ENVIRONMENTAL IMPACTS ON THE PRODUCTION OF SILICA PHYTOLITHS IN GRASSES- POTENTIAL IMPLICATIONS FOR GLOBAL SILICA CYCLING

The deposition of silica in the form of phytoliths is widespread in land plants. Levels of deposition are controlled by a combination of genetic and environmental factors, and vary substantial between and within taxa. Through the uptake and deposition of silica, terrestrial plants, particularly those that accumulate large amounts of phytoliths, play an important role in the global silicon cycle. Furthermore, biogenic silica plays an important role in many biological processes such as herbivore defense. It is thus important to develop a better understanding of sources of variation in silica deposition. The grass family (Poaceae) is of particular interest due to the high levels of silica accumulation within the family, the large extent of grass dominated habitats, and the economic importance of many grasses. Changes to environmental factors caused by climate change or other human activity may affect levels of silica uptake, which could have a substantial impact on silica cycling, particularly in areas with abundant grass cover. To explore this possibility, the effects of water stress and elevated temperature on silica uptake were evaluated in 57 grass species.

Leaf material was collected from grasses grown in growth chambers at the University of Sheffield, and subjected to elemental analysis at the University of York. The silicon concentration of individuals grown under a standard set of conditions was then compared to individuals grown under elevated temperatures or reduced watering. Preliminary results suggest that on average, raised temperatures led to a moderate decrease in silica accumulation, while increased water stress led to a moderate increase in silica accumulation. There was, however, substantial variation between species in the magnitude and direction of the effects of both temperature and water stress. This variation does not appear to be explained by the photosynthetic pathway, habitat preference, or phylogenetic history of species. Future work will focus on developing a better understanding of the sources of this variation, particularly the role of intraspecific variation in silica levels. Ultimately, a better understanding of how environmental conditions affect grass silica regimes will contribute to a better understanding of the effects that global climate change will have on silica cycling.