FUNGI IN ECOSYSTEM PROCESSES - CHAPTER 2 ppsx

2 Fungi and Primary Productivity: Making Nutrients Available 2.1 SOILS AND NUTRIENT AVAILABILITY Within ecosystems, primary production is carried out by autotrophic organisms. These organisms, plants, are able to fix carbon by the process of photosynthesis and build biomass by combining this fixed carbon with nutrient elements derived from the environment. The nutrients required for plant growth come from two main sources. The first source is the rock material underlying the soil. This rock may be of local origin, or of remote geology in areas that have been affected by glaciation. Rocks of the earth’s crust contain a variety of the essential mineral nutrients that plants need, but the minerals are bound in complex chemical forms that make them poorly available for plant uptake. By the action of environmental factors (wind, water, and physical disturbance) along with the activities of bacteria, fungi, and plant roots, the surface of rocks can be weathered and degraded to finer particles and the mineral nutrients released in a soluble form that can be accessed by plants. Some of these minerals will be carried in water to streams, rivers, and oceans, imparting fertility to these ecosystems. The second source of nutrients is by the breakdown or decomposition of dead plant and animal remains by microbes and animals. During decomposition, mineral nutrients are released in a soluble form as inorganic ions from the breakdown of the organic complexes within the plant and animal remains. This process is called mineralization, and provides fertility to the ecosystem. Decomposition and mineralization occur in terrestrial, freshwater, and marine ecosystems. In this chapter we will investigate the role that fungi play in these processes (Table 2.1). Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. The bulk of the chapter will deal with terrestrial ecosystems, as this is where most of the information on these processes had been derived. The impact of decomposition activity within terrestrial ecosystems has a profound effect on the fertility of streams and rivers by the process of leaching. Here, nutrient elements in water percolate through the soil into water cours es, carrying soluble nutrients derived in the terrestrial environment that have not been immobilized into land plant tissue. 2.1.1 Making Soils Soils are a complex composition of weathered mineral rock and organic material derived from dead plant and animal remains together with the living biota of bacteria, actinomycetes, fungi, protozoa, nematodes, soil TABLE 2.1 Ecosystem Services Provided by Fungi Ecosystem service Fungi functional group Soil formation Rock dissolution Lichens, Saprotrophs, Mycorrhizae Particle binding Saprotrophs, Mycorrhizae Providing fertility for primary production Decomposition or organic residues Saprotrophs, (Ericoid and ectomycorrhizae) Nutrient mineralization Saprotrophs, (Ericoid and ectomycorrhizae) Soil stability (aggregates) Saprotrophs, (Arbuscular mycorrhizae Primary production Direct production Lichens Nutrient accessibility Mycorrhizae Plant yield Mycorrhizae, pathogens Defense against pathogens Mycorrhizae, Endophytes, Saprotrophs Defense against herbivory Endophytes Plant community structure Plant–plant interactions Mycorrhizae, pathogens Secondary production As a food source Saprotrophs, Mycorrhizae Population/biomass regulation Pathogens Modification of pollutants Saprotrophs, Mycorrhizae Carbon sequestration and storage Mycorrhizae, (Saprotrophs) Note: Services to be considered in this chapter are in bold face. Fungal groups in parentheses are regarded as of lesser importance in that function. Chapter 228 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. microarthropods, and other small fauna (Coleman and Crossley, 1996). To equate a soil with “dirt,” which is essentially the abiotic component of soil, would be too simplistic. It is the holistic complement of abiotic and biotic components that makes the true, functional soil. Only by the close association and interaction of the component parts and the dynamic interaction between the biotic and abiotic components can the soil provide a continual source of nutrients for plant primary production. The importance of soil fertility has been known since the time