Treeline shifts in the Ural mountains affect soil organic matter dynamics

Historical photographs document that during the last century, forests have expanded upwards by 60–80 m into former tundra of the pristine Ural mountains. We assessed how the shift of the high‐altitude treeline ecotone might affect soil organic matter (SOM) dynamics. On the gentle slopes of Mali Iremel in the Southern Urals, we (1) determined the differences in SOM stocks and properties from the tundra at 1360 m above sea level (a.s.l.) to the subalpine forest at 1260 m a.s.l., and (2) measured carbon (C) and nitrogen (N) mineralization from tundra and forest soils at 7 and 20 °C in a 6‐month incubation experiment. C stocks of organic layers were 3.6±0.3 kg C m^?2 in the tundra and 1.9±0.2 kg C m^?2 in the forest. Mineral soils down to the bedrock stored significantly more C in the forest, and thus, total soil C stocks were slightly but insignificantly greater in the forest (+3 kg C m^?2). Assuming a space for time approach based on tree ages suggests that the soil C sink due to the forest expansion during the last century was at most 30 g C m^?2 yr^?1. Diffuse reflective infrared spectroscopy and scanning calorimetry revealed that SOM under forest was less humified in both organic and mineral horizons and, therefore, contained more available substrate. Consistent with this result, C mineralization rates of organic layers and A horizons of the forest were two to four times greater than those of tundra soils. This difference was similar in magnitude to the effect of increasing the incubation temperature from 7 to 20 °C. Hence, indirect climate change effects through an upward expansion of forests can be much larger than direct warming effects (Δ0.3 K across the treeline). Net N mineralization was 2.5 to six times greater in forest than in tundra soils, suggesting that an advancing treeline likely increases N availability. This may provide a nutritional basis for the fivefold increase in plant biomass and a tripling in productivity from the tundra to the forest. In summary, our results suggest that an upward expansion of forest has small net effects on C storage in soils but leads to changes in SOM quality, accelerates C cycling and increases net N mineralization, which in turn might stimulate plant growth and thus C sequestration in tree biomass.     

A PANEL PERFORMANCE PROCEDURE IMPLEMENTED IN R

Monitoring performance is essential for the efficient use of a sensory panel both during training and while carrying out product assessments. We present a concise procedure to monitor panel performance based on classical statistical methods. The program includes tests for the ability to discriminate between products, repeatability of assessments, scale use, agreement between panelists and a principal component analysis map of panelist means across attributes. The algorithm is implemented in R – a state‐of‐the‐art, freely available statistical software package. The program output is summarized in graphs and tables. This easily applicable panel performance procedure is aimed at improving sensory practice, especially in areas where the use of highly complex systems is not feasible.     

Earlier onset of the spring phytoplankton bloom in lakes of the temperate zone in a warmer climate

The decoupling of trophic interactions is potentially one of the most severe consequences of climate warming. In lakes and oceans the timing of phytoplankton blooms affects competition within the plankton community as well as food–web interactions with zooplankton and fish. Using Upper Lake Constance as an example, we present a model‐based analysis that predicts that in a future warmer climate, the onset of the spring phytoplankton bloom will occur earlier in the year than it does at present. This is a result of the earlier occurrence of the transition from strong to weak vertical mixing in spring, and of the associated earlier onset of stratification. According to our simulations a shift in the timing of phytoplankton growth resulting from a consistently warmer climate will exceed that resulting from a single unusually warm year. The numerical simulations are complemented by a statistical analysis of long‐term data from Upper Lake Constance which demonstrates that oligotrophication has a negligible effect on the timing of phytoplankton growth in spring and that an early onset of the spring phytoplankton bloom is associated with high air temperatures and low wind speeds.     

