Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs w... more Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), 'Puna'. Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg(-1) mineral N and 2 mg kg(-1) bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0-300 mg P pot(-1)) and nitrogen (N) (0-270 mg N pot(-1)) was examined. Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1.7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot(-1), respectively. Ptilotus could not downregulate P...
Few studies have investigated the response of perennial legumes to drought stress (DS) and their ... more Few studies have investigated the response of perennial legumes to drought stress (DS) and their ability, following rewatering, to regrow and restore photosynthetic activity. We examined these responses for two genotypes of drought-tolerant tedera (Bituminaria bituminosa var. albomarginata) and one genotype of lucerne (Medicago sativa). Plants were grown outdoors in 1-m deep PVC pots with a reconstructed field soil profile, regularly watered for 8 months (winter to mid-summer), and then moved to a glasshouse where either watering was maintained or drought was imposed for up to 47 days, before rewatering for 28 days. Drought stress greatly decreased shoot dry matter (DM) production in both species. Lucerne plants showed severe leaf desiccation after 21 days of withholding water. Relative leaf water content (RWC = 42%) and midday leaf water potential (LWP = −6.5 MPa) decreased in tedera in response to DS, whereas leaf angle (85 ∘ ) and lateral root DM both increased. Proline and pinitol accumulated in tedera leaves during DS, and their concentration declined after rewatering. Nine days after rewatering, previously drought-stressed tedera had similar RWC and LWP to well-watered control plants. In tedera and lucerne, 28 days after rewatering, photosynthesis and stomatal conductance were greater than in the well-watered controls. The lateral root DM for one tedera genotype decreased during the recovery phase but for lucerne, the lateral root DM did not change during either the drought or the recovery phases. Overall, the root systems in tedera showed greater plasticity in response to DS and rewatering than in lucerne. In conclusion, tedera and lucerne showed different physiological and morphological strategies to survive and recover from DS. Proline and soluble sugars may act as a carbon source for regrowth in tedera during recovery. In comparison with lucerne, tedera's more rapid recovery after rewatering should contribute to a greater aboveground DM yield under alternating dry and wet periods. Tedera genotypes are highly heterogeneous and selecting genotypes with enhanced concentrations of pinitol and proline could be a valuable tool to improve plant performance during DS and recovery.
Salinity tolerance, osmotic and ionic regulation abilities, desiccation tolerance, and gill morph... more Salinity tolerance, osmotic and ionic regulation abilities, desiccation tolerance, and gill morphometry of Uca subcylindrica, which inhabits semi-arid supratidal areas, were compared with more typically intertidal fiddler crabs, especially U. longisignalis. Salinity tolerance was less in U. subcylindrica (2â€"90%o) than in U. longisignalis (0.08â€" 1lO%o). Blood osmolality and sodium and chloride concentrations were regulated over a wide range of salinities in both species, but U. subcylindrica maintained a smaller gradient against the external medium at the lowest salinity at which it survived and at the higher salinities. The osmoregulatory responses were contrary to predictions based on field distributions, but U. subcylindrica generally survived desiccation longer and always tolerated a greater percent body water loss than U. longisignalis, U. rapax, and U. panacea. Differences in gill morphometrics among the four species were consistent with features accompanying increasing terrestriality.
ABSTRACT The impacts of broadleaf crop, pasture or fallow breaks within cereal-based cropping sys... more ABSTRACT The impacts of broadleaf crop, pasture or fallow breaks within cereal-based cropping systems are widely acknowledged, but most studies have focussed on the first cereal crop after the break. We report a series of four field experiments in a semi-arid cropping zone of Southern Australia in which the impacts of a range of Year 1 sequence options (crops, pasture and fallow) on Year 3 and 4 wheat crops were investigated. In three of the experiments, two phases of the same experiment were commenced in successive years, providing seven sequence phases. In three of the seven phases (at three of the four sites), the Year 1 treatments influenced the yield of Year 3 or Year 4 wheat crops by 0.6, 0.9 and 0.9 t ha−1, although different responses between phases of the same experiments at two sites provided clear evidence of significant seasonal interactions. Interactions of Year 1 sequence treatments with tillage, crop species/varieties and/or added P-fertiliser treatments in intervening years also occurred at some sites. The largest persistent yield impacts related to the preservation of differences in residual nitrogen (N), and in some cases water following Year 1 crops through subsequent dry seasons, which were frequent in most experimental phases. Higher residual N levels after legumes and canola could persist for 2–3 years and induce yield penalties due to “haying-off” when Year 3 or 4 wheat crops experienced dry spring conditions. Such effects were offset following Year 1 fallow due to increased residual water at depth. Increases in the cereal root diseases take-all (Gaeumannomyces tritici) and rhizoctonia (Rhizoctonia solani AG8) due to Year 1 wheat also persisted through dry seasons and reduced Year 3 wheat yield in some experiments. We found no evidence for a significant role for arbuscular mycorrhizal fungi in yield of Year 3 and 4 wheat crops. We demonstrate that large and significant yield impacts (>0.5 t ha−1), both positive and negative, can persist for 3–4 years in semi-arid environments as a result of water, N and disease inoculum legacies of Year 1 crop sequence choices. Prolonged dry periods help to preserve these legacies, so that persistent and unpredictable crop sequence effects will be a feature of cropping systems in semi-arid areas with variable climates.
