Evaluating the effect of flowering age and forest structure on pollen productivity estimates

Pollen productivity estimates (PPEs) are indispensable prerequisites for quantitative vegetation reconstructions. Estimates from different European regions show a large variability and it is uncertain whether this reflects regional differences in climate and soil or is brought about by different assessments of vegetation abundance. Forests represent a particular problem as they consist of several layers of vegetation and many tree species only start producing pollen after they have attained ages of several decades. Here we used detailed forest inventory data from north-eastern Germany to investigate the effect of flowering age and understory trees on PPEs. Pollen counts were obtained from 49 small to medium sized lakes chosen to represent the different forest types in the region. Surface samples from lakes within a closed forest of Fagus yielded disproportionate amounts of Fagus pollen, increasing its PPE and the variability of all other estimates. These samples were removed from further analysis but indicate a high trunk-space component that is not considered in the Prentice–Sugita pollen dispersal and deposition model. Results of the restricted dataset show important differences in PPEs based on the consideration of flowering age and understory position. The effect is largest for slow growing and/or late flowering trees like Fagus and Carpinus while it is minimal for species that flower early in their development like Betula and Alnus. The large relevant source area of pollen (RSAP) of 7?km obtained in this study is consistent with the landscape structure of the region.     

Effects of increasing atmospheric CO2 on vegetation

The increasing atmospheric CO₂ concentration probably will have significant direct effects on vegetation whether predicted changes in climate occur or not. Averaging over many prior greenhouse and growth chamber studies, plant growth and yield have typically increased more than 30% with a doubling of CO₂ concentration. Such a doubling also causes stomatal conductance to decrease about 37%, which typically increases leaf temperatures more than 1 °C, and which may decrease evapotranspiration, although increases in leaf area counteract the latter effect. Interactions between CO₂ and climate variables also appear important. In one study the growth increase from near-doubled CO₂ ranged from minus 60% at 12 °C to 0% at 19 °C to plus 130% at 34 °C, suggesting that if the climate warms, the average growth response to doubled CO₂ could be consistently higher than the 30% mentioned above. Even when growing in nutrient-poor soil, the growth response to elevated CO₂ has been large, in contrast to nutrient solution studies which showed little response. Several studies have suggested that under water-stress, the CO₂ growth stimulation is as large or large than under wellwatered conditions. Therefore, the direct CO₂ effect will compensate somewhat, if not completely, for a hotter drier climate. And if any climate change is small, then plant growth and crop yields will probably be significantly higher in the future high-CO₂ world.     

On the permanent hip-stabilizing effect of atmospheric pressure

Hip joint dislocations related to total hip arthroplasty (THA) are a common complication especially in the early postoperative course. The surgical approach, the alignment of the prosthetic components, the range of motion and the muscle tone are known factors influencing the risk of dislocation. A further factor that is discussed until today is atmospheric pressure which is not taken into account in the present THA concepts. The aim of this study was to investigate the impact of atmospheric pressure on hip joint stability.     

The influence of vegetation activity on the Dole effect and its implications for changes in biospheric productivity in the mid-Holocene

The Dole effect is defined as the difference between the oxygen isotope composition of atmospheric oxygen and seawater (currently 23.5 parts per thousand) and reflects the balance between processes and fractionations associated with O₂ consumption and production by the terrestrial and marine biospheres. Isotopic records from ice cores and ocean sediments provide a means of assessing variations in the Dole effect during the late Quaternary but the biogeochemical interpretation of these changes is limited because we are currently unable to account adequately for vegetation effects on the global isotopic balance of atmospheric O₂. Here, I show that the previously unquantified influence of canopy transpiration on the isotopic composition of atmospheric water vapour now closes the mass balance budget for the isotopes of atmospheric O₂ under the current climate. Using this new finding, the effects of vegetation on the Dole effect have been assessed at the global scale for the mid-Holocene (6000 years ago). The results indicate that the small reduction in the Dole effect in the mid-Holocene represented a fall in the ratio of terrestrial to marine gross primary production from 1.8 to 1.0. Improved understanding of the environmental and physiological processes controlling the oxygen isotopic composition of plants and their feedback on the isotopes of atmospheric O₂ offers considerable promise in quantitatively accounting for the changes in biospheric productivity associated with the Dole effect over glacial–interglacial cycles. In addition, such work should provide an as yet unexploited basis for testing the results of climate models against the oxygen isotope composition of Quaternary plant fossils.     

