. Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

/pdf/estimates-of-global-terrestrial-isoprene-emissions-using-2inhk36wkp.pdf

Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)

This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

The talk with present the key results of the IPCC Working Group III 5th assessment report. Concluding four years of intense scientific collaboration by hundreds of authors from around the world, the report responds to the request of the world's governments for a comprehensive, objective and policy neutral assessment of the current scientific knowledge on mitigating climate change. The report has been extensively reviewed by experts and governments to ensure quality and comprehensiveness.

Climate change 2014 - Mitigation of climate change

Evidence is mounting that the immense diversity of microorganisms and animals that live belowground contributes significantly to shaping aboveground biodiversity and the functioning of terrestrial ecosystems. Our understanding of how this belowground biodiversity is distributed, and how it regulates the structure and functioning of terrestrial ecosystems, is rapidly growing. Evidence also points to soil biodiversity as having a key role in determining the ecological and evolutionary responses of terrestrial ecosystems to current and future environmental change. Here we review recent progress and propose avenues for further research in this field.

Belowground biodiversity and ecosystem functioning

Contents
 	Summary	30	
I.	Allocation in perspective	31	
II.	Topics of this review	32	
III.	Methodology	32	
IV.	Environmental effects	33	
V.	Ontogeny	36	
VI.	Differences between species	40	
VII.	Physiology and molecular regulation	41	
VIII.	Ecological aspects	42	
IX.	Perspectives	45	
 	Acknowledgements	45	
 	References	45	
 	Appendices A1–A4	49	


Summary
We quantified the biomass allocation patterns to leaves, stems and roots in vegetative plants, and how this is influenced by the growth environment, plant size, evolutionary history and competition. Dose–response curves of allocation were constructed by means of a meta-analysis from a wide array of experimental data. They show that the fraction of whole-plant mass represented by leaves (LMF) increases most strongly with nutrients and decreases most strongly with light. Correction for size-induced allocation patterns diminishes the LMF-response to light, but makes the effect of temperature on LMF more apparent. There is a clear phylogenetic effect on allocation, as eudicots invest relatively more than monocots in leaves, as do gymnosperms compared with woody angiosperms. Plants grown at high densities show a clear increase in the stem fraction. However, in most comparisons across species groups or environmental factors, the variation in LMF is smaller than the variation in one of the other components of the growth analysis equation: the leaf area : leaf mass ratio (SLA). In competitive situations, the stem mass fraction increases to a smaller extent than the specific stem length (stem length : stem mass). Thus, we conclude that plants generally are less able to adjust allocation than to alter organ morphology.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.2011.03952.x

Biomass allocation to leaves, stems and roots: meta-analyses of interspecific variation and environmental control

(1)*Corresponding author: Address: Kreuzeckbahnstr.19 82467 Garmisch-Partenkirchen, Germany Phone: +49-8821-183130 E-mail: hans.papen@imk.fzk.de Introduction Approximately 65% of the African continent could be considered as native savannah in the past, but large portions of this area have been converted to agricultural land, namely rangeland and low intensity cropping systems. Land conversion triggers mineralization processes and a rapid reduction of soil carbon and nitrogen. It can be hypothesized that the conversion is accompanied by an increased loss of gaseous C and N compounds, which could in turn affect the carbon and nitrogen balance from the landscape to sub-continental scale. Dano Bontioli

https://publikationen.bibliothek.kit.edu/220072242/3815254

Soil-atmosphere exchange of N₂O, NO, CH₄ and CO₂ in natural savannah and savannah converted to agricultural land in Burkina Faso (W.Africa)

The application of livestock slurry in soils can lead to nitrogen (N) losses through ammonia (NH3 ) emission or nitrate (NO3 - ) leaching. Oxidized biochar has great potential to mitigate N losses due to its strong adsorption capacity, however, the effects of oxidized biochar in different soils treated with slurry are currently unclear. Here, we investigated the effect of untreated and oxidized biochar (applied at a rate of 50 kg C m-3 slurry) on reducing N losses in a laboratory experiment with three different soils (loamy sand, sandy loam, loam), amended with cattle slurry at an application rate of 73 kg N ha-1 . Oxidized biochar reduced NH3 emissions by 64-75% in all soils, while untreated biochar reduced NH3 emissions by 61% only in the loamy sand. Oxidized biochar significantly reduced the NO3 - content in the soil solution of the loamy sand in the early phase of the incubation, and it led to significantly higher NO3 - concentration in the same soil compared to slurry-only treatment at the end of the experiment, indicating a significant increase in NO3 - retention in this poor soil. We conclude that oxidized biochar can reduce N losses, both in the form of NH3 emission and NO3 - leaching, from cattle slurry applied to soil, particularly in soil with soil organic carbon (SOC) content < 1% and pH < 5, i.e., serve as a means for improving the quality of marginal and acidic soils. This article is protected by copyright. All rights reserved.

Improving nitrogen retention of cattle slurry with oxidized biochar - An incubation study with three different soils.

