Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

Understanding plant physiological responses to high temperature is an important concern pertaining to climate change. However, compared with terrestrial plants, information about aquatic plants remains limited. Since the degree of midday depression of photosynthesis under high temperature depends on soil water conditions, it is expected that emergent aquatic plants, for which soil water conditions are always saturated, will show different patterns compared with terrestrial plants. We investigated the diurnal course of the photosynthetic light-response curve and incident light intensity for a freshwater emergent plant, buckbean (Menyanthes trifoliata L.; Menyanthaceae) in a cool temperate region. The effect of midday depression was observed only on a very hot day, but not on a moderately hot day, in summer. The diurnal course of photosynthetic light-response curves on this hot day showed that latent morning reduction of photosynthetic capacity started at dawn, preceding the apparent depression around the midday, in agreement with results reported in terrestrial plants. We concluded that (1) midday depression of emergent plants occurs when the stress intensity exceeds the species’ tolerance, and (2) measurements of not only photosynthetic rate under field conditions but also diurnal course of photosynthetic light-response curve are necessary to quantify the effect of midday depression.

Characteristics and coordination of source-sink relationships in super hybrid rice

This paper discusses the characteristics of source and sink for super hybrid rice and how to coordinate its source-sink relationships for high-yielding cultivation. It is known that super hybrid rice possesses a higher net photosynthetic rate than non-hybrid rice because of its higher grain-leaf area ratio, better stornata traits and less midday depression. However, the sink of super hybrid rice remains large due to its large and numerous spikelets. Furthermore, the relocation of assimilates is smooth in super hybrid rice because of its well-developed vascular structure. However, due to the very large sink of super hybrid rice, it is relatively inefficient in supplying of assimilate products to spikelets, in particular to inferior spikelets. Therefore, reducing the discrepancy between source and sink in super hybrid rice is essential for developing high-yielding cultivation. This can only be achieved by planting cultivars adapted for local environments, raising strong seedling, setting up populations with a high photosynthetic efficiency for increasing the supply of source, and improving the field management in filling stages to the duration of supply of photosynthate to grains.

Effects of Potassium Fertilizer on Diurnal Change of Photosynthesis in Stevia Rebaudiana Bertoni

The effects of potassium fertilizer on diurnal change of photosynthesis in Stevia rebaudiana Bertoni had been studied. Diurnal changes of net photosynthetic rate (Pn) and environmental and physiological traits in leaves of Stevia rebaudiana Bertoni were measured using LI-6400 portable photosynthesis system. The results showed that optimal potassium fertilizer can increased chlorophyll content and improved photosynthesis rate and decreased the chlorophyll a/b ratio. At the same time, midday depression of photosynthesis abated or disappeared.