Allelochemical effects indirect

Principle Chlorophyll fluorescence is a sensitive and early indicator of damage to photosynthesis and to the physiology of the plant resulting from the effect of allelochemicals, which directly or indirectly affects the function of photosystem II (Bolhar-Nordenkemf et ah, 1989, Krause and Weiss 1991). This approach is convenient for a photosynthesis analysis in situ and in vivo and quick detection of otherwise invisible leaf damage. The photosynthetic plant efficiency was measured using the method of induced chlorophyll fluorescence kinetics of photosystem II [Fo, non-variable fluorescence Fm, maximum fluorescence Fv=Fm-Fo, variable fluorescence t /2, half the time required to reach maximum fluorescence from Fo to Fm and photosynthetic efficiency Fv/Fm]. 

Although indirect and probably quite rare, another route has been reported for allelochemical interference with plant-water relationships. Lovett and Duffield (47) identified benzylamine as an allelochemical in the leaf washings from the cruciferous weed Cametina sativa (L.) Crantz. Subsequent work showed benzylamine induced hydrophobic conditions in the soil, and these conditions could reduce water availability for plant growth (48). Thus, indirect action through changes in soil structure could be partially responsible for adverse effects on linseed (Linseed usitatissimm L.) and could enhance more direct allelopathic effects. 

Other cases concerning the direct and indirect effects of allelochemicals such as acetic acid produced during crop residue decomposition are presented in this symposium by J. M. Lynch. The emphasis of this discussion will not be a review of existing literature, but on establishing a conceptual framework for a realistic assessment of the allelopathic phenomena and the role and fate of allelochemicals in the soil. 

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