SUMMARY More than 400 species of vascular plants, in 87 genera, are acholophyllous and heterotrophic, but not directly parasitic upon autotrophs. They are usually, but incorrectly, described as 'saprophytes’since they are in fact nourished by means of specialized mycorrhizal associations. Although distributed world‐wide, they are most abundant and show the greatest species‐richness in the Neotropics and Palaeotropical regions. Their aerial parts range in size from a few centimetres to extensive liane types up to 40 m long. With few exceptions, their habitats are dense moist forests in which there is a surface accumulation of leaf litter, often in situations which are too shaded for autotrophic growth. Although the achlorophyllous mycorrhizal mode of life has evolved independently many times and in widely disparate taxonomic groups, such plants show strong convergent evolution in particular adaptations to their peculiar mode of life. Most prominant amongst these are reductions in the size of seed and embryo, and the lack of differentiation of the embryo at maturity. The number of seeds produced by each flower is typically very large and the shape, structure and surface features of seeds involving adaptation for wind dispersal show remarkable parallels in many species. Specific adaptations for zoochory are rare but well developed in a small number of genera, some of which produce scents like fungal fruit bodies or floral parts which mimic fungal sporocarps. Vegetative parts are often even more conspicuously reduced. Most myco‐heterotrophs are entirely subterranean for most of their lives and these stages exhibit adaptations consistent with a change in function from organs of absorption to organs of storage, shown by the almost universal loss of root hairs, decrease in surface area as exhibited in short cylindric‘vermiform’and tuberous roots or, in extreme cases, the complete suppression of roots and the formation of a swollen tuber or rhizome. Increased width of the root cortex often accommodates mycorrhizal infection and stores of carbohydrates and other materials obtained from the fungal symbiont. Mycorrhizal infection is confined to the below‐ground parts of the plants but may be found there in modified stems as well as in roots. In many genera, stems are exceptionally slender and thread‐like and their vascular tissues are either reduced to a single narrow cylinder of bicollateral bundles or, minimally, to four or six narrow bundles in the cortex. Secondary thickening is poorly developed in all but a tiny minority of species, lignification being confined to annular or, rarely, a few scalariform xylem vessels. Phloem is present in very small amounts and then mainly as parenchyma with sieve tubes frequently recorded as narrow and possibly with abherent sieve plates. Leaves are typically reduced to widely spaced achlorophyllous scales on the inflorescence axis. Occasionally, they are present only on underground rhizomes or tubers. The vascular supply to the leaf‐scales, normally reduced to a single trace, may be ab...

The magnitude of future climate change could be moderated by immediately reducing the amount of CO entering the atmosphere as a result of energy generation and by adopting strategies that actively remove CO from it. Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure. Managed croplands worldwide are already equipped for frequent rock dust additions to soils, making rapid adoption at scale feasible, and the potential benefits could generate financial incentives for widespread adoption in the agricultural sector. However, there are still obstacles to be surmounted. Audited field-scale assessments of the efficacy of CO capture are urgently required together with detailed environmental monitoring. A cost-effective way to meet the rock requirements for CO removal must be found, possibly involving the recycling of silicate waste materials. Finally, issues of public perception, trust and acceptance must also be addressed.

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Most land plants form mutualistic associations with arbuscular mycorrhizal fungi of the Glomeromycota, but recent studies have found that ancient plant lineages form mutualisms with Mucoromycotina fungi. Simultaneous associations with both fungal lineages have now been found in some plants, necessitating studies to understand the functional and evolutionary significance of these tripartite associations for the first time. We investigate the physiology and cytology of dual fungal symbioses in the early-diverging liverworts Allisonia and Neohodgsonia at modern and Palaeozoic-like elevated atmospheric CO2 concentrations under which they are thought to have evolved. We found enhanced carbon cost to liverworts with simultaneous Mucoromycotina and Glomeromycota associations, greater nutrient gain compared with those symbiotic with only one fungal group in previous experiments and contrasting responses to atmospheric CO2 among liverwort–fungal symbioses. In liverwort–Mucoromycotina symbioses, there is increased P-for-C and N-for-C exchange efficiency at 440 p.p.m. compared with 1500 p.p.m. CO2. In liverwort–Glomeromycota symbioses, P-for-C exchange is lower at ambient CO2 compared with elevated CO2. No characteristic cytologies of dual symbiosis were identified. We provide evidence of a distinct physiological niche for plant symbioses with Mucoromycotina fungi, giving novel insight into why dual symbioses with Mucoromycotina and Glomeromycota fungi persist to the present day.

Land-based enhanced rock weathering (ERW) is a biogeochemical carbon dioxide removal (CDR) strategy aiming to accelerate natural geological processes of carbon sequestration through application of crushed silicate rocks, such as basalt, to croplands and forested landscapes. However, the efficacy of the approach when undertaken with basalt, and its potential co-benefits for agriculture, require experimental and field evaluation. Here we report that amending a UK clay-loam agricultural soil with a high loading (10 kg/m 2 ) of relatively coarse-grained crushed basalt significantly increased the yield (21 ± 9.4%, SE) of the important C 4 cereal Sorghum bicolor under controlled environmental conditions, without accumulation of potentially toxic trace elements in the seeds. Yield increases resulted from the basalt treatment after 120 days without P-and K-fertilizer addition. Shoot silicon concentrations also increased significantly (26 ± 5.4%, SE), with potential benefits for crop resistance to biotic and abiotic stress.Elemental budgets indicate substantial release of base cations important for inorganic carbon removal and their accumulation mainly in the soil exchangeable pools.Geochemical reactive transport modelling, constrained by elemental budgets, indicated CO 2 sequestration rates of 2-4 t CO 2 /ha, 1-5 years after a single application of basaltic rock dust, including via newly formed soil carbonate minerals whose longterm fate requires assessment through field trials. This represents an approximately fourfold increase in carbon capture compared to control plant-soil systems without basalt. Our results build support for ERW deployment as a CDR technique compatible with spreading basalt powder on acidic loamy soils common across millions of hectares of western European and North American agriculture. K E Y W O R D Scarbon removal, crop productivity, mineral weathering, negative emissions technology, reactive transport modelling, silicon, soil acidification KELLAND Et AL. | 3659