Brown 1995). In good accordance with Green et al (1997), our data highlight that the photosynthetic response of lichens to their light environment is not so clear-cut as in vascular plants.…”

Diversity and functional traits of lichens in ultramafic areas: a literature‐based worldwide analysis integrated by field data at the regional scale

“…Several traits play a decisive role in the phases of dispersal and establishment of new thalli: most of them include attributes related to morphological characteristics of the spores, such as their shape, number, dimension and color (Armstrong 1981; Morando et al 2017). Some eco-physiological functions, such as substrate colonization, evapotranspiration or photon absorption, are strictly related to lichen growth form (Palmqvist 2000), whereas some features (e.g. thallus and epithecium colors or the presence of pruina) are involved in the protection from solar radiation (Giordani et al 2003).…”

Fire affects the functional diversity of epilithic lichen communities

“…Other traits were also included, which are expected to play simultaneous roles in lichen eco-physiology. For example, growth form can regulate several major functions in lichens, such as substrate colonization, evapo-transpiration or photons absorption (Palmqvist, 2000).…”