Fachbereich 13 - Biologie
Institut für Ökologie der Pflanzen
Ökophysiologie von CAM-Pflanzen, Pflanzen des Fynbos und der Namib

Photosynthesis in coastal and mountain Fynbos

Leaf carbon and nutrient status, nitrogen content and photosynthetic CO₂ exchange were investigated in 36 evergreen sclerophyllous species at two typical sites in the coastal and the mountain fynbos (South Africa). The study sites differed in soil nutrient composition and mean vegetation age. The species selected comprise the main fynbos elements (proteoid, ericoid and restioid) and vary in growth and leaf form, including broad mesophyllous to narrow leptophyllous shrubs or mid-height trees and wiry aphyllous hemicryptophytes.Thus, they allow a test of whether plants from functionally and morphologically different groups from these communities are distinguishable in their photosynthetic activity and photosynthetic nitrogen use efficiency. Furthermore, this broad range of species facilitates a re-evaluation of the relationship between photosynthesis and leaf nitrogen content in a range of structural types. Nitrogen and ion content were lower in soils of the coastal than the mountain fynbos. Leaf nitrogen content was low in plants of all groups, however only those of the proteoid and ericoid elements reflect these differences in soil nutrient availability. The comparison with published data of the other mediterranean climate-type ecosystems confirms that the nutrient-poor fynbos systems may at best be similar to the Australian heathlands. Photosynthetic activity was generally higher in proteoid coastal fynbos species than in the majority of the other plants, and they had the highest nitrogen use efficiency of all groups. All groups of both fynbos communities showed the same linear relationship between mean light saturated rates of photosynthesis and leaf nitrogen content, although the overall correlation was weak (r² = 0.28), but stronger for the coastal fynbos proteoids (r² = 0.37). When [N] was expressed on a leaf area basis, the data yielded even poorer relationships (r² = 0.16 and 0.26, respectively). This is consistent with earlier findings that mass-based calculations normally yield better correlations. On the other hand, leaf mass per area, and leaf form and size did not affect the relationship.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Prof. Dr. D.J. von Willert, Dr. W.B. Herppich, M. Herppich

Veröffentlichungen:

Herppich,M., W.B. Herppich, D.J. von Willert: Leaf nitrogen content and photosynthetic activity in relation to soil nutrient availability in coastal and mountain fynbos (South Africa). Basic and Applied Ecology 3, 329-337 (2001)