Responses of Platycerium Coronarium (Koenig.) Dev and Platycerium Bifurcatum (Cav.) c. chr. to Light and Water Stress in Nursery Enviroment

Environmental changes have enormous effects especially on plants physiology and growth. These changes will have significant impact on the growth and survival of plants in the changing of future climates. Canopy plants especially epiphytes which live in the forest canopy play an important role to their surroundings. Thus, this study was conducted to evaluate the growth and physiological response of Platycerium coronarium and Platycerium bifurcatum towards light and water stress. In light stress study, both species were grown under four treatments namely 20 μmol m-2s-1 (T1), 70 μmol m-2s-1 (T2), 200 μmol m-2s-1 (T3) and 1500 μmol m-2s-1 (T4). In water stress study, they were divided into five treatments which were watered once everyday (T1), watered to field capacity (T2), watered once in two weeks (T3), watered once in three weeks (T4) and not watered (T5). Growth responses were evaluated through the leaf length measurement, leaf area, sporotrophophyll weight, cover leaves weight, total dry weight and total leaf water content. Physiological responses were quantified by leaf gas exchange, chlorophyll fluorescence and whole plant transpiration rate. All measurements were carried out weekly for twelve weeks. Two experiments were conducted to determine whether both species were CAM plants by determining their leaf acidity and carbon 13 isotope (δ13 C) ratio. In light stress treatment, leaf length and leaf area of P. coronarium, was statistically different between treatments (p≤0.05). However, T1 had the lowest value in all growth parameters. Lowest light intensity reduces growth for this species. For P. bifurcatum, total leaf length was significantly different between treatments (p≤0.05). Higher light intensity treatment causes reduction in leaf length for this species. All leaf gas exchange parameters for P. coronarium were statistically different except for Ci (p≤0.05). However, highest light intensity (T4) reduces the Anet, D and WUE value. All treatments also had the value of Fv/Fm of healthy plant in the range from 0.82 to 0.84. P. coronarium were moderately affected in its physiological activity. For P. bifurcatum, significant differences were found for Anet, EL and WUE (p≤0.05). Highest light intensity (T4) showed lowest value in Anet. Fv/Fm in T3 and T4 were below 0.8 indicating that there was a sign of stress. P. bifurcatum was affected under high light intensity. Both species had no higher accumulation of acids at dusk compared to early morning and δ13 C showed both species are C3 plant thus suggesting that both species did not initiate CAM. In water stress treatments, total leaf length and leaf water content of P. coronarium, were significantly different for all treatments (p≤0.05). While for P. bifurcatum,significant differences were found in total leaf length, leaf area and leaf water content (p≤0.05). Higher water stress treatment (T5) reduced growth performance of both species. Anet, gs, EL, D and WUE were significantly different in all treatments of P. coronarium (p≤0.05). For P. bifurcatum, significant differences were found in Anet, gs, EL and D (p≤0.05). T5 reduced Anet,. gs and EL, however its Fv/Fm value was above 0.8 in both species. Both species was moderately affected by water stress. Higher acid accumulation was observed in early morning compared to dusk samples and all treatments were found to have C3 photosynthesis for both species. Therefore this indicates that water stress did not alter physiological pathway for both species

Epiphytic plants responses to light and water stress.

Epiphytes are plants susceptible to the current climate change due to continuous exposure of environmental changes. In this study, we review the epiphytes responses to fluctuations in their surrounding environments. Abiotic factors such as light and water are the important contributors towards the epiphytes growth. Epiphytes might suffer from environmental stresses namely high light intensity and water deficit, affecting its growth and physiological attributes. Epiphytes use several mechanisms to counter aforementioned problems and one of it is through changes of physiological pathways. Some of the epiphytes use Crassulacean Acid Metabolism (CAM) as protection system for survival in severe environments. Future studies should include more approaches used by this plant as defense mechanisms to such stresses and more studies on leaf anatomy, leaf structure and variations in biochemical components for further understanding of the mechanisms involved

Stable isotope ratio (δ13C) responses of Platycerium bifurcatum at different light intensity levels

