Body composition of beetles

The adult beetles differed in body dry mass between species and showed sexual dimorphism of body size, with females being larger than males (Fig. 1; for details, seeS2 Table), but the difference in body size between sexes was significant only forS. rubra (Mann-Whitney U test, p<0.05).

The sexes of the pupae were not determined; their mass was intermediate between the adult masses of the two sexes or larger than the masses of either (Fig. 1; for details, seeS2 Table).

The complete data on elemental content are presented inS1 Table. The carbon mean content in imagines ranged from 51.7 to 63.3% d.m. and did not differ significantly between species or sexes, except forA. rusticus females, which had a significantly higher carbon content than males and females of other species.Ch. mariana pupae had a significantly lower C content thanS. rubra pupae (Table 1).

The mean nitrogen content ranged from 6% to 10.9% and differed significantly between species and sexes. The N content was significantly lower in females of all the species, and the pupae showed the lowest values (Table 1).

Males of all three species had similar P levels (av. 0.64%, SD 0.1;Table 1). Male and femaleS. rubra did not differ in P content, but their pupae had a significantly lower P content than adults. The P content differed significantly between the sexes inA. rusticus, and the pupae ofCh. mariana had a significantly higher P content thanS. rubra pupae (Table 1).

The levels of the eight other elements did not differ significantly within species, with only three exceptions: Ca (lower in male than in femaleS. rubra, higher in male than in femaleA. rusticus, Mann-Whitney U test, p<0.05;Table 1), Mg (lower in male than in femaleS. rubra;Table 1), and Fe (higher in male than in femaleA. rusticus;Table 1). The interspecific differences appear to reflect taxonomic relationships at the level of the subfamilies Buprestidae and Cerambycidae (Table 1):Ch. mariana pupae had higher K and Mg contents and lower Fe, Zn and Cu contents thanS. rubra pupae.Ch. mariana males had higher Na and Mg contents and lower Fe, Zn, ad Cu contents thanS. rubra males.A. rusticus males had higher Ca content thanS. rubra males.

PCA allowed for a simultaneous comparison of multi-elemental stoichiometries in all sex, age and species categories of the beetles studied. On the plane determined by the first two axes (54.4% of the total variance), the beetles tended to group according to taxonomy (species and subfamily) and sex (Fig. 2). The 1st component was loaded mostly by the variance of Fe, Cu, N, and Mg, and the 2nd component was loaded by K, Mn and P levels. The clusters for both sexes ofS. rubra greatly overlapped but differed from the pupae of this species (Fig. 2). The other two species tended to differ between themselves and to maintain the body multi-elemental stoichiometry across developmental stages and across sexes; no overlap occurred between clusters forCh. mariana pupae,Ch. mariana males, and the clusters for the representatives of Cerambycidae (Fig. 2). These tendencies were partly confirmed as statistically significant by the ANOVA computed independently for the 1st and 2nd axis scores (Fig. 3).

Elemental content and ergosterol content in wood

The relative concentrations of all elements except carbon tended to increase during the decay process. In the material from corridors, the elemental concentrations were similar to those in highly decayed wood, with the exception of Na, Zn and Mg (concentrations highest in corridors;Fig. 4, seeS1 Table for complete data set). The relative increments of the increase in concentration during wood decay (from category 1 to 3) were highest for nitrogen (23-fold), phosphorus (14-fold), copper (6.3-fold) and potassium (4-fold); the other elemental concentrations increased by 18% (Mn) to 136% (Fe).

Ergosterol content in dead wood significantly increased along the decay gradient; each wood category significantly differed from the two others (Kruskal-Wallis test, p<0.05,Fig. 5). The respective median values were 39.6 µg/g (dry mass) for the undecayed wood, 169 µg/g for the moderately decayed wood and 385.7 µg/g for the highly decayed wood (seeS4 Table for more details).

