The effect of nitrogen on growth and key thallus components in the two tripartite lichens, Nephroma arcticum and Peltigera aphthosa

Abstract

Relationships between growth, nitrogen and concentration of unique biont components were investigated for the tripartite lichens Nephroma arcticum (L.) Torss. and Peltigera aphthosa (L.) Willd. Nitrogen availability was manipulated during 4 summer months by removing cephalodia and their associated N 2 fixation activity, or by weekly irrigation with NH 4 NO 3 . Chlorophyll and ribulose 1·5-biphosphate carboxylase/oxygenase (Rubisco), and chitin and ergosterol were used as photobiont and mycobiont markers, respectively. Nitrogen concentrations were similar in older and newer parts of the same thallus, varying between 2 and 5 g m -2 , with P. aphthosa having higher concentrations than N. arcticum. Both chlorophyll (Chl a) and chitin were linearly correlated with thallus N, but N. arcticum invested more in fungal biomass and had lower Chl a concentrations in comparison with P. aphthosa at equal thallus N. During the 4 months, control and Nfertilized thalli of N. arcticum increased in area by 0·2 m 2 m -2 and P. aphthosa by 0·4 m 2 m -2 . Thallus expansion was significantly inhibited in samples without cephalodia, but there was no effect on lichen weight gain. Mean relative growth rate (RGR; mg g -1 d -1 ) was 3·8 for N. arcticum and 8·4 for P. aphthosa, when time (d) reflected the lichen wet periods. RGR was 2-3 times lower when based on the whole time, i.e. when including dry periods. The efficiency (e) of converting incident irradiance into lichen biomass was positively and linearly correlated with thallus Chl a concentration to the same extent in both species. The slower growth rates of N. arcticum, in comparison with P. aphthosa, could then be explained by their lower nitrogen and Chl a concentrations and a subsequently lower light energy conversion efficiency. Functional and dynamic aspects of resource allocation patterns of the two lichens are discussed in relation to the above findings.

Growth and ecophysiological acclimation of the foliose lichen Lobaria pulmonaria in forests with contrasting light climates

“…Increased DM per area implies (1) higher solar radiation screening due to thicker layers of upper cortex and/or photobiont Green and Lange 1991;Ma´guas and Brugnoli 1996) and (2) increased waterholding capacity (Ma´guas and Brugnoli 1996;Gauslaa and Solhaug 1998) that may lengthen the duration of hydration events. Increased DM gain is related to the lichens' C acquisition, whereas area gain is also presumably determined by N acquisition (Sundberg et al 2001;Dahlman et al 2002) and water status since the expansion of fungal hyphae is regulated by turgor pressure (Wessels 1993). Therefore, the addition of nutrients and water increased the area gain in L. pulmonaria more than the addition of water alone (Fig.…”

CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones

“…This finding implies that respiration rate per unit nitrogen is lower if this N is present in photosynthetic components than other N compounds in the thallus. This further suggests that a lichen that can increase the number of photobionts with increasing N supply should be able to grow faster, supported by a higher efficiency of light energy conversion to lichen biomass with increasing Chl a concentration in the thallus (Palmqvist and Sundberg 2000;Sundberg et al 2001). However, N fertilisation of lichens can also reduce their vitality and may cause reduced rates of area expansion Dahlman et al 2002).…”

“…For instance, regulatory systems to optimise resource allocation in the thallus might be more or less developed depending on evolutionary lineage (Gargas et al 1995;Tehler 1996). Lichens are, moreover, constrained by a requirement for coordinated growth between the partners, so their ability to redirect resource investments in response to altered resource supply may be relatively low (Feige and Jensen 1992;Sundberg et al 2001;Dahlman et al 2002). Furthermore, C:N ratio optima may vary depending on photobiont (Palmqvist et al 1998), thallus morphology, or between populations from contrasting habitats .…”

Predicting lichen hydration using biophysical models

“…Despite an abundance of data, however, we still lack an easily applicable and mechanistic model that simulates the loss and uptake of water for longer time periods in situ based on variables that can be easily obtained and quantified (see Rundel 1982). Recent models of lichen productivity have been merely empirical, assessing metabolic active time from direct measurements of thallus water content using an impedance technique (Coxson 1991;Palmqvist and Sundberg 2000;Sundberg et al 2001;Dahlman and Palmqvist 2003;Gaio-Oliveira et al 2003. Although this is a robust method, it is technically complex and merely descriptive, giving an after-the-fact relationship between climate and growth that cannot be used for predictions.…”