A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy den... more A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy density on the light environment in different organs. The red:far-red ratio inside the stem of Datura ferox L. seedlings and the estimated phytochrome photoequilibrium were strongly reduced by the presence of neighbors forming canopies too sparse to cause any mutual shading at the level of the leaves. In such canopies, changes in plant density had limte effects on the light regime inside the leaves of the succulent Aeonium haworthfi (S.D.) Webb et Berth., particularly when the lamina was kept nearly normal to the direct rays of the sun. In field experiments using D. ferox and Sinapis alba L. seedlings, the elongation of the intemodes responded to various types of localized light-quality treatments that simulated different plant densities in sparse canopies. The responses were quantitatively similar to those elicited by changes in plant density. The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.
ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories acc... more ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses.In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.
The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to e... more The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet-B radiation (UV-B: 280-315 nm), due to the passage of the 'ozone hole' over this region. In the experiments reported in this article the effects of solar UV-B and UV-A (315-400 nm) on two UV-B defence-related processes: the accumulation of protective UV-absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV-absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane-pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °°°° C) than plants grown under attenuated UV. There was no measurable repair at 8 °°°° C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (L er ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV-B in southern Patagonia may be related to a low DNA repair capacity.
The distribution and ultrastructure of capitate glandular trichomes (GTs) in Flourensia species (... more The distribution and ultrastructure of capitate glandular trichomes (GTs) in Flourensia species (Asteraceae) have been recently elucidated, but their metabolic activity and potential biological function remain unexplored. Selective nonvolatile metabolites from isolated GTs were strikingly similar to those found on leaf surfaces. The phytotoxic allelochemical sesquiterpene (-)-hamanasic acid A ((-)HAA) was the major constituent (ca. 40%) in GTs. Although GTs are quaternary ammonium compounds (QACs)-accumulating species, glycine betaine was not found in GTs; it was only present in the leaf mesophyll. Two (-)HAA accompanying surface secreted products: compounds (1) 4-hydroxyacetophenone (piceol) and (2) 2-hydroxy-5-methoxyacetophenone, which were isolated and fully characterized (GC-MS, NMR), were present in the volatiles found in GTs. The essential oils of fresh leaves revealed ca. 33% monoterpenes, 26% hydrocarbon- and 30% oxygenated sesquiterpenes, most of them related to cadinene a...
An aqueous extract from Flourensia campestris (Asteraceae) dry aerial parts showed strong inhibit... more An aqueous extract from Flourensia campestris (Asteraceae) dry aerial parts showed strong inhibition on the germination and growth of Lactuca sativa. Based on bio-guided chromatographic fractionation of aq. extracts from dry and fresh leaves and spectroscopic means, (-)-hamanasic acid A (7-carboxy-8-hydroxy-1(2), 12(13)-dien-bisabolene (1)) was isolated as the most inhibitory active principle on germination (ECg 50 = 2.9 mM) and on root (ECr 50 = 1.5 mM)/shoot (ECs 50 = 2.0 mM) growth. As measured by GC, and correlated with a simple designed 2D-TLC, compound 1 was distributed throughout the plant, with a remarkably high concentration (1.6%) in the leaves and the inflorescences. At least a quarter of the amount of 1 was found in aqueous extracts suggesting that leaching would be a key route for its release into the environment. By contrast, leaf essential oils (HD) between 0.5 and 1.5 ll ml À1 did not show herbicidal effects and 1 was not found in them (TLC) nor among volatiles (HS-SPME). Volatile compositions were assessed by GC-FID and GC-MS and led to the identification of 23 compounds (4 monoterpenes and 19 sesquiterpenes) with a wide seasonal (spring-summer%) variation, represented principally by bicyclogermacrene (37-6%), spathulenol (4-32%), globulol (20-0%), beta-caryophyllene (15-6%), caryophyllene oxide (1-13%) and bicycloelemene (10-1%), respectively. The high amount of 1 in F. campestris together with its feasibility of being extracted with water suggest that (À)-hamanasic acid A is an allelochemical in this species. Species-specific studies must be carried out to evaluate the potential of 1 as a natural herbicidal compound.
