<Emphasis Type="Italic">Trichoderma</Emphasis>-enriched organic fertilizer can mitigate microbiome degeneration of monocropped soil to maintain better plant growth

Background and aims

Given the worldwide effort to improve the nitrogen (N) economy of crops, it is critical to understand the mechanisms of improved N uptake which have resulted from selection pressure for grain yield in Australian wheat (Triticum aestivum L.). Changes in root system traits and N uptake were examined in nine Australian wheat varieties released between 1958 and 2007.

Methods

Wheat varieties were grown in rhizo-boxes in a glasshouse. We measured nitrogen uptake and mapped root growth and proliferation to quantify root length density (RLD), root length per plant, root biomass, specific root length, and plant nitrogen uptake per unit root length.

Results

Selection for yield reduced total RLD and total root length, and increased N uptake per unit root length that overrode the reduction in root system size, effectively explaining the increase in N uptake. Importantly, N uptake in our experiment under controlled conditions matched field measurements, reinforcing the agronomic significance of the present study.

Conclusions

Wheat varieties released in Australia between 1958 and 2007 increased their N uptake, not because of increasing their root length and RLD, but for progressively increasing the efficiency of their root system in capturing N. Our collection of varieties is therefore an interesting model to probe for variation in the affinity of the root system for nitrate.

     

Root morphology and its contribution to a large root system for phosphorus uptake by <Emphasis Type="Italic">Rytidosperma</Emphasis> species (wallaby grass)

Aims

Rytidosperma species are native Australian grasses which have different growth rates and phosphorus (P) requirements. This study examined the role of root morphology traits in response to P supply.

Methods

Nine Rytidosperma species ranging from slow- to fast-growth were examined along with Lolium perenne and Bromus hordeaceus. Plants were grown in a glasshouse for 47 days in soil supplied with six levels of P between 0 and 60 mg P per pot. Root mass, length and diameter, root hair length and density, and extent of mycorrhizal colonisation were measured.

Results

Across all species there was a positive correlation (P < 0.001) between P uptake and root mass, length and root hair cylinder volume (RHCV; estimated using root diameter, root hair length and root length) at all levels of P supply. An exception was the RHCV of B. hordeaceus, where expected P uptake was not achieved due to a markedly reduced root length at low-P supply. For the Rytidosperma species, morphological plasticity for specific root length, root mass fraction and root hair length ranged from 1.5-fold to 2.7-fold between high- and low-P supply. However, across all species and P levels no single root morphological trait was identified for universally increasing the size of the root system and P uptake.

Conclusions

Fast-growing species took up more P as a result of an overall larger root mass, greater root length and larger RHCV.

     

Use of a gnotobiotic plant assay for assessing root colonization and mineral phosphate solubilization by <Emphasis Type="Italic">Paraburkholderia bryophila</Emphasis> Ha185 in association with perennial ryegrass (<Emphasis Type="Italic">Lolium perenne</Emphasis> L.)

Aims

The mechanisms by which rhizosphere bacteria increase the availability of mineral P precipitates for plant use are understudied. However, Paraburkholderia bryophila Ha185 is known to solubilize inorganic phosphate in vitro via a novel process. Therefore, this study aimed to demonstrate P solubilization by Ha185 in association with roots of perennial ryegrass (Lolium perenne L.).

Methods

We developed a gnotobiotic plant assay to assess P solubilization by Ha185 on ryegrass roots under various nutrient conditions. A green fluorescent protein (GFP)-tagged derivative of Ha185 was used in conjunction with fluorescent microscopy and confocal microscopy to visualize colonization of ryegrass roots.

Results

Ha185 solubilized mineral P (hydroxyapatite) in association with ryegrass roots and increased ryegrass growth by 20% under P-limited conditions. The GFP-tagged Ha185 strain colonized the rhizoplane and penetrated the primary root of ryegrass, possibly through “crack entry” at the point of lateral root emergence, but also by entering the epidermal cells via root hairs.

Conclusions

Ha185 supported ryegrass growth under P-limited conditions, indicating this strain may improve availability of soil P for uptake by ryegrass. Tools developed in this study have broad application in the study of rhizobacteria-plant interactions.

