An experiment was conducted to study the effects of thinning on fine root diameter, length and specific root length (SRL) of the first to fifth order roots in Chinese fir plantations in Lishui Forest Farm of Nanjing. Results showed that, with ascending root orders, the mean fine root diameter and length increased, while the mean SRL decreased significantly. Among tie five orders of roots, tie first order roots were the thinnest in diameter, the shortest in length, and the highest in SRL, but the fifth order roots were in reverse. Compared with tie control plots, thinning impacted significantly on fine root diameter, length and SRL (p＜0.05). Heavy intensity thinning (HIT) markedly decreased the mean diameter of the first to fifth order roots in subsurface soil, and the mean diameter of the first to third order roots in subsurface soil also decreased significantly under medium intensity thinning (MIT); and the mean length of the fourth order root in surface soil reduced significantly under MIT, while in subsurface soil, it also reduced markedly under MIT and light intensity thinning ( LIT), but elongated markedly under HIT; the mean SRL of the second order root in surface soil decreased significantly under HIT, but increased significantly in subsurface soil under MIT.%以南京溧水林场25年生的杉木人工林为研究对象,探讨了间伐对杉木人工林1～5级细根平均直径、长度和比根长的影响.结果表明:杉木人工林细根平均直径和根长随根序等级的增加而显著增加(p＜0.01或P＜0.05),而平均比根长则显著下降(p＜0.05).在杉木人工林5级根序中,1级细根平均直径最小、根长最短、比根长最高,5级根则相反.与对照相比,间伐对杉木人工林细根的直径、根长和比根长有显著影响(P＜0.05).其中,强度间伐减小了亚表层土壤(10～20 cm)内1～5级细根的平均直径,中度间伐减小了1～3级细根的平均直径(p＜0.05);表层土壤(0～10 cm)内的4级细根平均长度在中度间伐显著缩短,而亚表层土壤内的4级细根平均根长在强度间伐下显著伸长,但在中度和弱度间伐下显著缩短(p＜0.05);表层土壤内的2级细根平均比根长在强度间伐下显著减小,而亚表层土壤内的2级细根平均比根长在中度间伐下却显著增加(p＜0.05).
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