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

Abstract

Aiming to investigate whether a carbon-to-nitrogen equilibrium model describes resource allocation in lichens, net photosynthesis (NP), respiration (R), concentrations of nitrogen (N), chlorophyll (Chl), chitin and ergosterol were investigated in 75 different lichen associations collected in Antarctica, Arctic Canada, boreal Sweden, and temperate/subtropical forests of Tenerife, South Africa and Japan. The lichens had various morphologies and represented seven photobiont and 41 mycobiont genera. Chl a, chitin and ergosterol were used as indirect markers of photobiont activity, fungal biomass and fungal respiration, respectively. The lichens were divided into three groups according to photobiont: (1) species with green algae, (2) species with cyanobacteria, and (3) tripartite species with green algal photobionts and cyanobacteria in cephalodia. Across species, thallus N concentration ranged from 1 to 50 mg g dry wt., NP varied 50-fold, and R 10-fold. In average, green algal lichens had the lowest, cyanobacterial Nostoc lichens the highest and tripartite lichens intermediate N concentrations. All three markers increased with thallus N concentration, and lichens with the highest Chl a and N concentrations had the highest rates of both P and R. Chl a alone accounted for ca. 30% of variation in NP and R across species. On average, the photosynthetic efficiency quotient [K =(NP+R)/R)] ranged from 2.4 to 8.6, being higher in fruticose green algal lichens than in foliose Nostoc lichens. The former group invested more N in Chl a and this trait increased NP while decreasing R. In general terms, the investigated lichens invested N resources such that their maximal C input capacity matched their respiratory C demand around a similar (positive) equilibrium across species. However, it is not clear how this apparent optimisation of resource use is regulated in these symbiotic organisms.

Estimating impacts of lichens and bryophytes on global biogeochemical cycles

“…The net carbon uptake model is not able to determine which of the simulated strategies correspond to nitrogen-fixing lichens and bryophytes because there are no clear correlations between the ability to fix nitrogen and the productivity of a lichen or bryophyte species [Palmqvist et al, 2002]. Instead, the model calculates a weighted average of the carbon uptake of all strategies.…”

Habitat stress initiates changes in composition, CO2 gas exchange and C-allocation as life traits in biological soil crusts

“…Finally, Poorter et al (2012) showed that carbon partitioning acclimates to different habitat conditions and patterns of assimilate allocation are known to serve as excellent indicators for growth performance in vascular plants. Palmquist et al (2002) propose that lichens are able to optimise their resource investments between carbohydrate input and expenditure, suggesting that a carbon economy view might be a fruitful way to compare and understand the performance of different lichens. An acclimation of resource allocation was suggested to be related to environmental conditions (Palmquist et al, 2008).…”

Bromus tectorum litter alters photosynthetic characteristics of biological soil crusts from a semiarid shrubland

“…Notwithstanding this view, a link has been observed between lichen respiration and photosynthetic capacity (Palmqvist et al, 2002). The mechanisms underlying this are unclear, but lichen species with low photosynthetic capacity tend to have low respiration rates and vice versa (Palmqvist, 2000;Palmqvist et al, 2002). Our results suggest that a similar phenomenon may occur within a species.…”

“…In lichens, it is assumed that dark respiration is mainly attributed to fungal respiration because the mycobiont makes up the majority of the thallus (Palmqvist, 2000;Lange and Green, 2005). Notwithstanding this view, a link has been observed between lichen respiration and photosynthetic capacity (Palmqvist et al, 2002). The mechanisms underlying this are unclear, but lichen species with low photosynthetic capacity tend to have low respiration rates and vice versa (Palmqvist, 2000;Palmqvist et al, 2002).…”