Electrical impedance analysis was conducted using 4-year-old potted Satsuma mandarin (cv. Toyofuku-wase) trees to measure tree water status. Two electrodes were inserted to the tee trunk 3 cm apart and 3 mm in depth, and then capacitance and resistance at four frequencies of alternative current (0.1, 1, 10 and 100 kHz) were detected using an LCR meter which was connected to the electrodes. During drought treatments performed in June 2005 and October 2005, transpiration and photosynthesis rates in the leaves and the changes of the tree trunk diameter were simultaneously measured using a portable photosynthesis system and dendrometers, respectively. Resistance at the four frequencies increased as the duration of the drought treatment was longer, on the contrary capacitance, transpiration rate and photosynthesis rate decreased. Tree trunk diameter has daily fluctuated and then dramatically shrank at day 0 in June treatment and day 2 in October treatment. Relationship between parameters of the electrical impedance and other water related parameters was discussed.
The current definition of the evaporative cooling efficiency (ηc) can be applied only for a greenhouse with a wet pad-fan system, in which no sensible or latent heat is added to the air during the cooling process. However, ηc of the wet pad-fan system cannot be applied for a greenhouse with a fogging system, in which sensible and latent heat are added to the air during the cooling process. The purpose of this study is to define ηc correctly for a greenhouse with a fogging system and to describe the fogging process. For this purpose, the concept of un-cooled air was developed, which is the greenhouse air gaining sensible and latent heat from the cover, the floor and the plant surfaces. The dry bulb temperature of un-cooled air (Tu) was defined based on the sensible heat added to the air. Sensible heat strongly depends on the convective heat transfer coefficients in the greenhouse (i.e., between the air and the cover, the floor, the plant surfaces). Therefore, different relations expressing each coefficient were examined. ηc was defined using Tu and the measured values of the dry and wet bulb temperatures in the greenhouse with fog. Values of Tu and ηc were estimated in a greenhouse located in the Tokyo area, Japan, and cooled by intermittent fogging on a hot summer day. The results show that value of Tu was found to be not very sensitive to the selection of convective coefficients, with maximum relative error of 4% observed using different expressions for the convective coefficients from the literature. The assumption that the fogging process takes place in the greenhouse air at a constant wet bulb temperature is practically acceptable.
The effect of light quality, light intensity and photoperiod on stem elongation of chrysanthemum was studied using an image processing technique. The plant stem and internode elongation was higher in the dark than in the light, and the growth of chrysanthemum was promoted in dark period. The effect of light quality was more significant than that of light intensity and photoperiod on the growth of chrysanthemum. The growth of chrysanthemum was inhibited under blue light, and the relative elongation rate of internodes decreased with increasing intensity of blue light and irradiation duration. Chrysanthemum growth is regulated by the light condition during irradiation. This system is useful to build a model to describe the stem elongation relative to light condition for chrysanthemum, and to suggest effective production method with substitutes for chemical growth regulators.
Donor-receiver bioassay was designed to eliminate the effects of the competitive interference for resources from allelopathic effects. Seeds of cress (Lepidium sativum), lettuce (Lactuca sativa), timothy (Phleum pratense) or ryegrass (Lolium multiflorum) were incubated with 4-day-old buckwheat (Fagopyrum esculentum) seedlings for 3 days in Petri dishes under controlled laboratory condition. The growth of cress, lettuce, timothy and ryegrass seedlings was inhibited by the presence of buckwheat seedlings, and increasing the number of buckwheat seedlings increased the growth inhibition. One inhibiting substance was found in the culture solution in which buckwheat seedlings were hydroponically grown for 10 days. These results suggest that buckwheat seedlings may inhibit the neighboring plant growth due to exudation of allelopathic substance into the neighboring environment. Thus, the inhibitory effect of buckwheat was probably caused by allelopathic chemical reactions.
