Leaf and Root Growth, Carbon and Nitrogen Contents, and Gene Expression of Perennial Ryegrass to Different Nitrogen Supplies

Abstract

<jats:p>Nitrogen greatly impacts plant growth and development. The objective of this study was to characterize growth, nitrogen use, and gene expression of perennial ryegrass (<jats:italic>Lolium perenne</jats:italic>) in response to increasing nitrogen supplies. Perennial ryegrass (cv. Inspire) was grown in sand culture and irrigated with a half-Hoagland solution amended with 0, 0.5, 1.0, 2.5, 5.0, and 7.5 m<jats:sc>m</jats:sc> nitrogen. Leaf tissues were harvested at 10 days (first cutting) and 20 days (second cutting) and roots were harvested at 20 days. The relatively higher N supply (2.0–7.5 m<jats:sc>m</jats:sc>) resulted in a larger amount of leaf fresh and dry weight but lower root fresh and dry weight, especially for the second cutting. Root:leaf ratio was higher under low N, but lower under the high N treatment. Leaf N content was relatively higher under 2.5, 5, and 7.5 m<jats:sc>m</jats:sc> N than under the other three treatments, while 2.5 m<jats:sc>m</jats:sc> N exhibited relatively higher leaf carbon content for both cuttings. Leaf C:N ratio and leaf nitrogen use efficiency (LNUE) decreased with increasing N supplies for the first cutting but were higher under low N (0–1.0 m<jats:sc>m</jats:sc>) for both cuttings. Leaf C:N ratio and LNUE did not differ among low N and LNUE also remained unchanged among high N for the second cutting. Root N content increased, but the root C:N ratio and root N use efficiency (RNUE) decreased with increasing N supplies, especially under 2.5, 5.0, and 7.5 m<jats:sc>m</jats:sc> N. Low (0.5 m<jats:sc>m</jats:sc>), moderate (2.5 m<jats:sc>m</jats:sc>), and high (7.5 m<jats:sc>m</jats:sc>) N were chosen to examine the expression level of <jats:italic>NR</jats:italic> encoding nitrate reductase and <jats:italic>GS1b</jats:italic> encoding glutamine synthetase. Treatment of 0.5 m<jats:sc>m</jats:sc> N had higher expression levels of leaf <jats:italic>NR</jats:italic> than other two treatments for both cuttings and a higher level of leaf <jats:italic>GS</jats:italic> for the second cutting. Expression of <jats:italic>NR</jats:italic> in the roots did not vary among treatments but the expression of <jats:italic>GS</jats:italic> increased under 2.5 and 7.5 m<jats:sc>m</jats:sc>, compared with the 0.5 m<jats:sc>m</jats:sc> N. Differential leaf and root growth and physiological responses to low N (0 to 1 m<jats:sc>m</jats:sc>) and to moderate to high N (2.5 to 7.5 m<jats:sc>m</jats:sc>) could be used for examining the natural variation of N use in diverse perennial ryegrass populations.</jats:p>

Rapid Screening of Nitrogen Use Efficiency in Perennial Ryegrass (Lolium perenne L.) Using Automated Image-Based Phenotyping

“…It is as expected that greater biomass production was observed under the moderate N than that under low N ( Table 2 ). However, higher N application reduces NUE which is in agreement with previous reports ( Jiang et al, 2016 ). It was found that high plant tissue N content was correlated with low NUE ( Garcez and Monteiro, 2016 ).…”

“…Half-strength Hoagland solution ( Hoagland and Arnon, 1950 ) (100 ml) with modified N levels of 0.5 mM or 5 mM ( Jiang et al, 2016 ) was applied to each pot twice weekly. KNO 3 and Ca(NO 3 ) 2 were used as nitrate sources in the solution.…”

“…KNO 3 and Ca(NO 3 ) 2 were used as nitrate sources in the solution. Potassium and calcium levels were equalized across treatments by adding KCl and CaCl 2 into the lesser N treatment solution ( Jiang et al, 2016 ).…”

Nitrous Oxide Emission from Forage Plantain and Perennial Ryegrass Swards Is Affected by Belowground Resource Allocation Dynamics

“…In any case, N addition stimulated the root growth and development, enhancing the uptake of other nutrients [35]. Generally, more N was taken up as the N rate increased; thus, N fertilization reduced the C/N ratio in both below-and aboveground biomass, with this trend being most evident in the N300 treatment, indicating a luxury uptake of N, similar to earlier reports in maize straw [36] and grass swards [37].…”

Real-time monitoring of rhizosphere nitrate fluctuations under crops following defoliation

“…Following defoliation in hydroponics it is well-documented that the remnant vegetative tissue preferentially takes up more carbon than N [ 44 ], in order to restore the C:N ratio of the tissue due to substantially decreased photosynthetic rate [ 45 ]. Total N reserves stored as vegetative storage proteins in roots and stem bases have been found to be rapidly degraded after defoliation [ 46 ].…”