Rising atmospheric concentrations of CO 2 (C a ) can reduce stomatal conductance and transpiratio... more Rising atmospheric concentrations of CO 2 (C a ) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to C a . We hypothesized that plants regulate stomatal conductance optimally in response to rising C a . We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated C a . Elevated C a was ambient + 240 ppm, 60% higher than ambient C a . Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated C a , as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO 2 treatments. Whole-canopy CO 2 and H 2 O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between C a treatments, which had important effects on values of canopy-scale ITE. However, when C a treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to C a . The effect of elevated C a on photosynthesis increased with rising D. At high D, C a had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of C a on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with C a will allow us to predict the effects of C a on transpiration rate.
Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure defi... more Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure deficit (D). The mechanisms for the decrease in E at high D, known as the 'apparent feed-forward response', are strongly debated but explanations to date have exclusively focused on hydraulic processes. However, stomata also respond to signals related to photosynthesis. We investigated whether the apparent feed-forward response of E to D in the field can be explained by the response of photosynthesis to temperature (T), which normally co-varies with D in field conditions. As photosynthesis decreases with increasing T past its optimum, it may drive a decrease in stomatal conductance (g s ) that is additional to the response of g s to increasing D alone. If this additional decrease is sufficiently steep and coupling between A and g s occurs, it could cause an overall decrease in E with increasing D. We tested this mechanism using a gas exchange model applied to leaf-scale and whole-tree CO 2 and H 2 O fluxes measured on Eucalyptus saligna growing in whole-tree chambers. A peaked response of E to D was observed at both leaf and whole-tree scales. We found that this peaked response was matched by a gas exchange model only when T effects on photosynthesis were incorporated. We conclude that field-based studies of the relationship between E and D need to consider signals related to changing photosynthetic rates in addition to purely hydraulic mechanisms.
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are diffi... more The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2 ] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A max ), the potential electron transport rate (J max ), the maximum Rubisco activity (V cmax ) and leaf nitrogen concentration on mass (N m ) and area (N a ) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2 ]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10-20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated [CO 2 ] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2 ]. Tables of model parameter values for different European forest species are given. such as those compiled by and , are therefore invaluable for improving model predictions.
Xylem sap velocity of two dominant tree species, Eucalyptus crebra F. Muell. and Callitris glauco... more Xylem sap velocity of two dominant tree species, Eucalyptus crebra F. Muell. and Callitris glaucophylla J. Thompson & L.A.S. Johnson, in a native remnant forest of eastern Australia was measured in winter and summer during a prolonged (> 12 months) and extensive drought. The influence of vapour pressure deficit (VPD) and solar radiation levels on the velocity of sap was determined. Pronounced hysteresis in sap velocity was observed in both species as a function of VPD and solar radiation. However, the rotation of the hysteresis curve was clockwise for the response of sap velocity to VPD but anti-clockwise in the response of sap velocity to radiation levels. A possible reason for this difference is discussed.
ABSTRACT Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the... more ABSTRACT Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. Despite the pivotal role of gs in predictions of global water and carbon cycle changes, a global-scale database and an associated globally applicable model of gs that allow predictions of stomatal behaviour are lacking. Here, we present a database of globally distributed gs obtained in the field for a wide range of plant functional types (PFTs) and biomes. We find that stomatal behaviour differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model and the leaf and wood economics spectrum. We also demonstrate a global relationship with climate. These findings provide a robust theoretical framework for understanding and predicting the behaviour of gs across biomes and across PFTs that can be applied to regional, continental and global-scale modelling of ecosystem productivity, energy balance and ecohydrological processes in a future changing climate.
Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, wit... more Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, with the greatest increase in the west of the state. Rainfall is likely to be reduced across the state, apart from in the north-east. Projections suggest an increased incidence of bushfire and intense storms. Drought frequency may increase, especially in winter and spring. These
Objectives. To evaluate the psychosexual benefit obtained from multicomponent penile implant surg... more Objectives. To evaluate the psychosexual benefit obtained from multicomponent penile implant surgery in patients with erectile dysfunction. Methods. A psychosexual questionnaire was given to 35 patients undergoing penile prosthesis implantation before surgery and at 3 months, 6 months, and 1 year after surgery. The questionnaire consisted of 13 questions scored on a scale from 1 through 5. Results of the questionnaire were statistically analyzed for differences among the preoperative, 3-month postoperative, 6-month postoperative, and 1-year postoperative period. Results. The general linear model evaluation showed a significant difference for each overall combination of the following pairs: preoperative versus 3 months postoperative (P ϭ 0.0005) and 3 months postoperative versus 6 months postoperative (P ϭ 0.002). There was no overall difference between psychosexual total score at 6 months after surgery and 1 year after prosthesis implantation (P ϭ 0.85). The patients perceived improvement in their erectile ability and libido. Concern about obtaining and maintaining an erection during intercourse was significantly alleviated. There was an increase in the frequency of sexual activity and an improvement in satisfaction with sex life. A decrease in feelings of sadness, depression, anxiety, anger, frustration, and embarrassment related to sexual activity was also noted. Conclusions. The current study demonstrates significant improvement in the psychosexual well being of multicomponent penile implant recipients, with attainment of a high level of patient satisfaction up to 1 year after surgery.
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are diffi... more The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2 ] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A max ), the potential electron transport rate (J max ), the maximum Rubisco activity (V cmax ) and leaf nitrogen concentration on mass (N m ) and area (N a ) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2 ]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10-20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated [CO 2 ] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2 ]. Tables of model parameter values for different European forest species are given. such as those compiled by and , are therefore invaluable for improving model predictions.
Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO 2 concentratio... more Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO 2 concentration ([CO 2 ]) on European forest tree species were analysed using meta-analysis and modelling. Meta-analysis was used to determine mean responses across the data sets, and data were fitted to two commonly used models of stomatal conductance in order to explore response to environmental conditions and the relationship with assimilation. • Meta-analysis indicated a significant decrease (21%) in stomatal conductance in response to growth in elevated [CO 2 ] across all studies. The response to [CO 2 ] was significantly stronger in young trees than old trees, in deciduous compared to coniferous trees, and in water stressed compared to nutrient stressed trees. No evidence of acclimation of stomatal conductance to elevated [CO 2 ] was found. • Fits of data to the first model showed that growth in elevated [CO 2 ] did not alter the response of stomatal conductance to vapour pressure deficit, soil water content or atmospheric [CO 2 ]. Fits of data to the second model indicated that conductance and assimilation responded in parallel to elevated [CO 2 ] except when water was limiting. • Data were compared to a previous meta-analysis and it was found that the response of g s to elevated [CO 2 ] was much more consistent in long-term (> 1 yr) studies, emphasising the need for long-term elevated [CO 2 ] studies. By interpreting data in terms of models, the synthesis will aid future modelling studies of responses of forest trees to elevated [CO 2 ].
To quantify the impact that planting indigenous trees and shrubs in mixed communities (environmen... more To quantify the impact that planting indigenous trees and shrubs in mixed communities (environmental plantings) have on net sequestration of carbon and other environmental or commercial benefits, precise and non-biased estimates of biomass are required. Because these plantings consist of several species, estimation of their biomass through allometric relationships is a challenging task. We explored methods to accurately estimate biomass through harvesting 3139 trees and shrubs from 22 plantings, and collating similar datasets from earlier studies, in non-arid (>300 mm rainfall year À1 ) regions of southern and eastern Australia. Site-and-species specific allometric equations were developed, as were three types of generalised, multi-site, allometric equations based on categories of species and growth-habits: (i) speciesspecific, (ii) genus and growth-habit, and (iii) universal growth-habit irrespective of genus. Biomass was measured at plot level at eight contrasting sites to test the accuracy of prediction of tonnes dry matter of above-ground biomass per hectare using different classes of allometric equations. A finer-scale analysis tested performance of these at an individual-tree level across a wider range of sites. Although the percentage error in prediction could be high at a given site (up to 45%), it was relatively low (<11%) when generalised allometry-predictions of biomass was used to make regional-or estate-level estimates across a range of sites. Precision, and thus accuracy, increased slightly with the level of specificity of allometry. Inclusion of site-specific factors in generic equations increased efficiency of prediction of above-ground biomass by as much as 8%. Site-and-species-specific equations are the most accurate for site-based predictions. Generic allometric equations developed here, particularly the generic species-specific equations, can be confidently applied to provide regional-or estate-level estimates of above-ground biomass and carbon.
