Abstract:

In order to reveal the planting density effect on the growth of Populus tomentosa clones and put forward the most suitable cultivated white poplar varieties and management for different region through the regionalizing spacing cultivation experiment, to study spacing effect on genetic parameters for growth traits of Populus tomentosa clones, and to assess genotype by spacing interaction, the experiments including 4 clones and 7 spacings were established with completely random block design in Weixian County, Heibei Province. Results indicated that both height and diameter at breast height (DBH) between clones were always significant at the 1% level of probability. S86 and BT17 clones were superior to 1316 and B331; Effect of planting density on DBH was significant after one growth period at the 5% level probability and increasingly marked with age, on height was most significant at only 2,3-year ages. Spacing ×clone interaction was not remarkable for 4-year-old stand. For 4 clones, planting density with no less 833 trees/hm2 was used to establish closer plantation. The difference of DBH between clones gradually decreased with density and age increasing when spacing exceeded 833 trees/hm2, declined with spacing narrowing and went up with age growing less than 833 trees/hm2. But for close stand, the clonal genetic effect on H presented the trends to decrease at first and then increase with aging and spacing decreasing. For rare stand, there was a contrary fluctuation with aging. Planting density had not significant influence on the coefficient of genetic variation (CV) between clones for DBH . But the CV of clone by block interaction and of inner-clones were larger before two years than after two years. For height, the CV of inter-clones and of clone by block interaction were increasing with age at early growth period and then decrease with age, but CV of inner-clones gradually increased with age. The broad hereditability (H2) of DBH was remarkably different between spacings at the 1% level probability, but not significant between ages at the 5% level probability. H2 of height, derived from clone mean value, was not marked between spacings at the 5% level probability , but H2 of height calculated by clone individual value was significant difference between spacings at the 5% level probability, but H2 of Height calculated by both of methods was not significant between ages at the 5% level probability.