Papers by Marcus Schortemeyer
Functional Plant Biology, 2015
Understanding the response of sub-Antarctic plants to a warming climate requires an understanding... more Understanding the response of sub-Antarctic plants to a warming climate requires an understanding of the relationship of carbon gain and loss to temperature. In a field study on Heard Island, we investigated the responses of photosynthesis and respiration of the sub-Antarctic megaherb Pringlea antiscorbutica R. Br. to temperature. This was done by instantaneously manipulating leaf temperature in a gas exchange cuvette on plants adapted to natural temperature variation along an altitudinal gradient. There was little altitudinal variation in the temperature response of photosynthesis. Photosynthesis was much less responsive to temperature than electron transport, suggesting that Rubisco activity was generally the rate-limiting process. The temperature response of leaf respiration rates was greater in cold-grown (high altitude) plants compared with warm-grown (low altitude) plants. This thermal acclimation would enable plants to maintain a positive carbon budget over a greater temperature range.
Plant, Cell and Environment, 2002
In the present study the effect of elevated CO 2 on growth and nitrogen fixation of seven Austral... more In the present study the effect of elevated CO 2 on growth and nitrogen fixation of seven Australian Acacia species was investigated. Two species from semi-arid environments in central Australia (Acacia aneura and A. tetragonophylla) and five species from temperate southeastern Australia (Acacia irrorata , A. mearnsii, A. dealbata , A. implexa and A. melanoxylon) were grown for up to 148 d in controlled greenhouse conditions at either ambient (350 µ µ µ µ mol mol − − − − 1) or elevated (700 µ µ µ µ mol mol − − − − 1) CO 2 concentrations. After establishment of nodules, the plants were completely dependent on symbiotic nitrogen fixation. Six out of seven species had greater relative growth rates and lower whole plant nitrogen concentrations under elevated versus normal CO 2. Enhanced growth resulted in an increase in the amount of nitrogen fixed symbiotically for five of the species. In general, this was the consequence of lower whole-plant nitrogen concentrations, which equate to a larger plant and greater nodule mass for a given amount of nitrogen. Since the average amount of nitrogen fixed per unit nodule mass was unaltered by atmospheric CO 2 , more nitrogen could be fixed for a given amount of plant nitrogen. For three of the species, elevated CO 2 increased the rate of nitrogen fixation per unit nodule mass and time, but this was completely offset by a reduction in nodule mass per unit plant mass.
Communications in Soil Science Plant Analysis, Nov 11, 2008
... Perennial Ryegrass1 Marcus Schortemeyer,a Hana Šantrůčková,b and Michael J. Sadowskyc ... Soi... more ... Perennial Ryegrass1 Marcus Schortemeyer,a Hana Šantrůčková,b and Michael J. Sadowskyc ... Soil suspensions (2.5 mL) were analyzed immediately for fluorescein diacetate (FDA) hydrolytic activity according to the method of Schnuerer and Rosswall (1982). ...
For environmental and economical reasons, ammonium ought to be the preferred source of nitrogen f... more For environmental and economical reasons, ammonium ought to be the preferred source of nitrogen for plant nutrition. However, sole ammonium nutrition often leads to growth reductions, and the benefits of mixed nitrogen nutritionconsisting of both ammonium and nitratehave been difficult to prove on the field scale, although they have been often observed in model experiments. In order to determine the availability of ammonium in soils to maize seedlings and to investigate the strategies that plants employ in re¬ sponse to an enhanced ammonium supply, field trials and hydroponic experi¬ ments were carried out.
Annals of Botany, 1997
Four maize (Zea mays L.) hybrids were grown hydroponically for 4 weeks with 20 m ammonium or nit... more Four maize (Zea mays L.) hybrids were grown hydroponically for 4 weeks with 20 m ammonium or nitrate as the sole nitrogen source. Dry matter production was strongly depressed by ammonium nutrition in the hybrid Helga relative to plants grown on nitrate, and moderately decreased in the hybrid Melina. Ammonium had no inhibitory effect on total yield in the other two hybrids (Ramses and DK 261). The relative growth rate (RGR) of roots and shoots of the sensitive hybrid Helga decreased significantly under ammonium nutrition during the first 2 weeks of the experiment, while at the end of the experiment nitrogen form had no effect on the RGR in any of the four hybrids. The strong reduction in RGR of Helga in the early seedling stage was correlated with the accumulation of twice the concentration of free ammonium in the shoot tissue relative to the other hybrids. Helga was therefore unable to sufficiently detoxify ammonia in the roots. Root concentrations of water soluble carbohydrates (WSC) in Helga and Melina in the early seedling stage did not differ under ammonium and nitrate nutrition. In contrast, Ramses and DK 261 both had elevated WSC concentrations in ammonium-fed roots. It is hypothesized that a sufficient supply of carbon skeletons for ammonium assimilation in the roots is required for maximum growth under high ammonium concentrations, and that there is genotypic variability in this physiological trait.
