J Plant Ecol ›› 2020, Vol. 13 ›› Issue (3): 281-287.DOI: 10.1093/jpe/rtaa012

• Research Articles • Previous Articles     Next Articles

Soil nitrogen availability intensifies negative density-dependent effects in a subtropical forest

Fengmin Huang, Minxia Liang, Yi Zheng, Xubing Liu, Yuxin Chen, Wenbin Li, Shan Luo and Shixiao Yu*   

  1. Department of Ecology, School of Life Sciences/State Key Laboratory of Biocontrol, Sun Yat-sen University, Guangzhou, China

    *Corresponding author. E-mail: lssysx@mail.sysu.edu.cn
  • Received:2019-11-12 Revised:2020-02-25 Accepted:2020-03-20 Online:2020-03-21 Published:2020-06-01

Abstract:

Aims

The importance of density-dependent mortality in maintaining tree species diversity is widely accepted. However, density-dependent effects may vary in magnitude and direction with different abiotic conditions in forests. Theoretical predictions surmise that density-dependent effects may vary with soil available nitrogen (AN), but this still needs to be tested.

Methods

We analyzed the density-dependent effects on survival of newly germinated seedlings for 18 common species based on a long-term seedling census across environmental gradients in a subtropical forest. We also conducted a root lesion detection experiment for five species to investigate the potential effects of pathogens on variation in density-dependent disease between rich and poor AN environments.

Important Findings

The seedling dynamics analysis revealed that the strength of density-dependent effects increased with AN, shifting from neutral or positive with low AN to negative with high AN. Three of the five tree species had stronger density-dependent effects on root lesions in rich AN environments than in poor AN environments, which is consistent with the results of a long-term seedling dynamics analysis. We also found higher species diversity in rich AN environments, which may be promoted by the stronger negative density-dependent effects. Both the seedling dynamic analysis and root lesion detection experiment revealed stronger negative density-dependent effects in higher AN environment, resulting from stronger disease pressure by soil pathogens. Our study emphasized the importance of considering context dependence when testing the density dependence hypotheses.

Key words: density dependence, root lesions, soil available nitrogen, soil pathogen, subtropical forest

摘要:

负密度制约在维持森林群落物种多样性方面起重要作用。然而,在不同的非生物条件下密度制约效应的强度和方向有可能发生改变。理论预测密度制约效应随土壤可利用氮浓度上升而增强,但仍有待实验结果的验证。本研究基于黑石顶常绿阔叶林群落长达10年的幼苗动态调查数据,以18个常见树种的新生幼苗为研究对象,分析邻体密度制约作用如何在不同环境梯度下变化。通过收集上述目标种中的5个树种的野外幼苗进行根系损伤观察实验,研究在不同可利用氮环境中,土壤病原菌驱动的负密度制约效应是否存在差异。幼苗动态分析结果表明,负密度制约作用的强度随土壤可利用氮浓度的上升而增强。同种幼苗密度在土壤可利用氮浓度低的生境中表现为中性或正密度依赖效应,在土壤可利用氮浓度高的生境中则表现为负密度制约效应。根系损伤观察实验中,在土壤可利用氮浓度高的情况下,5个目标物种中有3个物种表现出更强的负密度制约作用,与幼苗动态分析的结果一致。此外,物种丰富度在土壤可利用氮浓度高的环境中比在浓度低的环境中更高。上述结果表明,在土壤可利用氮浓度高的环境中,更强的土壤病害加剧了负密度制约作用。我们的研究结果强调了负密度制约研究中考虑背景环境的重要性。

关键词: 密度制约, 根系损伤, 土壤可利用氮, 土壤病原菌, 亚热带森林