Monday paper: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes


Thaysen, E. M., Jessen, S., Ambus, P., Beier, C., Postma, D., and Jakobsen, I.. 2014. Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes. Biogeosciences, 11, 1077-1084. DOI:10.5194/bg-11-1077-2014.

Abstract

Dissolved inorganic carbon (DIC) fluxes across the vadose zone are influenced by a complex interplay of biological, chemical and physical factors. A novel soil mesocosm system was evaluated as a tool for providing information on the mechanisms behind DIC percolation to the groundwater from unplanted soil. Carbon dioxide partial pressure (pCO2), alkalinity, soil moisture and temperature were measured with depth and time, and DIC in the percolate was quantified using a sodium hydroxide trap. Results showed good reproducibility between two replicate mesocosms. The pCO2 varied between 0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L−1. The measured cumulative effluent DIC flux over the 78-day experimental period was 185–196 mg L−1 m−2 and in the same range as estimates derived from pCO2 and alkalinity in samples extracted from the side of the mesocosm column and the drainage flux. Our results indicate that the mesocosm system is a promising tool for studying DIC percolation fluxes and other biogeochemical transport processes in unsaturated environments.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Monday paper: Modelling microbial exchanges between forms of soil nitrogen in contrasting ecosystems


Pansu, M., Machado, D., Bottner, P., and Sarmiento, L.: Modelling microbial exchanges between forms of soil nitrogen in contrasting ecosystems, Biogeosciences, 11, 915-927, doi:10.5194/bg-11-915-2014, 2014.

The questions

It is well known that N and C combine to form organic molecules due to biological processes, although they come together from different pathways. C is extracted from carbon dioxide in the atmosphere and used to form reduced molecules thanks to photosynthesis, while mineral forms of nitrogen are extracted from soil by plant roots, just to be processed in a chain of links controlled by microbial activity. Although N and C cycles are strongly linked, published models of the N cycle are not always linked to the C cycle and are sometimes not fully mechanistic. After reviewing recent research, the authors of the paper raise some questions:

  • Can the rates of direct enzymatic C and N assimilation be considered to be the same (as in the direct microbial assimilation of all available organic N scheme)?
  • Can the transfers of C by microbial mortality and respiration cause simultaneous transfers of N into labile humus and inorganic forms to balance the microbial C:N ratio?
  • Can the assimilation of inorganic N be modelled to sustain microbial activity in the case of an N deficit during conversion of organic forms?
  • Can microorganisms be assumed to assimilate N from labile and stable organic molecules as well as N from the inorganic N pool?

 

Flow diagram for the MOMOS model coupled with a soil water module and a production module. MB is the microbial biomass, VL is the labile necromass (NC), VS is the stable necromass, HL is the labile humus and HS is the stable humus. Click to access the paper.
Flow diagram for the MOMOS model coupled with a soil water module and a production module. MB is the microbial biomass, VL is the labile necromass (NC), VS is the stable necromass, HL is the labile humus and HS is the stable humus. Click to download the paper.

The answers

The paper concludes that the hypothesis of microbial homeostasis can provide robust predictions at global scale, although microbial populations are not always independent of the external constraints. When an altitudinal transect is studied, microbial C:N ratios could be better modelled as decreasing during incubation and increasing with increasing C storage in cold conditions, where CO2-C respiration is reduced by low temperatures. The ratio of potentially mineralizable-15N/inorganic-15N and the 15N stock in plant debris and microorganisms was modelled as increasing with altitude, whereas the 15N storage in stable humus was modelled as decreasing with altitude. This predicts that there is a risk that mineralization of organic reserves in cold areas may increase global warming.

Biogeosciences

Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Will drinking tea get us thinking about soils? Yes, but only if you help us spread the word!


Taru Lehtinen
PhD candidate at the Faculty of Life and Environmental Sciences, University of Iceland
tmk2@hi.is

TeaBags-Taru-Summer2013
Meet Taru at EGU2014 in sessions SSS10.3 and SSS10.8.

The Tea Bag Index Project wants to create a global map on decomposition with the help of citizen scientists. We use teabags to collect vital information on the global carbon cycle. With our protocol (see our web page and our article: Keuskamp et al., 2013), citizen scientists worldwide can collect data without much effort or instrumentation.

