Temporal dynamics of ectomycorrhizal fungal communities in Shorea siamensis forest fragments

Investigating the dynamics of ectomycorrhizal fungal (EMF) communities in seasonally dry tropical forests is essential for sustainable management and for understanding the resilience of this forest type in future climate change scenarios. EMF communities in secondary forest fragments with Shorea siamensis as a single host tree species in central Thailand were sampled seasonally for 2.5 y. Ten EMF taxa were identified from ectomycorrhizal morphotypes, with/tomentella-thelephora and/russula-lactarius as the dominant taxa. Seasonal differences in EMF diversity were not detected; the dominant morphotypes were present in both seasons and their abundance varied. Most EMF taxa exhibited wide environmental ranges and only a few taxa were correlated with soil moisture. Seasonal dynamics of ectomycorrhizal colonization was likely influenced by climatic factors and the phenology of host species. Together, these results suggested that climatic variation may have a long-term and subtle influence on the composition of ectomycorrhizal communities.     

The maximum nitrate reductase activity of the seagrass Zostera noltii (Hornem.) varies along its vertical distribution

Maximum nitrate reductase (NR) activity was measured in two intertidal morphotypes of Zostera noltii (Hornem.) in Ria Formosa tidal lagoon, southern Portugal. The two morphotypes develop in the upper and lower limits of the intertidal meadows. The NR activity was measured using an in vivo method, without cell disruption. NR activity was 30-40 fold higher in leaves than in roots, which indicates that nitrate reduction is essentially made through the aerial part of the plant. The effects of assay temperature (5 °C steps, from 5 to 45 °C), pH (7, 8 and 9) and elevation (upper and lower intertidal) on leaf NR activity were tested in a factorial design (n=5). Both elevation and assay temperature had a significant effect on NR activity, but not pH. NR activity was always higher in the upper intertidal plants, at all temperatures. Activity peaks for upper and lower plants were, respectively, 6.12 μmol NO₂⁻ g⁻¹ DW 0.5 h⁻¹ at 25 °C, and 3.30 μmol NO₂⁻ g⁻¹ DW 0.5h⁻¹ at 35 °C. Further investigation on environmental factors concerning the intertidal environment must be developed, as they are probably responsible for the significant differences found between the values of NR activity in the upper and lower morphotype.     

Vegetative compatibility and phenotypic characterization as a means of determining genetic diversity of Aspergillus flavus isolates

Toxigenic Aspergillus species produce mycotoxins that are carcinogenic, hepatotoxic and teratogenic immunosuppressing agents in both human and animals. Kenya frequently experiences outbreaks of aflatoxicosis with the worst occurring in 2010, which resulted in 215 deaths. We examined the possible reasons for these frequent aflatoxicosis outbreaks in Kenya by studying Aspergillus flavus diversity, phenotypes and mycotoxin profiles across various agricultural regions. Using diagonal transect random sampling, maize kernels were collected from Makueni, Homa Bay, Nandi, and Kisumu counties. Out of 37 isolates, nitrate non-utilizing auxotrophs complementation test revealed 20 vegetative compatibility groups. We designated these groups by the prefix “KVCG”, where “K” represented Kenya and consequently assigned numbers 1–20 based on our findings. KVCG14 and KVCG15 had highest distribution frequency (n = 13; 10.8 %). The distribution of the L-, S- and S-/L-morphotypes across the regions were 57 % (n = 21); 7 % (n = 3) and 36 % (n = 13), respectively. Furthermore, a unique isolate (KSM015) was identified that had characteristics of S-morphotype, but produced both aflatoxins B and G. Coconut agar medium (CAM) assay, TLC and HPLC analyses confirmed the presence or absence of aflatoxins in selected toxigenic and atoxigenic isolates. Diversity index (H′) analyses ranged from 0.11 (Nandi samples) to 0.32 (Kisumu samples). Heterokaryon compatibility ranged from 33 % (for the Makueni samples, n = 3) to 67 % (Nandi samples, n = 6). To our knowledge, this is the first reported findings for A. flavus diversity and distribution in Nandi, Homa Bay and Kisumu counties and may assist current and future researchers in the selection of biocontrol strategies to mitigate aflatoxin contamination as has been researched in Makueni and neighbouring counties.     

