Drought-induced Changes in Shoot and Root Growth of Young Cotton Plants
Drought-induced Changes in Shoot and Root Growth of Young Cotton Plants
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1999
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通讯作者：
H. Cralle;S. El-Halawany;J. T. Cothren;S. Senseman
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作者：
H. Cralle;S. El-Halawany;J. T. Cothren;S. Senseman
了解植物对水分缺乏的反应对于模拟棉花生长、估计灌溉需求和培育抗旱品种具有重要意义。本研究考察了一个长季和一个短季棉花品种在短暂干旱和随后的恢复期后的茎和根生长情况。27℃左右，在日光灯照射下，在生长室内将种子种在填满粘土的罐中，播种后36 d分为干旱处理组和水分对照组。干旱13 d后取样，恢复期10 d后再次取样。没有基因型治疗的相互作用。干旱和恢复结束时，高度，叶片P.F. Pace, DEKALB Genetics Corporation, 3100 Sycamore Road， DEKALB, IL 60115；Sherif H. M. El-Halawany（已故），埃及吉萨农业部农业研究中心棉花研究所；J. Tom cothers，土壤与作物科学系，德州AM Scott A. Senseman，土壤与作物科学系，德州AM Masle and Passioura， 1987)。多项研究表明，干旱对棉花冠层发育有抑制作用。Krieg和Sung（1986）确定干旱会减少棉花的合聚枝上的叶子数量。当土壤有效水分比例低于51±15%时，温室棉花的叶面积也受到抑制（Rosenthal et al., 1987）。Cutler和Rains（1977）得出结论，黎明前叶片水势低于0.5 MPa时，叶片伸长率下降。55 d龄棉花植株在断水2 d后叶片扩张速度减慢，说明叶片生长比根系伸长对干旱更为敏感（Ball et al., 1994）。同样，McMichael和Quisenberry（1991）发现终末干旱降低了茎根比。干旱也减少了棉花根的生长、发育和分布（Malik et al., 1979; Taylor, 1983）。55 d龄棉花在截水6 d后根系生长减少（Ball et al., 1994）。干旱期间，伸长的根数量减少了35%。种植早熟品种可以减少棉花的耗水量，未来棉花品种的其他性状可能会进一步减少耗水量。Quisenberry等人（1981）发现，在旱地条件下，外来棉花品系在耐热性、根系生长、干物质积累和水分利用效率方面存在相当大的差异。Gerik和他的合著者（1996）比较了两种短季棉花品种，发现无论水分胁迫程度如何，其中一种Tamcot HQ95的产量都高于另一种GP74。他们得出结论，Tamcot HQ95的光合能力可能大于GP74。干旱时根系伸长可以帮助植物获得更深的水分，从而避免土壤表面附近的水分不足。当降水允许干旱后的恢复时，伸长也可以减少排水损失的水分（Ludlow和Muchow， 1990）。然而，如果土壤剖面中较深层的水分不可用，较长的根系可能会降低茎的干重和收获指数，因为它允许以牺牲芽为代价将光合作用优先分配给根系。本研究考察了一个长季和一个短季棉花品种在有限时间的干旱和随后的恢复期后的茎和根生长的各种措施。材料和方法将一株长季棉花“Stoneville 506”和一株短季棉花“Tamcot HQ95”种植在填充了粘土的花盆中（9升容积，20厘米深）（Absorb-N-Dry, Balcones Co., Flatonia， TX）。罐子底部的滤纸保留了粘土，同时允许排水。每盆播种两株植物，每隔一天用蒸馏水浇灌10 d。然后用0.90 g L 2020-20氮磷钾肥料（Peters Professional All Purpose Plant Food, Spectrum Group, Division of United Industries Corp., St. Louis, MO .）的营养液浇灌花盆，直到种植后36 d。之所以选择这种肥料，是因为土壤试验表明，熔融粘土的氮、磷和钾含量非常低，而且养分会很快从这种排水良好的土壤中滤出。试验185 JOURNAL of COTTON SCIENCE， vol . 3, Issue 4, 1999 .在荧光灯下的生长室内进行，光合光子通量密度为700 mol m s，持续16 h d。种植后36 d，将植株随机分为干旱处理组和水分对照组。干旱处理植株13 d不浇水。在干旱处理结束时（种植后49 d），对对照植株和干旱处理植株进行取样，测量其株高、节数、叶面积和主根长度。新鲜根的次生根长度由Comair根长度扫描仪（Commonwealth Aircraft Corp. Ltd, Melbourne, Australia）测量。在测定干重之前，将叶、茎、丝状根和次生根在90℃下干燥48小时。根据干重计算茎根重比。在播种后49 d，在10 d的恢复期对剩余的干旱处理植株进行浇水。在种植后59 d，两种处理均按上述方法取样。实验采用随机完全区组设计，分为两个区组。每个街区各有四盆。每个花盆里有两株植物。实验重复了两次。治疗和实验运行之间没有相互作用，因此将两个运行的数据合并进行统计分析。品种主效应不显著，因此也进行了跨品种汇总。本分析使用SAS系统（SAS Institute, Cary， NC）。结果与讨论干旱处理结束时，与对照相比，干旱处理植株的株高、叶面积、节数和茎叶干重均显著降低（P < 0.05）（表1）。此外，在播种后49天的采样中，干旱处理植株的茎根比低于对照（表2）。在干旱期结束时，两种处理的次生根长度、次生根和主根的干重均无差异（表3）。但此时（种植后49 d），干旱处理植株的主根长度显著（P < 0.01）高于对照。干旱处理植株的主根干重与对照相同，因此与干旱相关的伸长是以主根增粗为代价的。干旱处理的植株主根每长干重仅为0.011 g cm，而水分充足对照的相应测量结果如表1所示。干旱结束后49 d， Stoneville 506和Tamcot HQ95干旱处理和对照植株茎高、干重、叶面积、干重和节数的变化。†平均值后面是括号中平均值的标准误差。
An understanding of the response of plants to water deficits is important in efforts to model cotton (Gossypium hirsutum L.) growth, estimate irrigation needs, and breed drought-resistant cultivars. This study examined shoot and root growth of a longand a short-season cotton cultivar after a brief drought and subsequent recovery period. Seeds were planted in fritted clay-filled pots in a growth room under fluorescent lights at about 27 (C. Plants were divided at 36 d after planting into drought-treatment and