Research Feature: A New Grant to Study Carbon Dynamics in Forest Soils

In September, Kate Lajtha, professor in the Department of Botany and Plant Pathology, received a five-year grant to continue studies of carbon storage and accumulation in forest soils at the Andrews Experimental Forest. The grant was awarded through the National Science Foundation’s Long Term Research in Environmental Biology (LTREB) program and builds on 10 years of data collected through an international effort called the DIRT project.  In this Web interview, Kate discusses the project and what the new grant will enable.

What is the rational for the project and what is your main research question?

If you look at carbon pools in the terrestrial world, the amount of carbon that is stored in soils is two to three times that in vegetation. The carbon flux between soils and the atmosphere is large, with soil respiration representing about 10 times the carbon flux due to fossil fuel combustion. So the stability of soil carbon and whether it is a net release or a net gain can influence global carbon budgets significantly. Soil carbon is a long term stable pool so understanding how climate change, as well as how land management affects that pool is critical to understanding the carbon budget for the Earth.

In this project, our main research question is – how does the chemistry and the amount of forest litter – things like leaves, fir needles, and other detritus – affect the stabilization and sequestration of carbon in soils? We know that with global change, net primary production is going to change. We also know that there are huge questions about how forest management – activities such as thinning and harvesting – affect soil dynamics. It is very easy to tell the effects of forest management on the carbon balance for all the above-ground plant material, but the effects of forest management on the sequestration of soil carbon is not known. 

Understanding soil carbon dynamics is also just a very fundamental research question. When people try to understand the role of soils in sequestering carbon, there are debates about where the carbon is coming from. Is it all inputs from plant roots?  We feel that we have evidence that this is partly true, but that the contribution from above ground litter also matters very much. There are also other people who say that the stability of carbon is determined by soil mineralogy and not by plant production at all – that plants always produce more carbon than soils can sequester. 

This project will take place in the same study plots set up by the DIRT project in the Andrews Experiment Forest. DIRT stands for Detrital Input, Removal and Transfer and is an international network of sites where people are investigating the affect of climate change and forest management on soil carbon. Can you explain how the study plots are set up?

Our plots were set up in 1997 as part of the Long-term Ecological Research program at the Andrews. It is a manipulative experiment – climate and soil are the same and the thing we are changing is the inputs of carbon.We have control plots, double litter plots plus ‘no above ground litter plots’ where we’ve raked and removed all litter.  We also have plots where we have excluded all plant roots by digging one meter trenches around the perimeter of the plots and girdled all of the trees within them.  So, for example, the ‘no input’ plots, have no litter and no roots.  They are sort of like a litter bag experiment where we can observe the process of soil organic matter decomposition.  At the Andrews, the plots are 10 by 15 meters and there are three replicates of each treatment.

David Diaz, former student of Kate Lajtha, sweeping one of the DIRT plots.
David Diaz, a graduate student in soil science, sweeping one of the "no litter" plots.

What has your research shown so far?

Right now we have 10 years of data. Some of what we’ve found was predicted and some was surprising. We found predicted differences in the soil solution chemistry of the different plots. One of the unusual things we found comes from the work of Peter Bottomly and Dave Myrold from the Department of Crop and Soil Science and their students. Their work showed that the presence or absence of roots affects the microbial community dramatically but that the manipulations of above-ground inputs appeared not to effect enzyme dynamics or microbial populations very much. That could be because there have been too few years of treatments to show an effect, or it could be that it is just how things are.

What studies will the new grant enable?

The new grant is to do a more detailed analysis of the soil chemistry. It allows us to continue monitoring soil solution chemistry and look for changes in dissolved organic carbon. The way that above-ground litter would really influence carbon stabilization is by having dissolved organic carbon from that litter move into the soil – so this grant will support maintenance of that research as well as looking for detailed changes in different carbon pools. One of our big questions is whether the carbon is what we call light fraction or free carbon or more stabilized carbon in mineral-bound forms. 

The NSF LTREB program which awarded the grant really has a focus on long-term research – the kind that cannot usually be done with typical three-year research grants. They require you to already have six years of data before you even apply for a LTREB grant, so it really is a unique opportunity to look at questions with a long time frame.

The grant will also support one or two new graduate students – it is good timing since I’ve recently had a couple of students finish.  The project will also support research training of undergraduate honors students and be incorporated into an honors ecology course.

Who are the participants in this new grant?

