Plant strategies, biogeochemical feedbacks, and ecosystem function in Amazonian white-sand forests

Abstract

Ecosystem properties, such as productivity and biodiversity, can emerge from external, environmental variables such as climate and soil, but may also be a product of a dynamic feedback between the traits of the biological community and its resource environment. Amazonian white-sand forests are a model system to test these ideas. Scattered throughout the towering forests of the Amazon basin, white-sand forests are curious “habitat islands” that harbor a unique suite of short-stature trees with markedly different biological properties from that of the surrounding terra firme forest. In this dissertation, I explore the ecological mechanisms underlying this dramatic ecological discontinuity in the Amazon basin. My analyses in Chapter 1 reveal that the transition between white-sand and terra firme forests is closely associated with the ability of the forests to recycle nutrients, particularly nitrogen. In Chapter 2, I find that the hydrologic export of dissolved organic nitrogen may be the pivotal mechanism maintaining the chronic nitrogen-poor state of white-sand forests and that these losses may be exacerbated by plant traits related to herbivory defense. Then, I explore how belowground competition for nutrients shapes white-sand ecosystems (Chapter 3). Finally, I experimentally evaluate the hypothesis that soil nutrients can act as a barrier to terra firme tree species' ability to invade and persist within the white-sand plant community (Chapter 4). Taken together, my dissertation underscores the critical role of soil nutrient availability and plant functional strategies in shaping dramatic shifts in biodiversity, productivity, and carbon storage in the Amazon basin.