【摘要】 用根钻法和细根分级的方法研究了毛乌素沙地臭柏群落、臭柏灌丛、油蒿群落的细根(D≤2 mm,D为根直径)垂直分布,并用渐近线方程Y=1-βd[Y为从地表到一定深度的根量百分比累积值(0~1),d表示土层深度(cm),β为根系削弱系数]描述根系分布与土壤深度的关系。对不同径级臭柏、油蒿细根的β值、根长密度及根面积指数进行计算,结果表明:以15 cm为取样深度级,臭柏和油蒿群落活细根(D≤2 mm)的各月生物量平均值,在0~15 cm范围内最大,并且随土壤深度增加而减少。臭柏群落、臭柏灌丛、油蒿群落细根生物量垂直分布的β值差异不显著(P>0.5),但相应层次上的月平均细根生物量,臭柏群落是油蒿群落的6.7~14.6倍(P<0.05),臭柏灌丛是油蒿群落的14.0~19.2倍(P<0.05)。D≤1 mm与1 mm<D≤2 mm的细根重量百分比与土壤深度都呈对数关系,但D≤1 mm的细根与土壤深度的相关程度更高。根长密度与根面积指数在各土层的分布有极大的相似性。在臭柏群落、臭柏灌丛、油蒿群落中,D≤2 mm的细根根长密度和根面积指数随土壤深度的增加而减小。月平均值中,D≤2 mm、D≤1 mm、1 mm<D≤2 mm的细根在0~90 cm的根面积指数总和的大小都是:臭柏灌丛>臭柏群落>油蒿群落。更多还原

【Abstract】 Soil coring was used to obtain live fine roots(D≤2 mm,D is root diameter) sampled from each site taken randomly in the northern part of the Development and Management Research Center in the Mu Us Sandland.Root samples were collected five times from April to October of 2005 using 8cm diameter cores.Roots were separated into D≤1 mm and 1 mm<D≤2 mm diameter classes and dry weights were determined.A well-established asymptotic equation Y=1-βd [β= root persistence coefficient,d = soil depth(cm),and Y = percentage of total root weight from soil surface to depth d] was used to describe the relationship between the fine root vertical distribution and soil depth for the Sabina vulgaris community,the Sabina vulgaris cluster and the Artemisia ordosica community.The average root diameter was defined as the median of the root diameter distribution,and the root length density(RLD) and root area index(RAI) were calculated according to the regression equations obtained by a pilot experiment.The results are the following:(1) The means of biomass by month for live fine roots(D≤2 mm) reached a maximum at the 015 cm depth interval,but decreased with the increase in soil depth.About 50% of the fine roots occurred in the 020 cm depth and 90% occurred in the 059.7(or-73.7) cm depth.The fine root distribution pattern was similar in the S.vulgaris community,the S. vulgaris cluster and the A.ordosica community.However,differences were found in the average biomass for the same depth,in which the value for the S.vulgaris community was 6.714.6 times that of the A.ordosica community(P<0.05),and the value for the S.vulgaris cluster was 14.019.2 times that of the A.ordosica community(P<0.05).(2) In both S.vulgaris(community or cluster) and A.ordosica communities,the dry mass percentages of the roots of diameter classes of both D≤1 mm and 1 mm<D≤2 mm had a logarithmic relationship with soil depth,though the correlation was stronger for the former class(with a correlation coefficient of R2>0.97 and 0.81<R2<0.94,respectively).In the S.vulgaris community,the weight percentage for the fine root diameter class of 1 mm<D≤2 mm reached a maximum in the 1530 cm depth range and then decreased with increasing soil depth,however,for both the S.vulgaris cluster and the A.ordosica community,the maximum occurred in the 015 cm depth range.(3) The monthly average of RLD for the D≤1mm diameter class decreased with the soil depth.In April,the A.ordosica community had the maximum RLD and RAI in the 1530 cm depth,however,the maximum for S.vulgaris cluster(also in the 1530 cm depth) occurred in October.The remaining maxima lie in the 015cm depth range for the D≤1 diameter class of fine roots.In terms of the monthly average of RLD,the value for the S.vulgaris community was 11.2 times(P<0.05) and for the S.vulgaris cluster,14.5 times(P<0.05) that of A.ordosica community.The distributions of RAI across soil layers were similar for all three community types.The monthly means of the sums of the RAI within the 090 cm depth for the diameter classes of D≤2mm,D≤1mm and 1mm<D≤2mm decreased in this order: S.vulgaris cluster>S.vulgaris community>A.ordosica community.更多还原