Can ectomycorrhizal fungi circumvent the nitrogen mineralization for plant nutrition in temperate forest ecosystems?

Nitrogen (N) limits plant growth in many forest ecosystems. The largest N pool in the plant-soil system is typically organic, contained primarily within the living plants and in the humus and litter layers of the soil. Understanding the pathways by which plants obtain N is a priority for clarifying N cycling processes in forest ecosystems. In this review, the interactions between saprotrophic microorganisms and ectomycorrhizal fungi in N nutrition with a focus on the ability of ectomycorrhizal fungi to circumvent N mineralization for the nutrition of plants in forest ecosystems will be discussed. Traditionally, it is believed that in order for plants to fulfill their N requirements, they primarily utilize ammonium (NH₄⁺) and nitrate (NO₃⁻). In temperate forest ecosystems, many woody plants form ectomycorrhizas which significantly improves phosphorus (P) and N acquisition by plants. Under laboratory conditions, ectomycorrhizal fungi have also been proven to be able to obtain N from organic sources such as protein. It was thus proposed that ectomycorrhizal fungi potentially circumvent the standard N cycle involving N mineralization by saprotrophic microorganisms. However, in many forest ecosystems the majority of the proteins in the forest floor form complexes with polyphenols. Direct access of N by ectomycorrhizal fungi from a polyphenol-protein complex may be limited. Ectomycorrhizal fungi may depend on saprotrophic microorganisms to liberate organic N sources from polyphenol complexes. Thus, interactions between saprotrophic microorganisms and ectomycorrhizal fungi are likely to be essential in the cycling of N within temperate forest ecosystems.     

Can landscape and species characteristics predict primate presence in forest fragments in the Brazilian Amazon?

Habitat loss and fragmentation are global conservation concerns, but animal species do not respond to these threats in the same manner. At the Biological Dynamics of Forest Fragments Project (BDFFP), located 80 km north of Manaus, Amazonas, Brazil, the distribution and persistence of six native primate species differ among fragments that were isolated in 1980s. We identified both landscape and species characteristics predicting the presence of primates in these forest fragments. Fragment size positively and distance to nearest forested area negatively predicted primate species richness in the fragments; however, these relationships were not straightforward because these two variables were correlated. The proportion of fruit in a species’ diet was the most important factor predicting its presence in the forest fragments, with species relying primarily on frugivory faring poorly. Home range size was the second-best predictor of a species’ presence; however, some species with large home ranges were present in the 10-ha forest fragments. The extent to which the individual primate species traveled in and out of the fragments varied, suggesting that further research is necessary to determine the primary factors that lead to the animals’ use of the matrix. We conclude that in addition to conserving large tracts of habitat, reducing the isolation of the forest fragments through the creation of forest corridors and through the presence of additional forest fragments within the agricultural matrix may increase animal movement across the landscape. Such changes to the matrix may be critical for those species that do not readily traverse non-forested areas.     

Are roads and railroads barriers to bumblebee movement in a temperate suburban conservation area?

We investigated how habitat fragmentation affects the movement of marked bumblebees between plant patches in a temperate conservation area in metropolitan Boston, Massachusetts. Our study was conducted on populations of sweet pepperbush (Clethra alnifolia L. f.) separated by a road and natural woodland, and buttonbush (Cephalanthus occidentalis L.) separated by a railroad. Bumblebees showed high site fidelity and only rarely crossed roads or railroads. When bees captured at one sweet pepperbush population were moved across a road to a new sweet pepperbush population and released, they returned to their original site, some within 20 min of their capture. When all inflorescences were removed from one sweet pepperbush patch, most bees moved to another sweet pepperbush population on the same side of the road. The results show that while bumblebees have the ability to cross a road and railroad, these human structures may restrict bumblebee movement and act to fragment plant populations because of the innate site fidelity displayed by foraging bees. Moreover, marked bees were almost never observed to move between populations unless they were displaced, or forced to seek additional forage sites.     

