Seasonal changes in the photosynthetic capacity and leaf structure ofFatsia japonicaleaves grown in a shadehouse

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Abstract
The ornamental plant Fatsia japonica Decne & Planch is a cold-hardy species widely utilized in outdoor gardening in temperate regions. Seasonal changes in photosynthetic capacity, leaf anatomy and ultrastructure and the content of nitrogen, chlorophyll and dry matter have been studied in mature leaves of F. japonica grown in a shadehouse in three seasons of the year: autumn, winter and spring. Although there were no differences in leaf thickness between leaves sampled in the three seasons, winter samples had a meso- phyll cell cross-sectional area about 20% lower than those of autumn or spring. This led to a higher total value of the perimeter of mesophyll cell walls per unit length of abaxial epidemis (Ames/A) in winter samples. Specific leaf dry weight (SLDW) and relative dry weight both increased consistently in winter samples suggesting a high deposition of starch in the chloroplasts. Starch granules represented almost 50% of total chloroplast sectional area. In winter samples the number of chloroplast sections per unit of cell wall length was about 20% lower than in the two other seasons. However, the number of chloroplast sections per unit length of abaxial epidermis (chloroplast number) was fairly similar in the three seasons. The higher Ames/A from winter samples explains the constancy in chloroplast number throughout the three seasons. In spite of high accumulation of starch in winter samples, no significant differences were observed in the photosynthetic capacity per unit of leaf area between leaves sampled in the three seasons. However, the photosynthetic capacity per unit of nitrogen content in the winter samples was about 20% and 30% lower, respectively, than in autumn and spring samples; furthermore, this parameter was negatively correlated with the SLDW of corresponding leaves.