Research Article, J Plant Physiol Pathol Vol: 5 Issue: 2
Response of Photosynthetic Capacity to Soil Moisture in Xanthostemon chrysantus (F. Muell.) Benth.
*Corresponding Author : Ahmad Nazarudin MR
Forest Research Institute Malaysia (FRIM), 52109 Kepong, Selangor, Malaysia
E-mail: [email protected]
Received: March 30, 2017 Accepted: April 14, 2017 Published: April 20, 2017
Citation: Ahmad Nazarudin MR, Tsan FY (2017) Response of Photosynthetic Capacity to Soil Moisture in Xanthostemon chrysantus (F. Muell.) Benth. J Plant Physiol Pathol 5:2. doi: 10.4172/2329-955X.1000165
Response of Photosynthetic Capacity to Soil Moisture in Xanthostemon chrysantus (F. Muell.) Benth.
A study was carried out to investigate the physiological response of a landscape tree, Xanthostemon chrysantus (F. Muell.) Benth. planted at two urban sites in Kuala Lumpur. Photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs) and water use efficiency (WUE) at flushing, flowering and fruiting stages of the trees grown at Metropolitan Batu Park (MBP) and Pusat Bandar Manjalara (PBM) were recorded for a year during rainy and dry periods. Soil samples of both sites were also analysed for physical properties. Significant different in A, E, gs and WUE were observed at flushing stage of both rainy and dry periods. At flowering stage, significant different was noted in A for both periods, while variations only recorded among E and gs during dry period. Physiological traits at fruiting stage were similar at both periods for MBP and PBM. Trees at PBM had higher WUE at flushing during rainy and dry periods than those trees at MBP, showing higher capability of utilising water while reducing water lost through transpiration. The sandy loam soil of the study plots contains more than 67% of sand, reducing the moisture content, hence affecting photosynthetic capacity of the trees. Xanthostemon chrysantus however, can be considered as a hardy species because it can tolerate the harsh condition of the planting sites.
Keywords: Kuala Lumpur; Landscape; Urban forestry; Urban soil; Water use efficiency
Plant growth and development are closely associated to the internal and external influences. The internal factors include genetic makeup, photoassimilates and plant hormones. The external factors comprise of water, nutrients, temperature and light . In general, tree growth increases with availability of water and decreases with water shortage condition [2-4]. Under water shortage condition, reduced photosynthetic capacity was observed [5-7].
The ability of soil to retain moisture is crucial in plant growth. Soil moisture is influenced by the composition of silt, clay, organic matter and sand that forming the soil. Urban soil is often described to be highly disturbed, compacted, and of poor chemical and physical qualities [8-10]. Previous studies reported that the urban soil had other issues such as soil moisture availability [11,12] soil temperature  and soil aeration . Compaction alters the texture of the soil which leads to reduction of the soil moisture. As a consequence, the soil will not be able to provide sufficient water for plant growth. Parry et al.  stated that in tobacco plants, (Ribulose-1,5-bisphosphate carboxylase/oxygenase) RuBisCo activity, a key photosynthetic activity marker, gradually decreases with decreasing relative water content. A survey conducted for trees along Boston sidewalks found that a large number of trees did not survive their first two years and the average street tree lifespan in city neighbourhoods has been estimated to be only ten years . In other study by Nowak et al. , the average lifespan of the urban trees in Baltimore was found to be 15 years, with only 30% trees living past 15 years. These scenarios might be due to unfavourable planting site which includes the capability of the soil to retain moisture.
Urban trees are challenged with limited planting space, besides being infertile and compacted, hence limiting rooting space, reducing soil aeration and drainage [10,13,14]. The substance of the urban soil is also unpredictable as different soil types are placed together during land development. This condition will influence the soil texture and moisture content which eventually affects the physiological capacity of the trees. Thus, close monitoring on physiological performances such as photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs) and water use efficiency (WUE) of the urban trees is highly required.
