Fungal endophytes of turmeric (<Emphasis Type="Italic">Curcuma longa</Emphasis> L.) and their biocontrol potential against pathogens <Emphasis Type="Italic">Pythium aphanidermatum</Emphasis> and <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

Endophytic fungi have been isolated from the healthy turmeric (Curcuma longa L.) rhizomes from South India. Thirty-one endophytes were identified based on morphological and ITS–rDNA sequence analysis. The isolated endophytes were screened for antagonistic activity against Pythium aphanidermatum (Edson) Fitzp., and Rhizoctonia solani Kuhn., causing rhizome rot and leaf blight diseases in turmeric respectively. Results revealed that only six endophytes showed >?70% suppression of test pathogens in antagonistic dual culture assays. The endophyte T. harzianum TharDOB-31 showed significant in vitro mycelial growth inhibition of P. aphanidermatum (76.0%) and R. solani (76.9%) when tested by dual culture method. The SEM studies of interaction zone showed morphological abnormalities like parasitism, shriveling, breakage and lysis of hyphae of the pathogens by endophyte TharDOB-31. Selected endophytic isolates recorded multiple plant growth promoting traits in in vitro studies. The rhizome bacterization followed by soil application of endophyte TharDOB-31 showed lowest Percent Disease Incidence of rhizome rot and leaf blight, 13.8 and 11.6% respectively. The treatment of TharDOB-31 exhibited significant increase in plant height (85 cm) and fresh rhizome yield/plant (425 g) in comparison with untreated control under greenhouse condition. The confocal microscopy validates the colonization of the TharDOB-31 in turmeric rhizomes. The secondary metabolites in ethyl acetate extract of TharDOB-31 were found to contain higher number of antifungal compounds by high resolution liquid chromatograph mass spectrometer analysis. Thereby, endophyte T. harzianum isolate can be exploited as a potential biocontrol agent for suppressing rhizome rot and leaf blight diseases in turmeric.     

Soil colonization by Trametes versicolor grown on lignocellulosic materials: Substrate selection and naproxen degradation

The ability of Trametes versicolor to degrade soil pollutants has been widely studied. However, the use of such fungus in real soil applications has lead to dissimilar results mainly due to soil colonization limitations. Therefore, it is important to investigate techniques to improve the survival of this white rot fungus in soils. In the present study, several processed and unprocessed low-cost lignocellulosic substrates were employed as inoculum carriers for fungal growth prior to application in soil for bioaugmentation. The fungal growth was determined by means of laccase activity and ergosterol determinations; additionally, the degrading capacity was measured by the naproxen degradation test (ND24). Although T. versicolor was able to colonize all materials, the colonization and enzymatic production was higher on processed agricultural wastes with relative low C/N ratios than in raw lignocellulosic substrates. Soil colonization was successful under both sterile and non-sterile conditions when amended with processed agricultural wastes, yielding even higher laccase production in non-sterile conditions. Moreover, T. versicolor was able to degrade significant amounts of spiked naproxen after 24 h in sterile and non-sterile soil cultures, showing the best results when using a material based on wheat straw as carrier.     

Effect of inoculation method and plant growth medium on endophytic colonization of sorghum by the entomopathogenic fungus <Emphasis Type="Italic">Beauveria bassiana</Emphasis>

A study was conducted to determine the effect of inoculation method and plant growth medium on colonization of sorghum by an endophytic Beauveria bassiana. Colonization of leaves, stems, and roots by B. bassiana was assessed 20-days after application of the fungus. Although B. bassiana established as an endophyte in sorghum leaves, stems, and roots regardless of inoculation method (leaf, seed, or soil inoculation), plant growth medium (sterile soil, non-sterile soil, or vermiculite) apparently influenced colonization rates. Seed inoculation with conidia caused no stem or leaf colonization by the fungus in non-sterile soil but did result in substantial endophytic colonization in vermiculite and sterile soil. Leaf inoculation did not result in root colonization, regardless of plant growth medium. Endophytic colonization was greater in leaves and stems than roots. Endophytic colonization by B. bassiana had no adverse effects on the growth of sorghum plants. Leaf inoculation with a conidial suspension proved to be the best method to introduce B. bassiana into sorghum leaves for plants growing in either sterile or non-sterile soil. Further research should focus on the virulence of endophytic B. bassiana against sorghum stem borers.     

