[Effects of combined nitrogen and phosphorus addition on fine root traits of young Machilus pauhoi forest].

Both nitrogen (N) and phosphorus (P) are the main limiting elements for plant growth in terrestrial ecosystems. Fine roots play a critical role in plant growth. To reveal the effects of combined N and P addition on fine root traits of Machilus pauhoi, we performed a field N and P addition experiment in the midmonth from April to September in 2016 and 2017 in a 3-year M. pauhoi forest (N and P supply ratios were 8:1, 10:1, 12:1, 15:1). Both fine root morphological traits (specific root length, specific root area, average diameter, root tissue density) and stoichiometric traits (total carbon content, total nitogen content and carbon-nitrogen ratio) were analyzed. The results showed that the effects of combined application of N and P on fine root raits varied with seasons. In June, fertilization significantly increased specific root area, total nitrogen content and specific root length of 0-1 mm fine root, but decreased root tissuse density, carbon-nitrogen ratio and average diameter of 0-1 mm root. The most obvious change of fine root traits in June was found under the treatment with a N and P supply ratio of 12:1. In December, combined N and P addition significantly increased root tissue density, total nitrogen content, carbon-nitrogen ratio as well as fine root biomass with the diameter of 0-1 mm. The results of principal component analysis showed that different N and P supply ratios exerted different effects on the relationships among fine root traits. Fine root traits were distributed at both ends of Axis 1 when treated with 12:1 N:P, while distributed at Axis 1 and Axis 2 under other treaments. There was a significant negative correlation between fine root average diameter variation and the relative plant growh rate. The relationship among fine root traits, and between fine root traits and the relative growth rate of plant biomass were optimally coordinated at the treament with a N:P ratio of 12:1.氮磷是陆地生态系统植物生长的主要限制性元素,细根对植物生长具有重要影响。为了解氮磷配施对刨花楠人工幼林细根性状的影响,以3年生刨花楠人工幼林为对象,于2016年和2017年每年4—9月的每月中旬进行氮磷配施(添加比例分别为8∶1、10∶1、12∶1、15∶1),测定比根长、比表面积、平均直径、根组织密度、总碳、总氮含量及碳氮比等细根表型和养分性状指标,分析氮磷配施对细根性状的影响。结果表明: 氮磷配施对细根性状的影响在不同季节表现不同。6月,氮磷配施显著提高细根比表面积、总氮含量及0～1 mm的细根比根长,降低细根组织密度、碳氮比及0～1 mm细根直径,以氮磷比为12∶1处理最为明显,但在12月,氮磷配施则会显著提高细根组织密度、总氮含量、碳氮比及0～1 mm细根生物量。主成分分析发现,不同氮磷比添加对细根性状间关系影响不同,其中氮磷比为12∶1处理的细根性状分布在第1轴的两端,其他处理后的细根性状分布在第1轴和第2轴2个轴。细根平均直径变化量与全株生物量相对生长速率呈显著负相关,以氮磷比为12∶1的配施处理最有利于协调细根性状间关系,以及细根性状与全株生物量相对生长速率间的关系。.