Mature tropical urban trees are susceptible to root and trunk rot caused by pathogenic fungi. A m... more Mature tropical urban trees are susceptible to root and trunk rot caused by pathogenic fungi. A metagenomic survey of such fungi was carried out on 210 soil and tissue samples collected from 134 trees of 14 common species in Singapore. Furthermore, 121 fruiting bodies were collected and barcoded. Out of the 22,067 OTUs (operational taxonomic units) identified, 10,646 OTUs had annotation information, and most were either ascomycetes (63.4%) or basidiomycetes (22.5%). Based on their detection in the diseased tissues and surrounding soils and/or the presence of fruiting bodies, fourteen basidiomycetes (nine Polyporales, four Hymenochaetales, one Boletales) and three ascomycetes (three species of Scytalidium) were strongly associated with the diseased trees. Fulvifomes siamensis affected the largest number of tree species surveyed. The association of three fungi was further supported by in vitro wood decay studies. Genetic heterogeneity was common in the diseased tissues and fruiting bo...
Turfgrass is an important component of the urban landscape frequently considered as an alternativ... more Turfgrass is an important component of the urban landscape frequently considered as an alternative land cover to offset anthropogenic CO2 emissions. However, quantitative information of the potential to directly remove CO2 from the atmosphere by turfgrass systems is lacking, especially in the tropics. Most assessments have considered the carbon accumulated by grass shoots and soil, but not the release of CO2 to the atmosphere by soil respiration (i.e., soil CO2 efflux). Here, we measured at high-temporal resolution (30-min) soil CO2 efflux, production, and storage rate for nearly three years in a residential lawn of Singapore. Furthermore, we quantified the carbon capture related to biomass production and CO2 emissions from fossil fuel consumption associated with maintenance activities (e.g., mowing equipment). Warm and humid conditions resulted in relatively constant rates of soil CO2 efflux, CO2 storage in soil, and aboveground biomass production (3370, 652, 1671 Mg CO2 km-2 yr-1; respectively), while the systematic use of mowing machinery emitted 27 Mg CO2 km-2 yr-1. Soil CO2 efflux and CO2 mowing emissions represent carbon losses to the atmosphere, while CO2 storage in soil and biomass productivity represent gains of carbon into the ecosystem. Under a steady state in which soil CO2 losses are only compensated by atmospheric CO2 uptake by photosynthesis, an ideal clipping waste disposal management, in which no CO2 molecule returns to the atmosphere (i.e., clippings are not burnt), and a 3-week mowing regime, this site can act as a sink of 2296 Mg CO2 km-2 yr-1. In the scenario of incinerating all clippings, the lawn acts as an emission source of 1046 Mg CO2 km-2 yr-1. Thus, management practices that reduce mowing frequency together with clipping disposal practices that minimize greenhouse gas emissions are needed to make urban lawns a potential natural solution to mitigate global environmental change.
Leaf mechanical properties strongly influence leaf lifespan, plant–herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant–herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500–800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughne...
Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plantanimal interactions and ecosystem functions across the globe.
Philosophical Transactions of the Royal Society B: Biological Sciences, 1995
... in proportion to Vc and depends on the helical winding of cellulose microfibrils that develop... more ... in proportion to Vc and depends on the helical winding of cellulose microfibrils that develop in the wall following cell elongation (Preston 1974 ... direct path across dense woody fibres since the middle lamella between fibres is more brittle (eg Jeronimidis 1980 for wood; Lucas et al ...
Philosophical Transactions of the Royal Society B: Biological Sciences, 1991
Abstract The fracture toughness (specific work of fracture) of the leaf of the dicotyledonous ang... more Abstract The fracture toughness (specific work of fracture) of the leaf of the dicotyledonous angiosperm, Calophyllum inophyllum L.(Guttiferae), which has a lamina with a reticulate venation comprising secondary and tertiary veins only, was investigated by cutting, notched tensile and punch-and-die tests. Toughness was found to depend on the presence of veins in the fracture path, with both tensile and cutting tests in agreement that fracture at right angles to secondary veins was 2.5-3.0 times as tough as fracture parallel to them. Values ...
The fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measure... more The fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measured along a 'least tough' path using an instrumented cutting technique. Punch-and-die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration x 6-25) and the ratio of the two, the index of sclerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty-seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils).
