Thallus growth stage affects community-wide capacity for carbon metabolism in the alpine heath lichen Ochrolechia frigida

Fungi are obligate heterotrophs and possess a diverse suite of molecular tools for accessing and processing exogenous carbon. In lichenized fungi, the transfer of photosynthate from photobiont to mycobiont is central to carbohydrate economy; however, major differences in total carbon metabolism are expected to exist between components of the holobiont, that is photoautotrophy in the photobiont versus heterotrophy in the mycobiont and associated microbiota. As well as the nutritional role of sugar monomers, fungi and algae also modify polysaccharide polymers as part of their core cellular processes, for example maintaining cell wall structure (Yoshimi et al . 2016; Fuertes-Rabanal et al . 2025) and processing storage compounds (Wilson et al . 2010), while associated microbiota can be involved in scavenging, recycling (Sigurbjörnsdóttir et al . 2016) or an as-yet undetermined role in the lichen symbiosis (Hawksworth & Grube 2020).