watered-control groups. Plants were sampled after a 13-d drought and again after a 10-d recovery period. There were no treatment-by-genotype interactions. At the end of the drought and recovery, height, leaf P.F. Pace, DEKALB Genetics Corporation, 3100 Sycamore Road, DeKalb, IL 60115; Harry T. Cralle, Department of Soil and Crop Sciences, Texas AM Sherif H. M. El-Halawany (deceased), Cotton Research Institute, Agricultural Research Center, Ministry of Agriculture, Giza, Egypt; J. Tom Cothren , Department of Soil and Crop Sciences, Texas AM Scott A. Senseman, Department of Soil and Crop Sciences, Texas AM Masle and Passioura, 1987). Several studies have shown that drought inhibits cotton canopy development. Krieg and Sung (1986) determined that drought decreases the number of leaves on sympodial branches of cotton. Leaf area of glasshouse-grown cotton also was inhibited when the percentage of soil-available water was less than 51 ± 15% (Rosenthal et al., 1987). Cutler and Rains (1977) concluded that predawn leaf water potentials below $0.5 MPa were accompanied by decreased leaf elongation rate. Leaf expansion of 55-d-old cotton plants slowed after 2 d of withholding water, which meant that leaf growth was more sensitive than root elongation to drought (Ball et al., 1994). Similarly, McMichael and Quisenberry (1991) found that terminal drought decreased the shoot:root ratio. Drought also reduced the growth, development, and distribution of cotton roots (Malik et al., 1979; Taylor, 1983). Root growth of 55-d-old cotton was reduced after 6 d of withholding water (Ball et al., 1994). The number of roots elongating decreased by 35% during the drought. Planting early-maturing cultivars can decrease the amount of water used by cotton, and other traits in future cotton cultivars may further decrease the amount of water used. Quisenberry et al. (1981) found considerable variability for heat tolerance, root growth, dry matter accumulation, and water use efficiency among exotic cotton strains under dryland conditions. Gerik and co-authors (1996) compared two short-season cotton cultivars and found that one, Tamcot HQ95, yielded more than other, GP74, regardless of the level of water stress. They concluded that the photosynthetic capacity of Tamcot HQ95 might be greater than that of GP74. Root elongation during drought may help plants get deeper water, thus avoiding water deficits near the soil surface. Elongation also could reduce the water lost by drainage when precipitation allows recovery after the drought (Ludlow and Muchow, 1990). If, however, water is unavailable deeper in the soil profile, longer roots may reduce shoot dry weight and harvest index by allowing the preferential partitioning of photosynthate to roots at the expense of shoots. This study examined various measures of shoot and root growth of one longand one short-season cotton cultivar after a drought of limited duration and a subsequent recovery period. MATERIALS AND METHODS A long-season cotton, ‘Stoneville 506,’, and a short-season cotton, ‘Tamcot HQ95,’ were planted in pots (9-L volume, 20 cm deep) filled with fritted clay (Absorb-N-Dry, Balcones Co., Flatonia, TX). Filter paper at the bottom of the pots retained the fritted clay while allowing for drainage. Two plants were seeded per pot and were supplied with distilled water every