Vertical distribution of an ectomycorrhizal community in upper soil horizons of a young Norway spruce (Picea abies [L.] Karst.) stand of the Bavarian Limestone Alps

The vertical niche differentiation of genera of ectomycorrhiza (ECM) was assessed in a 17-year-old Norway spruce (Picea abies [L.] Karst.) plantation on a mountainous dolomitic site (1,050 m above sea level) of the Bavarian Limestone Alps. We determined ECM anatomotypes, recorded the abundance of corresponding ECM root tips and classified them into groups of ECM exploration types, which refer to the organisation and the extent of their extramatrical mycelia. The abundance of ECM was highest in the organic soil layers, compared to the mineral soil horizon. The ordination of the ECM communities and of the exploration types revealed segregation related to soil horizon properties. While Cenococcum geophilum preferred the organic soil layers, Lactarius spp., Tomentella spp. and Craterellus tubaeformis were generally most abundant in the mineral soil horizons. Cenococcum geophilum was the predominant species, possibly based on enhanced competitiveness under the prevailing site conditions. The short-distance exploration types (e.g. C. geophilum) preferentially colonised the organic soil layer, whereas the contact types (e.g. most of the Tomentella spp., C. tubaeformis) together with medium-distance types (e.g. Amphinema byssoides) were primarily associated with the underlying A-horizons. Therefore, the soil horizons had an important effect on the distribution of ECM and on their community structure. The spatial niche differentiation of ECM genera and exploration types is discussed in regard to specific physico-chemical properties of soil horizon and the assumed ecophysiological strategies of ECM.     

Abundance,diversity, and vitality of mycorrhizae of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) in lignite recultivation sites

Scots pine (Pinus sylvestris L.) stands cover large areas in the Lusatian and the Middle German lignite mining districts. Due to adverse chemical substrate conditions, the root systems of the trees are restricted to the ameliorated top-spoil and the organic forest floor layers. To investigate functioning of fine root systems under the prevailing site factors, we studied mycorrhizal colonization rate and frequency as well as mycorrhizal diversity, vitality and growth phases in Scots pine ecosystems along a chronosequence in both mining districts. Mycorrhizal rate was close to 100% in both districts. Mycorrhizal abundance was higher in the organic forest floor layer than the mineral soil layer. In total, 25 morphotypes were recorded. Diversity differed between the districts. The mycorrhizae of Amphinema byssoides, Tuber puberulum, Pinirhiza discolor, Pinirhiza cf. bicolorata and E-type were present in both mining areas. These morphotypes are typical of nutrient-rich soils with high pH values. Compared with the undisturbed sites, vitality of mycorrhizae was very high at the test sites on spoil substrate, correlating with the high growth dynamics of mycorrhizae at recultivation sites. A relatively high carbon flow to the mycorrhizal root systems at these sites seems likely. Thus, mycorrhizal root systems are able to cope with the ameliorated top-spoil and the organic layer. The main reason for the adaptation is the large number of ectomycorrhizal fungal species available in this area where Pinus sylvestris is indigenous.     

Morphotype community structure of ectomycorrhizas on Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings grown under elevated atmospheric CO2 and temperature

Mycorrhizas alter the acquisition of carbon and nutrients, thereby affecting numerous plant and ecosystem processes. It is important, therefore, to determine how mycorrhizal populations will change under possible future climate conditions. Individual and interactive effects of elevated atmospheric CO₂ concentration and atmospheric temperature were assessed in a 2×2 factorial design [ambient and elevated (200 ppm above ambient) CO₂ concentrations, and ambient and elevated (4°C above ambient) temperatures]. In June 1993, 2-year-old Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings were planted in 12 environment-tracking chambers (n=3) containing reconstructed, low-nitrogen, native forest soil. Climate treatments were imposed shortly thereafter, and the seedlings grew until June 1997. Soil cores were taken twice per year during the exposure period. We present findings on changes in the community structure of ectomycorrhizal (ECM) root tips, categorized into morphotypes using gross morphological traits. A diverse and stable community of morphotypes (a total of 40) was encountered; no more than 30 of which were seen at any sampling time. In the first sample, there were only 15 morphotypes found in the 12 chambers. Morphotype numbers increased during the first half of the experiment, remaining fairly constant thereafter. Near the end of the exposure, elevated-temperature treatments maintained more morphotypes than ambient treatments. However, overall, absolute measures (number of ECM tips) were affected primarily by CO₂ treatment, whereas proportional measures (e.g., Simpson’s index) were affected primarily by temperature. While some morphotypes were negatively affected seasonally by higher temperatures (putative Rhizopogon group), others (Cenococcum) seemed to thrive. Underlying the dominant patterns of change in diversity, driven by the Rhizopogon group, subdominant populations responded slightly differently. Community diversity through time tended to increase at a greater rate for all subdominant populations compared with the rate when dominant populations were included. Received: 16 August 1999 / Accepted: 2 March 2000     

