Environmental controls on photosynthetic rates of lower montane cloud forest vegetation in south-western Colombia

Abstract

A variety of microclimatic and edaphic factors have been shown to limit photosynthetic productivity in tropical montane cloud forest (TMCF) ecosystems. It is now understood that multiple controls may limit photosynthesis within individual TMCFs, and that the relative importance of each control varies between sites. This chapter describes the nutrient status, microclimate, leaf structural traits and photosynthetic gasexchange characteristics of lower montane cloud forest (LMCF) vegetation at the Centro de Estudios Ambientales Tambito site, a wet LMCF reserve located on the Pacific slopes of Colombia’s Western Cordillera. Neither periodic water shortage nor prolonged waterlogging was observed at Tambito. Total soil nitrogen and available phosphorus were above the range typically observed in lowland evergreen rain forests (LERF), while exchangeable calcium levels were lower. In terms of soil nutrient status, total nitrogen and available phosphorus at Tambito were above the range typically observed in more productive LERF, while exchangeable calcium levels were lower. Leaf nutrient contents observed at Tambito were broadly similar to values observed in LERF. Photosynthetic photon flux density (PPFD) remained well below the light-saturation level for leaf-scale photosynthesis (A) throughout the day during the wet season and for 21 hours day � 1 during the dry season. Cloudiness may reduce the competitive advantage of high Amax in canopy leaves, thereby increasing the fitness of alternative traits conferred by low specific leaf area, including nutrient-use efficiency and leaf longevity. Therefore, it was concluded that persistent PPFD limitation of photosynthesis may help to explain the prevalence of sclerophylly in tropical montane cloud forests.