BIOLOGICAL WEIGHTING FUNCTIONS FOR UV INHIBITION OF PHOTOSYNTHESIS IN THE KELP LAMINARIA HYPERBOREA (PHAEOPHYCEAE)¹

Abstract

Different wavelengths of sunlight either drive or inhibit macroalgal production. Ultraviolet radiation (UVR) effectively disrupts photosynthesis, but since UVR is rapidly absorbed in coastal waters, macroalgal photoinhibition and tolerance to UVR depend on the depth of attachment and acclimation state of the individual. The inhibition response to UVR is quantified with a biological weighting function (BWF), a spectrum of empirically derived weights that link irradiance at a specific wavelength to overall biological effect. We determined BWFs for shallow (0 m, mean low water [MLW]) and deep (10 m) Laminaria hyperborea (Gunnerus) Foslie collected off the island of Finnøy, Norway. For each replicate sporophyte, we concurrently measured both O2 evolution and (13) C uptake in 48 different light treatments, which varied in UV spectral composition and irradiance. The relative shape of the kelp BWF was most similar to that of a land plant, and the absolute spectral weightings and sensitivity were typically less than phytoplankton, particularly in the ultraviolet radiation A (UVA) region. Differences in BWFs between O2 and (13) C photosynthesis and between shallow (high light) and deep (low light) kelp were also most significant in the UVA. Because of its greater contribution to total incident irradiance, UVA was more important to daily loss of production in kelp than ultraviolet radiation B (UVB). Photosynthetic quotient (PQ) also decreased with increased UVR stress, and the magnitude of PQ decline was greater in deepwater kelp. Significantly, BWFs assist in the comparison of biological responses to experimental light sources versus in situ sunlight and are critical to quantifying kelp production in a changing irradiance environment.

Forecasted Co2 Modifies the Influence of Light in Shaping Subtidal Habitat1

“…In particular, UVB radiation can inhibit the photosynthesis in some macroalgae (van de Poll et al. 2001, Miller et al. 2009) and can have strong structuring effects in benthic communities (Bischof et al.…”

“…However, in many cases, it is not only the intensity of visible light but also UVR that structures communities (Bischof et al 1998b, Santas et al 1998. In particular, UVB radiation can inhibit the photosynthesis in some macroalgae (van de Poll et al 2001, Miller et al 2009) and can have strong structuring effects in benthic communities (Bischof et al 1998b, Molis et al 2003. However, how these habitats will continue to be structured by light under future climate change scenarios is relatively unknown, and current ecological knowledge may need to be integrated with knowledge of forecasted environmental conditions.…”

Sporogenesis Under Ultraviolet Radiation in Laminaria Digitata (Phaeophyceae) Reveals Protection of Photosensitive Meiospores Within Soral Tissue: Physiological and Anatomical Evidence1

“…The impact of UVR has been investigated in all life-history stages of kelps, from meiospores, gametophytes, and juvenile and adult sporophytes (Dring et al 1996, Roleda et al 2007a, Miller et al 2009). However, the effect of UVR on sporogenesis itself and the vitality and viability of spores released from sorus developed under different radiation (presence and absence of UVR) conditions has not been subjected to detailed investigation.…”

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

“…This calculation assumes a photosynthetic quotient (PQ) and respiratory quotient of 1. Although PQ changes with depth (Miller & Dunton, 2007) and light exposure (Miller et al, 2009) in L. hyperborea and varies interspecifically in brown algae (Thomas & Wiencke, 1991), an extensive literature search and correspondence with various European phycologists revealed no usable PQs for our interspecific comparison.…”