CO2 assimilation in young

M. Pinto

Departamento de Producci6n Agricola, Facultad de Ciencas Agrarias y Forestales, Universitad de , Casilla 1004, Santiago, Chile

Introduction assimilation during the season (Mooney et al., 1982). Due to the genetic variation of these (Hunziker et aL, 1975), it is trees Prosopis (Leguminoseae) are widely possible to find differences between indivi- distributed in the of North and dry regions duals. The objective of this work was to South America. Their biomass and fruit determine net C02 assimilation rates, which can be production very large (Pinto under different light intensities and C02 and Riveros, and their 1989), N2-fixing levels, in provenances of Chilean Algarro- ability (Felker and Clark, 1980) are impor- bo (Prosopis chilensis) which exhibited dif- tant characteristics to be considered within ferent rates of growth and to compare forestation programs. them with those of P. tamarugo and P. At present, water economy of most juliflora at different temperatures. important Prosopis species is well known (Mooney et aL, 1982; Acevedo et al., 1985a; Aravena and Acevedo, 1985) but data on the C02 assimilation by any Materials and Methods single species of Prosopis are lacking. According to Acevedo et al., (1985b), rates were measured on is a C3 and the C02 assimilation (A) Prosopis tamarugo P. chilensis under different intensities with net assimilation rates of other light Prosopis 350 ppm C02 in ambient air and under different species could be similar to that of some C02 concentrations at light saturation, on 18 mediterranean fruit trees (Wilson et aL, mo old plants of P. chilensis. Plants from 8 1974; Hanson, 1982; Mooney et al., provenances with high growth rates and 9 with low rates were cultivated in 15 1982). In old Prosopis trees, this assimila- growth 1 plastic with a mixture of and sandy soil tion could variations bags organic display large (Wilson (1:1, pH 6.5). One plant per provenance was et al., 1974) and in some cases assimila- selected for measurements. Two, which devel- tion rates could be too low to support fruit oped 20 cm from the apex on the main were selected and assimilation rates growth. This has been suggested as one stem, C02 measured in a Parkinson chamber (Parkinson reason for the observed occasional pre- et al., 1980) connected to an infrared gas ana- mature fall of fruits (Salvo, 1986). Proso- lyzer (ADC, LCA-2). Temperature in the cham- pis shows important variations in net C02 ber was 20°C. The different C02 concentrations were obtained by a gas diluter (ADC, 6D-600) relation (r=0.98; Ps0.05) between area of and the different light intensities using plastic stem section, measured 10 cm above the nets between the lamp (Hg 400 W General ground, and total dry matter per plant was esta- Electric) and the assimilation chamber. blished with plants of the same age from dif- ferent A measurements at different air temperatures provenances (Fig. 1). were made at light saturation, with 350 ppm C02- In this case, one provenance of each P. chilensis, P. and P. was se- tamarugo juliflora Results lected and 4 plants per provenance were used for measurements. area was determined by photographic prints and chlorophyll (a + b) The aerial biomass accumulation during content from 500 g of fresh leaves per plant the 18 mo the selected according to MacKenney (1941). Aerial bio- period by Algarro- mass was estimated by measuring the area of bo provenances is shown in Table I. Dif- the stem section of the plant. A significant cor- ferences between both types of plants were considerable. High growth prove- detected. The carboxylation efficiency nances also had a significantly greater (Ku and Edwards, 1977) was 5.62 x 10- leaf area than those with low growth rates. mol’ppm-1 C02 in plants with high growth, In these plants, this area was distributed 22% higher than those with low growth in 4 or 5 branches, whereas in low growth which had 4.6 x 10-2 mol-ppm-1 C02. provenances it was distributed only in one A values for young plants of P. chilen- stem. The chlorophyll content was similar sis, P. tamarugo and P. juliflora presented in both types of plants. a maximum value between 20 and 35°C. In P. tamarugo, A was significantly lower A was very different between both types than in the other (Fig. 4). of plants under different light and C02 species levels. High growth provenances had a maximal A 43% higher than those with low growth rates. However, at low light intensi- Discussion ties, the apparent quantum yield was simi- lar in both types of plants (Fig. 2). Plants Maximal C02 assimilation rates (A) ob- with high growth rates also presented served here on Prosopis plants are similar higher A at all C02 levels (Fig. 3). Dif- to those of other mediterranean C3 spe- ferences in the compensation point and cies (Mooney et aL, 1982). A values in C02 evolution in C02-free air were also C02-free air suggest that some prov- enances may have important photorespi- Differences in A observed here confirm ration rates. that it is possible, due to the great genetic Differences observed in A rates be- variability of Prosopis trees, to find photo- differences between individuals. tween the provenances, in this case, may synthetic not be related to differences observed in Optimal temperatures for net C02 assi- aerial biomass accumulation. Net C02 milation by young Prosopis plants were assimilation rate per unit leaf area is not similar in all studied species, in spite of always related to biomass production and the differences in the ecological conditions other factors may be more important (Gif- of their habitats. However, P. tamarugo, ford and Jenkins, 1982; Walker and Sivak, which comes from the driest region of 1986). Provenances with high growth Chile, had the lowest assimilation rates. rates had many branches and a greater Studies of stomatal conductance and leaf area development than those with low other leaf processes will be necessary to growth rates. explain these differences. Acknowledgments isoptopos estables, oxigeno-18 y deuterio. In: Estado actual del conocimiento sobre Prosopis tamarungo. (Habit M., ed.), FAO, U. de Tarapa- This work was supported by a grant from the ca, CONAF, Chile. pp. 263-269 International Foundation for Science, Sweden. Felker P. & Clark P.R. (1980) Nitrogen fixation (acetylene reduction) and cross inoculation in 12 Prosopis (mesquite) species. Plant Soil 57, 177-186 References Gifford R.M. & Jenkins C.L.D. (1982) Prospects of applying knowledge of photosynthesis toward improving crop production. In: Photosynthesis Acevedo E., Sotomayor D. & Zenteno D. Vol. 11 Development, Carbon Metabolism, and (1985a) Paramotros hidricos de tejidos foliares Plant Production (Godvindjee, ed.), Academic en Prosopis tamarugo Phil. In: Estado actual Press, London, pp. 419-457 del conocimiento sobre Prosopis tamarugo. Hanson J.D. (1982) Effect of light, temperature U. de (Habit M., ed.), FAO, Tarapaca, CONAF, and water stress on net photosynthesis in two Chile, pp. 271-277 populations of honey mesquite. J. Range Acevedo E., Sotomayor D. & Zenteno V. Manage 35, 455-458 (1985b) Antecedentes sobre mecanismo de Hunziker J.H., Poccio L.A., Naranjo C.A., Pala- fijacion de C02 en Prosopis tamarugo Phil. 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