Soil nitrification and foliar δ15N declined with stand age in trembling aspen and jack pine forests in northern Alberta,Canada

Aims

Seed germination and seedling emergence are vulnerable to water stress in arid environments. When precipitation is low and unpredictable during the early growing season, seeds near the sand surface often suffer from hydration/dehydration during germination. We investigated the responses of seedling emergence and survival of a sand dune grass with high sand stabilization value to amount and frequency of precipitation and depth of burial in sand.

Methods

Effects of amount and frequency of precipitation, burial and hydration/dehydration on seedling emergence of Leymus secalinus, were examined using standard procedures.

Results

Seedling emergence was affected by amount and frequency of monthly precipitation and depth of burial, and it decreased as precipitation frequency decreased with same amount of precipitation. Highest emergence percentage was obtained with 100 or 150 mm precipitation at 1–4 cm depth. Hydration/dehydration treatments decreased germination and increased dormancy percentage. Young seedlings with root lengths of 0–1 mm desiccated up to 30 days revived after rehydration.

Conclusions

Seedling emergence of L. secalinus is adapted to 150 mm monthly precipitation with frequency of 10–30 times per month, 1–4 cm burial depth and dehydration interval of 1–2 days. Alteration of amount and/or frequency of precipitation caused by climate change could markedly affect seedling emergence and population regeneration of this species.     

Responses of rhizomatous grass Phragmites communis to wind erosion: effects on biomass allocation

Background and aims

The ability of modifying biomass allocation to deal with different environmental stress is an important mechanism for plant population expansion and maintenance in the unstable dune environment where wind erosion persists. However, how biomass is partitioned between horizontal rhizome extension and vertical ramet growth in response to wind erosion has not been fully understood. The objective of this study was to explore how wind erosion affected the relationship between horizontal rhizome extension and vertical ramet growth using a common rhizomatous perennial grass, Phragmites communis.

Methods

We dug 300 cm?×?200 cm, 80 cm deep pits in a garden experiment plot. Clonal fragments of P. communis were planted individually at a depth of 40 cm in these pits for 4 weeks before treatments. Surface sand was gradually removed to the final depth of 0 (control), 10, 20, 30 and 40 cm (maximum sand removal). Ramet emergence time, rhizome-based and tiller-based ramet number, rhizome number and length, biomass of vertically and horizontally oriented structures were monitored at the end of the experiment.

Results

With increasing erosion depth, the proportion of tiller-based ramets (in total number of ramets) increased, whereas that of rhizome-based ramets decreased. With increasing erosion depth, the percentage of vertically oriented structures biomass in total biomass increased significantly, whereas that of horizontally oriented structures biomass decreased.

Conclusions

The changes in biomass allocation (i.e., more allocation in vertical than horizontal biomass) together with a trade-off in tiller-based and rhizome-based ramets may enable P. communis to make better use of the resources in erosion conditions and maximize plant population expansion and maintenance.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

Growth characteristics of ectomycorrhizal seedlings of Quercus glauca,Quercus salicina,and Castanopsis cuspidata planted on acidic soil

Key message

Seedlings of three Fagaceae species planted on acidic, infertile colluvial soil showed accelerated growth when inoculated with ectomycorrhizal fungi.

Abstract

We conducted a study with seedlings of Fagaceae species inoculated with ectomycorrhizal fungi to estimate their utility for growth in acidic soil conditions. We selected Quercus glauca, Quercus salicina and Castanopsis cuspidata as typical evergreen, broad-leaved, woody species of southwestern Japan. Seedlings were inoculated with Astraeus hygrometricus or Scleroderma citrinum, and planted in acidic, infertile colluvial soil collected from an abandoned site. Six months after planting, seedlings of the three species inoculated with A. hygrometricus were growing well, especially, Q. salicina. The growth of seedlings inoculated with S. citrinum was inferior to seedlings inoculated with A. hygrometricus. In contrast, seedlings without ectomycorrhizal fungi did not grow well. Differences in growth among the three types of seedlings were related to differences in the levels of nutrient acquisition. We concluded that Fagaceae seedlings inoculated with A. hygrometricus were best suited for acidic, infertile environments.     

The dual symbiosis between arbuscular mycorrhiza and nitrogen fixing bacteria benefits the growth and nutrition of the woody invasive legume Acacia cyclops under nutrient limiting conditions

Background and aims

Acacia cyclops is an invasive species within Mediterranean ecosystems, characteristically low in soil nutrients. Thus associations with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhiza (AM) may provide an advantage to these legumes. This study investigated the role of AM and NFB in the growth and nutritional physiology of A. cyclops.