Functional Plant Biology, 2015
Understanding the response of sub-Antarctic plants to a warming climate requires an understanding... more Understanding the response of sub-Antarctic plants to a warming climate requires an understanding of the relationship of carbon gain and loss to temperature. In a field study on Heard Island, we investigated the responses of photosynthesis and respiration of the sub-Antarctic megaherb Pringlea antiscorbutica R. Br. to temperature. This was done by instantaneously manipulating leaf temperature in a gas exchange cuvette on plants adapted to natural temperature variation along an altitudinal gradient. There was little altitudinal variation in the temperature response of photosynthesis. Photosynthesis was much less responsive to temperature than electron transport, suggesting that Rubisco activity was generally the rate-limiting process. The temperature response of leaf respiration rates was greater in cold-grown (high altitude) plants compared with warm-grown (low altitude) plants. This thermal acclimation would enable plants to maintain a positive carbon budget over a greater temperat...
Global Change Biology, 2000
The effect of elevated atmospheric CO 2 concentration (C a ) on soil carbon and nitrogen accumula... more The effect of elevated atmospheric CO 2 concentration (C a ) on soil carbon and nitrogen accumulation and soil microbial biomass and activity in a native Florida scrub oak community was studied. The plant community, dominated by Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated C a in open-top chambers. Buried subsoil bags were retrieved after 1 year of exposure to elevated C a . In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the ®rst after a long dry spell and the second after 25 mm of rainfall) and divided into rhizosphere and bulk soil. Soil organic matter accumulation (excluding roots) into the buried subsoil bags was lower in elevated than in ambient C a . Concentrations of soluble carbon and ninhydrin-reactive nitrogen (N ninh ) in the rhizosphere soil were reduced by elevated C a for the ®rst sampling date and unaffected for the second sampling date. Microbial activity, measured as¯uorescein diacetate (FDA) hydrolysis, decreased in elevated C a for the ®rst sampling date. Microbial biomass carbon and nitrogen in the bulk soil were unaffected by elevated C a . There was no effect of elevated C a on bacterial numbers in the rhizosphere.
Australian Journal of Plant Physiology, 2001
The growth reduction of wheat (Triticum aestivum L.) during and after waterlogging stress depends... more The growth reduction of wheat (Triticum aestivum L.) during and after waterlogging stress depends on the depth of water from the soil surface. In a pot experiment with 3-week-old plants, soil was waterlogged for 14 d at the surface, or at 100 or 200 mm below the surface, and pots were then drained to assess recovery. A fully drained treatment kept at field capacity served as control. During waterlogging, the relative growth rate of roots decreased more than that of shoots (by 6–27% for shoots, by 15–74% for roots), and plant growth was reduced proportionally as the water level was increased. Light-saturated net photosynthesis was reduced by 70–80% for the two most severe waterlogging treatments, but was little affected for plants in soil waterlogged at 200 mm below the surface. The number of adventitious roots formed per stem in plants grown in waterlogged soil increased up to 1.5 times, but the number of tillers per plant was reduced by 24–62%. The adventitious roots only penetrated 85–116 mm below the water level in all waterlogging treatments. Adventitious root porosity was enhanced up to 10-fold for plants grown in waterlogged soil, depending on water level and position along the roots. Porosity also increased in basal zones of roots above the water level when the younger tissues had penetrated the waterlogged zone. Fourteen days after draining the pots, growth rates of plants where the soil had been waterlogged at 200 mm below the surface had recovered, while those of plants in the more severely waterlogged treatments had only partially recovered. These findings show that the depth of waterlogging has a large impact on the response of wheat both during and after a waterlogging event so that assessment of recovery is essential in evaluating waterlogging tolerance in crops.