Xanthostemon chrysantus (F. Muell.) Benth. belongs to the family Myrtaceae. It is commonly known as golden penda. This species is indigenous to tropical northern Australia, New Caledonia, New Guinea, Indonesia and the Philippines . It is a medium-sized tree which reaches 10-15 m in height in its natural environment, but smaller in cultivation. This species is usually planted in newly established urban sites; hence, it needs to be monitored to ensure the survival. Thus, the objective of the study was to investigate the influence of soil moisture on photosynthetic rate (A), transpiration rate (E) stomatal conductance (gs) and water use efficiency (WUE) of X. chrysantus planted in urban sites. This study was also attempted to evaluate the species tolerance under local climate condition.
Materials and Methods
Two study plots were established at Metropolitan Batu Park, MBP (3°12’ 49” N; 101°40’ 43” E) and Pusat Bandar Manjalara, PBM (3°11’ 46” N; 101°37’ 55” E), respectively. Both sites are situated in Kuala Lumpur and managed by the Kuala Lumpur City Hall. All trees were raised from stem cuttings and aged about six year-old after planting, at the start of the observation.
A total of ten X. chrysanthus trees were randomly chosen from each sites. These trees were selected from the total of 21 and 17 trees available at MBP and PBM, respectively. Trees at MBP were planted 1-1.5 m away from the road shoulder. Meanwhile, at PBM, the trees were grown at 2 m width of road median. All trees were planted in 10 m of planting distance.
Climatological data from November 2010 to October 2011 were obtained from the Malaysian Meteorological Department. Data recorded at the existing weather station located at the Parliament House of Malaysia, situated approximately 5 km radius from both study plots were used. The distance is considered appropriate for climate studies according to Hubbard  and Larocque and Hall .
Randomly, an auger was used to collect 20 soil samples at 0-30 cm depth from each plot. The soil samples were sealed in plastic bags prior to analysis of the physical properties. Soil samples were air-dried on newspaper, while all trashes, plant roots and other humus were removed. It was then finely pulverised and a quarter of the soil sample was filled in a jar. Clean water was then top up until it reached about three quarter full of the jar. A teaspoon of powdered and non-foaming dishwasher detergent was mixed into the mixture. The jar was then tightly closed and hardly shook for 10 to 15 minutes in order to break the soil aggregates and separates the soil into individual mineral particles. After the jar was kept for about two days, the thickness of coarse sand, fine sand, silt, clay and the total deposit were determined. The percentage of each particle was then calculated by using the formula below:
Photosynthetic rate (A), transpiration rate (E) and stomatal conductance (gs) were recorded with flushing, flowering and fruiting branches, respectively. A total of three branches were randomly selected for each growth stage from each tree. Physiological measurements of the first fully expanded leaves from these branches were taken during short dry and rainy periods, each with persisted dryness or daily rain period of more than half an hour respectively, for three days.
A Portable Photosynthesis System, model Li-6400XT (LICOR Nebraska, USA) was used to gather photosynthetic capacity of the trees at 9.00 a.m. to 11.30 a.m. in sunny condition, at ambient humidity, while the temperature was maintained at 28°C. The measurements were taken at 1200 μmol photon m-2s-1 of quantum flux and the concentration of CO2 was between 360-400 μmol m-2s-1. The A was measured in μmol m-2s-1, while E and gs were measured in mmol m-2s-1 and mol m-2s-1, respectively. Water use efficiency (WUE) was then calculated as net assimilation to transpiration.
Descriptive analysis was carried out on rainfall data. Two sample t-test was performed to compare the soil texture and physiological traits of the trees between the two study plots.
Results and Discussion
The total rainfall received during the study period was 3,181.7 mm and the temperature ranged between 22.9-33.3°C. The average relative humidity was 76.4%. The monthly rainfall pattern showed two periods of high rainfall and two periods of low rainfall (Figure 1). The high rainfall occurred in April-May and November-December. The low rainfall, on the other hand, occurred in February-March and June-July. A total of 805.8 mm rainfall was received in April-May while only 441 mm rainfall was collected in February-March, showing 45.3% difference. In November-December, the total rainfall was 722.1 mm, giving a difference of about 10.39% as compared to that in April-May. The mean monthly temperature was somewhat consistent throughout the year. These results revealed that the climate of Malaysia encourages plant to growth as it has enough water supplies. Malaysia’s climate is described by a homogeneous temperature, high humidity and copious precipitation, categorized into dry and wet seasons . However, soil condition might be a factor that affects the plant growth.