RESUMEN En este trabajo nos propusimos analizar la distribución espacial de la heterogeneidad fis... more RESUMEN En este trabajo nos propusimos analizar la distribución espacial de la heterogeneidad fisonómica-funcional de la vegetación del Parque Nacional «El Palmar»(Argentina) como indicadora de invasibilidad. Se generó una estratificación de la vegetación actual mediante una clasificación no supervisada de imágenes Landsat ETM+ recientes, representativas de cada estación del año. Cada clase se caracterizó funcionalmente según la fenología dada por el patrón de variación del NDVI. Para la ...
The Abstracts that follow are arranged in numerical sequence by the abstract number. For Poster S... more The Abstracts that follow are arranged in numerical sequence by the abstract number. For Poster Sessions, the number preceded by PB (i.e., PB XXX) indicates the poster board number on which the poster will be mounted. A participatory, on-farm research project was initiated in 1992 in an effort to enhance mutual learning, knowledge, and experience of integrating cover crops into western Oregon vegetable production systems. A major goal of the project was to include growers, agribusiness representatives, governmental agency, Extension and university researchers in a collaborative learning process, emphasizing grower participation in the design and implementation of on-farm research and demonstration projects. To facilitate this participation from the planning stage forward, four "focus sessions" were hosted by lead farmers in different areas of the Willamette Valley to define growers' needs and interests relating to on-farm research and demonstration trials.
Ballar~, C.L., Scopel, A.L., Ghersa, C.M. and S~inchez, R.A., 1987. The population ecology of Dat... more Ballar~, C.L., Scopel, A.L., Ghersa, C.M. and S~inchez, R.A., 1987. The population ecology of Datura ferox in soybean crops. A simulation approach incorporating seed dispersal. Agric. Ecosystems Environ., A numerical model for simulating the population dynamics of Datura [erox L. (chamico, chinese thornapple) has been built based on previously reported data. In the model, a soybean field is divided into 0.7 × 0.7-m conceptual modules. A seed production sub-model simulates the annual seed output of each module, and a seed dispersal sub-model simulates the distribution of these propagules within the field in accordance to a specified dispersal pattern. Different model scenarios were generated by varying the proportion of seeds lost from the soil bank, the annual recruitment, the seedling mortality and the proportion of seeds exported from the field during crop harvest. The results obtained by simulation suggest that (1) seed dispersal due to crop harvesting tends to produce an exponential growth of weed seed production, (2) limited or no success could be attained in the control of D. ferox using procedures that kill the seedlings efficiently if combine harvesters are not adjusted so as to maximize the proportion of weed seeds that are exported from the field and (3) if cleaning debris continues to be returned to the ground during crop harvesting, the improvement in the efficiency of the grain/weed separating mechanisms does not provide an effective long-term strategy to avoid grain contamination problems. the capsules are ripe . In the field, germination takes
Collaea argentina (Fabaceae) and Abutilon pauciflorum (Malvaceae) are of high medicinal and ornam... more Collaea argentina (Fabaceae) and Abutilon pauciflorum (Malvaceae) are of high medicinal and ornamental value and are collected for pharmaceutical and ornamental purposes. However, one obstacle for plant production is the occurrence of seed dormancy. Here, we confirmed the occurrence of dormancy in these species, identified possible methods for breaking dormancy and assessed the dormancy condition after seed storage. Wet heat, physical and acid scarification were effective methods for breaking physical dormancy in both species. After four years of dry storage, a high proportion of C. argentina seeds were able to germinate (i.e. physical dormancy levels had reduced), whereas A. pauciflorum seeds continued to be dormant but were more sensitive to dormancybreaking treatments. These results should aid plant production and seed conservation of these two species.
To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on ... more To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on different aspects of the physiology of a wild plant, we carried out exclusion experiments in the field with the summer annual Datura ferox L. Solar UV-B incident over Buenos Aires reduced daytime seedling emergence, inhibited stem elongation and leaf expansion, and tended to reduce biomass accumulation during early growth. However, UV-B had no effect on calculated net assimilation rate. Using a monoclonal antibody specific to the cyclobutane-pyrimidine dimer (CPD), we found that plants receiving full sunlight had more CPDs per unit of DNA than plants shielded from solar UV-B, but the positive correlation between UV-B and CPD burden tended to level off at high (near solar) UV-B levels. At our field site, Datura plants were consumed by leaf beetles (Coleoptera), and the proportion of plants attacked by insects declined with the amount of UV-B received during growth. Field experiments showe...
Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth fo... more Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth following disturbance (e.g. fire, herbivory, animal injury). A dynamic and holistic study (sensu Hallé et al., 1978) was carried out in order to determine the architecture and the vegetative growth strategies, in plants collected from undisturbed and disturbed areas in the 'El Palmar' National Park. The architectural and morphological observations can be summarized as follows: (a) Tree architecture is determined by a monopodial trunk that produces tiers of orthotropic monopodial branches. (b) The root system consists of a tap root with woody primary lateral roots that exhibit plagiotropic growth and are typically found within the first few centimeters (ca. 4 cm) of the soil profile. (c) Root buds were produced in all (fire treated and control) plagiotropic root cuts when incubated under controlled conditions. Root suckers developed from the differentiation of parenchymatous cells produced by meristematic activity in the cambial zone. The ecological implications of vegetative reproduction on the invasive capacity of this species are discussed.
The Supporting Roots of Trees and Woody Plants: Form, Function and Physiology, 2000
Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth fo... more Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth following disturbance (e.g. fire, herbivory, animal injury). A dynamic and holistic study (sensu Hallé et al., 1978) was carried out in order to determine the architecture and the vegetative growth strategies, in plants collected from undisturbed and disturbed areas in the 'El Palmar' National Park. The architectural and morphological observations can be summarized as follows: (a) Tree architecture is determined by a monopodial trunk that produces tiers of orthotropic monopodial branches. (b) The root system consists of a tap root with woody primary lateral roots that exhibit plagiotropic growth and are typically found within the first few centimeters (ca. 4 cm) of the soil profile. (c) Root buds were produced in all (fire treated and control) plagiotropic root cuts when incubated under controlled conditions. Root suckers developed from the differentiation of parenchymatous cells produced by meristematic activity in the cambial zone. The ecological implications of vegetative reproduction on the invasive capacity of this species are discussed.
A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy den... more A fiber optic probe inserted into plant tissues was used to investigate the effects of canopy density on the light environment in different organs. The red:far-red ratio inside the stem of Datura ferox L. seedlings and the estimated phytochrome photoequilibrium were strongly reduced by the presence of neighbors forming canopies too sparse to cause any mutual shading at the level of the leaves. In such canopies, changes in plant density had limte effects on the light regime inside the leaves of the succulent Aeonium haworthfi (S.D.) Webb et Berth., particularly when the lamina was kept nearly normal to the direct rays of the sun. In field experiments using D. ferox and Sinapis alba L. seedlings, the elongation of the intemodes responded to various types of localized light-quality treatments that simulated different plant densities in sparse canopies. The responses were quantitatively similar to those elicited by changes in plant density. The evidence supports the hypothesis that, in stands formed by plants of similar size, the red:far-red ratio of the light that impinges laterally on the stems is among the earliest environmental cues that allow plants to detect local canopy density and adjust axis extension accordingly.
ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories acc... more ABSTRACT Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses.In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.
The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to e... more The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet-B radiation (UV-B: 280-315 nm), due to the passage of the 'ozone hole' over this region. In the experiments reported in this article the effects of solar UV-B and UV-A (315-400 nm) on two UV-B defence-related processes: the accumulation of protective UV-absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV-absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane-pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °°°° C) than plants grown under attenuated UV. There was no measurable repair at 8 °°°° C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (L er ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV-B in southern Patagonia may be related to a low DNA repair capacity.
The distribution and ultrastructure of capitate glandular trichomes (GTs) in Flourensia species (... more The distribution and ultrastructure of capitate glandular trichomes (GTs) in Flourensia species (Asteraceae) have been recently elucidated, but their metabolic activity and potential biological function remain unexplored. Selective nonvolatile metabolites from isolated GTs were strikingly similar to those found on leaf surfaces. The phytotoxic allelochemical sesquiterpene (-)-hamanasic acid A ((-)HAA) was the major constituent (ca. 40%) in GTs. Although GTs are quaternary ammonium compounds (QACs)-accumulating species, glycine betaine was not found in GTs; it was only present in the leaf mesophyll. Two (-)HAA accompanying surface secreted products: compounds (1) 4-hydroxyacetophenone (piceol) and (2) 2-hydroxy-5-methoxyacetophenone, which were isolated and fully characterized (GC-MS, NMR), were present in the volatiles found in GTs. The essential oils of fresh leaves revealed ca. 33% monoterpenes, 26% hydrocarbon- and 30% oxygenated sesquiterpenes, most of them related to cadinene a...