Leaf colour, size and toughness were investigated in five plant species important in the diet of ... more Leaf colour, size and toughness were investigated in five plant species important in the diet of Macaca fascicularis in Singapore. Leaf colour and size were examined as potential visual cues for food selection, whereas toughness mirrored fibre content, the inverse of food quality. As leaves matured, they changed colour and toughened. Leaf lightness and yellowness were strongly negatively correlated with toughness, but variation in both the red-green axis of the CIE Lab colour space and leaf size were not. Leaves selected as food by the macaques were distinguished by being very light, yellow to slightly green. Some leaves were dappled with red. The literature suggests that these leaves are relatively rich in protein without being tough and therefore would be sought after by primates. We argue that leaf colour is an important indicator of the nutritive value of leaves. Trichromatic vision is an important advantage in finding those palatable leaves that are dappled red. These would appear dark to dichromatic primates and be deceptive by making leaves look older (lower in quality) than they actually are. This would decrease the perceived window of feeding opportunity for such primates who would be at a disadvantage in trying to find these leaves. It is possible that trichromatic vision in catarrhine primates may have originally evolved for the detection of red coloration in the leaves of shade-tolerant tropical plants, enabling the better exploitation of a food resource.
Canopy-top leaves of the dominant tree species from two 0.96-ha plots in Brunei, northern Borneo,... more Canopy-top leaves of the dominant tree species from two 0.96-ha plots in Brunei, northern Borneo, were sampled for structural and chemical analysis. Thirteen species from the mixed dipterocarp forest at Andulau and 14 from the lowland heath forest at Badas were studied. The heath-forest species had significantly thicker leaves and were lower in nitrogen and ash concentration than those from the mixed dipterocarp forest. There were no significant differences between the two species groups in leaf mass per unit area (LMA), leaf fracture toughness, carbon concentration, 6l3CC, neutral detergent fiber concentration, sclerophylly index, and stomata1 density. A significant negative correlation between %C and SI3C was found for the species from the mixed dipterocarp forest, but not those from the heath forest.
Abstract Leaf mechanical properties strongly influence leaf lifespan, plantherbivore interaction... more Abstract Leaf mechanical properties strongly influence leaf lifespan, plantherbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data ...
Journal of Toxicology and Environmental Health-part A-current Issues, 2006
Environmental fates and effects of pharmaceuticals in the aquatic environment have been the focus... more Environmental fates and effects of pharmaceuticals in the aquatic environment have been the focus of recent research in environmental ecotoxicology. Worldwide studies of common over-the-counter pharmaceuticals have reported detectable levels in the aquatic environment, but there are few studies examining impacts on marine habitats. These drugs can affect the functions of various vertebrates and invertebrates. The stability of two pharmaceuticals, cyclizine (CYC) and prochlorperazine (PCZ), in seawater was examined under light and dark conditions, as well as the toxicity of these compounds to larvae of the barnacle Balanus amphitrite, which is a cosmopolitan marine organism found in most of the world's oceans. CYC was very stable under all the tested conditions. On the other hand, PCZ degraded in light but not in the dark, and was more stable in seawater than fresh water. For the barnacle larvae, the LC50 of prochlorperazine was 0.93 microg/ml and the LC50 for CYC was approximately 0.04 microg/ml.
Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plantanimal interactions and ecosystem functions across the globe.
A comparative study of the corrosion behavior of the 70/30 Cu-Ni alloy in a nutrient-rich simulat... more A comparative study of the corrosion behavior of the 70/30 Cu-Ni alloy in a nutrient-rich simulated seawater-based nutrient-rich medium in the presence and the absence of a marine aerobic Pseudomonas bacterium was carried out by electrochemical experiments, microscopic methods and X-ray photoelectron spectroscopy (XPS). The results of Tafel plot measurements showed the noticeable increase in the corrosion rate of the alloy in the presence of the Pseudomonas bacteria as compared to the corresponding control samples. The E1S data demonstrated that the charge transfer resistance, R ct , and the resistance of oxide film, R f , gradually increased with time in the abiotic medium; whereas, both of them dramatically decreased with time in the biotic medium inoculated with the Pseudomonas, indicative of the acceleration of corrosion rates of the alloy. The bacterial cells preferentially attached themselves to the alloy surface to form patchy or blotchy biofilms, as between the conditioning layers and the bacterial cells and the EPS in the biofilms, which was believed to connect with the loss of the passivity of the protective oxide film.
