Photosynthetic Rates of Six Maize Cultivars During Development

Abstract

Production estimates based on photosynthate accumulation are affected by changes in photosynthesis rates related to aging in different cultivars. The influence of leaf and plant age on photosynthetic rates was investigated in six maize (Zea mays L.) cultivars with maturity ratings ranging from <2300 to >3500 CHU (corn heat units). Photosynthesis and irradiance measurements were fitted to rectangular hyperbolas using a nonlinear fitting technique. These curves were analyzed as a function of cultivars, and leaf and plant age. For comparison among cultivars and age groups, photosynthesis was represented by P2000 (net photosynthetic rate at irradiance (I) = 2000 µmol m−2 s−1). In all cultivars, early leaves had lower P2000 values at a given leaf age than late maturing leaves. The P2000 values tended to increase to a maximum at the time of full individual leaf expansion and then decrease. The duration of maximum P2000 values for leaves nearest the ear were longer than for earlier or later developing leaves. Leaves nearest the ear for early maturing cultivars tended to have lower P2000 values than later maturing cultivars at comparable leaf ages. Plant photosynthesis patterns were the same for all cultivars in relation to plant age and phenological development. Photosynthesis (P2000) was low for the six‐leaf stage, reached a maximum just before tasselling, and then declined during brown silk, blister, and dent stages. A quadratic equation described the relationship between P2000 and plant age. The trend was for latermaturing cultivars to have significantly (P < 0.05) larger P2000 values than earlier‐maturing cultivars at comparable phenological stages. Significant cultivar differences were found in leaf development rate and length of vegetative period (P < 0.10).

Análise de crescimento e trocas gasosas na cultura de milho em plantio direto e convencional

“…A queda de A pode ainda estar relacionada a fatores fisiológicos, como início de senescência, variação da respiração, na eficiência quântica e em gs entre outros (DWYER e Stewart, 1986;STIRLING et al, 1994). Há relatos na literatura de que, sem estresses abióticos, A é maior na fase de floração e/ou de crescimento linear de grãos em relação ao crescimento vegetativo, em função de maior demanda dos drenos (DWYER e STEWART, 1986;DWYER et al, 1989;MACHADO et al, 1994). Também há relatos de que a máxima fotossíntese é atingida ao redor de uma semana após a expansão máxima da folha (DWYER et al, 1989).…”

“…Há relatos na literatura de que, sem estresses abióticos, A é maior na fase de floração e/ou de crescimento linear de grãos em relação ao crescimento vegetativo, em função de maior demanda dos drenos (DWYER e STEWART, 1986;DWYER et al, 1989;MACHADO et al, 1994). Também há relatos de que a máxima fotossíntese é atingida ao redor de uma semana após a expansão máxima da folha (DWYER et al, 1989). No entanto, também há autores que não observam esta resposta (RAWSON et al, 1978).…”

Water table management effects on photosynthesis, chlorophyll, crop yield, and water quality

“…(Gimenez et al, 1992). Photosynthesis rate also depends on variety of plant parameters such as genotype, plant stage, leaf age, leaf orientation and position, plant density, and assimilate demand by sink (Dwyer et al, 1989). Differences among genotypes may be due to morphology, resulting in different mesophyll resistances, or they may be explained by the timing and size of carbohydrate requirement of other parts of the plant, particularly the grain (Hunt and van der Poorten, 1985;Hesketh, 1963).…”

“…Bhagsari (1988) reported decreases in net photosynthesis and stomatal conductance with increasing leaf age for sweet potato under field conditions in full sunlight (above 1500 u mole m ^ s'^). Dwyer et al (1989) reported cultiver differences in photosynthèse rates as a function of plant age, and pointed that late-maturing cultivars had higher photosynthetic rates than early-maturing cultivars at comparable growth stages. Pearson et al (1984) observed that the photosynthesis rate for the upper canopy leaves of 85-day-old maize was three to six times higher than for the lower canopy leaves.…”

“…that affect the mechanism (Gimenez et al, 1992). Besides these factors, photosynthesis rate also depends on a variety of plant parameters such as, genotype, plant stage, leaf age, leaf orientation and position, plant density, and assimilate demand by sink (Dwyer et al, 1989). Photosynthesis responses for a variety of crops from several previous studies in general, and maize in particular have been documented in the literature (Bhagsari and Harmon, 1982;Bhagsari, 1988;Dwyer and Stewart, 1986;Dywer et al, 1991;Thiagarajah et al, 1981).…”