Growth variables of rice seedlings grown at different N supplies.

<p>Rice plants (<i>cv.</i> Shanyou 63 and Yangdao 6) were supplied with N at three different levels (low: 20 mg L⁻¹ N, intermediate: 40 mg L⁻¹ N, and high: 100 mg L⁻¹ N). Data are means ± SD of 5 individual plants. Variables were determined 40 days after the start of treatment.</p><p>Notes: Significant differences (<i>P</i><5%) between N supplies or varieties were indicated by different lowercase letters or different uppercase letters, respectively. RMR, SCMR and LMR represent root mass ratio, leaf sheath and culm mass ratio and leaf mass ratio, respectively. They were calculated as the ratio of separate dry mass to whole plant dry mass. SLW represents specific leaf weight, and was calculated as the ratio of leaf fresh weight to leaf area.</p

The relationships between initial Rubisco activity and (a) the ratio of mesophyll conductance (g_m) to Rubisco content, and (b) the ratio of total conductance (g_t) to Rubisco content on Shanyou 63 (solid cycles) and Yangdao 6 (open cycles).

<p>The lines represent the following regressions: (a) y = 0.39x−0.89 R² = 0.93 <i>P</i><0.01; (b) y = 0.54x−0.25 R² = 0.80 <i>P</i><0.05.</p

The relationships between leaf photosynthetic rate (<i>A</i>) and (a) leaf N content, and (b) Rubisco content and in Shanyou 63 (closed cycles) and Yangdao 6 (open cycles).

<p>The lines represent the following regression equations: (a) y = 0.12x+6.33 R² = 0.82 <i>P</i><0.01 for Shanyou 63; y = 0.17x−0.60 R² = 0.79 <i>P</i><0.01 for Yangdao 6; (b) y = 0.22x+8.59R² = 0.78 <i>P</i><0.01 for Shanyou 63; y = 0.40x−1.53 R² = 0.91 <i>P</i><0.01.</p

The relationship between initial Rubisco activity and the ratio of leaf photosynthetic rate (<i>A</i>) to Rubisco content on Shanyou 63 (solid cycles) and Yangdao 6 (open cycles).

<p>The line represents linear regression: y = 3.51x−0.53 R² = 0.88 <i>P</i><0.01.</p

The relationships between chloroplast size and photosynthetic N-use efficiency (PNUE), and the ratio of leaf photosynthetic rate (<i>A</i>) to Rubisco.

<p>The lines represent the following regression equations: (a) y = 91.04x/(x–2.87), R² = 0.53, <i>P</i><0.01; (b) y = 121.76x/(x–0.96), R² = 0.75, <i>P</i><0.01; (c) y = 180.56x/(x–2.12), R² = 0.72, <i>P</i><0.01; (d) y = 0.21x/(x–2.86), R² = 0.53, <i>P</i><0.01; (e) y = 0.29x/(x–0.95), R² = 0.69, <i>P</i><0.01; (f) y = 0.42x/(x–2.06), R² = 0.63, <i>P</i><0.01. Data sources: data of solid squares were collected from Wuyujing 3 (<i>Oryza sativa</i> L. ssp. japonica) with different N supplies; data of open squares were from Shanyou 63 with different N forms and water supply <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062036#pone.0062036-Li2" target="_blank">[42]</a>; data of solid and open cycles were from Shanyou 63 and Yangdao 6 with different N supplies.</p

Effects of N supply level on leaf photosynthesis in rice seedlings.

<p>Rice plants (<i>cv.</i> Shanyou 63 and Yangdao 6) were supplied with N at three different levels (low: 20 mg L⁻¹ N, intermediate: 40 mg L⁻¹ N, and high: 100 mg L⁻¹ N). Data are means ± SD of more than 20 individual chloroplasts for their length and thickness, and 5 individual plants for other variables.</p><p>Notes: Significant differences (<i>P</i><5%) between N supplies or varieties were indicated by different lowercase letters or different uppercase letters, respectively. <i>A</i>, g_s, g_m, N, Rubisco and PNUE represent leaf photosynthetic rate, stomatal conductance to CO₂, mesophyll conductance to CO₂, leaf nitrogen content, leaf Rubisco content, photosynthetic N-use efficiency, respectively.</p

Electron micrographs of chloroplasts in newly expanded leaves of Shanyou 63 (a, low-N supply; b, intermediate.-N supply; c, high-N supply) and Yangdao 6 (d, low-N supply; e, intermediate.-N supply; f, high-N supply).

<p>Bar = 1 µm. C, chloroplasts; M, mitochondrion; N, nucleus; SG, starch granules; CW, cell wall; arrows point to plasma membrane.</p

The relationships between the ratio of mesophyll conductance (g_m) to Rubisco content and (a) photosynthetic N-use efficiency (PNUE) and (b) the ratio of leaf photosynthetic rate (<i>A</i>) and Rubisco content on Shanyou 63 (solid cycles) and Yangdao 6 (open cycles).

<p>The lines represent the following regressions: (a) y = 32.89x+26.28 R² = 0.86 <i>P</i><0.01; (b) y = 0.096x−0.038 R² = 0.80 <i>P</i><0.05.</p

<i>A</i>/C_i response curves of newly expanded leaves in Shanyou 63 (a) and Yangdao 6 (b).

<p>The symbols of solid cycles, open cycles and solid triangles represent high, intermediate and low N supply, respectively.</p

The relationships between chloroplast size and the ratio of mesophyll conductance (g_m) to Rubisco content on Shanyou 63 (solid cycles) and Yangdao 6 (open cycles).

<p>Chloroplast surface area (S_chl) and volume (V_chl) were calculated from the Cesaro formula. The lines represent the following regressions: (a) y = 2.54x/(x−1.98) R² = 0.63 <i>P</i> > 0.05; (b) y = 2.99x/(x−0.73) R² = 0.88 <i>P</i><0.01; (c) y = 3.72x/(x−1.91) R² = 0.89 <i>P</i><0.01; (d) y = 1.15x+2.06 R² = 0.82 <i>P</i><0.05.</p