University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Agronomy & Horticulture -- Faculty Publications Agronomy and Horticulture Department 2005 Nitrogen supply affects root:shoot ratio in corn and velvetleaf (Abutilon theophrasti) Kimberly D. Bonifas University of Nebraska-Lincoln Daniel T. Walters University of Nebraska-Lincoln Kenneth G. Cassman University of Nebraska-Lincoln, [email protected] John L. Lindquist University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/agronomyfacpub Part of the Plant Sciences Commons Bonifas, Kimberly D.; Walters, Daniel T.; Cassman, Kenneth G.; and Lindquist, John L., "Nitrogen supply affects root:shoot ratio in corn and velvetleaf (Abutilon theophrasti)" (2005). Agronomy & Horticulture -- Faculty Publications. 416. https://digitalcommons.unl.edu/agronomyfacpub/416 This Article is brought to you for free and open access by the Agronomy and Horticulture Department at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Agronomy & Horticulture -- Faculty Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Weed Science, 53:670±675. 2005 Nitrogen supply affects root:shoot ratio in corn and velvetleaf (Abutilon theophrasti ) Kimberly D. Bonifas Competitive outcome between crops and weeds is affected by partitioning of new Daniel T. Walters biomass to above- and belowground plant organs in response to nutrient supply. This study determined the fraction of biomass partitioned to roots vs. shoots in corn Kenneth G. Cassman and velvetleaf in response to nitrogen (N) supply. Pots measuring 28 cm in diam Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583-0915 and 60 cm deep were embedded in the ground and each contained one plant of either corn or velvetleaf. Each plant received one of three N treatments: 0, 1, or 3 g N applied as ammonium nitrate in 2001, and 0, 2, or 6 g N in 2002. Measure- John L. Lindquist ments of total above- and belowground biomass were made at 10 sampling dates Corresponding author. Department of Agronomy during each growing season. The root:shoot ratio decreased over time for both corn and Horticulture, University of Nebraska, Lincoln, and velvetleaf as a result of normal plant growth and as N supply increased. Root: NE 68583-0915; [email protected] shoot ratio was greater for corn than for velvetleaf at comparable stages of devel- opment and at all levels of N supply. Both corn and velvetleaf display true plasticity in biomass partitioning patterns in response to N supply. Velvetleaf root:shoot ratio increased by 46 to 82% when N was limiting in 2001 and 2002, respectively, whereas corn root:shoot ratio increased by only 29 to 45%. The greater increase in biomass partitioned to roots by velvetleaf might negatively impact its ability to com- pete with corn for light when N supply is limited. Nomenclature: Velvetleaf, Abutilon theophrasti Medic., ABUTH; corn, Zea mays L. Key words: Biomass partitioning, ontogenetic drift, optimal partitioning theory, phenology. Corn production is vital to agriculture in the United hypothesized that when N supply is limited, C3 plants will States, with an estimated annual farm gate value of $23 have to increase their root growth proportionally more than billion (USDA 2005). Velvetleaf causes considerable eco- C4 plants to maintain a suf®cient level of tissue N to sustain nomic loss in corn and soybean [Glycine max (L.) Merr.] in photosynthetic rates and dry matter accumulation. the United States (Spencer 1984) and has the potential to The principal cause of yield loss in corn due to velvetleaf cause up to 80% yield loss in corn when not adequately is competition for light (Lindquist and Mortensen 1999). controlled (Lindquist et al. 1996). While market prices have Velvetleaf often grows taller than corn by mid-season, thus continued to decline in recent years, input costs for nitrogen shading corn leaves (Roeth 1987). Competition for light, fertilizer and weed control measures continue to rise, leading however, is also affected by competition for belowground to a decreased pro®t margin (Liebman et al. 2001). Along resources. Velvetleaf might no longer be such a strong com- with increasing control costs, factors such as herbicide resis- petitor for light if it is forced to invest more biomass in root tance and heightened environmental awareness have led to production and less in stem and leaf production when soil ecologically based weed management programs that focus N supply is limiting. on how components such as climate, edaphic properties, and Optimal partitioning theory predicts that, in response to resource availability affect crop and weed competitiveness a resource gradient, plants will optimize overall growth rate (Murphy and Lindquist 2002). by making all resources equally limiting and adjust their The quantity of roots plants produce