Platycerium bifurcatum is an epiphyte known as one of the common plant used for its ornamental value. Living in such environment, they were always exposed to several types of stresses such as water deficit and high light intensity. This plant is known as C3 plant and when exposed to stress environment, it might change its photosynthetic pathway to survive in harsh environment. For determination of the photosynthetic pathway used by plants, isotope screening technique was widely used. Therefore, the objective of this work was to classify the photosynthetic pathway type of P. bifurcatum through investigation of the carbon 13 isotope (δ13C) composition after they were subjected to different levels of light stress. In this study, P. bifurcatum were grown under four different Photosynthetic Active Radiation (PAR) levels which were 20 μm/m2s (T1), 70 μm/m2s (T2), 200 μm/m2s (T3) and 1500 μm/m2s (T4). All measurements were carried out after plants were subjected to 12 weeks of light stress. Two plants from each treatment were selected where two leaves from each plant were used as samples. Leaf samples were dried at 600oC for 48 hr and grounded. Plant responses were measured through its carbon isotope composition by using isotope ratio mass spectrometer. Results showed that there was no significant difference observed for both day and night samples. However, it was confirmed that all treatments were found to have C3photosynthesis in both day and night with T1 value of -27.04 ‰, T2 of -28.33 ‰, T3 of -27.82 ‰ and T4 of -25.61 ‰ at day and T1 with -28.11 ‰, T2 with -28.02 ‰, T3 with -28.50 ‰ and T4 with -27.01 ‰ at night. The results suggested that light stress does not alter the photosynthetic pathway of P.bifurcatum

Street orientation and side of the street greatly influence the microclimatic benefits street trees can provide in summer

Maintaining human thermal comfort (HTC) is essential for pedestrians because people outside can be more susceptible to heat stress and heat stroke. Modification of street microclimates using tree canopy cover can provide important benefits to pedestrians, but how beneficial and under what circumstances is not clear. On sunny summer days, microclimatic measures were made in residential streets with low and high percentages of tree canopy cover in Melbourne, Australia. Streets with east-west (E-W) and streets with north-south (N-S) orientation were repeatedly measured for air temperature, relative humidity, wind speed, solar radiation, and mean radiant temperature on both sides of the street between early morning and midafternoon. Physiological equivalent temperature was estimated to indicate HTC throughout the day. In streets with high-percentage canopy cover, air temperature, relative humidity, solar radiation, and mean radiant temperature were significantly lower than in streets with low-percentage canopy cover. The reductions in air temperature under high-percentage canopy cover were greater for E-W streets (2.1°C) than for N-S streets (0.9°C). For N-S streets, air temperature, mean radiant temperature, and solar radiation were greater on the east pavement in the early morning and greatest on the west pavement in the midafternoon. The midday thermal benefits are restricted to E-W streets, which are oriented in the same direction as the summer sun's zenith. High-percentage canopy cover reduced wind speeds but not enough to offset the other microclimate benefits. These findings can assist urban planners in designing street tree landscapes for optimal HTC in summer, especially in areas of high pedestrian density

Alley-cropping system can boost arthropod biodiversity and ecosystem functions in oil palm plantations

Oil palm (Elaeis guineensis) is among the fastest expanding crops, due to high global demand for vegetable oils. Large areas of forest are converted into oil palm plantation to meet the market demand in producing countries which causes rapid decline in tropical biodiversity, including arthropods. The alley-cropping system has the potential to promote faunal biodiversity, related ecosystem services and food security in agricultural landscapes. In alley-cropping, a main crop is intercropped with a secondary crop (often a food crop), secondary crops are cultivated in the alleys in between the main crop. We compared arthropod taxonomic richness, arthropod predators and decomposers between five alley-cropping treatments (pineapple, bamboo, black pepper, cacao, bactris), where oil palm is intercropped with another species. In addition, we sampled two control treatments: monoculture oil palm, aged seven and 15 years old. A total of 50,155 arthropod individuals were recorded using pitfall trap sampling, representing 19 orders and 28 families. Fourteen orders belonging to sub-phylum Insecta, three orders from Arachnida (Araneae; Acarinae; Scorpiones) and two orders from Myriapoda (Chordeumatida; Geophilomorpha). We detected an increase in beta-diversity of oil palm production landscape. Specifically, we found that the number of arthropod orders, families and abundance were significantly greater in alley-cropping farming plots than those in monoculture plots. In addition, alley-cropping treatments contained larger numbers of predators and decomposers. Our findings suggest that the alley-cropping system can become a key management strategy to improve biodiversity and ecosystem functions within oil palm production landscapes