Volatile constituents of Zingiber officinale rhizomes produced by in vitro shoot tip culture

Plantlets with rhizomes were produced in vitro from shoot tips of Zingiber officinale grown in both modified Gamborg's B5 (B5) and Murashige-Skoog (MS) media supplemented with various levels of growth regulators. The rhizomes accumulated the volatile oils similar to those formed in the original rhizome. In the oil from the rhizome grown in the modified B5 medium, the acyclic oxygenated monoterpenes predominated, while the oil from the rhizome grown in the modified MS medium consisted mainly of sesquiterpenes.     

The Impact of Physical Disturbance and Increased Sand Burial on Clonal Growth and Spatial Colonization of Sporobolus virginicus in a Coastal Dune System

Dune plants are subjected to disturbance and environmental stresses, but little is known about the possible combined effects of such factors on growth and spatial colonization. We investigated how clones of Sporobolus virginicus , a widespread dune species, responded to the independent and interactive effects of breakage of rhizomes, breakage position and burial regime. Horizontal rhizomes were severed at three different internode positions relative to the apex to span the range of damage by disturbance naturally observed or left intact, and apical portions exposed to two burial scenarios (ambient vs. increased frequency) for three months in the field. The performance of both parts of severed rhizomes, the apical portion and the remaining basal portion connected to clone containing four consecutive ramets, was compared with that of equivalent parts in intact rhizomes. Apical portions severed proximal to the third internode did not survive and their removal did not enhance branching on their respective basal portions. Severing the sixth or twelfth internode did not affect survival and rhizome extension of apical portions, but suppressed ramet production and reduced total biomass and specific shoot length. Their removal enhanced branching and ramet production on basal portions and changed the original rhizome growth trajectory. However, the gain in number of ramets in basal portions never compensated for the reduction in ramet number in apical portions. Recurrent burial increased biomass allocation to root tissues. Burial also stimulated rhizome extension only in intact rhizomes, indicating that disturbance interacts with, and counteracts, the positive burial effect. These results suggest that disturbance and recurrent burial in combination reduces the regeneration success and spread capacity of S . virginucus . Since global change leads to increasingly severe or frequent storms, the impact of disturbance and burial on clones could be greater in future and possibly prevent colonization of mobile dunes by the species.     

In vitro propagation and field establishment of Eulophia cullenii (Wight) Bl., a critically endangered orchid of Western Ghats, India through culture of seeds and axenic seedling-derived rhizomes

An efficient protocol has been devised for the propagation and field establishment of Eulophia cullenii (Wight) Bl., a terrestrial orchid having ornamental potentialities, and is critically endangered in Western Ghats, India. Seeds extracted from 60–90-d-old capsules germinated in ½ MS, ¼ MS, Knudson C, or Mitra liquid medium developed into 1.4–2.5-mm-diameter protocorms in 60 d. Supplementation of organic additives like coconut water, peptone, yeast extract, and casein acid hydrolysate (CH) significantly enhanced protocorm growth. Upon subculture onto agar-gelled Mitra medium fortified with 0.05% CH, 56% of protocorms regenerated into shoots through the formation of linear mini-rhizomes. The regenerated shoots grew vigorously in ½ MS, producing new rhizomes. Mature rhizomes from axenic seedlings produced maximum (13?±?1.4) shoots/whole rhizome in ½ MS fortified with 44.4 μM 6-benzylaminopurine (BAP), in 120–150 d. Horizontal and longitudinal halves of the rhizome also gave multiple shoots (6–8.5) in the presence of 44.4 μM BAP. Shoots or shoot clumps sub-cultured onto ½ MS basal medium produced roots followed by rhizomes in 60–150 d. Seedlings with mature rhizomes showed 70% establishment in the nursery and added a new rhizome at the end of one growth cycle. An average of 70.6% of the rhizomes originating from seedlings during the second growth cycle sprouted to produce new shoots, when planted in the native localities. Asymbiotic germination and cloning through rhizomes thus can provide a large number of vigorous plants of E. cullenii for ornamental exploitation as well as eco-restoration, if rhizome as storage organ is ensured in the propagule.     

