Above-Belowground Productivity Partitioning

Water availability controls on above-belowground productivity: Herbivory versus plant response

Ecosystems fix carbon from the atmosphere through photosynthesis, which is then allocated to aboveground plant structures, such as leaves and branches, or to belowground structures, such as roots. Our current understanding of the factors that control belowground carbon allocation is significantly weaker than aboveground allocation. Yet, in grasslands the amount of carbon that goes belowground each year is much larger than the amount of carbon allocated aboveground. Our rudimentary understanding of the controls of belowground carbon allocation and the ratio of aboveground to belowground carbon is a significant knowledge gap, as roots are a major input of organic material and nutrients into soil. Predictions of future carbon storage in these ecosystems hinge on our understanding of the effects of environmental variability on allocation of carbon belowground.

This study addresses the questions: How does precipitation affect the above/belowground partitioning of carbon? During drought periods, are above and belowground structures equally affected, or are roots affected less than leaves and branches? Finally, is the effect of precipitation on carbon allocation constant or does it vary from deserts to mesic grasslands? This project uses manipulative experiments installed in New Mexico, Colorado and Kansas to understand the effect of precipitation on the partitioning of carbon above versus belowground and the underlying mechanisms at the continental scale.

This work aims to test three novel hypotheses based on: (1) a plant-response mechanism, suggesting decreased belowground allocation with increasing water availability, and (2) a trophic-cascade mechanism, suggesting the opposite pattern derived from the differential sensitivity of root feeders and their predators to water availability. A final hypothesis (3) suggests that the magnitude of plant responses decreases from arid to mesic grasslands while the magnitude of the trophic-cascade phenomenon increases. The trophic-cascade mechanism may be constrained by the abundance of belowground predators in arid grasslands, which is greater in mesic ecosystems. The experimental design includes complementary field and microcosm experiments located in three different ecosystem types: Chihuahuan Desert Grassland, NM, Shortgrass Steppe, CO, and Tallgrass Prairie, KS. The field experiment includes additions and reductions of precipitation at each site. The microcosm experiment is based on monoliths subjected to 4 soil fauna treatments x 5 water manipulation levels. Soil fauna treatments consist of (1) soil devoid of fauna (just native bacteria and fungi), (2) defaunated soil inoculated with nematode root feeders, (3) defaunated soil inoculated with nematode root feeders and nematode predators, and (4) control. Microcosm tubes will be located in each of the water manipulation plots using individuals of the dominant grass species of each ecosystem type. Key for the implementation of our microcosm is finding a method for defaunating large volume of soil in a way that is effective and efficient. One of our first publications assessed alternative defaunation methods and identified a simple method that meets our criteria (Franco et al. 2017).

Osvaldo Sala
Diana Wall

National Science Foundation, Division of Environmental Biology

June 2015 — May 2018


Franco, A., M. A. Knox, W. Andriuzzi, C. Tomasel, O. E. Sala, and D. H. Wall. 2017. Nematode exclusion and recolonization in experimental soil microcosms. Soil Biology and Biochemistry 108: 78-83. PDF


Osvaldo Sala, The effect of climate change on arid and semi-arid ecosystems, Distinguish ecologist program, Colorado State University, Fort Collins, CO, March 2016

Osvaldo Sala, Climate change in arid lands: prediction, mitigation and communication. Grantham Institute, Imperial College, London, April 2016

Osvaldo Sala, The effect of climate change on ecosystem functioning, University of Puerto Rico, April 2016

Osvaldo Sala, Above-belowground partitioning of primary production as modulated by precipitation amount. Jornada Experimental Range Annual meeting, New Mexico State University, NM, July 2016

Laureano A. Gherardi, and Osvaldo E. Sala,. Effects of contrasting rooting distribution patterns on plant transpiration along a precipitation gradient Annual meeting of the Ecological Society of America, Fort Lauderdale, FL. August 2016

Osvaldo Sala. The Effects of climate change on ecosystem functioning. Purdue University, August 2016

Osvaldo Sala, Effects of Climate Change on Drylands, Institute of Ecology, Xalapa, Mexico. October 2016

André Franco, Matthew Knox, Walter Andriuzzi, Cecilia Tomasel, Diana Wall. Nematode exclusion and recolonization for experimental soil microcosms, Ecological Society of America, Fort Lauderdale, FL. August 2016.

9. Eden Senay, André Franco, Cecilia Tomasel, Diana Wall. An Endoparasitic Nematode Hunts a Suitable Host: Exploring the Dominant Grasses From the Shortgrass and Tallgrass Prairies, Front Range Student Ecology Symposium, Fort Collins, CO. February 2017.