Phytotoxicity dynamics of decaying plant materials

Abstract

Summary• Allelopathic effects of plant litter have been extensively studied, but less attention has been given to the dynamics of phytotoxicity during the decomposition processes.• Decomposition experiments were carried out on above-and below-ground plant materials of 25 species of different functional groups (nitrogen fixer, forbs, woody and grasses-sedges) in aerobic and anaerobic conditions. The phytotoxicity of aqueous extracts of decomposing material was assessed by bioassay in 30 d of laboratory and 90 d of litterbag decomposition experiments.• Phytotoxicity was widespread with c . 90% of the tested species showing significant phytotoxic releases. Phytotoxicity largely varied between different plant functional groups (nitrogen fixer > forbs = woody >> grasses-sedges) and was higher for leaf compared with root materials. In all species tested during decomposition, phytotoxicity rapidly decreased in aerobic conditions but sharply increased and became stable in anaerobic conditions.• The results demonstrate an unexpectedly widespread occurrence of phytotoxicity with clear dynamic patterns during the decomposition processes of plant materials. The ecological consequences of this might have been underestimated.

Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid‐state 13C NMR spectroscopy

“…Allelopathy is one possible explanation for deleterious effects of plant litter, but a major criticism of this hypothesis is that, despite the widespread presence of inhibitory allelopathic compounds in most plant residues (Rice, 1984), these compounds are rapidly degraded by soil microbial activity into nontoxic molecules (Schmidt & Lipson, 2004;Kaur et al, 2009). However, the inhibitory effects of litter can last from a few days to weeks in laboratory conditions (Xuan et al, 2005;Bonanomi et al, 2006), although early experiments have been criticized because they were often carried out under unrealistic laboratory conditions (e.g. powdered litter, decomposition in water suspension conditions, or litter extracts obtained with organic solvent) that make comparisons with field observations difficult (Inderjit & Callaway, 2003).…”

“…and Quercus ilex L.), and seven deciduous trees (Castanea sativa Mill., Fagus sylvatica L., Fraxinus ornus L., Populus nigra L., Quercus pubescens Willd., Robinia pseudoacacia L. and Salix alba L.). Three of these species are N-fixing (C. emerus, M. sativa and R. pseudoacacia) and are known to have a strong inhibitory effect (Bonanomi et al, 2006). Freshly abscised leaves were collected by placing nets under plants (> 20 randomly selected individuals for each species), dried at 40°C until a constant weight was reached and then stored at room temperature.…”

“…The same study showed that the inhibitory effect consistently changed with decomposition, with inhibition being greatest in the early stages of decomposition and then declining in aerobic conditions. Stimulation of growth may occur in the later stages of decomposition (Bonanomi et al, 2006). Allelopathy is one possible explanation for deleterious effects of plant litter, but a major criticism of this hypothesis is that, despite the widespread presence of inhibitory allelopathic compounds in most plant residues (Rice, 1984), these compounds are rapidly degraded by soil microbial activity into nontoxic molecules (Schmidt & Lipson, 2004;Kaur et al, 2009).…”

“…A recent paper (Bonanomi et al, 2006) demonstrated that the inhibitory effect of plant litter is not limited to a few 'allelopathic' species but is rather widespread across different plant functional groups, with the highest phytotoxicity shown by N fixer species, followed by forbs and woody species, and with limited phytotoxicity shown by grasses and sedges. The same study showed that the inhibitory effect consistently changed with decomposition, with inhibition being greatest in the early stages of decomposition and then declining in aerobic conditions.…”

“…The accumulation of plant litter has an important role in affecting plant community structure. Several studies have demonstrated that dense litter layers can limit the diversity of productive habitats by inhibiting species establishment through a variety of mechanisms, such as shading (Facelli & Pickett, 1991), mechanical impediment (Wedin & Tilman, 1993) and release of allelopathic compounds during litter decomposition (Bonanomi et al, 2006).…”