<Emphasis Type="Italic">Rhizophagus irregularis</Emphasis> as an elicitor of rosmarinic acid and antioxidant production by transformed roots of <Emphasis Type="Italic">Ocimum basilicum</Emphasis> in an in vitro co-culture system

Arbuscular mycorrhiza is a symbiotic association formed between plant roots and soil borne fungi that alter and at times improve the production of secondary metabolites. Detailed information is available on mycorrhizal development and its influence on plants grown under various edapho-climatic conditions, however, very little is known about their influence on transformed roots that are rich reserves of secondary metabolites. This raises the question of how mycorrhizal colonization progresses in transformed roots grown in vitro and whether the mycorrhizal fungus presence influences the production of secondary metabolites. To fully understand mycorrhizal ontogenesis and its effect on root morphology, root biomass, total phenolics, rosmarinic acid, caffeic acid and antioxidant production under in vitro conditions, a co-culture was developed between three Agrobacterium rhizogenes-derived, elite-transformed root lines of Ocimum basilicum and Rhizophagus irregularis. We found that mycorrhizal ontogenesis in transformed roots was similar to mycorrhizal roots obtained from an in planta system. Mycorrhizal establishment was also found to be transformed root line-specific. Colonization of transformed roots increased the concentration of rosmarinic acid, caffeic acid and antioxidant production while no effect was observed on root morphological traits and biomass. Enhancement of total phenolics and rosmarinic acid in the three mycorrhizal transformed root lines was found to be transformed root line-specific and age dependent. We reveal the potential of R. irregularis as a biotic elicitor in vitro and propose its incorporation into commercial in vitro secondary metabolite production via transformed roots.     

Processed Manure as Carrier to Introduce Trichoderma harzianum: Population Dynamics and Biocontrol Effect on Rhizoctonia solani

Manure pellets produced from processed swine faeces can be used as carrier material for the biocontrol fungus Trichoderma harzianum. The antagonist can grow and sporulate on the processed manure powder as the sole source of carbon and nutrients. The incorporation of conidia in pellets of the processed manure was shown to be feasible on a laboratory scale. Survival of the fungus in the pellets during storage was satisfactory. The population dynamics of T. harzianum were studied using a benomyl-resistance marker after introduction of conidia into soil. The antagonist could colonize and spread through a number of non-sterile soils and was able to establish a stable population over a period exceeding 125 days. Under sterile conditions, the propagation of T. harzianum in soil was much greater than under non-sterile conditions. The incorporation of antagonist conidia in pellets was found to be essential for the successful colonization of non-sterile soil. In growth chamber experiments, application of T. harzianum via processed manure pellets reduced damping-off of sugar beet seedlings caused by Rhizoctonia solani in artificially and naturally infested soil. In artificially infested soil, T. harzianum reduced the population of R. solani and protected beet seedlings from damping-off 3 weeks after introduction. The application of T. harzianum to naturally infested soil increased the number of healthy beet seedlings more than two-fold.     

Metabolomics Analysis Identifies Intestinal Microbiota-Derived Biomarkers of Colonization Resistance in Clindamycin-Treated Mice

Background

The intestinal microbiota protect the host against enteric pathogens through a defense mechanism termed colonization resistance. Antibiotics excreted into the intestinal tract may disrupt colonization resistance and alter normal metabolic functions of the microbiota. We used a mouse model to test the hypothesis that alterations in levels of bacterial metabolites in fecal specimens could provide useful biomarkers indicating disrupted or intact colonization resistance after antibiotic treatment.

Methods

To assess in vivo colonization resistance, mice were challenged with oral vancomycin-resistant Enterococcus or Clostridium difficile spores at varying time points after treatment with the lincosamide antibiotic clindamycin. For concurrent groups of antibiotic-treated mice, stool samples were analyzed using quantitative real-time polymerase chain reaction to assess changes in the microbiota and using non-targeted metabolic profiling. To assess whether the findings were applicable to another antibiotic class that suppresses intestinal anaerobes, similar experiments were conducted with piperacillin/tazobactam.