Tea Bag Index Project developed a simple and cheap method, which anyone can use to measure decomposition in the soil, simply by burying teabags. Tea Bag Index Project want to gather data points from all over the globe through the involvement of citizen scientists.

Two main questions to be answered with the data gathered:

  1. How do environmental conditions determine the speed of decomposition?
  2. How do environmental conditions determine how much is broken down?

Eventually, a global soil map of decomposition will be created that can be used for educational purposes and to make current climate models even more accurate.

What is about?

Decomposition (the decay of organic material) is a critical process for life on earth. Through decomposition, nutrients become available for plants and soil organisms to use as a food source in their metabolism and growth. When plant material decomposes, it loses weight and releases the greenhouse gas carbon dioxide (CO2) into the atmosphere. In cold environments, breakdown is slower than in warm environments, meaning more carbon is stored in the soil and less CO2 is released. Factors like moisture content, acidity, or nutrient content of soils can also influence how quickly plant material decomposes

IMG_0454

For better insight into global CO2 emissions from soils it is important to know more about decomposition in those different soils. Such an insight is important to improve climate models that show CO2 fluxes. To clarify the picture of global decomposition, we need a lot of information on different soil characteristics and related decomposition rates around the world. Large efforts have been taken to create a soil map of the world; however, predictions on the relations between soil an decomposition are often imprecise. It would be a great improvement if we could actually measure decomposition (rate and degree) globally.

Tea Bag Index Project developed a simple and cheap method to measure decomposition rate and degree. By burying everyday tea bags.

As tea is plant material, the weight loss of nylon teabags over time represents the decomposition of the plant material within an ecosystem. After three months buried in the soil of interest, the bags are dug up, dried and weighed. By burying two types of tea with different decomposition rates, we obtain information on how much and how fast plant material is broken down.

The importance of this research

Efforts have already been taken to map global soil and climate conditions; however an index for decomposition rate is still missing. Predictions of decomposition used in climate models are often imprecise.

The idea is to use the Tea Bag Index to collect data from around the world to feed databases in the global soil map, and to get as many citizen scientists as possible involved. This crowdsourcing approach will strengthen the dataset; due to the power-by-numbers principle; and it will increase awareness of soil science at the same time.

Soil receives very little attention in media coverage of environmental issues. Tea Bag Index Project specifically aims to involve school classes and youth groups as those have shown the highest response and most reliable data so far.

We hope to get as many school classes and youth groups as possible to get involved in the project! Tea Bag Index Project would be grateful for your help in spreading the word about this new method, and your support in making a global decomposition map reality!

If you want to discuss during EGU2014 send an email to Taru Lehtinen, and feel free to send comments to tbi@decolab.org! If you want to join our mailing list and hear more from us, look for the following link: http://www.decolab.org/tbi/mailinglist.php.

Additional information

Our web page: http://www.decolab.org/tbi/

Our mailing list: http://www.decolab.org/tbi/mailinglist.php

Know more

Keuskamp JA, Dingemans BJJ, Lehtinen T, Sarneel JM, Hefting MM. 2013. Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems. Methods in Ecology and Evolution 4, 1070-1075. DOI: 10.1111/2041-210X.12097.

Lehtinen T, Gísladóttir G, van Leeuwen JP, Bloem J, Steffens M, Ragnarsdóttir KV. 2014. Do aggregate stability and soil organic matter content increase following organic inputs? Geophysical Research Abstracts 16, EGU2014-905-1.

Lehtinen T, Schlatter N, Baumgarten A, Bechini L, Krüger J, Grignani C, Zavattaro L, Costamagna C, Spiegel H. 2014. Effect of crop residue incorporation on soil organic carbon (SOC) and greenhouse gas (GHG) emissions in European agricultural soils. Geophysical Research Abstracts 16, EGU2014-10278.

 

This post has been simultaneously published in the EGU Blog Network.

 

Monday paper: Soil carbon stocks and their variability across the forests, shrublands and grasslands of peninsular Spain


Doblas-Miranda, E., Rovira, P., Brotons, L., Martínez-Vilalta, J., Retana, J., Pla, M., and Vayreda, J. 2013. Soil carbon stocks and their variability across the forests, shrublands and grasslands of peninsular Spain. Biogeosciences, 10, 8353-8361. DOI: 10.5194/bg-10-8353-2013.