Our limited understanding of the processes that control the allocation of biomass in trees is one... more Our limited understanding of the processes that control the allocation of biomass in trees is one of the factors that hinders our ability to develop mechanistic models of tree growth. Furthermore, accurate assessment of carbon sequestration by forests is hampered by lack of information regarding below-ground biomass. Below-ground to above-ground biomass ratios (BGB:AGB) are known to vary with a number of environmental factors, tending to increase in drier, harsher conditions. However, there are few, good datasets of BGB:AGB ratios of large trees, especially native Australian species. We aimed to investigate the response of BGB:AGB to water availability and tree spacing in 10-year-old Eucalyptus camaldulensis growing in a plantation in a low rainfall area.
This paper describes the development and first results of the "Community Integrated Assessment Sy... more This paper describes the development and first results of the "Community Integrated Assessment System" (CIAS), a unique multi-institutional modular and flexible integrated assessment system for modelling climate change. Key to this development is the supporting software infrastructure, SoftIAM. Through it, CIAS is distributed between the community of institutions which has each contributed modules to the CIAS system. At the heart of SoftIAM is the Bespoke Framework Generator (BFG) which enables flexibility in the assembly and composition of individual modules from a pool to form coupled models within CIAS, and flexibility in their deployment onto the available software and hardware resources. Such flexibility greatly enhances modellers' ability to re-configure the CIAS coupled models to answer different questions, thus tracking evolving policy needs. It also allows rigorous testing of the robustness of IA modelling results to the use of different component modules representing the same processes (for example, the economy). Such processes are often modelled in very different ways, using different paradigms, at the participating institutions. An illustrative application to the study of the relationship between the economy and the earth's climate system is provided.
Resolving ecophysiological processes in elevated atmospheric CO 2 (C a ) at scales larger than si... more Resolving ecophysiological processes in elevated atmospheric CO 2 (C a ) at scales larger than single leaves poses significant challenges. Here, we describe a field-based experimental system designed to grow trees up to 9 m tall in elevated C a with the capacity to control air temperature and simultaneously measure whole-tree gas exchange. In western Sydney, Australia, we established the Hawkesbury Forest Experiment (HFE) where we built whole-tree chambers (WTC) to measure whole-tree CO 2 and water fluxes of an evergreen broadleaf tree, Eucalyptus saligna. A single E. saligna tree was grown from seedling to small tree within each of 12 WTCs; six WTCs were maintained at ambient C a and six WTCs were maintained at elevated C a , targeted at ambient C a +240 mol mol −1 . All 12 WTCs were controlled to track ambient outside air temperature (T air ) and air water vapour deficit (D air ). During the experimental period, T air , D air and C a in the WTCs were within 0.5 • C, 0.3 kPa, and 15 mol mol −1 of the set-points for 90% of the time, respectively. Diurnal responses of whole-tree CO 2 and water vapour fluxes are analysed, demonstrating the ability of the tree chamber system to measure rapid environmental responses of these fluxes of entire trees. The light response of CO 2 uptake for entire trees showed a clear diurnal hysteresis, attributed to stomatal closure at high D air . Tree scale CO 2 fluxes confirm the hypothesised deleterious effect of chilling night-time temperatures on whole-tree carbon gain in this subtropical Eucalyptus. The whole-tree chamber flux data add an invaluable scale to measurements in both ambient and elevated C a and allow us to elucidate the mechanisms driving tree productivity responses to elevated C a in interaction with water availability and temperature.
Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, sug... more Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO2 effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that:
Nocturnal water flux has been observed in trees under a variety of environmental conditions and c... more Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO(2) (elevated [CO(2)]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO(2)] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (J(s)) and leaf area (E(t)) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in J(s) and E(t) were observed during the severe drought period in the dry treatment under elevated [CO(2)], but not during moderate- and post-drought periods. Elevated [CO(2)] affected night-time sap flux density which included the stem recharge period, called 'tot...
Rising atmospheric concentrations of CO 2 (C a ) can reduce stomatal conductance and transpiratio... more Rising atmospheric concentrations of CO 2 (C a ) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to C a . We hypothesized that plants regulate stomatal conductance optimally in response to rising C a . We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate-controlled whole-tree chambers for 2 years at ambient and elevated C a . Elevated C a was ambient + 240 ppm, 60% higher than ambient C a . Leaf-scale gas exchange was measured throughout the second year of the study and leaf-scale ITE increased by 60% under elevated C a , as predicted. Values of leaf-scale ITE depended strongly on vapour pressure deficit (D) in both CO 2 treatments. Whole-canopy CO 2 and H 2 O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between C a treatments, which had important effects on values of canopy-scale ITE. However, when C a treatments were compared at the same D, canopy-scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy-scale ITE were not significantly different, indicating that ITE was not scale-dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to C a . The effect of elevated C a on photosynthesis increased with rising D. At high D, C a had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of C a on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with C a will allow us to predict the effects of C a on transpiration rate.
Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure defi... more Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure deficit (D). The mechanisms for the decrease in E at high D, known as the 'apparent feed-forward response', are strongly debated but explanations to date have exclusively focused on hydraulic processes. However, stomata also respond to signals related to photosynthesis. We investigated whether the apparent feed-forward response of E to D in the field can be explained by the response of photosynthesis to temperature (T), which normally co-varies with D in field conditions. As photosynthesis decreases with increasing T past its optimum, it may drive a decrease in stomatal conductance (g s ) that is additional to the response of g s to increasing D alone. If this additional decrease is sufficiently steep and coupling between A and g s occurs, it could cause an overall decrease in E with increasing D. We tested this mechanism using a gas exchange model applied to leaf-scale and whole-tree CO 2 and H 2 O fluxes measured on Eucalyptus saligna growing in whole-tree chambers. A peaked response of E to D was observed at both leaf and whole-tree scales. We found that this peaked response was matched by a gas exchange model only when T effects on photosynthesis were incorporated. We conclude that field-based studies of the relationship between E and D need to consider signals related to changing photosynthetic rates in addition to purely hydraulic mechanisms.
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are diffi... more The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2 ] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A max ), the potential electron transport rate (J max ), the maximum Rubisco activity (V cmax ) and leaf nitrogen concentration on mass (N m ) and area (N a ) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2 ]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10-20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated [CO 2 ] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2 ]. Tables of model parameter values for different European forest species are given. such as those compiled by and , are therefore invaluable for improving model predictions.
Xylem sap velocity of two dominant tree species, Eucalyptus crebra F. Muell. and Callitris glauco... more Xylem sap velocity of two dominant tree species, Eucalyptus crebra F. Muell. and Callitris glaucophylla J. Thompson & L.A.S. Johnson, in a native remnant forest of eastern Australia was measured in winter and summer during a prolonged (> 12 months) and extensive drought. The influence of vapour pressure deficit (VPD) and solar radiation levels on the velocity of sap was determined. Pronounced hysteresis in sap velocity was observed in both species as a function of VPD and solar radiation. However, the rotation of the hysteresis curve was clockwise for the response of sap velocity to VPD but anti-clockwise in the response of sap velocity to radiation levels. A possible reason for this difference is discussed.
ABSTRACT Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the... more ABSTRACT Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. Despite the pivotal role of gs in predictions of global water and carbon cycle changes, a global-scale database and an associated globally applicable model of gs that allow predictions of stomatal behaviour are lacking. Here, we present a database of globally distributed gs obtained in the field for a wide range of plant functional types (PFTs) and biomes. We find that stomatal behaviour differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model and the leaf and wood economics spectrum. We also demonstrate a global relationship with climate. These findings provide a robust theoretical framework for understanding and predicting the behaviour of gs across biomes and across PFTs that can be applied to regional, continental and global-scale modelling of ecosystem productivity, energy balance and ecohydrological processes in a future changing climate.
Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, wit... more Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, with the greatest increase in the west of the state. Rainfall is likely to be reduced across the state, apart from in the north-east. Projections suggest an increased incidence of bushfire and intense storms. Drought frequency may increase, especially in winter and spring. These
Objectives. To evaluate the psychosexual benefit obtained from multicomponent penile implant surg... more Objectives. To evaluate the psychosexual benefit obtained from multicomponent penile implant surgery in patients with erectile dysfunction. Methods. A psychosexual questionnaire was given to 35 patients undergoing penile prosthesis implantation before surgery and at 3 months, 6 months, and 1 year after surgery. The questionnaire consisted of 13 questions scored on a scale from 1 through 5. Results of the questionnaire were statistically analyzed for differences among the preoperative, 3-month postoperative, 6-month postoperative, and 1-year postoperative period. Results. The general linear model evaluation showed a significant difference for each overall combination of the following pairs: preoperative versus 3 months postoperative (P ϭ 0.0005) and 3 months postoperative versus 6 months postoperative (P ϭ 0.002). There was no overall difference between psychosexual total score at 6 months after surgery and 1 year after prosthesis implantation (P ϭ 0.85). The patients perceived improvement in their erectile ability and libido. Concern about obtaining and maintaining an erection during intercourse was significantly alleviated. There was an increase in the frequency of sexual activity and an improvement in satisfaction with sex life. A decrease in feelings of sadness, depression, anxiety, anger, frustration, and embarrassment related to sexual activity was also noted. Conclusions. The current study demonstrates significant improvement in the psychosexual well being of multicomponent penile implant recipients, with attainment of a high level of patient satisfaction up to 1 year after surgery.