Results

Colonization resistance began to recover within 5 days and was intact by 12 days after clindamycin treatment, coinciding with the recovery bacteria from the families Lachnospiraceae and Ruminococcaceae, both part of the phylum Firmicutes. Clindamycin treatment caused marked changes in metabolites present in fecal specimens. Of 484 compounds analyzed, 146 (30%) exhibited a significant increase or decrease in concentration during clindamycin treatment followed by recovery to baseline that coincided with restoration of in vivo colonization resistance. Identified as potential biomarkers of colonization resistance, these compounds included intermediates in carbohydrate or protein metabolism that increased (pentitols, gamma-glutamyl amino acids and inositol metabolites) or decreased (pentoses, dipeptides) with clindamycin treatment. Piperacillin/tazobactam treatment caused similar alterations in the intestinal microbiota and fecal metabolites.

Conclusions

Recovery of colonization resistance after antibiotic treatment coincided with restoration of several fecal bacterial metabolites. These metabolites could provide useful biomarkers indicating intact or disrupted colonization resistance during and after antibiotic treatment.     

Where are the seeds? Lack of floral morphs prevent seed production by the tristylous Pontederia cordata in South Africa

Reproduction is a crucial part of the successful establishment and spread of an invasive species. Invasive plants often produce seeds prolifically to spread into new ranges, yet the invasive macrophyte, Pontederia cordata L., does not appear to produce seeds in South Africa, limiting its invasive potential. Here, we aimed to determine what limits seed production of the tristylous P. cordata in South Africa, where it is widespread with impacts on the ecology of wetlands it invades, South Africa. We measured floral traits and pollen grain size from populations throughout the invasive range in South Africa to determine the relative proportion of tristylous morphs. We speculated that the absence of specialist native pollinators in the invasive range may be responsible for the absence of sexual reproduction and thus conducted a pollination study to determine whether flowers were visited. Thereafter, we hand pollinated 8865 flowers to conclude whether P. cordata exhibited an incompatibility system, which prevented seed production. The floral traits and pollen grain measurements were similar to those reported for short‐morphed flowers from the native range. The pollination study confirmed the absence of specialist insect visitors, while the hand‐pollination experiments resulted in no seed production. Only short‐morphed plants are present in South Africa, and the illegitimate pollination of short‐morphed plants prevents seed production. Vegetative spread through rhizome production is thus responsible for the invasion of P. cordata throughout South Africa. These findings suggest that control programs should target the plants'' rhizomes to prevent and reduce spread. More importantly, preventing the introduction of medium‐ and long‐morphed plants into South Africa is crucial to preclude P. cordata from producing seeds and enhancing invasion.     

Metabolism of Monoterpenes : Evidence for the Function of Monoterpene Catabolism in Peppermint (Mentha piperita) Rhizomes

l-Menthone of peppermint leaves is reduced to d-neomenthol which is glucosylated and transported to the rhizome, whereupon the β-d-glucoside is hydrolyzed, the aglycone oxidized back to l-menthone, and this ketone converted to l-3,4-menthone lactone. l-[G-³H]-3,4-Menthone lactone and its labeled progenitors, when incubated with excised mint rhizomes, gave rise to nonvolatile lipids as well as polar metabolites. The lipids thus generated consisted of labeled squalene and phytosterols in the nonsaponifiable fraction and C₁₄-C₂₆ fatty acids in the saponifiable fraction. These results imply degradation of the terpenoid to acetylcoenzyme A and reduced pyridine nucleotide, and reincorporation of label via these products. Starch and soluble carbohydrates were also found to be labeled; however, chemical degradation of the [³H]glucose obtained on hydrolysis of starch indicated the presence of tritium only on interior carbons, suggesting that labeling had occurred via reduced pyridine nucleotides. Analysis of the labeled organic acids revealed the presence of several hydroxy methylacyl intermediates suggesting the operation of a modified β-oxidation pathway in the degradation of the acyclic terpenoid skeleton. The results indicate that monoterpenes transported to the rhizome are oxidized to yield acetyl-coenzyme A and reduced pyridine nucleotides, and suggest that metabolic turnover of monoterpenes in mint represents a mechanism for recycling carbon and energy from foliar terpenes into other metabolites of the rhizome.     

