In order to elucidate the allelopathic effect of leaf litter leachates under laboratory conditions, a modified 'sandwich method', which places leaves between two layers of agar, was used. Fifty mg of leaves was used per 10 cm 2 cell. Agar concentrations at 0.5-1.0% were the best for gel support in determining radicle and hypocotyl elongation of lettuce. The optimum incubation time for bioassay was three days after imbibition onset. Among 20 typical tree species in Asia, Cymbopogon citratus and Derris scandens showed the strongest inhibitory activity determined by the sandwich method, followed by Piper betle, Tamarindus indica, and Gliricidia sepium. This bioassay seems to be a reliable method for screening allelopathic activity from leaf litter leachates.Keywords: allelopathy, leaf litter leachate, sandwich method.identify allelochemiclas in situ. However, the elucidation of allelochemicals and their involvement in the allelopathy phenomenon are difficult because of the lack of route-specific bioassay methodologies. From this viewpoint, we were developing several bioassay and assessment methods in order to explore route-specific identification of allelochemicals under laboratory conditions. Previously we reported on the assessment procedure referred to as the 'plant-box method' to evaluate allelopathy through root exudates (Fujii 1992). In this article, the laboratory-based assessment method for allelopathy through fallen leaves from trees, crops and weeds is reported. Leaf litter leachates play an important role in natural conditions, and in practical farming systems such as mulching by leaf litter. Mulching with straw is a common traditional farming system in the Japanese 'Shiki-wara'. The aim of this work was to evaluate the allelopathic activity from leaf litter leachates, which was placed between two layers of agar, using the sandwich method. MATERIALS AND METHODS Selection of gel-supportTo select a suitable gelling material, we tested several compounds such as agar, kaolinite, silica gel, gelatin and

Velvetbean(Mucuna pruriens (L.) DC. var. utilis oi Stizolobium deeringianum Piper et Tracy, synonymbut now not recommended)1>2) is a tropical legume, cultivated as green manureor as a cover crop. Velvetbean leaves are used as fodder, the seeds as food, and the seeds and stems as medicine in Africa and China.3) The yield of seeds reaches 1.5-2t/ha, and offresh leaves and stems comestc 20-30t/ha, this crop being one of the most productive ir the world.Mucuna pruriens has been reported to increase the graminaceous crop yield in mixed culture, but to smother notorious weeds such as nutsedge (Cyperus spp.) and alang-alang (Imperata cylindrica).4) We have screened allelopathic plants with seedling growth tests, and evaluated velvetbean as the most promising candidate.5 Field tests showed the least weed population in velvetbean stands in contrast to the stands of other crops and fallow conditions.6) A dwarf species of velvetbean, cv. ana (a cultivar in Brazil), was used. For the bioassay,5) ten lettuce seeds were placed in 4.5cm diameter Petri dishes containing 1.0ml oi the test solution on Whatman No. 1 filter papers, and were incubated at 25°C in the dark. The germinated seeds were counted and the hypocotyl and radicle growth was measuredon the 4th day. Fresh fully expanded leaves and roots of velvetbean were extracted with 80%etha-nol. The acid fraction of the extract inhibited the growth of lettuce seedlings. This fraction was subjected tc silica gel column chromatography (from 100% benzene tc 100% ethylacetate with a 5% step up, then to 100% methanol with a 5% step up, the active fraction being ethylacetate-benzene (50 : 50)), and HPLC with an ODS column (concave gradient from 1 5% methanol in 2% acetic acid to 99% methanol in 2% acetic acid), and the major inhibitor was identical to L-3,4-dihydroxyphenylalanine

Cyperus esculentus is an exotic clonal (or pseudoannual) weed in Japan, and its range is steadily increasing. To investigate its interclonal variation and phenotypic plasticity in response to water availability, five clones of C. esculentus, collected from different sites in Japan, were grown singly in pots placed outdoors under dry and wet conditions. All the traits examined showed considerable variation among the five clones. However, two clones from Tochigi were similar to each other; thus, they might have originated from the same founder population. The clone from Ibaraki was quite different from the others. Therefore, it is suggested that the Japanese populations of C. esculentus might have resulted from multiple introductions of genotypes from geographically separated and, hence, genetically differentiated, source populations. All the clones also showed considerable plasticity in response to water availability. Clones with a larger ramet number had a greater plasticity, whereas tuber size was invariant across water treatments. Highly plastic traits had generally low interclonal variation in plasticity. All the clones had high productivity and produced more ramets and tubers under wet conditions than under dry conditions. Moreover, water availability could partially regulate the mode of its reproduction; wet conditions favored tuber production (vegetative propagation) while dry conditions favored sexual reproduction. A number of trade‐offs occurred between the traits of clonal growth, storage and sexual reproduction, indicating that allocation among the competing functions/organs is mutually exclusive in plants. The results obtained here suggest that C. esculentus is more likely to invade wet habitats than dry habitats.

A glasshouse experiment was conducted to examine how the interactions of nutrient availability and partial ramet clipping affect growth, reproduction and biomass allocation of Cyperus esculentus, an invasive sedge. The plants sprouting from tubers were grown at low and high nutrient levels, and were subject either to no clipping, one, two or three clippings, with each clipping cutting half of the existing ramets at soil level. Our results show that nutrient availability and clipping frequency tended to independently affect most of growth, reproduction and biomass allocation parameters of Cyperus esculentus examined in the present study. Increased supply of nutrients led to an increase in plant productivity and its associated traits. All of the traits, except for the number of ramets, displayed a decreasing pattern with increasing clipping frequency, indicating that Cyperus esculentus had undercompensatory responses to ramet clipping. It is likely that the patterns of plants' response to clipping are species specific, and depend on morphological characters of species. Its susceptibility to ramet clipping can offer opportunities for controlling this invasive species through mechanical methods such as mowing. Clipping had little effects on biomass allocation; however, root weight fraction increased with increasing clipping frequency. While nutrient availability and clipping frequency had no influence on leaf carbon concentration at harvest, both of them increased leaf nitrogen concentration, and hence reduced leaf C/N ratio.