Red–far-red ratio of reflected light: a hypothesis of why early-season weed control is important in corn

Abstract

A plant's ability to detect and adjust morphologically to changes in light quality (red–far-red [R:FR] ratio) is one mechanism by which a crop plant responds to weeds. To test this hypothesis, two experiments were conducted where corn was grown in growth cabinets under different light environments. First, to determine the effect of R:FR ratio on corn growth and development, treatments of high R:FR (1.37) and low R:FR (0.67) ratio were compared. These were established by planting corn in pots and then placing trays of either turface (a baked clay medium with high R:FR) or commercial grass sod (low R:FR) on each side of a row of corn pots. Grass sod was used to simulate low-growing weeds. The low R:FR sod treatment resulted in corn plants which were taller, had larger leaves, and greater shoot–root ratio than plants growing in the high R:FR turface treatment. In the second experiment, the effect of R:FR ratio on corn leaf azimuth position was examined. This was accomplished by adding a third treatment where each corn row had sod placed on one side and turface on the other. The proportion of leaves in four azimuthal classes was recorded. In the presence of sod, the proportion of leaves perpendicular to the corn row decreased, and this altered the proportion of leaves in other classes. Therefore, corn seedlings detected changes in light quality caused by the presence of sod (which simulated low-growing weeds) and responded by adjusting carbon allocation and leaf orientation to optimize the interception of light quantity and quality. These results support our hypothesis that low-lying vegetation can alter the growth of corn seedlings before competition for resources occurs. This change in growth may help explain the importance of early-season weed control in corn.

Canopy structure, light interception, and photosynthetic characteristics under different narrow-wide planting patterns in maize at silking stage

“…The adjustments in leaf angle and leaf azimuth were in agreement with the results of Kasperbauer and Karlen (1994), and fitted the general pattern of phytochrome-mediated shade avoidance reaction of plants (Smith and Whitelam, 1997). The adjustment in leaf azimuth is a morphological mechanism of plants in response to changes in light quality [red-far-red (R:FR) ratio; Maddonni et al, 2002)] by plants responding to the presence of neighbors, such as weeds (Rajcan et al, 2004) or other plants of the same species (Maddonniet al, 2001b). Significant differences were observed in the leaf azimuthal distribution among planting patterns, which agreed with previous results (Girardin and Tollenaar, 1994).…”

Interação entre volume de vaso e competição com plantas daninhas sobre o crescimento da soja

“…A relação da radiação vermelho/vermelho distante, percebida principalmente pelos fitocromos, tem papel importante na indução de alterações moleculares, morfológicas e fisiológica das plantas (Liu et al, 2009). O sombreamento das plantas, detectado pela elevada incidência da luz vermelho distante, faz com que elas aloquem maior disponibilidade de recursos para investimento no crescimento da parte aérea, normalmente afetando o desenvolvimento do sistema de raízes e, com isso, podendo comprometer a disputa por recursos do solo (Rajcan et al, 2004;Liu et al, 2009).…”

Annuals sprouting adventitiously from the hypocotyl: their compensatory growth and implications for weed management

“…Relative growth rates of seedlings may differ from that of plants resprouting from the bud bank, as sprouters could have a competitive advantage over seedlings due to stored starch reserves and an existing root system (Loehle 2000;Latzel et al 2008). Even sparse weed cover can negatively alter crop growth by impacting the red-far-red ratio perceived by the crop (Rejcan & Swanton 2004). Consistent suppression of generatively regenerating plants by those regenerated vegetatively has been reported in annually disturbed arable fields in northern Colombia (Denslow 1985) and in urban plant communities (Latzel et al 2008).…”