Afforestation effects on SOC in former cropland: oak and spruce chronosequences resampled after 13 years

Chronosequences are commonly used to assess soil organic carbon (SOC) sequestration after land‐use change, but SOC dynamics predicted by this space‐for‐time substitution approach have rarely been validated by resampling. We conducted a combined chronosequence/resampling study in a former cropland area (Vestskoven) afforested with oak (Quercus robur) and Norway spruce (Picea abies) over the past 40 years. The aims of this study were (i) to compare present and previous chronosequence trends in forest floor and top mineral soil (0–25 cm) C stocks; (ii) to compare chronosequence estimates with current rates of C stock change based on resampling at the stand level; (iii) to estimate SOC changes in the subsoil (25–50 cm); and (iv) to assess the influence of two tree species on SOC dynamics. The two chronosequence trajectories for forest floor C stocks revealed consistently higher rates of C sequestration in spruce than oak. The chronosequence trajectory was validated by resampling and current rates of forest floor C sequestration decreased with stand age. Chronosequence trends in topsoil SOC in 2011 did not differ significantly from those reported in 1998, however, there was a shift from a negative rate (1998: ?0.3 Mg C ha^?1 yr^?1) to no change in 2011. In contrast SOC stocks in the subsoil increased with stand age, however, not significantly (P = 0.1), suggesting different C dynamics in and below the former plough layer. Current rates of C change estimated by repeated sampling decreased with stand age in forest floors but increased in the topsoil. The contrasting temporal change in forest floor and mineral soil C sequestration rates indicate a shift in C source‐sink strength after approximately 40 years. We conclude that afforestation of former cropland within the temperate region may induce soil C loss during the first decades followed by a recovery phase of yet unknown duration.     

Re-evolution of lost mandibular teeth in frogs after more than 200 million years, and re-evaluating Dollo's law

Dollo's law states that structures that are evolutionarily lost will not be regained. Recent phylogenetic studies have revealed several potential examples in which Dollo's law seems to be violated, where lost structures appear to have been regained over evolutionary time. However, these examples have recently been questioned and suggested to be methodological artifacts. In this article, I document a striking and incontrovertible phylogenetic example of the re-evolution of a lost, complex structure: mandibular teeth in the frog genus Gastrotheca. I use a time-calibrated phylogeny for 170 amphibian species to show that mandibular teeth were lost in the ancestor of modern frogs at least 230 million years ago (Mya) and have been regained in the last ～ 5-17 My. I review recent studies on trait re-evolution and show that this long period of trait absence prior to re-acquisition is largely unprecedented. I also argue that there are several methodological issues that may cause trait re-evolution to be hardest to detect under those conditions when it is most likely to occur, leading to erroneous failures to reject Dollo's law. Finally, I discuss a mechanism that may facilitate trait re-evolution, and the evolution of mandibular teeth in frogs as an example of developmental constraint.     

Ten years after: Release cutting around old oaks still affects oak vitality and saproxylic beetles in a Norway spruce stand

1. It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long-lasting this effect is and how it affects saproxylic beetles.
2. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140-year-old retained oaks in a commercial forest with Norway spruce (Picea abies).
3. We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce.
4. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no-release control.
5. After 10 years we still found a higher abundance of oak-associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control.
6. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.

     

Material structure, stiffness, and adhesion: why attachment pads of the grasshopper (Tettigonia viridissima) adhere more strongly than those of the locust (Locusta migratoria) (Insecta: Orthoptera)

The morphology, ultrastrucure, effective elastic modulus, and adhesive properties of two different smooth-type attachment pads were studied in two orthopteran species. Tettigonia viridissima (Ensifera) and Locusta migratoria (Caelifera) have a similar structural organization of their attachment pads. They both possess a flexible exocuticle, where the cuticular fibrils are fused into relatively large rods oriented at an angle to the surface. The compliant material of the pad contributes to the contact formation with the substrate. However, the pad material structure was found to be different in these two species. L. migratoria pads bear a thick sub-superficial layer, as well as a higher density of rods. The indentation experiments showed a higher effective elastic modulus and a lower work of adhesion for L. migratoria pads. When the indentations were made at different depths, a higher effective elastic modulus was revealed at lower indentation depths in both species. This effect is explained by the higher stiffness of the superficial pad layer. The obtained results demonstrate a clear correlation between density of the fibres, thickness of the superficial layer, compliance of the pad, and its adhesive properties. Such material structures and properties may be dependent on the preferred environment of each species.     

