Photosynthetic pigments of co-occurring Northeast Atlantic Laminaria spp. are unaffected by decomposition

Wright, Luka Seamus; Foggo, Andy

doi:10.3354/meps13886

Cited by 3 publications

(1 citation statement)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our data on the effect of decomposition on detrital photosynthesis and phenolic content, albeit somewhat scarce, are supported by several lines of evidence. Warm temperate kelp has a 42-45% lower total photosynthetic pigment concentration than cold temperate kelps (Wright and Foggo, 2021), suggesting it has lower photosynthetic capacity which is in line with the lower 48-50% lower photosynthetic activity reported here. Although Frontier et al (2021a) found no difference in net and gross primary production and photosynthetic efficiency (chlorophyll fluorescence) between in vitro L. hyperborea and L. ochroleuca, a subsequent field experiment by the same authors suggests declining photosynthetic efficiency with detrital age in L. ochroleuca and no change in L. hyperborea (Frontier et al, 2021b).…”

Section: Discussionsupporting

confidence: 88%

Climate‐driven shifts in kelp forest composition reduce carbon sequestration potential

Wright

Pessarrodona

Foggo

2022

Global Change Biology

View full text Add to dashboard Cite

The potential contribution of kelp forests to blue carbon sinks is currently of great interest but interspecific variance has received no attention. In the Northeast Atlantic, kelp forest composition is changing due to climate-driven poleward range shifts of cold temperate Laminaria digitata and L. hyperborea and warm temperate L. ochroleuca. To understand how this might affect the carbon sequestration potential of these ecosystems, we quantified interspecific differences in carbon export and decomposition alongside changes in detrital photophysiology and biochemistry. We found that while warm temperate kelp exports up to 71% more carbon per plant, it decomposes up to 155% faster than its boreal congeners. Elemental stoichiometry and polyphenolic content cannot fully explain faster carbon turnover, which may be attributable to contrasting tissue toughness or unknown biochemical and structural defences. Faster decomposition causes the detrital photosynthetic apparatus of L. ochroleuca to be overwhelmed after 20 d and lose integrity after 36 d, while detritus of cold temperate species maintains carbon assimilation. Depending on the photoenvironment, detrital photosynthesis could further exacerbate interspecific differences in decomposition via a potential positive feedback loop. Via compositional change such as the predicted prevalence of L. ochroleuca, ocean warming will therefore likely reduce the carbon sequestration potential of these temperate marine forests. Keywords biogeography; carbon budget uncertainty; carbon flux; climate change; C:N; decay; degradation; ecophysiology; erosion; photosynthesis Introduction Over the last decade humans have emitted around 11 billion tons of carbon per year (Canadell et al., 2021). In the Paris Agreement, 193 countries pledged to reduce this emission and enhance carbon sink capacity. Ocean-based biological carbon dioxide removal (CDR) is now acknowledged as an integral part of fulfilling this goal (Canadell et al., 2021). Such CDR may be facilitated by marine macrophytes, whose role in carbon sequestration was first recognised four decades ago (Smith, 1981) but has only recently come to mainstream attention as blue carbon (Canadell et al., 2021). Despite the potential involvement of marine vegetated habitats in CDR and their location within national jurisdiction, few ocean-based nationally determined contributions (NDCs) have been put forward by affluent Annex I parties such as the UK, US and Australia (Gallo et al., 2017) which hold some of the highest blue carbon wealth (Bertram et al., 2021). In part, this may be due to the ongoing debate on the blue carbon status of temperate kelp forests that dominate the coasts of these countries (Krause-Jensen et al., 2018). Therefore, identifying the magnitude and fate of carbon assimilated by these marine plants is key to our understanding of their carbon sequestration potential (CSP) and their consequent inclusion in blue carbon frameworks (Krause-Jensen et al., 2018). CSP is a function of carbon export and fate (Duarte and Cebriá...

show abstract

Section: Discussionsupporting

confidence: 88%

Climate‐driven shifts in kelp forest composition reduce carbon sequestration potential