Salt tolerance in Eucalyptus spp.: identity and response of putative osmolytes

In four species of salt-tolerant eucalypts (Eucalyptus raveretiana, E. spathulata, E. sargentii and E. loxophleba), we found substantial concentrations of quercitol – a cyclitol known for its accumulation in seeds of Quercus. Quercitol was absent in old foliage of E. globulus, a species noted for greater susceptibility to salinity, and also absent in the moderately tolerant E. camaldulensis, but, relative to other species, both had higher foliar concentrations of inositol. Simple sugars and cyclitols accumulated to osmotically significant concentrations in all species. The osmotic potential of expressed sap was always less than that of the external ‘soil’ solution and increasing salinity produced predictable reductions in growth and increases in ion concentrations in foliage of saplings of four eucalypt species. The more salt-tolerant species, E. spathulata, E. loxophleba and E. sargentii, were able to maintain well-regulated leaf Na⁺ concentrations even at 300 mol m⁻³ NaCl. These more salt-tolerant species also showed an apparent increase in net selectivity for K⁺ over Na⁺ as salinity increased, irrespective of the Na⁺ : Ca²⁺ ratio of the external medium (range 25 : 1 to 75 : 1; Ca²⁺ always ≥ 4.0 mol m⁻³). By contrast, E. globulus was unable to exclude Na⁺ when exposed to higher NaCl concentrations (e.g. 200 and 300 mol m⁻³). Carbon isotope signatures of foliage reflected imposed salinity but were not strongly enough correlated with growth to support previous suggestions that isotope discrimination be a means of evaluating salt tolerance. On the other hand, patterns of sugar and cyclitol accumulation should be further explored in eucalypts as traits contributing to salt tolerance, and with potential use as markers in breeding programmes.     

Flight characteristics of birds:

This is the first part of a study on flight characteristics of birds and presents an annotated list of flight speeds of 139 western Palearctic species. All measurements were taken with the same tracking radar and corrected for wind influence according to radar-tracked wind-measuring balloons. Graphical presentation of the birds' air speeds emphasizes the wide variation of speeds within species and allows easy comparison between taxonomic groups, species, and types of flight. Unlike theoretical predictions, speeds increase only slightly with size. The larger species seem to be increasingly limited to speeds close to their speed of minimum power consumption V_mp',. Released birds, apparently reluctant to depart with migratory speed, fly at considerably lower speeds than migrating conspecifics. While large birds seem to be limited to speeds around V _mp', smaller birds seem to be capable of selecting between various speeds, approaching predicted V _mp, when tending to remain airborne at low cost, but flying at much higher speeds when tending to make best progress at low cost (around predicted speed of maximum range V _mr,). Predictions of air speeds by aerodynamic models proved to be too low for small birds because the models do not account for the gain in speed attained by the reduction in profile drag during bounding flight of small passerines. The models predict excessive speeds for large birds because the power output available for flight seems to decline much more with size than previously assumed.     

Did Polyommatus icarus (Lepidoptera: Lycaenidae) have distinct glacial refugia in southern Europe? Evidence from population genetics

Pleistocene climatic oscillations strongly influenced the genetic composition of many species which are often divided into several genetic lineages. In this context, we studied the allozymes of a common and widely distributed butterfly, the common blue Polyommatus icarus, over a large part of Europe. The species had a rather high genetic diversity within populations with a strikingly high mean number of alleles per locus (2.98). In contrast, differentiation between populations was very low ( F _ST: 0.0187). Only a marginal trend of decline in genetic diversity from the south to the north was observed. Isolation-by-distance existed on a European scale ( r =  0.826), but not at a regional level. Regional differentiation between populations in western Germany was extremely low ( F _ST: 0.0041). It is probable that P. icarus was widely distributed in the Mediterranean region during the last ice age and expanded into central Europe in the postglacial period without major genetic erosion. Moderate present and past gene flow in an intact metapopulation structure may have occurred on local, regional and perhaps even continental scales.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 529–538.     

Indirect effects of soil moisture reverse soil C sequestration responses of a spring wheat agroecosystem to elevated CO2

Increased plant productivity under elevated atmospheric CO₂ concentrations might increase soil carbon (C) inputs and storage, which would constitute an important negative feedback on the ongoing atmospheric CO₂ rise. However, elevated CO₂ often also leads to increased soil moisture, which could accelerate the decomposition of soil organic matter, thus counteracting the positive effects via C cycling. We investigated soil C sequestration responses to 5 years of elevated CO₂ treatment in a temperate spring wheat agroecosystem. The application of ¹³C‐depleted CO₂ to the elevated CO₂ plots enabled us to partition soil C into recently fixed C (C_new) and pre‐experimental C (C_old) by ¹³C/¹²C mass balance. Gross C inputs to soils associated with C_new accumulation and the decomposition of C_old were then simulated using the Rothamsted C model ‘RothC.’ We also ran simulations with a modified RothC version that was driven directly by measured soil moisture and temperature data instead of the original water balance equation that required potential evaporation and precipitation as input. The model accurately reproduced the measured C_new in bulk soil and microbial biomass C. Assuming equal soil moisture in both ambient and elevated CO₂, simulation results indicated that elevated CO₂ soils accumulated an extra ～40–50 g C m^?2 relative to ambient CO₂ soils over the 5 year treatment period. However, when accounting for the increased soil moisture under elevated CO₂ that we observed, a faster decomposition of C_old resulted; this extra C loss under elevated CO₂ resulted in a negative net effect on total soil C of ～30 g C m^?2 relative to ambient conditions. The present study therefore demonstrates that positive effects of elevated CO₂ on soil C due to extra soil C inputs can be more than compensated by negative effects of elevated CO₂ via the hydrological cycle.     

