Differential responses of production and respiration to temperature and moisture drive the carbon balance across a climatic gradient in New Mexico

Southwestern North America faces an imminent transition to a warmer, more arid climate, and it is critical to understand how these changes will affect the carbon balance of southwest ecosystems. In order to test our hypothesis that differential responses of production and respiration to temperature and moisture shape the carbon balance across a range of spatio‐temporal scales, we quantified net ecosystem exchange (NEE) of CO₂ and carbon storage across the New Mexico Elevational Gradient, which consists of six eddy‐covariance sites representing biomes ranging from desert to subalpine conifer forest. Within sites, hotter and drier conditions were associated with an increasing advantage of respiration relative to production such that daily carbon uptake peaked at intermediate temperatures – with carbon release often occurring on the hottest days – and increased with soil moisture. Across sites, biotic adaptations modified but did not override the dominant effects of climate. Carbon uptake increased with decreasing temperature and increasing precipitation across the elevational gradient; NEE ranged from a source of ～30 g C m^?2 yr^?1 in the desert grassland to a sink of ～350 g C m^?2 yr^?1 in the subalpine conifer forest. Total aboveground carbon storage increased dramatically with elevation, ranging from 186 g C m^?2 in the desert grassland to 26 600 g C m^?2 in the subalpine conifer forest. These results make sense in the context of global patterns in NEE and biomass storage, and support that increasing temperature and decreasing moisture shift the carbon balance of ecosystems in favor of respiration, such that the potential for ecosystems to sequester and store carbon is reduced under hot and/or dry conditions. This implies that projected climate change will trigger a substantial net release of carbon in these New Mexico ecosystems (～3 Gt CO₂ statewide by the end of the century), thereby acting as a positive feedback to climate change.     

Using DNA Barcodes to Identify Bird Species Involved in Birdstrikes

Abstract: We determined effectiveness of using mitochondrial DNA barcodes (cytochrome c oxidase subunit 1 [CO1]) to identify bird-aircraft collision (birdstrike) cases that lacked sufficient feather evidence for morphological diagnosis. From September through December 2006, 821 samples from birdstrike events occurring in the United States were submitted for DNA analysis. We successfully amplified a CO1 DNA barcode product from 554 (67.5%) of the samples; 267 (32.5%) did not contain viable DNA and depended on morphological methods (microscopy) for Order or Family level identification. We deemed 19 cases inconclusive either because the DNA barcode recovered from the sample did not meet our 98% match criteria when compared to the Barcode of Life Database (BoLD) or because the DNA barcode matched to a set of ≥ 2 closely related species with overlapping barcodes, preventing complete species identification. Age of the sample (≤6 months) did not affect DNA viability, but initial condition of the sample and the collection method was critical to DNA identification success. The DNA barcoding approach has great potential in aiding in identification of birds (and wildlife) for airfield management practices, particularly in regions of the world that lack the vast research collections and individual expertise for morphologic identifications.     

An eddy covariance mesonet to measure the effect of forest age on land–atmosphere exchange

We deployed a mesonet of year‐round eddy covariance towers in boreal forest stands that last burned in ～1850, ～1930, 1964, 1981, 1989, 1998, and 2003 to understand how CO₂ exchange and evapotranspiration change during secondary succession. We used MODIS imagery to establish that the tower sites were representative of the patterns of secondary succession in the region, and Landsat images to show that the individual stands have changed over the last 22 years in ways that match the spatially derived trends. The eddy covariance towers were well matched, with similar equipment and programs, which maximized site‐to‐site precision and allowed us to operate the network in an efficient manner. The six oldest sites were fully operational for ～90% of the growing season and ～70% of the dormant season from 2001 or 2002 to 2004, with most of the missing data caused by low battery charge or bad signals from the sonic anemometers. The rates of midday growing‐season CO₂ uptake recovered to preburn levels within 4 years of fire. The seasonality of land–atmosphere exchange and growing‐season length changed markedly with stand age. The foliage in the younger stands (1989, 1998, and 2003 burns) was almost entirely deciduous, which resulted in comparatively short growing seasons that lasted ～65 days. In contrast, the older stands (1850, 1930, 1964, and 1981) were mostly evergreen, which resulted in comparatively long growing seasons that lasted ～130 days. The eddy covariance mesonet approach we describe could be used within the context of other ecological experimental designs such as controlled manipulations and gradient comparisons.     

KATBERGIA GEN. NOV., A NEW TRACE FOSSIL FROM UPPER PERMIAN AND LOWER TRIASSIC ROCKS OF THE KAROO BASIN: IMPLICATIONS FOR PALAEOENVIRONMENTAL CONDITIONS AT THE P/TR EXTINCTION EVENT

Abstract:  A new ichnogenus and ichnospecies of burrow, Katbergia carltonichnus , are described from Upper Permian and Lower Triassic rocks of the Karoo Basin, South Africa, where they are preserved in pedogenically modified overbank deposits that are interpreted as inceptisols subsequently gleysol overprinted. Sigmoidal burrows consist of a long (≥0.5 m) cylindrical tube, ranging from 1–2 cm in diameter, terminating in a slightly larger living chamber. The burrows are unlined and passively filled, preserving a hierarchy of scratch patterns on the burrow walls. Scratch patterns include longitudinal, transverse, and crescent-shaped markings found around the circumference of the burrow, but which are less densely concentrated on the burrow floor. Calcareous concretions are associated with burrowed siltstone intervals, generally restricted to the lowermost decimetre, with nodules nucleating around burrows. Stable δ¹³C and δ¹⁸O isotope data on calcite cement in the burrow fill, entombing siltstone, and associated calcareous nodules all cluster together when plotted, indicating that nodule formation occurred following burrow horizon abandonment and a rise in regional water table. Isotopic data reflect calcite precipitation under a semi-closed system in saturated conditions. A model for burrow emplacement, abandonment and infill, and subsequent cementation by calcite is presented demonstrating that previous interpretations of Late Permian and Early Triassic palaeosol types associated with the P/Tr extinction event must be re-evaluated.