Bryophyte gas‐exchange dynamics along varying hydration status reveal a significant carbonyl sulphide (COS) sink in the dark and COS source in the light

Abstract

Summary Carbonyl sulphide (COS) is a potential tracer of gross primary productivity (GPP), assuming a unidirectional COS flux into the vegetation that scales with GPP. However, carbonic anhydrase (CA), the enzyme that hydrolyses COS, is expected to be light independent, and thus plants without stomata should continue to take up COS in the dark.We measured net CO 2 (AC) and COS (AS) uptake rates from two astomatous bryophytes at different relative water contents (RWCs), COS concentrations, temperatures and light intensities.We found large AS in the dark, indicating that CA activity continues without photosynthesis. More surprisingly, we found a nonzero COS compensation point in light and dark conditions, indicating a temperature‐driven COS source with a Q 10 (fractional change for a 10°C temperature increase) of 3.7. This resulted in greater AS in the dark than in the light at similar RWC. The processes underlying such COS emissions remain unknown.Our results suggest that ecosystems dominated by bryophytes might be strong atmospheric sinks of COS at night and weaker sinks or even sources of COS during daytime. Biotic COS production in bryophytes could result from symbiotic fungal and bacterial partners that could also be found on vascular plants.

Gross Primary Productivity of Four European Ecosystems Constrained by Joint CO2 and COS Flux Measurements

“…COS, present in the atmosphere at an average mole fraction of 500 ppt, enters the plant leaf through the stomata in a similar way as CO 2 where it is catalyzed to hydrogen sulfide (H 2 S) and CO 2 in a one‐way reaction by the enzyme carbonic anhydrase (CA; Notni et al, ; Protoschill‐Krebs & Kesselmeier, ). In contrast to CO 2 , whose uptake is always accompanied by release through mitochondrial respiration, the uptake of COS is a one‐way flux (but see Gimeno et al, ), opening the opportunity to infer GPP at leaf and canopy scale as (Sandoval‐Soto et al, ): where F COS is the COS flux (pmol m −2 s −1 ) and χ COS (ppt) and χ CO2 (ppm) are the ambient mole fractions of COS and CO 2 , respectively. Equation is mathematically closed by the so‐called leaf relative uptake rate (LRU) as the ratio of fluxes per unit mole fraction for COS and CO 2 , which must be specified a priori or assessed independently.…”

Reviews and Syntheses: Carbonyl Sulfide as a Multi-scale Tracer for Carbon and Water Cycles

“…In these organisms, photosynthetic CO 2 uptake is limited by moisture availability and diel and seasonal variations in light. OCS uptake, on the other hand, continues in the dark even when photosynthesis ceases (Gimeno et al, 2017;Gries et al, 1994;Kuhn et al, 1999;Kuhn and 10 Kesselmeier, 2000).…”

“…The direction of flux is often determined by temperature and moisture conditions. For example, when conditions are hot and dry, abiotic processes in soil or biotic production in bryophytes can sometimes overtake consumption, resulting in an OCS source to the atmosphere (Gimeno et al, 2017;.…”

“…For example, culture-independent studies should attempt to determine whether microbial community structure and/or the abundance and diversity of genes encoding for CA or other enzymes (or their expression) are predictive for OCS consumption. In fact, recent soil surveys adopting these approaches have identified potential links between OCS consumption and the abundance of fungi (Sauze et al, 2017) and β-CA expression by Actinobacteria (Meredith et al, in prep). Culturedependent studies that broaden the collection of microbial isolates assessed for OCS activity are needed 5 to constrain the activities of CA classes and other enzymes for OCS.…”

“…This is because CO 2 and OCS fluxes are not necessarily coupled in lichens and bryophytes, and therefore OCS exchange cannot be modeled following the same approach as for vascular plants. Fortunately, the emission component from these organisms seems to be primarily driven by temperature (Gimeno et al, 2017) and the geographical extent of their contribution 5 is limited to areas where cryptogamic covers constitute a non-negligible biomass fraction or contribute significantly to other ecosystem biogeochemical cycles (Elbert et al, 2012). A first approach toward estimating the contribution of these communities would require compiling sensitivity parameters (to air moisture, temperature, and other variables as in Porada et al, 2014) to predict OCS exchange from climatic drivers for dominant species, functional types, or even whole communities from these regions.…”