Annals of Botany, 2004
A rapid leaf area development is a desirable trait in cereal crops. Differences between crop spec... more A rapid leaf area development is a desirable trait in cereal crops. Differences between crop species or genotypes in individual leaf growth characteristics are well documented, whereas less attention has been paid to differences in the relationships between leaf growth characteristics of successive leaves and tillers. The latter is important in determining differences in leaf area expansion at the whole shoot level and whole plant growth. We investigated the relationships between several leaf characteristics and leaf position on the main stem, tiller 1 and tiller 2, for two wheat (Triticum) species and three wild relatives of wheat (Aegilops spp.). These relationships were subsequently evaluated in relation to leaf area expansion of whole shoot (RGR la ), leaf photosynthetic characteristics, biomass allocation and whole plant growth (RGR dm ).
Tree Physiology, 2007
Mixtures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman are twice as productive a... more Mixtures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman are twice as productive as E. globulus monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N 2 fixation by A. mearnsii. To investigate whether N 2 fixation by A. mearnsii could account for the mixed-species growth responses, we assessed N 2 fixation by the accretion method and the 15 N natural abundance method. Nitrogen gained by E. globulus and A. mearnsii mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that A. mearnsii influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing A. mearnsii compared with E. globulus monocultures were due to N 2 fixation, the 10-year annual mean rates of N 2 fixation were 38 and 86 kg ha -1 year -1 in 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation by A. mearnsii could not be quantified on the basis of the natural abundance of 15 N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that A. mearnsii fixed significant quantities of N 2 when mixed with E. globulus. A decline in δ 15 N values of E. globulus and A. mearnsii with time, from 2 to 10 years, is further evidence that N 2 was fixed and cycled through the stands. The increased aboveground biomass production of E. globulus trees in mixtures when compared with monocultures can be attributed to increases in N availability.
Soil Biology and Biochemistry, 1996
Increases in the global atmospheric concentration of CO2 will not only directly affect the growth... more Increases in the global atmospheric concentration of CO2 will not only directly affect the growth of plants, but might also alter the living conditions for soil biota. This could lead to shifts in the size and composition of the soil microbial communities. In this study we investigated the response of heterotrophic bacteria, NH4+-oxidising bacteria, and Rhizobium leguminosarum bv. trifolii populations
Plant, Cell and Environment, 2003
This study investigated aerenchyma formation and function in adventitious roots of wheat ( Tritic... more This study investigated aerenchyma formation and function in adventitious roots of wheat ( Triticum aestivum L.) when only a part of the root system was exposed to O 2 deficiency. Two experimental systems were used: (1) plants in soil waterlogged at 200 mm below the surface; or (2) a nutrient solution system with only the apical region of a single root exposed to deoxygenated stagnant agar solution with the remainder of the root system in aerated nutrient solution. Porosity increased two-to three-fold along the entire length of the adventitious roots that grew into the water-saturated zone 200 mm below the soil surface, and also increased in roots that grew in the aerobic soil above the water-saturated zone. Likewise, adventitious roots with only the tips growing into deoxygenated stagnant agar solution developed aerenchyma along the entire main axis. Measurements of radial O 2 loss (ROL), taken using root-sleeving O 2 electrodes, showed this aerenchyma was functional in conducting O 2. The ROL measured near tips of intact roots in deoxygenated stagnant agar solution, while the basal part of the root remained in aerated solution, was sustained when the atmosphere around the shoot was replaced by N 2 . This illustrates the importance of O 2 diffusion into the basal regions of roots within an aerobic zone, and the subsequent longitudinal movement of O 2 within the aerenchyma, to supply O 2 to the tip growing in an O 2 deficient zone.
Plant, Cell and Environment, 1998
In this study we assessed the inherent relative growth rate (RGR) under controlled environment co... more In this study we assessed the inherent relative growth rate (RGR) under controlled environment conditions of 10 contrasting Acacia species from semi-arid and mesic environments. For several of the species, compound pinnate leaves produced early in the seedling stage, were gradually replaced by phyllodes (expanded petioles that form simple lamina). Other species either did not form phyllodes, or only did so to a minor degree by the end of the study. Phyllode production was dominant in the four slow-growing Acacia species from semi-arid environments (A.
