Fig.1

Net growth in height and ground diameter of P. simonii × P. nigra hybrids and their parents A: Net growth of plant height from 0 to 45 days; B: Net growth of ground diameter from 0 to 45 days. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.2

Leaf number, single leaf area and total leaf area of P. simonii × P. nigra hybrids and their parents A—C: Number of leaves per plant of 15，30 and 45 days. D—F: Single leaf area of 15, 30 and 45 days; G—I: Total leaf area of 15, 30 and 45 days. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.3

Chlorophyll content of P. simonii × P. nigra hybrids and their parents A: Chlorophyll content at 15 days; B: Chlorophyll content at 30 days; C: Chlorophyll content at 45 days. H1, H2 and H3 are the high growth potential progenitors respectively, L1, L2 and L3 are the low growth potential progenitors respectively, and FP and MP are the maternal and paternal parents respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.4

Net photosynthetic rate and transpiration rate of P. simonii × P. nigra hybrids and their parents A: Net photosynthetic rate at 15 days; B: Net photosynthetic rate at 30 days; C: Net photosynthetic rate at 45 days; D: Transpiration rate at 15 days; E: Transpiration rate at 30 days; F: Transpiration rate at 45 days. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.5

Maximum photochemical efficiency of Populus simonii × P. nigra hybrids and their parents A: Maximum photochemical efficiency at 15 days; B: Maximum photochemical efficiency at 30 days; C: Maximum photochemical efficiency at 45 days. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.6

Leaf water loss rate of P. simonii × P. nigra hybrids and their parents A: Leaf water loss rate of H1; B: Leaf water loss rate of H2; C: Leaf water loss rate of H3; D: Leaf water loss rate of L1; E: Leaf water loss rate of L2; F: Leaf water loss rate of L3; G: Leaf water loss rate of FP; H: Leaf water loss rate of MP. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively."

Fig.7

Leaf water loss rate at 12 hours of P. simonii × P. nigra hybrids and their parents"

Fig.8

Instantaneous water use efficiency and carbon isotope ratio of P. simonii × P. nigra hybrids and their parents A: Instantaneous water use efficiency at 15 days; B: Instantaneous water use efficiency at 30 days; C: Instantaneous water use efficiency at 45 days; D: Stable carbon isotope ratio. H1, H2 and H3 are the high growth potential progenitors, L1, L2 and L3 are the low growth potential progenitors, and FP and MP are the maternal and paternal parents, respectively. Different lowercase letters indicate significant differences between offspring and parental clones under the same treatment (P < 0.05)."

Fig.9

Correlation between growth traits and key indicators of photosynthesis and water use in P. simonii × P. nigra hybrids and their parents"