Are the declining trends in forest grouse populations due to changes in the forest age structure? A case study of Capercaillie in Finland

In Finland, Capercaillie (Tetrao urogallus) populations have a history of serious decrease starting from the mid-20th century. The decline is temporally in line with the expansion of modern forestry practices that created major changes in the landscape. We used tetraonid route-censuses from 18 forestry board districts and Finnish forest inventories (data on forest stand structure) to analyze the decline in 1965-1988. We used information theoretical model selection to evaluate a set of log-linear second order autoregressive models, allowing for spatially correlated process errors. The average trend throughout the country corresponded to an annual decline of 4.01% (mean of local trends) ± 0.24% (SEM), parallel to a half-life of 17 years. The decline was surprisingly uniform throughout the country (SD = 1.01%) and most parsimoniously explained by a geographically constant log-linear trend. At the large scale of observation applied here, population trends could not be explained by the proportional increase of younger forest age classes (<40 years old and <80 years old, respectively). Our analysis does not support the hypothesis that the decline in Capercaillie numbers is due to changes in the forest age structure, but we cannot exclude the possibility that other factors behind the decline may have interacted with forestry in general. From a conservation point of view, we caution against over-emphasizing the role of forest age especially at large spatial scales, but leaning also on other research, we recommend that more management efforts would go into the preservation of the overall forest cover and the original physiognomy in single forest patches.     

Soil–atmosphere greenhouse gas exchange in a cool,temperate Eucalyptus delegatensis forest in south-eastern Australia

Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH₄) sink, whilst producing little nitrous oxide (N₂O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil–atmosphere N₂O, CH₄ and CO₂ exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N₂-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO₂ exchange. CH₄ was taken up by the forest soil (?51.8 μg CH₄-C m^?2 h^?1) and was significantly correlated with relative saturation (S_r) of the soil. The soil within creek lines was a net CH₄ source (up to 33.5 μg CH₄-C m^?2 h^?1), whereas the wider forest soil was a CH₄ sink regardless of distance from the creek line. Soil N₂O emissions were small (<3.3 μg N₂O-N m^?2 h^?1) throughout the 2-week period, despite major rain and snowfall. Soil N₂O emissions only correlated with soil and air temperature. The presence of A. dealbata in the understorey had no influence on the magnitude of CH₄ uptake, N₂O emission or soil N parameters. N₂O production increased with increasing soil moisture (up to 50% S_r) in laboratory incubations and gross nitrification was negative or negligible as measured through ¹⁵N isotope pool dilution.The small N₂O emissions are probably due to the limited capacity for nitrification in this late successional forest soil with C:N ratios >20. Soil–atmosphere exchange of CO₂ was several orders of magnitude greater (88.8 mg CO₂-C m^?2 h^?1) than CH₄ and N₂O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22 kg CO₂-equivalents ha^?1 d^?1) during the 2-week measurement period, of which soil CH₄ uptake contributed only 0.3% and N₂O emissions offset only 0.3%.     

Lime-induced growth depression in Lupinus species: Are soil pH and bicarbonate involved?

In a series of experiments, the effect of elevated pH on root growth of different lupin genotypes and lime-tolerant Pisum sativum was assessed. Seedlings were cultivated in pH-controlled but unbuffered nutrient or test solutions with pH 5—8 under constant light or constant darkness. Moderately increased solution pH did not affect root elongation. At high pH, root elongation rates were reduced by less than 35%, L. luteus being most sensitive. In a further experiment, effects of 10 mM bicarbonate (HCO₃^-) and organic buffers (MES, TES) were examined. Bicarbonate severely affected root elongation of lupins, sensitivity increasing in the order Lupinus albus < L. angustifolius < L. luteus. Since the reduced root elongation was not accompanied by a decreased root weight, specific root weight was increased. Shoot growth was not affected by HCO₃^-. Addition of organic buffers to alkaline nutrient solution, similarly to HCO₃^-, reduced elongation of main roots, but not that of laterals. Both treatments increased citrate concentrations in roots of sensitive L. luteus, but not of tolerant L. albus. Other carboxylates were not related to growth inhibition. Xylem exudate pH was always below 5.8, indicating that HCO₃^- was probably not translocated to the shoot. It is concluded that HCO₃^- is a key factor for lime-induced growth inhibition of calcifuge lupins, with the roots, not the shoots, being primarily affected.     

