Mixotrophy: an uncharted carbon flux in the plant world

Project Information

MIXOTROPH

Grant agreement ID: 101045057

DOI

10.3030/101045057

EC signature date 2 May 2022

Start date 1 September 2022

End date 31 August 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 986 701,25

EU contribution

€ 1 986 701,25

Coordinated by

STICHTING NATURALIS BIODIVERSITY CENTER
Netherlands

Periodic Reporting for period 1 - MIXOTROPH (Mixotrophy: an uncharted carbon flux in the plant world)

Reporting period: 2022-09-01 to 2025-02-28

Summary of the context and overall objectives of the project

Plants have green leaves and use energy from sunlight to produce organic carbon. The vast majority of land plants transfer part of their organic carbon to root-associated ‘arbuscular mycorrhizal’ (AM) fungi, which help plants to take up nutrients and water from the soil. This carbon can be subsequently taken up by rare non-green ‘mycoheterotrophic’ plants that tap into the same fungal network. Recent evidence suggests that a wide range of green plants, particularly in the understory of forests, have the ability to take up carbon from AM fungi as well, a strategy known as ‘AM mixotrophy’. However, the plant and fungal diversity involved in AM mixotrophy are unknown. Likewise, the environmental drivers that influence carbon uptake have never been
measured, nor do we know about its evolution and geographic distribution. This is problematic because we are unable to quantify or understand the role of AM mixotrophy in our natural world. With field studies, laboratory experiments, and genetic screening of natural history collections, the MIXOTROPH project aims to (1) identify AM mixotrophic plants and their habitats; (2) reveal environmental drivers that regulate carbon uptake; (3) expose fungal networks that sustain AM mixotrophs; and (4) measure the magnitude of AM mixotrophy across evolutionary and geographic scales. If AM mixotrophy proves to be widespread, we will need to critically reassess our knowledge on carbon uptake by plants, with potential effects for carbon cycling models and conservation.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

One postdoc, two PhD candidates and one technician have been hired in the MIXOTROPH team. Plant material has been sampled in ten plots in temperate forests in Europe, two plots in tropical rain forest, and one plot in tropical grassland. In the temperate forest plots a consistent set of non-related plant species have biochemical signatures that qualifies them as potential AM mixotrophic plants. Based on these results, AM mixotrophy is potentially present in most of the sampled plots. DNA metabarcoding data of ectomycorrhizal fungi, arbuscular mycorrhizal fungi, and Mucoromycotina fine root endophytes has been generated to investigate which species of mycorrhizal fungi they share with surrounding autotrophic plant species. These data will also reveal how understory and overstory plants are linked by common mycorrhizal networks in the selected forests. More fieldwork in tropical forests is being planned. Experiments, in which carbon can be traced from ‘donor’ AM plants to AM mixotrophs are being designed and tested. These experiments are performed in the field, in large mesocosms, and in vitro. So far, the results from these experiments have been inconclusive. Finally, a first comparison of genome data in two families containing mycoheterotrophic, mixotrophic, and autotrophic AM species provides evidence for parallel genomic characteristics in AM mixotrophic plants, which can potentially be used for screening of AM mixotrophy across flowering plants.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Current results indicate that AM mixotrophy is potentially widespread in temperate forests, although restricted to a particular set of understory species. Ongoing work will investigate the potential occurrence of AM mixotrophy in tropical rainforests, and by which common mycorrhizal networks this phenomenon is supported. However, evidence from carbon pulse-trace experiments is essential to couple the observed patterns to AM mixotrophy.