SGS-LTER Impact of Labile and Recalcitrant Carbon Treatments on Plant Communities (Canopy Cover) in a Semiarid Ecosystem on the Central Plains Experimental Range, Nunn, Colorado, USA 2006-2012, ARS Study Number 3

This data package was produced by researchers working on the Shortgrass Steppe Long Term Ecological Research (SGS-LTER) Project, administered at Colorado State University. Long-term datasets and background information (proposals, reports, photographs, etc.) on the SGS-LTER project are contained in a comprehensive project collection within the Digital Collections of Colorado (http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429). The data table and associated metadata document, which is generated in Ecological Metadata Language, may be available through other repositories serving the ecological research community and represent components of the larger SGS-LTER project collection. Additional information and referenced materials can be found: http://hdl.handle.net/10217/85547. In a 10-year study, we assessed the influence of five carbon (C) treatments on the labile C and nitrogen (N) pools of historically N enriched plots on the Shortgrass Steppe Long Term Ecological Research site located in northeastern Colorado. For eight years, we applied sawdust, sugar, industrial lignin, sawdust + sugar, and lignin + sugar to plots that had received N and water additions in the early 1970s. Previous work showed that past water and N additions altered plant species composition and enhanced rates of nutrient cycling; these effects were still apparent 25 years later. We hypothesized that labile C amendments would stimulate microbial activity and suppress rates of N mineralization, whereas complex forms of carbon (sawdust and lignin) could enhance humification and lead to longer-term reductions in N availability. Results indicated that of the five carbon treatments, sugar, sawdust, and sawdust + sugar suppressed N availability, with sawdust + sugar being the most effective treatment to reduce N availability. The year after treatments stopped, N availability remained less in the sawdust + sugar treatment plots than in the high-N control plots. Three years after treatments ended, reductions in N availability were smaller (40-60%). Our results suggest that highly labile forms of carbon generate strong short- term N sinks, but these effects dissipate within one year of application, and that more recalcitrant forms reduce N longer. Sawdust + sugar was the most effective treatment to decrease exotic species canopy cover and increase native species density over the long term. Labile carbon had neither short- nor long-term effects on exotic species. Even though the organic amendments did not contribute to recovery of the dominant native species Bouteloua gracilis, they were effective in increasing another native species, Carex eleocharis. These results indicate that organic amendments may be a useful tool for restoring some native species in the shortgrass steppe.

本数据包由科罗拉多州立大学主管的短草草原长期生态研究（Shortgrass Steppe Long Term Ecological Research, SGS-LTER）项目的研究人员编制。该项目的长期数据集及背景资料（包括研究方案、报告、影像资料等）均收纳于科罗拉多数字馆藏（Digital Collections of Colorado）旗下的完整项目馆藏中，相关链接为：http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429。本数据集的数据表及采用生态元数据语言（Ecological Metadata Language）编制的关联元数据文档，可通过服务于生态研究领域的其他仓储获取，它们均为SGS-LTER项目完整馆藏的组成部分。更多相关信息及参考文献资料可访问：http://hdl.handle.net/10217/85547。

本研究为期10年，旨在评估5种碳（Carbon, C）处理方式对科罗拉多州东北部短草草原长期生态研究样地中历史氮富集样地的活性碳（labile C）与氮（N）库的影响。研究团队于1970年代早期对部分样地施加氮与水添加处理，随后连续8年向该类样地分别施加锯末、蔗糖、工业木质素、锯末+蔗糖以及木质素+蔗糖5种处理剂。既往研究表明，早期施加的水与氮添加处理改变了植物物种组成，提升了养分循环速率，且该效应在25年后仍可观测到。本研究提出如下假说：活性碳添加物可刺激微生物活性并抑制氮矿化速率，而复杂形态碳（锯末与木质素）则可增强腐殖化过程，从而长期降低氮有效性。

研究结果显示，在5种碳处理方式中，蔗糖、锯末以及锯末+蔗糖均可降低氮有效性，其中锯末+蔗糖的降氮效果最为显著。在处理停止后的第一年，锯末+蔗糖处理样地的氮有效性仍低于高氮对照组样地；处理结束3年后，氮有效性的降幅有所收窄（40%~60%）。本研究结果表明：高活性碳形态可快速形成短期氮汇，但该效应在施加后一年内即消散；而难降解碳形态则可更持久地降低氮有效性。从长期来看，锯末+蔗糖处理是降低外来物种盖度、提升本土物种密度的最优方案；而活性碳处理对外来物种既无短期效应，也无长期影响。尽管此类有机添加物未能促进优势本土物种格兰马草（Bouteloua gracilis）的恢复，但可有效提升另一种本土物种球穗苔草（Carex eleocharis）的种群数量。上述结果表明，有机添加物可作为短草草原生态系统中部分本土物种修复的有效手段。