Methods

Seedlings were inoculated with?naturally occurring?NFB, Glomus mosseae or both, and grown under glasshouse conditions for 5 months. Plants were cultivated in sand and supplied with a 20 % strength nutrient solution.?Xylem sap nutrients, photosynthetic rates, biomass and chemical compositions, were recorded.

Results

The dual inoculation decreased the colonization of both symbionts, compared to a single symbiosis with either symbiont. Despite low colonization levels, the dual symbiosis increased host biomass and relative growth rates. This was associated with increased photosynthetic rates and enhanced nutrition. Additionally, dual symbiotic plants had enhanced N and P acquisition and utilization rates. Xylem sap analysis showed higher levels of NH ₄ ⁺ being exported from the roots to the shoots in the dual symbiotic plants compared with other treatments.

Conclusions

These findings suggest the dual symbiosis is an important factor in the growth and development of A. cyclops under nutrient limiting conditions.     

Contribution of arbuscular mycorrhizal symbiosis to the survival of psammophilic plants after sea water flooding

Aims

Plants on coastal sand dunes are subjected to strong environmental fluctuations which affect their growth and survival. Sea water invasion of the dunar zone caused by storms is an important factor that determines the persistence of a plant community. In the present study, the benefits of arbuscular mycorrhiza on psammophilic plant species subjected to sea water flooding episodes were evaluated under controlled conditions and the effect of sea water on in vitro spore production was determined.

Methods

In a greenhouse experiment, the growth response of nine plant species to inoculation with Glomus intraradices in beach sand was evaluated. A second experiment was designed in order to test if plant survival under sea water flooding was influenced by the symbiosis. A third experiment was conducted in vitro to quantify the effect of sea water on the production of G. intraradices spores.

Results

Glomus intraradices was effective in promoting plant growth and survival in beach sand and promoted the survival of some species subjected to flooding events. Spore production was inhibited by 50% of sea water in the growth media, but not by 10% sea water.

Conclusions

Results obtained under controlled conditions indicated that arbuscular mycorrhiza can improve the establishment of certain dune plant species in beach sand as the symbiosis contributes to enhanced plant tolerance against occasional sea water flooding.     

Biofortification of wheat with zinc through zinc fertilization in seven countries

Background and aims

Phosphorus (P) is a commonly limiting nutrient for plant growth in natural environments. Many legumes capable of N₂-fixation require more P than non-legumes do. Some legume crops can use sparingly soluble forms of P such as iron phosphate much better than other species, but reports on the ability of woody legumes to access iron phosphate are rare.

Methods

Plants of four Acacia species (Acacia stipuligera F. Muell., A. ancistrocarpa Maiden & Blakely, A. stellaticeps Kodela, Tindale & D. Keith and A. robeorum Maslin), native to the Great Sandy Desert in north-western Australia, were grown in a glasshouse in river sand with different levels of iron phosphate, between 0 and 16?μg P g^?1 sand. Plant growth, tissue P concentrations, and pH and carboxylates in the rhizosphere were measured.

Results

Growth of A. stipuligera and A. ancistrocarpa was not responsive to increased P supply; in contrast, A. stellaticeps and A. robeorum produced significantly more root and shoot dry mass at 8 and 16?μg P g^?1 sand than at 0?μg P g^?1 sand; differences in root mass ratio were significant between species but not between P treatments. A. robeorum was the only species colonised by mycorrhizal fungi, and the colonisation percentage decreased with increasing P supply. In all species, P-uptake rates and tissue P concentrations were significantly higher at greater P supply. Rhizosphere pH and the amount of carboxylates in the rhizosphere decreased with increasing P supply.

Conclusions

Net P uptake increased with increasing P supply, showing that the present Acacia species can access P from iron phosphate. However, due to their inherently slow growth rate, enhanced P supply did not increase growth of two of the four studied species. The ability of the Acacia species to access P from iron phosphate is presumably related with carboxylate exudation and rhizosphere acidification.     

Nostoc, Microcoleus and Leptolyngbya inoculums are detrimental to the growth of wheat (Triticum aestivum L.) under salt stress

Background and aims

This study investigated the effect of cyanobacterial inoculants on salt tolerance in wheat.

