The importance of light quality in crop–weed competition

Abstract

Plant competition is thought to be driven by limiting resources. We propose that plant competition is triggered initially by the red to far-red light ratio (R:FR) originating from neighbouring plants, followed by a series of complex physiological processes, which exclude direct resource competition. Field experiments were conducted in 2005 and 2006 in which maize (Zea mays) was grown hydroponically. The effect of R:FR signal being reflected from the leaf surface of Amaranthus retroflexus was isolated by avoiding direct competition for light, water and nutrients. Results showed that the low R:FR reflected from the leaf surface of A. retroflexus did alter the carbon allocation pattern of maize when compared with maize growing free of weeds. Prior to silking, maize grown under low R:FR experienced temporal changes in plant height, persistent changes throughout the sampling period in root and shoot dry weights and rate of leaf appearance, but no changes in leaf area. At silking, low R:FR reduced ear and total plant dry weight. These results support the hypothesis that changes in R:FR acts as an early signal of pending competition by initiating a shade avoidance response. Data from this experiment suggest that once a plant is physiologically triggered into a shade avoidance response, these plants do so at a physiological cost, which may constrain plant development and possibly reduce reproductive fitness.

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

“…A competição com plantas daninhas estimula alterações do crescimento em altura e na relação parte aérea/raiz da soja, de forma que, morfologicamente, plantas de soja tendem a ser mais altas quanto maior for a competição com as plantas daninhas (Vollmann et al, 2010). Plantas da comunidade infestante refletem luz em determinado comprimento de onda, o que normalmente torna possível o reconhecimento de plantas vizinhas pelas culturas; assim, antes de a competição direta por água, luz e nutrientes se estabelecer, a cultura investe em estratégias para evitar o sombreamento pelas plantas daninhas (Liu et al, 2009). Esse efeito depende da qualidade da luz recebida, da cultura e da composição da comunidade infestante.…”

“…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).…”

Volunteer wheat (Triticum aestivum L.) competition in corn (Zea mays L.)

“…Corn height, leaf collar number, shoot dry weight, leaf dry weight and leaf area were all reduced in the presence of volunteer wheat. Altered growth rates were recorded by Liu et al (2009) in corn, when leaf tip emergence was delayed by weed competition. Liu et al (2009) did not see a reduction in corn leaf area, signaling that extreme competition is required to alter plant leaf area.…”

“…Altered growth rates were recorded by Liu et al (2009) in corn, when leaf tip emergence was delayed by weed competition. Liu et al (2009) did not see a reduction in corn leaf area, signaling that extreme competition is required to alter plant leaf area. Early weed competition with corn has resulted in a decreased rate in leaf emergence and leaf area (Page et al 2009).…”

“…The time of weed emergence relative to the crop is of primary importance in determining the outcome of crop-weed competition (O'Donovan 1992). The presence of established weeds at the time of corn seedling emergence has been shown to alter corn growth and development (Rajcan and Swanton 2001;Rajcan et al 2004;Liu et al 2009;Page et al 2009) and results in significant yield losses (Hall et al 1992;Knezevic et al 2002;Evans et al 2003). Volunteer winter wheat in southern Ontario begins germinating in the fall after wheat harvest, and is well established when corn emerges the next spring.…”