I am the principal investigator on the project and Bruce Caldwell, now also from the Department of Botany and Plant Pathology, is the co-principal investigator. We are also hoping that the many faculty who have been involved in the DIRT project so far will continue to be involved. For example, Dave Myrold and Peter Bottomley and their student have been very active in helping us understand the role of the microbial community in soil carbon and nitrogen dynamics and how that relates to the stability of carbon and carbon sequestration. 

We have also had many collaborations with researchers around the world – we have sent soil samples to researchers in other countries and had many visitors to the site. For example, I have a colleague from Hawaii that has looked at carbon-14 dates in the sites – she did some analysis after six years of the DIRT project and she will return now that the DIRT experiment has been running for 10 years.

We are running the project as an open facility – and we really encourage new projects. Come play in DIRT! 

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For more information about the LTREB grant or the DIRT project, please contact Kate Lajtha.

The following publications are also related to the work carried out at the Andrews' DIRT site:

Crow, S. E., K. Lajtha, T. R. Filley, C. W. Swanston , R. D. Bowden, and B. A. Caldwell.  2009. Alterations in plant inputs impact soil organic matter dynamics on different timescales in a deciduous and a coniferous forest. Global Biogeochemical Cycles, in press.

Crow, S.E., K. Lajtha, J. Brant, B. Caldwell, Y. Yano, R. D. Bowden, and E. Sulzman.  2009. Increased coniferous needle inputs accelerate decomposition of soil organic matter in an old-growth forest. Forest Ecology and Management, in press. 

Tóth, J.A., K. Lajtha, Z. Kotroczó,  Z. Krakomperger, B. Caldwell, R. Bowden, M. Papp. 2007. The Effect of Climate Change on Soil Organic Matter Decomposition. Acta Silvatica et Lignaria Hungarica 3: 75-85.

Crow, S. E., E. W. Sulzman, W. D. Rugh, R. D. Bowden, and K. Lajtha. 2006. Isotopic analysis of respired CO2 during decomposition of separated soil organic matter pools. Soil Biology & Biochemistry 38:3279-3291.

Crow, S. E., C. W. Swanston, K. Lajtha, J. R. Brooks, and H. Keirstead. 2007. Density fractionation of forest soils: methodological questions and interpretation of incubation results and turnover time in an ecosystem context. Biogeochemistry 85:69-90.

Crow, S. E., and R. K. Wieder. 2005. Sources of Co-2 emission from a northern peatland: Root respiration, exudation, and decomposition. Ecology 86:1825-1834.

Sollins, P., C. Swanston, M. Kleber, T. Filley, M. Kramer, S. Crow, B. Caldwell, K. Lajtha, and R. Bowden.  2006.  Organic C and N stabilization in a forest soil: evidence from sequential density fractionation. Soil Biology and Biochemistry 38:3313-3324.

Holub, S.M., K. Lajtha, J.D.H. Spears, J.A. Tóth, S.E. Crow, B.A.Caldwell, M. Papp, and P.T. Nagy. 2005. Organic matter manipulations have little effect on gross and net nitrogen transformations in two temperate forest mineral soils in the U.S.A and central Europe. Forest Ecology and Management 214:320-330.

Sulzman, E.W., J.B. Brant, R.D. Bowden, and K. Lajtha.  2005.  Contribution of aboveground litter, belowground litter, and rhizosphere respiration to total soil CO2 efflux in an old growth coniferous forest. Biogeochemistry 73:231 - 256

Lajtha, K., S. Crow, Y. Yano, S.S. Kaushal, E.W. Sulzman, P. Sollins, and J.D.H. Spears. 2005.  Detrital controls on soil solution N and dissolved organic matter in soils: a field experimentBiogeochemistry, 76:261-281.

Yano, Y., K. Lajtha, P. Sollins, and B.A. Caldwell. 2005. Chemistry and dynamics of dissolved organic matter in a temperate coniferous forest on Andic soils: Effects of litter qualityEcosystems 8: 286 - 300

Yano, Y., K. Lajtha, P. Sollins, and B.A. Caldwell. 2004. Chemical and seasonal controls on the dynamics of dissolved organic matter in a coniferous old-growth stand in the Pacific Northwest, USABiogeochemistry 71:197-223.

Spears, J.D.H. and K. Lajtha. 2004. The imprint of coarse woody debris on soil chemistry in the western Oregon Cascades. Biogeochemistry 71:163-175.