     

<Emphasis Type="Italic">Sedum</Emphasis> root foraging in layered green roof substrates

Background and aims

Layered profiles of designed soils may provide long-term benefits for green roofs, provided the vegetation can exploit resources in the different layers. We aimed to quantify Sedum root foraging for water and nutrients in designed soils of different texture and layering.

Methods

In a controlled pot experiment we quantified the root foraging ability of the species Sedum album (L.) and S. rupestre (L.) in response to substrate structure (fine, coarse, layered or mixed), vertical fertiliser placement (top or bottom half of pot) and watering (5, 10 or 20 mm week^?1).

Results

Water availability was the main driver of plant growth, followed by substrate structure, while fertiliser placement only had marginal effects on plant growth. Root foraging ability was low to moderate, as also reflected in the low proportion of biomass allocated to roots (5–13%). Increased watering reduced the proportion of root length and root biomass in deeper layers.

Conclusions

Both S. album and S. rupestre had a low ability to exploit water and nutrients by precise root foraging in substrates of different texture and layering. Allocation of biomass to roots was low and showed limited flexibility even under water-deficient conditions.

     

Colonization cues of leaf- and root-inhabiting bacterial microbiota of <Emphasis Type="Italic">Atractylodes lancea</Emphasis> derived in vitro and in vivo

Background and aims

Earthworms effect on plant growth is mediated by their dejections or “casts”, a complex mixture of organic matter, minerals and microbes. In casts, different processes such as organic matter mineralization and signal molecule production follow a complex temporal dynamics. An adaptation of root morphology to cast dynamics could allow an efficient nitrogen capture by the plant.

Methods

The plant Brachypodium distachyon was grown in a laboratory experiment with different proportions of casts of increasing ages. Casts were labelled with ¹⁵N to quantify the plant N uptake from the casts. Plant biomass and morphology, especially root system structure, were analysed.

Results

The age of casts had an effect on fine root length, highlighting the importance of the dynamics of cast maturation in root adaptation. Plant biomass production was affected by the interaction between the age and proportion of casts. A positive correlation between the ¹⁵N proportion in plant tissues and plant biomasses indicated that plants were more efficient in foraging N in casts than in the bulk soil.

Conclusions

Our results suggested that both a timely adaptation of the root system structure and a significant proportion of casts are necessary to observe a positive effect of casts on plant growth.

     

Inter- and intra-species intercropping of barley cultivars and legume species,as affected by soil phosphorus availability

Aims

Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability.

Methods

Four barley cultivars (Hordeum vulgare L.) and three legume species (Trifolium subterreneum, Ornithopus sativus and Medicago truncatula) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Above-ground biomass and shoot P were measured.

Results

Barley-legume intercrops had 10–70% greater P accumulation and 0–40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments.

Conclusions

Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P.

     

Low temperature and <Emphasis Type="Italic">Daphnia</Emphasis>-associated infochemicals promote colony formation of <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> and its harvesting

Objective

To explore the combined effects of temperature and Daphnia-associated infochemicals on colony formation of Scenedesmus obliquus to faciliate harvesting the algal biomass.

Results

A three-parameter modified Gaussian model fitted the changes of the number of cells per particle in S. obliquus induced by Daphnia culture filtrate well under any temperature. Decreases in temperature enhanced the induced–colony formation of Scenedesmus. The maximum colony size at 15–25 °C was significantly larger than those at 30–35 °C. An additional 1 or 2 days at low temperature was needed to reach the maximum colony size, which indicates the best harvest time for algal biomass.

Conclusion

Induced-colony formation of Scenedesmus by Daphnia culture filtrate at 15–25 °C is recommended to settle algal cells. This condition facilitates harvesting the biomass.

     

Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

Background and aims

Drought events, agricultural practices and plant communities influence microbial and soil abiotic parameters which can feedback to fodder production. This study aimed to determine which soil legacies influence plant biomass production and nutritional quality, and its resistance and recovery to extreme weather events.

