• Energy Research

Abstract. This paper aims to assess the spatial variability in the response of CO2 exchange to irradiance across the Arctic tundra during peak season using light response curve (LRC) parameters. This investigation allows us to better understand the future response of Arctic tundra under climatic change. Peak season data were collected during different years (between 1998 and 2010) using the micrometeorological eddy covariance technique from 12 circumpolar Arctic tundra sites, in the range of 64–74° N. The LRCs were generated for 14 days with peak net ecosystem exchange (NEE) using an NEE–irradiance model. Parameters from LRCs represent site-specific traits and characteristics describing the following: (a) NEE at light saturation (Fcsat), (b) dark respiration (Rd), (c) light use efficiency (α), (d) NEE when light is at 1000 μmol m−2 s−1 (Fc1000), (e) potential photosynthesis at light saturation (Psat) and (f) the light compensation point (LCP). Parameterization of LRCs was successful in predicting CO2 flux dynamics across the Arctic tundra. We did not find any trends in LRC parameters across the whole Arctic tundra but there were indications for temperature and latitudinal differences within sub-regions like Russia and Greenland. Together, leaf area index (LAI) and July temperature had a high explanatory power of the variance in assimilation parameters (Fcsat, Fc1000 and Psat, thus illustrating the potential for upscaling CO2 exchange for the whole Arctic tundra. Dark respiration was more variable and less correlated to environmental drivers than were assimilation parameters. This indicates the inherent need to include other parameters such as nutrient availability, substrate quantity and quality in flux monitoring activities.

ABSTRACT This study reports the effects of long-term elevated atmospheric CO 2 on root production and microbial activity, biomass, and diversity in a chaparral ecosystem in southern California. The free air CO 2 enrichment (FACE) ring was located in a stand dominated by the woody shrub Adenostoma fasciculatum . Between 1995 and 2003, the FACE ring maintained an average daytime atmospheric CO 2 concentration of 550 ppm. During the last two years of operation, observations were made on soil cores collected from the FACE ring and adjacent areas of chaparral with ambient CO 2 levels. Root biomass roughly doubled in the FACE plot. Microbial biomass and activity were related to soil organic matter (OM) content, and so analysis of covariance was used to detect CO 2 effects while controlling for variation across the landscape. Extracellular enzymatic activity (cellulase and amylase) and microbial biomass C (chloroform fumigation-extraction) increased more rapidly with OM in the FACE plot than in controls, but glucose substrate-induced respiration (SIR) rates did not. The metabolic quotient (field respiration over potential respiration) was significantly higher in FACE samples, possibly indicating that microbial respiration was less C limited under high CO 2 . The treatments also differed in the ratio of SIR to microbial biomass C, indicating a metabolic difference between the microbial communities. Bacterial diversity, described by 16S rRNA clone libraries, was unaffected by the CO 2 treatment, but fungal biomass was stimulated. Furthermore, fungal biomass was correlated with cellulase and amylase activities, indicating that fungi were responsible for the stimulation of enzymatic activity in the FACE treatment.

Abstract Many studies have reported that the Arctic is greening; however, we lack an understanding of the detailed patterns and processes that are leading to this observed greening. The normalized difference vegetation index (NDVI) is used to quantify greening, which has had largely positive trends over the last few decades using low spatial resolution satellite imagery such as AVHRR or MODIS over the pan-Arctic region. However, substantial fine scale spatial heterogeneity in the Arctic makes this large-scale investigation hard to interpret in terms of vegetation and other environmental changes. Here we focus on one area of the northern Alaskan Arctic using high spatial resolution (4 m) multispectral satellite imagery from DigitalGlobe™ to analyze the greening trend near Utqiaġvik (formerly known as Barrow) over 14 years from 2002 to 2016. We found that tundra vegetation has been greening (τ = 0.65, p = 0.01, NDVI increase of 0.01 yr−1) despite no overall change in vegetation community composition. The greening is most closely correlated to the number of thawing degree days (R 2 = 0.77, F = 21.5, p < 0.001) which increased in a similar linear trend over the 14 year study period (1.79 ± 0.50 days per year, p < 0.01, τ = −0.56). This suggests that in this Arctic ecosystem, greening is occurring due to a lengthening growing season that appears to stimulate plant productivity without any significant change in vegetation communities. We found that vegetation communities in wetter locations greened about twice as fast as those found in drier conditions supporting the hypothesis that these communities respond more strongly to warming. We suggest that in Arctic environments, vegetation productivity may continue to rise, particularly in wet areas.

Significance Wetlands are unique ecosystems because they are in general sinks for carbon dioxide and sources of methane. Their climate footprint therefore depends on the relative sign and magnitude of the land–atmosphere exchange of these two major greenhouse gases. This work presents a synthesis of simultaneous measurements of carbon dioxide and methane fluxes to assess the radiative forcing of natural wetlands converted to agricultural or forested land. The net climate impact of wetlands is strongly dependent on whether they are natural or managed. Here we show that the conversion of natural wetlands produces a significant increase of the atmospheric radiative forcing. The findings suggest that management plans for these complex ecosystems should carefully account for the potential biogeochemical effects on climate.

This dataset contains greenhouse gas fluxes of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) over permafrost affected features near Utqiaġvik, Alaska in a coastal wetland ecosystem on the Barrow Environmental Observatory (BEO). Static chamber flux measurements were acquired using a GASMET GT5000 Terra portable ambient temperature Fourier transform infrared (FTIR) gas analyzer. A clear, cylindrical polycarbonate chamber (50 centimeter (cm) in height and 20 cm in diameter) and chamber collars made out of PVC pipe (15 cm in height and 20 cm in diameter) were used to create a closed loop system for measuring fluxes throughout July of 2021, and June through August during 2022 and 2023. Chamber collars were inserted at a depth of 10 cm three to five days before sampling. By the 2023 field season, we had installed a total of 51 replicates throughout the BEO – 46 replicates consisting of unvegetated soil features and 5 replicates consisting of vegetated features. Environmental ancillary measurements were recorded during static chamber flux measurements at each collar location throughout the field campaigns. In 2021, soil surface temperatures were recorded using an infrared thermometer and in 2022 to 2023 soil temperatures were recorded within the top 4 cm of the active layer using a waterproof probe thermometer (UX-90205-22, Cole-Palmer Instrument Company, USA). Volumetric soil water content was measured within the top 20 cm of the active layer using a soil moisture probe (TDR 300 Fieldscout, Spectrum Technologies INC). Thaw depth was recorded using a graduated metal rod.