Relative contribution of UV radiation to litter breakdown in Australian
grasslands
Abstract
1. Grassy ecosystems cover ~40% of the global land
surface and are an integral component of the global carbon cycle. Grass
litter decomposes via a combination of ultraviolet radiation degradation
(which returns carbon to the atmosphere rapidly) and biological
decomposition (a slower carbon pathway). As such, decomposition and
carbon storage in grasslands may vary with climate and exposure to solar
radiation. We investigated rates of grass litter decomposition in
Australian temperate grasslands along a climate gradient to uncouple the
relative importance of UV radiation and climate on decomposition. 2.
Litterbags containing two common native grass species were deployed at
six grassland sites across a precipitation gradient (380-890 mm) in
south-eastern Australia. Bags were retrieved over 39 weeks to measure
mass loss from decomposition. We used shade treatments to partition UV
degradation from biological decomposition. 3. The shade treatment
consistently reduced the rate of decomposition relative to full-sun
treatments at all sites; there was no significant difference in the
effect size of the shade treatment among sites. The rate of
decomposition was positively correlated with rainfall midway through the
experiment, but there were no significant differences in total
decomposition among sites after 39 weeks. In general, the shape of
decomposition curves was more linear than has typically been observed in
global decomposition studies. 4. Synthesis: We found that UV exposure
was a strong contributor to litter decomposition in temperate Australian
grasslands. This effect was not influenced by climatic variables and may
be related to a period of photopriming prior to further biotic
decomposition. This study highlights the importance of litter
composition and UV exposure in our understanding of how decomposition
patterns contribute to global carbon cycling.