School of Ecosystem and Forest Sciences - Research Publications
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ItemResponses to heatwaves of gas exchange, chlorophyll fluorescence and antioxidants ascorbic acid and glutathione in congeneric pairs of Acacia and Eucalyptus species from relatively cooler and warmer climates(SPRINGER HEIDELBERG, 2015-12-01)KEY MESSAGE : Two species from warmer climates, but not the corresponding congeneric species from relatively cooler ones, decreased stomatal conductance upon heatwaves, and one of them showed significant decrease in the efficiency of open reaction centres of PSII in the light. In contrast, responses of major antioxidants ascorbic acid and glutathione to heatwaves were more similar between congeneric species than between species from similar climates. According to climate change predictions, heatwaves will increase in frequency and intensity. This can threaten survival of sensitive tree species. Heatwaves affect photosynthetic capacity and cause an imbalance between light driven electron transport and carbon fixation. This can increase the concentration of reactive oxygen species, and can cause photo-oxidative stress. Heat dissipation and antioxidants are crucial in plant defence against photo-oxidative stress. We hypothesised that stomatal regulations, heat dissipation as measured by chlorophyll fluorescence and responses of major antioxidants ascorbic acid and glutathione to heatwaves will vary according to the climate at the site of origin of tree species. Tree seedlings from warmer (Eucalyptus grandis, Acacia aneura) and cooler climates (Eucalyptus tricarpa, Acacia melanoxylon) were exposed to air temperatures about 5 °C above control levels for 5 days. The two species from warmer climates responded to heatwaves with stomatal closure restricting transpiration and carbon fixation, and E. grandis also significantly increased heat dissipation (as judged by decreased efficiency of open reaction centres of PSII in the light). Species from cooler climates kept stomata open allowing continuing carbon assimilation and transpirational cooling. Heatwaves did not reduce maximum quantum efficiency of PSII in Acacia species, with insignificant decreases in Eucalyptus species. Glutathione concentrations increased significantly upon heatwave in E. tricarpa (from cooler climates), showed a time-dependent response to heatwave in E. grandis (from warmer climates) with an increase at later stages, and showed a tendency to decrease upon heatwave in both Acacia species (non-significant only for A. melanoxylon). Ascorbic acid concentrations increased significantly in E. tricarpa (cooler climates), and did not change significantly in other species. The redox state of ascorbic acid or glutathione only changed significantly and transiently in response to heatwave in A. aneura (warmer climates; GSSG % and ASC %) and A. melanoxylon (cooler climates; GSSG %), but not Eucalyptus species. Therefore, differences in stomatal regulations upon heatwaves aligned with the origin of species in warmer or cooler climates, whereas responses of ascorbic acid and glutathione to heatwaves were more aligned with the two genera.
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ItemBark and leaf chlorophyll fluorescence are linked to wood structural changes in Eucalyptus saligna(OXFORD UNIV PRESS, 2014-01-01)Wood structure and wood anatomy are usually considered to be largely independent of the physiological processes that govern tree growth. This paper reports a statistical relationship between leaf and bark chlorophyll fluorescence and wood density. A relationship between leaf and bark chlorophyll fluorescence and the quantity of wood decay in a tree is also described. There was a statistically significant relationship between the leaf chlorophyll fluorescence parameter Fv/Fm and wood density and the quantity of wood decay in summer, but not in spring or autumn. Leaf chlorophyll fluorescence at 0.05 ms (the O step) could predict the quantity of wood decay in trees in spring. Bark chlorophyll fluorescence could predict wood density in spring using the Fv/Fm parameter, but not in summer or autumn. There was a consistent statistical relationship in spring, summer and autumn between the bark chlorophyll fluorescence parameter Fv/Fm and wood decay. This study indicates a relationship between chlorophyll fluorescence and wood structural changes, particularly with bark chlorenchyma.
