Forage radish and cereal rye cover crop effects on mycorrhizal fungus colonization of maize roots

Forage radish (Raphanus sativus L. var. longipinnatus) is being used by increasing numbers of farmers as a winter cover crop in the Mid-Atlantic USA. It is a non-host to arbuscular mycorrhizal fungi (AMF) and releases anti-fungal isothiocyanates (ITCs) upon decomposition in the winter. Field experiments were conducted to determine the effect of forage radish and cereal rye (Secale cereale L.) cover crops on arbuscular mycorrhizal fungus colonization of and P acquisition by a subsequent maize (Zea mays L.) silage crop. Cover crop treatments included forage radish, rye, a mix of forage radish and rye, and no cover crop. Mycorrhizal fungus colonization of maize roots at the V4 stage following forage radish cover crops was not significantly different from that in the no cover crop treatment. In 3 out of 6 site-years, a rye cover crop increased AMF colonization of V4 stage maize roots compared to no cover crop. These findings suggest that forage radish cover crops do not have a negative effect on AMF colonization of subsequent crops.     

Penetration,Development, and Reproduction of Heterodera schachtii on Fagopyrum esculentum,Phacelia tanacetifolia,Raphanus sativus,Sinapis alba,and Brassica oleracea

The penetration, development, and reproduction of a California population of the sugarbeet cyst nematode, Heterodera schachtii, was observed on cultivars of cabbage (Brassica oleracea), phacelia (Phacelia tanacetifolia), buckwheat (Fagopyrum esculentum), oilseed radish (Raphanus sativus), and white mustard (Sinapis alba). With the exception of the nonhost, phacelia, all were readily penetrated by second-stage juveniles of H. schachtii. After 38 days at 25 C, no cysts were observed on phacelia cv. Angelia or on the oilseed radish cv. Nemex and Pegletta. Cyst production was low (<2.5 cysts/plant) on the buckwheat cv. Tardo and Prego and most of the oilseed radish cultivars. Cyst production was intermediate (5-14 cysts/plant) on most of the white mustard cultivars, and high on cabbage (20-110 cysts/plant). In microplot studies conducted over 133 days (approx. 450 degree-days, base 8 C), the reproductive index for H. schachtii was greater than 1.0 for cultivars of phacelia, oilseed radish, and white mustard as welt as in fallow treatments, indicating the need for further research on the use of these crops under field conditions.     

Biology and interactions of two distinct monopartite begomoviruses and betasatellites associated with radish leaf curl disease in India

Background

Emerging whitefly transmitted begomoviruses are major pathogens of vegetable and fibre crops throughout the world, particularly in tropical and sub-tropical regions. Mutation, pseudorecombination and recombination are driving forces for the emergence and evolution of new crop-infecting begomoviruses. Leaf curl disease of field grown radish plants was noticed in Varanasi and Pataudi region of northern India. We have identified and characterized two distinct monopartite begomoviruses and associated beta satellite DNA causing leaf curl disease of radish (Raphanus sativus) in India.

Results

We demonstrate that RaLCD is caused by a complex of two Old World begomoviruses and their associated betasatellites. Radish leaf curl virus-Varanasi is identified as a new recombinant species, Radish leaf curl virus (RaLCV) sharing maximum nucleotide identity of 87.7% with Tomato leaf curl Bangladesh virus-[Bangladesh:2] (Accession number AF188481) while the virus causing radish leaf curl disease-Pataudi is an isolate of Croton yellow vein mosaic virus-[India] (CYVMV-IN) (Accession number AJ507777) sharing 95.8% nucleotide identity. Further, RDP analysis revealed that the RaLCV has a hybrid genome, a putative recombinant between Euphorbia leaf curl virus and Papaya leaf curl virus. Cloned DNA of either RaLCV or CYVMV induced mild leaf curl symptoms in radish plants. However, when these clones (RaLCV or CYVMV) were individually co-inoculated with their associated cloned DNA betasatellite, symptom severity and viral DNA levels were increased in radish plants and induced typical RaLCD symptoms. To further extend these studies, we carried out an investigation of the interaction of these radish-infecting begomoviruses and their associated satellite, with two tomato infecting begomoviruses (Tomato leaf curl Gujarat virus and Tomato leaf curl New Delhi virus). Both of the tomato-infecting begomoviruses showed a contrasting and differential interaction with DNA satellites, not only in the capacity to interact with these molecules but also in the modulation of symptom phenotypes by the satellites.

Conclusion

This is the first report and experimental demonstration of Koch's postulate for begomoviruses associated with radish leaf curl disease. Further observations also provide direct evidence of lateral movement of weed infecting begomovirus in the cultivated crops and the present study also suggests that the exchange of betasatellites with other begomoviruses would create a new disease complex posing a serious threat to crop production.     

