Growth characteristics and cold resistance of Pinus nigra var.austriaca

This paper deals with the growth characteristics and the related index of its cold resistance of Pinus nigra var.austriaca on the basis of the field investigation and experimental measurement.The results showed that young seedlings of P.nigra var.austriaca had a strong root system,long vertical roots,thick lateral roots,distinct structure,and a heavy fresh mass,a striking contrast with seedlings of P.tabulaeformis.The diameter growth of the one-year-old seedlings was obviously bigger than that of P.tabulaeformis.The fast growth period of height of seedlings occurred from late June to the late of August,with growth increment accounting for 42.3% of total one.Fast height growth period of 31-year-old P.nigra var.austriaca occurred during the 15-20th year,with the growth increment accounting for 32.1% of total.The height growth of P.nigra var.austriaca was slower than that of P.tabulaeformis,while the diameter growth was bigger than that of P.tabulaeformis,with an average annual volume growth of 0.007 4 m³,which is one time larger than that of P.tabulaeformis.The measurement of cold resistance showed that the exudation rate of electrolyte of P.nigra var.austriaca was higher than that of P.tabulaeformis at-20-40℃,the tissue's median lethal temperature(LT₅₀) of it was at-16.2℃,while that of P.tabulaeformis was at-17.9℃.The cold resistance of P.nigra var.austriaca was weaker than that of P.tabulaeformis.The relative low content of bound water,K⁺,carotenoid and ABA in the leaf tissue of P.nigra var.austriaca is the internal cause of its weak cold resistance.