The impact of the 2003 summer drought on the intra-annual growth pattern of beech (Fagus sylvatica L.) and oak (Quercus robur L.) on a dry site in the Netherlands

Climate change is expected to result in more extreme weather conditions over large parts of Europe, such as the prolonged drought of 2003. As water supply is critical for tree growth on many sites in North-Western Europe, such droughts will affect growth, species competition, and forest dynamics. To be able to assess the susceptibility of tree species to climate change, it is necessary to understand growth responses to climate, at a high temporal resolution. We therefore studied the intra-annual growth dynamics of three beech trees (Fagus sylvatica L.) and five oak trees (Quercus robur L.) growing on a sandy site in the east of the Netherlands for 2 years: 2003 (oak and beech) and 2004 (oak). Microcores were taken at 2-week intervals from the end of April until the end of October. Intra-annual tree-ring formation was compared with prior and contemporary records of precipitation and temperature from a nearby weather station.The results indicate that oak and beech reacted differently to the summer drought in 2003. During the drought, wood formation in both species ceased, but in beech, it recovered after the drought. The causes of species-specific differences in intra-annual wood formation are discussed in the context of susceptibility to drought.     

Changes in soil properties after afforestation of former intensively managed soils with oak and Norway spruce

In many European countries, surplus agricultural production and ecological problems due to intensive soil cultivation have increased the interest in afforestation of arable soils. Many environmental consequences which might rise from this alternative land-use are only known from forest establishment on less intensively managed or marginal soils. The present study deals with changes in soil properties following afforestation of nutrient-rich arable soils. A chronosequence study was carried out comprising seven Norway spruce (Picea abies (Karst.) L.) and seven oak (Quercus robur L.) stands established from 1969 to 1997 on former horticultural and agricultural soils in the vicinity of Copenhagen, Denmark. For comparison, a permanent pasture and a ca. 200-year-old mixed deciduous forest were included. This paper reports on changes in pH values, base saturation (BS_eff), exchangeable calcium, soil N pools (N_min contents), and C/N ratios in the Ap-horizon (0–25 cm) and the accumulated forest floor. The results suggest that afforestation slowly modifies soil properties of former arable soils. Land-use history seems to influence soil properties more than the selected tree species. An effect of tree species was only found in the forest floor parameters. Soil acidification was the most apparent change along the chronosequence in terms of a pH decrease from 6 to 4 in the upper 5 cm soil. Forest floor pH varied only slightly around 5. Nitrogen storage in the Ap-horizon remained almost constant at 5.5 Mg N ha^–1. This was less than in the mineral soil of the ca. 200-year-old forest. In the permanent pasture, N storage was somewhat higher in 0–15 cm depth than in afforested stands of comparable age. Nitrogen storage in the forest floor of the 0–30-year-old stands increased in connection with the build-up of forest floor mass. The increase was approximately five times greater under spruce than oak. Mineral soil C/N ratios ranged from 10 to 15 in all stands and tended to increase in older stands only in 0–5 cm depth. Forest floor C/N ratios were higher in spruce stands (26.4) as compared to oak stands (22.7). All stands except the youngest within a single tree species had comparable C/N ratios.     

Evaluation of corneal structures in myopic eyes more than twenty‐two years after photorefractive keratectomy

The aim of this study is to evaluate corneal epithelial thickness (CET), corneal densitometry (CD) in 84 myopic eyes (57 patients) more than 22 years after photorefractive keratectomy, using anterior segment‐optical coherence tomography (AS‐OCT) and Scheimpflug imaging system. The CET was significantly higher in all operated eyes than in unoperated eyes in central sector. A statistically significant increase in CD in corneal anterior layer of central sector was shown in groups of operated eyes with greater ablation depth respect to unoperated eyes. While there was no significant difference in CD between the operated eyes groups with lower ablation depth and unoperated eyes. A significant trend toward higher values in anterior CD with deeper ablations in central sector was found. These noninvasive imaging techniques allow to better understand the corneal remodeling process after photoablation and to monitor the patients over time.     

Analysis and application of NAT in Dongguan blood center more than 10 years

This report reviewed the efficacy of nucleic acid testing (NAT), derived from assaying and measuring data, using a Cobass201 system at the Dongguan blood center from 2008 to 2017. During this period, four blood screening models, each reflecting procedure improvements designed to improve residual risk (RR) assessment were assessed. A total of 716 846 blood donors were screened, detecting 1 395 positive by the mixed pool test, which were finally modified to 900 positive cases, after final detection by the separation-single test: detecting 6 HIV cases, 4 HCV cases and 890 HBV cases with a total positive rate of 1.25%. The lowest result was obtained from the twice administered enzyme-linked immunoassay (ELISA) test,used in conjunction with the single Cobas MPX v2.0 model,with rates of: 1/7 405 for HBV, 1/346 020 for HCV and 1/473 934 for HIV, respectively. NAT positive rate is not affected by different screening models. NAT is a recent detection method which can be used to good effect with ELISA, and is a worth while procedure for promoting blood transfusion safety.     

