Short-term effect of deep shade and enhanced nitrogen supply on Sphagnum capillifolium morphophysiology

Abstract

Sphagnum capillifolium mesocosms collected from an ombrotrophic blanket bog were subjected to controlled photon flux densities (control and shaded) and nitrogen (low and high) treatments between November 2003 and August 2004. Shading significantly reduced biomass of S. capillifolium (P \ 0.001), whilst nitrogen (N) supply significantly increased biomass (P \ 0.05) suggesting that S. capillifolium was limited by N. There was no significant interaction between shading and N on biomass. S. capillifolium responded to shading via morphophysiological and biochemical alterations to the photosynthetic tissues such as (1) break down of anthocyanins involved in photoprotection of chloroplasts, (2) translocation of N from mineralized N or old tissues and (3) allocation of translocated N to photosynthetic pigments. The results suggest that S. capillifolium can tolerate both low and high light intensities, as well as high N supply via morphophysiological responses but does not acclimate to deep shade, since biomass was reduced. Anthocyanins rather than carotenoids appear to play an essential role in photoprotection with translocation serving as the important source of N. It has been suggested that global change in temperature and N availability may lead to increased vascular plant growth that could increase shade leading to a shift from Sphagnum spp. to vascular species in peatlands. However, the species S. capillifolium appears to tolerate deep shade and high N deposition due to the mechanisms shown here suggesting that this species may continue to persist in peatland ecosystems.

Anatomical Effects of Temperature and UV-A + UV-B Treatments and Temperature-UV Interactions in the Peatmoss Sphagnum compactum

“…PAR was provided by cool white fluorescent lamps and was maintained at 300 mmol photons m 22 s 21 with a Quantum Scalar Laboratory radiometer QSL-100 with cosine-corrected detector (Biospherical Instruments, San Diego, CA) placed beneath a culture dish lid. This PAR level is consistent with saturation irradiances typical of bryophytes in general and peatmosses in particular (Williams and Flanagan 1998), as well as PAR levels used in recent greenhouse experiments on Sphagnum ecophysiology (Bonnett et al 2010). The ratios of PAR to (UV-A 1 UV-B) (Rozema et al 1997;Aphalo et al 2012) that we employed were ∼50 (for the higher UV level) and ∼130 (for the lower UV level), assuming a central wavelength of 550 nm .…”

“…Several species (e.g., Sphagnum capillifolium, Sphagnum magellanicum) are red colored in full sun but green or less red in shade, and sphagnorubin levels can increase late in the growing season (Rydin and Jeglum 2006). These observations suggest that sphagnorubin might function primarily to protect chloroplasts against photooxidative damage (though might also indirectly increase UV tolerance by neutralizing free radicals; Bonnett et al 2010). Sphagnum balticum responds to enhanced UV-B by increasing carotenoid pigments, which might have a screening function (Niemi et al 2002) but also likely reduce photoinhibition (Rice et al 2008).…”

“…Impacts on growth of Sphagnum magellanicum were observed in field analyses of peatlands of Argentinian Tierra del Fuego that are impacted by the southern ozone hole (Searles et al 1999;Robson et al 2003Robson et al , 2004. Lacking complex structure, a protective epidermis, and thick cuticle, bryophytes might be more vulnerable to UV damage than other plants (Bonnett et al 2010). These observations suggest that UV exposure or temperature-UV interactions might influence peatmoss anatomy at the microscopic level, issues that have not been well explored.…”

Symbiosis revisited: phosphorus and acid buffering stimulate N<sub>2</sub> fixation but not <i>Sphagnum</i> growth

“…The light level was chosen to mimic realistic field conditions where Phragmites australis and sedges in these fens create low but not limiting light levels for Sphagnum spp. (Bonnett et al, 2010;Kotowski and Diggelen, 2004).…”

Direction of illumination controls gametophyte orientation in seedless plants and related algae

“…To facilitate careful evaluation of results, investigations of the 5 selected taxa were conducted serially, with care taken to ensure that temperature and irradiance levels were the same during each experiment conducted with near-saturating levels of photosynthetically active radiation (PAR). [40][41][42][43][44] Experimental design Consistent with an initial hypothesis that light direction is not more important than gravity in controlling gametophyte orientation, under all experimental direction of illumination treatments, new growth of axial Sphagnum generated during the treatment period would be expected to orient toward the top of the overlying air-filled space, as in nature. Under the same hypothesis, under all experimental direction of illumination treatments, new growth of dorsiventral liverwort and fern gametophytes occurring during the treatment period would be expected to occur as in nature, with rhizoids extending into the underlying agar substratum.…”