Phosphorus (P) is a scarce, nonrenewable resource; its acquisition by plants decreases when soil ... more Phosphorus (P) is a scarce, nonrenewable resource; its acquisition by plants decreases when soil moisture declines, as anticipated under future climate-change scenarios. It is, therefore, important to understand plant responses and adaptations to dual moisture and P limitations, in order to maintain crop productivity and predict plant performance Advances in Agronomy, Volume 124 # 2014 Elsevier Inc.
Aims We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microb... more Aims We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microbes in the uptake of phosphorus (P) by Trifolium subterraneum from a pulse. Methods Plants were grown in sterilised pasture field soil with a realistic level of available P. There were five treatments, two of which involved AMF: 1) unsterilised field soil containing a community of AMF and heterotrophic organisms; 2) Scutellospora calospora inoculum (AMF); 3) microbes added as filtrate from the field soil; 4) microbes added as filtrate from the S. calospora inoculum; 5) no additions, i.e. sterilised field soil. After 11 weeks, plants were harvested: 1 day before (day 0), 1 day after (day 2) and 7 days after (day 8) the pulse of P (10 mg kg −1 ). Results There was no difference among treatments in shoot and root dry weight, which increased from day 0 to day 8. At day 0, shoots and roots of plants in the colonised treatments had higher P and lower Mn concentrations. After the pulse, the rate of increase in P concentration in the shoots was slower for the colonised plants, and the root Mn concentration declined by up to 50 % by day 2. Conclusions Plants colonised by AMF had a lower rate of increase in shoot P concentration after a pulse, perhaps because intraradical hyphae accumulated P and thus reduced its transport to the shoots.
Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbu... more Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (−AMF) addition of unsterilized field soil. After 9-10 weeks, half the pots received 15 mg P kg −1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant-available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ∼0.2-0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.
Study of plants with unusual phosphorus (P) physiology may assist development of more P-efficient... more Study of plants with unusual phosphorus (P) physiology may assist development of more P-efficient crops. Ptilotus polystachyus grows well at high P supply, when shoot P concentrations ( [P] ) may exceed 40 mg P g −1 dry matter (DM). We explored the P physiology of P. polystachyus seedlings grown in nutrient solution with 0-5 mM P. In addition, young leaves and roots of soil-grown plants were used for cryoscanning electron microscopy and X-ray microanalysis. No P-toxicity symptoms were observed, even at 5 mM P in solution. Shoot DM was similar at 0.1 and 1.0 mM P in solution, but was ∼14% lower at 2 and 5 mM P. At 1 mM P, [P] was 36, 18, 14 and 11 mg P g −1 DM in mature leaves, young leaves, stems and roots, respectively. Leaf potassium, calcium and magnesium concentrations increased with increasing P supply. Leaf epidermal and palisade mesophyll cells had similar [P]. The root epidermis and most cortical cells had senesced, even in young roots. We conclude that preferential accumulation of P in mature leaves, accumulation of balancing cations and uniform distribution of P across leaf cell types allow P. polystachyus to tolerate very high leaf [P].
