Analysis on root anatomical structure and hydraulic characteristics in different grape varietie

Abstract: 【Objective】Root is important for the growth and development of fruit tree. Compared with timber tree, the root of fruit tree is more susceptible to environmental stresses such as drought, saliniza-tion, and flooding, which cause weak growth, low fruit yield, and poor fruit quality. Summer Black, Vitis vinifera L.‘Muscat Hamburg’ and V. labruscana Bailey ×V. vinifera L.‘Shine Muscat’, which are the major cultivated varieties of grape in the regions with banking up to prevent cold in northern of Chi-na, were planted in some saline-alkali areas in recent years and showed problems such as weak growth and few absorption roots. The aim in this paper is to compare the differences in root hydraulic character-istics among the three varieties and to detect the soil traits affecting the anatomical structure and func-tion of the grape root.【Methods】Three individuals with similar vigor were selected for each variety,and the roots and rhizosphere soil were sampled in four cross directions at positions 0.2 m from the trunk and from soil layers of 0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm. The fine roots were separated into 3 diameter classes: Ⅰ≤1 mm, 1 mm <Ⅱ≤2 mm, 2 mm<Ⅲ≤3 mm. The root segments were used to make paraffin sections and then sectioned with a Leica RM2235 microtome with the thickness of 18 μm. The anatomical structure was observed using a Leica DM4000B biological microscope, and the pic-tures were taken with a Leica DFC450 CCD digital imaging system. The thickness of the phloem and the vascular cambium, the diameter of the xylem and the vessel, and the area of the vessel in the roots of different varieties of grapes were measured with a Motic 3000 imaging system. The root specific hy- draulic conductivity and root xylem embolism vulnerability index were calculated according to the Ha-gen–Poiseuille equation, which indicated that the larger the diameter of vessel, the greater the risk of embolism. The canonical correspondence analysis method was used to establish the relationship model between root indexes and soil factors, with root anatomical structure and hydraulic characteristic index-es as response variables, and soil physical and chemical properties as explanatory variables.【Results】 Compared with the other grapes of varieties, Muscat Hamburg had thicker xylem and larger proportion of root vessels in the same root diameter class, showing that it had a stronger ability of axial water trans-port in a saline soil environment. Muscat Hamburg had also large maximum and minimum diameters of the average vessels, the largest vessel, the highest root specific hydraulic conductivity, and the highest embolism fragility index, indicating that the root hydraulic conductivity of the grape is closely related to the duct area rather than the number of vessels. The strong salt tolerance of Muscat Hamburg was thus explained anatomically. The anatomical structure and function of grape roots were compared among different soil layers. The total length of the vascular bundles, consisting of phloem, vascular cambium and xylem, in Muscat Hamburg was significantly higher than in Summer Black and Shine Muscat in the 0-10 cm soil layer, while that in Summer Black was higher than in Muscat Hamburg and Shine Muscat in the 10-20 cm soil layer. Compared with the other soil layers, the root vessel area was larger and the root specific hydraulic conductivity was higher in the 5-15 cm soil layer. It is generally believed that the absorption function of roots in 0-20 cm soil layer was stronger than in deeper layers. The root structure was found to be more conducive to water transport in the 5-15 cm soil layer, which might be related to serious salinization in this soil layer. The canonical correspondence analysis exhibit- ed that the contents of soil ammonium, available phosphorus, and available potassium had more signifi- cant impact on root vessel roundness, root specific hydraulic conductivity and embolism vulnerability index, while ion concentration in soil was correlated positively with root phloem length, vascular cambi-um length and pericerp length. The increase in the length of the protective tissue tended to reduce the os-motic stress and ion toxicity suffered by the plant roots, but seemed to reduce the water absorption effi-ciency, resulting in water deficit, which may be one of the reasons for the poor growth of grapes in sa-line-alkali soil.【Conclusion】Stronger water drainage ability and higher salt tolerance were found in the roots of Muscat Hamburg compared with Summer Black and Shine Muscat. For fertilizer applica- tion to grapes grown in saline-alkali soils, attention should be paid upon achieve efficient use of fertiliz- ers through ditch fertilization and deep fertilization. The increased plant resistance and improved fruit quality can be achieved through adding phosphate fertilizer and washing salt and alkali.