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ItemDiurnal and seasonal variations in photosynthetic and morphological traits of the tree ferns Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) in wet sclerophyll forests of Australia(PERGAMON-ELSEVIER SCIENCE LTD, 2011-01-01)Steady state and dynamic responses of two tree fern species of contrasting origins, Dicksonia antarctica (of Gondwanan origin) and Cyathea australis (Pan-tropical), were studied over two consecutive years under field conditions in a wet sclerophyll forest of south-east Australia. Irrespective of their different origins, there were no significant differences in photosynthetic performance between the two species. Growth irradiance and leaf temperature, but not plant water status, was significantly related to photosynthetic and morphological traits. At a common leaf temperature, maximum light-use efficiency of photosystem II (Fv/Fm) was significantly lower in winter than in summer, suggesting some limitation to PSII efficiency potentially associated with cold winter mornings. Both species displayed seasonal acclimation in a number of measured photosynthetic parameters and frond traits (i.e. Fv/Fm, Asat, gs, NA, total chlorophyll, SLA). Acclimation of stomatal density to spatial variation in growth irradiance seemed limited in both species, although stomatal pattern differed between species. Because there were no significant differences between the two species in photosynthetic parameters, both species can be described by common carbon gain and water use models at the leaf scale.
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ItemShade does not ameliorate drought effects on the tree fern species Dicksonia antarctica and Cyathea australis(SPRINGER HEIDELBERG, 2010-04-01)We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under moderate and high light regimes to short-term water deficit followed by rewatering. Under adequate water supply, morphological and photosynthetic characteristics differed between species. D. antarctica, although putatively the more shade and less drought adapted species, had greater chlorophyll a/b ratio, and greater water use efficiency and less negative δ¹³C. Both species were susceptible to water deficit regardless of the light regime showing significant decreases in photosynthetic parameters (A max, V cmax, J max) and stomatal conductance (g s ) in conjunction with decreased relative frond water content (RWC) and predawn frond water potential (Ψpredawn). During the water deficit period, decreases in g s in both species started one day later, and were at lower soil water content, under moderate light compared with high light. D. antarctica under moderate light was more vulnerable to drought than all other plants as was indicated by greater decreases in Ψpredawn, lowest stomatal conductance, and photosynthetic rates. Both tree fern species were able to recover after a short but severe water stress.
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ItemEdge type affects leaf-level water relations and estimated transpiration of Eucalyptus arenacea(OXFORD UNIV PRESS, 2012-03-01)While edge effects on tree water relations are well described for closed forests, they remain under-examined in more open forest types. Similarly, there has been minimal evaluation of the effects of contrasting land uses on the water relations of open forest types in highly fragmented landscapes. We examined edge effects on the water relations and gas exchange of a dominant tree (Eucalyptus arenacea Marginson & Ladiges) in an open forest type (temperate woodland) of south-eastern Australia. Edge effects in replicate woodlands adjoined by cleared agricultural land (pasture edges) were compared with those adjoined by 7- to 9-year-old eucalypt plantation with a 25m fire break (plantation edges). Consistent with studies in closed forest types, edge effects were pronounced at pasture edges where photosynthesis, transpiration and stomatal conductance were greater for edge trees than interior trees (75m into woodlands), and were related to greater light availability and significantly higher branch water potentials at woodland edges than interiors. Nonetheless, gas exchange values were only ∼50% greater for edge than interior trees, compared with ∼200% previously found in closed forest types. In contrast to woodlands adjoined by pasture, gas exchange in winter was significantly lower for edge than interior trees in woodlands adjoined by plantations, consistent with shading and buffering effects of plantations on edge microclimate. Plantation edge effects were less pronounced in summer, although higher water use efficiency of edge than interior woodland trees indicated possible competition for water between plantation trees and woodland edge trees in the drier months (an effect that might have been more pronounced were there no firebreak between the two land uses). Scaling up of leaf-level water relations to stand transpiration using a Jarvis-type phenomenological model indicated similar differences between edge types. That is, transpiration was greater at pasture than plantation edges in summer months (most likely due to greater water availability at pasture edges), resulting in significantly greater estimates of annual transpiration at pasture than plantation edges (430 vs. 343lm(-2)year(-1), respectively). Our study highlights the need for landscape-level water flux models to account for edge effects on stand transpiration, particularly in highly fragmented landscapes.
