Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Leaf Litter Decomposition 2012-2014

Decomposition of leaf litter is a major source of nutrient transfer from vegetation to soils and an important carbon flux. In northern hardwood forests, litter decomposition might be affected by nutrient availability, species composition, stand age or structure, or access by soil decomposers. We investigated these factors in four stands at the Bartlett Experimental Forest in New Hampshire that have had nitrogen and phosphorus added in full factorial design since 2011. Leaf litter of early and late successional species was collected in 2012 and deployed in bags of two mesh sizes (63 µm and 2 mm) in two young and two mature stands and collected three times over the next 2 years. Decomposition was evaluated by fitting mass loss as an exponential function of time represented by growing degree days. Litter decomposed more quickly in the small mesh bags (p < 0.001), which excluded mesofauna. This result was surprising, but might be explained by the greater rigidity of the large mesh material making poor contact with the soil. The litter with a species composition characteristic of our young stands decomposed more quickly than the litter representing mature stands (p = 0.01 for species mix in the full model). The environment in which is was placed was not as important: Neither the age of the stand in which it was placed (p = 0.31), nor N addition (p = 0.59), P addition (p = 0.41), or the interaction of N and P addition (p = 0.13) were significant predictors of the decomposition rate, defined by fitting an exponential decay constant. Additional detail on the MELNHE project, including a datatable of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344 Litter was collected by Rick Bicher and sorted by species by middle school students. Litterbags were made, filled, and weighed by middle school students. Gracie Gilcrist and Jeff Merriam generated data for the chemical analyses.叶片凋落物分解是养分从植被向土壤转移的主要来源，亦是重要的碳通量过程。在北方硬木林中，凋落物分解可能受到养分有效性、物种组成、林分年龄或结构，以及土壤分解者可及性的影响。 我们于新罕布什尔州巴特莱特实验森林（Bartlett Experimental Forest）的4个林分中开展了相关研究，该区域自2011年起采用全因子设计施加氮、磷添加处理。 2012年，我们采集了演替早期与晚期物种的叶片凋落物，将其装入两种孔径（63 µm与2 mm）的分解袋中，分别放置于2个幼龄林分与2个成熟林分中，并在后续2年内分三次回收样品。 通过将质量损失拟合为以生长度日数表征的时间指数函数，以此评估凋落物分解程度。 孔径63 µm的小孔径分解袋可阻隔中型土壤动物，袋内凋落物的分解速率更快（p < 0.001）。这一结果出人意料，或可归因于大孔径材料刚性更强，难以与土壤形成良好接触。 具有幼龄林分物种组成特征的凋落物，其分解速率快于代表成熟林分的凋落物（全模型中物种组合的p值为0.01）。 凋落物放置的环境对分解速率影响较小：无论是放置林分的年龄（p = 0.31）、氮添加处理（p = 0.59）、磷添加处理（p = 0.41），还是氮磷添加的交互作用（p = 0.13），均未成为分解速率的显著预测因子——此处分解速率以指数衰减常数的拟合结果定义。 本数据集附带MELNHE项目（MELNHE project）的更多细节，包括林分描述数据表，以及包含项目说明与样地配置图的PDF文件，可通过以下链接获取：https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344 叶片凋落物由里克·比彻（Rick Bicher）采集，并由中学生按物种分类。分解袋的制作、装填与称重工作均由中学生完成。化学分析相关数据由格雷西·吉尔克里斯特（Gracie Gilcrist）与杰夫·梅里安（Jeff Merriam）生成。