Reassessing the impact of North Atlantic Oscillation on the sub-Saharan vegetation productivity

The Northern Atlantic Oscillation (NAO) has been shown to have a significant impact on the terrestrial ecosystem in the Sahelian region of Africa during the 1980s, and it has been strongly suggested that NAO may be a reliable predictor for the response of the Sahelian ecosystem to global climate variability. Using data from an extended period, we provide a reassessment for the impact of NAO on the Sahelian climate and ecosystem, and show that there is no consistent relationship between NAO and the ecosystem over Sahel. Statistical analysis on the NAO, vegetation, and precipitation data indicates that NAO influences the Sahelian vegetation productivity exclusively through its impact on precipitation. However, the relationship between the NAO index and Sahelian precipitation varies substantially with time. The correlation coefficient fluctuates between positive and negative values, and does not pass the 5% significance test during most of the twentieth century. The NAO system, although documented to govern the ecosystem dynamics over many other regions, does not have a consistent impact on the ecosystem over the Sahel. Therefore, the NAO index cannot produce a useful prediction on the ecosystem variability and changes in this region. This study provides an example that correlations based on short climate and ecological records (less than 20 years in this case) can be spurious and potentially misleading.     

Variation in the effects of vegetation and litter on recruitment across productivity gradients

1 We tested predictions about how the effect of vegetation and litter on seedling establishment varies among sites and herbaceous community types (sand barrens, prairies, fens). For both vegetation and litter, we also separated direct interactions from indirect interactions and interaction modifications along the gradient.
2 Although the intensity of the effects varied across sites, the direct effects of vegetation or litter alone were consistently facilitative along the productivity gradient. Predominance of facilitative effects may be due to the focus on the seedling establishment phase.
3 However, inclusion of indirect interactions and interaction modifications caused the net effects of both vegetation and litter to become largely negative. While one layer of biomass may be advantageous to ameliorate some moisture stress, the addition of another layer may be disadvantageous if this layer limits light proportionally more than it relieves moisture stress.
4 One exception to this pattern occurred at high productivity when the net effect of vegetation, even in the presence of litter, remained facilitative. The net effect of vegetation was competitive at low productivity and grew increasingly facilitative with productivity. Thus, indirect effects of litter may alter interaction patterns across this gradient.     

Deposition of spores and other particles on vegetation and soil

The rate of deposition of 20–30 μm diameter particles, including spores and pollen grains, on plant and other surfaces, is determined, first, by the frequency at which particles strike the surfaces and, secondly, by the proportion retained on the surface rather than rebounding into the airstream. Spores and pollen grains tagged with a radioactive marker were used to show that the impaction efficiency on leaves and stems depends very much on whether or not the surfaces are sticky or moist. If they are, the rate of deposition may approach that predicted aerodynamically. If the plant surfaces are dry, there is saltation of some spores and the effective rate of deposition is greatly reduced.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Meta-analysis of standing crop reduction byRhinanthus spp. and its effect on vegetation structure

We performed a quantitative literature review on the effect of the root hemiparasiteRhinanthus on vegetation standing crop. (1) Across all available experimental studies in mixed vegetation and in pots, above-ground biomass of co-occurring species is generally reduced, with on average 40% and 60% of the value in the controls respectively. Total above-ground biomass, as the sum of parasite biomass and biomass of co-occurring species, decreases in most cases. For field experiments this reduction amounts, on average, to 26% of the control value. This implies that there is no compensation by the parasites’ biomass for the loss of biomass of co-occurring species due to parasite infection. This can be attributed to the low resource-use efficiency of hemiparasites. Meta-analysis confirmed these trends. (2) In pot experiments, the negative effect of the parasite on the above-ground biomass of the host increases with the number ofRhinanthus plants. In field experiments, we found no relationship between biomass reduction andRhinanthus density. (3) Total above-ground biomass reduction in field experiments increases with standing crop of the vegetation. However, reduction in above-ground biomass of co-occurring species seems to decrease with standing crop. Functional and species diversity buffer the community against negative effects ofRhinanthus. (4) In field experiments, functional groups are affected differently byRhinanthus spp. Grasses and legumes are mostly strongly reduced by the hemiparasites. Non-leguminous dicots mostly benefit from the presence ofRhinanthus. (5) In one out of four weeding experiments,Rhinanthus spp. has a significant (positive) effect on species number. However, the response of plant diversity to invasion of parasitic plants requires further research.     