&amp;lt;p&amp;gt;Traditional destructive plant and soil water isotopic monitoring has provided important insights into root water uptake changes in drought and evapotranspiration partitioning across scales. Recently, non-destructive isotopic monitoring coupled with laser-based spectroscopy allow a better understanding of these and other questions with a higher spatial and temporal resolution. We investigated the changes in root water uptake profiles and eco-physiological characteristics (e.g. stomatal conductance, leaf water potential) of the grassland species &amp;lt;em&amp;gt;Centaurea jacea&amp;lt;/em&amp;gt; under varying environmental conditions (i.e. atmospheric demand, soil water availability) with a labeling experiment in fully-controlled laboratory conditions. We measured non-destructively the isotopic composition of soil water and of plant transpiration. With these measurements, daily root water uptake profiles were obtained using a multi-source mixing model embedded in a Bayesian statistical framework. We analyzed the daily changes of these profiles together with changes in environmental conditions and plant physiology-related variables to discover potential adaptation strategies of &amp;lt;em&amp;gt;C. jacea&amp;lt;/em&amp;gt; to water scarcity. Even in a dry soil (~ 10% soil water content), the studied grassland species was able to sustain high transpiration rates. This was accompanied by a very negative leaf water potential (~-3 MPa). Root water uptake profiles in both dry and wet conditions were very similar: root water uptake was highest in the soil layer 0-15 cm (up to 87%) and second highest (up to 40%) in the soil layer 45-60 cm. Before soil water content dropped below 12%, transpiration rate was mainly controlled by vapor pressure deficit. After this, a reduction of canopy conductance restricted gas leaf exchange. Instantaneous water use efficiency dropped when the soil was very dry, but intrinsic water use efficiency was maintained. Our comprehensive data set of plant-related and environmental variables allowed us to investigate at a 1-cm and daily scales the plant&amp;amp;#8217;s response to varying hydro-climatic conditions.&amp;lt;/p&amp;gt; 

Investigating root water uptake dynamics of a grassland species under varying hydro-climatic conditions with non-destructive isotopic monitoring

Self-succession of winter wheat (WW) in crop rotations results in substantial yield decline. This decline has been mostly attributed to the soil-borne fungus Gaeumannomyces graminis var. tritici (Ggt; take-all) causing earlier root senescence. A broad shift in the soil microbial community has also recently been proposed to confound this effect even in years without significant Ggt infestation in the field. We aimed to establish a mechanistic basis for the relationship between rotational position of WW and yield decline at an early wheat growth stage. To this end, an outdoor experiment with 1 m deep rhizotrons was set up using a sandy loam soil. WW was grown in soil after oilseed rape (KW1), soil after one season of WW (KW2) and soil after three successive seasons of WW (KW4). The plants were grown until the beginning of stem elongation (BBCH 30). At harvest, both shoot and root dry weight were markedly affected by the preceding crop, with a pronounced reduction of plant biomass of KW2 (-43%) and KW4 (-45%) compared to KW1. At BBCH 30, KW1 soil had much lower mineral N compared to KW2 (-49%) and KW4 (-39%). Non-purgeable organic C, a readily available energy source for soil microorganisms, was further reduced in successive WW rotations compared to KW1. Increased NH4+ and NPOC concentrations were found in root-affected soil compared to root-free bulk soil, indicating a strong hotspot for organic N mineralization in the rhizosphere. At the same time, the markedly higher shoot N concentration led to a lower C:N ratio of 31 for KW1 compared to KW2 and KW4, which had a C:N ratio of 46 and 44, respectively, suggesting a better exploitation of soil mineral N sources by KW1. In contrast, microbial biomass C and N were higher in KW2 and KW4 compared to KW1, pointing to enhanced microbial N immobilization in KW2 and KW4. The higher C:N ratio of WW straw compared to oilseed rape residues that are returned to the soil following harvest, obviously stimulated immobilization of soil N in microbial biomass, thereby limiting the availability of N for WW growth in KW2 and KW4. Root growth traits exhibited a strong response to WW rotational position, with higher root tissue density, root mean diameter and lower specific root length for KW1 compared to KW2 and KW4. Root length density (RLD) was overall higher in KW1 compared to KW2 (-29%) and KW4 (-31%), especially at 0-30 cm soil depth. Interestingly, higher RLD values for KW1 were also observed at the lowest depth of 60-100 cm compared to KW4, suggesting a strong effect of rotational position on nutrient accessibility in the subsoil. Successive WW invested more in acquisitive root traits that did not compensate for the reduction of biomass production. Our results highlight the effect of rotational position of WW on soil and plant properties and provide guidance for management-based adaptations at field level to improve WW productivity. 

Nicolas Brüggemann

Papers

Soil-atmosphere exchange of N₂O, NO, CH₄ and CO₂ in natural savannah and savannah converted to agricultural land in Burkina Faso (W.Africa)

Improving nitrogen retention of cattle slurry with oxidized biochar - An incubation study with three different soils.

Investigating root water uptake dynamics of a grassland species under varying hydro-climatic conditions with non-destructive isotopic monitoring

Preceding crop history modulates the early growth of winter wheat by influencing root growth dynamics and rhizosphere processes