The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are diffi... more The effects of elevated atmospheric CO 2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life-span of a tree. Long-term, processbased computer models must be used to extrapolate from shorter-term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta-analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field-based elevated [CO 2 ] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light-saturated photosynthetic rates (A max ), the potential electron transport rate (J max ), the maximum Rubisco activity (V cmax ) and leaf nitrogen concentration on mass (N m ) and area (N a ) bases. Across all experiments, light-saturated photosynthesis was strongly stimulated by growth in elevated [CO 2 ]. However, significant down-regulation of photosynthesis was also observed; when measured at the same CO 2 concentration, photosynthesis was reduced by 10-20%. The underlying biochemistry of photosynthesis was affected, as shown by a down-regulation of the parameters J max and V cmax of the order of 10%. This reduction in J max and V cmax was linked to the effects of elevated [CO 2 ] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO 2 ]. Tables of model parameter values for different European forest species are given. such as those compiled by and , are therefore invaluable for improving model predictions.
Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO 2 concentratio... more Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO 2 concentration ([CO 2 ]) on European forest tree species were analysed using meta-analysis and modelling. Meta-analysis was used to determine mean responses across the data sets, and data were fitted to two commonly used models of stomatal conductance in order to explore response to environmental conditions and the relationship with assimilation. • Meta-analysis indicated a significant decrease (21%) in stomatal conductance in response to growth in elevated [CO 2 ] across all studies. The response to [CO 2 ] was significantly stronger in young trees than old trees, in deciduous compared to coniferous trees, and in water stressed compared to nutrient stressed trees. No evidence of acclimation of stomatal conductance to elevated [CO 2 ] was found. • Fits of data to the first model showed that growth in elevated [CO 2 ] did not alter the response of stomatal conductance to vapour pressure deficit, soil water content or atmospheric [CO 2 ]. Fits of data to the second model indicated that conductance and assimilation responded in parallel to elevated [CO 2 ] except when water was limiting. • Data were compared to a previous meta-analysis and it was found that the response of g s to elevated [CO 2 ] was much more consistent in long-term (> 1 yr) studies, emphasising the need for long-term elevated [CO 2 ] studies. By interpreting data in terms of models, the synthesis will aid future modelling studies of responses of forest trees to elevated [CO 2 ].
To quantify the impact that planting indigenous trees and shrubs in mixed communities (environmen... more To quantify the impact that planting indigenous trees and shrubs in mixed communities (environmental plantings) have on net sequestration of carbon and other environmental or commercial benefits, precise and non-biased estimates of biomass are required. Because these plantings consist of several species, estimation of their biomass through allometric relationships is a challenging task. We explored methods to accurately estimate biomass through harvesting 3139 trees and shrubs from 22 plantings, and collating similar datasets from earlier studies, in non-arid (>300 mm rainfall year À1 ) regions of southern and eastern Australia. Site-and-species specific allometric equations were developed, as were three types of generalised, multi-site, allometric equations based on categories of species and growth-habits: (i) speciesspecific, (ii) genus and growth-habit, and (iii) universal growth-habit irrespective of genus. Biomass was measured at plot level at eight contrasting sites to test the accuracy of prediction of tonnes dry matter of above-ground biomass per hectare using different classes of allometric equations. A finer-scale analysis tested performance of these at an individual-tree level across a wider range of sites. Although the percentage error in prediction could be high at a given site (up to 45%), it was relatively low (<11%) when generalised allometry-predictions of biomass was used to make regional-or estate-level estimates across a range of sites. Precision, and thus accuracy, increased slightly with the level of specificity of allometry. Inclusion of site-specific factors in generic equations increased efficiency of prediction of above-ground biomass by as much as 8%. Site-and-species-specific equations are the most accurate for site-based predictions. Generic allometric equations developed here, particularly the generic species-specific equations, can be confidently applied to provide regional-or estate-level estimates of above-ground biomass and carbon.
