How eddy covariance flux measurements have contributed to our understanding of Global Change Biology

A global network of long‐term carbon and water flux measurements has existed since the late 1990s. With its representative sampling of the terrestrial biosphere's climate and ecological spaces, this network is providing background information and direct measurements on how ecosystem metabolism responds to environmental and biological forcings and how they may be changing in a warmer world with more carbon dioxide. In this review, I explore how carbon and water fluxes of the world's ecosystem are responding to a suite of covarying environmental factors, like sunlight, temperature, soil moisture, and carbon dioxide. I also report on how coupled carbon and water fluxes are modulated by biological and ecological factors such as phenology and a suite of structural and functional properties. And, I investigate whether long‐term trends in carbon and water fluxes are emerging in various ecological and climate spaces and the degree to which they may be driven by physical and biological forcings. As a growing number of time series extend up to 20 years in duration, we are at the verge of capturing ecosystem scale trends in the breathing of a changing biosphere. Consequently, flux measurements need to continue to report on future conditions and responses and assess the efficacy of natural climate solutions.     

A model of drop size distribution for a system with evaporation

Abstract. The size and shape of drops on leaf surfaces strongly affect their persistence. The relationship between volume and exposed surface area of drops on wheat leaves and the log-normal drop size distribution in a wheat canopy after rain are used to derive equations to describe how the total volume and drop number change with evaporation. Firstly, the behaviour of a single drop as it evaporates is considered and then equations describing the change in a population of drops with an initial log-normal distribution are derived. The time taken for all the drops to reach complete dryness is about thirty times that for the same volume of water spread uniformly over the surface with the same potential evaporation rate.     

Water balance of conifer logs in early stages of decomposition

Seasonal and long-term changes in the water balance of conifer logs during the first 8 years of decomposition were studied in an old-growth Pseudotsuga/Tsuga forest in the Oregon Cascade Mountains. Measurements were made of the moisture content of outer bark, inner bark, sapwood, and heartwood and of the flow of water into and out of logs of four species (Abies amabilis, Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla). After the logs had decomposed from 1 to 2 years, 38–47% of the canopy throughfall landing upon them ran off the surface, 29–34% leached from the bottom, and 21–30% was absorbed and evaporated. After 8 years of decomposition, water entering and then leaching from logs increased 1.3 times while runoff decreased a similar amount. The proportion of water stored by and evaporated from logs in this study indicates that in old growth forests they may intercept 2–5% of the canopy throughfall to the forest floor and that, even in early stages of decomposition, they may affect the hydrological cycle of Pacific Northwest old-growth forests.This is paper 2945 of the Forest Research Laboratory, Oregon State University, Corvallis     

Passive volatilization of gasoline from soil

Gasoline spills were simulated in the laboratory with three air‐dried soils, using a synthetic gasoline and unsaturated soil to quantify passive volatilization over a period of up to 16 d. The total and individual gasoline components were monitored as a function of time and depth in the soil.

The time required to deplete the overall gasoline concentration in the soil to 40% of the initial concentration ranged from 0.25 to 10 d for the three soils. Sand was the fastest, followed by loamy sand and silt loam. The volatilization rate of gasoline from soil was found to be dependent on soil, chemical type, and depth. Observation of individual components indicated that a wicking mechanism contributed to the gasoline flux toward the surface.     

Carbon dioxide and methane exchange of a north-east Siberian tussock tundra

Carbon dioxide, energy flux measurements and methane chamber measurements were carried out in an arctic wet tussock grassland located on a flood plane of the Kolyma river in NE Siberia over a summer period of 155 days in 2002 and early 2003. Respiration was also measured in April 2004. The study region is characterized by late thaw of the top soil (mid of June) and periodic spring floods. A stagnant water table below the grass canopy is fed by thawing of the active layer of permafrost and by flood water. The climate is continental with average daily temperature in the warmest months of 13°C (maximum temperature at midday: 28°C by the end of July), dry air (maximum vapour pressure deficit at midday: 28 hPa) and low rainfall of 50 mm during summer (July–September). Summer evaporation (July–September: 103 mm) exceeded rainfall by a factor of 2. The daily average Bowen ratio (H/LE) was 0.62 during the growing season. Net ecosystem CO₂ uptake reached 10 μmol m⁻² s⁻¹ and was related to photon flux density (PFD) and vapour pressure deficit (VPD). The cumulative annual net carbon flux from the atmosphere to the terrestrial surface was estimated to be about −38 g C m⁻² yr⁻¹ (negative flux depicts net carbon sink). Winter respiration was extrapolated using the Lloyd and Taylor function. The net carbon balance is composed of a high rate of assimilation in a short summer and a fairly large but uncertain respiration mainly during autumn and spring. Methane flux (about 12 g C m⁻² measured over 60 days) was 25% of C uptake during the same period of time (end of July to end of September). Assuming that CH₄ was emitted only in summer, and taking the greenhouse gas warming potential of CH₄ vs. CO₂ into account (factor 23), the study site was a greenhouse gas source (at least 200 g C_equivalent m⁻² yr⁻¹). Comparing different studies in wetlands and tundra ecosystems as related to latitude, we expect that global warming would rather increase than decrease the CO₂-C sink.     

