MATERIALS AND METHODS

The study was conducted in the nursery of the Faculty of Forestry, University of Putra Malaysia between May to August 2006. Uniform twenty five plants of Asplenium nidus were transplanted in pots (one plant in each pots) filled with potting mixture of coconut peat, loam and sand (3:1:1 v/v). Water stress treatments were initiated three weeks after transplanting (appearance of new fronds) conducting according Chang et al. (1995). The plants were subjected to five treatments with five replicates. The water regime treatments were well-watered (control) that were watered daily, moderate stress (T₁) watered once every three days, severe stress (T₂) watered once every seven days, highly severe drought (T₃) watered once every fourteen days and suspended without water or any treatment (T₄). Following are the definition of treatments:

Data collection: Once water stress progress, measurement of growth parameters including number of fronds, fronds length and frond width, frond area per plant as well as shoot and root per weight were measured every weeks while transpiration rate and chlorophyll content in the fronds one week before harvest.

Total frond area of Asplenium nidus was measured using LI-3100 Frond Area Meter (Lincoln NE, USA) after dismantling the pots and after transpiration rate and chlorophyll rate were measured.

Transpiration rate of three plants per treatment was measured during the late morning (9.00 to 12.00 am) using A LICOR 1600 steady state porometer (Lincoln NE, USA).

Chlorophyll content measurements of three fronds were conducted during the late morning (9.00 to 12.00 am) using Chlorophyll Meter (Minolta model SPAD-502). Statistical analysis was performed using statistical software. The one-way Analysis of Variances (ANOVA) was used to compare the means of more than two different estimates of population variance from the data.

Turkey’s Test was employed to detect significant differences among and between the treatments at the 0.05 α level.

RESULTS

Growth parameters i.e. fronds number per plant, frond length, frond width and frond area as well as dry weight of plants were measured after sixteen weeks of treatments.

The results are discussed as with the help of Table 1. Total frond length of Asplenium nidus was the highest in T₃ (110.64 cm) followed by control (99.99 cm), then T₁ (98.06 cm), T₂ (79.44 cm) and the lowest T₄ (27.74 cm). Statistically analysis showed the total frond length for T₄ was statistically lowered compared to other treatment. This indicates that lack of water suppressed the growth of the plant but still survived despite 16 weeks without watering.

Mean total frond width was the highest in control (27.4 cm), followed by T₃ (27.02 cm), T₁ (26.78 cm), T₂ (21.28 cm) and T₄ (8.78 cm). Total frond width for T₄ was statistically lower compared to other treatments.

Mean total frond area was the highest in control (697.28 cm²), followed by T₁ (644.27cm²), T₃ (627.98cm²), T₂ (510.44 cm²) and T₄ (263.39cm²). Total frond area for T₄ was statistically lower compared to other treatments.

Total number of fronds were the same for control (78) and T₁ (78) followed by T₃ (75), then T₂ (73) and the lowest T₄ (66). The analysis showed the total number of fronds for T₄ was statistically lowered compared to other treatment. This indicates that a lack of water will suppressed the growth of the plant but still survived despite sixteen weeks without watering.

Treatment T₁ had the highest total frond dry weight (12.6 g) followed by control (12.03 g), T₃ (11.28 g), T₂ (11.23 g) and lastly T₄ (5.04 g). Mean frond dry weight was statistically higher compared to T₄.

Table 1:	Mean and standard deviation (in bracket) of growth parameters to various water stress treatments
*Values followed by the same letter(s) are not statistically significant at the 0.05 alpha levels

Mean root dry weight for the treatment were 52.80, 38.99, 36.9, 29.69 and 28.22 g for control, T₃, T₁, T₂ and T₄ respectively. Mean root dry weight for control was the highest while T₄ was the lowest. Under water stress condition plants grew more to roots compare to shoots. Asplenium nidus has fiber root systems. Roots developing from the short stem grow into the decaying debris and with time, the entire mass becomes a sponge with soaks up an enormous amount of water after each period of rain. This mass of decaying matter thus supplies the fern with nutrients and water.

Root shoot ratio indicates the allocation root biomass with regard to shoot. Root shoot ratio was the highest is T₄ (6.73), followed by control (4.5), T₃ (4.07), T₁ (4.5) and T₂ (3.18). The severe water restriction had caused the plant to focus more on the root so that water can be absorbed by the plants.

The total dry matter production was the highest for control (64.83 g), (14.56 g) greater than T₄ (33.26 g) than followed by T₃ (50.27 g), T₁ (49.51 g) and T₂ (40.92 g). In terms of partitioning of total dry matter production during the treatments, plants grown allocated more to roots compared to the leaves at all levels of water stress. Throughout the water stress treatments, better and good foliage was observed in control treatment. This showed that Asplenium nidus were able to survive and growth under high moisture condition. Asplenium nidus despite without having water for 16 weeks still survives. However the production of total dry matter was greatly reduced in the severe water stressed plants.

Transpiration rate for control, T₁, T₂, T₃ and T₄ were 38.04, 41.19, 33.25, 31.48 and 9.54 μg/cm²/sec, respectively. T₁ was statistically higher other then the other treatments except for control while transpiration rate for T₄ was significantly the lowest.

As regard to chlorophyll content, clearly indicate that withholding water for sixteen weeks had a lower content of chlorophyll (105.70 SPAD Unit) as compared to control plants. This decreasing was accompoined with some chlorosis symptoms, yellowish frond and soft, thinned fronds. On the other hand, irrigation of plants every 14 days (T₃) gave a highest content of chlorophyll followed by T₁ and T₂ as compared with control plants.

DISCUSSION

Asplenium nidus showed morphological and physiological responses to the different cyclical water stress. The plants under higher water stress showed lower frond length, frond width, total frond area and mean dry weight compared to control plants. The reduction in length is due to the reduction of cell expansion and elongation (Thomas et al., 1999) and also in the reduction in length of the growing zone (Durand, 1995). This finding is consistent with finding by Fedorenko et al. (1995) on Medicago minima var. minima.

Plants subjected to water stress will reallocate growth to the roots so that more roots will be available to absorb moisture. Furthermore, the shoots are also reduced in size hence causing an increase in the root/shoot ratio in the severe water stress plants. This result concurs with study conducted by Chang et al. (1995) on Mimosa strigillosa which indicate water stress plants had higher root to shoot ratio.

Asplenium nidus responded physiologically to the different water stress levels. As the water stress increases, the frond transpiration rate decreases due to closing stomata. (Naderikharaji et al. (2008); Zhang et al., 2009). Present investigation clearly indicates that severe water stress decreases the chlorophyll content, these results were agreement with finding of .

Even though Asplenium nidus were affected by cyclic water stress, this study also showed that this plant can also survived long period of without watering such as in this study for sixteen weeks. This concur with Benzing (1990) which stated that epiphytic plants exhibit physiological and morphological traits that enable them to withstand intermittent drought. This characteristics may be due to different photosynthetic carbon flow pathway such as crassulacean acid metabolism. A study by Ong et al. (1986) showed that two epiphytic tropical ferns Drymoglossum piloselloides and Pyrrosia longifolia are obligate CAM plants which are able to withstand water stress. However, this need further study on the nature of photosynthetic pathway for Asplenium nidus.

CONCLUSION

This study showed Asplenium nidus growth parameter were affected by water stress but can survive for a long period without water due to increasing fibrous root system. This plant has a very high survival rate because it is one of the epiphytes species that can continue to grow under the highly stress condition.