Stoichiometric mismatch expressed as the Trophic Stoichiometric Ratio (TSR values)

TheTSR values were highest for the undecayed wood for all the nutrients (Table 2,S3 Table). After pooling the data for the three species and both sexes (Table 2), the stoichiometric mismatch of undecayed wood as food, represented by theTSR values, reached three orders of magnitude for N, two orders of magnitude for P, one order of magnitude for K, Na, Mg, Zn and Cu, and less than one order of magnitude for Fe. No stoichiometric mismatch was shown for Ca and Mn: theTSR values for these nutrients were lower than one. The stoichiometric mismatch was lower in moderately decayed wood (two orders of magnitude for N and P, one order of magnitude for K, Na, Mg, Zn and Cu) and even lower for highly decayed wood (one order of magnitude for N, P, K, Na, Zn and Cu). TheTSR values calculated for corridors were between those for moderately decayed wood and highly decayed wood for most of the elements but were the lowest for Na, Mg and Zn (Table 2).

Stoichiometry of xylophages

For the three major body components (C, N, P), the body composition of adult xylophagous beetles falls within the broad range of values found in the few other coleopteran taxa studied to date[3],[8],[27],[28]. It has been suggested that besides a taxonomic idiosyncrasy or a presumed body mass allometry, N and P content may reflect the feeding strategy of invertebrates, with predators having higher concentrations of N and P than herbivores and detritivores[3],[27]. The xylophagous beetles studied here do not confirm this generalization: their N content is close to the high values reported for carnivores, and their P content is intermediate between herbivores and carnivores[3],[27]. However, our results are consistent with species-specific data provided by Fagan et al.[3], who found high N levels in several cerambycid and buprestid beetles. Females of all three species studied here have significantly lower N concentrations than males of the same species, possibly associated with the higher fat content in the females.

Because the sex of pupae could not be determined, and the samples most likely contain individuals of both sexes, their average body composition should be intermediate between males and females. The position of pupae of the two species studied on the PCA plot (Fig. 3) suggests that they have relatively high C levels and low N and P levels. This result may be attributed to the higher C:N ratio of the chitinous exuvium left behind at eclosion and the fat reserves exhausted during the pupal stage.

Stoichiometry of wood decay

The concentrations of the nutrients (N, P, K, Ca, Mg) measured in the sapwood and heartwood of living gymnosperm trees[5] are an order of magnitude greater than in the undecayed wood of the dead pine stumps that we studied. The stumps, cut one to four years before the wood samples were taken for analysis, were remnants of trees cut when they were at least 80 years old. Palviainen et al.[6],[7] reported similarly low nutrient concentrations measured in pine stumps during the first five years of decay after cutting. Meerts[5] suggested that mineral nutrients in a living tree may be recycled from senescing sapwood. After cutting, the stumps are exposed to weathering and may be further depleted of nutrients until the fungal mycelium growing into the wood enriches it with nutrients, particularly N and P, imported from outside the system[29]–[31]. Even so, there is still a significant difference in the stoichiometries between partly decayed wood and the insects feeding on it. The nutritional composition of corridor material is similar to that of the wood from which the samples were taken (moderately and highly decayed), except for Na, Zn and Mg, which are present in the corridors at higher concentrations (Fig. 4). Most of the corridors that we measured originated from moderately decayed wood and less commonly from highly decayed wood. It is not clear whether the chemical composition of the wood is nonuniform and the larvae bore selectively in the more nutritious areas or whether the chemical composition of the corridors changed due to the more intense penetration of fungal mycelium following larval activity.

The dynamics of nutrient content in decaying wood

Two mechanisms contribute to the decrease of C:x ratios during decay, that is, to the enrichment of the wood with elements other than C, H and O: (i) the liberation of C as CO₂ due to microbial and animal respiration, and (ii) the import of nutrients from outside the system by fungal tissue (mycelium) growing into the decaying wood. To determine whether elements are imported in significant amounts during wood decay, we assessed the relative contributions of the two mechanisms from the stoichiometric proportions of specific elements in the wood at various stages of decay.

The initial (SRI) and final (SRF) stoichiometric ratios in decaying wood for a given element x may be expressed as:

(2)

(3)

wherepC_I andpX_I are initial relative concentrations of carbon and of elementx, respectively;C_I,C_F,X_I andX_F are the initial and final absolute amounts of carbon and of element x, respectively; α represents the proportion of carbon not released as CO₂ during decay; andβ represents the coefficient of enrichment of elementx.