Are there temporal trends in root architecture and soil aggregation for Hordeum vulgare breeding lines?

The crucial role of roots in mediating agricultural sustainability and food security is becoming more widely appreciated. Here we tested the potential impact of barley (Hordeum vulgare L.) breeding (German germplasm) on root architecture and possible ripple-on effects on soil aggregation. In a greenhouse study, we tested two barley breeding lines. We focused on very fine (<0.2 mm) and fine (0.2–1 mm) roots. Soil structure was measured as percentage of water-stable macroaggregates and aggregate size distribution from dry-sieving. Breeding of barley reduced very fine root length of one of the tested lines but had no effect on our measures of soil structure. Our results indicate that breeding practices need not lead to an overall decline in root length. While we did not find that reduced very fine root length propagated to negative effects on soil structure parameters, additional studies should address this important aspect in other crop lineages and soils.     

Variations in the soil microbial community composition of a tropical montane forest ecosystem: Does tree species matter?

We investigated tree species effects on the soil microbial community in the tropical montane forest on Mt. Kinabalu, in Malaysian Borneo. We investigated microbial composition (lipid profile) and soil physicochemical parameters (pH, moisture, total C, N and phenolics concentration) in top 5-cm soils underneath two conifers (Dacrycarpus imbricatus and Dacrydium gracilis) and three broad-leaves (Lithocarpus clementianus, Palaquium rioence and Tristaniopsis clementis). We found that the primary difference in microbial composition was between conifer versus broad-leaves. The abundance of specific microbial biomarker lipids correlated with soil pH, total C and N. We conclude that tree species have significant impacts on the soil microbial community through their effects on soil pH, total C and N.     

Wood-decaying fungi in boreal forest: are species richness and abundances influenced by small-scale spatiotemporal distribution of dead wood?

We tested whether the spatiotemporal distribution of Norway spruce (Picea abies) logs influenced species richness and abundances of wood-decaying fungi in two 2-km² boreal forest study sites in southeastern Norway. According to the random sample null-hypothesis equally large subsamples of logs should be equally efficient in sampling fungi from a regional species pool. Based on 0.25-ha plots at 1-ha grid resolution, we compared plots with high and low densities of ‘new logs’ (decay stages 1-5) and plots with ‘old logs’ (decay stages 5-8) present or absent. Based on visible sporocarps, 45 fungus species, including 15 redlisted, were identified among 4151 logs. When rarefying species accumulation curves to the same number of logs, we found no difference in species richness between old forest plots having high and low densities of new logs, or between plots where old logs were present or absent. Curves from young forest revealed fewer species than in old forest. Multiple regression analysis of six redlisted and six common species corroborated the rarefaction analysis in showing that the probability of occurrence was independent of the spatiotemporal distribution of logs for all but two common species. Aside from the fact that more dead wood harboured more wood-decaying fungi, we conclude that the spatiotemporal distribution of dead wood was of minor importance in determining species richness and abundances at the scales of <1 ha and <100 years. This suggests that wood-decaying fungi are not dispersal-limited at these scales, and it offers an optional element in forest management.     

Seeing the forest for the deer: Do reductions in deer-disturbance lead to forest recovery?

