Colonization Of Seedlings Research Articles

Arbuscular mycorrhiza effects on Faidherbia albida (Del.) A. Chev. growth under varying soil water and phosphorus levels in Northern Ethiopia

Tree seedling establishment, survival and growth in dryland areas is greatly impacted by water, land use effects and soil nutrient availability. Arbuscular mycorrhizal fungi (AMF) can have a substantial effect on water and nutrient uptake by seedlings and are affected by nutrient application, water availability and inoculum source. In this study, we examined the effect of AMF inoculation, phosphorus application levels, soil water status, and inoculum source on the growth of Faidherbia albida seedlings. Two greenhouse experiments were conducted on F. albida seedlings: to compare (a) ±AMF inoculation, at three levels of volumetric soil water content (field capacity (FC), 60% of FC and 20% of FC), and three AMF inoculum sources (derived from cultivated land, grazing land and area exclosure); (b) ±AMF inoculation, at four levels of phosphorus application (0, 25, 50 and 100 mg kg−1) and three AMF inoculum sources. Inoculation with AMF, higher soil water and higher P application significantly increased the growth of seedlings (P < 0.05). F. albida seedlings responded positively to increased water levels. The highest growth and AMF colonization of seedlings was recorded under the lowest water stress with AMF inoculum from area exclosure followed by grazing land inoculum source. The lowest growth was recorded under the highest water stress and cultivated land inoculum source. Plant growth and biomass were positively correlated with increased soil P application, however, AMF colonization decreased with increasing P application. Applying P and inoculating F. albida seedlings with indigenous AMF under low water stress enables optimum plant growth improvement in dryland farming systems.

Nurse species could facilitate the recruitment of mangrove seedlings after hydrological rehabilitation

Changes in hydrology are one of the main causes of mangrove degradation; however, the reforestation of mangrove has been the main restoration activity and very little information on how pioneer species can facilitate the colonization and development of the mangrove species is available. After carrying out a water reconnection as the sole restoration action, secondary succession has occurred in the mangrove rehabilitation area of Celestun (Yucatan, SE Mexico). Two pioneer species, Batis maritima and Salicornia virginica were observed in plots with different coverage (0%, 20%, 100%) where the three natural mangrove species were established, with Laguncularia racemosa as the dominant species in density. The greatest interstitial mean salinity (79.9g/kg) was recorded in the plots with 20% cover, while the lowest salinity (40.7g/kg) was recorded in the plots with 100% of coverage. At the end of sampling period nutrient content (carbon, nitrogen and phosphorus) and organic matter in the sediment were greatest in the plots with 100% cover, whereas the lowest concentrations were observed in the site devoid of vegetation. The percentage cover of S. virginica and B. maritima changed over time; in the plot that started with 100% cover it decreased until it disappeared at the end of the study period, whereas it increased in the plots with 20% and 0% cover. This study shows that B. maritima and S. virginica has a function as “facilitator species” initially colonizing the bare soil and modifying its conditions (decreasing interstitial salinity and increasing nutrient), which favored colonization and growing of mangrove seedlings.

Gluconacetobacter diazotrophicus exopolysaccharide protects bacterial cells against oxidative stress in vitro and during rice plant colonization

Background and aims The endophytic bacterium Gluconacetobacter diazotrophicus produces exopolysaccharides (EPS) that are required for biofilm formation and colonization of rice seedlings. Here we investigated whether EPS produced by the G. diazotrophicus strain Pal5 protects the bacteria against free radicals.