Fromequation (3), it follows that

(4)

A value ofβ>>1 would indicate an increase of the absolute amount of elementx in the wood during decay. The coefficientα is defined as:

(5)

whereM_I andM_F are initial and final masses of decaying wood, respectively.

The concentration of carbon decreases from 55% to 48.9% during decay (Table 1); thus,pC_F/pC_I  = 0.489/0.550 = 0.889. The unknown proportionM_F/M_I can approximated from literature data concerning the rates of decay of coarse woody debris (e.g.[32],[33]), including those of conifer stumps[34],[35]. The proportion of the remaining mass of woodd aftert years of decomposition is usually described with exponential model. The experimentally evaluated constantk may range between 0.020 and 0.1101, depending on the tree taxon, environmental conditions and the methods used[32]–[35]. Samples of wood at advanced stages of decay were taken from the stumps of trees cut 3 or 4 years before sampling. The model solved for 3 years of decay using these figures yields the proportion of remaining mass between 0.72 and 0.94 and solved for 4 years 0.64 to 0.92. Based on these estimates, the possible values of the coefficient α (eq. 5) may range from 0.57 to 0.84. The range ofβ values can be estimated for each elementX usingβ_x = α×SRI_x/SRF_x, whereSRI_x andSRF_x are the measured initial and finalC/X ratios. The results (Table 3) show that independently of the assumed value of α, the amounts of Na, Ca, Mg, Zn, Mn and Fe do not increase during decay (coefficients of enrichment do not deviate substantially from 1.0, ranging from 0.7 to 1.4 forα = 0.57 and from 1.0 to 2.1 forα = 0.84), but the contents of N, P, Cu and K increase several fold, independent of the assumed value ofα (Table 3). Thus, the change in the relative concentrations of these elements is not only the result of the carbon escape from decaying wood but also the result of the net import of these elements from outside of the system.

Although part of the additional N may be supplied by nitrogen-fixing bacteria, which are known to occur in decayed plant matter[36], fungi appear to be the only agents translocating other nutrients from outside of the system to the decaying wood. In fact, the ergosterol content (the fungal tissue proxy) increased along the decay gradient and differed significantly between dead wood categories (Fig. 5). The measured ergosterol contents cannot be simply recalculated into fungal biomass because the conversion factors are strongly dependent on the fungal species[37]. However, the contents of N, P. K and Cu in the mycelium of wood decaying fungi[38],[39] and in the fruiting bodies of mushrooms[38],[40] are two to three orders of magnitude higher than in undecayed wood (this study), while the contents of the other elements studied here differ less than one order of magnitude.

Thus, the increase in nutrient concentration in decaying wood may be attributed to the action of fungi. An experiment in which xylophagous beetle larvae were fed with fungi instead of wood[41] showed that fungi can be an adequate food source for these insects. Fungi inhabiting dead wood have been described as nutrient immobilizers[42], and our data support the view that fungi may serve as nutrient deliverers[6],[7],[30],[31],[43],[44]. The translocation of elements by fungi in the forest floor is a well-known phenomenon[29],[30],[45],[46].

Nutritional imbalance in wood-boring insects

The concentrations of elements in the imagines and pupae were one or more orders of magnitude greater than in the potential food of the larvae, except for Ca, Mn and Fe, which showed a less pronounced discrepancy (Table 1). The mismatch, expressed as theTSR value, is most striking for undecayed wood (three orders of magnitude for nitrogen) and diminishes as wood decay proceeds, but the differences remain large (Table 2; for full data set, seeS3 Table). The nutrient content of wood from corridors is close to that of highly decayed wood (Table 2). The most extreme differences are for N and P, which are, respectively, 1500–2000 and 500–900 times less concentrated in undecayed wood than in the beetles. The concentration differences for Cu, K and Na are also significant. Cu is approximately 86 times higher in beetles than in undecayed wood. The K and Na concentrations are 54 and 50 times higher, respectively, in the beetles than in undecayed wood (Table 2). Only Ca and Mn are available in excess. The other nutrients (K, Na, Mg, Fe, Zn, Cu) are much more scarce in dead wood, such that they may constrain the development of wood-eating larvae. All the elemental concentrations tend to increase as wood decay proceeds (Table 2,Fig. 4), although theTSR values remain quite high for N and P. Considering wood as the exclusive source of nutrients, xylophagous beetles seem to be faced with the most unbalanced diet of all organisms studied to date. Even termites live on a less unbalanced diet[16].

