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Giregon Olupot - Root contributions to soil organic carbon sequestration on the Northern Tablelands of NSW
Giregon is evaluating the impact of three landuses: 1. Improved pasture, 2. Native pasture and 3. Woodland on: The morphology and demographics of fine roots, profile distribution of fine root biomass, rate of decomposition of the root biomass as influenced by soil quality and root litter quality and fine root activity in relation to inputting carbon to the soil. His research is supported by the University of New England (UNE) Faculty Scholarship, with supplementary funding from PIIC.
Three quarters of terrestrial carbon is stored in the soil as soil organic matter about 50% of which originates from plant roots. Soil carbon budgets are therefore incomplete without a thorough understanding of roots inputs and longevity of this carbon in the soil. It has been postulated that the depth to which roots descend and decay, ultimately determine the fate of root carbon. In addition, root-derived carbon stays longer in the soil than carbon originating from the shoots. This has been attributed to a number of factors. First, roots are more lignified and suberised that shoots and therefore, have lower decomposition rates than shoots. Secondly, roots undergo “seasoning” in the soil right from the time they are formed, which makes them less degradable than shoot biomass. Thirdly, roots continuously release carbon-rich compounds into the soil that help boost microbial activity.
As these microbes break down the organic materials in the soil, they form polysaccharide gels and exo-polymers that help “glue” and stabilise soil aggregates. Stable aggregates are more likely to protect and store carbon for longer periods than fragile aggregates. Last and most importantly, it has been shown that roots may actually initiate the formation and stabilisation of soil aggregates into which carbon gets nucleated for long-term sequestration.
Giregon is extracting intact soil cores to a depth of one metre to extract roots for determination of morphological properties (length and diameter), biomass and the rate of decomposition. He has already collected data from one out of four sites within the Northern Tablelands of NSW and is progressing into the fourth out of six sampling intervals for a controlled field experiment in which he is disaggregating species-induced differences in rooting characteristics and decay rates for three selected grasses native to NSW. Fine root samples have been stained and Giregon will process the stained images of roots for morphological properties as soon as WinRHIZO (the software to use is operationalised).
Giregon has already synthesized the preliminary results from the work accomplished into conference papers. From the field survey of the impact of landuse on profile distribution of fine root biomass, he has shown that improved pastures produce the highest fine root biomass but about 80% of this biomass is in the top 30 cm of soil. The rate if decomposition of this biomass should shed more light on its potential for loss into the atmosphere. From the field experiment, there are significant differences among the species in terms of fine root biomass production. The interaction between species and soil depth as well as the level of shading are all significant, with all species yielding significantly higher fine root biomass in the open sun than under shade, regardless of whether a species is sun-loving or shade-loving.
Giregon hypothesises that wide-ranging environmental stresses common on the Northern Tablelands of NSW have conditioned native landuses to place relatively higher fine root biomass in deep soil horizons than improved landuses. Native landuses are, therefore, more effective in sequestering soil carbon than improved landuses. He hopes that his study will generate information that may help inform future changes to the existing landuses in NSW, with a view to improving productivity of the landuses, while ensuring better sequestration of carbon.