Potassium uptake of rye-grass (Lolium perenne) and red clover (Trifolium pratense) as related to root parameters

Summary Rye-grass (Lolium perenne) is known to be a strong competitor to red clover (Trifolium pratense) for soil K⁺ under conditions of low K availability in the soil. The objective of this study was to clarify whether this competitive behaviour of the two species can be explained by root morphology. Total K⁺ uptake ofL. perenne andT. pratense was studied under field conditions in relation to root fresh weight, root density, root cation exchange capacity, root surface and root length. The soil was an Alfisol, Udalf. All root parameters, when calculated per unit soil surface (M²), were higher inL. perenne than inT. pratense. In addition,L. perenne had longer root hairs and a denser root hair system thanT. pratense. The greatest difference in root morphology between species was root length, withL. perenne roots averaging 4–6 times longer than those ofT. pratense.Significant correlations were found between the total K⁺ uptake and all root parameters examined, with highest correlationsforroot fresh weight (r,0.92***T. pratense; 0.94***L. perenne) and root length (r, 0.91***T. pratense;r, 0.93***L. perenne). Potassium uptake per unit root fresh weight, root surface and root length were all significantly higher forT. pratense than for L. perenne. Differences in the rate of K⁺ uptake between species were particularly high when expressed per unit root length. Because of its greater root length and surface area,L. perenne can take up more soil K⁺ thanT. pratense, particularly where there is a low K^– supply in the soil. Under such conditionsL. perenne will be a particularly strong competitor toT. pratense.     

干热河谷土壤酶活性和车轴草生长对氮磷添加的响应

为了探讨干热河谷地区不同土地利用类型下土壤酶活性和植物生长对氮磷添加的响应以及二者之间的联系,采集了元谋干热河谷6种不同土地利用类型土壤,包括灌丛、草地、森林、新开垦农田(新农)、常年耕作农田(常农)、侵蚀裸地(裸地),并利用盆栽探索了土壤酶活性和车轴草(Trifolium repens L.)生长对氮(N)、磷(P)、氮磷(N+P)处理的响应特征。结果表明:(1)植物生物量受土地利用类型和处理双重因素影响,两者的交互作用对植物生物量具有显著作用。(2)除农田土壤(新农和常农)外,其他土地利用类型的土壤上植物生长受到养分添加的显著影响,其中添加P处理的生物量显著高于对照; 而N+P处理又显著高于单一的P添加; 而新农和常农不同养分处理间植物生物量差异不显著。(3)土壤酶活性受土地利用类型显著影响,但是不同养分添加处理之间土壤酶活性差异不显著; 土壤酶活性与植物生物量无显著相关性。综上,干热河谷土壤中植物生长的限制养分主要为磷,然而土壤酶活性则不受氮磷养分的限制,其活性主要与土地利用类型有关。