Modeling the Impact of Exotic Annual Brome Grasses on soil Organic Carbon Storage in a Northern Mixed-Grass Prairie

Annual brome grasses, Bromus japonicus and B. tectorum, are common invaders of northern mixed-grass prairie, and have been shown to alter the structure and function of prairie ecosystems, including plant biomass production and litter decomposition. To build on previous findings, our objective was to model the impact of annual brome grasses on soil organic carbon storage as a step towards forecasting ecological change. Specifically, we measured differences in carbon storage between patches dominated by annual bromes and perennial grasses, in addition to evaluating key plant functional characteristics that impact carbon storage. Using the CENTURY model, we simulated high- and low-brome vegetation based on differences in functional characteristics, allowing us to extrapolate the findings from the field study across a broader time scale. We sampled a prairie site in 1996 and 1997 to quantify differences between the high- and low-brome cover plots. High-brome plots averaged 40% brome cover, while the low-brome plots averaged 1% brome cover. We found differences in functional attributes for growth characteristics and litter quality, as well as minor differences in edaphic variables between the plots. Based on field measurements, more soil organic carbon was stored under high-brome vegetation than low-brome, but the differences were not statistically significant. Results from model simulations were consistent with field measurements, and suggested that this prairie ecosystem was not significantly impacted by the functional differences between high- and low-brome vegetation for the first 50 years after the brome invasion under historical management and climate. However, the model results also showed that the differences in soil organic carbon storage continue to diverge after 50 years and consequently could be significant in the future.     

A quantitative study of the effects of anaesthesia and stress of operation on gastric secretion in rats

Ether anaesthesia, present from 5 min before to 5 min after pyloric occlusion, significantly reduced gastric secretion in rats observed over a period of 2 hr. The reduction in gastric secretion was similar to that caused by surgical trauma resulting from acute pyloric ligation. The inhibitory effects induced by ether anaesthesia were found to wear off after 2 hr while those caused by surgical trauma persisted for 5 hr. These findings show conclusively that both surgical trauma and ether anaesthesia will depress gastric secretion in rats which are operated upon immediately before use in gastric secretory studies. Such effects are not present with the technique for pyloric occlusion described by the present authors.     

Antecedent Conditions Influence Soil Respiration Differences in Shrub and Grass Patches

Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of this study was to characterize the effect of antecedent moisture and temperature conditions on soil respiration in a grassland now dominated by shrubs. Continuous measurements of soil respiration, soil temperature, and soil moisture were made over the entire summer of 2005 within distinct vegetation microsites in this shrubland community—under grasses, shrubs, and in open spaces. We analyzed these data within a Bayesian framework that allowed us to evaluate the time-scale over which antecedent conditions influence soil respiration. The addition of antecedent conditions explained an additional 16% of the variation in soil respiration. High soil moisture during the preceding month increased respiration rates in both the grass and shrub microsites. However, the time period over which antecedent soil moisture influenced the temperature sensitivity of soil respiration was shorter in the shrub compared to the grass microsites (1 vs. 2 weeks, respectively). The depth of moisture was important; for example, for respiration under shrubs, near-surface moisture was more influential on the day of the respiration measurement but subsurface moisture was more influential on the antecedent time scale. Although more mechanistic studies are required, this study is the first to reveal that shrub encroachment changes the time scales over which soil moisture and temperature affect soil respiration.     

Management swing potential for bioenergy crops

Bioenergy crops are often classified (and subsequently regulated) according to species that have been evaluated as environmentally beneficial or detrimental, but in practice, management decisions rather than species per se can determine the overall environmental impact of a bioenergy production system. Here, we review the greenhouse gas balance and ‘management swing potential’ of seven different bioenergy cropping systems in temperate and tropical regions. Prior land use, harvesting techniques, harvest timing, and fertilization are among the key management considerations that can swing the greenhouse gas balance of bioenergy from positive to negative or the reverse. Although the management swing potential is substantial for many cropping systems, there are some species (e.g., soybean) that have such low bioenergy yield potentials that the environmental impact is unlikely to be reversed by management. High‐yielding bioenergy crops (e.g., corn, sugarcane, Miscanthus, and fast‐growing tree species), however, can be managed for environmental benefits or losses, suggesting that the bioenergy sector would be better informed by incorporating management‐based evaluations into classifications of bioenergy feedstocks.     