The N and P stoichiometric mismatches were similar in all three studied species. We found differences concerning other nutrients: the Na mismatch forCh. mariana is almost twice as high as that of the Cerambicidae beetles, whereas the Fe and Cu deficiencies forCh. mariana are two to one order of magnitude lower. Thus, according to this study, different taxa of xylophagous beetles occupying the same nutritional niche may be faced with different stoichiometric mismatches concerning elements other than N and P.

Nutritional limitations of xylophage life history and stoichiometric compensation by fungi

Walczyńska[19],[20], using experimental measurements of consumption, assimilation and growth efficiences of larvae feeding on pine wood (with stoichiometric conditions identical to the ones used in the present study), demonstrated that the low digestibility of wood may affect the life history ofS. rubra by prolonging the development time. This result poses the following question: is the development time long enough to concentrate essential nutrients to the levels required in the body? We calculated the minimum growth period needed to collect sufficient essential elementx (GP_x, years) as

(6)

whereB – average mass of a larva,A_X – concentration of elementx in the body of an imago or pupa,K – daily food consumption rate averaged through the development period (after Walczyńska[19]),F_X – concentration of elementx in food. The conversion efficiency of limiting nutrients was assumed at 100%, and seasonal changes in the food consumption rate were incorporated (nothing was consumed for half the year).

Eating an exclusive diet of undecayed wood would lengthen the time needed to form body tissues to an implausible 40 years for males and 85 years for females (Table 4), and the overall assimilation efficiency would drop to improbably low values. Based on field observations, the maximum development time forS. rubra was estimated at three years[25]. Only highly decayed pine stumps or the material from corridors could provide the beetles with enough of the most limiting nutrients. Larvae found in highly decayed stumps were quite well developed at the age of at least 1.5 years. The stumps were likely not highly decayed during early larval development. The great majority of larvae collected from stumps were found in moderately decayed wood, which is relatively poor in nutrients (Tables 2,4). The higher content of nutritive elements in material from corridors may suggest that larvae are capable of selecting areas of wood more heavily infected with fungi and thus providing adequate amounts of nutrients or that the activity of the larvae facilitates fungal infection through the corridors (Fig. 2). Nonetheless, the enriched chemical composition of material from corridors permits the beetles to complete their life cycle within their maximal lifetime in males (Table 4). The females must further prolong their life history to be able to assimilate the amount of nutrients sufficient to build up their bodies.

Wood-boring insects, enhancing the decomposition process of dead wood by mechanical grinding and fragmentation of the solid stumps, depend in turn on the fungal supplementation of their food with nutrients. Thus, elemental transport by fungi plays a pivotal role in the function of forest ecosystems: matching the stoichiometric balance between the trophic links.

