棉花根系生长和空间分布特征

CHARACTERIZING ROOT GROWTH AND SPATIAL DISTRIBUTION IN COTTON

结合田间根钻取样和图像扫描分析方法 ,研究了不同棉花品种根系的长度、直径和表面积动态及 0～ 10 0cm深和 0～ 4 0cm宽土壤范围内的空间分布特征。该方法与常规直尺测量结果相比相关系数R2 达到 0 .899(n =1318) ,显示了较好的可靠性。研究结果表明 ,棉花平均根长密度 (RLD)在花铃期为 1.2 1～ 1.2 7mm·cm-3 ,吐絮后降至 1.0 4～ 1.12mm·cm-3 ,收花时为 0 .76mm·cm-3 。棉花根平均直径在不同基因型间存在显著差异 ,抗虫杂交棉的根直径最粗 ,平均为 0 .5 2mm ;早熟类型品种根直径较细 ,平均为 0 .36mm。在土壤深度上根直径的差异不显著 ,但距棉行距离越远 ,根的平均直径越小。在明确根系长度和直径动态规律的基础上 ,提出了根表面积指数(RAI)的概念 ,与地上部叶面积指数具有相似的含义和生物学意义 ,且呈较好的指数相关关系 (R2 =0 .779)。RAI在生理发育时间 (PDT)小于等于 4 0前 ,其增长动态符合LOGISTIC生长规律 (R2 =0 .84 9) ,在PDT大于 4 0后 ,呈线性递减趋势 (R2 =0 .5 70～ 0 .895 ) ,且杂交抗虫棉的RAI在全生育期内均明显高于其它类型品种 ,而早熟类型品种相对略低。RAI空间分布特征表现为 ,开花前在浅根层内 (0～ 30cm)分布最多 ,花铃期以中层根系 (40～ 6 0cm)为主 ,吐絮后主要以深层

By combining root auger and image analysis methods for root sampling and measurement, this study investigated the dynamic characteristics of cotton plant root growth and the spatial distribution of root length, diameter and area. The experiment was conducted during 2001 and 2002 at an experiment station located in Anyang city, Henan Province. A root performance experiment of different genotypes was conducted in 2001 using 4 cotton cultivars: middle season hybrid `CRI29' with Bt, middle season variety `CRI35' without Bt, middle season variety `CRI32' with Bt and early season variety `CRI37' with Bt. Plant density was 60 000 plants per hectare. In 2002, the American middle season variety `33B' with Bt was included and measured in 40 cm×40 cm×100 cm deep soil pits. The soil was loam. Climate data from a nearby weather station were used to calculate the cotton physiological development time (PDT). Computation of PDT also integrated thermal effectiveness, photoperiod effectiveness, genetic effectiveness and its interactions. Root samples were collected at four distances from the cotton row: 0, 15, 25 and 35 cm. Root samples were collected from 40 cm×40 cm×100 cm deep soil pits and sampled every 10 cm from 0 to 100 cm soil depth at each location. The roots were sampled using a root auger that had a volume of 316.73 cm 3. The roots were washed form the soil core with all cotton roots collected in the samples. Cleaned roots were scanned to a black and white image at a resolution of 200 dpi. DT-SCAN software was used to calculate root length, root diameter and root surface area. Compared to the ruler measurement method to estimate root length density (RLD), the image analysis method using DT-SCAN for estimating RLD gave similar results (R 2=0.899, n=1 318). The results indicated that the RLD of cotton averaged 1.21-1.27 mm·cm -3 during flowering and boll stage, 1.04-1.12 mm·cm -3 after boll opening, and 0.76 mm·cm -3 during the harvest period. Root diameter was significantly different among genotypes (p=0.022), with the thickest root diameter of 0.52 mm in an insect resistant hybrid cultivar and the thinnest root diameter of 0.36 mm in the early maturation cultivar. Root diameters were not significantly different between soil layers but were significantly thinner with increasing distance from the cotton row. Because of the significant differences observed in root length and diameter among soil layers, distance from plant and genotypes, we developed a root area index (RAI) that has similar biological meaning as the leaf area index. The RAI and LAI were exponentially related (R 2 = 0.799). The dynamic time course of RAI fit a logistic growth pattern (R 2=0.849) with physiological development time (PDT) when the PDT was smaller than 40, and exhibited a linear decreasing pattern (R 2=0.570-0.895) when PDT was greater than 40. The highest RAI calculated was in the insect-resistant hybrid cultivar and the lowest in early maturation cultivar. The vertical and temporal changes in RAI were as follows: RAI was the greatest in the topsoil layer (0-30 cm) before flowering, in the mid soil layer (40-60 cm) during flowering and boll stage, and in the deep layer (70-100 cm) and at locations away from the cotton row after boll opening.