An aqueous extract from Flourensia campestris (Asteraceae) dry aerial parts showed strong inhibit... more An aqueous extract from Flourensia campestris (Asteraceae) dry aerial parts showed strong inhibition on the germination and growth of Lactuca sativa. Based on bio-guided chromatographic fractionation of aq. extracts from dry and fresh leaves and spectroscopic means, (-)-hamanasic acid A (7-carboxy-8-hydroxy-1(2), 12(13)-dien-bisabolene (1)) was isolated as the most inhibitory active principle on germination (ECg 50 = 2.9 mM) and on root (ECr 50 = 1.5 mM)/shoot (ECs 50 = 2.0 mM) growth. As measured by GC, and correlated with a simple designed 2D-TLC, compound 1 was distributed throughout the plant, with a remarkably high concentration (1.6%) in the leaves and the inflorescences. At least a quarter of the amount of 1 was found in aqueous extracts suggesting that leaching would be a key route for its release into the environment. By contrast, leaf essential oils (HD) between 0.5 and 1.5 ll ml À1 did not show herbicidal effects and 1 was not found in them (TLC) nor among volatiles (HS-SPME). Volatile compositions were assessed by GC-FID and GC-MS and led to the identification of 23 compounds (4 monoterpenes and 19 sesquiterpenes) with a wide seasonal (spring-summer%) variation, represented principally by bicyclogermacrene (37-6%), spathulenol (4-32%), globulol (20-0%), beta-caryophyllene (15-6%), caryophyllene oxide (1-13%) and bicycloelemene (10-1%), respectively. The high amount of 1 in F. campestris together with its feasibility of being extracted with water suggest that (À)-hamanasic acid A is an allelochemical in this species. Species-specific studies must be carried out to evaluate the potential of 1 as a natural herbicidal compound.
RESUMEN En este trabajo nos propusimos analizar la distribución espacial de la heterogeneidad fis... more RESUMEN En este trabajo nos propusimos analizar la distribución espacial de la heterogeneidad fisonómica-funcional de la vegetación del Parque Nacional «El Palmar»(Argentina) como indicadora de invasibilidad. Se generó una estratificación de la vegetación actual mediante una clasificación no supervisada de imágenes Landsat ETM+ recientes, representativas de cada estación del año. Cada clase se caracterizó funcionalmente según la fenología dada por el patrón de variación del NDVI. Para la ...
The Abstracts that follow are arranged in numerical sequence by the abstract number. For Poster S... more The Abstracts that follow are arranged in numerical sequence by the abstract number. For Poster Sessions, the number preceded by PB (i.e., PB XXX) indicates the poster board number on which the poster will be mounted. A participatory, on-farm research project was initiated in 1992 in an effort to enhance mutual learning, knowledge, and experience of integrating cover crops into western Oregon vegetable production systems. A major goal of the project was to include growers, agribusiness representatives, governmental agency, Extension and university researchers in a collaborative learning process, emphasizing grower participation in the design and implementation of on-farm research and demonstration projects. To facilitate this participation from the planning stage forward, four "focus sessions" were hosted by lead farmers in different areas of the Willamette Valley to define growers' needs and interests relating to on-farm research and demonstration trials.
