Impacts of exotic plant species Oxalis pes-caprae L. on species diversity of herbaceous vegetation understory of olive groves on Lesbos Island
The relationship between plant invasion and diversity of native plant communities was investigated in Mediterranean olive groves. Species abundances were recorded in close-paired plots with natural herbaceous vegetation understory of olive groves on Lesbos. Each paired plot consists of a control and an invaded plot. The exotic plant species Oxalis pes-caprae was absent from control plots, while it was dominant in invaded plots. The species richness, species diversity and species evenness were estimated per plot. The dominance of the biological invader caused a large reduction in species richness and species diversity of grassland communities. On the other hand the species abundances were found to be similar in reference and invaded plots. In addition the measurements’ year had a clear effect on the variation of species richness, diversity and evenness indices. In conclusion impacts of exotic plant species Oxalis pes-caprae on herbaceous vegetation on Lesbos were expressed as a significant decrease of biodiversity of Mediterranean-type grassland communities.
Presence and correlation with soil parameters of acari fauna in a pasture in Central Greece
Quality and quantity parameters of the acari fauna in the surface (0-5 cm depth) and sub-surface (5- 10 cm depth) soil were investigated in the present study. The sampling took place in a pasture located near Neochori, Karditsa, Central Greece, in May 2003. Organic matter, N, P, Ca, Mg, K and Na concentrations as well as pH value were measured in the same soil layers. In total 15 acari taxa were found, 14 in the 0-5 cm depth and four in the 5-10 cm depth. 92 % of the total number of individuals was found in the 0-5 cm depth. The most abundant taxa were Mycobatidae, Passalozetes sp. as well as immature Gryptostigmata. No Astigmata were found. N and Ca concentrations in the 0-5 depth were significantly greater than in the 5-10 depth. There were no significant differences between soil layers concerning pH value and organic matter, P, Mg, K and Na concentrations.
Study on the Mite fauna of a natural pasture interseeded with Lolium perenne
Α three year’s study on the acarofauna in a natural pasture interseeded with Lolium perenne, in County Ioannina, Greece, resulted in detection of 169 taxa. The most frequent and dominant taxa were: Peloptulus sp., immature stages of Cryptostigmata, Scheloribates sp1, Scheloribates sp2, Steneotarsonemus konoi, Tarsonemus lacustris, Cyta sp., Asca bicornis and Tyrophagus longrior. Significant differences of the total acari population was detected among the three years. The highest populations occurred during the first year. The study of seasonal fluctuation of the most dominant taxa for the three years were: immature stages of Cryptostigmata developed higher population densities during autumn and winder. The adult Cryptostigmata developed higher densities during winter. The taxon Steneotarsonemus konoi developed higher population densities during summer and autumn while taxa Asca bicornis and Cyta sp. during autumn and winter.
Effects of selenium on water economy of Melilotus officinalis (L.)
Elevated heavy metal pollution of soils in relation to drought phenomena have triggered the study of the synergistic effect of selenium (as Na2SeO4 solution) and water deficit on water relations of Melilotus officinalis (L.). For this purpose three selenium concentrations (0, 1 and 3 mg Se/lt) and two water regimes (well watered: WW and water stressed: WS) were tested. Apart from the microclimatic parameters, water potential, relative water content and stomatal conductance were measured. The results indicate that selenium affects the water economy of Melilotus officinalis by altering slightly leaf water potential and relative water content and by reducing significantly stomatal conductance.
Cutting and drought effects on productivity of legume – grass mixture
Cultivation of grass – legume mixtures is a usual management practice used in order to improve the quantity and quality of production. However, the results of several published reports related with the yield are conflicting. The purpose of this study was to investigate the effect of cutting on the productivity of the perennial legume and grass mixtures with and without irrigation. The experiment was established in Drama, Macedonia in northern Greece. Measurements were carried out during the spring and summer periods of the years 1996 and 1997. Two levels of irrigation and three levels of cuttings were enployed. Above ground dry biomass was measured in a pure crop of Medicago sativa, Festuca arundinacea and their 1:1 mixture as well. The Relative Production Index was calculated. Results have shown that: a) the two years total production of the mixture was higher than the production of pure Festuca, especially without irrigation, b) it did not differ from the production of the pure crop of Medicago, when cuttings were not applied, with and without irrigation, c) pure cultivation of Medicago was better cutting resistant than pure Festuca and mixture, and d) no irrigation reduced production in all treatments, but reduction was lower in the cut mixture.
