Contrasting grass nitrogen strategies reflect interspecific trade-offs between nitrogen acquisition and use in a semi-arid temperate grassland

Aims

The uptake and tolerance of antimonite [Sb(III)] and antimonate [Sb(V)] were investigated in two populations of Achillea wilhelmsii, one from strongly Sb-enriched mine soil, the other from uncontaminated soil, in comparison with non-metallicolous Silene vulgaris and Thlaspi arvense.

Methods

Tolerance was assessed from root elongation and biomass accumulation after exposure to a series of concentrations of Sb(III) or Sb(V) in hydroponics.

Results

For all the species Sb(III) was more toxic than Sb(V). S. vulgaris was the most Sb(III)-tolerant species, and A. wilhelmsii the most Sb(V)-tolerant one. There were no considerable interspecific differences regarding the root and shoot Sb concentrations. Sb(III) and Sb(V) tolerance and accumulation were not different between the metallicolous and the non-metallicolous A. wilhelmsii populations. Sb(III) uptake was partly inhibited by silicon. Sb(V) uptake was strongly inhibited by chloride.

Conclusions

There is uncorrelated variation among species in Sb(V) and Sb(III) tolerance, showing that plants sequester Sb(V) and Sb(III) in different ways. Sb(V) seems to be taken up via monovalent anion channels, and Sb(III) via silicon transporters, at least in part. The relatively high Sb(V) tolerance in A. wilhelmsii seems to be a species-wide property, rather than a product of local adaptation to Sb-enriched soil.

     

Species abundance is jointly determined by functional traits and negative density dependence in a subtropical forest in southern China

植物物种多度受功能性状和负密度依赖共同影响——以中国南亚热带黑石顶森林样地为例 影响植物群落中植物物种多度的因素较多,确定关键影响因素及阐明其具体机制一直是群落生态学的研究重点之一。目前确定性的影响因素主要有两大类：植物功能性状和负密度依赖。功能性状通过影响植物的竞争能力、资源的获取效率、对环境的适应能力等方面进而影响植物的多度;负密度依赖表现在同种或异种植物个体在空间上聚集,特异性的寄主(病原菌、昆虫等)传播容易导致植物个体(主要为幼苗和小树)死亡,种群发生自疏,进而影响植物的多度。到目前为止,单一探究植物功能性状或负密度依赖对植物多度影响机制的研究已有大量报道,而将两者结合来探讨对植物多度的影响的工作相对较少。为了更深入地探索影响植物多度的机制,本研究中我们综合分析了功能性状与负密度依赖对植物多度的影响。研究地点为广东省黑石顶亚热带森林50 ha大样地;功能性状方面选取了叶面积(LA)、比叶面 积(SLA)、叶片干物质含量(LDMC)、叶片氮含量(LNC)和最大电子传输速率(ETR_max);植物物种所受负密度依赖强度通过构建小树在样地两次普查期间的存活状况受邻体密度影响的层次贝叶斯模型计算;通过结构方程模型构建功能性状-负密度依赖-物种多度的内在联系框架。结构方程模型结果显示,物种多度受功能性状和负密度依赖共同作用,其中功能性状对物种多度的影响包括直接作用和通过负密度依赖的间接作用。具体来说,SLA对多度的影响包括直接和间接两种;LDMC和LNC仅间接影响物种多度;LA和ETR_max对多度只有直接影响;负密度依赖与物种多度之间存在直接的负相关关系,说明多度较高的物种受到的负密度依赖效应更强。结构方程模型对物种多度差异的解释度达到20%。以上结果表明,黑石顶植物多度分布是功能性状与负密度依赖共同作用的结果;比叶面积在所研究的因素中贡献最大。该项工作有助于提高我们对亚热带森林植物常见种和稀有种分布格局的理解。