Infestation of weed species in pre-planting of soybean in succession to winter crops

This study aimed to evaluate different crops and plant species planted after soybeans for one year, in terms of their potential to inhibit the occurrence of weed species. The following crops that were planted as second crop after soybeans were evaluated: (1) corn (Zea mays) planted at spacing of 90 cm between rows, intercropped with Brachiaria ruziziensis in the inter-rows; (2) sunflower (Helianthus annuus); (3) crambe (Crambe abyssinica); (4) radish (Raphanus sativus); (5) rapeseed (Brassica napus); and (6) winter fallow - no plantation after soybeans. Phytosociological characterization of weed species was carried out at the pre-planting of soybeans in the following cropping season. Estimations of relative abundance, relative frequence, relative dominance and Importance Value Index were made for each species present. Areas were also intra-characterized by the diversity coefficients of Simpson and modified Shannon-Weiner, and areas were compared using the Jaccard similarity coefficient for presence-only, by multivariate cluster analysis. In the short‑term (a single cropping season), cultivation of winter crops do contribute for lower occurrence of weed species at the pre-planting of soybeans on the subsequent cropping season. The suppressive effects depend both on the species grown in the winter and in the amount of straw left on the soil by these winter crops. Radish was more efficient in inhibiting the occurrence of weed species and rapeseed showed composition of infestation similar to that observed at the area under fallow.

STUDY OF AUTUMN-WINTER WEEDS IN PORTUGAL AND ITS ECOLOGICAL PREFERENCES

ABSTRACTThe conclusion of the dam project located in Alqueva, in Southern Portugal, has resulted in a significant increase of new irrigated areas, since 2006. This has meant that, in recent years, there have been progressive flora changes in farming systems traditionally implemented in the Alentejo region. The present work has analyzed the weed flora in an early stage of these changes, and the impact of environmental factors on the distribution of natural vegetation under Mediterranean climate conditions in the influence area of Alqueva. In 2007, 105 floristic surveys were carried out in autumn-winter crop plots or other soil use, and 264 species were identified. Families with higher expression were: Asteraceae, Poaceae, and Fabaceae. Only three species have been identified in more than half of farms, Avena sterilis, Phalaris minor and Lolium rigidum and they were part of the 15 species that revealed high and very high infestation degrees. Soil texture and extractable phosphorus have been determined as active ecological factors, according to the method of ecological profiles and Mutual Information. Therefore, these factores were those with the greatest influence on the species distribution. L.rigidum distribution showed to be associated with medium soil texture and A.sterilis distribution also showed to be associated with medium and fine soil texture soils, without showing ecological preference by extractable phosphorus. The distribution of P.minorwas not related to the soil texture but showed preference for soils with medium phosphorus content.

Cardiovascular, respiratory and metabolic responses to temperature and hypoxia of the winter frog Rana catesbeiana

The objective of the present study was to determine the effects of hypoxia and temperature on the cardiovascular and respiratory systems and plasma glucose levels of the winter bullfrog Rana catesbeiana. Body temperature was maintained at 10, 15, 25 and 35oC for measurements of breathing frequency, heart rate, arterial blood pressure, metabolic rate, plasma glucose levels, blood gases and acid-base status. Reducing body temperature from 35 to 10oC decreased (P<0.001) heart rate (bpm) from 64.0 ± 3.1 (N = 5) to 12.5 ± 2.5 (N = 6) and blood pressure (mmHg) (P<0.05) from 41.9 ± 2.1 (N = 5) to 33.1 ± 2.1 (N = 6), whereas no significant changes were observed under hypoxia. Hypoxia-induced changes in breathing frequency and acid-base status were proportional to body temperature, being pronounced at 25oC, less so at 15oC, and absent at 10oC. Hypoxia at 35oC was lethal. Under normoxia, plasma glucose concentration (mg/dl) decreased (P<0.01) from 53.0 ± 3.4 (N = 6) to 35.9 ± 1.7 (N = 6) at body temperatures of 35 and 10oC, respectively. Hypoxia had no significant effect on plasma glucose concentration at 10 and 15oC, but at 25oC there was a significant increase under conditions of 3% inspired O2. The arterial PO2 and pH values were similar to those reported in previous studies on non-estivating Rana catesbeiana, but PaCO2 (37.5 ± 1.9 mmHg, N = 5) was 3-fold higher, indicating increased plasma bicarbonate levels. The estivating bullfrog may be exposed not only to low temperatures but also to hypoxia. These animals show temperature-dependent responses that may be beneficial since during low body temperatures the sensitivity of most physiological systems to hypoxia is reduced

The land of the midnight sun: summer and winter journeys through Sweden, Norway, Lapland and Northern Finland - 1

Lisäpainokset: 3. p. London 1882, 4. p. London 1888.

The land of the midnight sun: summer and winter journeys through Sweden, Norway, Lapland and Northern Finland - 2

Lisäpainokset: 3. p. London 1882, 4. p. London 1888.

Winter 1967-68

Aerial view of a snow covered Brock University around late 1967 or early 1968. Construction of the Thistle Complex is still underway at this point.

Comparison of two measures of PSI electron transport in winter rye

The number of P700 (the reaction centre of Photosystem I) converted to P700+, in winter rye, was determined by measuring the absorbance change at 820nm . It was found, with a single turnover flash, that thylakoids isolated from cold grown plants have a 50% greater number of P700 oxidized than thylakoids isolated from warm grown plants. Incubation of thylakoids in the dark at 35 C did not change the number of P700 oxidized. The conversion of P700 to P700+ with a single flash can be compared to a steady state rate of electron transport using a Clark electrode. The results for P700 oxidation using the absorbance change at 820 nm measure effects within the PSI complex whereas the results obtained from a Clark electrode measures steady state electron transport between the cytochrome blf complex and the PSI complex. In contrast to the results for P700 oxidation it was shown, using a Clark electrode, that both thylakoids from cold grown plants and thylakoids incubated at in the dark 35 C exhibited 50% higher rates of electron transport than thylakoids from warm grown plants. The correlation between the higher rate of steady state PSI electron transport observed in thylakoids isolated from cold grown winter rye and number of active PSI reaction centres localizes the site of the increase to the PSI reaction centre. In contrast the lack of correlation after incubation at 35 C indicates the increase in the rate of light saturated electron transport in thylakoids isolated from cold grown plants and thylakoids incubated in the dark at 35 C occur by different mechanisms.

Niagara in summer and winter.

The dates for each issue have been estimated.