Abstract This study explores how climate and nutrients influence productivity of arctic wetland plants. The Green-excess Index (GEI) derived from Red, Green and Blue digital image brightness values from digital repeat photography (a.k.a. phenocams) was used to track the inter-annual variability in seasonal greening and above ground biomass for two dominant aquatic emergent graminoids on the Arctic Coastal Plain of northern Alaska: Carex aquatilis and Arctophila fulva. Four years of seasonal and inter-annual greening trends show strong differences in timing and intensity of greenness among species. Thawing degree-days (TDD, days above 0 °C) was a good predictor of GEI in both A. fulva and C. aquatilis. Employing regression tree analyses, we found a greening threshold of 46 TDD for A. fulva, after which GEI increased markedly, while C. aquatilis greened more gradually with a greening mid-point of 31 TDD. Based on long-term climate records and TDD thresholds, greening date has begun 16 thawing degree-days earlier over the past 70 years. To understand the effects of latitude and nutrients on seasonal greening, we compared southern sites and nutrient enriched sites with reference sites. We found statistically higher greenness in southern sites and enriched sites compare to reference sites in both plant species, supporting the role of nutrients and warmer temperatures as key factors enhancing productivity in arctic wetlands. In addition, this study provides an inexpensive, alternative method to monitor climate and nutrient effects at high frequency in arctic aquatic systems through camera-derived GEI greenness and has the potential to bridge the gap between plot level and satellite based observations given its strong relationships with biomass and NDVI.

中文翻译：

---

从 phenocams 观察到的气候和营养对北极湿地植物物候的影响

摘要 本研究探讨了气候和养分如何影响北极湿地植物的生产力。来自数字重复摄影（又名 phenocams）的红色、绿色和蓝色数字图像亮度值的绿色过量指数 (GEI) 用于跟踪季节性绿化和地上生物量的年际变化，用于两种主要水生禾本科植物阿拉斯加北部的北极沿海平原：Carex aquatilis 和 Arctophila fulva。四年的季节性和年际绿化趋势表明，物种之间的绿化时间和强度存在很大差异。解冻度天数（TDD，高于 0 °C 的天数）是 A. fulva 和 C. aquatilis 中 GEI 的良好预测指标。采用回归树分析，我们发现 A. fulva 的绿化阈值为 46 TDD，之后 GEI 显着增加，而 C. aquatilis 逐渐变绿，绿化中点为 31 TDD。根据长期气候记录和 TDD 阈值，在过去 70 年中，绿化日期提前了 16 个解冻度日。为了了解纬度和养分对季节性绿化的影响，我们将南部地点和营养丰富的地点与参考地点进行了比较。我们发现，与两种植物物种的参考地点相比，南部地点和富集地点的绿度在统计上更高，支持养分和温度升高作为提高北极湿地生产力的关键因素的作用。此外，这项研究提供了一种廉价的、