Environmentally driven shift between alternative female morphotypes in the mottled shore crab

Precocious maturity is an important life history trait and might be advantageous if the juvenile habitat is risky. Larvae of the mottled shore crab Pachygrapsus transversus settle to the benthic habitat at a very large size, undergo a brief juvenile development and mature within a few months at a size about a fourth of the asymptotic maximum size for this species. This strategy may rely on the capacity of this species to molt to a juvenile-like morphotype (mI) in which reproduction is suppressed. In the laboratory, winter temperature triggered the puberty molt for a large proportion of juveniles, and still allowed high growth rates if combined with long photoperiod. This would result in a large number of juvenile crabs to join the adult reproductive stock in spring, at the beginning of the breeding season. Adult morphs (mII) grow faster under winter conditions, and therefore might be able to direct resources to reproduction during summer. Yet, females held in captivity without any interaction with conspecifics failed to maintain their reproductive status and often reversed to mI stages. In contrast, when a potential mate was presented, all crabs held their mII status, regardless of whether interaction involved visual, visual + chemical, or visual + chemical + tactile cues. Males discriminate female morphs, and physical interactions, including the inspection of mate receptivity and copulation, took longer when they were interacting with mII females. More than a trade-off between growth and reproduction, sustaining a breeding condition in P. transversus females is apparently a bet for successful mating in the presence of a suitable male conspecific.     

Variability of the upper incisors in the cave bears (Carnivora,Ursidae) from the Caucasus and Urals

Morphometric and morphotypic variability of the cave bear upper incisors from two different geographic regions (Caucasus and Urals), different stratigraphic periods (middle and late Pleistocene), and bearing different mitochondrial haplogroups (kudarensis and ingressus) was studied. The specific diet of the cave bears, i.e. hard vegetables, led to noticeable differences between their incisors and the incisors of the brown bear (Ursus arctos). It was found that the upper incisors of the Caucasian cave bears from different stratigraphic periods demonstrate consistent development of their morphology. The late Pleistocene cave bears from the Urals show a greater similarity to the Caucasian cave bears from earlier periods than with the cave bears from later periods. Our results suggest that the incisor morphology has evolved independently in the Caucasian and Ural cave bears as they belong to different phylogenetic lineages and display different ways of adaptation to local environmental conditions.     

Morphological and physiological differences between two morphotypes of Zostera noltii Hornem. from the south-western Iberian Peninsula

The morphological and physiological differences between two morphotypes of Z. noltii Hornem. were studied in the intertidal meadows on the south-western Iberian Peninsula (Palmones river estuary and Ria Formosa). A small-leaved morphotype (SM) grows mainly at high intertidal sites, meadow edges or in recently deposited sandbanks, whereas a large-leaved morphotype (LM) generally thrives in well-structured beds or in deeper places. This study deals with the morphological, biochemical and physiological differences between these morphotypes as well as the ecological implications of the occurrence of different morphotypes in the same meadow. Shoot length, leaf width, rhizome internode length, roots per node, root length, leaf nutrient and pigment contents, and photosynthetic rates of both morphotypes were compared. The below-ground architecture (root and rhizome complex) of both morphotypes was more developed in sites characterized by higher hydrodynamics and/or a lower nitrogen content in sediments. Both morphotypes showed similar values for photosynthetic efficiency, dark respiration rate and compensation irradiance. On the other hand, the net photosynthetic capacity was much greater (5-fold) for the SM. This difference could explain the greater growth rate and faster leaf turnover rate of the SM compared with the LM. The occurrence of the SM in newly settled areas (and in the meadow edges) could be explained on the basis of its higher growth rate, which would allow a faster spreading of the meadow and/or better recovery after burial resulting from stormy weathers. Received: 20 December 1998 / Received in revised form: 21 April 1999 / Accepted: 23 April 1999