The δ13C value is widely used to assess the effects of drought on water status in plants. However, there is little information regarding the δ13C signature in different organs of rice. We conducted a field study to ...The δ13C value is widely used to assess the effects of drought on water status in plants. However, there is little information regarding the δ13C signature in different organs of rice. We conducted a field study to examine whether the δ13C among different plant parts would be affected by the intensities of drought, and to evaluate genotypic variation in δ13C fluctuation among plant parts affected by drought intensities. Two cultivars, “Nipponbare” (Oryzasativa ssp. japonica) and “Kasalath” (O. sativa ssp. indica), were grown in the field with a line-source sprinkler system. The δ13C values of panicles, flag leaves, straws, culms, and roots were measured from plant samples. The δ13C value increased as drought stress increased, especially in the panicles and roots. “Nipponbare” showed higher values of δ13C than “Kasalath” under the well-watered and mild drought stress conditions, but there was no significant difference between the genotypes in the δ13C value under the severe drought stress condition. The variation in δ13C value among different plant parts was also increased with increasing drought stress. In contrast, these variations were small under well-watered conditions. Furthermore, there was much greater variation in the δ13C value among different plant parts in “Kasalath” than in “Nipponbare” when the plants were grown under drought stress conditions. A significant negative relationship was observed between the δ13C value of panicles and shoot dry matter production, suggesting that the δ13C value of panicles may be the best indicator of plant water status in rice.展开更多
Soil erosion by water resulting in gully formation is a common occurrence in western Kenya. Establishment of local and sustainable countermeasures to prevent gully development/expansion in western Kenya is an urgent i...Soil erosion by water resulting in gully formation is a common occurrence in western Kenya. Establishment of local and sustainable countermeasures to prevent gully development/expansion in western Kenya is an urgent issue. This study presents the proposal to prevent gully development/expansion by planting Eucalyptus trees in gully prone regions. A survey study was undertaken in Kenya from 2008 to 2011. Roots of adjacent Eucalyptus citriodora trees fused forming a dense network of closely woven mass of root system holding large amount of soil thereby checking erosion by water and hence gully development. The network of roots among adjacent Eucalyptus trees also supported the standing and normal growth of the other Eucalyptus trees whose root systems were completely free from soil. Recognizable aging and breakdown of root networks were not observed during the survey period.展开更多
In the study area located in Western Kenya near the Lake Victoria, severe soil erosion occurred and it thought to relate to vegetation degradation caused by overgrazing. The livestock density estimated by analyzing sa...In the study area located in Western Kenya near the Lake Victoria, severe soil erosion occurred and it thought to relate to vegetation degradation caused by overgrazing. The livestock density estimated by analyzing satellite image (1.39 TLU/ha for available grazing lands) was lower than that of measured for seven farmers’ grazing lands using GPSs (4.41 TLU/ha, 2011) with variation from 0.83 to 12.36 TLU/ha. Thus, it is clear that the grasslands used by farmers are limited compared with the area of estimated available land for grazing identified by analyzing the satellite image. According to growth-consumption rate model that was developed by the Nyangito et al. (2008) in southeastern Kenya, if livestock density reaches over 7 TLU/ha, pasture growth rate became lower than consumption rate. Grass biomasses of the grazing lands were kept low (less than 50 g/50 × 50 cm2) under high livestock density (three farmers out of seven were higher than 7 TLU/ha). In addition, rainfall pattern is very unstable and we observed stunted growth of grasses during dry spells. Therefore, we concluded that overgrazing. It means that inhibition of continuous re-growth of grasses due to high grazing pressure has been occurred even for small area and contributed to the soil erosion.展开更多
文摘The δ13C value is widely used to assess the effects of drought on water status in plants. However, there is little information regarding the δ13C signature in different organs of rice. We conducted a field study to examine whether the δ13C among different plant parts would be affected by the intensities of drought, and to evaluate genotypic variation in δ13C fluctuation among plant parts affected by drought intensities. Two cultivars, “Nipponbare” (Oryzasativa ssp. japonica) and “Kasalath” (O. sativa ssp. indica), were grown in the field with a line-source sprinkler system. The δ13C values of panicles, flag leaves, straws, culms, and roots were measured from plant samples. The δ13C value increased as drought stress increased, especially in the panicles and roots. “Nipponbare” showed higher values of δ13C than “Kasalath” under the well-watered and mild drought stress conditions, but there was no significant difference between the genotypes in the δ13C value under the severe drought stress condition. The variation in δ13C value among different plant parts was also increased with increasing drought stress. In contrast, these variations were small under well-watered conditions. Furthermore, there was much greater variation in the δ13C value among different plant parts in “Kasalath” than in “Nipponbare” when the plants were grown under drought stress conditions. A significant negative relationship was observed between the δ13C value of panicles and shoot dry matter production, suggesting that the δ13C value of panicles may be the best indicator of plant water status in rice.
文摘Soil erosion by water resulting in gully formation is a common occurrence in western Kenya. Establishment of local and sustainable countermeasures to prevent gully development/expansion in western Kenya is an urgent issue. This study presents the proposal to prevent gully development/expansion by planting Eucalyptus trees in gully prone regions. A survey study was undertaken in Kenya from 2008 to 2011. Roots of adjacent Eucalyptus citriodora trees fused forming a dense network of closely woven mass of root system holding large amount of soil thereby checking erosion by water and hence gully development. The network of roots among adjacent Eucalyptus trees also supported the standing and normal growth of the other Eucalyptus trees whose root systems were completely free from soil. Recognizable aging and breakdown of root networks were not observed during the survey period.
文摘In the study area located in Western Kenya near the Lake Victoria, severe soil erosion occurred and it thought to relate to vegetation degradation caused by overgrazing. The livestock density estimated by analyzing satellite image (1.39 TLU/ha for available grazing lands) was lower than that of measured for seven farmers’ grazing lands using GPSs (4.41 TLU/ha, 2011) with variation from 0.83 to 12.36 TLU/ha. Thus, it is clear that the grasslands used by farmers are limited compared with the area of estimated available land for grazing identified by analyzing the satellite image. According to growth-consumption rate model that was developed by the Nyangito et al. (2008) in southeastern Kenya, if livestock density reaches over 7 TLU/ha, pasture growth rate became lower than consumption rate. Grass biomasses of the grazing lands were kept low (less than 50 g/50 × 50 cm2) under high livestock density (three farmers out of seven were higher than 7 TLU/ha). In addition, rainfall pattern is very unstable and we observed stunted growth of grasses during dry spells. Therefore, we concluded that overgrazing. It means that inhibition of continuous re-growth of grasses due to high grazing pressure has been occurred even for small area and contributed to the soil erosion.
