Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress

Abstract

Summary• Lichen responses towards nitrogen stress, both increased exposure and deprivation of N, were investigated by measuring N uptake, growth, ergosterol, chitin and Chl a in two tripartite nitrogen-fixing species, Nephroma arctium and Peltigera aphthosa .• The lichens were irrigated with different N forms, enriched in 15 N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m − 2 . Nitrogen deprivation was induced by removing the nitrogen-fixing cephalodia.• The lichens took up 11-134 mg N m − 2 of the added N, corresponding to 1-4% of their total thallus N. Uptake was 4 times higher for NH 4 + than for NO 3 − , and the highest 15 N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species.• It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.

Nitrogen uptake in relation to excess supply and its effects on the lichens Evernia prunastri (L.) Ach and Xanthoria parietina (L.) Th. Fr.

“…One can argue that this might be the result of both nitrate and ammonium being assimilated from the fertiliser. Although nitrate can be assimilated by lichens (Crittenden 1996), it is known that green algal lichens have a much higher affinity for ammonium compared to nitrate (Crittenden 1996;Dahlman et al 2002Dahlman et al , 2004. This higher affinity for ammonium is supported by the results presented here, as there was nearly a 1:1 relation between final thallus N and N uptake from ammonium ( Fig.…”

“…The control treatment was sprayed once a week with 1 l m À2 of artificial rainwater without P (Tamm 1953;Dahlman et al 2002). The fertilised treatments received 1.8, 3.4, 6.8, 21 or 86 mM of NH 4 NO 3 (0.05, 0.1, 0.2, 0.6 or 2.4 g N m À2 ), with 1% of ( 15 NH 4 )NO 3 , dissolved in the same amount of artificial rainwater as the control, and were also sprayed once a week.…”

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

“…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). It must, therefore, be emphasised that the relationships established here reflect broad-scale patterns across lichens and discussions concerning likely responses of a particular lichen to varying N supply will require more detailed intraspecific studies.…”

“…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 .…”

Potential Approaches to Developing Lichen-Based Critical Loads and Levels for Nitrogen, Sulfur and Metal-Containing Atmospheric Pollutants in North America

“…The negative effects on lichens may instead be an indirect effect from competition with nitrogen-favoured vascular plants (Cornelissen et al, 2001). Dahlmann et al (2002) found that among about 500 lichens which both have green algae and cyanobacterias as their photobiont most species seem to be rather resistant towards even high nitrogen additions.…”