Mature tropical urban trees are susceptible to root and trunk rot caused by pathogenic fungi. A m... more Mature tropical urban trees are susceptible to root and trunk rot caused by pathogenic fungi. A metagenomic survey of such fungi was carried out on 210 soil and tissue samples collected from 134 trees of 14 common species in Singapore. Furthermore, 121 fruiting bodies were collected and barcoded. Out of the 22,067 OTUs (operational taxonomic units) identified, 10,646 OTUs had annotation information, and most were either ascomycetes (63.4%) or basidiomycetes (22.5%). Based on their detection in the diseased tissues and surrounding soils and/or the presence of fruiting bodies, fourteen basidiomycetes (nine Polyporales, four Hymenochaetales, one Boletales) and three ascomycetes (three species of Scytalidium) were strongly associated with the diseased trees. Fulvifomes siamensis affected the largest number of tree species surveyed. The association of three fungi was further supported by in vitro wood decay studies. Genetic heterogeneity was common in the diseased tissues and fruiting bo...
Turfgrass is an important component of the urban landscape frequently considered as an alternativ... more Turfgrass is an important component of the urban landscape frequently considered as an alternative land cover to offset anthropogenic CO2 emissions. However, quantitative information of the potential to directly remove CO2 from the atmosphere by turfgrass systems is lacking, especially in the tropics. Most assessments have considered the carbon accumulated by grass shoots and soil, but not the release of CO2 to the atmosphere by soil respiration (i.e., soil CO2 efflux). Here, we measured at high-temporal resolution (30-min) soil CO2 efflux, production, and storage rate for nearly three years in a residential lawn of Singapore. Furthermore, we quantified the carbon capture related to biomass production and CO2 emissions from fossil fuel consumption associated with maintenance activities (e.g., mowing equipment). Warm and humid conditions resulted in relatively constant rates of soil CO2 efflux, CO2 storage in soil, and aboveground biomass production (3370, 652, 1671 Mg CO2 km-2 yr-1; respectively), while the systematic use of mowing machinery emitted 27 Mg CO2 km-2 yr-1. Soil CO2 efflux and CO2 mowing emissions represent carbon losses to the atmosphere, while CO2 storage in soil and biomass productivity represent gains of carbon into the ecosystem. Under a steady state in which soil CO2 losses are only compensated by atmospheric CO2 uptake by photosynthesis, an ideal clipping waste disposal management, in which no CO2 molecule returns to the atmosphere (i.e., clippings are not burnt), and a 3-week mowing regime, this site can act as a sink of 2296 Mg CO2 km-2 yr-1. In the scenario of incinerating all clippings, the lawn acts as an emission source of 1046 Mg CO2 km-2 yr-1. Thus, management practices that reduce mowing frequency together with clipping disposal practices that minimize greenhouse gas emissions are needed to make urban lawns a potential natural solution to mitigate global environmental change.
Leaf mechanical properties strongly influence leaf lifespan, plant–herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant–herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500–800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughne...
Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plantanimal interactions and ecosystem functions across the globe.
Philosophical Transactions of the Royal Society B: Biological Sciences, 1995
... in proportion to Vc and depends on the helical winding of cellulose microfibrils that develop... more ... in proportion to Vc and depends on the helical winding of cellulose microfibrils that develop in the wall following cell elongation (Preston 1974 ... direct path across dense woody fibres since the middle lamella between fibres is more brittle (eg Jeronimidis 1980 for wood; Lucas et al ...
Philosophical Transactions of the Royal Society B: Biological Sciences, 1991
Abstract The fracture toughness (specific work of fracture) of the leaf of the dicotyledonous ang... more Abstract The fracture toughness (specific work of fracture) of the leaf of the dicotyledonous angiosperm, Calophyllum inophyllum L.(Guttiferae), which has a lamina with a reticulate venation comprising secondary and tertiary veins only, was investigated by cutting, notched tensile and punch-and-die tests. Toughness was found to depend on the presence of veins in the fracture path, with both tensile and cutting tests in agreement that fracture at right angles to secondary veins was 2.5-3.0 times as tough as fracture parallel to them. Values ...
The fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measure... more The fracture toughness of sun-leaves of 42 tropical tree species growing in Singapore was measured along a 'least tough' path using an instrumented cutting technique. Punch-and-die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration x 6-25) and the ratio of the two, the index of sclerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty-seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils).
