Changes in the growth of aerial parts depending on irrigation cycle
The leaf stalks of plants introduced to indoor vertical walls grow too long or outgrow the walls, and this phenomenon can be attributed to too low indoor light intensity or excessive moisture in the underground part of plants, which is known to reduce their ornamental values and growth (
Ro et al., 2003). The growth characteristics of each plant that was watered once per 1, 3, 5 and 7 days for 3 months. The plant length of
Peperomia clusiifolia watered at the intervals of 3 and 5 days was slightly longer than other treatment groups, but the results were not statistically significant (
Table 1). The number of leaves of
Peperomia clusiifolia watered at the interval of 7 days tended to be high, but not statistically significant. There was also no significant difference in chlorophyll content and leaf color between treatment groups (
Table 1). The plant length of
Ardisia pusilla ‘Variegata’ did not show any significant difference between irrigation cycles, which was similar to the results of
Jang et al. (2013). In terms of the number of leaves, the group watered at the interval of 5 days tended to be slightly low, but not statistically significant. No change in chlorophyll content and leaf color was observed.
The plant length of
Aglaonema ‘Siam-Aurora’ tended to show a slight increase depending on the cycle of irrigation, and the number of leaves at the irrigation cycle of 7 days slightly decreased, but not statistically significant. It was found that the shorter the cycle of irrigation, the higher the content of chlorophyll, and that the longer the cycle of irrigation, the the lower the content of chlorophyll (
Table 1).
Aglaonema did not show any significant difference in plant length and the number of leaves between irrigation cycles, and no change in the chlorophyll content and color of leaves was also observed.
Dieffenbachia ‘Marianne’ did not show any significant difference in plant length between irrigation cycles, but when the interval was long (7 days), the number of leaves was significantly reduced. This can be attributed to the increasing abscission of leaves caused by drying. In addition, the content of chlorophyll was relatively low at the irrigation cycle of 7 days, and in terms of the color of leaves,
Dieffenbachia ‘Marianne’ showed a decrease in the L value, an increase in the a value and a decrease in the b value, showing changes in the color of leaves such as a slight decrease in brightness, a decrease in the color of yellow and a slight increase in the color of red (
Table 1).
Choi and Kim (2014) reported that it is difficult to maintain the patterns and colors of leaves of
Epipremnum aureum under different conditions of indoor light intensity and humidity, but, in this study, the plant length of
Epipremnum aureum at short irrigation cycles tended to be slightly long. The differences, however, were not significant and there was also no significant difference in the number of leaves. Its chlorophyll content and leaf color also did not show any significant difference (
Table 1). The plant length and the number of leaves of
Hedera helix at the irrigation cycle of 5 days slightly increased. The content of chlorophyll at the irrigation cycle of 3 days slightly increased, but not statistically significant. There was also no significant difference in the color of leaves (
Table 1).
Changes in the photosynthetic activity and stomatal conductance of foliage plants depending on the cycle of irrigation were analyzed (
Figs 1 and
2). There was no difference in the photosynthetic activity of
Aglaonema between treatment groups, and the stomatal conductance tended to decrease as the cycle of irrigation increased (
Fig. 2A).
Dieffenbachia ‘Marianne’ showed a slight increase in photosynthetic activity when it was watered at the interval of 7 days, but not statistically significant, and there was also no difference in stomatal conductance (
Fig. 2D).
Aglaonema ‘Siam-Aurora’ showed a slight increase in photosynthetic activity at the irrigation cycles of 5 and 7 days (
Fig. 1B), and its stomatal conductance was very low at the interval of 1 day, and high at the intervals of 3, 5 and 7 days (
Fig. 2B). In the case of
Peperomia clusiifolia, the amount of photosynthesis was higher than the amount of respiration only at the irrigation cycle of 3 days (
Fig. 1G), but other treatment groups showed a higher amount of respiration than photosynthesis. The stomatal conductance of
Peperomia clusiifolia at the irrigation cycle of 3 days was also high (
Fig. 2G).
Hedera helix showed a slightly high photosynthetic activity and a high stomatal conductance at the irrigation cycles of 5 and 7 days (
Figs. 1F and
2F).
Ardisia pusilla ‘Variegata’ showed a slightly high photosynthetic activity and stomatal conductance when it was watered everyday and once per 5 days, while
Epipremnum aureum showed a relatively high photosynthetic activity and stomatal conductance only when it was watered once per 3 days (
Figs. 1 and
2).
