Life on earth is dominated by the poorly understood organisms that live in the plant-soil continuum. I examine the mechanisms through which large scale human activities affect plant-soil interactions. Within this context I explore two different themes: plant-soil feedbacks and plant water use. In both lines of research it is my expectation that results will improve natural resource management. For example, I have examined the potential for calcium addition, soil compaction, and activated carbon addition to ameliorate the effects of anthropogenic nitrogen deposition, soil disturbance, and exotic plant growth, respectively. My research, therefore, is expected to have applications in range management, agriculture and silviculture.

PLANT-SOIL FEEDBACKS

Recent theoretical and empirical research suggests that plant-soil feedbacks (PSFs) may be a critical but underappreciated factor that can explain plant community development. Most research on PSFs, however, has been performed on over-simplified theoretical or experimental systems. My research uses field (Fig. 1), laboratory, and theoretical approaches to measure PSFs, typically in invaded plant systems. Furthermore, through my research, I determine the relative importance of PSF mechanisms to other mechanisms that have been suggested to explain plant growth (e.g., competition, propagule pressure). I also use this research to help guide the development of novel plant management techniques (Fig. 1).

Fig. 1. My research on plant-soil feedbacks in invaded systems led me to develop a novel native plant restoration technique that utilizes activated carbon as a soil amendment to inhibit plant-microbe communication. Panel A shows a large plant-soil feedback experiment in Winthrop, WA, USA. Panel B shows native grasses growing vigorously in an activated carbon treated plot that is surrounded by untreated soil. The untreated soil is dominated by exotic-invasive plants (e.g., Poa bulbosa and Centaurea diffusa).

Using a large, multi-factor field experiment in a shrub-steppe system in Washington, I found that soil history was more important to the distribution of native and exotic plants than competition from established or germinating plants, shading, tillage, or propagule addition. Exotic plants in this system appear to facilitate their own growth by maintaining high mycorrhizal infection rates despite suppressing total fungal biomass. In addition to plant-microbe interactions, I have found that nematode populations are smaller and net nitrogen mineralization rates are faster in exotic- than native-dominated soils. Despite a historical emphasis on resource competition within plant generations in the field of ecology, my work suggests that the PSFs that develop over multiple plant generations and/or the disturbances that fundamentally alter soil biology and chemistry are critical to plant community development. This work was made possible by funding from the USDA NRICGP, the Switzer Foundation, and the Utah State Agricultural Experimental Station and Alaska EPSCOR.

Where PSFs are important to exotic plant growth, it may be possible to use an understanding of these feedbacks to develop species-specific approaches to exotic plant management. As a first attempt to follow this line of research, I performed an activated carbon addition experiment. Activated carbon addition was expected to sever plant-soil communication and decrease the benefit of plant-soil feedbacks realized by exotic plants. In support of this prediction, activated carbon addition reduced microbial abundance and diversity and the growth of two dominant exotic species. Activated carbon addition also increased the growth of two dominant native grasses (Fig. 1). This management approach has gained attention and is being replicated at a larger scale by other researchers and land managers.

Most PSF studies have been performed under greenhouse conditions using plant monocultures so the importance of PSFs to plant communities under field conditions remains a major question. To address this question, I have established paired PSF experiments in the field and in the greenhouse. These experiments will assess PSFs for individual plant species, as has been done in other studies. These experiments also produced the first explicit tests of PSFs for plant communities. Data from these experiments will determine if current theoretical and greenhouse-derived data overestimate or underestimate the importance of PSFs in field conditions.

Fig. 2. I have recently developed a plant-soil feedback model for 16 plants species and their attendant soil communities (Panel A). Unlike previous models, this model describes plant-soil feedbacks for a diverse plant community and, importantly, describes plant and microbial biomass responses over time. I have used this model to predict how plant-soil feedbacks are likely to affect plant biomass (Panel B). The model shows a negative relationship between plant-soil feedback and plant production. In other words, plants with negative plant-soil feedbacks are predicted to be more productive in communities than in monoculture and plants with positive plant-soil feedbacks are predicted to be less productive in communities than in monoculture. Furthermore, this effect increases with species richness, but saturates at low species richnesses (Panel C). This research provides a strong and novel additional explanation for the long-observed ‘diversity-productivity’ relationship. Kulmatiski et al. 2012 (Proc. Of the Royal Society B).

Fig. 3. Experimental results have supported model predictions, showing a negative relationship between overyielding (a measure of plant production) and plant-soil feedback (Panel A). Furthermore, a simple plant-soil feedback model was able to explain variation in plant growth without considering any other factors (i.e., sampling effects or complementarity). Kulmatiski et al. 2012 (Proc. Of the Royal Society B).