Site and temporal variation of soil respiration in European beech, Norway spruce, and Scots pine forests

Global warming and changes in rainfall amount and distribution may affect soil respiration as a major carbon flux between the biosphere and the atmosphere. The objectives of this study were to investigate the site to site and interannual variation in soil respiration of six temperate forest sites. Soil respiration was measured using closed chambers over 2 years under mature beech, spruce and pine stands at both Solling and Unterlüß, Germany, which have distinct climates and soils. Cumulative annual CO₂ fluxes varied from 4.9 to 5.4 Mg C ha^?1 yr^?1 at Solling with silty soils and from 4.0 to 5.9 Mg C ha^?1 yr^?1 at Unterlüß with sandy soils. With one exception soil respiration rates were not significantly different among the six forest sites (site to site variation) and between the years within the same forest site (interannual variation). Only the respiration rate in the spruce stand at Unterlüß was significant lower than the beech stand at Unterlüß in both years. Soil respiration rates of the sandy sites at Unterlüß were limited by soil moisture during the rather dry and warm summer 1999 while soil respiration at the silty Solling site tended to increase. We found a threshold of ?80 kPa at 10 cm depth below which soil respiration decreased with increasing drought. Subsequent wetting of sandy soils revealed high CO₂ effluxes in the stands at Unterlüß. However, dry periods were infrequent, and our results suggest that temporal variation in soil moisture generally had little effect on annual soil respiration rates. Soil temperature at 5 cm and 10 cm depth explained 83% of the temporal variation in soil respiration using the Arrhenius function. The correlations were weaker using temperature at 0 cm (r² = 0.63) and 2.5 cm depth (r² = 0.81). Mean Q₁₀ values for the range from 5 to 15 °C increased asymptotically with soil depth from 1.87 at 0 cm to 3.46 at 10 cm depth, indicating a large uncertainty in the prediction of the temperature dependency of soil respiration. Comparing the fitted Arrhenius curves for same tree species from Solling and Unterlüß revealed higher soil respiration rates for the stands at Solling than in the respective stands at Unterlüß at the same temperature. A significant positive correlation across all sites between predicted soil respiration rates at 10 °C and total phosphorus content and C‐to‐N ratio of the upper mineral soil indicate a possible effect of nutrients on soil respiration.     

The symmetry of competitive interactions in mixed Norway spruce,silver fir and European beech forests

Questions

We aim for a better understanding of the different modes of intra‐ and inter‐specific competition in two‐ and three‐species mixed‐forests. How can the effect of different modes of competitive interactions be detected and integrated into individual tree growth models? Are species interactions in spruce–fir–beech forests more associated with size‐symmetric or size‐asymmetric competition? Do competitive interactions between two of these species change from two‐ to three‐species mixtures?

Location

Temperate mixed‐species forests in Central Europe (Switzerland).

Methods

We used data from the Swiss National Forest Inventory to fit basal area increment models at the individual tree level, including the effect of ecological site conditions and indices of size‐symmetric and size‐asymmetric competition. Interaction terms between species‐specific competition indices were used to disentangle significant differences in species interactions from two‐ to three‐species mixtures.

Results

The growth of spruce and fir was positively affected by increasing proportions of the other species in spruce–fir mixtures, but negative effects were detected with increasing presence of beech. We found that competitive interactions for spruce and fir were more related to size‐symmetric competition, indicating that species interactions might be more associated with competition for below‐ground resources. Under constant amounts of stand basal area, the growth of beech clearly benefited from the increasing admixture of spruce and fir. For this species, patterns of size‐symmetric and size‐asymmetric competitive interactions were similar, indicating that beech is a strong self‐competitor for both above‐ground and below‐ground resources. Only for silver fir and beech, we found significant changes in species interactions from two‐ to three‐species mixtures, but these were not as prominent as the effects due to differences between intra‐ and inter‐specific competition.

Conclusions

Species interactions in spruce–fir–beech, or other mixed forests, can be characterized depending on the mode of competition, allowing interpretations of whether they occur mainly above or below ground level. Our outcomes illustrate that species‐specific competition indices can be integrated in individual tree growth functions to express the different modes of competition between species, and highlight the importance of considering the symmetry of competition alongside competitive interactions in models aimed at depicting growth in mixed‐species forests.