Methods

Unicyanobacterial crusts of Nostoc, Leptolyngbya and Microcoleus were established in sand pots. Salt stress was targeted at 6 and 13 dS m^?1, corresponding to the wheat salt tolerance and 50 % yield reduction thresholds, respectively. Germinated wheat seeds were planted and grown for 14 (0 and 6 dS m^?1) and 21 (13 dS m^?1) days by which time seedlings had five emergent leaves. The effects of cyanobacterial inoculation and salinity on wheat growth were quantified using chlorophyll fluorescence, inductively coupled plasma-optical emission spectrometry and biomass measurements.

Results

Chlorophyll fluorescence was negatively affected by soil salinity and no change was observed in inoculated wheat. Effective photochemical efficiency correlated with a large range of plant nutrient concentrations primarily in plant roots. Inoculation negatively affected wheat biomass and nutrient concentrations at all salinities, though the effects were fewer as salinity increased.

Conclusions

The most likely explanation of these results is the sorption of nutrients to cyanobacterial extracellular polymeric substances, making them unavailable for plant uptake. These results suggest that cyanobacterial inoculation may not be appropriate for establishing wheat in saline soils but that cyanobacteria could be very useful for stabilising soils.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

Effect of hydrogen peroxide on the uptake of chlordane by Cucurbita pepo

Background and aims

Plant species can have a major effect on erosion dynamics and soil losses by retaining sediment transported during concentrated runoff. Identifying plant functional traits that influence and predict a species ability for sediment trapping is therefore of great interest, especially to improve management and restoration of degraded lands.

Methods

Sediment trapping ability of four morphologically contrasted species, the broadleaf species Buxus sempervirens and Lavandula angustifolia, and the coniferous species Juniperus communis and Pinus nigra, were investigated with flume experiments. Six functional traits describing stem, leaf and the overall plant morphology, were measured on seedlings. Analyses were performed to compare species efficiency in sediment trapping and to identify traits related to the amount of sediment trapped.

Results

Sediment trapping (RTS) was the highest upslope of Lavandula and the lowest upslope of Juniperus. Principal component analysis showed that RTS was best correlated (positively) with canopy density, described by plant biomass and leaf area per unit volume of plant. Leaf area and plant roundness were also positively related to RTS but to a lesser extent.

Conclusions

The results of this experimental study suggest that canopy completeness, leaf morphology and plant shape influence sediment retention by plants. Such knowledge may improve the diagnosis of land vulnerability to erosion and the prediction of ecosystem functioning after ecological restoration by the construction of bioengineering works in gully floors.     

Overexpression of a novel salt stress-induced glycine-rich protein gene from alfalfa causes salt and ABA sensitivity in Arabidopsis

Key message

We cloned a novel salt stress-induced glycine-rich protein gene ( MsGRP ) from alfalfa. Its overexpression retards seed germination and seedling growth of transgenic Arabidopsis after salt and ABA treatments.

Abstract

Since soil salinity is one of the most significant abiotic stresses, salt tolerance is required to overcome salinity-induced reductions in crop productivity. Many glycine-rich proteins (GRPs) have been implicated in plant responses to environmental stresses, but the function and importance of some GRPs in stress responses remain largely unknown. Here, we report on a novel salt stress-induced GRP gene (MsGRP) that we isolated from alfalfa. Compared with some glycine-rich RNA-binding proteins, MsGRP contains no RNA recognition motifs and localizes in the cell membrane or cell wall according to the subcellular localization result. MsGRP mRNA is induced by salt, abscisic acid (ABA), and drought stresses in alfalfa seedlings, and its overexpression driven by a constitutive cauliflower mosaic virus-35S promoter in Arabidopsis plants confers salinity and ABA sensitivity compared with WT plants. MsGRP retards seed germination and seedling growth of transgenic Arabidopsis plants after salt and ABA treatments, which implies that MsGRP may affect germination and growth through an ABA-dependent regulation pathway. These results provide indirect evidence that MsGRP plays important roles in seed germination and seedling growth of alfalfa under some abiotic stress conditions.     

Decomposition of organic substrates at eroding vs. depositional landform positions

Introduction

Proper understanding of how rate of OM decomposition varies across a given watershed is important to determine the potential of soil erosion to induce terrestrial carbon (C) sequestration. However, as of yet, our understanding of the spatial variability of rate of organic matter (OM) decomposition (k) across a watershed is incomplete, at best.

Aim

The objective of this study is to determine how rates of organic substrate decomposition vary on the surface and in soil profiles of eroding vs. depositional landform positions.

Methods

To determine rate of organic substrate decomposition in eroding vs. depositional landform positions, a field litterbag decomposition study was conducted in Tennessee Valley, Northern California using in situ foliage (from grasses and a shrub) and two standard substrates (filter paper and birch tongue depressors, that served as proxies for OM that is relatively easier vs. harder to breakdown during microbial decomposition). We conducted the experiment at 3–4 depths at each landform position.

