Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis ... more Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis that the proportion of a root system exposed to compact soil anduor the timing at which this exposure occurs determines shoot growth responses was tested. Broccoli (Brassica oleracea var. italica cv. Greenbelt) seedlings were grown in pot experiments with com- pact, loose and localized soil
Page 1. Trees (2006) 20:725733 DOI 10.1007/s00468-006-0087-x ORIGINAL ARTICLE Effects of leaf an... more Page 1. Trees (2006) 20:725733 DOI 10.1007/s00468-006-0087-x ORIGINAL ARTICLE Effects of leaf and branch removal on carbon assimilation and stem wood density of Eucalyptus grandis seedlings DS Thomas · KD Montagu · JP Conroy ...
We hypothesized that seedlings grown under water-limited conditions would develop denser wood tha... more We hypothesized that seedlings grown under water-limited conditions would develop denser wood than seedlings grown under well-watered conditions. Three Eucalyptus species (E. grandis Hill (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis Endl.) were grown in a temperature-controlled greenhouse for 19 weeks with watering treatments (well-watered and water-limited) applied at six weeks. The water-limitation treatment consisted of four drought cycles. Wood density increased by between 4 and 13% in the water-limited seedlings, but this increase was mainly due to extractive compounds embedded in the cell wall matrix. Once these compounds were removed, the increase was 0 -9% and was significant for E. grandis only. Water-limitation significantly reduced mean vessel lumen area, however, this was balanced by a trend toward greater vessel frequency in waterlimited plants, and consequently there was no difference in the proportion of stem area allocated to vessels. Conduit efficiency value was lowest in the water-limited plants, indicating that there was a cost in terms of stem hydraulic conductivity for decreasing vessel lumen area. Wood density was negatively correlated with vessel lumen fraction in well-watered plants, but this relationship broke down in the water-limited plants, possibly because of the significantly larger proportion of the stem taken up by pith in water-limited seedlings. Diurnal variation in leaf water potential was positively correlated with wood density in well-watered plants. This relationship did not hold in the water-limited plants owing to the collapse of the pressure gradient between soil and leaf. We conclude that drought periods of greater than 1 month are required to increase wood density in these species and that increases in wood density appear to result in diminished capacity to supply water to leaves.
Wood density influences both the physiological function and economic value of tree stems. We exam... more Wood density influences both the physiological function and economic value of tree stems. We examined the relationship between phosphorus (P) supply and stem wood density of Eucalyptus grandis Hill ex Maiden seedlings grown with varying soil P additions and determined how changes in wood anatomy and biomass partitioning affect the relationship. Plant height, stem diameter and total biomass increased by 400-500% with increasing P supply. Stem wood density decreased sharply from 520 to 380 kg m -3 as P supply increased to 70 mg P kg soil -1 . Further increases in P supply to 1000 mg P kg soil -1 had no effect on wood density. The increase in wood density at low soil P supply arose principally from enhanced secondary wall thickening of stem fiber cells. Cell wall thickness increased from 3.6 to 4.5 µm as soil P supply decreased. Because fiber cell diameter was independent of soil P (12 µm ± 0.3), the proportion of the stem occupied by cell wall material increased as P supply declined. The enhanced secondary wall thickening of stem fiber cells at low P supply was not associated with changes in whole-plant biomass partitioning. Instead, low P supply appeared to alter biomass partitioning within the stem in favor of secondary wall thickening. Thus, increased wood density in E. grandis seedlings grown at low P soil supply was associated with inhibited stem cambial activity, resulting in an increased proportion of photoassimilates available for secondary wall thickening of fiber cells.
... Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall envi... more ... Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments Matthew J. Searson, Dane S. Thomas, Kelvin D. Montagu and Jann P. Conroy (Vol. ... Matthew J. SearsonA,D, Dane S. ThomasB, Kelvin D. MontaguC and Jann P. ConroyA ...
