Abstract
Velvetleaf (Abutilon theophrasti) is a highly competitive weed in agroecosystems that is well-studied for its efficient nitrogen (N) acquisition, yet research on its phosphorus (P) uptake is lacking. One pathway may be through symbioses with arbuscular mycorrhizal fungi (AMF) which increase nutrient acquisition. These AMF benefits can be further enhanced by soil amendment with biochar, although effects may vary with different biochar production characteristics. We implemented a fully factorial nutrient and biochar addition experiment in a greenhouse for six months to determine how AMF nutrient uptake impacts plant growth and how these effects vary between two biochar types. We measured total above- and belowground biomass, plant tissue concentration (N and P), AMF colonization and activity rates, and soil media N and P availability. Overall, we observed few statistically significant results, however AMF N uptake may have been more beneficial to velvetleaf than AMF P uptake as evidenced by increased biomass and tissue N concentrations in treatments where N was only accessible by AMF. Additionally, by maintaining root to shoot ratios biochar may have provided plants with N and P (through sorption of nutrients to surfaces or its inherent properties) when nutrients were more difficult to access. We also found variable plant responses across the two biochar types used. Understanding how nutrient and biochar additions can influence weed competition is important for anticipating potential undesirable consequences of novel soil amendments such as biochar.
Highlights
Velvetleaf Abutilon theophrasti is a financially devastating weed in the upper Midwest and Eastern United States (Spencer, 1984)
We found some evidence for interactive effects between biochar and nutrient treatments, and our two produced biochars caused variable plant responses
Our results suggest that nutrient type and form may influence velvetleaf performance
Summary
Velvetleaf Abutilon theophrasti is a financially devastating weed in the upper Midwest and Eastern United States (Spencer, 1984). While velvetleaf primarily reduces crop yield by shading out other plants (Akey, 1989; Lindquist and Mortensen, 1999), aboveground biomass increases may be due to successful competition for nutrients belowground (Bonifas et al, 2005; Barker et al, 2006; Vitousek et al, 2010). Belowground competition for N is welldocumented between velvetleaf and crops (Bonifas et al, 2005; Barker et al, 2006; Lindquist et al, 2007; Bonifas and Lindquist, 2009), competition for phosphorus (P) acquisition is less studied. One potentially advantageous way to compete for P may be through symbioses with arbuscular mycorrhizal fungi (AMF) (Smith and Read, 2008).
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