Fridley Jason D
CB 3280, Coker Hall, University of North Carolina, Chapel Hill, NC, 27599-3280, USA.
Oecologia. 2002 Jul;132(2):271-277. doi: 10.1007/s00442-002-0965-x. Epub 2002 Jul 1.
Experimental evidence that plant species diversity has positive effects on biomass production appears to conflict with correlations of species diversity and standing biomass in natural communities. This may be due to the confounding effects of a third variable, resource availability, which has strong control over both diversity and productivity in natural systems and may conceal any positive effects of diversity on productivity. To test this hypothesis, I independently manipulated resource availability (soil fertility) and sown species diversity in a field experiment and measured their individual and interactive effects on productivity. Although fertility was a far stronger predictor of productivity than diversity, the effect of diversity on productivity significantly increased with fertility. Relative yield analyses indicated that plant mixtures of high fertility treatments significantly "overyielded," or were more productive than expected based on monoculture yields of component species. In contrast, plant mixtures of low fertility treatments had significantly lower-than-expected yields. The effect of diversity on productivity was also driven by sampling effects, where more species-rich mixtures were more likely to include particularly productive species. Unexpectedly, the strength of sampling effects was largely insensitive to fertility, although the particular species most responsible for sampling effects did change with fertility. These results suggest that positive effects of species diversity on ecosystem productivity in natural systems are likely to be masked by variation in environmental factors among habitats.
植物物种多样性对生物量生产具有积极影响，这一实验证据似乎与自然群落中物种多样性和现存生物量的相关性相冲突。这可能是由于第三个变量——资源可用性的混杂效应，它对自然系统中的多样性和生产力都有很强的控制作用，可能会掩盖多样性对生产力的任何积极影响。为了验证这一假设，我在田间实验中独立操纵了资源可用性（土壤肥力）和播种的物种多样性，并测量了它们对生产力的单独和交互影响。尽管肥力比多样性更能预测生产力，但多样性对生产力的影响随着肥力的增加而显著增强。相对产量分析表明，高肥力处理的植物混合物显著“超产”，即比基于组成物种单作产量预期的产量更高。相比之下，低肥力处理的植物混合物产量显著低于预期。多样性对生产力的影响也受到抽样效应的驱动，物种丰富度更高的混合物更有可能包含特别高产的物种。出乎意料的是，抽样效应的强度在很大程度上对肥力不敏感，尽管对抽样效应最有影响的特定物种确实会随肥力而变化。这些结果表明，自然系统中物种多样性对生态系统生产力的积极影响可能会被不同栖息地环境因素的变化所掩盖。
