Influences of Environmental Factors on Leaf Morphology of Chinese Jujubes

<div><p>Rainfall and temperature are the primary limiting factors for optimum quality and yield of cultivated jujube (<i>Ziziphus jujuba</i> Mill.). Adaptation to arid and cool environments has been and remains an important goal of many jujube improvement programs. This study summarized the survey results of 116 Chinese jujube varieties grown at 33 sites in China. The objective was to identify the environmental factors that influence leaf morphology, and the implications for breeding and introduction of new jujube varieties. Jujube leaf morphological traits were evaluated for their potential relationships with mean annual temperature (MAT) and mean annual precipitation (MAP). The results showed that many leaf morphological traits had a strong linear relationship with local precipitation and temperature. Longer veins per unit area (VLA) and reduced leaf area and leaf perimeter were typical of arid areas. VLA was inversely related to MAT and MAP at the centers of origin of jujube. There was a positive relationship between leaf shape (perimeter²/area) and both MAT and MAP. These results indicated that leaf vein traits of Chinese jujubes might have resulted from their adaptation to environmental factors in the course of long-term evolution. Principal component analysis allocated the 116 jujube varieties to three different groups, differentiated on the basis of morphological and physiological leaf characteristics. Jujube varieties from the Hebei, Shandong, Henan, southern Shanxi and central Shaanxi provinces were closely related, as were varieties from northwest Shanxi and northeast Shaanxi provinces, and varieties from the Gansu and Ningxia provinces. These close relationships were partially attributed to the frequent exchanges of varieties within each group. Leaf venation characteristics might be used as reference indices for jujube variety introduction between different locations.</p></div

Geographic and climatic characteristics (1951–2012) of the 33 sampling sites for jujube leaves in northern China.

<p>Geographic and climatic characteristics (1951–2012) of the 33 sampling sites for jujube leaves in northern China.</p

Relationships between jujube leaf traits of vein length per unit area (VLA), and leaf shape (perimeter²/area) and the climatic factors of mean annual precipitation (MAP) and mean annual temperature (MAT) in 33 sampling sites across northern China.

<p>Each dot represents 1of the 33 sampling sites in China. Error bars represent standard deviations.</p

Comparisons of vein length per unit area (VLA) (a), area (b) and perimeter (c) of jujube leaves of 21 representative jujube varieties sampled in 33 sites in northern China.

<p>The jujube varieties are represented by different capital letters for the sake of clarity. The error bars are standard deviations of the variables concerned. The least significant difference (LSD) multiple comparison tests were conducted for VLA (df = 62, F = 21.10, p<0.05), leaf area (df = 62, F = 112.472, p<0.05), and leaf perimeter (df = 62, F = 8.016, p<0.05), respectively. Different lowercase letters above error bars for each component indicate statistically significantly different mean values (p<0.05).</p

Distribution of the 33 sampling sites (counties or districts) of jujube leaves in northern China (34°–39° N and 102°–117° E; small map at top center).

<p>The dots represent the origin growth areas of the various jujube varieties where jujube leaves were collected.</p

Principal components analysis of leaf morphological traits of 116 jujube varieties from 33 sites in northern China.

<p>All jujube varieties are divided into three groups: GROUP 1 (filled squares), GROUP 2 (filled triangles up), and GROUP 3 (filled circles). The seven provinces where the 33 sampling sites are located are represented by numbers for the sake of brevity. Members of GROUP 1 were mainly from Hebei, Shandong, Henan, southern Shanxi and central Shaanxi Provinces; Members of GROUP 2 were mainly from northwest Shanxi and northeast Shaanxi. Members of GROUP 2 were mainly from Gansu and Ningxia Provinces.</p

Comparisons of vein length per unit area (VLA), leaf area and leaf perimeter of jujube leaves sampled in three jujube cultivation areas (ASYH, HLP, and AVHN area) in China.

<p>The error bars are standard deviations of jujube production area concerned. (a) VLA (df = 35, F = 60.702, P<0.05); (b) leaf area (df = 35, F = 22.650, P<0.05); (c) leaf perimeter (df = 35, F = 8.726, P<0.05), as determined by LSD multiple comparison tests.</p

Sensitivity to <i>R</i>.

<p>Sensitivity to <i>R</i>.</p

Model performance in the different instances.

<p>Model performance in the different instances.</p

Visiting sequence of assigned facilities with padding dummy facility.

<p>Visiting sequence of assigned facilities with padding dummy facility.</p