Possible dual roles of an allelopathic compound, cis-dehydromatricaria ester
The aqueous extract of the root ofSolidago altissima was lethal to nematodes. The major compound isolated from the toxic fraction wascis-dehydromatricaria ester (methyl 2-decene-4,6,8-triynoate), which is already known as an allelopathic compound of a composite showing growth-inhibition to a rice seedling. This compound showed high toxicity to plant-parasite nematodes. A composite exudes one defending substance against both competitive plants and plant-parasite nematodes.
Effect of desert plant ecophysiological adaptation on soil nematode communities
Abstract Nutrient source limitation in desert ecosystems enhances competition among plant communities, leading to creation of microhabitats beneath the shrubs that can determine composition and abundance of soil organisms. The aim of the study was to determine the effect of plant ecophysiological adaptation on soil nematode communities in the rhizosphere of tightly interweaving shrubby communities. Soil samples were collected monthly under the canopies of three perennial desert shrubs: Artemesia herba-alba, possessing the allelopathic ability to dominate in relationships with other plants; Reaumuria negevensis, a salt-resistant plant; and Noea mucronata, a typical dry desert shrub. An inter-plant area was used as a control. The results demonstrated that soil water content (SWC) and total organic carbon (Corg) were significantly different under different plants and inter-plant areas, with the highest values found under R. negevensis (SWC) and N. mucronata and R. negevensis (Corg). Plant parasite and omnivore-predator nematodes were more sensitive to the ecophysiological individual features of observed plants versus the total number of nematodes and bacteria- and fungi-feeding nematodes. Generally accepted ecological indices such as Wasilewska (WI), trophic diversity (T), maturity (MI, MMI), basal (BI), enrichment (EI), structure (SI), and channel (CI), pointed to specific ecological conditions under canopies of the observed plants.
Experimental studies on the early stages of secondary succession
To study secondary successional sequences and mechanisms, denudation experiments were conducted in Central Japan with the removal of dominants, laying burned soil on the surface, and turning over the top- and subsoil. The early stages of secondary succession were predictable as to species and life-form composition. The biomass — the degree of succession (DS) relationship and the DS-isopleth showed phasic changes within a seral stage. The rate of succession (RS) was also calculated. In the establishment of weed communities with crops, the critical time for weeding, the allowable limit of weeds, etc. were found in relation to the distribution pattern, adaptive strategy of species, interspecific and intraspecific density regulations. In seasonal denudation experiments, the month of denudation affected the regular phenological pattern of weedy species, although normal replacement of summer annuals by winter annuals was usual. The population dynamics of buried-seeds in the soil, the adaptive strategies of the dominants and the role of allelopathy were discussed as the main forces of secondary succession in its early stages.