In eucalypts the reduction in CO 2 assimilation and total leaf area at low phosphorus (P) supply ... more In eucalypts the reduction in CO 2 assimilation and total leaf area at low phosphorus (P) supply is not associated with lower leaf total P concentrations. We tested the hypothesis that the leaf concentration of inorganic phosphorus ([P i ]) may be a better indicator of P nutrition status in Eucalyptus grandis W. Hill ex Maiden by growing seedlings in P deficient soil supplemented with P supplies ranging from 3 to1000 mg kg À1 . Height, biomass accumulation, gas exchange, chlorophyll fluorescence and concentrations of total P ([P t ]), organic P ([P o ]) and [P i ] of the last fully expanded leaves were measured when harvested at 19 weeks. All parameters of growth increased with larger applications of soil P with most becoming saturated at additions of 500 mg P kg À1 soil. Soil P supply had larger effects on biomass and canopy leaf area, by both increased in leaf initiation and expansion, than on CO 2 assimilation (A). Leaf [P t ] and [P o ] concentrations were largely invariant to soil P supply and were not correlated with any of the measured growth and photosynthetic parameters. By contrast, leaf [P i ] increased from 171 to 398 mg kg À1 with increasing soil P supply. Furthermore, number of leaves, total leaf area and seedling biomass increased exponentially with leaf [P i ], while individual leaf area and A increased linearly with leaf [P i ], and quantum yield of photosystem II similarly increased, and non-photochemical quenching decreased, with increasing leaf [P i ]. The response of A to internal CO 2 concentration (C i ) indicated that at lower P supplies A became increasingly restricted by limitations associated with Rubisco and RuBP regeneration. Stomatal limitation may in part be masking the full effect of P supply on A as C i declined with either increasing soil P or leaf [P i ] supply. We conclude that leaf [P i ] was a potentially better indicator than [P t ] or [P o ] for correlating the effects of soil P supply on growth and photosynthesis of E. grandis. Furthermore, as A achieved at saturating C a increased with increasing P supply leaf [P i ], these findings suggest that a greatly increased rate of canopy assimilation could be achieved at higher P supply in response to the expected increase in global CO 2 levels. #
A fundamental tool in carbon accounting is tree-based allometry, whereby easily measured variable... more A fundamental tool in carbon accounting is tree-based allometry, whereby easily measured variables can be used to estimate aboveground biomass (AGB). To explore the potential of general allometry we combined raw datasets from 14 different woodland species, mainly eucalypts, from 11 sites across the Northern Territory, Queensland and New South Wales. Access to the raw data allowed two predictor variables, tree diameter (at 1.3-m height; D) and tree height (H), to be used singly or in various combinations to produce eight candidate models. Following natural log (ln) transformation, the data, consisting of 220 individual trees, were re-analysed in two steps: first as 20 species-site-specific AGB equations and, second, as a single general AGB equation. For each of the eight models, a comparison of the species-site-specific with the general equations was made with the Akaike information criterion (AIC). Further model evaluation was undertaken by a leave-one-out cross-validation technique. For each of the model forms, the species-site-specific equations performed better than the general equation. However, the best performing general equation, ln(AGB) = −2.0596 + 2.1561 ln(D) + 0.1362 (ln(H)) 2 , was only marginally inferior to the species-site-specific equations. For the best general equation, back-transformed predicted v. observed values (on a linear scale) were highly concordant, with a slope of 0.99. The only major deviation from this relationship was due to seven large, hollow trees (more than 35% loss of cross-sectional stem area at 1.3 m) at a single species-site combination. Our best-performing general model exhibited remarkable stability across species and sites, when compared with the species-site equations. We conclude that there is encouraging evidence that general predictive equations can be developed across sites and species for Australia's woodlands. This simplifies the conversion of long-term inventory measurements into AGB estimates and allows more resources to be focused on the extension of such inventories.
