In this study, we tested the hypothesis that functional traits associated with nutrient impoverishment contribute to enhancing shade-tolerance (survival at low light) for the juveniles of canopy tree species in Bornean rain forests. To test the hypothesis, survival and functional traits (biomass allocation, leaf dynamics and foliar nutrient concentration) were investigated as a function of light conditions for saplings of 13 species in three forests with different levels of nutrient availability. As predicted by the hypothesis, the species in the severely nutrient-poor site (a tropical heath forest on nutrient-poor soils) showed greater shade-tolerance (>91% survival for 8 mo at 5% global site factor) than in the other two sites (mixed dipterocarp forests) (54–87% survival). Across the species, greater shade-tolerance was associated with a higher biomass allocation to roots, a slower leaf production and a higher foliar C concentration, which are considered as C-conservation traits under nutrient impoverishment. These results suggest that the juveniles of the canopy species occurring on nutrient-poor soils can enhance shade-tolerance by the same mechanisms as the adaptation to nutrient impoverishments. Tree species in nutrient-poor environments may be selected for surviving also in shaded conditions.

This study investigated the effects of light and soil fertility, on arbuscular mycorrhizal fungi (AMF) colonization, and the growth responses (height and dry mass) of Syzygium seedlings. Seedlings of four Syzygium spp. were grown for 2 y in six different light treatments at the research station of the Sinharaja Forest, Sri Lanka. The light treatments exposed seedlings to: (1) 3%; (2) 16%; (3) 50%; (4) 100% of full sun (control); (5) short periods (2 h d−1) of direct sunlight; and (6) long periods (6 h d−1) of direct sunlight. In the 16% of full sun treatment five sets of fertilizer applications supplied: (1) magnesium; (2) potassium; (3) phosphorus; (4) all three nutrients combined; and (5) no fertilizer (control). The Syzygium species had the greatest mycorrhizal colonization in brighter treatments that provided direct light. Comparison across species revealed S. firmum to have moderate mycorrhizal colonization but high total dry mass. Syzygium operculatum had high percentages of mycorrhizal colonization while S. rubicundum had low percentages of mycorrhizal colonization especially in deep shade. Syzygium makul showed moderate levels of mycorrhizal colonization and dry mass, but low height growth. Among fertilizer applications, phosphorus enhanced seedling growth and mycorrhizal colonization for all species. However, species showed decreased growth with high amounts of potassium and combined fertilizer applications. Results suggest that AMF colonization will be highest, and Syzygium spp. growth greatest, beneath canopy openings large enough to receive direct sun in phosphorus-rich soils.