Influence of fungal isolates on germination and growth of perennial ryegrass

Summary The influence of fungi isolated from perennial ryegrass roots on the germination and development of seedlings of perennial ryegrass was investigated. The basic procedure employed was to sterilise the seed surface and then inoculate with fungi and plant in non-sterile soil. It was realised that the fungal isolate inoculated on to the sterile seed surface would not remain dominant in the root region of the host and would have an influence on the host which would decline with time from when the seed germinated. This was because it would have to face antagonism from the normal components of the root microflora present in the non-sterile soil.Trichoderma viride delayed the emergence of the seedlings and reduced the production of herbage, an observation consistent with results of some other investigators. A sterile hyaline fungus stimulated the emergence of the seedlings, but subsequent tests showed that the presence of the microflora of the seed coat, or the soil microflora, or the sterile hyaline fungus was effective in promoting the rate of germination of seed that had been surface sterilised. Leaching seed in water brought about an increase in the rate of seed germination, and it is suggested that there might be a germination inhibitor soluble in water present in the seed coat, which might be inactivated by saprophytic micro-organisms.     

Age-specific seasonal storage dynamics of<Emphasis Type="Italic">Phragmites australis</Emphasis> rhizomes: a preliminary study

Age-specific seasonal rhizome storage dynamics of a wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Japan, were investigated from April to October 2000. For each sampling date, above- and below-ground biomass and age-specific rhizome bulk density, ?_rhiz were measured. Seven rhizome age classes were recognized, from <1 year to six years old, based on their position within the branching hierarchy as main criteria and rhizome color, condition of nodal sheaths and condition of the shoots attached to vertical rhizomes as secondary criteria. P. australis stand was moderately productive, having a net aerial and below-ground production of 1980 and 1240 g m^?2, respectively, and a maximum mean shoot height of 2.33 ± 0.12 m. In spring, shoot growth started at the expense of rhizome reserves, decreasing the rhizome biomass as well as ?_rhiz. Both parameters reached the seasonal minimum in May followed by a subsequent increase, indicating a translocation of reserves to rhizomes from shoots after they become self supporting. For each sampling date, ?_rhiz increased with rhizome age. Given that the quantity of reserves remobilized by the rhizomes for spring shoot growth, as assessed by the drop in bulk density from April to May, were positively correlated (r = 0.97, P < 0.05) with rhizome age, it is proposed that for spring shoot formation older rhizomes remobilize stored reserves more actively than younger ones. Given that the accumulation of rhizome reserves (rise in bulk density) from May to August, May to September or May to November was negatively correlated (r = 0.97, 0.92 and 0.87, respectively, P < 0.05) with rhizome age, it seemed possible that younger rhizomes were ‘recharged’ at a higher rate than older ones. These resource allocation mechanisms pertaining seasonal rhizome storage dynamics are of paramount importance in formulating management and conservation strategies of wetlands and aquatic habitats. Our results indicate that a harvest of above-ground biomass from May to June would be more effective in reducing the growth than a harvest in July to August or later, when rhizome reserves have already been replenished. However, the latter may remove a larger shoot bound nutrient stock, still preserving a healthy stand for the subsequent years.     

An in vitro culture model to study the dynamics of colonic microbiota in Syrian golden hamsters and their susceptibility to infection with Clostridium difficile

