Evolutionary history biases inferences of ecology and environment from δ13C but not δ18O values.

Closely related taxa are, on average, more similar in terms of their physiology, morphology and ecology than distantly related ones. How this biological similarity affects geochemical signals, and their interpretations, has yet to be tested in an explicitly evolutionary framework. Here we compile and analyze planktonic foraminiferal size-specific stable carbon and oxygen isotope values (δ13C and δ18O, respectively) spanning the last 107 million years. After controlling for dominant drivers of size-δ13C and size-δ18O trends, such as geological preservation, presence of algal photosymbionts, and global environmental changes, we identify that shared evolutionary history has shaped the evolution of species-specific vital effects in δ13C, but not in δ18O. Our results lay the groundwork for using a phylogenetic approach to correct species δ13C vital effects through time, thereby reducing systematic biases in interpretations of long-term δ13C records-a key measure of holistic organismal biology and of the global carbon cycle.

Modeling of biotic and abiotic processes affecting phosphate oxygen isotope ratios in a mineral-water-biota system.

Abiotic and biotic reactions operate side by side in the cycling of phosphorus (P) in the environment, but the relative roles of these two reactions vary both spatially and temporally. In biotic reactions, the uptake and release of P are catalyzed by enzymes and thus change phosphate oxygen isotope ratios, while in abiotic reactions, the absence of hydrolysis-condensation reactions results in no apparent changes in isotope composition, except short-term kinetic isotope effect due solely to preferential ion exchange. Therefore, isotope method could be a promising tool to differentiate relative roles of these two reactions in the environment but the relationship of the dynamic concentration and isotope exchange at the biota-water interface is largely unknown. In this study, we aimed to develop a process-based isotope model underpinning the competition of abiotic (sorption, desorption, and ion exchange) and biotic (uptake, metabolism, and release) reactions during uptake and recycling of ferrihydrite-bound P by E. coli. Our model comprises equations describing the partitioning relationship among different P pools and their corresponding oxygen isotope compositions and is based exclusively on oxygen isotope exchange at multiple sites including mineral surface, aqueous phase, and bacterial cells. The process-based model adequately reproduced the measured concentration and isotope compositions over time. Furthermore, parametric and sensitivity analyses using the model indicated that the rate of biological uptake of P was the major factor controlling the changes of phosphate isotope composition. In conclusion, our model provides new insights into a mechanistic aspect of isotope exchange and could be potentially useful for future efforts to understand the interplay of biotic and abiotic factors on phosphorus cycling in natural environments.

Distortion of homeostatic signaling proteins by simulated microgravity in rat hypothalamus: A(16) O/(18) O-labeled comparative integrated proteomic approach.

Microgravity generates oxidative stress in central nervous system, causing distortion of various vital signaling cascades involved in many homeostatic functions. Here, we performed comparative (16) O/(18) O labeled integrated proteomic strategy to observe the differential expression of signaling proteins involved in homeostasis. In this study, rat-tail suspension model is employed to induce simulated microgravity in CNS. By wide proteomic analysis, total of 35 and 97 significantly differentially expressed proteins were found by HPLC/ESI-TOF and HPLC-Q-TOF analysis, respectively. Among the total of 132 proteins quantified, 25 proteins were found related to various signaling cascades. Protein Thy-1, 14-3-3 gamma, 14-3-3 epsilon, 14-3-3 theta, 14-3-3 eta, and 14-3-3 beta/alpha proteins, calmodulin and calcium/calmodulin-dependent protein kinase type-II subunit beta were found upregulated under the influence of simulated microgravity. These proteins are found involved in disrupting homeostatic pathways like sleep/wake cycle, drinking behavior, hypothalamic-pituitary-adrenocortical regulation and fight and/or flee actions under stress. Furthermore, MS results for protein Thy-1 were verified by Western blot analysis showing the quantification accuracy of MS instruments. Results presented here will serve as means to understand the mechanism of action of microgravity and further reference for future detailed study of consequences of microgravity on astronauts and their possible countermeasures.

Bulk leaf delta(18)O and delta(13)C reflect the intensity of intraspecific competition for water in a semi-arid tussock grassland.

We investigated the extent to which plant water and nutrient status are affected by intraspecific competition intensity and microsite quality in a monodominant tussock grassland. Leaf gas exchange and stable isotope measurements were used to assess the water relations of Stipa tenacissima tussocks growing along a gradient of plant cover and soil depth in a semi-arid catchment of Southeast Spain. Stomatal conductance and photosynthetic rate decreased with increasing intensity of competition during the wet growing season, leading to foliar delta(18)O and delta(13)C enrichment. A high potential for runoff interception by upslope neighbours exerted strong detrimental effects on the water and phosphorus status of downslope S. tenacissima tussocks. Foliar delta(15)N values became more enriched with increasing soil depth. Multiple stepwise regression showed that competition potential and/or rhizosphere soil depth accounted for large proportions of variance in foliar delta(13)C, delta(18)O and delta(15)N among target tussocks (57, 37 and 64%, respectively). The results presented here highlight the key role that spatial redistribution of resources (water and nutrients) by runoff plays in semi-arid ecosystems. It is concluded that combined measurement of delta(13)C, delta(18)O and nutrient concentrations in bulk leaf tissue can provide insight into the intensity of competitive interactions occurring in natural plant communities.