Conversion of pastures to plantation forests has been proposed as a means to increase rates of ca... more Conversion of pastures to plantation forests has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere thereby reducing net greenhouse gas emissions from human activities. However, several studies have indicated that soil C stocks decrease after planting conifer (mainly pine) trees into pasture. This loss of soil C detracts from the role that plantation forests can play in net C sequestration. Here, we used a paired site (a grazed native pasture with the C 4 grass Themeda triandra dominant, and an adjacent 16-year-old Pinus radiata plantation) to compare all C and nitrogen (N) pools (including soil, litter on the floor, below-ground and above-ground biomass) in the two ecosystems and to estimate the rate of C sequestration after the land use change from the native pasture to the pine plantation. Soil C and N stocks from soil surface down to 1 m under the pine plantation were significantly less than under the native pasture by 20% (57.3 Mg C ha À1 vs. 71.6 Mg C ha À1 ) and 15% (5.6 Mg N ha À1 vs. 6.7 Mg N ha À1 ), respectively. Much more C and N was stored in litter on the floor in the pine plantation than in the native pasture (8.0 Mg C ha À1 vs. 0.03 Mg C ha À1 , and 119.0 kg N ha À1 vs. 0.9 kg N ha À1 ), and in biomass (95.0 Mg C ha À1 vs. 2.5 Mg C ha À1 and 411.5 kg N ha À1 vs. 62.8 kg N ha À1 ). Carbon stored in coarse tree roots was alone sufficient to compensate the C loss from soil after the land use change. Much more C and N was deposited annually to above-ground litter in the pine plantation than in the native pasture (2.18 Mg C ha À1 year À1 vs. 0.22 Mg C ha À1 year À1 , and 32.8 kg N ha À1 year À1 vs. 5.9 kg N ha À1 year À1 ), but less to below-ground litter (through fine root death) (2.71 Mg C ha À1 year À1 vs. 3.57 Mg C ha À1 year À1 and 38.9 kg N ha À1 year À1 vs. 81.4 kg N ha À1 year À1 ). The shift in net primary production from below-ground dominance to above-ground dominance after planting trees onto the pasture, and the slower turnover of litter in the plantation, played a key role in the reduction in soil C in the plantation ecosystem. In conclusion, planting pine trees onto a native temperate Australian pasture sequestered a significant amount of C (net 86 Mg C ha À1 , averaging 5.4 Mg C ha À1 year À1 ) from the atmosphere in 16 years despite the loss of 14 Mg C ha À1 from the soil organic matter. Crown
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.
Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis ... more Plants growing in soils typically experience a mixture of loose and compact soil. The hypothesis that the proportion of a root system exposed to compact soil anduor the timing at which this exposure occurs determines shoot growth responses was tested. Broccoli (Brassica oleracea var. italica cv. Greenbelt) seedlings were grown in pot experiments with com- pact, loose and localized soil
Page 1. Trees (2006) 20:725733 DOI 10.1007/s00468-006-0087-x ORIGINAL ARTICLE Effects of leaf an... more Page 1. Trees (2006) 20:725733 DOI 10.1007/s00468-006-0087-x ORIGINAL ARTICLE Effects of leaf and branch removal on carbon assimilation and stem wood density of Eucalyptus grandis seedlings DS Thomas · KD Montagu · JP Conroy ...
We hypothesized that seedlings grown under water-limited conditions would develop denser wood tha... more We hypothesized that seedlings grown under water-limited conditions would develop denser wood than seedlings grown under well-watered conditions. Three Eucalyptus species (E. grandis Hill (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis Endl.) were grown in a temperature-controlled greenhouse for 19 weeks with watering treatments (well-watered and water-limited) applied at six weeks. The water-limitation treatment consisted of four drought cycles. Wood density increased by between 4 and 13% in the water-limited seedlings, but this increase was mainly due to extractive compounds embedded in the cell wall matrix. Once these compounds were removed, the increase was 0 -9% and was significant for E. grandis only. Water-limitation significantly reduced mean vessel lumen area, however, this was balanced by a trend toward greater vessel frequency in waterlimited plants, and consequently there was no difference in the proportion of stem area allocated to vessels. Conduit efficiency value was lowest in the water-limited plants, indicating that there was a cost in terms of stem hydraulic conductivity for decreasing vessel lumen area. Wood density was negatively correlated with vessel lumen fraction in well-watered plants, but this relationship broke down in the water-limited plants, possibly because of the significantly larger proportion of the stem taken up by pith in water-limited seedlings. Diurnal variation in leaf water potential was positively correlated with wood density in well-watered plants. This relationship did not hold in the water-limited plants owing to the collapse of the pressure gradient between soil and leaf. We conclude that drought periods of greater than 1 month are required to increase wood density in these species and that increases in wood density appear to result in diminished capacity to supply water to leaves.