Clostridium difficile infections (CDI) are caused by colonization and growth of toxigenic strains of C. difficile in individuals whose intestinal microbiota has been perturbed, in most cases following antimicrobial therapy. Determination of the protective commensal gut community members could inform the development of treatments for CDI. Here, we utilized the lethal enterocolitis model in Syrian golden hamsters to analyze the microbiota disruption and recovery along a 20-day period following a single dose of clindamycin on day 0, inducing in vivo susceptibility to C. difficile infection. To determine susceptibility in vitro, spores of strain VPI 10463 were cultured with and without soluble hamster fecal filtrates and growth was quantified by quantitative PCR and toxin immunoassay. Fecal microbial population changes over time were tracked by 16S ribosomal RNA gene analysis via V4 sequencing and the PhyloChip assay. C. difficile culture growth and toxin production were inhibited by the presence of fecal extracts from untreated hamsters but not extracts collected 5 days post-administration of clindamycin. In vitro inhibition was re-established by day 15, which correlated with resistance of animals to lethal challenge. A substantial fecal microbiota shift in hamsters treated with antibiotics was observed, marked by significant changes across multiple phyla including Bacteroidetes and Proteobacteria. An incomplete return towards the baseline microbiome occurred by day 15 correlating with the inhibition of C. difficile growth in vitro and in vivo. These data suggest that soluble factors produced by the gut microbiota may be responsible for the suppression of C. difficile growth and toxin production.     

Density regulation during the regeneration of two monocarpic bamboos: self-thinning or intraclonal regulation?

Abstract. The population dynamics of two monocarpic bamboos, Sasa kurilensis and S. tsuboiana, were studied for more than 10 years after establishment following mass flowering. Both species show vigorous rhizomatous vegetative reproduction after growing up to maturity, but horizontal expansion in the seedling stage was much more vigorous in S. tsuboiana than in S. kurilensis. The pattern of changes in culm density in the two species was strikingly similar: culm densities of both species increased until they reached full-density states, after which they decreased in accordance with seedling growth. However, the mode of regulation in culm density was different. S. kurilensis seedlings were composed of only a few culms and scarcely extended their rhizomes during the observation period. Such poor lateral expansion resulted in asymmetric competition as observed in many non-clonal plants, and consequently their culm density decreased as a result of the mortality of genets due to self-thinning. In S. tsuboiana seedlings, the number of culms per genet increased considerably by frequent tillering and sprouting from rhizomes. However, after reaching full density state, the Bud Utility Ratio (BUR), (the proportion of the rhizome nodes with culms to the total number of rhizome nodes), decreased drastically. In this manner, S. tsuboiana regulated culm density intraclonally as is observed in the stable states of many clonal plants. Hence it is important for the understanding of the regeneration process in clonal species to clarify when and how their seedlings extend rhizomes during their growth.     

The growth of saprophytic fungi on root surfaces

Summary Data are provided on the growth of non-pathogenic soil fungi on root surfaces. By growing roots from non-sterile soil into sterile vermiculite, and by regular isolation of fungi from the roots which had grown into the sterile vermiculite, it was shown that fungal growth down roots is slow. It is suggested that in the colonization of roots by non-pathogenic fungi successive lateral colonization from the soil is of greater importance than the growth of fungi down roots.     

Rhizome development ofPhragmites australis in a reed community

Variations in the height, shoot density, biomasses of above- and below-ground parts and rhizome distributions ofPhragmites australis were investigated along a line-transect in a reed community at Yufutsu Mire, Hokkaido. Relationships of performance of the reed plants to soil conditions and species compositions were also examined. Three types of rhizome development were recognized in reed plants; (1) the central part of the reed community, characterized by well developed rhizomes and dense aerial shoots, (2) the intermediate part, characterized by development of rhizomes along both the peat and surface layers and very dense aerial shoots, and (3) the marginal part, characterized by development of rhizomes only along the peat layer and sparse aerial shoots. Observation showed that rhizomes in the surface layer actively produced aerial shoots, whereas rhizomes in the peat layer contributed to the spreading of their distribution range. With the growth of rhizomes, organic debris originating from dead rhizomes and roots accumulated in the mineral soil to promote organic soil formation. In dense parts of the reed stand, species composition was poor because of the shading and litter accumulation by reed plants. The effects of microtopography and water level on the establishment of reed seedlings were also considered.     