Native Australian perennial herbaceous legumes with potential to be developed as pasture plants f... more Native Australian perennial herbaceous legumes with potential to be developed as pasture plants for the medium-low rainfall zones of the wheatbelt were collected and screened. The aim was to identify species with characteristics suited for domestication and adaptation for difficult environments, such as highly acid soils, poorly fertile soils, and areas with low rainfall or prone to drought. A literature
Aims Many Australian legumes have evolved in low-phosphorus (P) soils and low-rainfall areas. The... more Aims Many Australian legumes have evolved in low-phosphorus (P) soils and low-rainfall areas. Therefore a study was made of the interaction of soil [P] and water availability on growth, photosynthesis, water-use efficiency (WUE) and P nutrition of two Australian native legumes with pasture potential, Cullen australasicum and C. pallidum, and the widely grown exotic pasture legume, lucerne (Medicago sativa). † Methods Plants were grown in a glasshouse at 3, 10 and 30 mg P kg 21 dry soil for 5 months. At week 10, two drought treatments were imposed, total pot dried (all-dry) and only top soil dried (top-dry), while control pots were maintained at field capacity. † Key Results Shoot dry weight produced by lucerne was never higher than that of C. australasicum. For C. pallidum only, shoot dry weight was reduced at 30 mg P kg 21 dry soil. The small root system of the Cullen species was quite plastic, allowing plants to access P and moisture efficiently. Lucerne always had a higher proportion of its large root system in the top soil layer compared with Cullen species. All species showed decreased photosynthesis, leaf water potential and stomatal conductance when exposed to drought, but the reductions were less for Cullen species, due to tighter stomatal control, and consequently they achieved a higher WUE. All species showed highest rhizosphere carboxylate concentrations in the all-dry treatment. For lucerne only, carboxylates decreased as P supply increased. Citrate was the main carboxylate in the control and top-dry treatments, and malate in the all-dry treatment. † Conclusions Multiple adaptive responses of Cullen species and lucerne favoured exploitation of low-P soils under drought. The performance of undomesticated Cullen species, relative to that of lucerne, shows their promise as pasture species for environments such as in south-western Australia where water and P are limiting, especially in view of a predicted drying and warming climate.
Background and aims Medicago sativa L. is widely grown in southern Australia, but is poorly adapt... more Background and aims Medicago sativa L. is widely grown in southern Australia, but is poorly adapted to dry, hot summers. This study aimed to identify perennial herbaceous legumes with greater resistance to drought stress and explore their adaptive strategies. Methods Ten herbaceous perennial legume species/ accessions were grown in deep pots in a sandy, lowphosphorus field soil in a glasshouse. Drought stress was imposed by ceasing to water. A companion M. sativa plant in each pot minimised differences in leaf area and water consumption among species. Plants were harvested when stomatal conductance of stressed plants decreased to around 10% of well watered plants.
Page 1. RESEARCH ARTICLE Prioritisation of novel pasture species for use in water-limited agricul... more Page 1. RESEARCH ARTICLE Prioritisation of novel pasture species for use in water-limited agriculture: a case study of Cullen in the Western Australian wheatbelt RG Bennett • MH Ryan • TD Colmer • D. Real Received: 4 February ...
The present paper compares standard and novel methods for analysing aggregated patterns of plant ... more The present paper compares standard and novel methods for analysing aggregated patterns of plant death in designed field experiments; these methods include binomial (BN), beta-binomial (BBN), logistic-normal-binomial (LNB), BN models with random blocks, BN models with smooth-scale spatial components and principal coordinates of neighbour matrices (PCNM). PCNM is a relatively new technique used in ecology to determine how much observed variability can be explained by spatial and environmental variables, and has not yet been applied to agricultural studies. The survival data of two pasture species, collected from a designed field experiment that was replicated at multiple locations, were used. First, the occurrence of overdispersion was tested using the BN and BBN distributions. Goodness-of-fit tests proved that the BBN model provided a better description (better fit) of the observed data in some cases than did the BN distribution, indicating overdispersion was present. When overdispersion was not present, the BN distribution was adequate to describe the data, and the use of the BBN distribution was superfluous. It is then shown that the PCNM approach, the BN model with smooth-scale spatial components and the LNB model were able to account for some of the variation as spatial variability, thus reducing the species effect compared with that explained under the standard BN model. The amount of variation among species according to the BN model and the BN model with random blocks was similar. Therefore, it is argued that the novel PCNM approach warrants further testing when exploring the spatial variability in designed experiments in agriculture and using LNB, PCNM and BN with smooth-scale spatial components may provide better predictions of species effects than do other, more conventional, approaches.
Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs w... more Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), 'Puna'. Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg(-1) mineral N and 2 mg kg(-1) bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0-300 mg P pot(-1)) and nitrogen (N) (0-270 mg N pot(-1)) was examined. Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1.7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot(-1), respectively. Ptilotus could not downregulate P...
Few studies have investigated the response of perennial legumes to drought stress (DS) and their ... more Few studies have investigated the response of perennial legumes to drought stress (DS) and their ability, following rewatering, to regrow and restore photosynthetic activity. We examined these responses for two genotypes of drought-tolerant tedera (Bituminaria bituminosa var. albomarginata) and one genotype of lucerne (Medicago sativa). Plants were grown outdoors in 1-m deep PVC pots with a reconstructed field soil profile, regularly watered for 8 months (winter to mid-summer), and then moved to a glasshouse where either watering was maintained or drought was imposed for up to 47 days, before rewatering for 28 days. Drought stress greatly decreased shoot dry matter (DM) production in both species. Lucerne plants showed severe leaf desiccation after 21 days of withholding water. Relative leaf water content (RWC = 42%) and midday leaf water potential (LWP = −6.5 MPa) decreased in tedera in response to DS, whereas leaf angle (85 ∘ ) and lateral root DM both increased. Proline and pinitol accumulated in tedera leaves during DS, and their concentration declined after rewatering. Nine days after rewatering, previously drought-stressed tedera had similar RWC and LWP to well-watered control plants. In tedera and lucerne, 28 days after rewatering, photosynthesis and stomatal conductance were greater than in the well-watered controls. The lateral root DM for one tedera genotype decreased during the recovery phase but for lucerne, the lateral root DM did not change during either the drought or the recovery phases. Overall, the root systems in tedera showed greater plasticity in response to DS and rewatering than in lucerne. In conclusion, tedera and lucerne showed different physiological and morphological strategies to survive and recover from DS. Proline and soluble sugars may act as a carbon source for regrowth in tedera during recovery. In comparison with lucerne, tedera's more rapid recovery after rewatering should contribute to a greater aboveground DM yield under alternating dry and wet periods. Tedera genotypes are highly heterogeneous and selecting genotypes with enhanced concentrations of pinitol and proline could be a valuable tool to improve plant performance during DS and recovery.
Salinity tolerance, osmotic and ionic regulation abilities, desiccation tolerance, and gill morph... more Salinity tolerance, osmotic and ionic regulation abilities, desiccation tolerance, and gill morphometry of Uca subcylindrica, which inhabits semi-arid supratidal areas, were compared with more typically intertidal fiddler crabs, especially U. longisignalis. Salinity tolerance was less in U. subcylindrica (2â€"90%o) than in U. longisignalis (0.08â€" 1lO%o). Blood osmolality and sodium and chloride concentrations were regulated over a wide range of salinities in both species, but U. subcylindrica maintained a smaller gradient against the external medium at the lowest salinity at which it survived and at the higher salinities. The osmoregulatory responses were contrary to predictions based on field distributions, but U. subcylindrica generally survived desiccation longer and always tolerated a greater percent body water loss than U. longisignalis, U. rapax, and U. panacea. Differences in gill morphometrics among the four species were consistent with features accompanying increasing terrestriality.
ABSTRACT The impacts of broadleaf crop, pasture or fallow breaks within cereal-based cropping sys... more ABSTRACT The impacts of broadleaf crop, pasture or fallow breaks within cereal-based cropping systems are widely acknowledged, but most studies have focussed on the first cereal crop after the break. We report a series of four field experiments in a semi-arid cropping zone of Southern Australia in which the impacts of a range of Year 1 sequence options (crops, pasture and fallow) on Year 3 and 4 wheat crops were investigated. In three of the experiments, two phases of the same experiment were commenced in successive years, providing seven sequence phases. In three of the seven phases (at three of the four sites), the Year 1 treatments influenced the yield of Year 3 or Year 4 wheat crops by 0.6, 0.9 and 0.9 t ha−1, although different responses between phases of the same experiments at two sites provided clear evidence of significant seasonal interactions. Interactions of Year 1 sequence treatments with tillage, crop species/varieties and/or added P-fertiliser treatments in intervening years also occurred at some sites. The largest persistent yield impacts related to the preservation of differences in residual nitrogen (N), and in some cases water following Year 1 crops through subsequent dry seasons, which were frequent in most experimental phases. Higher residual N levels after legumes and canola could persist for 2–3 years and induce yield penalties due to “haying-off” when Year 3 or 4 wheat crops experienced dry spring conditions. Such effects were offset following Year 1 fallow due to increased residual water at depth. Increases in the cereal root diseases take-all (Gaeumannomyces tritici) and rhizoctonia (Rhizoctonia solani AG8) due to Year 1 wheat also persisted through dry seasons and reduced Year 3 wheat yield in some experiments. We found no evidence for a significant role for arbuscular mycorrhizal fungi in yield of Year 3 and 4 wheat crops. We demonstrate that large and significant yield impacts (>0.5 t ha−1), both positive and negative, can persist for 3–4 years in semi-arid environments as a result of water, N and disease inoculum legacies of Year 1 crop sequence choices. Prolonged dry periods help to preserve these legacies, so that persistent and unpredictable crop sequence effects will be a feature of cropping systems in semi-arid areas with variable climates.