Leaf colour, size and toughness were investigated in five plant species important in the diet of ... more Leaf colour, size and toughness were investigated in five plant species important in the diet of Macaca fascicularis in Singapore. Leaf colour and size were examined as potential visual cues for food selection, whereas toughness mirrored fibre content, the inverse of food quality. As leaves matured, they changed colour and toughened. Leaf lightness and yellowness were strongly negatively correlated with toughness, but variation in both the red-green axis of the CIE Lab colour space and leaf size were not. Leaves selected as food by the macaques were distinguished by being very light, yellow to slightly green. Some leaves were dappled with red. The literature suggests that these leaves are relatively rich in protein without being tough and therefore would be sought after by primates. We argue that leaf colour is an important indicator of the nutritive value of leaves. Trichromatic vision is an important advantage in finding those palatable leaves that are dappled red. These would appear dark to dichromatic primates and be deceptive by making leaves look older (lower in quality) than they actually are. This would decrease the perceived window of feeding opportunity for such primates who would be at a disadvantage in trying to find these leaves. It is possible that trichromatic vision in catarrhine primates may have originally evolved for the detection of red coloration in the leaves of shade-tolerant tropical plants, enabling the better exploitation of a food resource.
Canopy-top leaves of the dominant tree species from two 0.96-ha plots in Brunei, northern Borneo,... more Canopy-top leaves of the dominant tree species from two 0.96-ha plots in Brunei, northern Borneo, were sampled for structural and chemical analysis. Thirteen species from the mixed dipterocarp forest at Andulau and 14 from the lowland heath forest at Badas were studied. The heath-forest species had significantly thicker leaves and were lower in nitrogen and ash concentration than those from the mixed dipterocarp forest. There were no significant differences between the two species groups in leaf mass per unit area (LMA), leaf fracture toughness, carbon concentration, 6l3CC, neutral detergent fiber concentration, sclerophylly index, and stomata1 density. A significant negative correlation between %C and SI3C was found for the species from the mixed dipterocarp forest, but not those from the heath forest.
Abstract Leaf mechanical properties strongly influence leaf lifespan, plantherbivore interaction... more Abstract Leaf mechanical properties strongly influence leaf lifespan, plantherbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data ...
Journal of Toxicology and Environmental Health-part A-current Issues, 2006
Environmental fates and effects of pharmaceuticals in the aquatic environment have been the focus... more Environmental fates and effects of pharmaceuticals in the aquatic environment have been the focus of recent research in environmental ecotoxicology. Worldwide studies of common over-the-counter pharmaceuticals have reported detectable levels in the aquatic environment, but there are few studies examining impacts on marine habitats. These drugs can affect the functions of various vertebrates and invertebrates. The stability of two pharmaceuticals, cyclizine (CYC) and prochlorperazine (PCZ), in seawater was examined under light and dark conditions, as well as the toxicity of these compounds to larvae of the barnacle Balanus amphitrite, which is a cosmopolitan marine organism found in most of the world's oceans. CYC was very stable under all the tested conditions. On the other hand, PCZ degraded in light but not in the dark, and was more stable in seawater than fresh water. For the barnacle larvae, the LC50 of prochlorperazine was 0.93 microg/ml and the LC50 for CYC was approximately 0.04 microg/ml.
Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter... more Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plantanimal interactions and ecosystem functions across the globe.
A comparative study of the corrosion behavior of the 70/30 Cu-Ni alloy in a nutrient-rich simulat... more A comparative study of the corrosion behavior of the 70/30 Cu-Ni alloy in a nutrient-rich simulated seawater-based nutrient-rich medium in the presence and the absence of a marine aerobic Pseudomonas bacterium was carried out by electrochemical experiments, microscopic methods and X-ray photoelectron spectroscopy (XPS). The results of Tafel plot measurements showed the noticeable increase in the corrosion rate of the alloy in the presence of the Pseudomonas bacteria as compared to the corresponding control samples. The E1S data demonstrated that the charge transfer resistance, R ct , and the resistance of oxide film, R f , gradually increased with time in the abiotic medium; whereas, both of them dramatically decreased with time in the biotic medium inoculated with the Pseudomonas, indicative of the acceleration of corrosion rates of the alloy. The bacterial cells preferentially attached themselves to the alloy surface to form patchy or blotchy biofilms, as between the conditioning layers and the bacterial cells and the EPS in the biofilms, which was believed to connect with the loss of the passivity of the protective oxide film.
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Papers by Amy M F Choong