《专业英语》lesson8专业 枝条与根系整形修剪

The ingredients controlling root/shoot balance
1. Water Regulation of water supply through the use of techniques such as partial root drying (PRD) and regulated deficit irrigation (RDI) can provide effective means of reducing water use and enhancing plant water efficiency as well as a way to influence vegetative and reproductive growth.
第八讲 Training and Pruning of
ShooTerminology Training - control of the shape, size and direction of plant growth Orientation of the plant in space
Roots also serve as the site for the synthesis of gibberellins (GA); they may also be sites involved in the interconversion of shoot-derived GA. GA activity related with dwarfing phenotype of rootstock.
Auxin can also be derived from roots; the root cap appears to be the most likely site of synthesis. IAA levels have been shown to change with the developmental age of roots and with other factors such as high mechanical soil impedance.
More direct support for the role of carbohydrates in the shoot has been forthcoming from studies involving auxin. Some anatomical characteristics of dwarfing rootstocks have been attributed to a higher ratio of carbohydrate to auxin than evident with vigorous rootstocks. Dwarfing rootstocks contain more starch reserves and the accumulation of leaf starch is known to down regulate photosynthesis.
Pruning - Judicious removal of plant parts Controls shape, size, fruit load
II. The principles concerning pruning and training Root: shoot ratio There is an innate balance between the dry matter partitioned to the shoot and its root. This balance defines and co-ordinates the relationships between processes taking place within the shoot and root.
2. Hormonal 2.1 The influence of root on shoot Cytokinins are synthesised in the roots and transported to the shoot via the xylem, in the transpiration stream. In the shoot, cytokinins can influence growth, photosynthesis and leaf senescence. In apple, root pruning reduces shoot cytokinin levels that in turn influence flowering, pre-harvest drop and shoot growth. Cytokinin concentration in xylem sap could increase as the vigour of rootstock increase. Drought stress resulted in a large reduction in shoot cytokinin which was caused by the inhibition of transport although cytokin production in root was increased.
The higher ratio of xylem to phloem tissue in rootstocks as vigour increases may be a reflection of differences in hormone action and/or transport. The available evidence suggest that the leaf canopy (leaf area), as a source of auxin, determines the amount of xylem that develops (Doley and Letyon 1968; Hess and Sachs 1972).
Roots respond to the amount of available soil water, and communicate with the shoot to affect a co-ordinated response, using abscisic acid (ABA) in the transpiration stream. When the ABA signal arrives in the leaf, the aerial control of water use efficiency is affected, by alteration of stomatal conductance. Leaf growth may also be affected. The ability of semi-invigorating and dwarfing rootstocks to export ABA in the xylem sap to the shoots is currently being investigated.
Adverse conditions in the rhizosphere have been shown to affect the amount of GA exported from the root. For example, low temperatures reduce GA in root sap and this, in turn, reduces shoot length.
Crotch: 胯部，分 叉处，树杈
Crown：露顶，根 颈部位
Tap root: Scaffold branch: 主枝 Sprout：苗芽、徒长枝 Root sucker： 萌蘖
A more recent and novel approach involves the restriction of root growth and development by growing trees within semipermeable membranes buried in the soil. Experimental studies have shown, with apple, that through root-restriction (by planting trees within root confining, but water permeable fabric membranes) vigorous rootstocks can be made to behave in a way similar to those of dwarfing rootstocks. The observed reductions in shoot growth due to restricted root growth were achieved in the absence of changes in plant water relations, suggesting that water shortage was not the growth inhibitor.
2.2 The influence of shoot on root The role of auxin in initiating cell wall loosening and cell extensibility has long been known, as has its ability to be transported basipetally in the phloem and by the polar auxin transport pathway. Auxin movement is predominantly in parenchymatous and cambial cells (proto-xylem and –phloem), and it can move acropetally as well. High accumulations of auxin favour differentiation into xylem elements. Conversely, low concentrations of auxin promote phloem development.
Recent work at HRI-East Malling suggests that the level of IAA in the bark of different apple rootstocks was fairly constant, and that the rate of transport changes (Kamboj et al. 1997). In dwarfing apple rootstocks the movement of IAA appears to be slower on a stem cross-sectional area basis, compared to invigorating rootstocks, despite there being relatively more transport tissue (phloem). Earlier work has shown that a higher phloem : xylem ratio was found to be associated with dwarfing, compared to vigorous rootstocks.