Photosynthetic characteristics in relation to leaf traits in eight co-existing pioneer tree species in Central Sulawesi, Indonesia

Abstract

Tropical pioneer tree species are considered as a functional group characterized by a suite of ecological characteristics such as high light demand and high photosynthetic capacities. This study compared the photosynthetic characteristics of eight co-existing pioneer tree species in 3–4-y-old and about 6-m-tall secondary forest stands in Sulawesi, Indonesia. Its objectives were (1) to determine the range and interspecific variation in six photosynthetic parameters, and (2) to identify morphological and chemical leaf traits that can predict light-saturated net photosynthetic rates (on a leaf area or leaf mass basis, A_max-area or A_max-mass). Species averages of A_max-area in sun leaves ranged between 14.2 and 20.3 μmol m⁻² s⁻¹ (mean 17.5) which is high compared with literature data. Among the co-existing species, average leaf size (56–896 cm²) differed by a factor of 16, specific leaf area (SLA, 10.7–21.4 m² kg⁻¹) and leaf nitrogen content (19.6–33.9 g kg⁻¹) twofold. At the species level, A_max-area was not correlated with leaf N content but decreased significantly with leaf size. A_max-mass showed a higher interspecific variation than A_max-area, and was positively correlated with SLA and leaf N content (slope: 13.4 nmol CO₂ g N⁻¹ s⁻¹). Both, A_max-area and A_max-mass were more closely related to leaf morphological attributes than to leaf N. We conclude that the tropical pioneer tree species studied do not form a homogeneous functional group in terms of photosynthetic performance. Rather, a considerable variation in leaf morphology and nitrogen content exists, which also shows up in a substantial variation in A_max-mass and, to a lesser extent, in A_max-area.