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管理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（包括提案、报告、影像资料等）均收纳于科罗拉多数字馆藏下的综合项目馆藏中，相关链接为http://digitool.library.colostate.edu/R/?func=collections&collection_id=3429。本数据集的数据表与配套元数据文档（以生态元数据语言（Ecological Metadata Language）生成）可通过服务于生态研究社区的其他仓储获取，属于SGS-LTER项目综合馆藏的组成部分。更多相关信息及参考资料可访问：http://hdl.handle.net/10217/85547。
本研究为期10年，旨在评估5种碳（C）处理对位于科罗拉多州东北部的短草草原长期生态研究站点内历史氮富集样地的活性碳与氮（N）库的影响。研究团队于1970年代早期对这些样地施加了氮与水添加处理，随后的8年间，分别向样地施加锯末、蔗糖、工业木质素、锯末+蔗糖、木质素+蔗糖5种处理。此前的研究表明，过往的水与氮添加操作改变了植物物种组成，提升了养分循环速率，且该效应在25年后依然显著。
本研究提出如下假设：活性碳添加将刺激微生物活动并抑制氮矿化速率，而复杂形态的碳（锯末与木质素）可增强腐殖化作用，进而长期降低氮有效性。研究结果显示，在5种碳处理中，蔗糖、锯末、锯末+蔗糖均抑制了氮有效性，其中锯末+蔗糖是降低氮有效性效果最优的处理方式。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：高活性碳形态可形成较强的短期氮汇，但该效应在施用后一年内便会消散；而更难降解的碳形态则可更持久地降低氮有效性。长期来看，锯末+蔗糖是降低外来物种盖度、提升本土物种密度效果最优的处理方式。活性碳对外来物种既无短期影响，亦无长期影响。尽管有机改良剂未能帮助优势本土物种格兰马草（Bouteloua gracilis）完成种群恢复，但可有效提升另一种本土物种薹草（Carex eleocharis）的种群数量。上述结果表明，有机改良剂或可作为修复短草草原本土物种的有效工具。