Poplar Trees （Populus canadensis Moench） Initiate Vegetative Storage Protein Accumulation During New Shoot Development in Spring

: It was generally assumed that the accumulation of vegetative storage protein (VSP) in poplar trees and/or temperate hardwoods did not occur in spring. To test this assumption, the accumulation of the 32-kDa VSP and the differential expression of a gene encoding for the protein in poplars were investigated using light and electron microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and reverse transcription-polymerase chain reaction (RT-PCR). We report, for the first time, that poplar trees initiated VSP accumulation in new shoots during the development of new shoots in spring under conditions of high temperature and long days. The amount of 32-kDa VSP increased gradually in the stem of new shoots and in two-year-old branches, but there were no detectable changes in its abundance in the bark tissues of trunks during new shoot development. Based on the presence of a 286-bp DNA fragment that is identical to the VSP gene bspA, encoding for the 32-kDa VSP in Populus deltoids Bartr. ex Marsh., the differential expression of the 32-kDa VSP gene in P. canadensis Moench was revealed by RT-PCR. The results indicated that the 32-kDa VSP gene was expressed strongly in new shoots, relative weakly in two-year-old branches and was not expressed in the trunk during new shoot development. This pattern of VSP accumulation and VSP gene space-time differential expression may be an important mechanism by which stored nitrogen compounds are used preferentially to exogenously available nitrogen and, in addition, the dynamic pattern may also have a role in the regulation of nitrogen metabolism, especially nitrogen uptake by the roots.

Wood Physical and Mechanical Properties of Populus × canadensis Moench and Populus ×euramericana(Dode) Guinier cv. Gelrica

The physical-mechanical properties of Populus x canadensis Moench and Populus x euramericana （Dode） Guinier cv. Gelrica were studied to provide theoret- ical and scientific bases for the directional breeding and efficient use of artificial forests with P. canadensis and P. euramericana Gelrica. The results showed the air-dried density, basic density of P. canadensis were 0.468 g/cm3 and 0.372 g/cm3, respectively; the shrinkage coefficient of radial, tangential and volume were 0.133%, 0.270% and 0.553%, respectively;the modulus of elasticity in static bending, the bending strength and the compressive strength parallel to grain were 9 302.99 MPa, 79.69 MPa and 40.32 Mpa, respectively. As for the P. euramericana Gelrica, the air-dried density, basic densitywere 0.453 and 0.355 g/cm3, respectively; the shrink- age coefficient of radial, tangential and volume were 0.205%, 0.304% and 0.554%, respectively; the modulus of elasticity in static bending, the bending strength and the compressive strength parallel to grain were 9 014.44, 55.87 and 33.09 Mpa respectively. Comprehensive analysis of the indicators showed that the properties of P. canadensis were better than those of P.euramericana Gelrica.

杨树对草木犀的化感作用

研究了‘中辽1号’杨(Populus×canadensis cv.‘Zhongliao 1’)叶片、根系、根际土浸提液对草木犀[Melilotus officinalis(Linn.)Pall.]种子萌发的化感效应。研究表明:杨树叶片、根系浸提液对草木犀种子萌发及幼苗生长的化感效应为负效应,起到了抑制作用,且浓度越大抑制效果越明显,相同浓度的叶片浸提液抑制作用大于根系浸提液的抑制作用;高浓度杨树根际土浸提液对草木犀种子萌发及幼苗生长的化感效应为负,起到了抑制作用,但低浓度杨树根际土浸提液的化感效应为正效应,起到了促进作用。初步认为,杨树林下适宜种植草木犀。