カキ‘平核無’樹の推定純光合成速度および果実生産性との関係

Abstract

Relationship between canopy net photosynthesis and fruit production was analyzed with 40 Japanese persimmon 'Hiratanenashi' trees grown under current common practices. Canopy net photosynthetic rates were estimated by using a multiple regression analysis of leaf net photosynthetic rates (Pn) and our recent models (Yamamoto and Hata, 1991). These models take into consideration seasonal changes in form and structure of fruit trees and the distribution of radiation flux at leaf surfaces in fruit tree crowns (Yamamoto, 1988).1. The Pn distribution plot against most single factors exhibit widely scattered patterns because the measurements were taken under field conditions. However, significant curves were obtained when Pn was plotted against several meteorological and edaphic factors and leaf characteristics and activities. Light-saturation value of Pn (about 21 mgCO2•dm-2•hr-1) was about 1, 400 μpmol•m-2•sec-1 of photosynthetic photon flux density (PPFD)2. The coefficient of variables of the multiple regression was 80% when all factors except dark respiration rate, as independent variables, were considered. It was 76% when meteorological elements, soil water potential, time factors, and their powers were included. The latter regression analysis gave a practical formula for estimates of Pn. Furthermore, the coefficient of variables was 64% when only PPFD and its powers were used, suggesting that PPFD is the dominating factor in Pn values under field conditions.3. On 22 July, a bright sunny day, when the leaf area had become maximum, the daily total amount of net photosythetic product for 13 hr (DTPP) and the daily mean net photosynthetic rate (DMPn) were calculated for each tree. The above mentioned multiple regression formula was applied, incorporating the total leaf areas, hourly distribution of leaf area frequency of leaf irradiance. The estimated DTPP which is closely related to total leaf number (TLN) ranged from 390 to 1, 400 gCO2•tree-1•(13 hr)-1. The estimated DMPn varied slightly about a mean of 15.5 mgCO2•dm-2hr-1. DTPP became large at about 2.3 in leaf area index (LAI, ) and was negatively correlated to daily mean PPFD at leaf surface (DMPPFD). DMPn was negatively correlated to both LAIc and mean leaf area density (MLAD). Therefore, it was suggested that tree crown having too large DTPP had dark leaf irradiance and low DMPn.4. The mean yield of fruit per tree (MYF) for 2 years was low in trees having DTPP greater than 770 gCO2•tree-1•(13 hr)-1. There was a negative correlation between DTPP and mean peel color (MPC) for 2 years. Furthermore, many trees in which DMPn were around 15.5 mgCO2•dm-2 ? hr-1 developed a large number of flower buds per tree (NFB) and had high MYF values.5. Relative distribution ratio of photosynthetic product into fruit (RDR), equivalent to MYF/DTPP, decreased with increasing TLN and tree vigor. RDR was positively correlated to DMPPFD, MNF, MYF and MPC.6. Three dimensional pillar-shaped graphs show extremely low yields of fruit under conditions of low RDR, which correlates with low leaf irradiance, low net photosynthetic rate and few flower buds on account of excessive vigor.