不同根型苜蓿根颈变化特征分析

在甘肃省3个不同生态区(天水半湿润区、兰州半干旱区和武威干旱区),应用Marquez-Ortiz法和Johnson法对根茎型“清水”苜蓿(Medicago sativa L.cv.“Qingshui”)、根蘖型野生黄花苜蓿(native M.falcata material)和“甘农2号”杂花苜蓿(M.varia Martin.cv.“Gannong No.2”)及直根型“陇东”苜蓿(M.sativaL.c v.“Longdong”)生长前3年的根颈特性进行了连续研究,结果表明,在3个生态区,不同根型苜蓿根颈特性差异显著,其中根茎型“清水”苜蓿根颈直径和分枝直径均较细,根颈入土深度较深,根颈分枝数较多;根蘖型野生黄花苜蓿和“甘农2号”杂花苜蓿的根颈直径和分枝直径均较粗,根颈入土深度相对较浅,根颈分枝数与根茎型“清水”苜蓿差异不显著;直根型“陇东”苜蓿的各项指标介于根茎型与根蘖型苜蓿之间,与根蘖型苜蓿更接近.根茎型、根蘖型苜蓿的水平伸展特性在不同生态区和不同土壤质地生长当年和生长第2年均未表现,生长第3年根茎/根蘖性状在3个生态区均得到表达,但根茎率/根蘖率不同.根茎率在天水半湿润区最高,盛威干旱区最低;根蘖率在武威干旱区和兰州半干旱区较高,天水半湿润区较低,且根茎率/根蘖率随生育时期的延长呈增加趋势.结荚期根茎型“清水”苜蓿在天水半湿润区根茎率为76.7％,兰州半干旱区、武威干旱区分别为43.5％和39.0％.根蘖型黄花苜蓿和“甘农2号”杂花苜蓿的根蘖率在兰州半干旱区为61.2％和50.6％,在武威干旱区为58.7％和54.7％,在天水半湿润区为44.5％和36.3％.

Analysis of dynamic variations in crown characteristics ofdifferent root-type alfalfa plants

Alfalfas are divided into tap-rooted, branch-rooted, creep-rooted and rhizome-rooted plant types. Rhizome-rooted alfalfa is a relative independence germplasm resource with great genetic distance between rhizome-rooted alfalfa and international registry of other alfalfa varieties. It is an important gene-pool for alfalfa breeding and varietal improvement. Retrospective review on past papers shows that a huge amount of work have focused on introduction, breeding, productive performance, resistance and genetic diversity of tap-rooted and creeping-rooted alfalfas. Also the mechanisms, genetic characters and environment impacts of branch-rooted alfalfa have been extensively documented. However, only a few studies have focused on rhizome-rooted alfalfa and fewer still on the contrasts among different root-type alfalfas. Therefore, four alfalfa materials with three root-types (rhizome-rooted Medicago sativa L. cv. "Qingshui", creep-rooted native M. falcata material, creep-rooted M. varia Martin.cv. "Gannong No.2" and tap-rooted M. sativa L.cv. "Longdong") were used to determine the differences in crown characteristics in the semi-humid region of Tianshui, semi-arid region of Lanzhou and arid region of Wuwei in Gansu Province. The results showed significant differences among different root-type alfalfas regarding crown characteristics, crown diameter and crown branch diameter. Rhizome-rooted alfalfa was relatively thinner with deeper crown depth and more crown branches. Crown diameter and crown branch diameter of creep-rooted alfalfa were relatively thicker with shallower crown depth. There was no significant difference in crown branches between rhizome-rooted and creep-rooted alfalfa. The indexes of tap-rooted alfalfa were between those of rhizome-rooted and creep-rooted alfalfas, but were much closer to those of creep-rooted alfalfa. Experiments showed that temperature, fixed growth number of years and ecological zones obviously influenced alfalfa crown characteristics. Within 3 years of growth, crown diameter of all the root-type alfalfas was remarkably influenced by growth temperature. Crown diameter growth was generally faster in summer/autumn than in winter/spring. Horizontal extensions of creep-rooted and rhizome-rooted alfalfas were not detected at the different experimental sites and soil textures in the first and second years of growth. In the third year, plants appeared rhizome and creeping characters at three experimental sites but with different rhizome or creeping rates. Rhizome rate of rhizome-rooted alfalfa was highest in Tianshui and lowest in Wuwei. Creeping rate of creep-rooted alfalfa was higher in Wuwei and Lanzhou, and lower in Tianshui. Both rhizome and creeping rates increased with growth stage. Rhizome rate of rhizome-rooted M. sativa L. cv. "Qingshui" at podding stage reached 76.7%, 43.5% and 39.0% in Tianshui, Lanzhou and Wuwei, respectively. Creeping rates of creep-rooted native M. falcata material and creep-rooted M. varia Martin. cv. "Gannong No.2" reached 61.2 % and 50.6% in Lanzhou, 58.7% and 54.7 % in Wuwei and 44.5% and 36.3% in Tianshui, respectively.