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Azolla filiculoides Lam. jest paprotką wodną współżyjącą z azot-wiążącą sinicą Anabaena, która budzi zainteresowania ze względu na możliwość jej wykorzystania w postaci nawozu zielonego. Azolla stała się obiektem badań na całym świecie. Wiedza na temat fizjologicznych i ekologicznych czynników wpływających na wzrost paproci jest istotna w badaniach przyrodniczych ukierunkowanych na jej praktyczne stosowania. Celem tej pracy było zbadanie w warunkach kontrolowanych wpływu różnych form azotu na jego właściwości oksydoredukcyjne (Eh) i przyrost biomasy Azolli, Stwierdzono, że optymalny zakres potencjału redoks wzrostu Azolli zawiera się w przedziale 550-600 mV, a pobór formy azotu azotanowego w podłożu wydaje się być preferowany przez paprotkę w stosunku do azotu wiązanego z atmosfery prze sinicę Anabaenę.
The aim of the study was to test the usefulness of split rhizotrone technique to investigate the effect of localized soil anoxia on root and shoot developement, using maize as a test plant. The experiment was performed in 6 split rhizotrons enabling differentiation of soil aeration status in each half of the rhizotron by blowing nitrogen or air through them. The rhizotrone consists of two parts (each 16.6 dm3 in volume) inclined with an angle 60°. Each part is constructed of 1 mm thick stainless steel plate with a glass inner wall for root observation and has dimensions 84 cm x 40.5 cm x 5.0 cm. The rhizotrons were filled in with a brown loess soil material (Eutric Camhisol) from Ap horizon (from Eli/6wka, near Lublin). Maize seedlings with the roots splitted between the rhizotrone halves (eukivars KLG 2210 and DEA) were used in the experiments. Until the stress period the soil moisture tension of 20-80 kPa provided good water and air conditions. At a stage of 8 leaves three treatments were applied for a period of 7 days; an oxic control (P/P), a localized anoxia with 50% of the roots in nitrogen treated part (P/A), and a complete anoxia (A/A) with gas nitrogen in both parts. During the stress period diurnal elongation rates of primary roots (by marking positions of the tips each day) as well as distribution of two indicators of soil oxygenation status with depth viz. of oxygen diffusion rate (ODR) and of redox potential (Eh) in soil were measured. Shoot elongation rates were monitored with a potentiometer attached to the youngest leaf. Microscopic photographs of cross- sections of the caps and of apical meristems of primary roots at 400 magnification were made to show the changes in their anatomy due to anoxia. Chemical analysis of the shoots was performed after the stress period. For each cultivar the experiment was repeated three times. The investigations performed allowed the following conclusions to be drown out: 1. The split rhizotrone was shown to be a useful technique to study behaviour of the primary maize roots under localized anoxia conditions. 2. The ODR and Eh distribution with depth showed deterioration of oxygenation status (drop of ODR from control values above 100 |µg m-2 s-1 to the level 30 µg m-2 s-1, decrease of Eh from control values above 550 mV to the level, 300 mV) due to replacement of the soil air with gaseous nitrogen. 3. Root elongation rates under anoxic conditions (both under complete - A/A, and localized - A/P anoxia) were on the level of about 50% of the controle (P/P) during first 4 days and decreased practically to zero by the end of the stress period. In turn, the oxic part of the rhizotrone combined with localized anoxia treatment of the same plant (P/A) exhibited compensation effect and was characterized by stimulation of the root elongation rate up to 80%. This effect was especially distinct after 2-5 days of the stress duration and then tended to decrease. 4Distribution of the root mass in depth under anoxic treatments was characterized by concentration of about 80% of the root mass within first 10 cm of the soil. 5.Microscopic photographs of the root tips showed, under anoxic conditions, shorter meristematic zone, smaller number of mitosis, beginning of aerenchyma formation and dying of the cells at a distance of 1 mm from the root cap. 6.The shoots responded to applying anoxia to both rhizotrone parts by 20% reduction of the growth rate. 7.Both root and shoot elongation rates were correlated also with the temperature. 8.Oxygen deficiency in soil resulted in an increase of exchangeable manganese, what was reflected by its increased concentration in the maize shoots.
The aim of the study was to investigate the influence of soil redox resistance on denitrification rate in soil material of 9 profiles from Poland and Germany. The soil samples from particular horizons were incubated under water saturation, in closed bottles, in an atmosphere of gaseous nitrogen containing 3 % acetylene at a temperature of 20°C for 5 days. The values of redox potential, pH, and the evolution of carbon dioxide and nitrous oxide were measured after 12, 24, 48, and 120 hours. The rate of nitrous oxide evolution in relation to native carbon mineralization, redox potential and soil reaction is discussed. Denitrification rate showed maximum at pH 6.3-7.3 and Eh 150-300 mV. It was positively correlated with redox resistance (t400).
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