other day for 10 d. The pots were then watered with a nutrient solution of 0.90 g L of 2020-20 NPK fertilizer (Peters Professional All Purpose Plant Food, Spectrum Group, Division of United Industries Corp., St. Louis, MO) until 36 d after planting. This fertilizer was selected because soil tests showed that the fritted clay had very low levels of N, P, and K and that nutrients would be quickly leached from this well-drained soil. Water or nutrient solution, when applied, was added until an excess drained from the bottom of the pot. The experiment 185 JOURNAL OF COTTON SCIENCE, Volume 3, Issue 4, 1999 was conducted in a growth room under fluorescent lights providing a photosynthetic photon flux density of 700 )mol m s for 16 h d. Temperature was maintained at 127 (C. At 36 d after planting, plants were randomly divided into drought-treatment and watered-control groups. The drought-treated plants were not watered for 13 d. At the end of this drought treatment (49 d after planting), control and drought-treated plants were sampled and height, number of nodes, leaf area, and taproot length were measured. Secondary root length of fresh roots was measured by a Comair Root Length Scanner (Commonwealth Aircraft Corp. Ltd, Melbourne, Australia). Leaves, stems, and tap and secondary roots were dried for 48 h at 90 (C before dry weights were determined. The shoot:root weight ratio was calculated from the dry weights. At 49 d after planting, the remaining droughttreated plants were watered during a 10-d recovery period. At 59 d after planting, both treatments were sampled as described above. The experiment was a randomized complete block design with two blocks. Each block had four pots of each cultivar. Each pot had two plants. The experiment was repeated twice. There was no interaction between treatment and experimental run, so data from the two runs were pooled for statistical analysis. The cultivar primary effect was insignificant, so data also were pooled across cultivar. This analysis used the SAS System (SAS Institute, Cary, NC). RESULTS AND DISCUSSION At the end of the drought treatment, droughttreated plants had significantly (P < 0.05) lower height, less leaf area, fewer nodes, and lower dry weights of stems and leaves than did the controls (Table 1). Additionally, the drought-treated plants had a lower shoot:root ratio (Table 2) than did the controls at this sampling, 49 d after planting. There were no differences between the two treatments in the lengths of the secondary roots or in the dry weight of the secondary or taproots at the end of the drought period (Table 3). However, the droughttreated plants had a significantly (P < 0.01) greater tap root length than did the controls at this time (49 d after planting). The taproot dry weight in the drought-treated plants was identical to that of controls, so the drought-related elongation occurred at the expense of taproot thickening. While the drought-treated plants had a taproot dry weight per length of only 0.011 g cm, the corresponding measurement for the well-watered controls were Table 1. Heights and dry weights of stem, leaf area and dry weight, and node number in drought-treated and control plants of Stoneville 506 and Tamcot HQ95 at the end of the drought, 49 d after planting.† Means are followed by standard errors of the mean in parentheses.