Wood density influences both the physiological function and economic value of tree stems. We exam... more Wood density influences both the physiological function and economic value of tree stems. We examined the relationship between phosphorus (P) supply and stem wood density of Eucalyptus grandis Hill ex Maiden seedlings grown with varying soil P additions and determined how changes in wood anatomy and biomass partitioning affect the relationship. Plant height, stem diameter and total biomass increased by 400-500% with increasing P supply. Stem wood density decreased sharply from 520 to 380 kg m -3 as P supply increased to 70 mg P kg soil -1 . Further increases in P supply to 1000 mg P kg soil -1 had no effect on wood density. The increase in wood density at low soil P supply arose principally from enhanced secondary wall thickening of stem fiber cells. Cell wall thickness increased from 3.6 to 4.5 µm as soil P supply decreased. Because fiber cell diameter was independent of soil P (12 µm ± 0.3), the proportion of the stem occupied by cell wall material increased as P supply declined. The enhanced secondary wall thickening of stem fiber cells at low P supply was not associated with changes in whole-plant biomass partitioning. Instead, low P supply appeared to alter biomass partitioning within the stem in favor of secondary wall thickening. Thus, increased wood density in E. grandis seedlings grown at low P soil supply was associated with inhibited stem cambial activity, resulting in an increased proportion of photoassimilates available for secondary wall thickening of fiber cells.
... Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall envi... more ... Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments Matthew J. Searson, Dane S. Thomas, Kelvin D. Montagu and Jann P. Conroy (Vol. ... Matthew J. SearsonA,D, Dane S. ThomasB, Kelvin D. MontaguC and Jann P. ConroyA ...
In eucalypts the reduction in CO 2 assimilation and total leaf area at low phosphorus (P) supply ... more In eucalypts the reduction in CO 2 assimilation and total leaf area at low phosphorus (P) supply is not associated with lower leaf total P concentrations. We tested the hypothesis that the leaf concentration of inorganic phosphorus ([P i ]) may be a better indicator of P nutrition status in Eucalyptus grandis W. Hill ex Maiden by growing seedlings in P deficient soil supplemented with P supplies ranging from 3 to1000 mg kg À1 . Height, biomass accumulation, gas exchange, chlorophyll fluorescence and concentrations of total P ([P t ]), organic P ([P o ]) and [P i ] of the last fully expanded leaves were measured when harvested at 19 weeks. All parameters of growth increased with larger applications of soil P with most becoming saturated at additions of 500 mg P kg À1 soil. Soil P supply had larger effects on biomass and canopy leaf area, by both increased in leaf initiation and expansion, than on CO 2 assimilation (A). Leaf [P t ] and [P o ] concentrations were largely invariant to soil P supply and were not correlated with any of the measured growth and photosynthetic parameters. By contrast, leaf [P i ] increased from 171 to 398 mg kg À1 with increasing soil P supply. Furthermore, number of leaves, total leaf area and seedling biomass increased exponentially with leaf [P i ], while individual leaf area and A increased linearly with leaf [P i ], and quantum yield of photosystem II similarly increased, and non-photochemical quenching decreased, with increasing leaf [P i ]. The response of A to internal CO 2 concentration (C i ) indicated that at lower P supplies A became increasingly restricted by limitations associated with Rubisco and RuBP regeneration. Stomatal limitation may in part be masking the full effect of P supply on A as C i declined with either increasing soil P or leaf [P i ] supply. We conclude that leaf [P i ] was a potentially better indicator than [P t ] or [P o ] for correlating the effects of soil P supply on growth and photosynthesis of E. grandis. Furthermore, as A achieved at saturating C a increased with increasing P supply leaf [P i ], these findings suggest that a greatly increased rate of canopy assimilation could be achieved at higher P supply in response to the expected increase in global CO 2 levels. #