Fungal wood decomposer activity induces niche separation between two dominant tree species seedlings regenerating on coarse woody material

Decomposition subsystems have an essential role in forest dynamics but few studies demonstrate the effect of microbial decay traits on seedling regeneration. In the present study, we focused on seedling regeneration on coarse woody material (CWM), which is an important regeneration site for forest tree species, and the effects of wood decay type according to fungal decay preference for wood structural components on seedling colonization. Effects of log properties including wood decay type and other environmental variables on seedling density were evaluated by ordination methods and generalized linear models. In total, 22 woody species were recorded as seedlings on Pinus densiflora logs. By ordination analysis, white rot in heartwood and brown rot in sapwood, as well as canopy openness and log diameter, showed significant association with seedling communities. The factors selected for a generalized linear model for explaining seedling densities of the two dominant seedling species Cryptomeria japonica and P. densiflora included brown rot in sapwood and white rot in heartwood, but the effects were different: a positive effect of brown rot on C. japonica and a negative effect of white rot on P. densiflora. These results suggested that wood decay type could induce niche separation between dominant tree species regenerating on CWM.

Interactive effects of wood decomposer fungal activities and bryophytes on spruce seedling regeneration on coarse woody debris

AbstractDecaying logs are important seedbeds in boreal and subalpine forests. However, biotic and abiotic factors and their interactions related to seedling colonization patterns on logs remain unclear. In the present study, we evaluated the influence of bryophyte communities, wood decay type (white‐, brown‐, and soft‐rot) owing to decomposer fungal activities, and environmental abiotic factors on seedling establishment in an old‐growth subalpine coniferous forest in Japan. Among the tree species recorded on the conifer logs, Picea jezoensis var. hondoensis was the most dominant. Log surfaces were covered with distinctive patches of liverwort Scapania bolanderi and moss Pleurozium schreberi (approximately 33% cover for each). Redundancy analysis showed that brown‐rot in sapwood significantly affects the bryophyte and seedling community on the logs. Generalized linear models suggested that the total bryophyte cover, Scapania cover, and white‐rot in heartwood positively associate with Picea seedling density, whereas Pleurozium cover and basal area of adjacent Picea adults negatively associate with Picea seedling density. Results of structural equation modeling suggested that the brown‐rot of sapwood positively associates with Scapania cover that has a positive effect on Picea seedling density. Furthermore, brown‐rot of sapwood inhibited the Pleurozium cover, thus contributing to the Scapania dominance on the logs. These results suggest that fungal wood decomposer activities affect colonization of Picea seedlings in an indirect way via structuring bryophyte community on the logs.

Regeneration processes on coarse woody debris in mixed forests: do tree germinants and seedlings have species‐specific responses when grown on coarse woody debris?

Summary Tree regeneration on coarse woody debris (CWD) is considered to be one the most ecologically valuable aspects of CWD in forest systems. However, most studies have focused solely on uncovering the differences in establishment and growth on CWD (regarded as a homogeneous substrate) in comparison with the forest floor. Our study concentrates on the underlying mechanisms of germinant and seedling colonization patterns and demographic responses relative to various properties of CWD. We analysed the effects of CWD properties (decay class, form, species and diameter) on: (i) germinant and seedling annual counts; (ii) annual germinant and seedling survival; and (iii) seedling growth and height. Our study comprised three species (beech, fir and spruce) over 7‐year span in two old‐growth stands in the Western Carpathians, and employed generalized linear models and mixed models to test for differences between species. CWD properties affected regeneration at the germination stage. There were some demographic differences between species relative to CWD properties. Decay class had the most pronounced effect on beech, not only on its establishment but also survival and growth. Beech and spruce established and survived in higher densities on beech CWD, while their height growth was enhanced on conifer‐derived CWD, particularly on spruce CWD. Stumps enhanced establishment of all species and survival of conifer seedlings. Synthesis. Our study shows that CWD properties do influence seedling establishment, growth, height distribution and survival. Moreover, there may be trade‐offs between seedling growth and survival among tree species growing on different species of CWD. This highlights the need to include CWD heterogeneity as a factor that can affect the role of CWD in regeneration in forest ecosystems.

