Research On The Growth Regulation Of Cupressus Gigantea Before Transplantation

Cupressus gigantea is a national Class I key protected species,a rare tree species unique to Tibet.It is distributed only in the middle reaches of the Yarlung Zangbo River at an altitude of 3000～3400m,and above the floodplain and dry slopes of the river valley.Cupressus gigantea has a wide crown,tall and straight trunk,and strong and developed lateral roots.It is an important tree species for urban and rural greening and barren mountain forestation in southeastern Tibet.In this paper,5 years old Cupressus gigantea seedlings,12 years old Cupressus gigantea cultivated saplings and Cupressus gigantea trees in the wild are used as experimental materials to study the crown structure,branch resolution factors and photosynthetic characteristics of Cupressus gigantea saplings;The effect of seedling growth;the effect of cut size,pruning method,cut mulching and cutting season on cut healing;the influence of root pruning intensity on the growth of Cupressus gigantea seedlings and the effect of root pruning season and backfilling substrate on the rooting of Cupressus gigantea seedlings.The results show:1)The crown profile curve of Cupressus gigantea can be better fitted by Richard’s equation and linear regression equation.The estimation model of crown volume and surface area is the best allometric growth model with the combination of tree height,crown length and crown width,and R~2 is above 0.94.2)Pruning has a significant effect on the growth of Cupressus gigantea seedlings,but has no significant effect on the growth of ground diameter.Pruning can promote the growth of Cupressus gigantea seedlings and inhibit the growth of ground diameter.After heavy pruning,Cupressus gigantea seedlings can quickly adjust the stomata to reduce water consumption,which is closer to the pruning threshold and is more suitable for transplantation.Short cuts are more efficient in water use and are conducive to the accumulation of organic matter.Thinning will weaken the overall growth of the plant.3)After 1 year of pruning,most of the cuts of Cupressus gigantea can be closed normally,and more than 8%of the cuts are completely closed.When pruning branches,15～20mm large branches have slow healing speed and long closing time,so they should be trimmed as soon as possible;the knife makes the cut smooth,which is not conducive to the invasion of pests and diseases;mulching can promote the early formation of callus,and it is recommended that large branches be mulched after pruning.After the first annual growth cycle of pruning,spring is the stage where the healing rate is faster,and the healing ability of summer pruning is the best.4)Root cutting can significantly inhibit the growth of Cupressus gigantea seedling height and ground diameter.The higher the cutting strength,the more obvious the inhibition.Root cutting can also significantly inhibit the accumulation of photosynthetic organic matter in Cupressus gigantea,and gradually return to the level before cutting roots after 45 days.However,leaf water use efficiency increased after root cutting,and leaves with severe root cutting had higher SPAD values and water potential.Root cutting also stimulates the germination of new roots.Both the rooting rate and the number of new roots of seedlings increase with the increase of root cutting intensity.5)After the roots were cut off,the root system recovered after one growing season,and a large number of fibrous roots and lateral roots grew again at the cut,indicating that the root regeneration ability of Cupressus gigantea is strong.Root cutting in summer has the best new root quantity index and new root morphology development for young trees of Cupressus gigantea,while root cutting is relatively poor in winter.The new roots of Cupressus gigantea saplings grow fastest in sandy soil,and the number of new roots in sand mulch is the largest.The formation rate of callus from the roots of Cupressus gigantea in the sand mulch is as high as 100%.