Results

The effect of erosional transport (surface to surface transfer of topsoil and associated SOM from eroding to depositional landform positions) and burial (after deposition of eroded SOM by successive erosional events) on decomposition rate of eroded SOM was different depending on the nature of eroding and depositional landform positions considered. The k of organic substrates at 25?cm soil depth in the depositional positions was up to 2 orders of magnitude higher than on the surface of the eroding positions. Results of this litterbag decomposition study suggest that transport of SOM from topsoil of eroding positions to the surface of depositional positions can reduce its k; but burial of eroded SOM in soil profiles at the depositional positions can lead to increasing k.

Conclusion

Because erosion-induced C sequestration is a function of changes in rate of OM decomposition and input post-compared to pre-erosion, our findings suggest that higher rates of plant productivity in eroding watersheds is needed to create and maintain a C sink in such eroding watersheds.     

Response of Populus tremula to heterogeneous B distributions in soil

Background

Poplars accumulate inordinate amounts of B in their leaves and are candidate plants for the remediation of B contaminated soil. We aimed to determine the effect of heterogeneous B distribution in soil by comparing the growth and B accumulation of young Populus tremula trees growing in soil with heterogeneous and homogeneous B distributions.

Methods

The first of two experiments focused on the tolerance and B accumulation of P. tremula under heterogeneous soil B distributions, while the second was designed to study fine root growth under such conditions in detail.

Results

Growth and B accumulation of P. tremula were unaffected by the spatial distribution of B. Root and shoot growth were both reduced simultaneously when leaf B concentrations increased above 800 mg kg^?1. In the heterogeneous soil B treatments, root growth was more reduced in spiked soil portions with B concentrations >20 mg kg^?1. Fine root length growth was stronger inhibited by B stress than secondary growth.

Conclusions

The root growth responses of P. tremula to B are primarily a systemic effect induced by shoot B toxicity and local toxicity effects on roots become dominant only at rather high soil B concentrations. Local heterogeneity in soil B should have little influence on the phytoremediation of contaminated sites.     

Drivers of spatial variability in urban plant and soil isotopic composition in the Los Angeles basin

Aims

Plant litter decomposition plays an important role in the storage of soil organic matter in terrestrial ecosystems. Conversion of native vegetation to agricultural lands and subsequent land abandonment can lead to shifts in canopy structure, and consequently influence decomposition dynamics by alterations in soil temperature and moisture conditions, solar radiation exposure, and soil erosion patterns. This study was conducted to assess which parameters were more closely related to short-term decomposition dynamics of two predominant Mediterranean leaf litter types.

Methods

Using the litterbag technique, we incubated leaf litter of Pinus halepensis and Rosmarinus officinalis in two Mediterranean land-uses with different degree of vegetation cover (open forest, abandoned agricultural field).

Results

Fresh local litter lost between 20 and 55% of its initial mass throughout the 20-month incubation period. Rosemary litter decomposed faster than pine litter, showing net N immobilization in the early stages of decomposition, in contrast to the net N release exhibited by pine litter. Parameters related to litter quality (N content or C:N) or land-use/site conditions (ash content, an index of soil deposition on litter) were found to explain the cross-site variability in mass loss rates for rosemary and Aleppo pine litter, respectively.

Conclusions

The results from this study suggest that decomposition drivers may differ depending on litter type in this Mediterranean ecosystem. While rosemary litter was degraded mainly by microbial activity, decomposition of pine litter was likely driven primarily by abiotic processes like soil erosion.     

Both the mevalonate and the non-mevalonate pathways are involved in ginsenoside biosynthesis

Key Message

When one of them was inhibited, the two pathways could compensate with each other to guarantee normal growth. Moreover, the sterol biosynthesis inhibitor miconazole could enhance ginsenoside level.

Abstract

Ginsenosides, a kind of triterpenoid saponins derived from isopentenyl pyrophosphate (IPP), represent the main pharmacologically active constituents of ginseng. In plants, two pathways contribute to IPP biosynthesis, namely, the mevalonate pathway in cytosol and the non-mevalonate pathway in plastids. This motivates biologists to clarify the roles of the two pathways in biosynthesis of IPP-derived compounds. Here, we demonstrated that both pathways are involved in ginsenoside biosynthesis, based on the analysis of the effects from suppressing either or both of the pathways on ginsenoside accumulation in Panax ginseng hairy roots with mevinolin and fosmidomycin as specific inhibitors for the mevalonate and the non-mevalonate pathways, respectively. Furthermore, the sterol biosynthesis inhibitor miconazole could enhance ginsenoside levels in the hairy roots. These results shed some light on the way toward better understanding of ginsenoside biosynthesis.     

