EAGER: Collaborative Proposal: Linking physiology and morphology in Grassland evolution via a novel analytical technique

Grasslands cover ~40% of Earth’s land surface, playing a key role in terrestrial life, global climate and critical human resources (the grass family includes all cereal crops like rice and wheat). Although they appeared ~70 million years ago, the spread of grasslands began only ~22 million years ago, with tropical savanna ecosystems present by ~8 million years ago.

Grass evolution and ecosystem change likely coincided with evolving climates, landscapes and animals. The best way to identify fossil grasses is from microscopic silica pieces (“phytoliths”), left behind in sedimentary rocks when the rest of the plant has decomposed. Phytoliths have shapes characteristic of particular grass types, but no method exists that can reveal the photosynthesis type (C3 or C4) of the grass that produced them.

This project tests a new method to use phytoliths to measure the chemistry of un-decomposed carbon inside them; thus, the photosynthetic type of the grasses that produced them. This will allow researchers to answer questions about the past and possible future of grasslands. For example, what grasses grew in the earliest savannas and what photosynthesis did they use?

What caused the spread of the C4 grasses, and what will happen as Earth’s atmosphere and climate continue to change?

This cross-disciplinary project will utilize precision sample preparation and in-situ analytical methods to characterize 1. the distribution of disseminated and occluded carbon in phytoliths, and 2. the carbon isotopic ratios of these reservoirs, reflecting photosynthetic pathway. The project will first compare leaf and phytolith chemistry of greenhouse-grown specimens and move on to soils with the ultimate goal of application to fossil systems.

The proposed method, once fully developed, can be executed at many laboratories world-wide and will represent a major leap forward in analytical phytology. This work will have applications to a wide range of topics including the relationships between grassland and hominid evolution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.