Decomposition of plant residues at low temperatures separates turnover of nitrogen and energy rich tissue components in time
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Carbon and nitrogen loss patterns from stems and leaves from Elephant grass (Miscanthus × ogiformis Honda cv. Giganteus), and five commonly used cover crop species: Hairy vetch (Vicia villosa Roth), Italian ryegrass (Lolium multiflorum L.), Crimson clover (Trifolium incarnatum L.), Rye (Secale cereale L.), and Radish (Raphanus sativus L.) were examined at 3 and 9 °C. The stratified incubation system allowed `dry' recovery of the decomposing plant residues with minimal soil contamination and without loss of soluble substances. The recovered materials were characterized biochemically and by light and scanning electron microscopy. When the data was analysed across all treatments and sampling dates, there was no significant effect of temperature on N loss, whereas C loss was significantly affected (P<0.0001) by temperature. Decomposition at 3 °C led to wider C-to-N ratios in the plant residues. At 3 °C there was no net immobilization of N, whereas at 9 °C net immobilization was strong in the L. multiflorum and M. × ogiformis treatments. The biochemical and microscopic evidence supports that microbial growth and macro-polymer utilization was reduced at 3 °C. It was apparent that the dicot materials leaked substantially more carbon during the early phase of decomposition, whereas in the monocot materials and especially in the M. × ogiformis treatment the microbial growth and substrate utilization must have been contained within the decomposing tissues. Based on this evidence, we propose that the decomposition of intracellular low molecular substances and proteins can be viewed as a process separate from the decomposition of macro-polymers in cell walls. At higher temperatures these processes coincide and thus the distinctiveness is blurred, whereas at low temperatures they may occur more separated in time as well as space due to leaking.
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