Morphological and topological responses of roots to defoliation and nitrogen supply in Lolium perenne and Festuca ovina

Abstract

Summary• This study examined morphological and topological responses of nodal root axes to defoliation in a fast-and a slow-growing grass species.• Vegetative tillers of both Lolium perenne and Festuca ovina were grown on slant boards and either left intact or subjected to repeated defoliation, under both a high nitrogen (N) and a low N supply. Root length, diameter and branching characteristics were measured on individual nodal root axes.• The total axis root length of F. ovina was less when plants had been defoliated. Root axis weight, primary root axis length and primary root diameter were also less with defoliation than an undefoliated control, under high N. Under low N conditions the root axes of F. ovina had a more randomly branched topology without defoliation. For L. perenne under low N conditions, the length of the primary root axis was longer with defoliation than in an undefoliated control, while the primary root axis diameter decreased. By contrast to F. ovina , the root axes of L. perenne had a more randomly branched topology without defoliation only when supplied with high N.• The greatest plasticity in branching caused by defoliation was observed under high N for L. perenne and under low N for F. ovina . Although grass root axis topology has, in general, a herringbone in structure, the nodal root system can alter root axis structure in response to defoliation.

The effects of clipping and soil moisture on leaf and root morphology and root respiration in two temperate and two tropical grasses

“…Previously, herbivory has been reported to decrease total root system length and root diameter (Dawson et al 2004). In this study, clipping increased SRL in one species, P. pratensis, and had no effect on that variable in the other three species.…”

“…In this study, clipping increased SRL in one species, P. pratensis, and had no effect on that variable in the other three species. Thus, while defoliation may reduce total root system length (Dawson et al 2004) or biomass (Detling et al 1979;Holland et al 1992), findings of this study suggest that the efficiency of resource capture per unit root mass may be unaffected or increased by clipping. It is worth pointing out that P. pratensis experienced the highest clipping intensity and was the only species that increased SRL in response to clipping.…”

“…Plasticity in plant traits has been hypothesized to have evolved in response to temporal and spatial heterogeneity of soils (Farley and Fitter 1999;Callaway et al 2003). Studies have shown that root length and proliferation is associated with the availability of nutrients in soil patches (Eissenstat 1991;Eissenstat and Achor 1999;Gordon and Jackson 2000) and specific root length (root length per g root, SRL) is influenced by soil moisture and aboveground herbivory (Katterer et al 1995;Dawson et al 2004;Anderson et al 2007). Variability in shoot and root traits is associated with variation in the functional properties of those structures, such as tissue metabolic demand and acquisition efficiency of light and CO 2 by leaves and water and nutrients by roots (Derner and Briske 1999;Farley and Fitter 1999).…”

Host shoot clipping depresses the growth of weedy hemiparasitic Pedicularis kansuensis

“…5). Defoliation was suggested to cause temporary reduction in root growth (Dawson 2004;Dunn and Engel 1971;Van Hoveln et al 2011) and capacity for mineral nutrient absorption (Volesky et al 2011). The reduction in root biomass and nutrient content of clipped E. nutans was not robust (except for a significant decrease in root P content), most likely due to strong compensatory growth (and roots' absorptive surface) in the 4 months after shoot clipping.…”

Genetic differences in root mass of Lolium perenne varieties under field conditions

“…Rooting depth and root density are strongly influenced by soil physical characteristics such as soil type and bulk density (Houlbrooke et al 1997;Steingrobe et al 2000), as well as by soil chemical and biological factors (Davidson 1969;Powell 1977;Hoogerkamp et al 1983;He et al 1999;Scheu 2003;Kutschera et al 2009) and climatic conditions (Evans 1971;Gales 1979;Troughton 1980). Furthermore, rooting of grasses is influenced by agricultural management factors: most importantly, fertilization (Fairley 1985;Ennik et al 1980;Forde and Lorenzo 2001), mowing and grazing strategies (Evans 1971(Evans , 1972Ennik and Baan Hofman 1983;Deinum 1985;Dawson et al 2003), and grassland age (Van Eekeren et al 2008). Finally, rooting is influenced by genetic characteristics: several studies have reported genetic differences in root biomass between various grass species (Van Eekeren et al 2010;Cougnon et al 2013) and varieties of perennial ryegrass (Bonos et al 2004;Crush et al 2007), and in root weight of wild versus bred perennial ryegrasses (Crush et al 2009).…”