Comparative Study of Litter Quality, Decay Rates and Nutrient Fluxes of Invasive Species, Austroeupatorium inulifolium and Cymbopogon nardus

Abstract

Invasion of alien species into new habitats poses serious threats to their vegetation andecosystem processes. Austroeupatorium inulifolium, an invasive species, has been rapidlyinvading degraded grasslands dominated by Cymbopogon nardus, another invasive, in theKnuckles Conservation Area (KCA). Invasive plants with rapid growth rates and elevatedleaf nutrient concentrations could alter decomposition process and nutrient release patterns.This study was aimed at studying the litter quality, decay rates and nutrient release patterns ofAustroeupatorium and Cymbopogon. In situ litterbag experiment was conducted in less andhighly invaded grasslands at KCA. Surface litter and standing litter (above-ground) also havebeen quantified to assess the contribution of C3 and C4 plants to soil nutrient pool.

Litterbags (n=40) were prepared with air-dried litter samples of Austroeupatorium andCymbopogon and were distributed in highly-invaded (HIG) and less invaded (LIG) sites (byAustroeupatorium). Litterbags were collected at different time intervals and chemicallyanalysed. The decomposition rate was calculated using loss of litter biomass. The surfacelitter was estimated using randomly placed quadrates (0.0625 cm2). Standing litter biomasswas quantified by clipping quadrates (0.25 m2) to the ground level. Contributions to abovegroundlitterfall by C3 and C4 plants were assessed. The results were statistically analysedand compared using Minitab 14.0.

Higher mass loss was observed with Austroeupatorium litter than that of Cymbopogon inboth less and highly invaded habitats. Austrosupatorium litter quality (in terms of N and P) ishigher than that of Cymbopogon. Leaf litter of Austroeupatorium showed significantly lowerC:N and C:P ratios compared to Cymbopogon. Nitrogen and phosphorus release patternsduring decomposition found to be slow in both Austroeupatorium and Cymbopogonirrespective of their habitats. Austroeupatorium showed relatively higher decomposition ratethroughout the study period compared to Cymbopogon. The surface litter and standing litterbiomasses were significantly higher in HIG compared to LIG. In both habitats, C3 plantscontributed more to the standing litter biomass than that of C4 plants. Austroeupatoriumplants contributed more to the total C3 biomass in both LIG and HIG.

The present results suggest that due to higher quality and decomposition rates ofAustroeupatorium litter, the invasion may leads to changes in the soil nutrient pools and alsotheir cycling processes. Long-term soil studies need to be carried out in order to investigatethese findings further.