Is phytotoxicity of Phragmites australis residue influenced by decomposition condition, time and density?

Abstract

Phragmites australis is an invasive wetland plant and allelopathy appears to contribute to its invasiveness. We studied dynamics of physicochemical characteristics and phytotoxicity through residue decomposition of Phragmites with and without soil under different conditions and density over time. Physicochemical variables (water-soluble phenolics, dissolved organic carbon, specific ultraviolet absorbance, pH, electrical conductivity, osmotic potential and some anions, namely PO43–, Cl–, NO2–, NO3– and SO42–) of extracts were more consistent and showed normal range in aerobic rather than anaerobic conditions. ‘Residue alone’ and ‘residue with soil’ extracts exhibited significant inhibition on germination and growth of Poa labillardierei and Lactuca sativa initially but reduced over time in aerobic conditions whereas the inhibition increased sharply and remained almost stable in anaerobic conditions (P ≤ 0.001). Regression analyses showed that water-soluble phenolics were a significant predictor of the inhibitory effects on germination and growth of tested species compared with other variables in the extracts. Long-term decomposed residues exhibited significant effects on germination and growth of Melaleuca ericifolia (P ≤ 0.01) depending on residue density in soil. The results demonstrated that decomposition condition and soil incorporation coupled with residue density may play a crucial role over time in dynamics of physicochemical variables and associated phytotoxicity. The study contributes to understanding of the ecological consequences of phytotoxins in residue decomposition, partially explaining the invasion process of Phragmites in wetlands and thereby improving wetland management.