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We investigated the effects of planting density and relative ground height (distance from the water table) on the early establishment of two introduced tree species [Mongolian pine ( Pinus sylvestris var. mongolica) and white poplar ( Populus alba var. pyramidalis)] in the Mu Us Sandy Land of China; we used GLMM to analyze experimental effects. In total, 14 afforestation plots (seven plots per species) with variable relative ground heights were established on a shifting sand dune. Trees were planted at intervals of 3, 5, and 7 m, and the distances between neighboring trees were fixed within plots. Planting intervals and numbers of neighboring trees were treated as measures of planting density, and relative ground height was treated as an indicator of water supply stability. For both species, tree survival rates decreased with increasing planting interval; the number of neighboring trees had a positive effect on survival. The effect of relative ground height differed between species. Pine tree survival rates decreased with increased relative ground height, while the survival rates of poplar trees were unaffected. We recommend that pine trees be planted at high density on lower sectors of sand dunes to prevent wind erosion in early spring. Poplar trees should be planted at high density without reference to relative ground height for the provision of fuelwood. [ABSTRACT FROM AUTHOR]

Abstract: Moisture is a primary limiting factor that affects plant growth. To determine the ideal amount of irrigation water for the growth of individual Populus bolleana Lauche, the major protective species around Qira oasis in southern edge of Taklimakan Desert in Xinjiang, China, we studied the moisture of soil layers with depth between 0-80cm and the response of P. bolleana''s water status such as moisture content, stomatal characteristics, leaf water potential, stem sapflow and stem diameter to different irrigation based on the field monitoring data. The results showed that the moisture content of soil layers with depth of 0-80cm gradually increased with irrigation increasing, especially when irrigation was more than 30 liters. When irrigation was 30 and 40 liters, the daily leaf water potential presented an obvious unimodal trend: the predawn and midday leaf water potential increased significantly. Along with the irrigation increased from 10 to 40 liters, sapflow and stomatal conductance followed a trend of first decreases and then increases. When irrigation was 30 liters, the daily mean stem diameter and contraction of P. bolleana reached their peaks, indicating that irrigating more than 30 liters of water could improve the water status of P. bolleana and prevent it from drought stress. Thus, we concluded that the ideal irrigation amount for the normal growth of individual P. bolleana should be 30 liters per year. [Copyright &y& Elsevier]

The white poplar (Populus alba) is widely distributed in Central Asia and Europe. There are natural populations of white poplar in Irtysh River basin in China. It also can be cultivated and grown well in northern China. In this study, we sequenced the genome of P. alba by single-molecule real-time technology. De novo assembly of P. alba had a genome size of 415.99 Mb with a contig N50 of 1.18 Mb. A total of 32,963 protein-coding genes were identified. 45.16% of the genome was annotated as repetitive elements. Genome evolution analysis revealed that divergence between P. alba and Populus trichocarpa (black cottonwood) occurred ~5.0 Mya (3.0, 7.1). Fourfold synonymous third-codon transversion (4DTV) and synonymous substitution rate (ks) distributions supported the occurrence of the salicoid WGD event (~ 65 Mya). Twelve natural populations of P. alba in the Irtysh River basin in China were sequenced to explore the genetic diversity. Average pooled heterozygosity value of P. alba populations was 0.170±0.014, which was lower than that in Italy (0.271±0.051) and Hungary (0.264±0.054). Tajima's D values showed a negative distribution, which might signify an excess of low frequency polymorphisms and a bottleneck with later expansion of P. alba populations examined.