沙蒿群落对氮水交互驱动作用的响应

Nitrogen deposition is one of the key driving factors leading to global changes, and the global ecosystems have been detrimentally impacted by increasing nitrogen deposition. To understand how the components, structures and functions of vegetation ecosystems in drylands, are affected by global changes including nitrogen deposition, has been ranked as the top priority subject in scientific community. However, the responses of desert ecosystems to nitrogen deposition are paid fewer attentions for long time, and there are few researches focusing on typical sand- fixed shrub communities. This program selects Artimisia ordosica which is a typical and representative sand-fixed community in semi-arid deserts as the object of study, to investigate the responses of its vegetation and soil environment to interactive effects of nitrogen and water, under the control experiment treatments of three precipitation scenarios and six gradients of nitrogen addition. Three components are highlighted in the program, which are shrub and herbaceous plants, biological crusts and soil. The aims of the research are to unveil the succession process of A. ordosica community and the changes of soil environment driven by the interactive effects of nitrogen and water, and try to figure out the N load threshold (critical load) resulting in the changes of the community. The projected results can be used as guide to manage the shrublands for desertification control, and also is an important supplement for the scope of the responses of terrestrial ecosystems to nitrogen input.

氮沉降是全球环境变化的关键驱动因子之一，日益增加的氮沉降严重影响着全球各类生态系统。了解包括氮沉降在内的全球变化，如何影响干旱地区植被生态系统的组成、结构、功能，已被列为科学的顶级优先主题，然而，氮沉降对荒漠生态系统的影响长期受到忽视，典型固沙灌木群落对氮素输入的响应研究非常匮乏。项目针对沙蒿这一典型和具有代表性的固沙灌木群落，在三种降水量情形下，采用氮添加控制试验，主要研究：（1）沙蒿群落灌草层对氮水交互驱动作用的响应；（2）沙蒿群落生物结皮层对氮水交互驱动作用的响应；（3）氮水交互作用对土壤环境的影响。项目旨在揭示氮水交互作用下，沙蒿群落植被组成结构的演化及土壤环境的变化，尝试确定导致其变化的临界氮载荷，为固沙灌木林的管理和调控提供理论依据和案例支持，预期成果也是陆地植被生态系统对氮沉降响应的重要补充。

氮沉降是全球环境变化的关键驱动因子之一，日益增加的氮沉降严重影响着全球各类生态系统。了解包括氮沉降在内的全球变化，如何影响干旱地区植被生态系统的组成、结构、功能，已被列为科学的顶级优先主题，然而，氮沉降对荒漠生态系统的影响长期受到忽视，典型固沙灌木群落对氮素输入的响应研究非常匮乏。项目针对沙蒿这一典型和具有代表性的固沙灌木群落，在三种降水量情形下，采用氮添加控制试验，主要研究：（1）沙蒿群落灌草层对氮水交互驱动作用的响应；（2）沙蒿群落生物结皮层对氮水交互驱动作用的响应；（3）氮水交互作用对土壤环境的影响。. 项目研究结果显示：水分添加促进了沙蒿群落植物多样性增加，而氮素添加的影响并不显著；群落中草本植物的相对多度随水氮添加呈增加趋势，而灌木则呈下降趋势；水分添加提高了杂类草生产力和一年生草本生产力，而氮素添加提高了禾草生产力；水分和氮素添加虽能够改善土壤水氮有效性，但对土壤pH、有机碳和全氮的影响较为微弱。因此，氮沉降和降水增加能够促进沙蒿群落中草本繁荣而灌木衰退。水氮添加条件下，禾草大量增加引起表层土壤水分减少，是造成灌木衰退的重要原因。在未来降水和氮沉降持续增加的情景下，以沙蒿为代表的固沙灌木群落具有向草原植被转变的趋势。该研究成果，有助于深入了解荒漠植物群落对全球变化的响应过程和内在机制，并可为固沙灌木林的管理和调控提供有力支持。