The nitrogen handling characteristics of white clover (Trifolium repens L.) cultivars and a perennial ryegrass (Lolium perenne L.) cultivar

TY - JOUR

T1 - The nitrogen handling characteristics of white clover (Trifolium repens L.) cultivars and a perennial ryegrass (Lolium perenne L.) cultivar

AU - Griffith, G. S.

AU - Cresswell, A.

AU - Allen, Debra

PY - 2000/11

Y1 - 2000/11

N2 - Ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) have contrasting responses to soil mineral N availability and clover has the ability to fix atmospheric N2 symbiotically. It has been hypothesized that these differences are the key to understanding grass—clover coexistence and vegetative dynamics in pastures. However, the whole plant response of clover and ryegrass to mineral N availability has not been fully characterized and inter-cultivar variability in the N-handling dynamics of clover has not been assessed. A detailed experimental study to address these issues was undertaken. For all clover cultivars and ryegrass, mass specific mineral N uptake rates (of whole plants) were similar saturating functions of mineral N availability. For all clover cultivars total N assimilation rates, whole plant C : N ratios and root : shoot ratios were independent of mineral N availability. Clover growth rates were also independent of mineral N availability except for a slight (<10%) reduction at very low N availability levels. Specific N2 fixation rate (whole plant) was precisely controlled to ensure fixation balanced the deficit between mineral N uptake and the total N assimilation required to maintain constant whole plant C : N ratio. There was always a deficit between N uptake and the total N assimilation required to maintain C : N ratio. Consequently, some N2 fixation remained engaged even at high mineral N availability levels. All inter-cultivar variation in N2 fixation dynamics could be attributed to variations in growth rate. Clover mass specific growth rate declined as plant size increased. Ryegrass specific growth rate, whole plant C : N ratio and root : shoot ratio were dependent on N availability. Increased N availability led to increased growth rate and decreased C : N and root : shoot ratios. Specific growth rate was also dependent on plant size, growth rate declining as plant size increased. It is concluded that clover inter-cultivar variation in field performance is unlikely to be a consequence of variation in N-handling characteristics. Inter-cultivar differences in growth rate are likely to be a much more important source of variation.

AB - Ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) have contrasting responses to soil mineral N availability and clover has the ability to fix atmospheric N2 symbiotically. It has been hypothesized that these differences are the key to understanding grass—clover coexistence and vegetative dynamics in pastures. However, the whole plant response of clover and ryegrass to mineral N availability has not been fully characterized and inter-cultivar variability in the N-handling dynamics of clover has not been assessed. A detailed experimental study to address these issues was undertaken. For all clover cultivars and ryegrass, mass specific mineral N uptake rates (of whole plants) were similar saturating functions of mineral N availability. For all clover cultivars total N assimilation rates, whole plant C : N ratios and root : shoot ratios were independent of mineral N availability. Clover growth rates were also independent of mineral N availability except for a slight (<10%) reduction at very low N availability levels. Specific N2 fixation rate (whole plant) was precisely controlled to ensure fixation balanced the deficit between mineral N uptake and the total N assimilation required to maintain constant whole plant C : N ratio. There was always a deficit between N uptake and the total N assimilation required to maintain C : N ratio. Consequently, some N2 fixation remained engaged even at high mineral N availability levels. All inter-cultivar variation in N2 fixation dynamics could be attributed to variations in growth rate. Clover mass specific growth rate declined as plant size increased. Ryegrass specific growth rate, whole plant C : N ratio and root : shoot ratio were dependent on N availability. Increased N availability led to increased growth rate and decreased C : N and root : shoot ratios. Specific growth rate was also dependent on plant size, growth rate declining as plant size increased. It is concluded that clover inter-cultivar variation in field performance is unlikely to be a consequence of variation in N-handling characteristics. Inter-cultivar differences in growth rate are likely to be a much more important source of variation.

KW - C:N ratios

KW - growth rates

KW - Lolium perenne

KW - nitrogen fixation

KW - nitrogen uptake

KW - plant size

KW - Trifolium repens

UR - http://hdl.handle.net/2160/43202

U2 - 10.1093/jexbot/51.352.1879

DO - 10.1093/jexbot/51.352.1879

M3 - Article

VL - 51

SP - 1879

EP - 1892

JO - Journal of Experimental Botany

JF - Journal of Experimental Botany

SN - 0022-0957

IS - 352

ER -