Plant Biology, 2008
Productivity and climate models often use a constant Q 10 for plant respiration, assuming tight c... more Productivity and climate models often use a constant Q 10 for plant respiration, assuming tight control of respiration by temperature. We studied the temperature response of leaf respiration of two cold climate species (the Australian tree Eucalyptus pauciflora and the subantarctic megaherb Pringlea antiscorbutica, both measured in a field setting) on a short timescale (minutes) during different times within a diel course, and on a longer timescale, using diel variations in ambient temperature. There were great variations in Q 10 depending on measuring day, measuring time and measuring method. When Q 10 was calculated from short-term (15 min) manipulations of leaf temperature, the resulting values were usually markedly smaller than when Q 10 was calculated from measurements at ambient leaf temperatures spread over a day. While for E. pauciflora, Q 10 estimates decreased with rising temperature (corroborating the concept of a temperature-dependent Q 10 ), the opposite was the case for P. antiscorbutica. Clearly, factors other than temperature co-regulate both leaf respiration rates and temperature sensitivity and contribute to diel and seasonal variation of respiration.
Oecologia, 1999
In this study we assessed the impact of elevated CO2 with unlimited water and complete nutrient o... more In this study we assessed the impact of elevated CO2 with unlimited water and complete nutrient on the growth and nitrogen economy of ten woody Acacia species that differ in relative growth rate (RGR). Specifically, we asked whether fast- and slow-growing species systematically differ in their response to elevated CO2. Four slow-growing species from semi-arid environments (Acacia aneura, A. colei, A. coriacea and A. tetragonophylla) and six fast-growing species from mesic environments (Acacia dealbata, A. implexa, A. mearnsii, A. melanoxylon, A. irrorata and A. saligna) were grown in glasshouses with either ambient (˜350 ppm) or elevated (˜700 ppm) atmospheric CO2. All species reached greater final plant mass with the exception of A. aneura, and RGR, averaged across all species, increased by 10% over a 12-week period when plants were exposed to elevated CO2. The stimulation of RGR was evident throughout the 12-week growth period. Elevated CO2 resulted in less foliage area per unit foliage dry mass, which was mainly the result of an increase in foliage thickness with a smaller contribution from greater dry matter content per unit fresh mass. The net assimilation rate (NAR, increase in plant mass per unit foliage area and time) of the plants grown at elevated CO2 was higher in all species (on average 30% higher than plants in ambient CO2) and was responsible for the increase in RGR. The higher NAR was associated with a substantial increase in foliar nitrogen productivity in all ten Acacia species. Plant nitrogen concentration was unaltered by growth at elevated CO2 for the slow-growing Acacia species, but declined by 10% for faster-growing species. The rate of nitrogen uptake per unit root mass was higher in seven of the species when grown under elevated CO2, and leaf area per unit root mass was reduced by elevated CO2 in seven of the species. The absolute increase in RGR due to growth under elevated CO2 was greater for fast- than for slow-growing Acacia species.
New Phytologist, 2007
The present study shows that the relative contributions of leaf area ratio (LAR) and net assimila... more The present study shows that the relative contributions of leaf area ratio (LAR) and net assimilation rate (NAR) to variation among species in relative growth rate (RGR) depend on growth temperature. We grew three subantarctic and three alpine Poa species at daytime temperatures of 7, 12 and 17 degrees C, and analysed interspecific and temperature-related variation in RGRs by growth analysis. Variation in NAR accounted for most of the interspecific differences in RGR at low growth temperature, whereas variation in both NAR and LAR contributed strongly to interspecific differences in RGR at high growth temperature. For most species, the increase in RGR from 7 to 12 degrees C was attributable to an increase in LAR, whereas the increase in RGR from 12 to 17 degrees C was attributable to an increase in NAR. There were no differences between native subantarctic and alpine species in the plasticity of growth responses to temperature. However, Poa annua, a species introduced to the subantarctic, showed much greater growth plasticity than other species. There was little difference among species in tolerance of high-temperature extremes.
New Phytologist, 2002
The effect of different durations of waterlogging and subsequent drainage is described for 3-wk-o... more The effect of different durations of waterlogging and subsequent drainage is described for 3-wk-old wheat ( Triticum aestivum ) plants.
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Papers by Marcus Schortemeyer