Growth of crustose lichens: a review

Abstract

R.A. and Bradwell, T., xxxx: Growth of crustose lichens: a review. Geogr. Ann., 92A (X): xx-xx. AbstractCrustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (lichenometry). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development, 2) radial growth rates (RGR, mm yr -1 ), 3) the growth rate-size curve, and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenised fungal hypothallus. Recent data suggest that 'primary' areolae may develop from free-living algal cells on the substratum while 'secondary' areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the 'asymptotic' type of curve recorded in foliose and placodioid species; the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature 'reproductive' areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.

Carbon Budgets of Biological Soil Crusts at Micro-, Meso-, and Global Scales

“…Lichenometry has been widely used to date surfaces, mainly in studies on glacier retreat in both hemispheres (Innes 1988;Winchester and Harrison 2000;Roberts et al 2010), or to calculate the growth rate of a thallus by direct measurements at time intervals (Armstrong and Bradwell 2010;Sancho and Pintado 2004;Sancho et al 2011). Annual thallus enlargement measured in lichenometric studies can be transformed to thallus weight gain after determining the thallus weight per unit area (Raggio et al 2012).…”

Dispersal patterns of meiospores shape population spatial structure of saxicolous lichens

“…It is worth noting here that the relatively small size of the largest Rhizocarpon thalli, compatible with an average age in the order of decades (Armstrong & Bradwell 2010), indicated an early stage of lichen colonization. This suggests a "modern age" recolonization phase after the restorations ended in the 1910s and 1960s (Sergi 2012 …”

“…Higher humidity at the bottom of the wall may enhance the motility of algal zoospores involved in the formation of primary areolae of Rhizocarpon thalli (Armstrong & Bradwell 2010).…”

“…Information on the structure and dynamics of lichen populations is fundamental to improve conservation effectiveness (Scheidegger & Werth 2009;Ellis 2012;Spitale & Nascimbene 2012), environmental monitoring techniques (Armstrong & Bradwell 2010;Giordani & Brunialti 2015), and Cultural Heritage management (Gazzano et al 2009). Dispersal limitations and establishment constraints are addressed to explain the dynamics of lichen populations (Scheidegger & Werth 2009;Ellis 2012;Schei et al 2012).…”

Long-term changes in biological soil crust cover and composition

“…Bryophyte cover can increase rapidly in the absence of disturbance (Antos et al 1983;Bates et al 2009), and young mosses can grow more rapidly than older mosses (Barker et al 2005). Lichens generally have slow growth rates that may decline with age (Armstrong and Bradwell 2010). Crustose lichens can invade soon after disturbance (Johansen et al 1984) but may take a long time to increase in cover.…”