Effect of moisture evaporation from diatomaceous earth pellets on storage stability of Steinernema glaseri

Induction of anhydrobiosis and storage stability of entomopathogenic nematodes are influenced by moisture availability. Decreasing moisture content in diatomaceous earth (DE) pellets containing the Steinernema glaseri NJ-43 strain and its effect on survival time and infectivity of the nematode were determined. Pelletisation was performed in a vortex mixer, using DE Celite® 209 as the desiccant material. Pellets were stored at room temperature (23?±?2°C) and high relative humidity (96–100%). Nematode survival and infectivity against last instar greater wax moth, Galleria mellonella, were tested daily. Initial average and average equilibrium moisture content in pellets were 66.7% and 13.6%, respectively, and the infective juveniles mean survival time was 8.8 days. A moisture transfer model based on diffusion and evaporation was evaluated to predict moisture fluctuations within the pellets. We concluded that 84% of variation in S. glaseri infectivity on G. mellonella larvae was explained by the survival of the nematode, whereas 52% of variation in S. glaseri survival was explained by the loss of moisture from the pellets. The moisture transfer model achieved 78% reliability in predicting moisture content and fluctuations. Therefore, the mechanisms of moisture diffusion and evaporation from the surface to the surrounding atmosphere contribute significantly to moisture loss from the pellets.     

CCK-octapeptide injected in CSF decreases meal size and daily food intake in sheep

Cholecystokinin octapeptide (CCK-OP) is a potent and specific suppressor of feeding when administered as a continuous lateral cerebral ventricular injection in fasted sheep, and we have proposed that endogenous CCK-OP in the brain is released during meals and acts to terminate feeding. In previous studies, however, only relatively short-term effects of CCK-OP on feeding were examined. In the first experiment of the present series sheep were adapted to a 6-hr feeding period per day. CCK-OP injected continuously for 6 hr into the lateral ventricles reduced feeding during the entire feeding period (809 ± 72 g, sham; 695 ± 71 g, carrier; 505 ± 69 g, CCK-OP; p<0.05). In addition mean feed intake for the two days (injection + first post injection day) was significantly reduced by CCK-OP; thus with CCK-OP, sheep did not compensate by the day after injection for the decreased feed intake on injection day. In a second experiment CCK-OP was injected into the lateral ventricles only during four consecutive 15 min meals 2 hours apart. With a dose of 0.159 pmoles/min CCK-OP, size of the second meal was reduced, but with 0.638 pmoles/min CCK-OP feeding during each of the first two meals was reduced and cumulative intake for the four meals was decreased. These results indicate that CCK-OP administered centrally can have long-term effects on feeding, and under appropriate conditions, could result in negative energy balance.     

Beta-adrenergic control of trans-cutaneous evaporative cooling mechanisms in birds

Summary The decreasing effect of -adrenergic blockade on skin resistance to vapor diffusion and the onset of cutaneous water evaporation in the pigeon (Columba livia) was investigated. Oral administration of 1, 2.3 and 5 mg propranolol to pigeons (268±53 g) initiated intensive trans-cutaneous water evaporation (CWE) up to 29.1 mg H₂O·cm^–2·h^–1 in resting birds at 30°C air temperature (Ta), but had only a slight effect on CWE of birds exposed to 50 °C Ta.After 7 h of effective -adrenergic blockade (oral administration of 5 mg propranolol), skin and body temperature stabilized at 39.0±0.5 °C and 41.0±0.7 °C, compared to 40.2±0.8 °C and 41.9±0.6 °C in the control group, respectively. A slight hypothermia was accompanied by feather fluffing.Intradermal injection of 0.001, 0.01 and 0.12 mg propranolol also caused intensive CWE. Local -adrenergic blockade in relatively low blocker doses (0.001 and 0.01 mg propranolol) decreased skin resistance from a high value of 44.5 s·cm^–1 to about 6.0 s·cm^–1, and caused a sharp increase in CWE from a control value of about 4 to a high of 26.4 mg H₂O·cm^–2·h^–1 during the first two hours of exposure to 30°C Ta.The possible role of -adrenergic blockade in regulation of trans-cutaneous water evaporation of latent heat dissipation is discussed.