Takahiro Wajima

Dynamics of water and ion transport driven by corn canopy in the Yellow River basin

Water and ion balance in a corn field in the semi-arid region of the upper Yellow River basin (Inner Mongolia, China) was analyzed with special reference to transpiration stream and selective nutrient uptake driven by the crop canopy. During the crop development stage (June 7 to July 17, 2005), crop transpiration and soil evaporation were evaluated separately on a daily basis, and concentrations of NO3−, PO43−, K+, Na+, Ca2+, Mg2+ and Cl− ions in the Yellow River water, irrigation water, ground water, soil of the root zone and xylem sap of the crop were analyzed.The crop transpiration accounted for 83.4% of the evapotranspiration during the crop development stage. All ions except for Na+ were highly concentrated in the xylem sap due to the active and selective uptake of nutrients by roots. In particular, extremely high concentrations of the major essential nutrients were found in the nighttime stem exudate, while these concentrations in the river water, the irrigation water, the ground water and the root-zone soil were lower. On the other hand, Na+, which is not the essential element for crop growth, was scarcely absorbed by roots and was not highly concentrated in the xylem sap. Consequently, Na+ remained in the ground water and the root-zone soil at higher concentrations. These results indicate that during the growing season, crop transpiration but not soil evaporation induces the most significant driving force for mass flow (capillary rise) transporting the ground water toward the rhizosphere, where the dynamics of ion balance largely depends on the active and selective nutrient uptake by roots.

Deriving a reduction factor for woody part of culm for bamboo Phyllostachys pubescens

We determined the reduction factor for the woody part of culm for one of the largest bamboo species, Phyllostachys pubescens Mazel ex Houz. The determined reduction factor enables us to convert the cross-sectional area of the whole culm into that of the culm wall. We collected 650 cross-cutting sample culms from a stand of P. pubescens in Mt. Toshima, Kumamoto Prefecture, western Japan. For the cut-end surface, the external culm diameter and culm wall thickness were measured, and then the cross-sectional area of the whole culm and the culm wall were computed. The cross-sectional area of the culm wall was strongly correlated with that of the whole culm. The regression analysis between these cross-sectional area indicated that the reduction factor for P. pubescens was 0.311, independent of the magnitude of the cross-sectional area. The independence implied that the determined reduction factor could be directly applied to convert the apparent culm volume into wood volume. Implications of the reduction factor for estimating transpiration and carbon stock of P. pubescens stands were discussed. The Monte Carlo simulation revealed that at least, but not more than, 60–70 cross-cutting culms collected from 20 culms are necessary for the reduction factor when estimating the stand level transpiration and carbon stock.

Evaluation of canopy transpiration rate by applying a plant hormone "abscisic acid"

A method for evaluation of temporal changes in canopy transpiration rate and stomatal conductance in crop fields by using a plant hormone abscisic acid (ABA) has recently been developed. The method was applied to a corn canopy at different growth stages in the upper Yellow River basin, China. Diurnal changes in the canopy transpiration rate and stomatal conductance were evaluated at the initial stage with a leaf area index (LAI) of 0.37 on June 7 and the crop development stage with an LAI of 4.39 on July 15, 2005. The proportions of the accumulated transpiration rate during daytime to the accumulated evapotranspiration were 24% and 74% at the initial and crop development stages, respectively. Stomatal conductance varied in parallel with transpiration rate in the initial stage of the crop. However, in the crop development stage with low soil water content, stomatal conductance reached the maximum value at 10:00 a.m. and thereafter decreased rapidly at around noon with high evaporative demand to corn canopy. This shows the midday stomatal closure was caused by excessive water stress to corn canopy in the crop development stage. Thus, the proposed method with ABA application is useful for evaluation of temporal changes in transpiration rate and stomatal conductance, and hence, can detect the plant water stress.

Varietal differences in the chlorogenic acid, anthocyanin, soluble sugar, organic acid, and amino acid concentrations of eggplant fruit

Summary Eggplant (Solanum melongena L.) is an important crop in Japan, with a long history of cultivation. Although many eggplant cultivars and lines have been developed, their nutrient concentrations, including phenolic compounds, have not been investigated in detail. In the present study, we investigated varietal differences in the concentrations of taste (e.g., soluble sugars, organic acids, and amino acids) and functional (e.g., chlorogenic acid, anthocyanins, and amino acids) compounds in eggplant fruit using 34 cultivars and lines with diverse growth habits, fruit shapes, sizes, and colours. The concentrations of taste and functional compounds differed among cultivars and lines. Variations in chlorogenic acid [0.1 – 2.5 mg g–1 fresh weight (FW)] and anthocyanin (0.0 – 0.4 A532 units g–1 FW) concentrations were greater than those of soluble sugars (e.g., sucrose, 0.5 – 1.7 mg g–1 FW; glucose, 7.6 – 13.7 mg g–1 FW; fructose, 6.2 – 15.0 mg g–1 FW) and organic acids (e.g., citric acid, 0.07 – 0.21 mg g–1 FW; malic acid, 0.9 – 1.9 mg g–1 FW). We also found that the coefficient of variation in amino acid concentrations varied with amino acid. Glutamine (27.4 – 135.8 mg 100 g–1 FW) and arginine (4.5 – 23.1 mg 100 g–1 FW) had the largest variation between varieties. These results indicate the importance of cultivar selection to optimise the concentrations of ingredients and will contribute to improvements in the functionality of eggplant through breeding.