WATER USE

What keeps these ancient critters around? These are white rhino which graze on grasses. Black rhinos, in contrast, are browsers and feed on woody plants. Savannas are defined by the unusual mix of trees and grasses allowing both grazers and browsers to coexist. Though many hypotheses have been developed, it is still not clear why grasses do not outcompete trees or vice versa. In research supported by the Mellon foundation, I am continuing to develop a technique that combines a novel tracer technique with micrometeorological and soil water modeling to measure how trees and grasses share soil resources. Results are providing a potential explanation for how trees and grasses coexist. Results are also helping improve understanding of hydrological cycles by allowing predictions of how much water individual plant species remove from specific soil depths. An understanding of tree and grass coexistence is necessary to allow predictions of the effects of climate change on trees and grasses and alternatively how these changes in tree and grass abundance are likely to feedback to climate change.

To measure differences in water use between exotic and native plants in the shrub-steppe of Washington State, I have used measures of soil moisture and isotopic composition to demonstrate that exotic plants extracted shallow soil water before most native plants became active in the spring. This suggests that exotic plants may maintain dominance by altering the timing of shallow water use. After this work, which relied on the natural abundance of stable isotopes, I decided to use manipulative experiments to get a better understanding of water use.

I am now pursuing a similar line of research in South Africa. In this research I am using several techniques to determine the timing, location, and extent of water-use by grasses, tree seedlings, shrubs, and trees in an effort to define niche space in a savannah system. Historically, it has been difficult to measure root activity because the fragile fine roots that absorb water are buried in dense soils and difficult to observe. To resolve this problem, we are injecting (Figs. 4 and 5) deuterated water into specific soil depths at specific times of the year.

Fig. 4. While the wildlife do cause some delays in our research, we have had great success in determining root activity in the savanna systems in Kruger National Park using a pulse-labeling approach. This approach involves drilling and injecting a hydrological tracer into about 100,000 holes each year – good work if you want Popeye’s formarms.

Fig. 5. Once we get our samples from tracer plots there is still a lot of work to be done to get the water out of those samples using batch cryogenic distillation techniques – torches, check, liquid nitrogen check, isotopes, check, hotwiring electronics, check – this must be science.

Fig. 6. These tracer studies let us know where and when plants access soil water. All plants appear to rely on shallow soils in the sub-tropical savannas of Kruger Park, but trees rely on very slightly deeper soils (Panel A). Trees also access water from beyond their crowns while grasses obtain over 98% of their water from immediately below their stems. Kulmatiski et al. 2010 (New Phytologist).

Fig. 7. The tracer technique we use indicates the proportion of tracer uptake by different plants but not the amount of water taken up by different plants. Determining the amount of water taken up requires estimates of transpiration – and this isn’t easy. We have to protect our micrometeorological stations from large animals (A), take thousands of leaf conductance measurements (B), install soil moisture probes, and clip, dry and scan a lot of plant material (D). This work wouldn’t be possible without the heroic efforts of Isaac, Wisani, Rudolph and our game guards (A), Valephi (B), Michael Mazzacavallo and Wisani (C) or Lauren Hierl (D).

Fig. 8. In the end, the work is coming together nicely and producing very high quality predictions of soil water storage. (Manuscript in preparation).

Fig. 9. To test our predictions of plant water use, we have built a set of 8 x 8 m rainout shelters in Satara, Kruger Park that create fewer but larger precipitation events (a real engineering feat - for beginners). This experiment will help test the predicted effects of climate change on the savannah ecosystem.

In addition to my own work, I have enjoyed collaborating with others. My role in these collaborations is typically as an ecosystem ecologist. While at Yale I worked with researchers on the effects of coarse woody debris and a terrestrial vertebrate on ecosystem processes in Puerto Rico. Also with Kristiina Vogt and others, I worked on the effects of nitrogen saturation on forest ecosystems in the northeastern US. While at USU, I worked with Karen Beard and graduate students on the long-term effects of native ungulate herbivory on nutrient cycling and on the role of gopher activity and soil compaction in exotic plant growth in Washington. Also at USU I have collaborated with Karen Mock to determine whether the invasive Phragmites australis has hybridized with a EurAsian strain. I am now also collaborating with a mathematician, Justin Heavilin, on a model of plant-soil feedbacks, a statistician, John Stevens, on a Bayes model for the meta-analytical review of ecological data, and with a microbial ecologist, Jenny Norton, on genetic analyses of soil microbial communities. Most recently, I have begun calloborating with Peter Adler (USU), John Bradford (USGS) and Steven Higgins (Germany) on models examining the role of water use in plant community development.

Publications:

Italics indicates graduate students

In press:
1. Kulmatiski, A., Beard, K.H. Run silent run deep: tree seedlings use deep roots to establish. Oecologia.

In review:
1. Warren, C.P., Kulmatiski, A., Beard, K.H. Non-native plants shift patterns of water use in a shrub-steppe community. Plant and Soil.

Published:
1. Kulmatiski, A., Heavilin, J., Beard, K.H. 2012. Plant-soil feedbacks provide an alternative explanation for diversity-productivity relationships. Proceedings of the Royal Society B. 279(1740): 3020-3026.

2. Beard, K.H., Kulmatiski, A. Introduction, establishment, and spread: 50 years of invasion ecology since Elton: a book review. Invited Submission. Ecology.

3. Kulmatiski A., J. Heavilin, K.H. Beard. 2011. Testing a three-species plant-soil feedback model. Journal of Ecology. 99(2): 542-550.