Phytotoxic effects of root exudates of mat-rush (Lomandra longifolia Labill.), which accumulated in the soil by the continuous mat-rush cultivation were evaluated for the growth of lettuce (Lactuca sativa L.) and mat-rush seedlings. A soil with continuous mat-rush cultivation for over three years was used for this study. A 210 ml of soil was amended with the different fineness of 1.53 g activated charcoals (AC): coarse-AC and fine-AC. The soils without the AC amendment (non-AC) and without previous mat-rush cultivations (control) were also prepared. The stem length, root length, and fresh shoot and root weight of lettuce grown in the non-AC soil were reduced to 67, 24 and 55% of those found in the control, respectively. The soil amended with the coarse and fine AC improved these growth parameters. The growth reduction of plants grown in the non-AC soil may likely appear to be related to allelochemicals exuded from the mat-rush root because there were negligible changes in soil physical and chemical properties between the non-AC and AC amended soils. The detrimental effects of soils used for a continuous mat-rush cultivation on following plant growth can be ameliorated by the addition of AC to the soil.
We developed a chlorophyll fluorescence imaging system that is capable of capturing chlorophyll fluorescence intensity images (F683 and F730) of plant leaves at liquid nitrogen temperature (77 K). F683 is mainly emitted from photosystem (PS) II and light harvesting complex (LHC) II and F730 is mainly emitted from PS I and LHC I, therefore the ratio image of F730 to F683 (i.e. F730/F683) indicates the relative changes in the status of the light energy utilization in the photosystems, e.g. state transition, and can be used to produce maps of relative levels of light stress over a leaf's surface. Using this system, we assessed the heterogeneously distributed light stresses over kidney bean leaf surfaces, caused by light irradiance and representative photosynthesis inhibitor (DCMU and DTT) infiltration treatments. As a result, F730/F683 increased in the light-irradiated leaf areas but remained at a lower value in the DCMU- and DTT-infiltrated leaf areas. These results prove that this 77 K chlorophyll fluorescence imaging system is capable of assessing the light stress that is heterogeneously distributed over a leaf surface.
The validity of a developed control logic for operation a fog cooling system was verified in a naturally ventilated greenhouse at durations of fog cooling system operation cycles (tf+s) of 60, 120 and 240 s, then at constant duration of fog cooling system operation (tf) of 35 s. The capabilities of the proposed control logic were evaluated from the viewpoint of changes in dry bulb (or air) temperature (Tdi) and relative humidity (RHi) inside the greenhouse. Even when the tf+s was changed, the control logic was capable of controlling the operation of the fog cooling system with appropriate tf. Short tf+s would contribute to minimize not only changes in Tdi and RHi, but also foliage wetting. At a constant tf, the control logic could lengthen duration of fog cooling system stand-by (ts) that also prevented excessive fogging when the potential evaporation of sprayed water inside the greenhouse was low. The proposed control logic can be implemented for controlling the operation of a fog cooling system not only at constant tf but also at constant ts.
Cavitation causes embolisms followed by a considerable decrease in xylem conductance: embolisms pose a serious obstacle to the continued uptake of water. Assuming that acoustic emissions (AEs) with high similarity would be generated from cavitation at the same element when refilling occurred, this study investigated the generation of such an AE in a rubber tree's leaf vein. Cross-correlation analyses between the filtered AE waveforms showed the existence of AEs with a cross-correlation coefficient greater than 0.97. That result indicated that some AEs came from the same element in a leaf vein where cavitation and refilling occurred repeatedly. Assuming that a pair of AEs with a high cross-correlation coefficient corresponded to the same embolism, the relationship between daily diameter change (DDC) and number of embolisms showed a better linear relation than that between DDC and total events of AE.
The means of inoculation with arbuscular mycorrhizal (AM) fungi [Gigaspora margarita, Glomus fasciculatum, Gl. mosseae, Gl. sp. R10, Gl. aggregatum] were investigated in four strawberry (Fragaria × ananassa Duch., cv. Tochiotome, Toyonoka, Nyoho and Nohime) cultivars in Japan. Twelve weeks after inoculation, growth parameters were measured. Number of leaves, leaf area, number of roots, dry weights of leaves and roots showed significantly greater values in Glomus fasciculatum plot than in non-inoculated plot in ‘Tochiotome’ and ‘Toyonoka’, in Gl. mosseae plot of ‘Nyoho’ and ‘Nohime’. AM fungal infection occurred in all combinations of strawberry cultivars and AM fungal species, though the infection level differed among the combinations. In this case, Glomus fasciculatum had high affinity with ‘Tochiotome’ and ‘Toyonoka’, and Gl. mosseae with ‘Nyoho’ and ‘Nohime’.