of the development of agricultural practices in the Nile delta. The consequences of loss of stability of the tightly coupled interactions among the biotic and abiotic soil entities through mismanagement of agricultural soils and in combination with changes in climate result in the loss of soil fertility, as well as soil erosion and reduced crop yield. Much of this has been seen in recent years in sub-Sahalian Africa and is caused by the attempts to sustain a greater population than the carrying capacity of the land. In the historical past, we have witnessed wars and conflicts over religion, politics, and water. It is highly likely that future conflicts will be over the availability of fertile soils, especially if the predictions of global popul ation increase are correct (Brown, 1995; Meadows et al., 1992). Soils do not just occur; they are created by the breakdown of parent rock into mineral particles. The surface ionic exchange properties of these mineral particles give soil its fertility. The rate of exchange between ions bound to the surface of soil particles and those within the soil solution impart the fertility to soil. The greater the degree of dissociation of ions into soil solution, the more fertile the soil becomes, as plants are best able to access freely soluble nutrients. We shall see that fungi are important in creating these soil particles, modifying their chemical composition and association with organic matter and their ability to modify the physical structure of soil, which in turn influences the porosity, water-holding capacity, and overall stability of the soil. Weathering of parent rock material may be accomplished by a variety of abiotic factors. Brady and Weil (1999) describe the processes of mineral rock breakdown caused by weathering by wind and water, freeze/thaw cycles, and the effects of weak acids, formed by carbon dioxide combining with rain water. There are, however, a number of biotic factors that also influence the rate of parent rock breakdown, which in turn influences the development of soils. There is considerable literature suggesting that lichens play a significant role in the formation of soils. The soils that are formed are the substrates for the development of vascular plant communities, whose contribution to primary production through photosynthesis would be reduced in the absence of lichens. In addition, both saprotrophic and mycorrhizal fungi can be associated with mineral rock dissolution. The close and possibly synergistic association between fungi and bacteria, especially in the mycorrhizal habit, also enhances the dissolution of rock to release mineral nutrients. Fungi and Primary Productivity 29 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. A. The Role of Lichens in Soil Formation Lichens are a symbiotic association of algae and, primarily, ascomycete fungi. Some 15,000 species of lichen have been identified. They are often able to survive extreme environments of heat, cold, and drought that other organisms are less able to tolerate. It is in these climatically extreme or oligotrophic (nutrient- impoverished) environments that lichens become important actors in the formation of soils. Approximately 8% of terrestrial ecosystems are lichen- dominated, and in many of these systems, the ground cover by lichens is often very high, up to 100% (Honegger, 1991) (Table 2.2). The definition of a lichen is a subject discussed by Hawksworth (1988). Definitions range from Berkely’s 1869 suggestion that “it is quite impossible to distinguish some lichens from fungi” to Hawksworth’s 1983 definition of “a stable self-supporting association of a fungus (mycobiont) and an alga or Cyanobacteria (photobiont).” Later, Hawksworth revised the definition to “A lichen is a stable self-supporting association of a mycobiont and a photobiont in which the mycobiont is the exhabitant,” which suggests that the photobiont resides within the fungal tissue. Indeed, Sanders (2001) consider s lichens to be “the interface between mycology and plant morphology.” The algal symbiont is usually a green or yellow-green eucaryotic alga and sometimes a blue-green procaryotic Cyanobacteria. The algae are restricted to the upper zones of fungal tissue, where light is maximal for photosynthesis. The fungal associate is usually an Ascomycete