The importance of street trees for human thermal comfort in a warming climate

© 2015 Dr. Ruzana Adibah Mohd SanusiTree microclimate and human thermal comfort are important for urban residents in summer as trees can improve street microclimate for pedestrians through shade and transpiration. It is important to know how trees provide microclimate and human thermal benefits and in what circumstances they provide the most benefit to the urban environment. This thesis provides greater understanding as to the influence of extreme heat weather events on street microclimate and human thermal comfort. The assessment of street microclimate modification under the trees was done in all studies through measurements of air temperature, relative humidity, solar radiation, Mean Radiant Temperature (Tmrt) and wind speed. The human-biometeorological index of Physiological Equivalent Temperature (PET) was used for the assessment of human thermal comfort. Cooling benefits from trees depend upon the percentage of canopy cover, street orientation, the side of the street being assessed and time of the day. The air temperature in treed streets could be 2.1°C cooler, and the human thermal comfort perceived by pedestrians could be 4.6°C cooler in high-canopy cover streets than in low-canopy cover streets. These microclimate benefits were greatly influenced by the street orientation due to the influence of sun’s zenith. In addition, the differences in cooling benefit amongst three different tree species were primarily determined by the difference in the cumulative shade provided by leaves, branches and twigs are important in determining the microclimate and human thermal comfort benefits from trees. These differences were captured and quantified using digital full frame photography from which Plant Canopy Area Index (PCAI) was estimated underneath individual tree canopies. Platanus x acerifolia trees were the most prone to leaf loss due to a heat wave event compared to Ulmus procera and Eucalyptus scoparia with 44% of the canopy lost. This canopy loss of P. acerifolia due to the heat wave event also changed the cooling benefits of the P. acerifolia trees and lead to a PET benefit reduction from 6.6°C to 1.6°C after the heat wave. This thesis has been successful in identifying and quantifying some of the key factors that influence street microclimate and human thermal comfort benefits provided by trees. The research outcomes from this thesis contribute to the knowledge and future direction of urban forest planning and management in particular for the provision of ecosystem services provided by street trees in the form of microclimate and human thermal comfort benefits

Leaf chlorophyll fluorescence and gas exchange response to different light levels in Platycerium bifurcatum

Problem statement: Platycerium bifurcatum (Cav.) C. Chr. is epiphytes which lives in forest canopy and commonly used for its ornamental value. In these environments, they were always exposed to many types of stresses such as high light intensity. Light intensity plays an important role in affecting plant's physiological performance. Therefore, the purpose of this study was to investigate physiological responses of P. bifurcatum to light stress. Approach: In this study, P. bifurcatum were grown under four different Photosynthetic Active Radiation (PAR) levels which were 20 μmol m -2 sec -1 (T1), 70 μmol m -2 sec -1 (T2), 200 μmol m -2 sec -1 (T3) and 1500 μmol m-2 sec -1 (T4). Leaf gas exchange and chlorophyll fluorescence were used to evaluate the stress response of various levels of light intensity. All measurements were carried out on weekly basis for twelve weeks. Results: Results showed that A net value of T1, T2 and T3 in the range near to the average A net value for most epiphytes. Conversely, T4 showed lower value in A net with 1.797 μmol CO 2 m -2 sec -1. Fv/Fm ratio in T3 and T4 were below 0.8 indicates that there was a sign of stress occurred in these treatments. However A net of T3 was not affected although there have been event of photoinhibition observed in the treatment. On the contrary, T4 was fully affected by high light intensity as there was a reduction of Fv/Fm ratio and also A net. T1 and T2 of A net and Fv/Fm ratio values ranged of unstressed plants after subjected to light treatment. Conclusion: Measurement of leaf chlorophyll fluorescence and gas exchange are useful to detection of light stress in P. bifurcatum. Different levels of light intensity were significantly affecting physiological attributes of P. bifurcatum