Soil physical properties
Soil analysis showed that both PBM and MBP having loamy sand type of soil, containing less than 15% of clay as compared to silt and sand (Table 1). High percentage of sand was found from MBP and PBM of about 67.52% and 69.41%, respectively. The soil thus had high permeability which influenced the water holding capacity. Both study plots also had significant difference in both fine and coarse sand contents. The coarse sand content of MBP was about 31.74%, while 50.43% for that sampled from PBM. High content of coarse sand increases infiltration rate, therefore soil moisture was significantly lower at PBM as compared to MBP (Table 1). In comparison, soil at MBP had more than 100% of soil moisture content as compared to the soil at PBM. However, the soil moistures for both study plots were still very low due to high sand content.
|Soil moisture (%)||5.89 ± 2.37||2.70 ± 0.46||*|
|Clay (%)||15.02 ± 5.12||13.94 ± 1.33||ns|
|Silt (%)||17.47 ± 4.08||16.66 ± 1.75||ns|
|Fine sand (%)||35.78 ± 8.54||18.98 ± 1.45||**|
|Coarse sand (%)||31.74 ± 10.65||50.43 ± 2.55||*|
Table 1: Comparison of soil physical properties between the study plots.
Although both sites received approximately the same amount of rainfall, the difference in coarse sand content reduced the soil moisture, causing different physiological responses between those trees. In general, tree growth increases with rainfall and decreases with drought [3,4,22]. According to Sassaki et al. , several classical changes associated with water stress were expressed as low biomass, decrease in leaf growth, delay in leaf emergence, and higher accumulation of root biomass.
The leaf gas exchange investigation revealed that A, E and gs of the trees in both study plots were higher during flushing as compared to flowering and fruit development stages (Table 2). The values of A, E and gs dropped at flowering stage and increased slightly during fruit development stage (Table 2).
|Physiological Response||Growth Stages||Season||Sites||T-test|
|Flushing||Rainy||8.38 ± 3.54||5.95 ± 1.11||*|
|Dry||8.05 ± 3.08||5.69 ± 0.57||**|
|Flowering||Rainy||6.19 ± 2.11||3.70 ± 1.45||***|
|Dry||4.87 ± 1.86||3.18 ± 1.45||**|
|Fruiting||Rainy||6.56 ± 2.33||5.41 ± 1.46||ns|
|Dry||5.81 ± 1.11||5.09 ± 1.01||ns|
|Flushing||Rainy||2.31 ± 1.30||1.23 ± 0.57||**|
|Dry||2.02 ± 0.98||1.10 ± 0.43||**|
|Flowering||Rainy||1.25 ± 0.59||0.93 ± 0.42||ns|
|Dry||1.21 ± 0.68||0.71 ± 0.33||*|
|Fruiting||Rainy||1.69 ± 0.88||1.26 ± 0.36||ns|
|Dry||1.68 ± 0.82||1.08 ± 0.35||ns|
|Flushing||Rainy||0.25 ± 0.23||0.10 ± 0.04||*|
|Dry||0.17 ± 0.12||0.06 ± 0.05||**|
|Flowering||Rainy||0.08 ± 0.11||0.05 ± 0.03||ns|
|Dry||0.07 ± 0.05||0.04 ± 0.03||*|
|Fruiting||Rainy||0.12 ± 0.10||0.08 ± 0.06||ns|
|Dry||0.11 ± 0.10||0.06 ± 0.02||ns|
|Water Use Efficiency||Flushing||Rainy||4.03 ± 1.26||5.84 ± 2.47||*|
|Dry||4.29 ± 0.86||5.83 ± 1.20||*|
|Flowering||Rainy||5.68 ± 2.32||4.25 ± 1.29||ns|
|Dry||4.85 ± 2.40||4.87 ± 1.55||ns|
|Fruiting||Rainy||4.32 ± 1.22||4.39 ± 0.10||ns|
|Dry||3.99 ± 1.37||5.01 ± 1.19||*|
Table 2: Physiological traits at flushing, flowering and fruiting stages in X. chrysanthus during rainy and dry periods.