Maternal effects and carbohydrate changes of Pinus pinaster after inoculation with Fusarium circinatum

Key message

Carbohydrate differences in offspring as a consequence of maternal effects explain transgenerational tree-pathogen interactions.

Abstract

The expression of disease is increasingly recognised as being influenced by maternal effects, given that environmental conditions experienced by mother trees affect tolerance in offspring. It is hypothesised that plant carbohydrates could mediate transgenerational tree-pathogen interactions. The carbohydrate content of Pinus pinaster seedlings obtained from two contrasting maternal environments was studied and seedlings from the two environments were challenged with Fusarium circinatum. The representative mid-infrared spectra of samples in the range of the carbohydrates diagnosed higher proportion of methylesterified pectic polysaccharides and lower proportion of nonesterified pectic polysaccharides for inoculated than for control seedlings. Total carbohydrate content of seedlings from the unfavourable environment did not differ much from total carbohydrate content of seedlings from the favourable maternal environment. However, glucose was 13 % higher and uronic acids 11 % lower in seedlings from the favourable environment after inoculation in comparison to seedlings from the unfavourable maternal environment which had their carbohydrate contents unaltered after inoculation. It is concluded that plant carbohydrates mediate transgenerational tree-pathogen interactions.     

Inadequate root uptake may represent a major component limiting rice to use urea as sole nitrogen source for growth

Background and aims

Urea represents over 50 % of nitrogen fertilizers applied worldwide to crop production, however one-third of nitrogen fertilized could be recovered by crops. Previous studies have provided useful knowledge of urea-related plant nitrogen-nutrition, whereas information about crop growth-response to urea without its external degradation seems limiting. We thus assess the ability of rice seedlings to use urea at a physiological level.

Methods

Rice growth on urea versus other nitrogen regimes was tested under aseptic conditions. Activity of urease and GS was analyzed; urea, ammonium, total nitrogen and expression of a nitrogen limitation-responsive gene OsDUR3 were examined.

Results

Growth phenotyping revealed urea-dose-dependent growth improvement but significant growth reduction associated with nitrogen-deficiency of plants compared to those on other nitrogen-sources, indicating a physiological impediment of effective urea utilization by rice. Enzymatic assay showed that activities of urease and GS were well expressed in plants supplied with urea. Low concentrations of urea and ammonium were detected in rice (particularly in roots) on 1 mM urea or other nitrogen-forms, and a less nitrogen-content was determined in urea-fed plants. Additionally, the strongest OsDUR3-expression occurred in seedlings on no-nitrogen or 1 mM urea.

Conclusions

We suggest that insufficient urea-absorption but not assimilation represents likely a factor contraining rice to use urea as sole nitrogen-source.     

Phenotypic screening of pecan seedling rootstocks in search of nematode resistance

Key Message

Open-pollinated seedstocks for pecan vary in phenology and composition predictably based on their provenance of origin in ways that impact performance.

Abstract

Open-pollinated rootstocks of pecan (Carya illinoinensis), water hickory (Carya aquatica), and their hybrids (Carya × lecontei) were screened for nematode resistance in outdoor above-ground box-plots. Seedstocks were selected to represent the broad geographic range of species diversity. Seedlings were inoculated with eggs of Meloidogyne partityla, the primary nematode pest of Carya, and were harvested after 1 year. All seedlings, except one, manifested nematode damage at moderate to high levels. Evidence of galling was greatest in seedlings from the southern provenance (Mexico), which rated comparably with seedlings from ‘Elliott’. No sources of resistance to Meloidogyne partityla were observed. The box structure allowed harvest of complete root systems and evaluation of plant composition in greater detail than previously observed. Seedlings from the southern provenance were generally distinguishable from other provenances in timing of seasonal growth, stem diameter and seedling height, which is consistent with previous observations. Root and stem dry weights were greatest in seedlings from the southern provenance, as expected based on size measurements. Percent root water varied significantly as a function of seedstock origin, and was negatively correlated with leaf weight. Leaf weights were positively correlated with dates of growth initiation. Uninfected control plants were not observed in this screening effort, and their absence limits the interpretation of patterns. Implications of these observations, as evidence of regional adaptation, merit further exploration by research.