The leaf size-number trade-off in Central Amazonian forest saplings

Link To Share This Poster: https://cdmcd.co/q9YL5w
Live Discussion Link: https://cdmcd.co/QM8kAn

Kiumars Edalati, Jiayu Li, Nathan J. B. Kraft and Marcel Caritá Vaz, Department of Ecology & Evolutionary Biology, University of California, Los Angeles, CA

Background/Question/Methods
In the plant kingdom, various trade-offs prevent any single species from maximizing both resource acquisition and survival when resources become scarce. For instance, shaded plants can maximize light capture by increasing leaf size. Large leaves, however, suffer higher transpiration rates, which may lead to desiccation during unusually dry seasons. Given the significant resource investment represented by leaf production in plants growing in shaded environments, leaf size must trade-off with leaf number. However, our current understanding of the ecological implications of this leaf size-number trade-off is still very limited, especially for tropical forest plants, which are predicted to suffer more intense and frequent droughts due to climate change. This lack of knowledge is due to the high number of plant species and highly heterogeneous environmental factors, especially light intensity.
Here, we ought to test the strength of the leaf size-number trade-off in tropical understory saplings, while also considering sapling size, light intensity, and specific leaf area. We measured the mean leaf size (surface area and dry mass), total leaf number, diameter at breast-height, and crown illumination for 495 saplings. These saplings were sampled from 286 simple-leaved species, found in a 25-hectare plot in a hyperdiverse forest in the Central Amazon, Brazil.
Results/Conclusions
Our Bayesian model fits our data relatively well (R2 =0.68) and shows a strong negative correlation between leaf dry mass and the total number of leaves per sapling (R= -0.96; CI95%=[-0.94;-0.99]). This correlation is even stronger (R= -0.99; CI95%=[-0.99;-1.00]) between average leaf area and the number of leaves per saplings. Variation in leaf number could also be explained by specific leaf area while differences in light intensity had little to no effect. Based on these results, the trade-off between leaf size and number is robust and strong among these tropical saplings. Therefore, plants with smaller leaves tend to have more leaves compared to plants with larger leaves, but those with thinner leaves tend to have less leaves. This resource allocation trade-off allows species' to diverge in their responses to challenges such as thermoregulation, water loss, and resistance to herbivory. Furthermore, we will investigate this trade-off among compound-leafed saplings that have a more sophisticated leafing display, and see where they fit along the leaf size-number trade-off. Understanding these fundamental trade-offs among saplings will prove essential to develop predictive models of species' differential responses to the increasing challenges imposed by global climate change.