Photosynthetic responses of New Zealand Sphagnum species

Abstract

Samples of New Zealand Sphagnum moss (S. cristatum and S. australe) were collected from different sites in both the North and South Islands of New Zealand. Optimal conditions for photosynthesis and carbon assimilation for each species were determined from gas exchange and photosystem II (PSII) chlorophyll a fluorescence measurements under a range of photon flux densities (PFD), temperatures and water contents (WC). All samples displayed a typical light saturation response, saturating at 111–266 μmol m‐2 s‐1, which is generally lower than reported for Northern Hemisphere species. Little difference was found in the photosynthetic response to light between the different New Zealand moss species or between samples from different sites. Greater differences were found within S. cristatum samples of different colour. Brown samples of S. cristatum reached light saturated photosynthesis at a higher PFD, and had lower photosynthetic rates, lower quantum efficiencies, and higher light compensation points than green samples. This is attributed to the screening effect of the pigments in the brown moss. Green moss samples of S. cristatum had an optimum WC of 1200–2000% dry weight, whereas the brown samples of the same species had a wider range of optimum WC of 1400–3000% dry weight. Photosynthesis declined rapidly at WC below the optimum and more gradually at higher WC. Optimal temperatures for net photosynthesis were found to be 20–25°C in two species studied from two South Island sites, with similar rates measured in all samples over the temperature range investigated. Although broadly similar to Sphagnum photosynthetic responses reported elsewhere, specific differences were noted and possible reasons for this are discussed.