Half or whole root systems of micropropagated `Gala' apple (Malus ×domestica Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO3- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO3- concentration, but both significantly reduced NO3- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO3- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO3- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO3- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO3- concentration. This correlation may simply reflect the fact that water stress affected both NO3- concentration in roots and leaf gas exchange in the same direction.
Jun Ying Zhao, Li Jun Wang, Pei Ge Fan, Zhan Wu Dai and Shao Hua Li
Panpan Meng, Ying Ge, Qianjin Cao, Jie Chang, Peng Pan, Chi Liu, Yijun Lu and Scott X. Chang
Lycoris species have appealing characteristics for potting plants, cut flowers, and landscaping decorations, including attractive foliage, which is very similar to that of cymbidium. Lycoris species have been extensively propagated and marketed in Asia. Understanding the response of Lycoris spp. to irradiance intensity will help the horticultural industry improve the production of potting plants of those species. We studied the responses of photosynthesis, growth, and biomass allocation of potted Lycoris spp. (L. chinensis, L. longituba, and L. sprengeri) bulbs grown under three levels of irradiance, i.e., 100%, 70%, and 30% full sunlight. We found that in terms of biomass production L. chinensis can be cultivated under all levels of irradiance studied from full to 30% sunlight. For L. longituba, high irradiance levels increased the rate of net photosynthesis. For both L. chinensis and L. longituba, the full sunlight treatment produced the most attractive plants characterized by shorter, wider, and darker green leaves, features that appeal to consumers. However, none of the growth traits of L. sprengeri were affected by the irradiance treatment over the entire experimental period. It can be concluded that potting plants of L. chinensis and L. longituba are best produced under full sunlight, whereas L. sprengeri can be produced under irradiance levels from 30% to full sunlight.