Effects of girdling on arbuscular mycorrhizal colonization and root hair development of litchi seedlings

Litchi (Litchi chinenis Sonn.) is a woody mycorrhizal fruit tree. Hypha and root hairs are the most important structures for nutrition and water absorption in litchi. Girdling is an important technique in litchi cultivation. However, the effects of girdling on arbuscular mycorrhiza (AM) colonization and root hair development remain unknown. To understand the effects of girdling on AM and root hairs in litchi, the carbohydrate content, enzyme activities related to sucrose metabolism, AM colonization, and length and density of root hairs were measured under girdling, wounding and control conditions in the roots of one-year-old seedlings. Results showed that sufficient carbohydrates were available for AM and root hairs in the mycorrhizal roots of litchi in the wounding and control groups. Girdling significantly decreased the concentrations of glucose at 3days (3D), 1 week (1W), 2 weeks (2W), 1 month (1M) and 2 months (2M) after treatment, of fructose at 3D, 1W, 2W, 1M and 2M after treatment, of sucrose at 1W, 2W, 1M and 2M after treatment, and of starch at 2W, 1M and 2M after treatment. Consistent with its effects on carbohydrates, girdling significantly reduced arbuscular colonization (1M and 2M) and root hair length (1M). The correlations of arbuscular colonization and root hair length with concentrations of carbohydrates (fructose, sucrose and starch) were significant only under girdling treatment. Under conditions of hexose starvation caused by girdling, litchi seedlings exhibited significantly upregulated neutral invertase activity in sucrose-cleaving parts and downregulated sucrose phosphate synthase and sucrose synthase (synthesis direction) in sucrose synthesis parts. The correlations of arbuscular colonization with levels of sucrose-cleaving enzymes (neutral invertase and acid invertase) and root hair length with levels of sucrose-cleaving enzymes (neutral invertase and acid invertase) were also significant only under girdling treatment. Our findings indicated that AM colonization was more sensitive to carbohydrates than root hair length in litchi seedlings. Furthermore, girdling likely affected AM colonization and root hair length by decreasing the carbohydrate contents and regulating the activities of sucrose-metabolising enzymes.

Biological Control of Lettuce Drop and Host Plant Colonization by Rhizospheric and Endophytic Streptomycetes.

Lettuce drop, caused by the soil borne pathogen Sclerotinia sclerotiorum, is one of the most common and serious diseases of lettuce worldwide. Increased concerns about the side effects of chemical pesticides have resulted in greater interest in developing biocontrol strategies against S. sclerotiorum. However, relatively little is known about the mechanisms of Streptomyces spp. as biological control agents against S. sclerotiorum on lettuce. Two Streptomyces isolates, S. exfoliatus FT05W and S. cyaneus ZEA17I, inhibit mycelial growth of Sclerotinia sclerotiorum by more than 75% in vitro. We evaluated their biocontrol activity against S. sclerotiorum in vivo, and compared them to Streptomyces lydicus WYEC 108, isolated from Actinovate®. When Streptomyces spp. (106 CFU/mL) were applied to S. sclerotiorum inoculated substrate in a growth chamber 1 week prior lettuce sowing, they significantly reduced the risk of lettuce drop disease, compared to the inoculated control. Interestingly, under field conditions, S. exfoliatus FT05W and S. cyaneus ZEA17I protected lettuce from drop by 40 and 10% respectively, whereas S. lydicus WYEC 108 did not show any protection. We further labeled S. exfoliatus FT05W and S. cyaneus ZEA17I with the enhanced GFP (EGFP) marker to investigate their rhizosphere competence and ability to colonize lettuce roots using confocal laser scanning microscopy (CLSM). The abundant colonization of young lettuce seedlings by both strains demonstrated Streptomyces' capability to interact with the host from early stages of seed germination and root development. Moreover, the two strains were detected also on 2-week-old roots, indicating their potential of long-term interactions with lettuce. Additionally, scanning electron microscopy (SEM) observations showed EGFP-S. exfoliatus FT05W endophytic colonization of lettuce root cortex tissues. Finally, we determined its viability and persistence in the rhizosphere and endorhiza up to 3 weeks by quantifying its concentration in these compartments. Based on these results we conclude that S. exfoliatus FT05W has high potential to be exploited in agriculture for managing soil borne diseases barely controlled by available plant protection products.

