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.     

Methods to Reduce Avian Bycatch in Small Mammal Studies Using Snap Traps

ABSTRACT Avian bycatch, a common and undesired occurrence in small mammal studies, should be minimized by researchers. We examined effects of trap covering, treadle color (copper or yellow plastic), trap size (mouse or rat), and trap weathering (traps <1 yr or ≥ 1 yr old) on avian bycatch during 3 years. We found that covered traps caught 81% fewer birds and 70% fewer small mammals than did uncovered traps, that mouse traps caught 30% more birds and 38% more small mammals than did rat traps, and no capture differences for treadle color or trap weathering. Covered traps effectively reduced avian bycatch and should be used when reduced small-mammal capture rates are acceptable.     

Last‐century changes of alpine grassland water‐use efficiency: a reconstruction through carbon isotope analysis of a time‐series of Capra ibex horns

The ecophysiological response of an alpine grassland to recent climate change and increasing atmospheric CO₂ concentration was investigated with a new strategy to go back in time: using a time‐series of Capra ibex horns as archives of the alpine grasslands' carbon isotope discrimination (¹³Δ). From the collection of the Natural History Museum of Bern, horns of 24 males from the population of the Augstmatthorn–Brienzer Rothorn mountains, Switzerland, were sampled covering the period from 1938 to 2006. Samples were taken from the beginning of each year‐ring of the horns, representing the beginning of the horn growth period, the spring. The horns' carbon ¹³C content (Δ¹³C) declined together with that of atmospheric CO₂ over the 69‐year period, but ¹³Δ increased slightly (+0.4‰), though significantly (P<0.05), over the observation period. Estimated intercellular CO₂ concentration increased (+56 μmol mol^?1) less than the atmospheric CO₂ concentration (+81 μmol mol^?1), so that intrinsic water‐use efficiency increased by 17.8% during the 69‐year period. However, the atmospheric evaporative demand at the site increased by approximately 0.1 kPa between 1955 and 2006, thus counteracting the improvement of intrinsic water‐use efficiency. As a result, instantaneous water‐use efficiency did not change. The observed changes in intrinsic water‐use efficiency were in the same range as those of trees (as reported by others), indicating that leaf‐level control of water‐use efficiency of grassland and forests followed the same principles. This is the first reconstruction of the water‐use efficiency response of a natural grassland ecosystem to last century CO₂ and climatic changes. The results indicate that the alpine grassland community has responded to climate change by improving the physiological control of carbon gain to water loss, following the increases in atmospheric CO₂ and evaporative demand. But, effective leaf‐level water‐use efficiency has remained unchanged.     

Energetics of reproduction: consequences of divergent selection on egg size, food limitation, and female age for egg composition and reproductive effort in a butterfly

Using lines artificially selected on egg size and being subjected to a restricted and an unrestricted feeding treatment, we examined the relationships between egg size, egg number, egg composition, and reproductive investment in the butterfly Bicyclus anynana . Despite a successful manipulation of egg size, correlated responses to selection in larval time, pupal mass, pupal time, longevity, fecundity, or the amount of energy allocated to reproduction were virtually absent. Thus, there was no indication for an evolutionary link between offspring size and reproductive investment. Egg composition, in contrast, was affected by selection, with larger eggs containing relatively more lipid and water, but less protein and energy compared to smaller eggs. Hence, females producing large eggs did not have to sacrifice fecundity due to adjustments in egg composition. Food limitation per se caused only minor changes in egg composition, and there was no general reduction in egg provisioning with female age. The latter was restricted to food-limited females, whereas egg quality remained remarkably similar throughout the females' life in control groups. We conclude that neglecting changes in biochemical egg composition, depending on genetic background, food availability, and female age, may introduce substantial error when estimating reproductive effort, and may ultimately lead to invalid conclusions.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 403–418.     

Motility Events of Trichocyst Insertion in Paramecium tetraurelia*

SYNOPSIS. Following electroshock-induced extrusion of its inserted trichocysts, Paramecium tetraurelia rapidly begins replacement of the population of lost organelles. Light microscopy of the cortical insertion of new trichocysts reveals a series of characteristic motility activities. An uninserted trichocyst in the cyclotic flow of the cell appears to be “captured” and removed to the noncyclotic, subcortical regions. The trichocyst then makes a series of saltatory motions which apparently serve to transport it to the cortex, with proper orientation (tip first) for insertion. Trichocyst saltations end with either cortical insertion of the organelle, or return to cyclosis. If the trichocyst is inserted, it makes a series of unique pivoting movements around the motionless tip. This form of motility, termed “wobble,” continues for a short period of time. After cessation of wobble, the insertion of the trichocyst is apparently complete, since no further motility is observed. With the aid of these observations it was possible to identify saltatory motility as the means for transporting trichocysts to the cortex for insertion, and also to observe a motility of unknown significance (wobble) apparently associated with the process of cortical insertion.     

Preparation, Properties, and Composition of Nereis vitellin, the Yolk Protein of the Annelid, Nereis virens

In the literature, oogenesis in nereid annelids is considered to be a model system because, unlike other system studied, nereid oocytes are thought to synthesize the bulk of their yolk protein themselves. As the first step to test the validity of this hypothesis, nereid yolk protein was characterized biochemically. Vitellin, the main fraction of the soluble yolk proteins, was prepared from Nereis virens oocytes. Preparation, purification, and some physical characteristics of this green-colored protein Nereis vitellin are described. The molecular weight was determined by gel chromatography as 420,000 daltons. With regard to the amino acid composition, Nereis vitellin was found to resemble both insect vitellins and an average protein, as defined by other authors. Methionine and cysteine were found in traces only. By staining procedures, Nereis vitellin was characterized as lipoglycoprotein. Nereis vitellin was also prepared from the coelomic fluid of gravid females of Nereis virens .     

Colonization history in Fennoscandian rodents

Fennoscandia probably constitutes one of the best places on earth to study faunal history. During the height of the most recent glacial period Fennoscandia was completely covered with ice. Thus, the majority of extant species must originate from ancestors who survived the latest glaciation in non-glaciated areas outside Fennoscandia. Moreover, the geography and geological history of Fennoscandia suggests that post-glacial recolonization by land mammals must have been restricted to specific routes in time and space. Phylogeographic surveys of mitochondrial DNA (mtDNA) variation in Fennoscandian rodents have demonstrated that glacial history and patterns of post-glacial colonization have played a major role in shaping present day patterns of genetic differentiation within species. Thus, the genetic imprints of historical demographic conditions and vicariant geographic events have been retained within species and can be used to infer the history of populations. The field vole (Microtus agrestis) is used to illustrate these data and processes. Comparisons are made with phylogeographic surveys of the bank vole (Clethrionomys glareolus) , the eastern house mouse (Mus musculus) and the wood lemming (Myopus schisticolor) as well as a few other species for which less extensive studies have been performed. The main patterns of post-glacial colonization of Fennoscandia by rodents are described. The effects of timing and patterns of colonization on contemporary population genetic structure and levels of genetic variation are discussed. Specifically, the effects of hybridization and introgression as well as founder events and bottlenecks are explored.