Methods

In a greenhouse experiment, soil legacy effects on Lolium perenne were examined, first under optimal conditions, and subsequently during and after drought. We used subalpine grassland soils previously cultivated for two years with grass communities of distinct functional composition, and subjected to combinations of climatic stress and simulated management.

Results

The soil legacy of climatic stress increased biomass production of Lolium perenne and its resistance and recovery to a new drought. This beneficial effect resulted from higher nutrient availability in soils previously exposed to climatic stresses due to lower competitive abilities and resistance of microbial communities to a new drought. This negative effect on microbial communities was strongest in soils from previously cut and fertilized grasslands or dominated by conservative grasses.

Conclusion

In subalpine grasslands more frequent climatic stresses could benefit fodder production in the short term, but threaten ecosystem functioning and the maintenance of traditional agricultural practices in the long term.

     

N transfer in three-species grass-clover mixtures with chicory,ribwort plantain or caraway

Background and aims

There is substantial evidence that legume-derived Nitrogen (N) is transferred to neighboring non-legumes in grassland mixtures. However, there is sparse information about how deep rooted non-legume forage herbs (forbs) influence N transfer in multi-species grasslands.

Methodology

Red clover (Trifolium pretense L.) was grown together with perennial ryegrass (Lolium perenne L.) and one of three forb species: chicory (Cichorium intybus L.), ribwort plantain (Plantago lanceolata L.) or caraway (Carum carvi L.) in a field experiment. During the first year after the establishment, red clover leaves were labeled with ¹⁵N-urea to determine the N transfer from red clover to companion ryegrass and forbs.

Results

On an annual basis, up to 15 % of red clover N was transferred to the companion ryegrass and forbs, but predominantly to the grass. The forb species did not differ in their ability to take up clover N, but biomass production and soil N acquisition was higher in chicory and plantain than in caraway.

Conclusions

Grass relied to a great extent on clover N, whereas forbs relied on soil N. Soil ¹⁵N-enrichment indicated that N transfer occurred in the upper soil layers and that a dependence on clover-derived N did not necessarily give grass a growth advantage.

     

Fine-root trait plasticity of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>) and spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) forests on two contrasting soils

Aim

The fine roots of trees may show plastic responses to their resource environment. Several, contrasting hypotheses exist on this plasticity, but empirical evidence for these hypotheses is scattered. This study aims to enhance our understanding of tree root plasticity by examining intra-specific variation in fine-root mass and morphology, fine-root growth and decomposition, and associated mycorrhizal interactions in beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) forests on soils that differ in resource availability.

Methods

We measured the mass and morphological traits of fine roots (i.e. ≤ 2 mm diameter) sampled to 50 cm depth. Fine-root growth was measured with ingrowth cores, and fine-root decomposition with litter bags. Mycorrhizal fungal biomass was determined using ingrowth mesh bags.

Results

Both tree species showed more than three times higher fine-root mass, and a ten-fold higher fine-root growth rate on sand than on clay, but no or marginal differences in overall fine-root morphology. Within the fine-root category however, beech stands had relatively more root length of their finest roots on clay than on sand. In the spruce stands, ectomycorrhizal mycelium biomass was larger on sand than on clay.

Conclusions

In temperate beech and spruce forests, fine-root mass and mycorrhizal fungal biomass, rather than fine-root morphology, are changed to ensure uptake under different soil resource conditions. Yet enhancing our mechanistic understanding of fine-root trait plasticity and how it affects tree growth requires more attention to fine-root dynamics, the functional diversity within the fine-roots, and mycorrhizal symbiosis as an important belowground uptake strategy.

     

Taxonomic and ecological patterns in root traits of <Emphasis Type="Italic">Carex</Emphasis> (Cyperaceae)

Background and aims

In Malawi, strategies are being sought to boost maize production through improvements in soil fertility. This study assessed the impact of intercropping maize (Zea mays) with pigeon pea (Cajanus cajan) in Lixisols of Malawi on yield, biological N fixation, soil aggregation, and P forms within soil aggregates.

