Kominoski John S, Rosemond Amy D, Benstead Jonathan P, Gulis Vladislav, Maerz John C, Manning David W P
Ecol Appl. 2015 Apr;25(3):856-65. doi: 10.1890/14-1113.1.
Particulate organic matter (POM) processing is an important driver of aquatic ecosystem productivity that is sensitive to nutrient enrichment and.drives ecosystem carbon (C) loss. Although studies of single concentrations of nitrogen (N) or phosphorus (P) have shown effects at relatively low concentrations, responses of litter breakdown rates along gradients of low-to-moderate N and P concentrations are needed to establish likely interdependent effects of dual N and P enrichment on baseline activity in stream ecosystems. We established 25 combinations of dissolved inorganic N (DIN; 55-545 µg/L) and soluble reactive P (SRP; 4-86 µg/L) concentrations with corresponding N:P molar ratios of 2-127 in experimental stream channels. We excluded macroinvertebrates, focusing on microbially driven breakdown of maple (Acer rubrum L.) and rhododendron (Rhododendron maximum L.) leaf litter. Breakdown rates, k, per day (d-1) and per degree-day (dd-l), increased by up to 6X for maple and 12× for rhododendron over our N and P enrichment gradient compared to rates at low ambient N and P concentrations. The best models of k (d- and dd-1) included litter species identity and N and P concentrations; there was evidence for both additive and interactive effects of N and P. Models explaining variation in k dd-1 were supported by N and P for both maple and rhododendron (R =0.67 and 0.33, respectively). Residuals in the relationship between k dd-1 and N concentration were largely explained by P, but residuals for k dd-1 and P. concentration were less adequately explained by N. Breakdown rates were more closely related to nutrient concentrations than variables associated with measurements of two mechanistic parameters associated with C loss (fungal biomass and microbial respiration rate). We also determined the effects of nutrient addition on litter C: nutrient stoichiometry and found reductions in litter C:N and C:P along our experimental nutrient gradient. Our results indicate that microbially driven litter processing rates increase across low-to-moderate nutrient gradients that are now common throughout human-modified landscapes.
颗粒有机物（POM）处理是水生生态系统生产力的重要驱动因素，对养分富集敏感，并驱动生态系统碳（C）损失。尽管对单一浓度的氮（N）或磷（P）的研究已表明在相对较低浓度下会产生影响，但仍需要研究凋落物分解速率在低至中等N和P浓度梯度下的响应，以确定N和P双重富集对溪流生态系统基线活动可能产生的相互依赖效应。我们在实验溪流渠道中建立了25种溶解无机氮（DIN；55 - 545 µg/L）和可溶性活性磷（SRP；4 - 86 µg/L）浓度的组合，相应的N:P摩尔比为2 - 127。我们排除了大型无脊椎动物，重点关注微生物驱动的枫香（Acer rubrum L.）和杜鹃花（Rhododendron maximum L.）落叶的分解。与低环境N和P浓度下的速率相比，在我们的N和P富集梯度上，枫香的每日（d⁻¹）和每度日（dd⁻¹）分解速率k分别提高了6倍，杜鹃花提高了12倍。k（d⁻¹和dd⁻¹）的最佳模型包括凋落物物种身份以及N和P浓度；有证据表明N和P存在加性和交互效应。解释k dd⁻¹变化的模型在枫香和杜鹃花中均得到了N和P的支持（R分别为0.67和0.33）。k dd⁻¹与N浓度之间关系的残差在很大程度上由P解释，但k dd⁻¹与P浓度之间的残差由N解释得不够充分。分解速率与养分浓度的关系比与与C损失相关的两个机制参数（真菌生物量和微生物呼吸速率）测量相关的变量更密切。我们还确定了养分添加对凋落物C:养分化学计量的影响，并发现沿着我们的实验养分梯度，凋落物C:N和C:P降低。我们的结果表明，在现在人类改造景观中常见的低至中等养分梯度上，微生物驱动的凋落物处理速率会增加。
