Growth, Nodulation and Nitrogen Fixation in Stylosanthes: Effect of Different Day/Night Root Temperatures

Abstract

Nodulated plants of six varieties of Stylosanthes were grown at a constant temperature of 30°C for 21 days in a controlled environment and then for a further 21 days at a range of day/night root temperatures. Dry matter and nitrogen content of S. hamata cv. Verano and CPI40264A were measured after growth at day/night root temperatures of 30/30, 40/30, 50/30, 60/30 and 60/35°C. Similarly, growth and nitrogen content were measured for Verano, CPI40264A, S. guianensis cv. Oxley and cv. Cook, S. humilis cv. Lawson and S. scabra cv. Seca after growth at root temperatures of 25/20, 25/25, 30/25, 30/30, 35/30 and 40/30°C. There were strong interactions of root temperature with variety and harvest time (31 and 42 days) but all varieties grew well even at the highest temperatures (50-60°C) provided they were supplied with nitrogen. Symbiotically dependent plants of S. hamata cv. Verano were more tolerant of high root temperatures and maintained better growth and nitrogen fixation at 40/30°C than those of CPI40264A, especially after the 31 day harvest. All six varieties responded similarly, but to differing extents, to the lower range of root temperatures. Nitrogen fixation was more severely affected than dry weight by high root temperature. R. A. Date: Crecimiento, nodulacion y fijacion de nitrogeno en Stylosanthes; efectos de distintas temperaturas diurnas/nocturnas de la raiz.R E S U M E N Se cultivaron plantas noduladas de seis variedades de Stylosanthes bajo una temperatura constante de 30°C durante 21 dias en un ambiente controlado y luego durante otros 21 dias bajo una variedad de temperaturas diurnas/nocturnas de la rai'z. Se midieron la materia seca y el contenido de nitrogeno de S. hamata cv. Verano y CPI40264A despues de crecer bajo temperaturas diurnas/nocturnas de la rai'z de 30/30, 40/30, 50/30, 60/30 y 60/35°C. Asimismo, se midieron el crecimiento y contenido de nitrogeno para Verano, CPI40264A, S. guianensis cv. Oxley y cv. Cook, S. humilis cv. Lawson y S. scabra cv. Seca despues de crecer bajo temperaturas de rai'z de 25/20, 25/25, 30/25, 30/30, 35/30 y 40/30°C. Se presentaron interacciones fuertes de temperatura de la rai'z con variedad y tiempo de cosecha (31 y 42 dias), pero todas las variedades crecieron bien incluso bajo las temperaturas mas elevadas (50-60°C), siempre y cuando tuvieran nitrogeno a disposicion. Las plantas de dependencia simbiotica de 5. hamata cv. Verano se mostraron mas tolerantes de las altas temperaturas de la rai'z y mantuvieron mejor crecimiento y fijacion de nitrogeno bajo 40/30°C que las de CPI40264A, especialmente despues de la cosecha a los 31 di'as. Las seis variedades respondieron de manera similar pero en distinto grado bajo la escala inferior de temperaturas de la rai'z. La fijacion de nitrogeno se vio mas afectada que la materia seca por la temperatura elevada de la rai'z.

Rising CO2 in the field does not offset warming or drought constraints on leaf growth of a C3 forage

“…Soil temperature varied between 16.5 and 24.0°C under Control and warmed regimes (Figure 1d). The maximum soil temperature (24°C) on 3 May was below the 30/40°C night/day root temperature for optimal growth and nitrogen fixation in Stylosanthes (Date, 1989). Under the heated regimes, the soil temperature was 1.5°C higher, especially during the night (Figure 1d).…”

“…Wind speed rarely exceeded 1.5 m s -1 and only once reached 2.0 m s -1 on 14 June (Figure 1c). The maximum canopy temperature on 17 June in the warmed plot (33.5°C, Figure 2) was not stressful for S. capitata because its optimum temperature for growth is between 30 and 40°C (Date, 1989). Soil temperature varied between 16.5 and 24.0°C under Control and warmed regimes (Figure 1d).…”