Chionochloa rubra leaf litter decomposition at Mt Tongariro, New Zealand

Concept: Decomposition rates are an important component of carbon
sequestration rates in soils, potentially mitigating future climate
change. Here we aim to better understand decomposition’s relationship with
temperature in natural conditions. Structure: In snow-tussock grassland
dominated by Chionochloa rubra var. rubra on Mount Tongariro, Tongariro
National Park, New Zealand, we measured decomposition of Chionochloa leaf
litter along an ~ 700 m altitudinal gradient, as a space-for-temperature
experiment, representing 4.2ºC of warming. For litter, we haphazardly
collected attached, but achlorophyllous leaves, which were cut into 5 cm
long segments and pooled per site. We examined decomposition rates in a
full reciprocal translocation of litter bags between 8 plots as both the
origin of 8 litter types and the 8 destinations of plating out of litter
bags, over 4 years using 6 replicates. Litter decomposition bags, 20 cm x
25 cm in size, were of black nylon rectangular mesh with a pore size of 2
mm. We used 3.00 g of litter per bag, applied a wet/dry weight correction,
and measured litter remaining after each time period. Bag recovery was 91
%. We went on to model decomposition's relationships to environmental
variates. Results: Litter decomposed progressively over time, but at the
same rate along the altitudinal gradient. There was no home-field
advantage. In terms of litter quality, decomposition rates were related
only to litter lignin, or fibre or litter N. Only decomposition at Year 4,
and that only when organised by litter destination, showed a relationship
to mean annual temperature jointly with soil C, and this was only weak and
implausible. When studied across the full reciprocal transplant, there
were no significant interactions between Origin and Destination data with
or without Years. Therefore litter from each plot decomposed at the same
rate as other plots’ litter at all altitudes, allowing for small, often
irregular differences in litter quality and micro-environment.