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Canopy structure versus physiology effects on net photosynthesis of mountain grasslands differing in land use.
Wohlfahrt, Georg1, Bahn, Michael1, Newesely, Christian1, Sapinsky, Sigrid1, Tappeiner, Ulrike1,2, Cernusca, Alexander1, 1 2
ABSTRACT- The present paper aims at investigating how changes in canopy structure and species physiology associated with the abandonment of mountain grasslands affect their net photosynthesis. For this purpose a vegetation-atmosphere-transfer (VAT) model, which explicitly takes into account the structural and functional properties of the various canopy components and species, is employed. Three sites differing in land use are investigated, a meadow, a pasture and an abandoned area. Model simulations agree reasonably with measured net photosynthetic rates, the meadow featuring the highest daily CO2 uptake, followed by the pasture and the abandoned area. A detailed process analysis suggests this ranking to be mainly due to bulk canopy physiology, which decreases from the meadow to the pasture and the abandoned area, reflecting species composition and species-specific photosynthetic capacities. Differences between the canopies with regard to canopy structure are found to be of minor importance: The amounts of green, photosynthetically active plant matter are too similar to be a major source of variation in net photosynthesis. Large differences exist between the canopies with regard to the amount of photosynthetically inactive phytoelements, most of them are though accumulated close to the ground, where they exert little influence on canopy net photosynthesis.
KEY WORDS: model, abandonment, dead plant matter, radiation absorption