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ItemInteractive effects of high irradiance and moderate heat on photosynthesis, pigments, and tocopherol in the tree-fern Dicksonia antarctica(CSIRO PUBLISHING, 2009-01-01)Effects of high irradiance and moderate heat on photosynthesis of the tree-fern Dicksonia antarctica (Labill., Dicksoniaceae) were examined in a climate chamber under two contrasting irradiance regimes (900 and 170 µmol photons m-2 s-1) and three sequential temperature treatments (15°C; 35°C; back to 15°C). High irradiance led to decline in predawn quantum yield of photochemistry, Fv/Fm (0.73), maximal Rubisco activity (Vcmax; from 37 to 29 µmol m-2s-1), and electron transport capacity (Jmax; from 115 to 67 µmol m-2 s-1). Temperature increase to 35°C resulted in further decreases in Fv/Fm (0.45) and in chlorophyll bleaching of high irradiance plants, while Vcmax and Jmax were not affected. Critical temperature for thylakoid stability (Tc) of D. antarctica was comparable with other higher plants (c. 47°C), and increases of Tc with air temperature were greater in high irradiance plants. Increased Tc was not associated with accumulation of osmotica or zeaxanthin formation. High irradiance increased the xanthophyll cycle pigment pool (V+A+Z, 91 v. 48 mmol mol-1 chlorophyll-1), de-epoxidation state (56% v. 4%), and α-tocopherol. Temperature increase to 35°C had no effect on V+A+Z and de-epoxidation state in both light regimes, while lutein, β-carotene and α-tocopherols increased, potentially contributing to increased membrane stability under high irradiance.
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ItemEffects of sudden exposure to high light levels on two tree fern species Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) acclimated to different light intensities(CSIRO PUBLISHING, 2009-01-01)We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under shade or variable light (intermittent shade) to sudden exposure to high light levels. Steady-state gas exchange as well as dynamic responses of plants to artificial sunflecks indicated that difference in growth light environment had very little effect on the tree ferns' capacities to utilise and acclimate to prevailing light conditions. Two weeks of exposure to high light levels (short-term acclimation) led to decreases in all photosynthetic parameters and more negative predawn frond water potentials, mostly irrespective of previous growth light environments. After 3months in high light levels (long-term acclimation), D. antarctica fully recovered, while C. australis previously grown under variable light, recovered only partially, suggesting high light level stress effects under the variable light environments for this species.
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ItemExtraordinary drought of 2003 overrules ozone impact on adult beech trees (Fagus sylvatica)(Springer, 2006)The extraordinary drought during the summer of 2003 in Central Europe allowed to examine responses of adult beech trees (Fagus sylvatica) to co-occurring stress by soil moisture deficit and elevated O3 levels under forest conditions in southern Germany. The study comprised tree exposure to the ambient O3 regime at the site and to a twice-ambient O3 regime as released into the canopy through a free-air O3 fumigation system. Annual courses of photosynthesis (Amax), stomatal conductance (gs), electron transport rate (ETR) and chlorophyll levels were compared between 2003 and 2004, the latter year representing the humid long-term climate at the site. ETR, Amax and gs were lowered during 2003 by drought rather than ozone, whereas chlorophyll levels did not differ between the years. Radial stem increment was reduced in 2003 by drought but fully recovered during the subsequent, humid year. Comparison of AOT40, an O3 exposure-based risk index of O3 stress, and cumulative ozone uptake (COU) yielded a linear relationship throughout humid growth conditions, but a changing slope during 2003. Our findings support the hypothesis that drought protects plants from O3 injury by stomatal closure, which restricts O3 influx into leaves and decouples COU from high external ozone levels. High AOT40 erroneously suggested high O3 risk under drought. Enhanced ozone levels did not aggravate drought effects in leaves and stem.
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ItemInternal conductance to CO2 transfer of adult Fagus sylvatica: variation between sun and shade leaves and due to free-air ozone fumigation(Elsevier, 2007)Abstract not available due to copyright.