• 1.Denno RF, Fagan WF (2003) Might nitrogen limitation promote omnivory among carnivorous arthropods?Ecology84:2522–2531 Available:http://www.esajournals.org/doi/abs/10.1890/02-0370. [DOI] [PubMed] [Google Scholar]
• 2.Hessen DO, Elser JJ, Sterner RW, Urabe J (2013) Ecological stoichiometry: An elementary approach using basic principles. Limnol Oceanogr58:2219–2236 Available:http://www.aslo.org/lo/toc/vol_58/issue_6/2219.html. [Google Scholar]
• 3.Fagan WF, Siemann E, Mitter C, Denno RF, Huberty AF, et al. (2002) Nitrogen in insects: implications for trophic complexity and species diversification. Am Nat160:784–802 Available:http://www.ncbi.nlm.nih.gov/pubmed/18707465. [DOI] [PubMed] [Google Scholar]
• 4.Schneider K, Kay AD, Fagan WF (2010) Adaptation to a limiting environment: the phosphorus content of terrestrial cave arthropods. Ecol Res25:565–577 Available:http://www.springerlink.com/index/10.1007/s11284-009-0686-2. [Google Scholar]
• 5.Meerts P (2002) Mineral nutrient concentrations in sapwood and heartwood: a literature review. Ann For Sci59:713–722 Available:http://www.edpsciences.org/10.1051/forest:2002059. [Google Scholar]
• 6.Palviainen M, Finér L, Laiho R, Shorohova E, Kapitsa E, et al. (2010) Phosphorus and base cation accumulation and release patterns in decomposing Scots pine, Norway spruce and silver birch stumps. For Ecol Manage260:1478–1489 Available:http://linkinghub.elsevier.com/retrieve/pii/S0378112710004408. [Google Scholar]
• 7.Palviainen M, Finér L, Laiho R, Shorohova E, Kapitsa E, et al. (2010) Carbon and nitrogen release from decomposing Scots pine, Norway spruce and silver birch stumps. For Ecol Manage259:390–398 Available:http://linkinghub.elsevier.com/retrieve/pii/S0378112709007762. [Google Scholar]
• 8.Elser JJ, Fagan WF, Denno RF, Dobberfuhl DR, Folarin a, et al. (2000) Nutritional constraints in terrestrial and freshwater food webs. Nature408:578–580 Available:http://www.ncbi.nlm.nih.gov/pubmed/11117743. [DOI] [PubMed] [Google Scholar]
• 9.Rumpold BA, Schlüter OK (2013) Nutritional composition and safety aspects of edible insects. Mol Nutr Food Res57:802–823 Available:http://www.ncbi.nlm.nih.gov/pubmed/23471778. [DOI] [PubMed] [Google Scholar]
• 10.Joern A, Provin T, Behmer ST (2012) Not just the usual suspects: Insect herbivore populations and communities are associated with multiple plant nutrients. Ecology93:1002–1015 Available:http://www.ncbi.nlm.nih.gov/pubmed/22830354. [DOI] [PubMed] [Google Scholar]
• 11.Cohen A (2005) Insect diets: science and technology. CRC Press.
• 12.Karimi R, Folt CL (2006) Beyond macronutrients: element variability and multielement stoichiometry in freshwater invertebrates. Ecol Lett9:1273–1283 Available:http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2006.00979.x/abstract. [DOI] [PubMed] [Google Scholar]
• 13.Quigg A, Irwin AJ, Finkel ZV (2011) Evolutionary inheritance of elemental stoichiometry in phytoplankton. Proc Biol Sci278:526–534 Available:http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3025679&tool=pmcentrez&rendertype=abstract. [DOI] [PMC free article] [PubMed] [Google Scholar]
• 14.Twining BS, Baines SB (2013) The trace metal composition of marine phytoplankton. Ann Rev Mar Sci5:191–215 Available:http://www.ncbi.nlm.nih.gov/pubmed/22809181. [DOI] [PubMed] [Google Scholar]
• 15.Schneider T, Keiblinger KM, Schmid E, Sterflinger-Gleixner K, Ellersdorfer G, et al. (2012) Who is who in litter decomposition? Metaproteomics reveals major microbial players and their biogeochemical functions. ISME J6:1749–1762 Available:http://www.ncbi.nlm.nih.gov/pubmed/22402400. [DOI] [PMC free article] [PubMed] [Google Scholar]