or a Deuteromycete, with occasional Basidiomyctes that are TABLE 2.2 Taxonomic Diversity of Lichen Mycobionts and Photobionts (%) Lichens Lichen mycobiont Ascomycotina 98 Basidiomycotina 0.4 Deuteromycotina 1.6 Lichen photobiont Green algae 85 Cyanobacteria 10 Green algae plus Cyanobacteria 3–4 Lichen structure Homoeomerous (nonstratified) thalli 55 Placodioid or sqamulose thalli 20 Foliose or fructose heteromerous (stratified) thalli 25 Source: After Honegger (1991). Chapter 230 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. restricted to the genus Omphalina (Hawksworth, 1988). Fungi usually form the basal portion of the lichen, which may be differentiated into a stalklike structure or podetia. Fungal tissues form the greater proportion of the biomass of lichens and are the supporting tissue for the algal symbiont. In addition to the combination of algae and fungi, other nonphotosynthetic bacteria may also be present within the lichen (Banfield et al., 1999), also playing a role in soil biogenesis. Brady and Weil (1999) show that biogeochemical weathering of rock is a function of water availability, the presence of organic acids, and complexation processes. Specifically, water is involved in hydration, hydrolysis, and dissolution. Hydration of oxides of iron and aluminum is an important process in rock degradation; for example, hematite (Fe 2 O 3 ) is converted into ferrihydrate (Fe 10 O 15 ·9H 2 O). Hydrolysis is important in the release of essential nutrients for plant growth. For example, potassium is released from microcline, a feldspar by the following reaction: KAlSi 3 O 8 þ H 2 O , HAlSi 3 O 8 þ K þ þ OH 2 : Dissol- ution allows the dissociation of anions and cations from complex materials. For example, gypsum dissolves to release calcium and sulfate ions. In dry areas, the structure of lichens acts as a point of condensation of water and a site on which atmospheric water can collect (Lange et al., 1994). They are therefore nuclei for water-related rock-weathering processes. A review of rock weathering by lichens is given by Chen et al. (2000). The presence of living organisms increases the carbon dioxide concentration in the atmosphere because of their respiration. In the localized area around lichens and lichen communities on rocks, the condensed water mixes with carbon dioxide to form carbonic acid. This weak organic acid is an important agent of dissolution of the calcite found in limestone and marble ðCaCO 3 þ H 2 CO 3 , Ca þþ þ 2HCO 2 3 Þ: Lichens and soil fungi and bacteria are organisms that produce organic acids, such as oxalic, citric, lichenic, and tartaric acids, which in turn contribute to the chemical weathering of rocks. These acids increase hydrog en ion concentration in the environment, lowering pH and increasing the solubility of aluminum and silicon. They also form chelation products (complexes between inorganic ions and organic molecules) and release inorganic nutrient elements. For example, oxalic acid dissolves solid muscovite to produce soluble inorganic potassium and soluble chelated aluminum (K 2 [Si 6 Al 2 ]Al 4 O 20 (OH) 4 þ 6C 2 O 4 H 2 þ 8H 2 O , 2K þ þ 8OH 2 þ 6C 2 O 4 Al þ þ 6Si(OH) 4 0 ). Oxalic acid is known to be produced by fungal hyphae, whereas lichenic acid is specific to lichens. Crustose lichens, which are composed of a flat and crustlike thallus, are often the first organisms to colonize outcrops of bare rock. They are able to scavenge water and nutrients from the atmosphere and rain and dew to support their slow rate of growth, and are also able to tolerate complete desiccation. During their growth on the surface of rocks and in rock crevices, the acids they produce solubilize the rock and assist in its physical Fungi and Primary Productivity 31 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. breakdown. This action of lichens has been reported to cause significant damage to both buildings and sculptures made of rock (Chen et al., 2000). In their study of contrasting terricolous (ground-dwelling) lichen forms, Asta et al. (2001) divide the type of association between the lichen thallus and underlying substrate into three categories. Type 1 lichens, represented by the genus Baeomyces, have a very intimate association between the lichen body and the underlying substrate; Type 2 