Root growth in biopores—evaluation with in situ endoscopy

Background and aims

The significance of biopores for nutrient acquisition from the subsoil depends on root-soil contact, which in turn is influenced by root architecture. The aim of this study was to detect differences regarding the architecture and root-soil contact of homorhizous barley roots (Hordeum vulgare L.) and allorhizous oilseed rape roots (Brassica napus L.) growing in biopores.

Methods

In situ endoscopy was used as a technique that allows non-destructive display of pore wall characteristics and root morphology inside large biopores under field conditions.

Results

For both crops, about 85 % of all roots did establish contact to the pore wall. However, according to their different root architecture, the two crops varied in their strategy of resource acquisition: While barley was characterized by thin vertical or ingrowing roots, most of them in direct contact to the pore wall, oilseed rape established contact to the pore wall predominantly via lateral roots.

Conclusions

Root morphological and pore wall assessment with in situ endoscopy in combination with detailed studies of soil biochemical and soil physical parameters of the pore wall is considered an essential prerequisite for more precise future modelling of nutrient acquisition and uptake.     

Quantifying the effect of soil compaction on three varieties of wheat (Triticum aestivum L.) using X-ray Micro Computed Tomography (CT)

Aims

X-ray Micro Computed Tomography (CT) enables interactions between roots and soil to be visualised without disturbance. This study examined responses of root growth in three Triticum aestivum L. (wheat) cultivars to different levels of soil compaction (1.1 and 1.5?g?cm^?3).

Methods

Seedlings were scanned 2, 5 and 12?days after germination (DAG) and the images were analysed using novel root tracking software, RootViz3D?, to provide accurate visualisation of root architecture. RootViz3D? proved more successful in segmenting roots from the greyscale images than semi-automated segmentation, especially for finer roots, by combining measurements of pixel greyscale values with a probability approach to identify roots.

Results

Root density was greater in soil compacted at 1.5?g?cm^?3 than at 1.1?g?cm^?3 (P?=?0.04). This effect may have resulted from improved contact between roots and surrounding soil. Root diameter was greater in soil at a high bulk density (P?=?0.006) but overall root length was reduced (P?=?0.20). Soil porosity increased with time (P?<?0.001) in the uncompacted treatment.

Conclusions

RootViz3D? root tracking software in X-ray CT studies provided accurate, non-destructive and automated three dimensional quantification of root systems that has many applications for improving understanding on root-soil interactions.     

Soil nutrient patchiness and plant genotypes interact on the production potential and decomposition of root and shoot litter: evidence from short-term laboratory experiments with Triticum aestivum

Aims

The purpose of this study was to test the hypotheses that soil nutrient patchiness can differentially benefit the decomposition of root and shoot litters and that this facilitation depends on plant genotypes.

Methods

We grew 15 cultivars (i.e. genotypes) of winter wheat (Triticum aestivum L.) under uniform and patchy soil nutrients, and contrasted their biomass and the subsequent mass, carbon (C) and nitrogen (N) dynamics of their root and shoot litters.

Results

Under equal amounts of nutrients, patchy distribution increased root biomass and had no effects on shoot biomass and C:N ratios of roots and shoots. Roots and shoots decomposed more rapidly in patchy nutrients than in uniform nutrients, and reductions in root and shoot C:N ratios with decomposition were greater in patchy nutrients than uniform nutrients. Soil nutrient patchiness facilitated shoot decomposition more than root decomposition. The changes in C:N ratios with decomposition were correlated with initial C:N ratios of litter, regardless of roots or shoots. Litter potential yield, quality and decomposition were also affected by T. aestivum cultivars and their interactions with nutrient patchiness.

Conclusions

Soil nutrient patchiness can enhance C and N cycling and this effect depends strongly on genotypes of T. aestivum. Soil nutrient heterogeneity in plant communities also can enhance diversity in litter decomposition and associated biochemical and biological dynamics in the soil.     

Phosphorus enhances Al resistance in Al-resistant Lespedeza bicolor but not in Al-sensitive L. cuneata under relatively high Al stress

Background and Aims

Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit crop production worldwide. Lespedeza bicolor is a leguminous forage species that grows very well in infertile, acidic soils. The objective of this study was to investigate the effects of Al and P interactions on growth of Lespedeza and the distributions of Al and P in two different Al-resistant species, and to explore whether P can ameliorate the toxic effect of Al in the two species.

Methods

Two species, Lespedeza bicolor and L. cuneata, were grown for 30 d with alternate Al and P treatments in a hydroponics system. Harvested roots were examined using a root-system scanner, and the contents of Al, P and other nutrient elements in the plants were determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Haematoxylin staining was used to observe the distribution of Al in the roots of seedlings. After pre-culture with or without P application, organic acids in the exudates of roots exposed to Al were held in an anion-exchange resin, eluted with 2 m HCl and then analysed using high-performance liquid chromatography (HPLC).