Abstract

Accurate estimates of C stocks and fluxes of soil organic carbon (SOC) are needed to assess the impact of climate and land use change on soil C uptake and soil C emissions to the atmosphere. Here, we present an assessment of SOC stocks in forests, shrublands and grasslands of peninsular Spain based on field measurements in more than 900 soil profiles. SOC to a depth of 1 m was modelled as a function of vegetation cover, mean annual temperature, total annual precipitation, elevation and the interaction between temperature and elevation, while latitude and longitude were used to model the correlation structure of the errors. The resulting statistical model was used to estimate SOC in the ∼8 million pixels of the Spanish Forest Map (29.3 × 106 ha). We present what we believe is the most reliable estimation of current SOC in forests, shrublands and grasslands of peninsular Spain thus far, based on the use of spatial modelling, the high number of profiles and the validity and refinement of the data layers employed. Mean concentration of SOC was 8.7 kg m−2, ranging from 2.3 kg m−2 in dry Mediterranean areas to 20.4 kg m−2 in wetter northern locations. This value corresponds to a total stock of 2.544 Tg SOC, which is four times the amount of C estimated to be stored in the biomass of Spanish forests. Climate and vegetation cover were the main variables influencing SOC, with important ecological implications for peninsular Spanish ecosystems in the face of global change. The fact that SOC was positively related to annual precipitation and negatively related to mean annual temperature suggests that future climate change predictions of increased temperature and reduced precipitation may strongly reduce the potential of Spanish soils as C sinks. However, this may be mediated by changes in vegetation cover (e.g. by favouring the development of forests associated to higher SOC values) and exacerbated by perturbations such as fire. The estimations presented here provide a baseline to estimate future changes in soil C stocks and to assess their vulnerability to key global change drivers, and should inform future actions aimed at the conservation and management of C stocks.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Monday paper: A dual isotope approach to isolate soil carbon pools of different turnover times


Torn, M. S., Kleber, M., Zavaleta, E. S., Zhu, B., Field, C. B., and Trumbore, S. E. 2013. A dual isotope approach to isolate soil carbon pools of different turnover times. Biogeosciences, 10, 8067-8081. DOI: 10.5194/bg-10-8067-2013.

Abstract

Soils are globally significant sources and sinks of atmospheric CO2. Increasing the resolution of soil carbon turnover estimates is important for predicting the response of soil carbon cycling to environmental change. We show that soil carbon turnover times can be more finely resolved using a dual isotope label like the one provided by elevated CO2 experiments that use fossil CO2. We modeled each soil physical fraction as two pools with different turnover times using the atmospheric 14C bomb spike in combination with the label in 14C and 13C provided by an elevated CO2 experiment in a California annual grassland. In sandstone and serpentine soils, the light fraction carbon was 21–54% fast cycling with 2–9 yr turnover, and 36–79% slow cycling with turnover slower than 100 yr. This validates model treatment of the light fraction as active and intermediate cycling carbon. The dense, mineral-associated fraction also had a very dynamic component, consisting of ∼7% fast-cycling carbon and ∼93% very slow cycling carbon. Similarly, half the microbial biomass carbon in the sandstone soil was more than 5 yr old, and 40% of the carbon respired by microbes had been fixed more than 5 yr ago. Resolving each density fraction into two pools revealed that only a small component of total soil carbon is responsible for most CO2 efflux from these soils. In the sandstone soil, 11% of soil carbon contributes more than 90% of the annual CO2 efflux. The fact that soil physical fractions, designed to isolate organic material of roughly homogeneous physico-chemical state, contain material of dramatically different turnover times is consistent with recent observations of rapid isotope incorporation into seemingly stable fractions and with emerging evidence for hot spots or micro-site variation of decomposition within the soil matrix. Predictions of soil carbon storage using a turnover time estimated with the assumption of a single pool per density fraction would greatly overestimate the near-term response to changes in productivity or decomposition rates. Therefore, these results suggest a slower initial change in soil carbon storage due to environmental change than has been assumed by simpler (one-pool) mass balance calculations.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Monday paper: Effects of belowground litter addition, increased precipitation and clipping on soil carbon and nitrogen mineralization in a temperate steppe