lichens, corresponding to the genus Peltgera, have a leafy thallus and an elaborate but less intimate system of attachment to the substrate. In Type 3 lichens, which correspond to the genus Cladonia,the primary thallus is almost absent and the podetia have little contact with the substrate. Using thin sections for light and electron microscopy, Asta et al. (2001) showed that the lichen–rock interface is primarily associated with the fungal component of the lichen and that the fungal structures consist of both individual hyphae and differentiated rhizomorphs. Altho ugh these rhizomorphs are thought to be important for translocating water and nutrients, they do not have clearly differentiated internal structures for translocation (Sanders, 1997), as do the rhizomorphs of some ectomycorrhizal fungi (Duddridge et al., 1980). Asta et al. (2001) showed that the interface between substratum and lichen Baeomyces was more structured and resulted in reorientation of mineral particles, biodegradation of the walls of plant debris, and bonding between these elements. In contrast, Cladonia had a more diffuse association with the substrate; fungal hyphae escape from the lichen body and are incorporated into the soil. The production of polysaccharides by fungal hyphae is also important in the development of organomineral complexes, which bind mineral particles together. Asta et al. (2001) also showed that the lichen complex contained lichen-specific bacterial colonies, but they did not speculate on their role in the rock degradation process. Banfield et al. (1999) also commented that the classic concept of the structure of lichens as an upper layer of fungal hyphae containing photosynthetically active algae or Cyanobacteria ignored the fact that the fungal matrix is also a refuge for a community of nonphotosynthetic bacteria. The diversity and function of these nonphotosynthetic bacteria is largely unknown. They have elaborated the lichen/mineral rock-weathering zone model of Barker and Banfield (1998) and applied the concept to the rhizospheres of vascular plants. A representation of the zone model is shown in Fig. 2.1 and shows Zone 1 as the region of generation of lichen acids in the photosynthetic region of the lichen. Zone 2 consists of the area of biophysical disaggregation, in which the fungal and nonphotosynthetic bacteria interact closely with weathered mineral rock particles, fungal hyphae, and rhizomorphs, which penetrate into fissures in the rock. Hyphal aggregations become narrower as the hyphae penetrate deeper into the underlying rock until only single hyphae exist (Ascaso and Wierzchos, 1995). Zone 2 is the area of most intense mineral weathering with maximal Chapter 232 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. FIGURE 2.1 Model indicating the four zones of activity within a mineral-weathering lichen as depicted by Banfield et al. (1999). In zone 1, photosynthetic members generate carbon and crystalline lichenic acids. In zone 2, there is direct contact among microbes, organic products, and the mineral surface. In zone 3, organic acids act to solubilize rock in the presence of direct rock/organism contact, particularly fungal hyphal penetration into cracks. Zone 4 is characterized by unweathered rock and inorganic chemical reactions. Fungi and Primary Productivity 33 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. contact among cells, secreted polymers, and mineral surfaces, where complexes among the minerals, clay particles, and organic polymers are formed at the nanometerscale. Here metal– lichen acid complexes occur that do not occur deeper in the rock (Ascaso and Wierzchos, 1995), such as complexes of ferric oxide in Acarospora sinoptica , aluminum in Tremolecia atrata, copper oxalate in Acarospora rugulosa and Lecidia theiodes, and complexing of copper in the cortex of Lecidia lacteal and copper-psoromic acid in Lecidella bullata.Inthe underlying Zone 3, solutions containing lichen-derived organic acids effect chemical solubilization of the parent rock material. This is primarily a biogeochemical interaction and is not mediated by direct microbial contact. Finally, the bottom of Zone 3 represents the unweathered rock, which water can penetrate but not carry organic acids. Ascaso and Wierzchos (1995) point out that there is a temporal