Seedling regeneration on decayed pine logs after the deforestation events caused by pine wilt disease

Coarse woody debris (CWD) forms an important habitat suitable for tree seedling establishment, and the CWD decay process influences tree seedling community. In Japan, a severe dieback of Pinus densiflora Sieb. &amp; Zucc. caused by pine wilt disease (PWD) damaged huge areas of pine stands but creates huge mass of pine CWD. It is important to know the factors influencing seedling colonization on pine CWD and their variations among geographical gradient in Japan to expect forest regeneration in post-PWD stands. I conducted field surveys on the effects of latitude, climates, light condition, decay type of pine logs, and log diameter on tree seedling colonization at ten geographically distinct sites in Japan. In total, 59 tree taxa were recorded as seedlings on pine logs. Among them, 13 species were recorded from more than five sites as adult trees or seedlings and were used for the analyses. A generalized linear model showed that seedling colonization of Pinus densiflora was negatively associated with brown rot in sapwood, while that of Rhus trichocarpa was positively associated with brown rot in heartwood. Regeneration of Ilex macropoda had no relationships with wood decay type but negatively associated with latitude and MAT, while positively with log diameter. These results suggested that wood decay type is a strong determinant of seedling establishment for certain tree species, even at a wide geographical scale; however, the effect is tree species specific.

Cambios globales en los manglares del golfo de Urabá (Colombia): entre la cambiante línea costera y la frontera agropecuaria en expansión

Accelerated mean sea level rise and deforestation are two global changes severely impacting mangroves along the Colombian Caribbean coast, but little has been discussed about them for the Gulf of Uraba. The objective of this review is to synthesize the published literature on such topics available to date for this area. This gulf holds extensive areas, structurally different from the rest of the Caribbean, which are shrinking and degrading as a consequence of: a) coastal erosion and sea level rise; b) selective logging and agricultural expansion; and c) watershed deforestation and sediment exports to the estuaries. The Atrato River delta, and several microdeltas located along the eastern coast have expanded, while the Rionegro Cove has remained relatively unchanged, at least during the 20th century. The eastern coast, with the smalles mangrove patches, have eroded at a rate of various meters per year due to the littoral drift currents. In the vicinity of the Turbo municipality, selective logging for different purposes has reduced the mean tree-diameter in Rhizophora mangle and has increased the importance value of Laguncularia racemosa, thus altering above ground biomass and carbon reservoirs. Agricultural expansion has been responsible for shrinking inland Avicennia germinans-stands. High deforestation rates in the coastal plains and watersheds in the banana agricultural district have increased river sediment load that has accumulated in the deltas. Mangroves in these areas trap significant amounts of sediments, with likely negative effects on colonization and survival of seedlings and benthic macroinvertebrates. In conclusion, in the Gulf of Uraba significant global changes, both natural and anthropogenic, currently occur within the littoral zone as well as within the coastal watersheds, and they require an urgent implementation of adaptive measures within the management plans for mangrove ecosystems and the coastal zone.

Inoculation of ectomycorrhizal fungi contributes to the survival of tree seedlings in a copper mine tailing