At MBP, A of flushing branch was about 8.38 μmol m-2s-1 and reduced to 6.19 μmol m-2s-1 at flowering stage during rainy period, showing a reduction of 26.13% (Table 2). It was then increased by about 5.64% at fruiting stage. In addition, reduced E of about 45.89% during flowering stage was also recorded. However, it augmented to 26.04% at fruiting stage. Meanwhile, gs at flowering stage were greatly reduced to 68%. Later at fruiting stage, gs increased for up to 33.33%. Urban et al.  also reported that both A and gs in Mangifera indica were markedly lower in the leaves at flowering as compared to flushing stage. A and gs were declined during flowering stage in M. indica . In this study, similar patterns of A, E and gs were also recorded during dry period but the rates were slightly lower than those measured in rainy period. This is due to a lesser amount of water in the soil, reducing the biochemical processes. These results were in agreement with the reports of Bloch et al. , who also found reduction in physiological capacity due to increased drought stress. Plants react to water deficit condition with a rapid closure of stomata to avoid further water loss via transpiration [23,26], which indirectly influences carbon dioxide diffusion into the leaf . In addition, Medrano et al.  stated that water stress reduces A in leaves of higher plants due to stomata closure in the short-term, and due to photoinhibition damage and inactivation of RuBisCO in the long-term.
In this study, X. chrysanthus at both study plots had a similar trend of physiological capacity. However, lower rates of all the physiological traits were recorded at PBM (Table 2). A at flushing and flowering stages were significantly differed between the two study plots in both periods. It was found higher for the trees planted at MBP as compared to that with the trees at PBM. On the other hand, A was not significantly different between trees of the two study plots at fruiting stage. Meanwhile, there was no significant difference in terms of E at flowering stage in trees of both study plots during rainy period, but it differed significantly in dry period. The similar trend was also shown for gs during flowering stage.
There was also a significant different in WUE observed during flushing in both rainy and dry period between the sites, although a same amount of rainfall was received. At flushing stage, WUE of the trees at PBM was significantly higher than MBP, 31% and 26.4% during rainy and dry period, respectively. These results revealed that X. chrysanthus at PBM has better ability to utilise water and reduce water lost through transpiration than those trees grown at MBP. In other words, trees grown at higher sand content area at PBM were more tolerance with low moisture content in the soil. It shows that X. chrysanthus is able to adapt with the harsh urban soil. McCarthy et al.  stated that in environments with limited water resources, trees with low total water use or transpiration may be advantageous. Xanthostemon chrysanthus also has cuticle layer present on the leaves surfaces, acting as water permeability barrier that prevents evaporation of water from the epidermal surface.
Higher values of physiological traits during flushing showed that the leaves at this stage were actively involved in biochemical processes in order to produce photoassimilates that will be used for reproductive development. Photosynthetic capacity of a leaf usually declines after maturity stage has reached [30,31]. In other study on Cecropia longipes and Urera caracasana, A also dramatically declined with leaf age .
Lower plant physiological performances at PBM were possibly due to plant response to lesser soil moisture as compared to MBP. Other possibility was rapid reduction in stomatal aperture at PBM as plant defense mechanism to reduce water loss. Reduction of gs led to reduced photosynthetic capacity. These results suggested that X. chrysanthus is able to withstand such planting condition with high sand and low moisture content. Thus, this species can be recommended to be planted for urban landscape.
In conclusion, physiological measurements showed that A, E and gs were higher during flushing stage, as compared to flowering and fruiting stages. However, these physiological traits were found higher during fruit development as compared to those recorded during flowering stage. This physiological pattern was similar for both sites, but A, E and gs values were slightly lower during dry period. It shows that A, E and gs were influenced by the availability of water in the planting soil which affected by the sand content. Trees at PBM had higher WUE, showing that the trees were more efficient in utilising moisture for their physiological processes under water constraint condition. However, X. chrysanthus can be considered as a good option for the urban landscape because it is able to adapt to the harsh urban soil.
Financial support for this project was granted by the Ministry of Agriculture and Agro-based Industry Malaysia (05-03-10-SF1030). The field assistance provided by Rosfarizal Kamaruzaman, Saiful Azahari Zainal Abidin and Mohd Rizal Kasim is greatly appreciated. We thank Kuala Lumpur City Hall for their input and site permission.
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