Methods

Maize and pigeon pea were grown intercropped in pots, with varying degrees of root interaction in order to understand the relative importance of biochemical versus physical rhizospheric interactions. Following harvest, soils were separated into aggregate fractions using wet-sieving, and the nutrient content of all fractions was assessed.

Results

The proportion of macroaggregates and microaggregates increased by 52 and 111%, respectively, in the intercropping treatment compared to sole maize, which significantly increased organic P storage in the microaggregates of intercropped compared to sole maize (84 versus 29 mg P kg^?1, respectively). Biologically fixed N increased from 89% in the sole pigeon pea to 96% in the intercropped system.

Conclusions

Intercropping maize with pigeon pea can have a significant and positive impact on soil structure as well as nutrient storage in these high P-sorbing soils. This is caused primarily by physical root contact and to a lesser degree by biochemical activities.

     

Plant organic N uptake maintains species dominance under long-term warming

Background and aims

There is ample experimental evidence for shifts in plant community composition under climate warming. To date, however, the underlying mechanisms driving these compositional shifts remain poorly understood.

Methods

The amount and form of nitrogen (N) available to plants are among the primary factors limiting productivity and plant coexistence in terrestrial ecosystems. We conducted a short-term ¹⁵N tracer experiment in a ten-year warming and grazing experiment in an alpine grassland to investigate the effects of warming and grazing on plant uptake of NO₃^?-N, NH₄⁺-N, and glycine-N. Four dominant plant species (Kobresia humilis, Potentilla anseria, Elymus nutans, Poa annua) were selected. Results We found that 10-years of warming decreased plant uptake of inorganic N by up to 80% in all species. In contrast, warming increased the uptake of organic N in K. humilis, P. anseria, and E. nutans but not in P. annua. Results showed that plant relative biomass increased hyperbolically with the ratio of the plant species total uptake of available N and plant community uptake of available N. And a significant positive correlation between plant species uptake of soil glycine-N and the uptake of total available N.

Conclusions

The stable relative biomass of plant species is largely dependent on organic N uptake by plants. We conclude that plant organic N uptake maintains species dominance under long-term warming.

     

Comments on “unravelling community assemblages through multi-element stoichiometry in plant leaves and roots across primary successional stages in a glacier retreat area” by Jiang <Emphasis Type="Italic">et al.</Emphasis>

Aims

We examined novel ways of non-destructively measuring root weight, plant growth and water use efficiencies to improve the detection of treatment effects in plant phenotyping in pot culture.

Method

Two genotypes each of maize, sunflower and soybean were grown in 4 L ANOVApot®s in the Twinpot Water Management System (TWMS) of a constant water table. Measurement of pot weights and pot water losses (weekly and by drip rate) over time allowed the derivation of plant biomass gain and Water Use Efficiences (WUE). The destructive harvest at 31 days provided weights of plant parts and derived estimates of fresh root weight without physical recovery.

Results

Derived estimates of whole plant biomass were highly correlated with harvested whole plant dry weights (r?=?0.97) and fresh shoot weights (r?=?0.99), while estimates of non-recovered fresh root weights were highly correlated with harvested shoot fresh weights (r?=?0.86) and recovered root fresh weights (r?=?0.85). WUEs based on actual water loss and drop counts varied significantly across species and between maize cultivars.

Conclusions

Constant water table plant culture in pots allows measures of roots without physical recovery, in situ crop growth and WUEs based on water losses and drip rates.

     

Involvement of reactive oxygen species and Ca<Superscript>2+</Superscript> in the differential responses to low-boron in rapeseed genotypes

Background and aims

Invasive weeds may exert negative impact on other plant species and soil processes. The observed negative impact of an invasive weed species may be driven by allelopathy or nutrient availability.

Methodology

Sorghum halepense is one of the worst invasive weeds in crop fields. We quantified the species richness in the S. halepense-invaded communities and communities not yet invaded by the weed. Sorghum soil and no-sorghum soil were analysed for total phenolics, microbial activity, available nitrogen (N) and organic carbon. Manipulative experiments were carried out to understand the interference potential of S. halepense. Soil was amended with root or shoot leachate of S. halepense, and its impact on plant growth and soil properties was studied.