component to the development of the lichen –soil interaction, which microbial populations and diversity increase as the weathering continues and a more diverse soil structure develops. In contrast to this evidence of the role of lichens in the weathering of rock and the destruction of buildings and monuments made of rock, Mottershead and Lucas (2000) present evidence to suggest that the cover of Aspicilia calcarea and Diploscistes diacapsis lichens on calcareous stonework in Europe can protect against rock solubilization. They show evidence that lichen-protected areas of gypsum were 15 mm higher than adjacent uncovered areas, where the lichen layer increases the rate of shedding rainwater containing acidic pollutants that would have eroded the rock surface. In addition, the aerial parts of the lichen trap particles of dust, which together with dead parts of the lichen (Crittenden, 1991) contribute to the organic component of the protosoil produced, thus after a period of time (usually years), lichens contribute significantly to the formation of the mineral component of a new soil and to some degree to the organic component. B. The Role of Fungi in Rock Breakdown Fungi alone produce organic acids that are capable of breaking down rock. Ascaso and Wierzchos (1995) cite studies by Eckhardt (1985) that show that yeasts and filamentous fungi, such as Aspergillus niger, alone are involved in rock solubilization, releasing cations from amphibolite, biotite, and orthoclase. Penicillium and yeasts were also found to be able to dissolve calcium-rich rocks, such as limestone, marble, and calcium phosphate (Chang and Li, 1998). In addition, Connolly et al. (1998) showed that the white rot wood decay fungus Resinicium bicolor could solubilize strontianite sand to release the strontium contained within. This fungus was then able to translocate strontium through mycelial cords and secrete it, along with calcium oxalate crystals, in newly advancing zones of the mycelium in decaying wood. This activity demonstrates that not only does strontium behave similarly to calcium in fungal metabolism Chapter 234 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. but that this saprotrophic fungus can move strontium from the parent mineral substrate into a decomposing wood resource. The importance of translocation of nutrients, carbon, and water will be raised again throughout this book. This ability of fungal hyphae—on their own or as differentiated translocatory organs (rhizomorphs, strands, or cords)—is an important physiological trait of fungi that provides them with a mechanism to move materials within their own bodies (thalli) in relation to gradients of suppl y and demand. This movement of materials may occur at very small scales (mm to cm range), or in differentiated organs over distances of meters to tens of meters. At the ecosystem scale of resolution, this long-distance movement of nutrients, carbon, and water can have a profound effect on ecosystem function and the modification of heterogeneously distributed resources. Hirsch et al. (1995) showed a loose relationship among fungi, bacteria, and coccal cells (thought to be algae) that together form an endolithic community in sandstone and granite. Fungal species present included Alternar ia, Aspergillus, Aureobasidium, Candida, Cladosporium, Paecilomyces, Phoma, Penicillium, and Sporobolomyces. The production of organic acids by this assemblage of organisms was suggested to be responsible for the dissolution of rock, allowing the invasion by bacteria and other fungal species. In culture, Aspergillus niger has been shown to effect the solubilization of fluorapatite (Nahas et al., 1990). In a similar study, fungi were found in small holes (3–10 mm diameter) in feldspars and horneblende (Jongmans et al., 1997). It was shown that these holes were produced by micromolar concentrations of organic acids (succinic, citric, oxalic, formate, and malate) secreted by saprotrophic and ectomycorrhizal fungi associated with the overlying pine forest ecosystem. Thin sections of feldspars observed under the microscope have revealed fungal hyphae bearing cross walls in hyphal-generated tunnels in the rock (Hoffland et al., 2001, 2002). Fungi in symbiotic association with plant roots, mycorrhizae, have also been shown to play a