Glomalin and Conservation in Humboldt County The 1996 discovery of the soil glue glomalin is changing our understanding of the impact of elevated carbon dioxide, while giving important clues to forest health, watersheds, revegetation, wildfire and carbon sequestration. Here I share what I have found so others may read and draw their own conclusions, and relate it to my own experience, Humboldt County issues and stories from the news.

Sunday, July 11, 2004

53. Fungal-Mediated Plant Coexistence  

This summary of articles relating elevated CO2 to increased biodiversity from CO2 Science magazine. Elevated CO2 and local plants and fungi are often enough to give native plants competitive edges in the long run. We have now shown the need for fungi in forests, the product glomalin they produce, the need for large old trees and the carbon exudates they produce, the qualities of soil glue, examples of glomalin destruction, forest practices for maximizing carbon storage at reduced risk of fire, and the critical role of this activity in restoring severely impacted watersheds.
53. Fungal-Mediated Plant Coexistence
(www.co2science.org)
Volume 6, Number 53: 31 December 2003
In a recent review of this intriguing concept, Hart et al. (2003) say "coexistence is a biological riddle, because the tendency towards competitive exclusion should favor a monoculture." Monocultures, however, are rare in nature; and Hart et al. note that several scientists (Janos, 1980; Hetrick et al., 1989; Allen and Allen, 1990; Hetrick et al., 1994) have suggested that arbuscular mycorrhizal fungi (AMF) - a common group of symbiotic soil fungi - may be "important agents promoting plant coexistence," which concept forms the basis of their review. Hart et al. begin by differentiating between two types of studies of AMF effects on plant coexistence. Coarse-scale studies are defined as those that compare the outcome of plant competition with AMF presence or absence, which they say should be "relevant to the outcome of plant interactions mainly in early successional ecosystems," where AMF "are either absent or are in low abundance and patchily distributed." Fine-scale studies, on the other hand, are defined as those that compare the outcome of plant competition when all experimental treatments contain AMF and the manipulations "involve the composition and diversity of AMF, and the ways in which they interact with plants and their soil environment." These experiments, they say, "are more relevant to later-successional situations, in which AMF are more abundant and less patchy, and the roots of most plants come into contact with them."Concentrating primarily on the latter category of experiments, Hart et al. note that "higher AMF diversity could lead to higher plant coexistence simply by increasing the probability of individual plant species associating with a compatible and effective AMF partner." In addition, they point out that shared mycelial networks "might promote plant species coexistence by equalizing the distribution of soil resources among competitively dominant and subdominant host species," noting that "soil nutrients and plant-derived carbon might flow through the network from dominant to subordinate host plants, because of a concentration gradient created initially when the dominant plant takes up more nutrients than does a subordinate plant." The former of these phenomena - the plant-to-plant transfer of nutrients - has been observed by Malcova et al. (1999) under laboratory conditions and by Walter et al. (1996) in the field. Likewise, the second phenomenon - the plant-to-plant transfer of carbon - has been observed by Grime et al. (1987), Graves et al. (1997) and Robinson and Fitter (1999).In concluding their review, Hart et al. say "our understanding of fine-scale factors is just starting to develop," and in this regard we note that many experiments conducted in recent years have added elevated levels of atmospheric CO2 to the mix of experimental variables considered within this context.Several such studies are described in our Subject Index under the heading Biodiversity (Fungi), where it may be seen, as noted in the review of Hart et al., that (1) the presence of soil fungi helps to maintain, and sometimes even increase, the biodiversity of various ecosystems, and (2) elevated levels of atmospheric CO2 help these fungi to better perform this important function. Also, under the Subject Index heading of Fungi, one can read how these principles operate in Grasses, Herbaceous Plants and Woody Plants, and how they help to enhance Carbon Sequestration.It is also interesting, in this regard, to go back to the book of Idso (1989) -- Carbon Dioxide and Global Change: Earth in Transition -- and read what he wrote about the subject nearly a decade and a half ago:"Considerable evidence may be mustered to support [an] optimistic view of the effects of atmospheric CO2 enrichment on species diversity. Looking to the past, for example, several studies of Tertiary floras have demonstrated that many montane taxa of that period regularly grew among mixed conifers and broadleaf shclerophylls (Axelrod, 1944a, 1944b, 1956, 1976, 1987), whereas today these forest zones are separated from each other by fully 1,000 m in elevation and 10-20 km or more in distance (Axelrod, 1988). Indeed, during this many-million-year period, when the CO2 content of the atmosphere was generally much greater than it is today (Volk, 1987), all three forest zones merged to form a 'super' ecosystem, which, in the words of Axelrod (1988), "was much richer than any that exists today." Even under current conditions, in fact, modern forestry experiments have demonstrated that trees planted in mixtures sometimes grow better than they do in single-species plantings (Brown and Harrison, 1983; Carlyle and Malcolm, 1986a; Carlyle and Malcolm, 1986b; Chapman et al., 1988)."One mechanism by which this type of mutualism may be fostered has to do with the stimulation of vesicular-arbuscular mycorrhizal fungi, which are ubiquitous in most terrestrial ecosystems (Gerdemann, 1968; Read et al., 1976) and the most prevalent of all soil fungi (Gerdemann and Nicolson, 1963). These unseen inhabitants of the soil provide a number of benefits to the plants they 'service.' They increase the absorption of water and nutrients by the plant, protect the plant from soil-borne diseases, and reduce the incidence of nematode infection of roots (Ingham, 1988). And as Johnson and McGraw (1988) have noted, 'their vigor may be expected to reflect the vigor of their hosts,' which with CO2 enrichment would be expected to increase. Consequently, whereas community ecology paradigms of the past, based largely on data pertaining to above-ground interactions, have tended to stress relatively short food chains with competition and antagonism as major organizing forces in community development, Edwards and Stinner (1988) note that, today, 'ecologists studying biotic interactions in soil systems generally have observed complex food webs, a great diversity of organisms, and a wide range of symbiotic interactions.' Indeed, many endomycorrhizae (Chiariello et al., 1982), as well as certain ectomycorrhizae (Reid and Woods, 1969; Read et al., 1985), have even been demonstrated to actively transfer nutrients between individual plants of both the same and different species. In fact, seedlings of some plants will not grow at all unless they interact with the mycorrhizae of an adjacent host plant (Warcup, 1988), while in other situations, both seed germination and initial plant growth rates are greatly stimulated by the presence of such fungi (Clements and Ellyyard, 1979; Masuhara and Katsuya, 1989). As a result, Moore (1988) contends that mutualism is common below ground and that it 'can have profound effects on the structure and activity of soil microbial communities, the decomposition of organic matter, and ultimately plant growth'."Yes, as the saying goes, "everything old is new again." It's been shown over and over that arbuscular mycorrhizal fungi and atmospheric CO2 enrichment make a truly dynamic duo when it comes to getting plants to "cooperate" in both maintaining and enhancing ecosystem biodiversity.Sherwood, Keith and Craig Idso
ReferencesAllen, E.B. and Allen, M.F. 1990. The mediation of competition by mycorrhizae in successional and patchy environments. In: Grace, J.B. and Tilman, D. (Eds.). Perspectives in Plant Competition. Academic Press, New York, NY, pp. 367-389. Axelrod, D.I. 1944a. The Oakdale flora (California). Carnegie Institute of Washington Publication 553:147-166.Axelrod, D.I. 1944b. The Sonoma flora (California). Carnegie Institute of Washington Publication 553: 167-200.Axelrod, D.I. 1956. Mio-Pliocene floras from west-central Nevada. University of California Publications in Geological Science 33: 1-316.Axelrod, D.I. 1976. Evolution of the Santa Lucia fir (Abies bracteata) ecosystem. Annals of the Missouri Botanical Garden 63: 24-41.Axelrod, D.I. 1987. The Late Oligocene Creed flora, Colorado. University of California Publications in Geological Science 130: 1-235.Axelrod, D.I. 1988. An interpretation of high montane conifers in western Tertiary floras. Paleobiology 14: 301-306.Brown, A.F.H. and Harrison, A.F. 1983. Effects of tree mixtures on earthworm populations and nitrogen and phosphorus status in Norway Spruce (Picea abies) stands. In: Lebrum, P.H., Andrea, H.M., De Medts, A., Gregoire-Wibo, C. and Wauthy, G. (Eds.). New Trends in Soil Biology. Proceedings of the VIII International Colloquium on Soil Zoology. Louvain-la-Neure, Belgium, pp. 101-108.Carlyle, J.C. and Malcolm, D.C. 1986a. Nitrogen availability beneath pure spruce and mixed larch + spruce