Results

Out of four S. halepense-sites, lower plant species richness was observed in one site compared to uninvaded sites. S. halepense-invaded soil had higher levels of total phenolics and lower levels of available N. Higher inhibition in the root growth of Brassica juncea or Bidens pilosa was observed in root leachate-amended soil than shoot leachate-amended soil. Shoot leachate-amended soil had higher levels of total phenolics and available N than root leachate-amended soils. Significant reduction in the available N was observed in soil amended with root leachate. Significant decline in the total phenolics over a period of time was observed in soil amended with root leachate or shoot leachate of S. halepense. Higher CO₂ release was observed 24 h after amending soil with root leachate or shoot leachate of S. halepense.

Conclusions

Sorghum halepense interference potential in its soil is likely due to lower levels of available N. Greater reduction in root dry weight of assay species in root leachate amended soil compared to shoot leachate amended soil was likely due to lower levels of available N in root leachate-amended soil. Relative interference potential of both root and shoot leachates or extracts should be evaluated in allelopathy bioassays and further experiments should be designed to distinguish the role of allelochemicals and nutrient availability in plant growth inhibition.

     

<Emphasis Type="Italic">Mesorhizobium jarvisii</Emphasis> sv. astragali as predominant microsymbiont for <Emphasis Type="Italic">Astragalus sinicus</Emphasis> L. in acidic soils,Xinyang, China

Background and aims

Common bean (Phaseolus vulgaris L.) nodulates with a wide range of rhizobia. Amongst these is Bradyrhizobium, which is inefficient but able to induce profuse nodulation on this crop. Based on this observation, we tested whether co-inoculating bradyrhizobia with a more standard common bean symbiont, Rhizobium tropici, could stimulate growth and nodulation of common bean, thus contributing to a more effective symbiosis.

Methods

Rhizobium tropici was co-inoculated with two Bradyrhizobium strains applied at three different doses (10⁴, 10⁶, and 10⁸ CFU seed^?1) under sterile conditions, and at a single dose (10⁸ CFU seed^?1) in non-sterile soil. Plant biomass, nodulation, and N accumulation in plant tissues were evaluated.

Results

Co-inoculated plants produced more nodules, and accumulated more shoot dry biomass and nitrogen than plants inoculated with R. tropici alone under gnotobiotic conditions. Significant responses were observed at the highest inoculum dose and a significant correlation between dose and shoot dry weight was observed. Co-inoculation increased biomass and N accumulation in non-sterile soil, although with a smaller magnitude.

Conclusions

Altogether, our findings suggest that the co-inoculation with bradyrhizobia contributed to an improved symbiotic interaction between R. tropici and common beans.

     

Regulation of dauciform root formation and root phosphatase activities of sedges (<Emphasis Type="Italic">Carex</Emphasis>) by nitrogen and phosphorus

Aims

Dauciform roots (DR) are formed by some Cyperaceae under phosphorus (P) deficiency. To advance our understanding of their physiological function, I ask: Is DR formation regulated by shoot P status or external P supply? How does it respond to nitrogen (N)? Do DR enhance root monoesterase, diesterase or phytase activities and ability to utilize organic P?

Methods

Greenhouse experiments were carried out with two Carex species grown in sand with (1) different combinations of N and P supply, (2) local supply of N or P to root halves, and (3) different organic P forms.

Results

Carex flava produced DR in all treatments. The density of DR and phosphatase activities increased with N supply; they were regulated by shoot P status and external N (but not P) supply. All phosphatase activities increased with DR density. Carex muricata produced no DR and had lower diesterase activity than C. flava but both species grew equally well with diester-P.

Conclusions

DR and phosphatase activities are regulated by both N and P supply. Similar growth responses to nutrients in both species suggest small costs and benefits of DR under experimental conditions but confirmation is needed for plants grown on natural soils.