High levels of deer browsing can prevent canopy tree regeneration, but little is known about changes to forest size-structure following long-term deer herd reductions. We monitored changes in forest stand structure and composition in southwestern Ontario, Canada, over 28-years using permanent plots. Our study site was the largest remaining tract of Carolinian (deciduous) forest in Canada (11 km²), a habitat type that contains up to a fifth of Canada’s species at risk and is under intense anthropogenic pressures. We recorded declines in all tree size classes between 1981 and 1996, during which densities of white-tailed deer (Odocoileus virginianus) reached a peak of 55 deer km⁻². Despite significant and sustained deer herd reductions between 1996 and 2009, which reduced deer densities to 7 deer km⁻², there was limited recruitment of small trees and declines in basal area of tree species that were sensitive to deer browsing. Our results suggest that recovery from herbivory is a protracted process during which canopy tree regeneration may continue to decline despite a reduction in browsing pressure due to deer culling. Large declines in canopy-tree densities in Carolinian forests may lead to forest size-structures and herbaceous plant communities that resemble rare oak savanna habitat, creating difficult decisions for conservation managers aiming to protect rare and endangered species within native ecosystems. We recommend that managers protect Carolinian forest stands and encourage canopy tree regeneration by increasing seed sources of native trees. While deer control is essential in reducing forest damage, our results highlight the need to explore other forms of active management to expedite otherwise slow increases in tree density.     

Is there a better source of huperzine A than Huperzia serrata? Huperzine A content of Huperziaceae species in China

A precise and selective reversed phase high-performance liquid chromatographic method was developed for quantifying huperzine A (HupA) in samples of the Huperziaceae in China. This method was used to quantify the levels of HupA in samples of Huperzia serrata collected from a single population at different times of the year, in different organs of the same H. serrata plant, and from different geographical locations of H. serrata plants in China. For different species of Huperziaceae, the highest content of HupA was found in Phlegmariurus carinatus. Members of the genus Phlegmariurus possessed higher levels of HupA than Huperzia species. H. serrata plants growing in humid forests contained significantly more HupA than plants growing in less humid environments. Finally, HupA content varied significantly by season, with the highest levels being found in mid fall and the lowest levels in early spring, suggesting that HupA is turned over in the plant.     

Does forest type and vegetation patchiness influence horizontal distribution of soil Collembola in two neighbouring forest sites?

The influence of forest type and heterogeneity of understory vegetation on the horizontal distribution of soil living Collembola was studied in two neighbouring mountain forest sites—a 180-year old beech forest and a 70-year old natural spruce forest. Four homogenous patches with different understory vegetation were chosen within each forest site and sampled 12 times between 1997 and 1998. A total of 56 collembolan species were identified, 51 in the beech forest and 48 in the spruce site. Twenty-three species were rare—they were recorded with low constancy and density. Although both forest sites differed in soil type, humus form and soil chemical parameters, the species composition of their collembolan communities was quite similar (77% shared species). Nevertheless, soil collembolan communities of both forest sites were clearly delimited on both qualitative (presence–absence) and quantitative (in density of individual species) levels as well as in terms of total collembolan density. Mean collembolan density reached 26 650–44 030 ind/m² in the beech patches compared to 44 470–68 050 ind/m² found in the spruce patches. Considerably higher densities of several species in one forest site may indicate more suitable habitat. In spite of similar species composition and minor differences in qualitative parameters among different vegetation patches within one forest site, there was clear variation in density of individual species, particularly between patches with and without herb vegetation. This could reflect different microclimatic conditions, additional litter supply from herbs or indirect interactions of Collembola with their roots.     

Are There Arid Land Soilscapes in Southwestern Europe?

No studies have proven the existence of soil assemblages typical of arid lands in Europe. This study was carried out in a representative territory of the southeastern part of the Iberian Peninsula, Almería province, which is the driest part of Europe, to determine if soils characteristic of arid lands are present. In order to analyse the spatial distribution of soils, the authors made use of mathematical tools previously developed in biodiversity and pedodiversity analysis, such as richness, entropy indices, abundance distribution models, diversity‐area relationships and nested subset analysis. The study demonstrates that the soil types or pedotaxa are typical of mountainous arid lands. Shallow and weakly developed soils (e.g. Leptosols, Regosols and Arenosols), Calcisols, Gypsisols and Solonchaks, cover most of the study area, and pedodiversity analysis demonstrates that the pedotaxa spatial patterns follow the same regularities as in other areas, environments and scales. In view of the fact that the class of landscapes identified in this study is unique in Europe, the Tarbernas desert and other arid lands sites of the study area merit preservation as part of the European geological, geomorphological and pedological heritage. Copyright © 2015 John Wiley & Sons, Ltd.     

