Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi.

Fine roots play a significant role in plant and ecosystem respiration (RS); therefore, understanding factors controlling that process is important both to advancing understanding and potentially in modelling carbon (C) budgets. However, very little is known about the extent to which ectomycorrhizal (ECM) identity may influence RS or the underlying chemistry that may determine those rates. In order to test these relationships, we examined RS, measured as O₂ consumption, of first-order ECM root tips of Pinus sylvestris L. and Quercus robur L. saplings in relation to their ECM fungal symbionts and associated nitrogen (N), C and non-structural carbohydrate concentrations. Roots of P. sylvestris were colonized by Rhizopogon roseolus, Tuber sp. 1 and an unknown species of Pezizales. Fungal species colonizing Q. robur roots were Hebeloma sp., Tuber sp. 2 and one unidentified ECM fungus described as Tuber-like based on ECM morphology. ECM RS rates for different host species were significantly different and more than 97% of the variation in RS within a host species was explained by ECM root tip N concentrations. This may indicate that some of the variability in fine root RS–N relationships observed between and within different host species or their functional groups may be related to intraspecific host species differences in root tip N concentration among ECM fungal associates.

Seedlings of forest tree species are exposed to a number of abiotic (organ loss or damage, light shortage) and biotic (interspecific competition) stress factors, which may lead to an inhibition of growth and reproduction and, eventually, to plant death. Growth of the host and its mycorrhizal symbiont is often closely linked, and hence, host damage may negatively affect the symbiont. We designed a pot experiment to study the response of light-demanding Pinus sylvestris and shade-tolerant Fagus sylvatica seedlings to a set of abiotic and biotic stresses and subsequent effects on ectomycorrhizal (ECM) root tip colonization, seedling biomass, and leaf nitrogen content. The light regime had a more pronounced effect on ECM colonization than did juvenile damage. The interspecific competition resulted in higher ECM root tip abundance for Pinus, but this effect was insignificant in Fagus. Low light and interspecific competition resulted in lower seedling biomass compared to high light, and the effect of the latter was partially masked by high light. Leaf nitrogen responded differently in Fagus and Pinus when they grew in interspecific competition. Our results indicated that for both light-demanding (Pinus) and shade-tolerant (Fagus) species, the light environment was a major factor affecting seedling growth and ECM root tip abundance. The light conditions favorable for the growth of seedlings may to some extent compensate for the harmful effects of juvenile organ loss or damage and interspecific competition.

The purpose of this study was to examine the effects of oxidative stress caused by hydroperoxide (H(2)O(2)) in the presence of iron ions (Fe(2+)) on mitochondria of the amoeba Acanthamoeba castellanii. We used isolated mitochondria of A. castellanii and exposed them to four levels of H(2)O(2) concentration: 0.5, 5, 15, and 25 mM. We measured basic energetics of mitochondria: oxygen consumption in phosphorylation state (state 3) and resting state (state 4), respiratory coefficient rates (RC), ADP/O ratios, membrane potential (DeltaPsi(m)), ability to accumulate Ca(2+) , and cytochrome c release. Our results show that the increasing concentrations of H(2)O(2) stimulates respiration in states 3 and 4. The highest concentration of H(2)O(2) caused a 3-fold increase in respiration in state 3 compared to the control. Respiratory coefficients and ADP/O ratios decreased with increasing stress conditions. Membrane potential significantly collapsed with increasing hydroperoxide concentration. The ability to accumulate Ca(2+) also decreased with the increasing stress treatment. The lowest stress treatment (0.5 mM H(2)O(2)) significantly decreased oxygen consumption in state 3 and 4, RC, and membrane potential. The ADP/O ratio decreased significantly under 5 mM H(2)O(2) treatment, while Ca(2+) accumulation rate decreased significantly at 15 mM H(2)O(2). We also observed cytochrome c release under increasing stress conditions. However, this release was not linear. These results indicate that as low as 0.5 mM H(2)O(2) with Fe(2+) damage the basic energetics of mitochondria of the unicellular eukaryotic organism Acanthamoeba castellanii.