Secondary metabolites produced by a root‐inhabiting sterile fungus antagonistic towards pathogenic fungi

Aims: A sterile red fungus (SRF) isolated from cortices of roots of both wheat (Triticum aestivum cv. Gamenya) and ryegrass (Lolium rigidum cv. Wimmera) was found to protect the hosts from phytopathogens and promote plant growth. In this work, the major secondary metabolites produced by this SRF were analysed, and their antibiotic and plant‐growth‐promoting activities investigated. Methods and Results: Two main compounds, veratryl alcohol (VA) and 4‐(hydroxymethyl)‐quinoline, were isolated from the culture filtrate of the fungus. In antifungal assays, VA inhibited the growth of Sclerotinia sclerotiorum and Pythium irregulare even at low amounts, while high concentrations (>100 μg per plug) of 4‐(hydroxymethyl)‐quinoline were needed. Both metabolites revealed weak inhibition of Rhizoctonia solani. Furthermore, both compounds showed a growth promotion activity on canola (Brassica napus) seedlings used as bioassays. Conclusions: Isolation and characterization of the main secondary metabolites from culture filtrates of a root‐inhabiting sterile fungus are reported. The biological assays indicate that these secondary metabolites may have a role in both plant growth regulation and antifungal activity. Significance and Impact of the Study: This study provides a better understanding of the metabolism of a cortical fungus that may have a useful role in the biological suppression of root‐infecting soil‐borne plant pathogens.     

Do litter-mediated plant-soil feedbacks influence Mediterranean oak regeneration? A two-year pot experiment

Background & Aims

Oak seedling establishment is difficult and may be partly explained by litter-mediated interactions with neighbors. Litter effects can be physical or chemical and result in positive or negative feedback effects for seedlings. Mediterranean species leaves contain high levels of secondary metabolites which suggest that negative litter effects could be important.

Methods

Seedlings of Quercus ilex and Quercus pubescens were grown for two years in pots with natural soil and litter inputs from 6 Mediterranean woody species, artificial litter (only physical effect) or bare soil.

Results

Litter types had highly different mass loss (41–80%), which correlated with soil organic C, total N and microbial activity. Litter of Q. pubescens increased soil humidity and oak seedlings aerial biomass. Litters of Cotinus coggygria and Rosmarinus officinalis, containing high quantities of phenolics and terpenes respectively, decomposed fast and led to specific soil microbial catabolic profiles but did not influence oak seedling growth, chemistry or mycorrhization rates.

Conclusions

Physical litter effects through improved soil humidity seem to be predominant for oak seedling development. Despite high litter phenolics content, we detected no chemical effects on oak seedlings. Litter traits conferring a higher ability to retain soil moisture in dry periods deserve further attention as they may be critical to explain plant-soil feedbacks in Mediterranean ecosystems.

     

Do spatial patterns of clonal fragments and architectural responses to defoliation depend on the structural blue-print? An experimental test with two rhizomatous Cyperaceae

Clonal architecture is involved in performance of clonal fragments, as it determines spatial distribution of ramets. It is expected to rely on the species-specific expression of several architectural traits (structural blue-print). However, in contrasting environments, realized clonal architectures may differ, due to phenotypic plasticity. In this paper, we compared clonal architectures between two rhizomatous ecologically close Cyperaceae (Carex divisa and Eleocharis palustris) in non-defoliated and defoliated conditions. Two questions were addressed. (1) How much do the structural blue-print and resulting colonization and occupation of space differ between both species? (2) Does the structural blue-print constrain plastic responses of clonal architecture to defoliation? Traits related to performance, spatial pattern, architecture and biomass allocation of clonal fragments were monitored through an original non-destructive mapping method. In non-defoliated conditions, both species showed similar biomass but contrasting architectures and patterns of biomass allocation to rhizomes that resulted in different spatial patterns. The rhizome network of C. divisa, which consisted in only two primary rhizomes but several branches, was involved in resource storage rather than in spatial colonization. Conversely, E. palustris produced on average six primary rhizomes that grew in the whole horizontal plane, maximizing both occupation and colonization of space. These differences in structural constraints coupled with allometric relationships, resulted in differential responses to defoliation. In C. divisa, the costs associated to defoliation caused a decrease in branching, limiting the area occupied and number of ramets produced by clonal fragments, but increasing ramet density. Conversely, the weakly branched rhizome network of E. palustris was not affected by defoliation. Both spatial strategies (consolidation vs. colonization) are likely to provide ecological advantages allowing their coexistence in grazed meadows.