Mason Norman W H, Orwin Kate, Lambie Suzanne, Woodward Sharon L, McCready Tiffany, Mudge Paul
Landcare Research Private Bag 3127 Hamilton 3240 New Zealand.
Landcare Research PO Box 40 Lincoln 7640 New Zealand; Present address: 27 Delaware Cres Christchurch New Zealand.
Ecol Evol. 2016 Apr 2;6(10):3079-91. doi: 10.1002/ece3.1964. eCollection 2016 May.
Plant functional traits are thought to drive variation in primary productivity. However, there is a lack of work examining how dominant species identity affects trait-productivity relationships. The productivity of 12 pasture mixtures was determined in a 3-year field experiment. The mixtures were based on either the winter-active ryegrass (Lolium perenne) or winter-dormant tall fescue (Festuca arundinacea). Different mixtures were obtained by adding forb, legume, and grass species that differ in key leaf economics spectrum (LES) traits to the basic two-species dominant grass-white clover (Trifolium repens) mixtures. We tested for correlations between community-weighted mean (CWM) trait values, functional diversity, and productivity across all plots and within those based on either ryegrass or tall fescue. The winter-dormant forb species (chicory and plantain) had leaf traits consistent with high relative growth rates both per unit leaf area (high leaf thickness) and per unit leaf dry weight (low leaf dry matter content). Together, the two forb species achieved reasonable abundance when grown with either base grass (means of 36% and 53% of total biomass, respectively, with ryegrass tall fescue), but they competed much more strongly with tall fescue than with ryegrass. Consequently, they had a net negative impact on productivity when grown with tall fescue, and a net positive effect when grown with ryegrass. Strongly significant relationships between productivity and CWM values for LES traits were observed across ryegrass-based mixtures, but not across tall fescue-based mixtures. Functional diversity did not have a significant positive effect on productivity for any of the traits. The results show dominant species identity can strongly modify trait-productivity relationships in intensively grazed pastures. This was due to differences in the intensity of competition between dominant species and additional species, suggesting that resource-use complementarity is a necessary prerequisite for trait-productivity relationships.
植物功能性状被认为是驱动初级生产力变化的因素。然而，缺乏研究探讨优势物种身份如何影响性状与生产力关系的工作。在一项为期3年的田间试验中测定了12种牧草混合物的生产力。这些混合物以冬季活跃的黑麦草（多年生黑麦草）或冬季休眠的高羊茅为基础。通过向基本的两种优势草种——白三叶混合物中添加在关键叶经济谱（LES）性状上存在差异的杂草、豆科植物和禾本科植物，获得了不同的混合物。我们测试了所有样地以及基于黑麦草或高羊茅的样地中群落加权平均（CWM）性状值、功能多样性和生产力之间的相关性。冬季休眠的杂草物种（菊苣和车前草）的叶片性状与单位叶面积（高叶片厚度）和单位叶干重（低叶干物质含量）的高相对生长率一致。这两种杂草物种与任何一种基础草种一起生长时都达到了合理的丰度（分别与黑麦草、高羊茅一起生长时，占总生物量的平均值分别为36%和53%），但它们与高羊茅的竞争比与黑麦草的竞争激烈得多。因此，它们与高羊茅一起生长时对生产力有净负面影响，而与黑麦草一起生长时则有净正面影响。在基于黑麦草的混合物中观察到生产力与LES性状的CWM值之间存在极显著关系，但在基于高羊茅的混合物中未观察到。功能多样性对任何性状的生产力都没有显著的正向影响。结果表明，优势物种身份可强烈改变集约放牧牧场中的性状与生产力关系。这是由于优势物种与其他物种之间竞争强度的差异，表明资源利用互补性是性状与生产力关系的必要前提。