• 16.Sterner RW, Elser JJ (2002) Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere. Princeton: Princeton University Press.
• 17.Ayres MP, Wilkens RT, Ruel JJ, Lombardero MJ, Vallery E (2000) Nitrogen Budgets of Phloem-Feeding Bark Beetles with and without Symbiotic Fungi. Ecology81:2198–2210 Available:http://www.jstor.org/stable/info/177108. [Google Scholar]
• 18.Haack RA, Slansky FJ (1987) Nutritional ecology of wood feeding Coleoptera, Lepidoptera and Hymenoptera. In: Slansky FJ, Rodriguez JGeditors. Nutritional eclology of insects, mites, spiders, and related invertebrates. New York: John Wiley & Sons Inc. pp.449–486.
• 19.Walczyńska A (2007) Energy budget of wood-feeding larvae of Corymbia rubra (Coleoptera: Cerambycidae). Eur J Entomol104:181–185 Available:http://www.eje.cz/pdfarticles/1216/eje_104_2_181_Walczynska.pdf. [Google Scholar]
• 20.Walczyńska A (2012) How does a xylem-feeder maximize its fitness?Bull Entomol Res102:644–650 Available:http://www.ncbi.nlm.nih.gov/pubmed/23146159. [DOI] [PubMed] [Google Scholar]
• 21.Walczyńska A (2010) Is wood safe for its inhabitants?Bull Entomol Res100:461–465 Available:http://www.ncbi.nlm.nih.gov/pubmed/19939320 Accessed 25 January 2011.. [DOI] [PubMed] [Google Scholar]
• 22.Douglas AE (2009) The microbial dimension in insect nutritional ecology. Funct Ecol23:38–47 Available:http://blackwell-synergy.com/doi/abs/10.1111/j.1365-2435.2008.01442.x. [Google Scholar]
• 23.Mooshammer M, Wanek W, Zechmeister-Boltenstern S, Richter A (2014) Stoichiometric imbalances between terrestrial decomposer communities and their resources: mechanisms and implications of microbial adaptations to their resources. Front Microbiol5:22 Available:http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3910245&tool=pmcentrez&rendertype=abstract. [DOI] [PMC free article] [PubMed] [Google Scholar]
• 24.Klamer M, Bååth E (2004) Estimation of conversion factors for fungal biomass determination in compost using ergosterol and PLFA 18:2ω6,9. Soil Biol Biochem36:57–65 Available:http://linkinghub.elsevier.com/retrieve/pii/S0038071703002931. [Google Scholar]
• 25.Dominik J, Starzyk JR (2004) Owady uszkadzaja˛ce drewno. (Wood Damaging Insects). Warsaw: PWRiL.
• 26.Esseen P-A, Ehnström B, Ericsson L, Sjöberg K (1997) Boreal forests. Ecol Bull46:16–47. [Google Scholar]
• 27.González AL, Fariña JM, Kay AD, Pinto R, Marquet P a. (2011) Exploring patterns and mechanisms of interspecific and intraspecific variation in body elemental composition of desert consumers. Oikos120:1247–1255 Available:http://doi.wiley.com/10.1111/j.1600-0706.2010.19151.x. [Google Scholar]
• 28.Sun X, Zhou X, Small GE, Sterner R, Kang H, et al. (2013) Energy storage and C:N:P variation in a holometabolous insect (Curculio davidi Fairmaire) larva across a climate gradient. J Insect Physiol59:408–415 Available:http://www.sciencedirect.com/science/article/pii/S0022191013000310. [DOI] [PubMed] [Google Scholar]
• 29.Boddy L, Watkinson SC (1995) Wood decomposition, higher fungi, and their role in nutrient redistribution. Can J Bot73:1377–1383 Available: 10.1139/b95-400. [DOI] [Google Scholar]
• 30.Watkinson SC, Bebber D, Darrah P, Fricker M, Tlalka M, et al. (2006) The role of wood decay fungi in the carbon and nitrogen dynamics of the forest floor. In: Gadd GMeditor. Fungi in Biogeochemical Cycles. Cambridge: Cambridge University Press. pp.151–181. doi:doi: 10.2277/0521845793. [DOI]
• 31.Clinton PW, Buchanan PK, Wilkie JP, Smaill SJ, Kimberley MO (2009) Decomposition of Nothofagus wood in vitro and nutrient mobilization by fungi. Can J For Res39:2193–2202 Available:http://www.nrcresearchpress.com/doi/abs/10.1139/X09-134. [Google Scholar]