Ballar~, C.L., Scopel, A.L., Ghersa, C.M. and S~inchez, R.A., 1987. The population ecology of Dat... more Ballar~, C.L., Scopel, A.L., Ghersa, C.M. and S~inchez, R.A., 1987. The population ecology of Datura ferox in soybean crops. A simulation approach incorporating seed dispersal. Agric. Ecosystems Environ., A numerical model for simulating the population dynamics of Datura [erox L. (chamico, chinese thornapple) has been built based on previously reported data. In the model, a soybean field is divided into 0.7 × 0.7-m conceptual modules. A seed production sub-model simulates the annual seed output of each module, and a seed dispersal sub-model simulates the distribution of these propagules within the field in accordance to a specified dispersal pattern. Different model scenarios were generated by varying the proportion of seeds lost from the soil bank, the annual recruitment, the seedling mortality and the proportion of seeds exported from the field during crop harvest. The results obtained by simulation suggest that (1) seed dispersal due to crop harvesting tends to produce an exponential growth of weed seed production, (2) limited or no success could be attained in the control of D. ferox using procedures that kill the seedlings efficiently if combine harvesters are not adjusted so as to maximize the proportion of weed seeds that are exported from the field and (3) if cleaning debris continues to be returned to the ground during crop harvesting, the improvement in the efficiency of the grain/weed separating mechanisms does not provide an effective long-term strategy to avoid grain contamination problems. the capsules are ripe . In the field, germination takes
Collaea argentina (Fabaceae) and Abutilon pauciflorum (Malvaceae) are of high medicinal and ornam... more Collaea argentina (Fabaceae) and Abutilon pauciflorum (Malvaceae) are of high medicinal and ornamental value and are collected for pharmaceutical and ornamental purposes. However, one obstacle for plant production is the occurrence of seed dormancy. Here, we confirmed the occurrence of dormancy in these species, identified possible methods for breaking dormancy and assessed the dormancy condition after seed storage. Wet heat, physical and acid scarification were effective methods for breaking physical dormancy in both species. After four years of dry storage, a high proportion of C. argentina seeds were able to germinate (i.e. physical dormancy levels had reduced), whereas A. pauciflorum seeds continued to be dormant but were more sensitive to dormancybreaking treatments. These results should aid plant production and seed conservation of these two species.
To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on ... more To study functional relationships between the effects of solar ultraviolet-B radiation (UV-B) on different aspects of the physiology of a wild plant, we carried out exclusion experiments in the field with the summer annual Datura ferox L. Solar UV-B incident over Buenos Aires reduced daytime seedling emergence, inhibited stem elongation and leaf expansion, and tended to reduce biomass accumulation during early growth. However, UV-B had no effect on calculated net assimilation rate. Using a monoclonal antibody specific to the cyclobutane-pyrimidine dimer (CPD), we found that plants receiving full sunlight had more CPDs per unit of DNA than plants shielded from solar UV-B, but the positive correlation between UV-B and CPD burden tended to level off at high (near solar) UV-B levels. At our field site, Datura plants were consumed by leaf beetles (Coleoptera), and the proportion of plants attacked by insects declined with the amount of UV-B received during growth. Field experiments showe...
Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth fo... more Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth following disturbance (e.g. fire, herbivory, animal injury). A dynamic and holistic study (sensu Hallé et al., 1978) was carried out in order to determine the architecture and the vegetative growth strategies, in plants collected from undisturbed and disturbed areas in the 'El Palmar' National Park. The architectural and morphological observations can be summarized as follows: (a) Tree architecture is determined by a monopodial trunk that produces tiers of orthotropic monopodial branches. (b) The root system consists of a tap root with woody primary lateral roots that exhibit plagiotropic growth and are typically found within the first few centimeters (ca. 4 cm) of the soil profile. (c) Root buds were produced in all (fire treated and control) plagiotropic root cuts when incubated under controlled conditions. Root suckers developed from the differentiation of parenchymatous cells produced by meristematic activity in the cambial zone. The ecological implications of vegetative reproduction on the invasive capacity of this species are discussed.
The Supporting Roots of Trees and Woody Plants: Form, Function and Physiology, 2000
Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth fo... more Melia azedarach L., a weedy tree that typically reproduces by seeds, may exhibit clonal growth following disturbance (e.g. fire, herbivory, animal injury). A dynamic and holistic study (sensu Hallé et al., 1978) was carried out in order to determine the architecture and the vegetative growth strategies, in plants collected from undisturbed and disturbed areas in the 'El Palmar' National Park. The architectural and morphological observations can be summarized as follows: (a) Tree architecture is determined by a monopodial trunk that produces tiers of orthotropic monopodial branches. (b) The root system consists of a tap root with woody primary lateral roots that exhibit plagiotropic growth and are typically found within the first few centimeters (ca. 4 cm) of the soil profile. (c) Root buds were produced in all (fire treated and control) plagiotropic root cuts when incubated under controlled conditions. Root suckers developed from the differentiation of parenchymatous cells produced by meristematic activity in the cambial zone. The ecological implications of vegetative reproduction on the invasive capacity of this species are discussed.
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