stands growing on a deep peat. I. Net mineralization measured by field and laboratory incubations. Plant and Soil 93: 95-113.Carlyle, J.C. and Malcolm, D.C. 1986b. Nitrogen availability beneath pure spruce and mixed larch + spruce stands growing on a deep peat. II. A comparison of N availability as measured by plant uptake and long-term laboratory incubations. Plant and Soil 93: 115-122.Chapman, K., Whittaker, J.B. and Heal, O.W. 1988. Metabolic and faunal activity in litters of tree mixtures compared with pure stands. Agriculture, Ecosystems and Environment 24: 33-40.Chiariello, N., Hickman, J.C. and Mooney, H.A. 1982. Endomycorrhizal role for interspecific transfer of phosphorus in a community of annual plants. Science 217: 941-943.Clements, M.A. and Ellyyard, R.K. 1979. The symbiotic germination of Australian terrestrial orchids. American Orchid Society Bulletin 48: 810-816.Edwards, C.A. and Stinner, B.R. 1988. Interactions between soil-inhabiting invertebrates and microorganisms in relation to plant growth and ecosystem processes: An introduction. Agriculture, Ecosystems and Environment 24: 1-3.Gerdemann, J.W. 1968. Vesicular-arbuscular mycorrhizae and plant growth. Annual Review of Phytopathology 6: 397-418.Gerdemann, J.W. and Nicolson, T.H. 1963. Spores of mycorrhizal Endogone species extracted from soil by wet sieving and decanting. Transactions of the British Mycological Society 46: 235-244.Graves, J.D. et al. 1997. Intraspecific transfer of carbon between plants linked by a common mycorrhizal network. Plant and Soil 192: 153-159.Grime, J.P. et al. 1987. Floristic diversity in a model system using experimental microcosms. Nature 328: 420-422.Hart, M.M., Reader, R.J. and Klironomos, J.N. 2003. Plant coexistence mediated by arbuscular mycorrhizal fungi. TRENDS in Ecology and Evolution 18: 418-423.Hetrick, B.A.D. et al. 1989. Relationship between mycorrhizal dependence and competitive ability of two tall grass prairie grasses. Canadian Journal of Botany 67: 2608-2615.Hetrick, B.A.D. et al. 1994. Effects of mycorrhizae, phosphorus availability, and plant density on yield relationships among competing tall grass prairie grasses. Canadian Journal of Botany 72: 168-176.Idso, S.B. 1989. Carbon Dioxide and Global Change: Earth in Transition. IBR Press, Tempe, AZ.Ingham, R.E. 1988. Interactions between nematodes and vesicular-arbuscular mycorrhizae. Agriculture, Ecosystems and Environment 24: 169-182.Janos, D.P. 1980. Mycorrhizae influence tropical succession. Biotropica 12: 56-64.Johnson, N.C. and McGraw, A.-C. 1988. Vesicular-arbuscular mycorrhizae in taconite tailings. II. Effects of reclamation practices. Agriculture, Ecosystems and Environment 21: 143-152.Malcova, R. et al. 1999. Influence of arbuscular mycorrhizal fungi and simulated acid rain on the growth and coexistence of the grasses Calamagrostis villosa and Deschampsia flexuosa. Plant and Soil 207: 45-57.Masuhara, G. and Katsuya, K. 1989. Effects of mycorrhizal fungi on seed germination and early growth of three Japanese terrestrial orchids. Scientia Horticulturae 37: 331-337.Moore, J.C. 1988. The influence of microarthropods on symbiotic and non-symbiotic mutualism in detrital-based below-ground food webs. Agriculture, Ecosystems and Environment 24: 147-159.Read, D.J., Francis, R. and Finlay, R.D. 1985. Mycorrhizal mycelia and nutrient cycling in plant communities. In: Fitter, A.H., Atkinson, D., Read, D.J. and Usher, M.B. (Eds.). British Ecological Society Special Publication 4: Ecological Interactions in Soil, pp. 193-217.Read, D.J., Koucheki, H.K. and Hodgson, T. 1976. Vesicular-arbuscular mycorrhizae in natural ecosystems. I. The occurrence of infection. New Phytologist 77: 641-653.Reid, C.P.P. and Woods, F.W. 1969. Translocation of 14C-labelled compounds in mycorrhizae and its implications in interplant nutrient cycling. Ecology 50: 179-187.Robinson, D. and Fitter, A. 1999. The magnitude and control of carbon transfer between plants linked by a common mycorrhizal network. Journal of Experimental Botany 50: 9-13.Volk, T. 1987. Feedbacks between weathering and atmospheric CO2 over the last 100 million years. American Journal of Science 287: 763-779.Walter, L.E.F. et al. 1996. Interspecific nutrient transfer in a tall grass prairie plant community. American Journal of Botany 83: 180-184.Warcup, J.H. 1988. Mycorrhizal associations and seedling development in Australian Lobelioideae (Campanulaceae). Australian Journal of Botany 36: 461-472.

31 December 2003
Copyright © 2004. Center for the Study of Carbon Dioxide and Global Change (www.co2science.org).
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TN Nursery is a state certified tree nursery specializing in native plants and trees, shrubs, fern, and perennials as well as pond plants and wetland mitigation.
 
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