Variation in Photosynthetic Properties Among Bog Plants

Plant functional types (PFTs) are used to make generalizations in modeling how plants impact ecosystem functioning. In boreal bogs the number of plant species is small, but several PFTs are represented, namely sedges, deciduous and evergreen dwarf-shrubs, as well as hummock, lawn, and hollow Sphagna. Despite the use of PFTs in modeling, the value of PFTs to describe the photosynthetic properties of bog plants has not been systematically studied. We aim to quantify the photosynthetic properties of typical bog plant species and assess how well PFT divisions reflect differences among species. We measured photosynthetic light response and physiological state of photosystem II of 19 species, monthly, over a growing season. Differences were assessed using principal component analysis and mixed models. Photosynthetic properties separated Sphagna into traditional PFTs, of which hollow species had the highest gross photosynthesis. Sphagnum photosynthesis had large seasonal variation, as monthly differences exceeded those among PFTs or species. The photosynthetic properties of vascular plants differed widely among species but did not follow traditional PFTs. Vascular plant seasonal changes were of less importance than interspecific differences. The results justify using PFTs to describe the ability of bog Sphagna to bind carbon, but do not justify the same approach for vascular plants.