To advance our understanding of the effects of inoculation with ectomycorrhizal fungi (EMF) on seedling colonization in mine wastelands, we conducted a field experiment in a copper tailing. Six-month-old seedlings of Japanese red pine (Pinus densiflora) and oak (Quercus variabilis) separately inoculated with three EMF species (Pisolithus sp., Cenococcum geophilum, Laccaria laccata) were transplanted to the copper tailing. The survival rates of tree seedlings were monitored monthly, and growth (biomass and height), contents of nutrients and heavy metals (K, P, Ca, Mg, Cu, Zn), and mycorrhizal infection rates of seedlings were determined 6 months after planting. Oak seedlings exhibited higher survival rates than pine seedlings after 6 months of growth on the tailing. EMF inoculations of pine seedlings significantly enhanced their survival, growth, and nutrient uptake. In contrast, EMF inoculations of oak seedlings improved growth only in terms of biomass. Additionally, EMF inoculation caused pine seedlings to accumulate more Cu and Zn in roots compared to non-inoculated seedlings, whereas inoculation inhibited the accumulation of heavy metals in shoots. However, similar results were not observed in oak seedlings. Observations of roots indicated that the rates of mycorrhizal infection of both tree species had dramatically declined at harvest time. In conclusion, ectomycorrhizal symbioses can improve the survival and performance of pine seedlings in mine tailings. The present study provided direct evidence of the importance of EMF inoculation of seedlings to the reforestation of mine wastelands.

Effects of warming on ectomycorrhizal colonization and nitrogen nutrition of Picea asperata seedlings grown in two contrasting forest ecosystems.

Ectomycorrhiza (ECM) plays an important role in plant nitrogen (N) nutrition and regulates plant responded to climate warming. We conducted a field experiment in a natural forest and a plantation in the eastern Tibetan Plateau to estimate the warming effects of open-top chambers (OTC) on ECM and N nutrition of Picea asperata seedlings. Four-year warming significantly decreased ECM colonization, ECM fungal biomass, fine root vigor, and the N concentration of leaf, stem and coarse root, but significantly increased fine root N concentration and N content of leaf, stem, fine root and whole plant in natural forest. Contrarily, warming induced no obvious change in most of these parameters in plantation. Moreover, warming decreased rhizospheric soil inorganic N content in both forests. Our results showed that four-year warming was not beneficial for ECM colonization of P. asperata seedlings in the two forests, and the seedlings in natural forest were more sensitive and flexible to experimental warming than in plantation. The changes of ECM colonization and fine root biomass for effective N uptake would be good for plant growth and remit N leaching under future warming in natural forest.

Soil Incorporation of Cruciferous Plant Residues As a Control Strategy FOR PANTOEA ANANATIS COLONIZATION OF ONION SEEDLINGS

The effect of cruciferous plant residues (milled seeds of mustard and rapeseed meals) on the colonization of onion (Allium cepa L.) seedling roots by Pantoea ananatis was investigated. These materials incorporated into a peat medium at a dosage of 0.5% (w/v) decreased the colonization of onion seedlings by the pathogenic bacterium. These materials showed also a positive effect on the growth of onion seedlings, increasing fresh plant weight by three to fivefolds. Moreover, the total microorganism population was higher in the peat medium additioned with plant materials than in the control. An increase in the total number of bacteria and actinomycetes was observed, which may have caused a higher suppressiveness of the peat medium towards P. ananatis. On the other hand, the biological active compounds released from crucifers may have inhibited the growth of the bacterium.

The Novel Lipopeptide Poaeamide of the Endophyte Pseudomonas poae RE*1-1-14 Is Involved in Pathogen Suppression and Root Colonization.

Endophytic Pseudomonas poae strain RE*1-1-14 was originally isolated from internal root tissue of sugar beet plants and shown to suppress growth of the fungal pathogen Rhizoctonia solani both in vitro and in the field. To identify genes involved in its biocontrol activity, RE*1-1-14 random mutagenesis and sequencing led to the identification of a nonribosomal peptide synthetase (NRPS) gene cluster predicted to encode a lipopeptide (LP) with a 10-amino-acid peptide moiety. The two unlinked gene clusters consisted of three NRPS genes, designated poaA (cluster 1) and poaB and poaC (cluster 2), spanning approximately 33.7 kb. In silico analysis followed by chemical analyses revealed that the encoded LP, designated poaeamide, is a structurally new member of the orfamide family. Poaeamide inhibited mycelial growth of R. solani and different oomycetes, including Phytophthora capsici, P. infestans, and Pythium ultimum. The novel LP was shown to be essential for swarming motility of strain RE*1-1-14 and had an impact on root colonization of sugar beet seedlings The poaeamide-deficient mutant colonized the rhizosphere and upper plant cortex at higher densities and with more scattered colonization patterns than the wild type. Collectively, these results indicate that Pseudomonas poae RE*1-1-14 produces a structurally new LP that is relevant for its antagonistic activity against soilborne plant pathogens and for colonization of sugar beet roots.