role in the dissolution of parent rock material in more established soils. Sometimes fungi alone are capable of this activity, but often it is an evolved partnership between the mycorrhizal fungi and bacteria that work in a consortium. Azcon et al. (1976) showed that there were interactions between bacteria and arbuscular mycorrhizae of lavender, allowing the acquisition of phosphorus by the host plant from that released from rock phosphate by the rhizospheric microbial community. They showed there was a degree of synergism between the bacteria and mycorrhizal fungi and differences in behavior between the two mycorrhizal fungal species selected (Table 2.3). In their study of maize root systems, however, Berthelin and Leyval (1982) compared the ability of arbuscular mycorrhizal root systems of maize to nonsymbiotic rhizospheric microflora and combinations of the two in the weathering of micas. In experimental systems, measures of maize growth (bioma ss) and potassium, calcium, and magnesium uptake (derived from the breakdown of biotite) were Fungi and Primary Productivity 35 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. similar in plants with nonsymbiotic rhizospheric microflora and arbuscular mycorrhizal root systems, but there was no synergistic effect of the combination of mycorrhizae and bacteria. Suggesting the role of arbuscular mycorrhizal fungi alone in rock breakdown, Mojallala and Weed (1978) showed that mycorrhizal soybeans used weathered potassium from the biotites, phlogopite, and muscovite. The potassium released, however, was insufficient to sustain the enhanced growth of the mycorrhizal plants so that the tissue concentration of potassium was less in mycorrhizal than nonmycorrhizal plants. Electron microprobe analysis of the biotites showed that arbuscular mycorrhizal fungi increased the rock weathering with extensive potassium and some aluminum release from the edges of the phlogopite but not from muscovite (Hinsinger and Jaillard, 1993). The rate of release of potassium from phlogopite by ryegrass roots is related to the potassium demand by the plant. They did not, however, attribute these changes in parent rock chemistry and physics directly to the action of fungi or bacteria. Plant acquisition of nutrients from insoluble or poorly soluble sources is also enhanced by consortia of mycorrhizae, saprotrophic fungi, and bacteria. Singh and Kapoor (1998) showed that mung bean plants in association with a consortium of phosphate-solubilizing organisms could better obtain phosphorus from rock phosphate than each organism alone. The consortium consisted of the arbuscular mycorrhizal fungus Glomus fasciculatum, fungal saprotroph Cladosporium herbarum, and the bacterium Bacillus circulans. A field demonstration of the effect of rhizospheric microbial communities (including arbuscular mycorrhizae) on the release of phosphate from rock phosphate comes from the study of Vanlauwe et al. (2000) in Nigeria. The addition of rock phosphate to crops planted on low-P soils showed an immediate response in terms of increased mycorrhizal colonization and enhanced growth. This increase in growth showed a combined effect of the mycorrhizae TABLE 2.3 Interactions Between Bacteria and Arbuscular Mycorrhizae of Lavender in the Acquisition of Phosphorus from Rock Phosphate Plant growth Phosphorus uptake into plant Bacteria a . Control d . Control AM (E3) b . Control . Control AM (E3) þ bacteria .AM (E3) . Bacteria alone AM (YV) c . Control, . AM (E3) .Control, .AM (E3) AM (YV) þ bacteria . AM (YV) . AM (YV) a Mixture of Pseudomonas spp. and Agrobacterium spp. b Isolate E3 was thought to be Glomus fasciculatus. c Isolate YV was thought to be Glomus mosseae. d Control consisted of heat-killed bacteria and filtered mycorrhizal fungal washings. Source: Data from Azcon et al. (1976). Chapter 236 Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved. [...]