Non-invasive determination of plant biomass with microwave resonators

Non-invasive and rapid determination of plant biomass would be beneficial for a number of research aims. Here, we present a novel device to non-invasively determine plant water content as a proxy for plant biomass. It is based on changes of dielectric properties inside a microwave cavity resonator induced by inserted plant material. The water content of inserted shoots leads to a discrete shift in the centre frequency of the resonator. Calibration measurements with pure water showed good spatial homogeneity in the detection volume of the microwave resonators and clear correlations between water content and centre frequency shift. For cut tomato and tobacco shoots, linear correlations between fresh weight and centre frequency shift were established. These correlations were used to continuously monitor diel growth patterns of intact plants and to determine biomass increase over several days. Interferences from soil and root water were excluded by shielding pots with copper. The presented proof of principle shows that microwave resonators are promising tools to quantitatively detect the water content of plants and to determine plant biomass. As the method is non-invasive, integrative and fast, it provides the opportunity for detailed, dynamic analyses of plant growth, water status and phenotype.     

Molecular phylogeny of the endemic East African flightless grasshoppers Altiusambilla Jago, Usambilla (Sjöstedt) and Rhainopomma Jago (Orthoptera: Acridoidea: Lentulidae)

Abstract.  A molecular phylogeny of endemic flightless grasshoppers is presented for the three Lentulidae genera Altiusambilla Jago, 1981 , Usambilla Sjöstedt, 1909 and Rhainopomma Jago, 1981 based on DNA sequences (16S rRNA locus). Parsimony, distance and likelihood reconstructions were performed using different assumptions on sequence evolution. The generated phylogenies agree in almost all parts of the calculated trees and support the monophyly of the observed genera. It was shown that Usambilla and Rhainopomma are more closely related to each other, Altiusambilla being a separate clade. However, the investigated East African lentulid genera are clearly separated from South African taxa, underlining the monophyly of East African genera. Usambilla olivacea is re-established. Populations of Rhainopomma montanum from the Taita Hills of Kenya and from the West Usambara mountains of Tanzania are two separate species not closely related to each other. Rhainopomma samples from the North Pare mountains of Tanzania belong to a hitherto undescribed species.     

High microbial activity on glaciers: importance to the global carbon cycle

Cryoconite holes, which can cover 0.1–10% of the surface area of glaciers, are small, water-filled depressions (typically <1 m in diameter and usually <0.5 m deep) that form on the surface of glaciers when solar-heated inorganic and organic debris melts into the ice. Recent studies show that cryoconites are colonized by a diverse range of microorganisms, including viruses, bacteria and algae. Whether microbial communities on the surface of glaciers are actively influencing biogeochemical cycles or are just present in a dormant state has been a matter of debate for long time. Here, we report primary production and community respiration of cryoconite holes upon glaciers in Svalbard, Greenland and the European Alps. Microbial activity in cryoconite holes is high despite maximum temperatures seldom exceeding 0.1 °C. In situ primary production and respiration in cryoconites during the summer is often comparable with that found in soils in warmer and nutrient richer regions. Considering only glacier areas outside Antarctica and a conservative average cryoconite distribution on glacial surfaces, we found that on a global basis cryoconite holes have the potential to fix as much as 64 Gg of carbon per year (i.e. 98 Gg of photosynthesis minus 34 Gg of community respiration). Most lakes and rivers are generally considered as heterotrophic systems, but our results suggest that glaciers, which contain 75% of the freshwater of the planet, are largely autotrophic systems.