Measurement of the nucleation of atmospheric aerosol particles

The formation of new atmospheric aerosol particles and their subsequent growth have been observed frequently at various locations all over the world. The atmospheric nucleation rate (or formation rate) and growth rate (GR) are key parameters to characterize the phenomenon. Recent progress in measurement techniques enables us to measure atmospheric nucleation at the size (mobility diameter) of 1.5 (±0.4) nm. The detection limit has decreased from 3 to 1 nm within the past 10 years. In this protocol, we describe the procedures for identifying new-particle-formation (NPF) events, and for determining the nucleation, formation and growth rates during such events under atmospheric conditions. We describe the present instrumentation, best practices and other tools used to investigate atmospheric nucleation and NPF at a certain mobility diameter (1.5, 2.0 or 3.0 nm). The key instruments comprise devices capable of measuring the number concentration of the formed nanoparticles and their size, such as a suite of modern condensation particle counters (CPCs) and air ion spectrometers, and devices for characterizing the pre-existing particle number concentration distribution, such as a differential mobility particle sizer (DMPS). We also discuss the reliability of the methods used and requirements for proper measurements and data analysis. The time scale for realizing this procedure is 1 year.     

Forest vegetation affecting the deposition of atmospheric elements to soils

Atmospheric inputs of elements/ions into the soil through bulk precipitation and throughfall (precipitation below tree canopies) were monitored monthly at two forested catchments (Lesni Potok and Liz) in central and southwestern Bohemia, respectively. The annual deposition fluxes (expressed in μg/mg m^?2 yr^?1) of Al, As, Ba, Be, Ca, Cd, Cl^?, F^?, Fe, K, Mg, Mn, N_tot, Na, Ni, Pb, Rb, SO ₄ ^2? , Sr and Zn between 1997 and 2005 were calculated from their concentrations in monthly collected samples of both precipitation types. The flux of H⁺ was calculated from the monthly pH values as well. The more pristine character of the Liz catchment was manifested in lower inputs of anions of strong inorganic acids (mostly of anthropogenic origin) and of H⁺ in spite of higher precipitation amounts at the site. The comparison of fluxes in bulk precipitation (BP) and throughfall (TH) has shown significantly higher values for Rb, K, Mg, Mn, F^?, Ca, SO ₄ ^2? , Sr, Ba and Cl^? in the latter flux. It is declared that high fluxes of these elements/ions in TH significantly affect the forest soil water chemistry and that the forest vegetation significantly contributes to the mobilization of several elements in soil and to their redistribution throughout the soil profile.     

Comparing global models of terrestrial net primary productivity (NPP): importance of vegetation structure on seasonal NPP estimates

Estimates of the seasonal absorbed fraction of photosynthetically active radiation (FPAR) and net primary productivity (NPP) are compared among four production efficiency models (PEMs) and seven terrestrial biosphere models simulating canopy development. In addition, the simulated FPARs of the models are compared to the FASIR-FPAR derived from NOAA-AVHRR satellite observations. All models reproduce observed summergreen phenology of temperate deciduous forests rather well, but perform less well for raingreen phenology of savannas. Some models estimate a much longer active canopy in savannas than indicated by satellite observations. As a result, these models estimate high negative monthly NPP during the dry season. For boreal and tropical evergreen ecosystems, several models overestimate LAI and FPAR. When the simulated canopy does respond to unfavourable periods, the seasonal NPP is largely determined by absorbed photosynthetically active radiation (APAR). When the simulated canopy does not respond to unfavourable periods, the light use efficiency (LUE) influences the seasonal NPP more. However, the relative importance of APAR and LUE can change seasonally.