A fundamental tool in carbon accounting is tree-based allometry, whereby easily measured variable... more A fundamental tool in carbon accounting is tree-based allometry, whereby easily measured variables can be used to estimate aboveground biomass (AGB). To explore the potential of general allometry we combined raw datasets from 14 different woodland species, mainly eucalypts, from 11 sites across the Northern Territory, Queensland and New South Wales. Access to the raw data allowed two predictor variables, tree diameter (at 1.3-m height; D) and tree height (H), to be used singly or in various combinations to produce eight candidate models. Following natural log (ln) transformation, the data, consisting of 220 individual trees, were re-analysed in two steps: first as 20 species-site-specific AGB equations and, second, as a single general AGB equation. For each of the eight models, a comparison of the species-site-specific with the general equations was made with the Akaike information criterion (AIC). Further model evaluation was undertaken by a leave-one-out cross-validation technique. For each of the model forms, the species-site-specific equations performed better than the general equation. However, the best performing general equation, ln(AGB) = −2.0596 + 2.1561 ln(D) + 0.1362 (ln(H)) 2 , was only marginally inferior to the species-site-specific equations. For the best general equation, back-transformed predicted v. observed values (on a linear scale) were highly concordant, with a slope of 0.99. The only major deviation from this relationship was due to seven large, hollow trees (more than 35% loss of cross-sectional stem area at 1.3 m) at a single species-site combination. Our best-performing general model exhibited remarkable stability across species and sites, when compared with the species-site equations. We conclude that there is encouraging evidence that general predictive equations can be developed across sites and species for Australia's woodlands. This simplifies the conversion of long-term inventory measurements into AGB estimates and allows more resources to be focused on the extension of such inventories.
Conversion of pastures to plantation forests has been proposed as a means to increase rates of ca... more Conversion of pastures to plantation forests has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere thereby reducing net greenhouse gas emissions from human activities. However, several studies have indicated that soil C stocks decrease after planting conifer (mainly pine) trees into pasture. This loss of soil C detracts from the role that plantation forests can play in net C sequestration. Here, we used a paired site (a grazed native pasture with the C 4 grass Themeda triandra dominant, and an adjacent 16-year-old Pinus radiata plantation) to compare all C and nitrogen (N) pools (including soil, litter on the floor, below-ground and above-ground biomass) in the two ecosystems and to estimate the rate of C sequestration after the land use change from the native pasture to the pine plantation. Soil C and N stocks from soil surface down to 1 m under the pine plantation were significantly less than under the native pasture by 20% (57.3 Mg C ha À1 vs. 71.6 Mg C ha À1 ) and 15% (5.6 Mg N ha À1 vs. 6.7 Mg N ha À1 ), respectively. Much more C and N was stored in litter on the floor in the pine plantation than in the native pasture (8.0 Mg C ha À1 vs. 0.03 Mg C ha À1 , and 119.0 kg N ha À1 vs. 0.9 kg N ha À1 ), and in biomass (95.0 Mg C ha À1 vs. 2.5 Mg C ha À1 and 411.5 kg N ha À1 vs. 62.8 kg N ha À1 ). Carbon stored in coarse tree roots was alone sufficient to compensate the C loss from soil after the land use change. Much more C and N was deposited annually to above-ground litter in the pine plantation than in the native pasture (2.18 Mg C ha À1 year À1 vs. 0.22 Mg C ha À1 year À1 , and 32.8 kg N ha À1 year À1 vs. 5.9 kg N ha À1 year À1 ), but less to below-ground litter (through fine root death) (2.71 Mg C ha À1 year À1 vs. 3.57 Mg C ha À1 year À1 and 38.9 kg N ha À1 year À1 vs. 81.4 kg N ha À1 year À1 ). The shift in net primary production from below-ground dominance to above-ground dominance after planting trees onto the pasture, and the slower turnover of litter in the plantation, played a key role in the reduction in soil C in the plantation ecosystem. In conclusion, planting pine trees onto a native temperate Australian pasture sequestered a significant amount of C (net 86 Mg C ha À1 , averaging 5.4 Mg C ha À1 year À1 ) from the atmosphere in 16 years despite the loss of 14 Mg C ha À1 from the soil organic matter. Crown
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.
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