• 32.Russell MB, Woodall CW, Fraver S, D'Amato AW, Domke GM, et al. (2014) Residence Times and Decay Rates of Downed Woody Debris Biomass/Carbon in Eastern US Forests. Ecosystems17:765–777 Available:http://link.springer.com/10.1007/s10021-014-9757-5. [Google Scholar]
• 33.Fukasawa Y, Katsumata S, Mori AS, Osono T, Takeda H (2014) Accumulation and decay dynamics of coarse woody debris in a Japanese old-growth subalpine coniferous forest. Ecol Res29:257–269 Available:http://link.springer.com/10.1007/s11284-013-1120-3. [Google Scholar]
• 34.Tobin B, Black K, McGurdy L, Nieuwenhuis M (2007) Estimates of decay rates of components of coarse woody debris in thinned Sitka spruce forests. Forestry80:455–469 Available:http://forestry.oxfordjournals.org/cgi/doi/10.1093/forestry/cpm024. [Google Scholar]
• 35.Garrett LG, Oliver GR, Pearce SH, Davis MR (2008) Decomposition of Pinus radiata coarse woody debris in New Zealand. For Ecol Manage255:3839–3845 Available:http://linkinghub.elsevier.com/retrieve/pii/S0378112708002776. [Google Scholar]
• 36.Roskoski JP (1980) Nitrogen fixation in hardwood forests of the northeastern United States. Plant Soil54:33–44 Available:http://link.springer.com/10.1007/BF02181997. [Google Scholar]
• 37.Niemenmaa O, Galkin S, Hatakka A (2008) Ergosterol contents of some wood-rotting basidiomycete fungi grown in liquid and solid culture conditions. Int Biodeterior Biodegradation62:125–134 Available:http://linkinghub.elsevier.com/retrieve/pii/S0964830508000024. [Google Scholar]
• 38.Vetter J (2005) Mineral composition of basidiomes of Amanita species. Mycol Res109:746–750 Available:http://linkinghub.elsevier.com/retrieve/pii/S095375620861477X. [DOI] [PubMed] [Google Scholar]
• 39.Campos JA (2011) Nutrients and trace elements content of wood decay fungi isolated from oak (Quercus ilex). Biol Trace Elem Res144:1370–1380 Available:http://www.ncbi.nlm.nih.gov/pubmed/21748305. [DOI] [PubMed] [Google Scholar]
• 40.Rudawska M, Leski T (2005) Macro- and microelement contents in fruiting bodies of wild mushrooms from the Notecka forest in west-central Poland. Food Chem92:499–506 Available:http://linkinghub.elsevier.com/retrieve/pii/S0308814604006272. [Google Scholar]
• 41.Tanahashi M, Matsushita N, Togashi K (2009) Are stag beetles fungivorous?J Insect Physiol55:983–988 Available:http://www.ncbi.nlm.nih.gov/pubmed/19607834. [DOI] [PubMed] [Google Scholar]
• 42.Dighton J (2007) Nutrient Cycling by Saprotrophic Fungi in Terrestrial Habitats. In: Kubicek CP, Druzhinina IS, editors. Environmental and Microbial Relationships. Springer Berlin Heidelberg. pp.287–300. Available: 10.1007/978-3-540-71840-6_16. [DOI]
• 43.Lindahl BD, Ihrmark K, Boberg J, Trumbore SE, Högberg P, et al. (2007) Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forest. New Phytol173:611–620 Available:http://www.ncbi.nlm.nih.gov/pubmed/17244056. [DOI] [PubMed] [Google Scholar]
• 44.Lindahl BD, Taylor AFS, Finlay RD (2002) Defining nutritional constraints on carbon cycling in boreal forests–towards a less “phytocentric” perspective. Plant Soil242:123–135 Available:http://www.springerlink.com/index/V0257708411214Q2.pdf. [Google Scholar]
• 45.Cairney J (2005) Basidiomycete mycelia in forest soils: dimensions, dynamics and roles in nutrient distribution. Mycol Res109:7–20 Available:http://linkinghub.elsevier.com/retrieve/pii/S0953756208613696 Accessed 2 March 2012.. [DOI] [PubMed] [Google Scholar]
• 46.Boddy L, Hynes J, Bebber DP, Fricker MD (2009) Saprotrophic cord systems: dispersal mechanisms in space and time. Mycoscience50:9–19 Available:http://www.springerlink.com/index/10.1007/s10267-008-0450-4. [Google Scholar]

Supplementary Materials

Data Availability Statement

The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files.