Shin Yabuta

Eclipse Effects on CO2 Profile within and above Sorghum Canopy

Abstract We analyzed the effects of a partial solar eclipse (22 July 2009) on microclimate including vertical gradients of CO2 concentrations ([CO2]), so called [CO2] profile, in a mature sorghum canopy. Together with CO2 measurement, major photosynthetic drivers of microclimate, light intensity, temperature and atmospheric H2O concentration ([H2O]) were also measured simultaneously at the same place and height. [CO2] at 6.0, 3.2, 2.1, 1.4, 0.7, 0 m above the ground (canopy height was 3.2 m) increased by 5.8, 4.8, 9.0, 7.8, 6.4, 7.6μmol mol-1, respectively, from 1 hour before the eclipse maximum to the eclipse maximum, during which theincident solar radiation above the canopy dropped by 1473 μmol photons m-2 s-1. However, it declined by 3.4, 10.6, 10.8, 6.0, 5.4, and 5.8μmol mol-1, respectively, from the eclipse to 1 hour later,during which the incident radiation increased by 1350μmol photons m-2 s-1. The [CO2] profile during the eclipse was uniform except for higher [CO2] near the ground. Comparative analysis of theeffect of light intensity on the microclimate during the eclipse-induced light decreasing phase (ELDP) and eclipse-induced light increasing phase (ELIP) revealed that [CO2], [H2O], temperature and relative humidity (RH) are significantly correlated with the light intensity above the canopy in a nearly linear fashion. Furthermore it indicated that detected less light-reacted canopy photosynthesis at a higher layer within the canopy during ELIP might be due to slower response of stomatal opening (than closing) to the light intensity above the canopy.

Effects of vertical gradient of leaf nitrogen content on canopy photosynthesis in tall and dwarf cultivars of sorghum.

Abstract The vertical profile of leaf nitrogen (N) content per unit leaf area (NLA) is important for increasing crop productivity via optimizing N use for canopy photosynthesis. To investigate the effects of plant height on the optimality, we analyzed the NLA profiles with respect to light gradient twice during vegetative growth in canopies of tall and dwarf cultivars of sorghum. The gradients of the NLA profiles relative to the light gradients were similar in the two cultivars although the vertical light gradient was steeper in the dwarf cultivar with doubled leaf area density (LAD). This suggests that light attenuation is more influential on the NLA profile than is plant height or LAD. The advantage of the observed NLA profile for the canopy CO2 uptake as compared to the uniform NLA profile was similar in the cultivars except when the N allocation rate to the canopy decreased relative to the leaf area expansion in the dwarf cultivar. These results suggested that the optimality of the advantage of the NLA gradient may not be directly influenced by the plant height, but by the balance between N allocation and leaf area expansion. The balance may be altered by the difference in the biomass allocation in the shoot between the tall and dwarf sorghum. These factors are to be taken into consideration in breeding programs that target stature in order to potentially increase production in sorghum. Key words:

Flowering Pattern of Biodiesel Plant Jatropha in Frost- and Drought-Prone Regions of Botswana

ABSTRACT Jatropha has gained interest as a potential biodiesel feedstock. Nevertheless, its oil production decreases significantly in frost- and drought-prone regions. In this study, we characterized the flowering pattern of Jatropha in Botswana in the 2014/2015 season. Extensive springtime pruning synchronized Jatropha regrowth in summer and effectively stimulated growth after frost damage. Flowering started in February 2015 and peaked in April and May. Wide variations in flowering frequency were observed among different Jatropha accessions. Trees flowering in February and March produced fruit in May, but most trees only flowered in April and May and did not yield fruit because of cold snaps. These observations suggested that harvesting seed before wintertime is the key to improve Jatropha production in the Botswana climate. This study highlighted the importance of inducing early flowering by developing new agricultural managements. These may include frost cover and sun shades to prevent stress-induced damage, canopy control by pruning, optimization of fertilization practice, and/or introduction of superior Jatropha varieties.