Ecophysiology of C3 and C4 plants in terms of responses to extreme soil temperatures

Extreme soil temperatures are the main limitation to the expansion of agriculture. In Brazil, this also affects the second crop, which is usually performed every year. We investigated the influence of soil temperature on the ecophysiology of two plant species with different mechanisms of CO2 assimilation: maize (C4) and bean (C3). The plants, in the vegetative phase, were subjected to three soil temperatures: low (9-12 A degrees C), ambient (25-30 A degrees C), and high (27-42 A degrees C). Our results indicate that both low and high soil temperatures negatively affected the photosynthetic process of the studied plants. The reduction of CO2 assimilation rates under low soil temperature was mainly due to stomatal closure, while under high soil temperatures, it was related to decreased carboxylation rates. Short-term exposure to extreme soil temperatures affects the root system growth and, in maize plants, leads to impaired shoot dry mass accumulation. Besides that, stresses caused by high soil temperature reduced the relative water content of the leaves, causing an increase in leaf temperature and cells rupture.