The cyle of irrigation showed different effects on the growth of the aerial part of foliage plants in the indoor bio-wall system depending on the species of foliage plants, but the low photosynthetic activity of plants caused by a low light intensity in indoor environments seemed to lower the vegetative growth of plants. Improper fertilization and irrigation in a low vegetative state have a negative impact on the growth of plants. For this reason, it will be more necessary to conduct additional studies under different fertilization conditions for efficient and sustainable management for indoor bio-wall systems.
Changes in the characteristics of underground parts depending on irrigation cycle
The root activity of testing plants depending on the cycle of irrigation was examined. While
Peperomia clusiifolia showed a high root activity when it was watered at the interval of 7 days (
Fig. 3F),
Aglaonema did not show any difference between treatment groups.
Ardisia pusilla ‘Variegata’ showed a higher root activity at the irrigation cycles of 3 and 7 days than at the irrigation cycle of 1 day (
Fig. 3C), and
Dieffenbachia ‘Marianne’ showed a higher root activity at long irrigation cycles than at the cycle of 1 day (
Fig. 3D).
Aglaonema ‘Siam-Aurora’ also showed a higher root activity at slightly long irrigation cycles than at the interval of 1 day, and
Epipremnum aureum watered at the interval of 3 days was found to be good for the activity of roots (
Fig. 3E).
The development of roots of
Peperomia clusiifolia at different irrigation cycles was measured, and was found to be accelerated at long irrigation cycles. The length of roots at the longest cycle of irrigation (7 days) was also the longest, and the fresh weight of roots at the irrigation cycles of 3 and 7 days was higher than at the interval of 1 day. These results indicate that a proper irrigation cycle for
Peperomia clusiifolia is 3 or 7 days, but considering that drying was also observed at the interval of 7 days, watering once per 3 days seems to be suitable for the plant (
Figs. 4G and
5G).
The total number of roots of
Ardisia pusilla ‘Variegata’ was not found to be significantly affected by the cycle of irrigation. Short roots were observed more in the treatment groups of short irrigation cycles, and the number of long roots was higher in the treatment groups of long irrigation cycles, indicating that the cycle of irrigation affects the development of roots. The length and fresh weight of roots were also high when the cycle of irrigation was 7 days (
Figs. 4C and
5C).
The total number of roots of
Aglaonema ‘Siam-Aurora’ rather decreased when it was watered at the interval of 7 days. The development of roots at the irrigation cycles of 1 and 3 days was different. Roots of 5 cm or shorter were observed more at the interval of 1 day, while roots of 10 cm or longer were observed more at the interval of 3 days. The fresh weight of roots at the irrigation cycle of 3 days was the highest, indicating that watering once per 3 days is suitable for the development of roots (
Fig. 5B). The root development patterns of
Aglaonema were also similar to those of
Aglaonema ‘Siam-Aurora’ but differences between treatment groups were not significant.
The total number of roots of
Dieffenbachia ‘Marianne’ at the irrigation cycle of 3 days was about 2 times higher than other treatment groups, and the development of roots at the intervals of 1 and 7 days was relatively lower. No significant difference was observed in the length of roots between the 3 treatment groups. The fresh weight of roots at the intervals of 1, 3 and 7 days was 2.0, 3.9 and 1.6 g respectively and the fresh weight was found to be the highest at the irrigation cycle of 3 days, indicating that watering once per 3 days is suitable for the development of roots (
Figs. 4D and
5D).
In the case of
Epipremnum aureum, the total number of roots at the irrigation cycles of 3 and 7 days was higher than that at the interval of 1 day, and the length of roots was also longer at the intervals of 3 and 7 days. In addition, compared to the fresh weight of roots at the interval of 1 day (2.5 g), watering once per 3 and 7 days (4.1 and 3.8 g respectively) was found to be suitable for the development of roots (
Fig. 5E).
The development of roots of
Hedera helix at different irrigation cycles was measured, short roots tended to be observed more at the irrigation cycles of 3 and 7 days, but there was no significant difference in the total number of roots. In terms of the length of roots, long roots were observed more when it was watered at the interval of 7 days, and the fresh weight of roots also tended to be slightly higher at the interval of 7 days (
Fig. 5F).
The growth characteristics of the underground part of the 7 foliage plants, introduced to an indoor vertical bio-wall system that used a bottom watering method, at different irrigation cycles were examined, and the overall growth of the underground part of the plants watered at the interval of 3 days was found to be good. Although irrigation cycles need to be managed differently depending on the species of plants, it seems that watering once per 3 and 5 days has a positive impact on changes in the aerial part of plants and the development of their underground part.