Ma, L., Guo, C., Xin, X., Yuan, S., Wang, R. 2013. Effects of belowground litter addition, increased precipitation and clipping on soil carbon and nitrogen mineralization in a temperate steppe. Biogeosciences 10, 7361-7372. DOI: 10.5194/bg-10-7361-2013

Abstract

Soil carbon (C) and nitrogen (N) cycling are sensitive to changes in environmental factors and play critical roles in the responses of terrestrial ecosystems to natural and anthropogenic perturbations. This study was conducted to quantify the effects of belowground particulate litter (BPL) addition, increased precipitation and their interactions on soil C and N mineralization in two adjacent sites where belowground photosynthate allocation was manipulated through vegetation clipping in a temperate steppe of northeastern China from 2010 to 2011. The results show that BPL addition significantly increase soil C mineralization rate (CMR) and net N mineralization rate (NMR). Although increased precipitation-induced enhancement of soil CMR essentially ceased after the first year, stimulation of soil NMR and net nitrification rate continued into the second year. Clipping only marginally decreased soil CMR and NMR during the two years. There were significant synergistic interactions between BPL addition (and increased precipitation) and clipping on soil CMR and NMR, likely to reflect shifts in soil microbial community structure and a decrease in arbuscular mycorrhizal fungi biomass due to the reduction of belowground photosynthate allocation. These results highlight the importance of plants in mediating the responses of soil C and N mineralization to potentially increased BPL and precipitation by controlling belowground photosynthate allocation in the temperate steppe.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.

Monday paper: Soil organic carbon dynamics of black locust plantations in the middle Loess Plateau area of China


Lu, N., Liski, J., Chang, R. Y., Akujärvi, A., Wu, X., Jin, T. T., Wang, Y. F., Fu, B. J. 2013. Soil organic carbon dynamics of black locust plantations in the middle Loess Plateau area of China. Biogeosciences 10, 7053-7063. DOI: 10.5194/bg-10-7053-2013

Abstract

Soil organic carbon (SOC) is the largest terrestrial carbon pool and sensitive to land use and cover change; its dynamics are critical for carbon cycling in terrestrial ecosystems and the atmosphere. In this study, we combined a modeling approach and field measurements to examine the temporal dynamics of SOC following afforestation (Robinia pseudoacacia) of former arable land at six sites under different climatic conditions in the Loess Plateau during 1980–2010, where the annual mean precipitation ranging from 450 mm to 600 mm. The results showed that the measured mean SOC increased to levels higher than before afforestation when taking the last measurements (i.e., at age 25 to 30 yr) at all the sites, although it decreased at the wetter sites in the first few years. The accumulation rates of SOC were 1.58 to 6.22% yr−1 in the upper 20 cm and 1.62 to 5.15% yr−1in the upper 40 cm of soil. The simulations reproduced the basic characteristics of measured SOC dynamics, suggesting that litter input and climatic factors (temperature and precipitation) were the major causes for SOC dynamics and the differences among the sites. They explained 88–96, 48–86 and 57–74% of the variations in annual SOC changes at the soil depths of 0–20, 0–40, and 0–100 cm, respectively. Notably, the simulated SOC decreased during the first few years at all the sites, although the magnitudes of decreases were smaller at the drier sites. This suggested that the modeling may be advantageous in capturing SOC changes at finer timescale. The discrepancy between the simulation and measurement was a result of uncertainties in model structure, data input, and sampling design. Our findings indicated that afforestation promoted soil carbon sequestration at the study sites during 1980–2010. Afforestation activities should decrease soil disturbances to reduce carbon release in the early stage. The long-term strategy for carbon fixation capability of the plantations should also consider the climate and site conditions, species adaptability, and successional stage of recovery.

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Biogeosciences (BG) is an international scientific journal dedicated to the publication and discussion of research articles, short communications and review papers on all aspects of the interactions between the biological, chemical and physical processes in terrestrial or extraterrestrial life with the geosphere, hydrosphere and atmosphere. The objective of the journal is to cut across the boundaries of established sciences and achieve an interdisciplinary view of these interactions. Experimental, conceptual and modelling approaches are welcome. More at Biogeosciences homepage.