and the ability of biomass partitioning patterns to obtain the most limiting those roots to take up N will affect competition, and plants resource (Hilbert 1990; Mooney et al. 1985; Robinson competing for N are capable of showing plasticity in root 1986). Plants that encounter limited nutrient or water sup- growth and N uptake (Gedroc et al. 1996; Harmens et al. ply are expected to partition more biomass to their roots 2000; McConnaughay and Coleman 1999; Reynolds and and less to their stems and leaves. Accordingly, in limiting D'Antonio 1996). An understanding of the effects of N light environments, plants are expected to partition more supply on crop and weed growth and competition is critical new biomass to stem and leaf production and less to root because N inputs are required to sustain corn yields at cur- production. Several documented cases exist where plants re- rent levels. spond in accordance with optimal partitioning theory Corn utilizes the C4 photosynthetic pathway, whereas vel- (Mooney et al. 1985; Reynolds and D'Antonio 1996). vetleaf utilizes the C3 photosynthetic pathway. One of the However, it has been argued that some of these cases might functional differences that occurs as a result of the different result instead from changes in partitioning during normal photosynthetic pathways is photosynthetic N use ef®ciency plant growth and development (Coleman et al. 1994; Ged- (PNUE), the ratio of photosynthetic rate to N content in roc et al. 1996; McConnaughay and Coleman 1999). On- the leaf. PNUE is greater in C4 than in C3 plants (Brown togenetic drift is a term used to describe the phenotypic 1978, 1985; Sage and Pearcy 1987). Therefore, it could be changes that occur as a result of normal plant growth and 670 x Weed Science 53, September±October 2005 development (Evans 1972). Because plants growing under the rows of pots and around the edge of the site to more different environmental conditions have different growth closely simulate ®eld conditions and provide an added wind rates, plants of the same age might not be the same size or buffer for the treated plants in 2002. Total density, includ- at the same developmental stage and are not necessarily on- ing potted plants, was 1 plant m22 in 2001 and 5 plants togenetically identical (Evans 1972). m22 in 2002. Ontogenetic drift can create potential problems in the The experiment was arranged in three replicate blocks interpretation of data from experiments on biomass parti- across the ®eld slope in a randomized complete block de- tioning. If optimal partitioning theory holds true, then sign. Blocks contained 10 replicate sample pots per treat- plants grown in limiting soil nutrient environments will par- ment to accommodate for weekly destructive sampling. tition a larger percentage of new biomass to roots as opposed Each pot contained one corn or velvetleaf plant and received to shoots, and they will have a higher root:shoot ratio. How- one of three N treatments. The N treatments administered ever, early in ontogeny plants will have a higher root:shoot were 0, 1, or 3 g N per pot in 2001, and 0, 2, or 6 g N ratio because of normal processes of early root growth and per pot in 2002. The N treatments were increased in 2002 establishment (Bazzaz et al. 1989). A key issue, therefore, is because corn plants reached a maximum biomass of over whether a higher root:shoot ratio observed in plants grown 300 g plant21 in 2001. Assuming a whole plant N concen- in low nutrient environments results from plasticity pre- tration of 2%, a 300 g plant requires 6 g N. Therefore, the dicted by optimal partitioning theory or by slowed growth increase was made to ensure adequate N supply for corn to rates and stress-induced differences in stage of development. reach its potential biomass in 2002. The N treatments were The terms ``apparent plasticity'' and ``true plasticity'' have applied at planting in the form of ammonium nitrate dis- been used to describe differences observed in biomass par- solved in 500 ml distilled water. Macro and micronutrients titioning patterns, where apparent plasticity is attributed to other than N were non-limiting and provided by means of ontogenetic drift coupled with plasticity in growth rates, a weekly addition of 250 ml of a dilute nutrient solution whereas true plasticity results from actual plasticity in bio- containing 0.15 g KCl, 0.31 g CaCl2´2H20, 0.09 g 3 24 mass partitioning patterns (McConnaughay and Coleman MgSO4´7H20, 0.04 KH2PO4, 5.1 10 gH3BO3, 5.9 3 24 3 24 3 1999). If there is no true plasticity, plants growing at dif- 10 g MnCl2´4H20, 2.2 10 g ZnSO4´7H20, 5.0 25 3 25 ferent rates will have different root:shoot ratios when com- 10 g CuSO4´5H20, 6.5 10 gNa2MoO4´2H20, and 3 23 pared at the same time, but their root:shoot ratios will be 2.2 10 g FeCl3´6H20.