4. Kulmatiski A., Beard, K.H. 2011. Long-term plant growth legacies overwhelm short-term plant growth effects on soil microbial community structure. Soil Biology and Biochemistry. 43(4): 823-830.

5. Kulmatiski A. 2011. Changing soils to manage plant communities: Activated carbon as a restoration tool in ex-arable fields. Restoration Ecology. 19(101): 102-110.

6. Kulmatiski A., K.H. Beard, K.E. Mock, J.C. Gibson, L. Ahearn-Meyerson. 2010. Historical and current distribution of the native and non-native genotypes of Phragmites australis in northern Utah. Western North American Naturalist. 70(4): 541-552.

7. Kulmatiski, A., R.J.T. Verweij, K.H. Beard, E.C. February. 2010. A depth-controlled tracer technique measures vertical, horizontal and temporal patterns of water use by trees and grasses in a subtropical savanna. New Phytologist. 188(1): 199-209.

8. Kulmatiski A., K.H. Beard, J. Stevens, S.M. Cobbold. 2008. Plant-soil feedbacks: a meta-analytical review. Ecology Letters. 11(9): 980-992

9. Kulmatiski A., K.H. Beard. 2008. Decoupling plant-growth from land-use legacies in soil microbial communities. Soil Biology and Biochemistry. 40(5): 1059-1068.

10. Kyle, G.P., K.H. Beard, A. Kulmatiski. 2008. Pocket gophers change plant species composition in a shrub steppe ecosystem. Western North American Naturalist. 68(3): 374-381

11. Kulmatiski A., Kardol P. 2008. Invited Submission. Getting plant-soil feedbacks out of the greenhouse: conceptual and experimental approaches. Beyschlag W. (ed) In: Progress in Botany Vol. 69: 449-472.

12. Kulmatiski A., Vogt K.A., Vogt D.J., Wargo, P., Tilley J.P., Siccama T.G., Sigurdardottir R., Ludwig D. 2007. Nitrogen and calcium additions increase forest growth in Northeastern USA spruce-fir forests. Canadian Journal of Forest Research. 37(9):1574-1585.

13. Kyle G.P., K.H. Beard, A. Kulmatiski. 2007. Reduced soil compaction enhances growth of non-native plant species. Plant Ecology. 193(2):223-232.

14. Rexroad E., K.H. Beard, A. Kulmatiski. 2007. Soil, plant, and arthropod response to 35 and 55 years of native ungulate grazing in shrub-steppe communities. Western North American Naturalist. 67(1): 16-25.

15. Kulmatiski, A., K.H. Beard, J.M. Stark. 2006. Soil history as a primary control on plant invasion in abandoned agricultural fields. Journal of Applied Ecology. 43(5): 868-876.

16. Kulmatiski A. 2006. Exotic plants establish persistent communities. Plant Ecology. 187(2):261-275.

17. Kulmatiski A., K.H. Beard, J.M. Stark. 2006. Exotic plant communities shift water-use timing in a shrub-steppe ecosystem. Plant and Soil. 288(1-2): 271-284.

18. Kulmatiski, A., K.H. Beard. 2006. Activated carbon as a restoration tool: potential for control of invasive plants in abandoned agricultural fields. Restoration Ecology. 14(2) 251-257.

19. Kulmatiski A., K.H. Beard, J.M. Stark. 2004. Finding endemic soil-based controls on weed growth. Weed Technology 18:115-120.

20. Kulmatiski A., D.J. Vogt, T.G. Siccama, J.P. Tilley, K. Kolesinskas, T.W. Wickwire, B.C. Larson. 2004. Landscape determinants of soil carbon and nitrogen storage in Southern New England. Soil Science Society of America Journal 68(6): 2014-2022.

21. Kulmatiski A., K.H. Beard. 2004. Reducing sampler error in soil research. Soil Biology and Biochemistry. 36(2):383-385.

22. Kulmatiski A., D.J. Vogt, T.G. Siccama, K.H. Beard. 2003. Detecting nutrient pool changes in rocky forest soils. Soil Science Society of America Journal 67:1282-1286.

23. Beard K.H., K.A. Vogt, A. Kulmatiski. 2002. Top-down effects of a terrestrial frog on forest nutrient dynamics. Oecologia 133(4):583-593.

In preparation:
1. Beard K.H., Kulmatiski A. Fewer, larger precipitation events encourage woody plant growth in a subtropical savanna. Nature Climate Change.

2. Kulmatiski A., Anderson-Smith, A. Simplifying foodwebs is likely to decrease plant productivity. Oikos.

3. Kulmatiski A., K.H. Beard, J. Heavilin. Plant-soil feedbacks in the field and greenhouse predict community dynamics of species common to the intermountain west, USA. Ecological Applications.

4. Mazzacavallo M., A. Kulmatiski, K.H. Beard. Tree and grass water use in a xeric, clay savanna. Ecohydrology.

5. Kulmatiski A., J. Norton, K.H. Beard. Defining plant effects on microbial community composition and structure. Ecological Applications.