Impact of tree decline on spatial patterns of seedling-mycorrhiza interactions: Implications for regeneration dynamics in Mediterranean forests

In the last decades, an increasing number of forest decline events and widespread tree mortality have been reported worldwide as a consequence of different global change drivers. Such a general decrease in tree health and cover has a large potential to impact mycorrhizal communities, but this issue remains largely unexplored.We used a Bayesian framework to analyze the impact of Quercus suber decline on spatial patterns of seedling-mycorrhiza interactions in mixed Mediterranean forests in Southern Spain, and evaluate the relative importance of this symbiosis as a driver of oak seedling establishment.Our models showed that the spatial variability found in the patterns of oak seedling colonization by both arbuscular mycorrhizas and ectomycorrhizas was partially linked to the process of Q. suber decline. Moreover, seedling survival and growth was influenced by the intensity of mycorrhizal colonization, but in quite unexpected ways. Arbuscular mycorrhizas had a larger effect on seedling performance than ectomycorrhizas, and the effects of both groups were negative or neutral but never positive.We conclude that because the spatial distribution of the seedling-mycorrhiza association responded to the identity and health status of individual trees, and mycorrhizal infection did in turn affect seedling performance, tree decline might affect forest dynamics through changes in plant–soil biota feedbacks.

Interactive effects of juvenile defoliation, light conditions, and interspecific competition on growth and ectomycorrhizal colonization of Fagus sylvatica and Pinus sylvestris seedlings.

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.

Beneficial rhizospheric microorganisms mediated plant growth promotion and suppression of aflatoxigenic fungal and aflatoxin contamination in groundnut seeds

The potential of root-colonising antagonistic microbial biocontrol agents was evaluated for their ability to improve plant growth and suppress aflatoxigenic fungal and aflatoxin contamination in groundnut. By considering root colonisation of groundnut seedlings, plant growth promotion and antagonism against aflatoxigenic Aspergillus flavus as preliminary criteria, eight rhizobacteria and nine Trichoderma spp. were selected and characterised for their beneficial traits. These strains gave varying results for IAA production, phosphate solubilisation, ACC deaminase, chitinase and siderophore production. Under laboratory and greenhouse conditions, these strains significantly (P < 0.05) suppressed seed-borne and rhizospheric population of A. flavus and improved seed quality variables. However, cdELISA results revealed that none of the biocontrol strains were effective in reducing aflatoxin level in seed. Based on the overall performance, Pseudomonas fluorescens 2bpf, Bacillus sp. Bsp-3/aM and Trichoderma atroviride UMDBT-Dha.Tat8 were used for field trials in the form of talcum powder formulations. Under field conditions, biocontrol agents improved seedling emergence, plant biomass and pod yield. Seeds harvested from plots treated with biocontrol agents showed significant (P < 0.05) reduction in A. flavus infection and aflatoxin production after 6 months' storage. Use of microbial strains with multiple beneficial traits is advantageous in bioformulation development. Hence, in future, these formulations will play a major role as biofertilisers and biopesticides, which can reduce the usage of agrochemicals up to greater extents in groundnut production.

