Population dynamics of gyrinid beetles

Summary Survival chances have been estimated for populations of the waterbeetle Gyrinus marinus Gyll. from capture-recapture sequences in 1974–1978. The average weekly survival chance is estimated as 0.9247 in spring, decreasing to 0.7701 in autumn; males survive longer than females. Survival shows little variation in time or space (variation coefficient V<0.1). Survival chance did not significantly decrease with age. Freshly emerged tenerals apparently have a lower survival chance than older beetles. The survival chance during hibernation (October–April) is about 0.33, with a greater variation between years (V=0.7) than between populations (V=0.4).Communication N⁰ 301 of the Biological Station, Wijster     

Microbial responses to salt-induced osmotic stress

Summary Soil columns were exposed to balanced (low Na⁺) or unbalanced (high Na⁺) high-salt solutions for a period of 7 days followed by 7 days of stress reflief. Total numbers of bacteria released into the perfusates rose under both types of stress, but the proportion of displaced bacteria that were viable fell significantly. Relief from both types of stress stimulated rapid increases in the number of viable micro-organisms released from soil. Examination of the soils at the end of the relief periods revealed that soils exposed to stress contained more viable bacteria than the non-stressed controls. However, high levels of balanced stress led to a significant decrease in species diversity within the microbial population, but a similar effect was not observed in soils exposed to unbalanced, high Na⁺ stress. These results suggest that, while salt stress may cause a significant reduction in the number of microorganisms in a soil, a large portion of the microbial population can rapidly adapt to marked changes in salinity.     

Effects of NaCl stress on proline and cation accumulation in salt sensitive and tolerant turfgrasses

Summary Concentrations of proline, sodium and potassium in shoot tissues of five turfgrass species were measured following exposure to 170 mM NaCl salinity stress. Salt tolerant ‘Fults’ alkaligrass and ‘Dawson’ red fescue restricted the accumulation of Na-ions to significatnly low levels compared to the salt sensitive Kentucky bluegrasses (‘Adelphi’ and ‘Ram I’) and ‘Jamestown’ red fescue. Accumulation of proline began in all species within 24 h of initiation of salt stress but at a more rapid rate and higher overall concentration for ‘Fults’ alkaligrass. Proline levels were variable and too low in relation to sodium accumulations to have any significant osmoregulatory role in salt tolerance among all cultivars tested with the possible exception of alkaligrass.     

Differential response of Trifolium species to 4-(2,4-dichlorophenoxy)butyric acid treatments

The differential response of white clover ( Trifolium repens L. cv. Regal Ladino) and berseem clover ( Trifolium alexandrinum L. cv. Mississippi ecotype) was investigated by treating greenhouse cultured plants with 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB). Berseem clover plants were significantly injured by a treatment concentration of 0.6 kg ha^-1 of 2,4-DB, whereas white clover plants were not injured by treatment levels below 2.4 kg ha^-1. The metabolism of 2,4-DB in cell suspension cultures of white clover and berseem clover was investigated using [ring-¹⁴C]-2,4-DB and non-labeled 2,4-DB. White clover cell cultures metabolized ca 4-fold more 2,4-DB than berseem cultures over a 44-h treatment period. The decrease in berseem cell population was 4-fold greater than the decrease in white clover cell population in response to the 8 μ M 2,4-DB treatment. The herbicide and its [ring-¹⁴C]-labeled metabolites were isolated from treated cells and medium after 44 h by partition and thin-layer chromatography. White clover cells metabolized 90% of the [¹⁴C]-2,4-DB and berseem clover cells metabolized 22% of the herbicide. The major portion of the radiolabel was in the glycoside fractions from extracts of both species. The differential response of Trifolium species to 2,4-DB is implied to be due to the differential rate of 2,4-DB metabolism to a glycoside by the clover plants.