... Hemicellulose Pectin Fungal enzyme system Lignin peroxidase, manganese peroxidase, glucose oxidase, cellobiose oxidase, arylalcohol oxidase, glyoxaloxidase, laccases Exo-1,4-b glucanase, endo-1,4-b glucanase, 1,4-b-glucosidases Endo-1,4-b xylanases, endo-1,4-b mannases, 1,4-b xylosidases, 1,4-b-D mannosidases, 1,4-b glucosidases, a-L arabinosidases, a-glucuronidases, a-galactosidases, acetylxylan esterases,... Kaempferol 3-glucoside 4-Coumaric acid ester 6-Isopentenylnaringenin 5-Pentadecylresorcinol Chrysin dimethyl ether Quercetin 7,30 -dimethylether Sakuranetin Lueone Pinocembrin Source: After Harborne (1997) Copyright 20 03 by Marcel Dekker, Inc All Rights Reserved Source Oak leaf Birch leaf Hops resin Mangifera fruit peel Heliochrysum leaf Wedelia leaf Ribes leaf gland Lupin leaf Poplar leaf Fungi and... N P 423 6 6484 44 32 36 55 28 3.8 3.7 2. 7 891 — 1107 2. 6 — 2. 5 0.8 — 0 .2 3854 3590 3144 43 — 26 4.6 — 3 .2 1046 — 6 02 3.7 — 1.1 0 .2 — 0.1 Source: From Vogt et al (1985); Boddy and Watkinson (1995) where wood can represent 30 –40% of the total biomass and 1 to 4 and 0.1 to 0.8 kg ha21 y21 of N and P, respectively Decomposition of woody debris and the mineralization of the nutrients contained within is... citing the work of Tisdall and Oades (19 82) This process spans five orders of magnitude, from the cementation of clay particles, each on the order of 0 . 2- mm diameter, through their interaction with microbial debris and interactions with living bacteria and fungi (20 mm scale), making aggregates in the 20 0-mm range to soil crumbs are at 20 00 mm in diameter (Table 2. 6) The importance of bacteria and fungi. .. Polygalacturonases, endo-1,4-a polygalacturonase, exo-1,4-a polygalacturonase, pectinlysases, pectinesterases Source: Information compiled from Sinsabaugh and Liptak (1997) Copyright 20 03 by Marcel Dekker, Inc All Rights Reserved Fungi and Primary Productivity 57 and total phosphorus into decomposing wood, however, ranged from 2. 2 to 4.4 mg g21 wood for P and 43 to 139 mg g21 for P at the time when... importance of fungal biomass in the high-organic-matter-content soils of the tundra ecosystems of Siberia Hyphal lengths of 393 and 27 m g21 dry weight soil were found in the Levinson-Lessing Valley, supporting typical tundra plant communities of dwarf willow communities and polygon soils, whereas low values of 9 m g21 dry weight soil can be found in the more fertile, lower-organic-content brown earth soils... Coniferous leaves 20 to 31 20 to 58 63 to 327 Wood 36 to 63 17 to 35 29 4 to 327 Fungi and Primary Productivity TABLE 2. 15 Changes in Plant Forms, Their Residues, the Dominant Fungal Groups Effecting Plant Litter Decomposition and the Interactions Between Fungi and Animals During Plant Seral Succession from Herbaceous Ground Cover to High Forest Changes in dominant fungal groups “Sugar fungi, ” ascomycetes,... Copyright 20 03 by Marcel Dekker, Inc All Rights Reserved 48 Chapter 2 nutrient immobilization in fungal biomass, binding of organic material with mineral material in soil to increase aggregate formation and aggregate stability as well as the decomposition of organic matter, are integrated functions carried our by fungi in association with other soil organisms (Beare et al., 1994a,b) 2. 1.3 Breaking Down... 0.10 4.08 7.47 9.80 12. 16 1.93 0.46 10 .23 16.13 23 .03 Source: After Gobran et al (1998) with kind permission of Kluwer Academic Publishers Copyright 20 03 by Marcel Dekker, Inc All Rights Reserved 38 Chapter 2 TABLE 2. 5 Comparison Between Rhizosphere and Bulk Soil Content of Weatherable Minerals Expressed as Mineral Intensity as a Percentage of the Quartz Peak at 100 Mineral Amphibole Interstratified vermiculite... the net carbon gain was calculated to be approximately 126 mg C m2 day21 Using a factor of approximately 25 0 foggy days per year at their research site, they calculated an annual gross primary production of 32 g C m 22; however, by factoring in respiration carbon loss the figure for net carbon gain by 100% lichen cover is on the order of 16 g C m 22 y21 Similarly, fast photosynthetic responses for cyanobacterial . intense mineral weathering with maximal Chapter 23 2 Copyright 20 03 by Marcel Dekker, Inc. All Rights Reserved. FIGURE 2. 1 Model indicating the four zones of activity within a mineral-weathering. and interactions with living bacteria and fungi (20 mm scale), making aggregates in the 20 0-mm range to soil crumbs are at 20 00 mmin diameter (Table 2. 6). The importance of bacteria and fungi in. be considered in this chapter are in bold face. Fungal groups in parentheses are regarded as of lesser importance in that function. Chapter 22 8 Copyright 20 03 by Marcel Dekker, Inc. All Rights