Hydration as a possible colonization cue: Rain may promote seed release from black cottonwood trees

Within the Salicaceae, the poplar trees and willow shrubs display an r-selection reproductive strategy, with the production of vast numbers of seeds but these are tiny, viability lasts only a few weeks, and very few seedlings establish and mature to contribute to the woodland populations. The timing of seed release is consequently critical and for cottonwoods, riparian poplars, seed release has been reported to follow the spring peak in river flow. To investigate the prospective coordination between environmental conditions and seed release we undertook daily observations of black cottonwoods (Populus trichocarpa) over four summers along the lower Duncan River in southeastern British Columbia, Canada. Seed release involved a sequence of pulses with the first after about 400 cumulative degree days (base 5°C) in the growth season. There were four or five pulses annually with each extending one to six days and occurring through June and July and unexpectedly, into early August. The pulses of seed release were not coordinated with changes in river flow but all 18 pulses over the four years followed rain events. We thus conclude that in a humid climate mountain ecoregion, rain and possibly post-rain warming may provide environmental cues that trigger cottonwood seed release. This hygrisence could retain the near-mature seeds on the maternal tree, prolonging their viability, and their release after rain would provide moist substrates, benefitting seedling establishment. We further conclude that in a humid ecoregion, the river flow pattern would be less important for riparian seedling colonization than in semi-arid regions, where summer rain is sparse. In all ecoregions, occasional high river flows are essential for the fluvial geomorphic disturbance that creates the barren seedling colonization sites, and also to exclude flood-intolerant upland vegetation from encroaching into the riparian recruitment zones.

Influence of tree species and salvaged soils on the recovery of ectomycorrhizal fungi in upland boreal forest restoration after surface mining

Surface mining in the Canadian boreal forest involves the removal of vegetation and soils, resulting in the local loss of biodiversity and ecosystem functioning. Ectomycorrhizal (EM) fungi are critical to ecosystem processes; however, their recovery following reclamation is not well understood. This study investigated the importance of reclamation cover soils (forest floor material, peat, and subsoil) and tree seedling species (Populus tremuloides Michx., Pinus banksiana Lamb., and Picea glauca (Moench) Voss) in structuring the community composition of EM fungi. We used 1-year-old seedlings to assay cover soils in the field for 3 months, and grew seedlings in each of the cover soils in a growth chamber assay for 5 months. Nonmetric multidimensional scaling indicated host identity structured the community composition of EM fungi in the field, while both host identity and cover soil influenced the composition of EM fungi in the growth chamber. However, pre-colonization of seedlings by nursery fungi complicates interpretation of field results. The rate of EM fungus colonization of seedlings collected across both assays was relatively low, approximately 23%. Our results indicate cover soils used in reclamation of surface-mined landscapes retain propagules of EM fungi, and using a wide variety of tree species in upland boreal forest restoration may increase the diversity of EM fungi recovered.

Effect of seed storage temperature on fine root development and mycorrhizal colonization of young Populus nigra seedlings

Abstract Key message Seed storage temperature influences root anatomy of the endangered Populus nigra, and consequently may alter nutrient absorption. A lower temperature during seed storage (−20 and −196 °C) may preserve the potential for a suitable root system development after germination. Context Seed storage conditions can be an important determinant of later seedling growth of Populus nigra L., an endangered tree species. Aims We tested whether long-term seed storage temperature, −10, −20 or −196 °C, affects the pattern of seedling root traits responsible for resource acquisition as compared to seedlings of fresh seeds. Methods We analysed the morphology, anatomy, degree of mycorrhizal colonization, and biochemical composition of roots developed from seed stored for 24 months at five different temperatures (from 3 to −196 °C) commonly used to preserve genetic resources. Results Except for root anatomy, we found no relationship between seed storage temperature and the root traits of seedlings. Among the various storage conditions, the proportion of roots with primary development in the first four orders was similar in seedlings developed from fresh seeds of from seeds stored at −196 or −20 °C. Nitrogen content in the roots was positively correlated with the proportion of (i) roots with primary development and (ii) the cortex width in the root diameter. Conclusions Higher temperatures during seed storage reduced the proportion of roots with absorptive function (with primary development). Therefore, for preservation of P. nigra seeds we recommend lower temperatures such as −20 and −196 °C.