Wright

Pessarrodona

Foggo

2022

Global Change Biology

View full text Add to dashboard Cite

show abstract

Genus-specific response of kelp photosynthetic pigments to decomposition

Wright,

Kregting

2023

Mar Biol

View full text Add to dashboard Cite

Detritus is widely considered to be dead organic matter. However, recent studies have shown that kelp detritus can be functionally equivalent to the attached plant. This is significant, because detritus makes up ~ 42% of all plant biomass. In the Northeast Atlantic, studies on detrital photobiology have been restricted to the genus Laminaria. Here, we present data from a 46 d in situ experiment investigating the effect of decomposition on detrital photosynthetic pigment concentrations and stoichiometry in four Northeast Atlantic kelp species from three genera. We corroborate the lack of a decomposition effect on pigments of cold temperate Laminaria species as identified by previous studies but show that the photophysiology of other kelp genera responds differently. While Saccharina latissima displays an idiosyncratic parabolic response, the annual and thermally plastic kelp Saccorhiza polyschides seems to become less pigmented with increasing detrital age. If S. polyschides becomes increasingly dominant in future parts of a warmer Northeast Atlantic, this may translate to lower detrital photosynthetic potential at the forest scale. However, given our somewhat ambiguous data on this species, this conjecture requires further investigation into detrital photosynthesis.

show abstract

Temperature sensitivity of detrital photosynthesis

Wright,

Simpkins,

Filbee-Dexter

et al. 2023

Annals of Botany

View full text Add to dashboard Cite

Background and Aims Kelp forests are increasingly considered blue carbon habitats for ocean-based biological carbon dioxide removal, but knowledge gaps remain in our understanding of their carbon cycle. Of particular interest is the remineralisation of detritus, which can remain photosynthetically active. Here, we study a widespread, thermotolerant kelp (Ecklonia radiata) to explore detrital photosynthesis as a mechanism underlying temperature and light as two key drivers of remineralisation. Methods We used meta-analysis to constrain the thermal optimum (Topt) of E. radiata. Temperature and light were subsequently controlled over a 119-day ex situ decomposition experiment. Flow-through experimental tanks were kept in darkness at 15 °C or under a subcompensating maximal irradiance of 8 µmol photons m−2 s−1 at 15, 20 or 25 °C. Photosynthesis of laterals (analogues to leaves) was estimated using closed-chamber oxygen evolution in darkness and under a saturating irradiance of 420 µmol photons m−2 s−1. Key Results T opt of E. radiata was 18 °C across performance variables (photosynthesis, growth, abundance, size, mass and fertility), life stages (gametophyte and sporophyte) and populations. Our models predict that a temperature of >15 °C reduces the potential for E. radiata detritus to be photosynthetically viable, hence detrital Topt ≤ 15 °C. Detritus is viable under subcompensating irradiance, where it performs better than in darkness. Comparison of net and gross photosynthesis indicates that elevated temperature primarily decreases detrital photosynthesis, whereas darkness primarily increases detrital respiration compared with optimal experimental conditions, in which detrital photosynthesis can persist for ≥119 days. Conclusions T opt of kelp detritus is ≥3 °C colder than that of the intact plant. Given that E. radiata is one of the most temperature-tolerant kelps, this suggests that photosynthesis is generally more thermosensitive in the detrital phase, which partly explains the enhancing effect of temperature on remineralisation. In contrast to darkness, even subcompensating irradiance maintains detrital viability, elucidating the accelerating effect of depth and its concomitant light reduction on remineralisation to some extent. Detrital photosynthesis is a meaningful mechanism underlying at least two drivers of remineralisation, even below the photoenvironment inhabited by the attached alga.

show abstract

Photosynthetic pigments of co-occurring Northeast Atlantic Laminaria spp. are unaffected by decomposition

Cited by 3 publications

References 22 publications

Climate‐driven shifts in kelp forest composition reduce carbon sequestration potential

Climate‐driven shifts in kelp forest composition reduce carbon sequestration potential

Genus-specific response of kelp photosynthetic pigments to decomposition

Temperature sensitivity of detrital photosynthesis

Contact Info

Product

Resources

About