Do secondary forests act as refuges for old growth forest animals? Recovery of ant diversity in the Atlantic forest of Brazil

The extent to which secondary forests occupying degraded and abandoned lands provide suitable habitat for forest-adapted species is an important conservation issue in times of vanishing old growth forests. We used ants (Hymenoptera: Formicidae), a functionally important and diverse group of invertebrates, to investigate the recovery of soil taxa during secondary forest succession in the Atlantic Forest of Southern Brazil. We compared the resilience of epigeic vs. hypogeic ant assemblages. For this purpose we established 27 sites that encompassed a chronosequence from pastures to old growth forests on two contrasting soil types. Our results are based on a collection of 35 508 individuals in 40 genera.Richness and composition of ant assemblages in secondary forests have recovered slowly and have not approached conditions typical of old growth forests. The distribution of genera along the successional stages was arranged in a nested pattern where ant genera of younger successional stages were a subset of genera present in older stages. Edaphic conditions had no influence on the recovery process. Overall, richness of ants was lower at study sites with water-logged soils than at sites where soils did not exhibit hydromorphic properties. The hypogeic ant assemblage recovered more slowly than the epigeic assemblage.Our results show that secondary forests do not act as refuges for many forest-adapted animals which are currently restricted to discontinuous patches of old growth forest in the highly endangered Atlantic Forest of Brazil. Moreover, estimated recovery times of 50 to several hundred years suggest it would take much longer than previously presumed for complete recolonization.     

Are we approaching ‘peak timber’ in the tropics?

Over the past few decades, tropical timber production in many Asia–Pacific countries has been akin to the symmetric logistic distribution curve, or ‘Hubbert Curve’, observed in the exploitation of many non-renewable resources—a rapid increase in production followed by a peak and then decline. There are three principal reasons why logging of native tropical forests resembles the mining of a non-renewable resource: the standard cutting cycle of 30–40 years is too brief to allow the wood volume to regenerate; tropical logging catalyses considerable deforestation; and the bulk of logging is undertaken by multinational corporations with little interest in long-term local sustainability. Unless something fundamental changes, we believe tropical forests will continue to be overharvested and cleared apace, leading to an inevitable global decline in tropical timbers of non-plantation origin. It has become common these days to speak of ‘peak oil’. In the tropics, we suggest that we should also begin to discuss the implications of ‘peak timber’.     

Citric acid extraction—An underestimated method in forest nutrition?

Since recent studies reveal citric acid to be favorable for estimating plant‐available P in soils, we investigated if it can also be used for assessing other nutrients. According to our results, it provides stronger correlations with the tree nutrition for Mg (beech, spruce), Ca+K (beech) and Fe (spruce) than the standard methods for determining exchangeable cations. Thus, when estimating plant‐available P by citric acid‐extraction, these cations should be additionally measured in ICP analysis.     

Changes in nutrient pools,microbial biomass and microbial activity in soils after transit through the gut of three endogeic earthworm species of the genus Postandrilus Qui and Bouché, 1998

Purpose

Endogeic earthworms play a significant role in biogeochemical cycles due to the large amount of soil they ingest, and because after transit through their guts, casts usually show differences in nutrient contents and microbial populations with bulk soil. Here, we studied how three endogeic earthworm species, Postandrilus majorcanus, Postandrilus sapkarevi and Postandrilus palmensis, inhabiting soils in Majorca island (Balearic Islands, W Mediterranean), modify nutrient pools and microbial communities of soil.

Materials and methods

To do this, we analysed C, N and P pools, microbial biomass (phospholipid fatty acids, PLFA) and microbial activity (fluorescein diacetate hydrolysis, FDA) in paired samples of bulk soil and fresh casts.