Phosphorus (P) is a scarce, nonrenewable resource; its acquisition by plants decreases when soil ... more Phosphorus (P) is a scarce, nonrenewable resource; its acquisition by plants decreases when soil moisture declines, as anticipated under future climate-change scenarios. It is, therefore, important to understand plant responses and adaptations to dual moisture and P limitations, in order to maintain crop productivity and predict plant performance Advances in Agronomy, Volume 124 # 2014 Elsevier Inc.
Aims We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microb... more Aims We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microbes in the uptake of phosphorus (P) by Trifolium subterraneum from a pulse. Methods Plants were grown in sterilised pasture field soil with a realistic level of available P. There were five treatments, two of which involved AMF: 1) unsterilised field soil containing a community of AMF and heterotrophic organisms; 2) Scutellospora calospora inoculum (AMF); 3) microbes added as filtrate from the field soil; 4) microbes added as filtrate from the S. calospora inoculum; 5) no additions, i.e. sterilised field soil. After 11 weeks, plants were harvested: 1 day before (day 0), 1 day after (day 2) and 7 days after (day 8) the pulse of P (10 mg kg −1 ). Results There was no difference among treatments in shoot and root dry weight, which increased from day 0 to day 8. At day 0, shoots and roots of plants in the colonised treatments had higher P and lower Mn concentrations. After the pulse, the rate of increase in P concentration in the shoots was slower for the colonised plants, and the root Mn concentration declined by up to 50 % by day 2. Conclusions Plants colonised by AMF had a lower rate of increase in shoot P concentration after a pulse, perhaps because intraradical hyphae accumulated P and thus reduced its transport to the shoots.
Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbu... more Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (−AMF) addition of unsterilized field soil. After 9-10 weeks, half the pots received 15 mg P kg −1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant-available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ∼0.2-0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.
Study of plants with unusual phosphorus (P) physiology may assist development of more P-efficient... more Study of plants with unusual phosphorus (P) physiology may assist development of more P-efficient crops. Ptilotus polystachyus grows well at high P supply, when shoot P concentrations ( [P] ) may exceed 40 mg P g −1 dry matter (DM). We explored the P physiology of P. polystachyus seedlings grown in nutrient solution with 0-5 mM P. In addition, young leaves and roots of soil-grown plants were used for cryoscanning electron microscopy and X-ray microanalysis. No P-toxicity symptoms were observed, even at 5 mM P in solution. Shoot DM was similar at 0.1 and 1.0 mM P in solution, but was ∼14% lower at 2 and 5 mM P. At 1 mM P, [P] was 36, 18, 14 and 11 mg P g −1 DM in mature leaves, young leaves, stems and roots, respectively. Leaf potassium, calcium and magnesium concentrations increased with increasing P supply. Leaf epidermal and palisade mesophyll cells had similar [P]. The root epidermis and most cortical cells had senesced, even in young roots. We conclude that preferential accumulation of P in mature leaves, accumulation of balancing cations and uniform distribution of P across leaf cell types allow P. polystachyus to tolerate very high leaf [P].