Our limited understanding of the processes that control the allocation of biomass in trees is one... more Our limited understanding of the processes that control the allocation of biomass in trees is one of the factors that hinders our ability to develop mechanistic models of tree growth. Furthermore, accurate assessment of carbon sequestration by forests is hampered by lack of information regarding below-ground biomass. Below-ground to above-ground biomass ratios (BGB:AGB) are known to vary with a number of environmental factors, tending to increase in drier, harsher conditions. However, there are few, good datasets of BGB:AGB ratios of large trees, especially native Australian species. We aimed to investigate the response of BGB:AGB to water availability and tree spacing in 10-year-old Eucalyptus camaldulensis growing in a plantation in a low rainfall area.
This paper describes the development and first results of the "Community Integrated Assessment Sy... more This paper describes the development and first results of the "Community Integrated Assessment System" (CIAS), a unique multi-institutional modular and flexible integrated assessment system for modelling climate change. Key to this development is the supporting software infrastructure, SoftIAM. Through it, CIAS is distributed between the community of institutions which has each contributed modules to the CIAS system. At the heart of SoftIAM is the Bespoke Framework Generator (BFG) which enables flexibility in the assembly and composition of individual modules from a pool to form coupled models within CIAS, and flexibility in their deployment onto the available software and hardware resources. Such flexibility greatly enhances modellers' ability to re-configure the CIAS coupled models to answer different questions, thus tracking evolving policy needs. It also allows rigorous testing of the robustness of IA modelling results to the use of different component modules representing the same processes (for example, the economy). Such processes are often modelled in very different ways, using different paradigms, at the participating institutions. An illustrative application to the study of the relationship between the economy and the earth's climate system is provided.
Resolving ecophysiological processes in elevated atmospheric CO 2 (C a ) at scales larger than si... more Resolving ecophysiological processes in elevated atmospheric CO 2 (C a ) at scales larger than single leaves poses significant challenges. Here, we describe a field-based experimental system designed to grow trees up to 9 m tall in elevated C a with the capacity to control air temperature and simultaneously measure whole-tree gas exchange. In western Sydney, Australia, we established the Hawkesbury Forest Experiment (HFE) where we built whole-tree chambers (WTC) to measure whole-tree CO 2 and water fluxes of an evergreen broadleaf tree, Eucalyptus saligna. A single E. saligna tree was grown from seedling to small tree within each of 12 WTCs; six WTCs were maintained at ambient C a and six WTCs were maintained at elevated C a , targeted at ambient C a +240 mol mol −1 . All 12 WTCs were controlled to track ambient outside air temperature (T air ) and air water vapour deficit (D air ). During the experimental period, T air , D air and C a in the WTCs were within 0.5 • C, 0.3 kPa, and 15 mol mol −1 of the set-points for 90% of the time, respectively. Diurnal responses of whole-tree CO 2 and water vapour fluxes are analysed, demonstrating the ability of the tree chamber system to measure rapid environmental responses of these fluxes of entire trees. The light response of CO 2 uptake for entire trees showed a clear diurnal hysteresis, attributed to stomatal closure at high D air . Tree scale CO 2 fluxes confirm the hypothesised deleterious effect of chilling night-time temperatures on whole-tree carbon gain in this subtropical Eucalyptus. The whole-tree chamber flux data add an invaluable scale to measurements in both ambient and elevated C a and allow us to elucidate the mechanisms driving tree productivity responses to elevated C a in interaction with water availability and temperature.
Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, sug... more Under elevated atmospheric CO2 concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO2 effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that:
Nocturnal water flux has been observed in trees under a variety of environmental conditions and c... more Nocturnal water flux has been observed in trees under a variety of environmental conditions and can be a significant contributor to diel canopy water flux. Elevated atmospheric CO(2) (elevated [CO(2)]) can have an important effect on day-time plant water fluxes, but it is not known whether it also affects nocturnal water fluxes. We examined the effects of elevated [CO(2)] on nocturnal water flux of field-grown Eucalyptus saligna trees using sap flux through the tree stem expressed on a sapwood area (J(s)) and leaf area (E(t)) basis. After 19 months growth under well-watered conditions, drought was imposed by withholding water for 5 months in the summer, ending with a rain event that restored soil moisture. Reductions in J(s) and E(t) were observed during the severe drought period in the dry treatment under elevated [CO(2)], but not during moderate- and post-drought periods. Elevated [CO(2)] affected night-time sap flux density which included the stem recharge period, called 'tot...
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Papers by Craig Barton