Liana seedling growth in response to fertilisation in a neotropical forest understorey

I tested the hypothesis that lianas grow taller and/or produce more biomass with higher soil nutrient availability despite severe light limitation in the forest understorey. Young seedlings of Callichlamys latifolia (Bignoniaceae), Duliocarpus major, and D. olivaceus (Dilleniaceae) were grown along a light gradient (0.8-2.2% of full sun) in the undisturbed soil of a lowland tropical rain forest on Barro Colorado Island (Panama) for 19 months. An equal number of seedlings was either supplied with NPK fertiliser equivalent to 220 kg N ha(-1) year(-1) or remained without fertilisation. Seedling survival was not significantly different among species and was not affected by either light availability or fertilisation. Biomass and height increased linearly with increasing light availability in seedlings of all species. Under fertilisation, biomass production was 50% higher in D. olivaceus irrespective of light availability, increased in C. latifolia only in relatively bright microsites, and was not affected in D. major across the entire light gradient. Seedling height was generally less affected by fertilisation with only C. latifolia seedlings growing taller in fertilised plots of a relatively high light availability. Biomass allocation changed little across the light gradient in any species. The strong biomass response to fertilisation in D. olivaceus was correlated with an increased biomass allocation to leaves at the expense of stems with only small changes in root mass fraction. The other two species showed no fertilisation effects on biomass allocation. I conclude that extreme light limitation does not preclude growth responses to nutrient addition in tropical lianas, but species differ in this respect.