Results and discussion

The mineral and organic N contents were generally enhanced in casts produced by all three earthworm species. However, inorganic P and organic C contents were only higher in P. sapkarevi (32 %, only P) and P. majorcanus casts (100 % for both soil nutrient pools) than in bulk soil. Bacterial and fungal biomass were only higher than in bulk soil in P. majorcanus casts (65 and 100 %, respectively), but without effects on microbial activity, that was lower in P. palmensis casts (26 %). Earthworm gut transit strongly influenced the soil microbial community structure, resulting in differences between casts and soils.

Conclusions

The increased nutrient mineralization (6-, 1.3- and 1.4-fold for N, C and P, respectively) in casts produced by these earthworm species is of particular importance because of the amount of casts released and the seasonal variations in earthworm activity, which may favour plant growth.     

Are hotspots of evolutionary potential adequately protected in southern California?

Reserves are often designed to protect rare habitats, or “typical” exemplars of ecoregions and geomorphic provinces. This approach focuses on current patterns of organismal and ecosystem-level biodiversity, but typically ignores the evolutionary processes that control the gain and loss of biodiversity at these and other levels (e.g., genetic, ecological). In order to include evolutionary processes in conservation planning efforts, their spatial components must first be identified and mapped. We describe a GIS-based approach for explicitly mapping patterns of genetic divergence and diversity for multiple species (a “multi-species genetic landscape”). Using this approach, we analyzed mitochondrial DNA datasets from 21 vertebrate and invertebrate species in southern California to identify areas with common phylogeographic breaks and high intrapopulation diversity. The result is an evolutionary framework for southern California within which patterns of genetic diversity can be analyzed in the context of historical processes, future evolutionary potential and current reserve design. Our multi-species genetic landscapes pinpoint six hotspots where interpopulation genetic divergence is consistently high, five evolutionary hotspots within which genetic connectivity is high, and three hotspots where intrapopulation genetic diversity is high. These 14 hotspots can be grouped into eight geographic areas, of which five largely are unprotected at this time. The multi-species genetic landscape approach may provide an avenue to readily incorporate measures of evolutionary process into GIS-based systematic conservation assessment and land-use planning.     

Do general spatial relationships for microbial biomass and soil enzyme activities exist in temperate grassland soils?

In heterogeneous environments such as soil it is imperative to understand the spatial relationships between microbial communities, microbial functioning and microbial habitats in order to predict microbial services in managed grasslands. Grassland land-use intensity has been shown to affect the spatial distribution of soil microorganisms, but so far it is unknown whether this is transferable from one geographic region to another. This study evaluated the spatial distribution of soil microbial biomass and enzyme activities involved in C-, N- and P-cycling, together with physico-chemical soil properties in 18 grassland sites differing in their land-use intensity in two geographic regions: the Hainich National Park in the middle of Germany and the Swabian Alb in south-west Germany. Enzyme activities associated with the C- and N-cycles, namely β-glucosidase, xylosidase and chitinase, organic carbon (C_org), total nitrogen (N_t), extractable organic carbon, and mineral nitrogen (N_min) were higher in the Swabian Alb (Leptosols) than in the Hainich National Park (primarily Stagnosols). There was a negative relationship between bulk density and soil properties such as microbial biomass (C_mic, N_mic), urease, C_org, and N_t. The drivers (local abiotic soil properties, spatial separation) of the enzyme profiles (β-glucosidase, chitinase, xylosidase, phosphatase, and urease) were determined through a spatial analysis of the within site variation of enzyme profiles and abiotic properties, using the Procrustes rotation test. The test revealed that physical and chemical properties showed more spatial pattern than the enzyme profiles. β-glucosidase, chitinase, xylosidase, phosphatase, and urease activities were related to local abiotic soil properties, but showed little spatial correlation. Semivariogram modeling revealed that the ranges of spatial autocorrelation of all measured variables were site specific and not related to region or to land-use intensity. Nevertheless, land-use intensity changed the occurrence of spatial patterns measurable at the plot scale: increasing land-use intensity led to an increase in detectable spatial patterns for abiotic soil properties on Leptosols. The conclusion of this study is that microbial biomass and functions in grassland soils do not follow general spatial distribution patterns, but that the spatial distribution is site-specific and mainly related to the abiotic properties of the soils.