The temperature responses of soil respiration in deserts: a seven desert synthesis

The temperature response of soil respiration in deserts is not well quantified. We evaluated the response of respiration to temperatures spanning 67°C from seven deserts across North America and Greenland. Deserts have similar respiration rates in dry soil at 20°C, and as expected, respiration rates are greater under wet conditions, rivaling rates observed for more mesic systems. However, deserts differ in their respiration rates under wet soil at 20°C and in the strength of the effect of current and antecedent soil moisture on the sensitivity and magnitude of respiration. Respiration increases with temperature below 30°C but declines for temperatures exceeding 35°C. Hot deserts have lower temperature sensitivity than cold deserts, and insensitive or negative temperature sensitivities were predicted under certain moisture conditions that differed among deserts. These results have implications for large-scale modeling efforts because we highlight the unique behavior of desert soil respiration relative to other systems. These behaviors include variable temperature responses and the importance of antecedent moisture conditions for soil respiration.     

Evidence for nuclear processing of progesterone receptors in rat placenta

The distribution of the progesterone receptor (Rp) in cytosolic and nuclear compartments of placenta has been studied in intact and ovariectomized (Ovx) rats on the 14th day of pregnancy. Removal of estradiol (E) and progesterone (P) by Ovx caused a 50% decrease in progesterone receptors from cytosolic and nuclear compartments. Estradiol replacement restored binding to intact levels. Progesterone, given 19 h after E, induced an additional 3-fold increment in the number of cytosolic and nuclear binding sites 1 h later. Four hours after progesterone the number of receptor sites in the placenta fell 60%, signifying processing. This was followed 4 h later by reversal of processing mechanisms leading to full recovery of nuclear and cytoplasmic binding sites. Actinomycin D (0.6 mg/ani) was found to have no influence on these events. On the other hand cycloheximide (0.5 mg/ani) completely prevented processing of binding sites when administered at the same time as progesterone or 2 h before, but did not influence the unmasking of nuclear sites which occurred 1 h after a progesterone challenge. The cycloheximide block to processing was partial when given 2 or 3 h after progesterone (61 and 43% complete, respectively). The full complement of receptors was processed when cycloheximide treatment was delayed 3.75 h after progesterone administration. These findings have led to the view that processing represents rapid and reversible changes in binding properties of the receptor rather than a gain or loss of receptor protein per se. The findings of this study suggest that a hypothetical substance, "processin", whose production is blocked by cycloheximide binds to the receptor and in some undefined manner inhibits ligand-receptor interaction within 4 h after an in vivo progesterone challenge. Nuclear accumulation of receptor induced by progesterone was not accompanied by cytoplasmic depletion of receptor nor was the apparent loss of processed nuclear receptor due to recycling of receptor to cytoplasm. We propose that nuclear receptors continually recycle within the nucleus in masked and unmasked states regulated by delicate interplay between progesterone and processin.     

Effects of Sibship and the Presence of Multiple Predators on the Behavior of Green Frog (Rana clamitans) Tadpoles

In nature, prey are exposed to multiple predators simultaneously. We examined the effects of the cues of two potential predators, mosquitofish and odonate larvae, individually and in combination on the behavior of green frog (Rana clamitans) tadpoles. In addition to examining the behavioral response of green frog tadpoles to multiple predators, we examined variation in behavior among tadpoles from different egg masses (i.e. different sibships). Sibships differed in activity level and there was a significant predator cue by sibship interaction. Two sibships were relatively more active in the control and odonate predator cue treatments but showed reduced activity in treatments containing mosquitofish cues, whereas the remaining sibships showed consistently low levels of activity in all predator cue treatments, including the control. The use of the vegetated side of the aquarium did not differ between tadpoles exposed to the different predator cues. Sibship had no effect on tadpoles’ use of the vegetated side of the aquarium, and there was no interaction between sibship and predator cue. Our results suggest that green frogs did not respond to simultaneous exposure to multiple predator cues any differently than they did to exposure to individual predator cues. More importantly, our results suggest variation, possibly genetically based, in behavioral responses of tadpoles to predators, and thus selection on these behaviors is possible. Of particular interest is that there was variation in behavioral responses to a non‐native predator (Gambusia affinis), suggesting an evolutionary response to an invasive predator is possible.