     

Seasonal changes of leaf surface contamination in beech, oak, and ginkgo in relation to leaf micromorphology and wettability

The leaf surfaces of beech, oak and ginkgo have been investigated with respect to contamination with particles during one growing season. Based on the observation that particles are removed from water-repellent leaves by rain (Lotus effect) the three species were selected because they differ in leaf surface micromorphology and wettability. Leaves of beech are smooth, lacked wax crystals and were ±wettable. Those of ginkgo were rough because their cells were convex and were densely covered by wax crystals, resulting in permanent water repellency. Leaves of oak were covered by waxes and were water repellent when young, but, a few weeks after leaf expansion had ceased the waxes were rapidly eroded. These differences in wettability resulted in different amounts of contamination. Ginkgo collected a very small number of particles during the whole vegetation period. In beech the contamination was significantly higher, but fairly constant, whereas oak leaves accumulated particles with age.     

Meiotic nondisjunction of chromosomes 1, 17, 18, X, and Y in men more than 80 years of Age

In order to evaluate a possible paternal age effect, testicular sperm cells from three men aged 81, 82, and 83 yr were analyzed by two-color- and three-color-fluorescence in situ hybridization for disomy rates of chromosomes 1, 17, 18, X, and Y as well as for diploidy frequencies. A minimum of 1500 sperm cells per donor and probe was evaluated due to the low number of spermatozoa in the preparations. Diploidy and disomy frequencies were in the same range as found in men aged <30 yr, a slight increase only being noticed for XY nuclei.     

Mechanical properties and water vapor transmission in some blends of cassava starch edible films

The continuous increase of consumer interest in quality, convenience and food quality has encouraged further research into edible films and coatings from natural polymers, such as polysaccharides. Ecoefficient products are the new generation of biobased products prepared with sustainable materials, that agree with ecological and economic requirements including environmentally acceptable disposal of post-user waste. The numerous potential applications of natural polymers such as polysaccharides stimulated the study with edible films based on cassava starch. Blends of glycerol (GLY) and polyethylene glycol (PEG) as plasticizers, and glutaraldehyde (GLU) as crosslinking agent were prepared in order to determine the mechanical properties and water vapor transmission of those films. A response surface methodology was applied on the results to identify the blend with the best mechanical properties and lowest water vapor transmission. The crosslinking effect of glutaraldehyde in the films can be observed. The plasticizing action of polyethylene glycol was restrained by more than 0.5 g of glutataraldehyde. The use of glycerol was less evident for this property even after 284 h of contact time with water vapor.     

Investigation into the structural, morphological, mechanical and thermal behaviour of bacterial cellulose after a two-step purification process

Bacterial cellulose (BC) is a natural hydrogel, which is produced by Acetobacter xylinum (recently renamed Gluconacetobacter xylinum) in culture and constitutes of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. Here, a two-step purification process is presented that significantly improves the structural, mechanical, thermal and morphological behaviour of BC sheet processed from these hydrogels produced in static culture. Alkalisation of BC using a single-step treatment of 2.5 wt.% NaOH solution produced a twofold increase in Young's modulus of processed BC sheet over untreated BC sheet. Further enhancements are achieved after a second treatment with 2.5 wt.% NaOCl (bleaching). These treatments were carefully designed in order to prevent any polymorphic crystal transformation from cellulose I to cellulose II, which can be detrimental for the mechanical properties. Scanning electron microscopy and thermogravimetric analysis reveals that with increasing chemical treatment, morphological and thermal stability of the processed films are also improved.     

Four years continuous record of CH4-exchange between the atmosphere and untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany

In order to gain information about seasonal and interannual variations of CH₄-fluxes at a spruce control site, a limed spruce site and a beech site of the Höglwald Forest, Bavaria, Germany, complete annual cycles of CH₄-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH₄ fluxes observed for the different sites were: +12.4 to –69.4 g CH₄ m^–2 h^–1 (spruce control site), +11.7 to –51.4 g CH₄ m^–2 h^–1 (limed spruce site), and –4.4 to –167.3 g CH₄ m^–2 h^–1 (beech site). Lowest rates of atmospheric CH₄-uptake or even a weak net-emission of CH₄ by the soils were observed during winter/spring times, whereas highest rates of CH₄-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH₄-uptake rates were –1.82 kg CH₄-C ha^–1 yr^–1 at the spruce control site, –1.31 kg CH₄-C ha^–1 yr^–1 at the limed spruce site, and –4.84 kg CH₄-C ha^–1 yr^–1 at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH₄-fluxes of approx. 1 kg CH₄-C ha^–1 yr^–1, multiple year measurements of CH₄-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH₄. By comparison of CH₄-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH₄-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH₄-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH₄-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH₄ fluxes were soil moisture and soil temperature. Field measurements of CH₄ concentrations in the soil profile and laboratory measurements of CH₄-oxidation and CH₄-production activity on soil samples taken from different soil depths showed that the CH₄-flux at the Höglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH₄ within the soil. Highest CH₄-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH₄-production activity was found in the organic layer.