Allsopp N, Stock W D
Department of Botany, University of Cape Town, Private Bag, 7700, Rondebosch, South Africa.
Oecologia. 1992 Aug;91(2):281-287. doi: 10.1007/BF00317797.
The interaction of density and mycorrhizal effects on the growth, mineral nutrition and size distribution of seedlings of two perennial members of the Fabaceae was investigated in pot culture. Seedlings of Otholobium hirtum and Aspalathus linearis were grown at densities of 1, 4, 8 and 16 plants per 13-cm pot with or without vesicular-arbuscular (VA) mycorrhizal inoculum for 120 days. Plant mass, relative growth rates, height and leaf number all decreased with increasing plant density. This was ascribed to the decreasing availability of phosphorus per plant as density increased. O. hirtum was highly dependent on mycorrhizas for P uptake but both mycorrhizal and non-mycorrhizal A. linearis seedlings were able to extract soil P with equal ease. Plant size distribution as measured by the coefficient of variation (CV) of shoot mass was greater at higher densities. CVs of mycorrhizal O. hirtum plants were higher than those of non-mycorrhizal plants. CVs of the facultatively mycorrhizal A. linearis were similar for both mycorrhizal and non-mycorrhizal plants. Higher CVs are attributed to resource preemption by larger individuals. Individuals in populations with high CVs will probably survive stress which would result in the extinction of populations with low CVs. Mass of mycorrhizal plants of both species decreased more rapidly with increasing density than did non-mycorrhizal plant mass. It is concluded that the cost of being mycorrhizal increases as plant density increases, while the benefit decreases. The results suggest that mycorrhizas will influence density-dependent population processes of faculative and obligate mycorrhizal species.
在盆栽试验中，研究了密度与菌根效应相互作用对豆科两种多年生植物幼苗生长、矿质营养及大小分布的影响。将硬毛奥氏豆（Otholobium hirtum）和线叶阿斯巴豆（Aspalathus linearis）的幼苗，按照每13厘米花盆1株、4株、8株和16株的密度种植，分别接种或不接种泡囊-丛枝（VA）菌根菌剂，培养120天。植株质量、相对生长速率、株高和叶片数均随种植密度增加而降低。这归因于随着密度增加，单株植物可利用的磷减少。硬毛奥氏豆对菌根吸收磷高度依赖，但菌根和非菌根的线叶阿斯巴豆幼苗从土壤中吸收磷同样容易。用地上部质量变异系数（CV）衡量的植株大小分布在较高密度时更大。菌根化的硬毛奥氏豆植株的CV高于非菌根植株。对于兼性菌根的线叶阿斯巴豆，菌根和非菌根植株的CV相似。较高的CV归因于较大个体对资源的抢占。CV高的种群中的个体可能在胁迫中存活，而CV低的种群可能灭绝。两种菌根化植物的质量随密度增加的下降速度比非菌根化植物质量更快。研究得出结论，随着植物密度增加，菌根化的成本增加，而益处减少。结果表明，菌根将影响兼性和专性菌根物种的密度依赖性种群过程。
