Morphology and response of roots of pasture species to phosphorus and nitrogen nutrition

Abstract

The root morphology of ten temperate pasture species (four annual grasses, four perennial grasses and two annual dicots) was compared and their responses to P and N deficiency were characterised. Root morphologies differed markedly; some species had relatively fine and extensive root systems (Vulpia spp., Holcus lanatus L. and Lolium rigidum Gaudin), whilst others had relatively thick and small root systems (Trifolium subterraneum L. and Phalaris aquatica L.). Most species increased the proportion of dry matter allocated to the root system at low P and N, compared with that at optimal nutrient supply. Most species also decreased root diameter and increased specific root length in response to P deficiency. Only some of the species responded to N deficiency in this way. Root morphology was important for the acquisition of P, a nutrient for which supply to the plant depends on root exploration of soil and on diffusion to the root surface. Species with fine, extensive root systems had low external P requirements for maximum growth and those with thick, small root systems generally had high external P requirements. These intrinsic root characteristics were more important determinants of P requirement than changes in root morphology in response to P deficiency. Species with different N requirements could not be distinguished clearly by their root morphological attributes or their response to N deficiency, presumably because mass flow is relatively more important for N supply to roots in soil.

Phosphate uptake by white clover (Trifolium repensL.) genotypes with contrasting root morphology

“…Previous results with these genotypes showed no evidence for differences in growth rate (Crush et al 2005b). The results confirm that selection for high SRL will confer on white clover the improvements in P acquisition predicted and observed for other species (Fitter 1985;Hutchings & De Kroon 1994;Jungk 1996;Hill et al 2006). Roots of the STR genotype absorbed more P cm -1 root length when P was relatively available, presumably because of their larger surface area per unit length.…”

“…Phosphate (P) diffuses very slowly in soil (Nye & Tinker 1977), and movement of P to the root surface is the rate-limiting step in P acquisition by plants. Plants with finely divided roots that colonise a large volume of soil are more efficient in obtaining P than plants with coarse, unbranched roots (Fitter 1985;Föhse et al 1991;Hutchings & De Kroon 1994;Jungk 1996;Hill et al 2006). This was shown experimentally for white clover (Trifolium repens L.) grown with Agrostis by Jackman & Mouat (1972).…”

Functional response of Quercus robur L. to taproot pruning: a 5-year case study

“…Other strategies also minimize the negative effect of resource limitation. Morphological and biochemical alterations of functional traits (qualitative adjustments), such as specific leaf area (SLA) and specific root length (SRL), may also enable a plant to adapt to resource limitations (Freschet et al 2010;Hill et al 2006;Kerkhoff et al 2006;Ryser and Eek 2000). Changes in root length may reduce the overlapping of roots among different plants (Valverde-Barrantes et al 2013).…”

Reduction in Root Secondary Growth as a Strategy for Phosphorus Acquisition

“…root length per mass of root tissue) was negatively correlated with P availability, with a 30% reduction in root diameter from high P to low P (Powell, 1974). In a study of the root morphology of temperate pasture species, a reduction in root diameter, root mass density, and an increase in specific root length were observed under P stress (Hill et al, 2006). Reduced lateral root diameter also has been described under low P in water hyacinth (Eichhornia crassipes) and maize (Zea mays; Xie and Yu, 2003;Zhu and Lynch, 2004).…”