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Plant-soil negative feedback ( NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant-soil NF., The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance ( NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments., Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon ( AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted 13C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species-specific toxicity., Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self- DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant-soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

• 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. [ABSTRACT FROM AUTHOR]