棉花、苜蓿细根生长和死亡的季节变化

摘要

Roots have two functions,“source”and “sink”,which are important for substance and energy ex-change between plants and soil.Understanding these processes requires studies of the dynamics of fine root growth and mortality.This study reports on the growth,death and turnover of fine roots in cotton (Gossypium hirsutum)and alfalfa (Medicago sativa )using minirhizotron techniques over different seasons.The fine root growth rate [G,cm/(cm3 ·d)],death rate [M,cm/(cm3 ·d)]and the ratio of growth to death (R)were de-termined.Results showed that the average standing crop of cotton in the growing season is 8.0 mm/cm3 ,with that of alfalfa being 14.8 mm/cm3 in 2011 and 8.0 in 2012.The average G and M of cotton in the growing sea-son are 0.056 and 0.011 mm/(cm3 · d)respectively,with those of alfalfa being 0.026 and 0.007 mm/(cm3 ·d)in 2011 and 0.041 and 0.028 in 2012.The G of cotton decreased rapidly from the end of May to mid-July,increased from mid-July to early September and then decreased.The G of alfalfa showed a consistent trend in 2011 and 2012,peaking from mid-June to mid-July and from early August to early September.The M of both cotton and alfalfa decreased from mid-June to mid-July and then increased to reach the maximum by the end of the growing season.The R of cotton and alfalfa decreased gradually from May to October,with cotton R>1 and alfalfa R<1.The estimated turnover rate is different according to whether it is calculated in terms of maximum or mean biomass.Mean biomass calculations increased turnover rates by about 22% compared with maximum biomass.During the growing season,the standing crop and G of cotton and alfalfa showed unimodal and bimodal peaks respectively,but the M of both rose continuously.At same time,cotton had a higher turn-over rate to meet water and nutrient requirements.%以棉花和紫花苜蓿为研究对象，以现存量、生长速率（G，cm／cm3·d）、死亡速率（M，cm／cm3·d）和生死之比（R）为基本参数，采用微根管技术对棉花和苜蓿细根的生长、死亡以及周转进行动态研究。结果表明，在生长季内，棉花平均细根现存生物量为8．025 mm／cm3，2011年苜蓿为14．830 mm／cm3，高于2012年苜蓿（8．026 mm／cm3），棉花细根 G 和 M 分别为0．056和0．011 mm／（cm3·d），2011年苜蓿分别为0．026和0．007 mm／（cm3·d），2012年分别为0．041和0．028 mm／（cm3·d）。棉花 G 变化趋势为5月底－7月中旬迅速下降，7月中旬到9月初上升，此后下降，2011和2012年苜蓿 G 变化趋势一致，分别在6月中旬－7月中旬和8月初－9月初形成峰值。棉花和苜蓿 M 相似，均是在6月中旬到7月中旬降低，此后开始增加，在生长季末达到最大。R 在生长季呈逐渐减少的趋势，但棉花在生长季末 R＞1，苜蓿则是 R＜1。用最大细根现存量和平均细根现存量估算得到细根周转率不同，以平均细根现存量得到细根周转率比以最大细根现存量增加了22％。通过对棉花和苜蓿细根比较研究，棉花和苜蓿在不同季节细根现存生物量和生长动态不同，棉花呈单峰曲线，苜蓿呈双峰曲线，而棉花和苜蓿死亡动态则是随着季节变化持续升高，同时棉花以较高的周转速率满足了植物对水分和养分的需求。