     

The impact of <Emphasis Type="Italic">Carpobrotus</Emphasis> cfr. <Emphasis Type="Italic">acinaciformis</Emphasis> (L.) L. Bolus on soil nutrients,microbial communities structure and native plant communities in Mediterranean ecosystems

Background and aims

Carpobrotus spp. are amongst the most impactful and widespread plant invaders of Mediterranean habitats. Despite the negative ecological impacts on soil and vegetation that have been documented, information is still limited about the effect by Carpobrotus on soil microbial communities. We aimed to assess the changes in the floristic, soil and microbial parameters following the invasion by Carpobrotus cfr. acinaciformis within an insular Mediterranean ecosystem.

Methods

Within three study areas a paired-site approach, comparing an invaded vs. a non-invaded plot, was established. Within each plot biodiversity indexes, C and N soil content, pH and microbial biomass and structure (bacterial and fungal) were assessed.

Results

Invaded plots showed a decrease of α-species richness and diversity. The least represented plant species in invaded plots were those related to grassland habitats. In all invaded soils, a significant increase of carbon and nitrogen content and a significant decrease of pH were registered. Carpobrotus significantly increased bacterial and fungal biomass and altered soil microbial structure, particularly favoring fungal growth.

Conclusions

Carpobrotus may deeply impact edaphic properties and microbial communities and, in turn, these strong modifications probably increase its invasive potential and its ability to overcome native species, by preventing their natural regeneration.

     

Differences in water-use strategies along an aridity gradient between two coexisting desert shrubs (<Emphasis Type="Italic">Reaumuria soongorica</Emphasis> and <Emphasis Type="Italic">Nitraria sphaerocarpa</Emphasis>): isotopic approaches with physiological evidence

Background and aims

Understanding the responses of different plant species to changes in available water sources is critical for accurately modeling and predicting species dynamics. Our study aimed to explore whether there were differences in water-use strategies between the two coexisting shrubs (Reaumuria soongorica and Nitraria sphaerocarpa) in response to different amounts of summer precipitation.

Methods

We conducted 3 years of field observations at three sites along an aridity gradient from the middle to lower reaches of the Heihe River basin, northwestern China. Stable oxygen composition (δ¹⁸O) in plant xylem water, soil water and groundwater were analyzed concurrently with ecophysiological measurements at monthly intervals during the growing seasons.

Results

Water source for coexisting R. soongorica and N. sphaerocarpa did not differ at the sites with high precipitation, but significantly differed in more arid locations. The N. sphaerocarpa was more sensitive to summer precipitation than R. soongorica in terms of predawn water potential, stomatal conductance and foliage carbon-isotope discrimination.

Conclusions

The plants relying on groundwater maintained consistent water use strategies, but not plants that took up precipitation-derived water. We also found that the difference in water source uptake between the coexisting species was more apparent in more arid locations.

     

<Emphasis Type="Italic">Epichloë</Emphasis> exudates promote in vitro and in vivo arbuscular mycorrhizal fungi development and plant growth

Background and aims

We studied, through exudates employment, the effect of Epichloë (endophytic fungi), both independently and in association with Bromus auleticus (grass), on arbuscular mycorrhizal fungi (AMF) colonization, host and neighbouring plants biomass production and soil changes.

Methods

Through in vitro and greenhouse experiments, Epichloë endophytes effect on AMF development was evaluated. In vitro studies of exudates effect on Gigaspora rosea and Rhizophagus intraradices were performed using root or endophyte exudates. A 6-month greenhouse experiment was conducted to determine Bromus auleticus endophytic status effect and endophyte exudates role in biomass production, neighbouring plants mycorrhizal colonization and soil properties.

Results

Endophyte exudates and E+ plant root exudates promoted in vitro AMF development in the pre-infective stage of G. rosea and in carrot root culture mycelium of R. intraradices in a dose-response relationship, while control media and E- plants exudates had no effect. R. intraradices colonization and plant growth was clearly increased by endophytes and their exudates.

Conclusions

This is the first work evidencing the direct effect of Epichloë endophytes and infected plants root exudates on AMF extramatrical development. While higher levels of AMF colonization were observed in E+ plants, no clear effect was detected in neighbouring plants colonization, plant biomass or soil properties.