Native Australian perennial herbaceous legumes with potential to be developed as pasture plants f... more Native Australian perennial herbaceous legumes with potential to be developed as pasture plants for the medium-low rainfall zones of the wheatbelt were collected and screened. The aim was to identify species with characteristics suited for domestication and adaptation for difficult environments, such as highly acid soils, poorly fertile soils, and areas with low rainfall or prone to drought. A literature
Aims Many Australian legumes have evolved in low-phosphorus (P) soils and low-rainfall areas. The... more Aims Many Australian legumes have evolved in low-phosphorus (P) soils and low-rainfall areas. Therefore a study was made of the interaction of soil [P] and water availability on growth, photosynthesis, water-use efficiency (WUE) and P nutrition of two Australian native legumes with pasture potential, Cullen australasicum and C. pallidum, and the widely grown exotic pasture legume, lucerne (Medicago sativa). † Methods Plants were grown in a glasshouse at 3, 10 and 30 mg P kg 21 dry soil for 5 months. At week 10, two drought treatments were imposed, total pot dried (all-dry) and only top soil dried (top-dry), while control pots were maintained at field capacity. † Key Results Shoot dry weight produced by lucerne was never higher than that of C. australasicum. For C. pallidum only, shoot dry weight was reduced at 30 mg P kg 21 dry soil. The small root system of the Cullen species was quite plastic, allowing plants to access P and moisture efficiently. Lucerne always had a higher proportion of its large root system in the top soil layer compared with Cullen species. All species showed decreased photosynthesis, leaf water potential and stomatal conductance when exposed to drought, but the reductions were less for Cullen species, due to tighter stomatal control, and consequently they achieved a higher WUE. All species showed highest rhizosphere carboxylate concentrations in the all-dry treatment. For lucerne only, carboxylates decreased as P supply increased. Citrate was the main carboxylate in the control and top-dry treatments, and malate in the all-dry treatment. † Conclusions Multiple adaptive responses of Cullen species and lucerne favoured exploitation of low-P soils under drought. The performance of undomesticated Cullen species, relative to that of lucerne, shows their promise as pasture species for environments such as in south-western Australia where water and P are limiting, especially in view of a predicted drying and warming climate.
Background and aims Medicago sativa L. is widely grown in southern Australia, but is poorly adapt... more Background and aims Medicago sativa L. is widely grown in southern Australia, but is poorly adapted to dry, hot summers. This study aimed to identify perennial herbaceous legumes with greater resistance to drought stress and explore their adaptive strategies. Methods Ten herbaceous perennial legume species/ accessions were grown in deep pots in a sandy, lowphosphorus field soil in a glasshouse. Drought stress was imposed by ceasing to water. A companion M. sativa plant in each pot minimised differences in leaf area and water consumption among species. Plants were harvested when stomatal conductance of stressed plants decreased to around 10% of well watered plants.
Page 1. RESEARCH ARTICLE Prioritisation of novel pasture species for use in water-limited agricul... more Page 1. RESEARCH ARTICLE Prioritisation of novel pasture species for use in water-limited agriculture: a case study of Cullen in the Western Australian wheatbelt RG Bennett • MH Ryan • TD Colmer • D. Real Received: 4 February ...
The present paper compares standard and novel methods for analysing aggregated patterns of plant ... more The present paper compares standard and novel methods for analysing aggregated patterns of plant death in designed field experiments; these methods include binomial (BN), beta-binomial (BBN), logistic-normal-binomial (LNB), BN models with random blocks, BN models with smooth-scale spatial components and principal coordinates of neighbour matrices (PCNM). PCNM is a relatively new technique used in ecology to determine how much observed variability can be explained by spatial and environmental variables, and has not yet been applied to agricultural studies. The survival data of two pasture species, collected from a designed field experiment that was replicated at multiple locations, were used. First, the occurrence of overdispersion was tested using the BN and BBN distributions. Goodness-of-fit tests proved that the BBN model provided a better description (better fit) of the observed data in some cases than did the BN distribution, indicating overdispersion was present. When overdispersion was not present, the BN distribution was adequate to describe the data, and the use of the BBN distribution was superfluous. It is then shown that the PCNM approach, the BN model with smooth-scale spatial components and the LNB model were able to account for some of the variation as spatial variability, thus reducing the species effect compared with that explained under the standard BN model. The amount of variation among species according to the BN model and the BN model with random blocks was similar. Therefore, it is argued that the novel PCNM approach warrants further testing when exploring the spatial variability in designed experiments in agriculture and using LNB, PCNM and BN with smooth-scale spatial components may provide better predictions of species effects than do other, more conventional, approaches.
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