Plants, animals, and microbes vary in features such as their physical structure and their chemistry. This kind of variation in important because it influences how organisms interact with each other and how they affect the environment around them. Plants are a good example of this because they vary dramatically in their structure and in the chemistry of their tissues. This is why, for example, humans can eat corn but not oak leaves. Variation in plant quality determines what tissues can be eaten and by whom. All animals and microbes on land either consume plant tissues or consume other organisms that do. Consequently, variation in the quality of plant tissue is central to ecological processes on land. Plant quality can influence two kinds of ecological processes. First, plant chemistry influences the growth and abundance of herbivores and predators. Second, plant chemistry influences the rate at which nutrients such as nitrogen and phosphorus become available in the soil. Therefore, plant chemistry links processes above ground (like herbivory) with processes below ground (like nutrient availability). A critical point here is that these links are dynamic. When herbivores chew leaves, leaf chemistry changes, influencing how nutrients become available in soil. Conversely, soil nutrients influence the chemistry of plants and therefore interactions between herbivores and predators. These are key pathways of feedback that link together ecological processes above and below ground. The proposed work will integrate over 25 years of research on this topic by the PI. By synthesizing and integrating work across many environments (forests, prairie, deserts, agricultural fields), the PI will help to unify studies of ecological processes above and below ground, and examine common features among habitats. A new synthetic framework will be developed for future work that links ecological processes at different scales.
The synthesis will be published in volumes broadly accessible to researchers and students of ecology. Links will be emphasized to issues of societal importance including crop pest management, invasive species management, and conservation biology. New courses will be developed for graduate and undergraduate students and workshops will foster participation by under-represented groups.
Despite its great diversity, all life on Earth shares a common chemistry. Molecules like proteins, DNA, and lipids occur throughout the Earth’s ecosystems, from the tops of mountains, through the depths of soil, to the bottom of our oceans. These molecules provide energy and nutrients for most living organisms, including us; we eat this complex chemistry. At its most basic, life is a mixture of complex chemicals, held in a membrane (the cell wall), designed to keep our chemistry different from that of the non-living world. Where do these "life chemicals" come from? Most organisms, including bacteria and fungi, get the energy and nutrients to make their own chemistry by exploiting plants or the organisms that eat them. "Primary producers" like the trees in our back yards, the broccoli in our gardens, and the tiny planktonic algae that live in our lakes and oceans, have the trick of capturing energy from the sun and nutrients from the environment to make their own chemistry. In turn, the quality of the chemicals made by plants dictates the quality of food that almost most organisms eat. Which poses a fundamental question: how variable is the chemistry made by plants, and how much does that variation matter to the multitude of organisms that rely on it? My work on this project has explored how much variation plants introduce into the chemistry of life on Earth, and the consequences of that variation for the ecology of our planet. In studying this, I wanted to develop a way of looking at the world’s ecosystems that would help us understand the ecology of many different systems at the same time – from large predators and their prey in National Parks like Yellowstone, to the bacteria and fungi that "eat" dead leaves in streams and soils, to the bacteria that consume dead algae as they sink as "marine snow" in our oceans. My work has focused on the fact that some of life’s chemistry is easy to break apart and some is much harder. For example, humans can’t get enough energy to live by eating only wood, because the lignin and cellulose it contains are just too hard for us to break apart; mostly, those molecules just pass right through us. Some bacteria and fungi can use wood for energy, but much more slowly than they could use the sugar produced by sugar cane. Critically, the differences in chemistry made by plants matter greatly to the quality of the food consumed by everything else. This variation in chemistry, when we look across the habitats on Earth, has an impact on many ecological factors, including the number of individuals and the number of species that plant communities can support on the "chemical landscape." Simultaneously, as predators eat their prey, as herbivores eat their plants, and as all of these organisms die, they return this complex chemistry back to our soils, streams, lakes and oceans for decomposition. Chemistry matters here too. The speed of decomposition also depends on the chemistry of life, and varies enormously from hours to millennia. This is profoundly important because decomposition returns the critical elements (nitrogen, phosphorus, carbon, and others) back into the environment to be used once again by plants. This global "recycling project" maintains all life on earth as nutrients are passed from organisms to decomposers, from decomposers to the environment, and then back into plants. My work shows that we can link together all of these processes, and the rates at which they happen, if we understand the chemistry of plants. The molecules produced by plants link the predators at the tops of food chains (sharks, lions, humans) with the recycling of nitrogen and phosphorus in our soils and waters. In turn, that recycling of nutrients determines the chemistry of plants that supports herbivores and predators, including us. Plant chemistry provides a unifying theme from which we can link the activities of the largest and the smallest organisms on earth. What do we gain from this understanding? As we manage our food, fiber and livestock production, we can do this more efficiently if we understand how the chemistry of plants influences life processes. From the sustainable production of cattle to the protection of corn from root pests, our farmers rely on the interactions between plant chemistry and the rest of life. Additionally, as we seek new medicines to ensure our future wellbeing, many are still produced from the complex chemistry of plants. Why? Because the same chemistry that inhibits microbial activity in soil may inhibit microbial activity in our blood. Our "antibiotics" are often just the chemicals made by other organisms to survive their daily struggles. In short, support from NSF has allowed me to develop a general view of how plant chemistry helps us understand the ecology of life, including our own.