Key Results

Lespedeza bicolor exhibited a stronger Al resistance than did L. cuneata; Al exclusion mechanisms may mainly be responsible for resistance. P application alleviated the toxic effect of Al on root growth in L. bicolor, while no obvious effects were observed in L. cuneata. Much less Al was accumulated in roots of L. bicolor than in L. cuneata after P application, and the P contents in both roots and shoots increased much more for L. bicolor than for L. cuneata. Lespedeza bicolor showed a higher P/Al ratio in roots and shoots than did L. cuneata. P application decreased the Al accumulation in root tips of L. bicolor but not in L. cuneata. The amount of Al-induced organic acid (citrate and malate) exudation from roots pre-cultured with P was much less than from roots without P application; no malate and citrate exudation was detected in L. cuneata.

Conclusions

P enhanced Al resistance in the Al-resistant L. bicolor species but not in the Al-sensitive L. cuneata under relatively high Al stress, although P in L. cuneata might also possess an alleviative potential. Enhancement of Al resistance by P in the resistant species might be associated with its more efficient P accumulation and translocation to shoots and greater Al exclusion from root tips after P application, but not with an increased exudation of organic acids from roots.Key words: Lespedeza bicolor, L. cuneata, Al toxicity, Al resistance, root morphology, phosphorus     

Accumulation mechanisms and subcellular distribution of Cu in maize grown on soil treated with [S, S]-ethylenediamine disuccinic acid

Aims

Many studies have proved that EDTA (ethylenediaminetetraacetic acid), EDDS ([S, S’]-ethylenediamine disuccinic acid), and other chelating agents significantly enhance phyto-extraction of copper (Cu) from soil. However, some key factors, such as changes in membrane permeability of root cells and subcellular distribution of Cu and Cu-EDDS complex in leaves and roots, remain unresolved.

Methods

A pot-culture experiment was conducted using soil artificially contaminated with Cu to different degrees to compare its effect on the above factors and the relationship between them in maize (Zea mays L.).

Results

Treatment with 0.5–6.0?mmol?kg^?1 (soil) EDDS increased membrane permeability in root cells significantly (p?<?0.05). Chelated Cu accounted for 14.6%–17.4% of the total Cu content of roots and 77.7%–78.8% of that of leaves and was distributed mainly in cell walls in both.

Conclusions

EDDS increases Cu accumulation in shoots mainly by increasing the content of soluble Cu in soil and membrane permeability of root cells. Cu in soil may be absorbed through the apoplastic pathway into the root xylem, translocated to the shoots, and accumulated there as a Cu-EDDS complex.     

Role of roots in cadmium accumulation of two water spinach cultivars: reciprocal grafting and histochemical experiments

Background and Aims

Cultivars of water spinach (Ipomoea aquatica Forsk.) differ widely in their shoot cadmium (Cd) concentration. Previously, we suggested that low-Cd cultivars are better able to retain Cd in their roots and thus prevent root-to-shoot Cd translocation. In this study, we explored the roles of roots and shoots in Cd accumulation in a high-Cd (T308) and low-Cd cultivar (QLQ).

Methods

We used reciprocal grafting to determine the importance of roots and shoots in Cd accumulation, and a dithizone histochemical method to investigate Cd distribution in the roots.

Results

The T308 scion with QLQ rootstock accumulated less Cd than the shoot of non-grafted T308. The QLQ scion with T308 rootstock showed a significantly higher Cd concentration than that in the shoot of non-grafted QLQ. Cadmium induced thicker phellem formation in the main roots of QLQ than in those of T308 and only QLQ showed thickening of the outer cortex cell walls in lateral roots.

Conclusions

Shoot Cd accumulation was primarily determined by root-to-shoot Cd translocation, not root Cd uptake. The thicker phellem and outer cortex cell walls in QLQ than in T308 may be one reason why QLQ roots were able to retain more Cd, and thus reducing Cd translocation to shoots.     

Assessing variability in root traits of wild Lupinus angustifolius germplasm: basis for modelling root system structure

Background and aims

Intra-specific variation in root system architecture and consequent efficiency of resource capture by major crops has received recent attention. The aim of this study was to assess variability in a number of root traits among wild genotypes of narrow-leafed lupin (Lupinus angustifolius L.), to provide a basis for modelling of root structure.

Methods

A subset of 111 genotypes of L. angustifolius was selected from a large germplasm pool based on similarity matrices calculated using Diversity Array Technology markers. Plants were grown for 6?weeks in the established semi-hydroponic phenotyping systems to measure the fine-scale features of the root systems.

Results

Root morphology of wild L. angustifolius was primarily dominated by the taproot and first-order branches, with the presence of densely or sparsely distributed second-order branches in the late growth stage. Large variation in most root traits was identified among the tested genotypes. Total root length, branch length and branch number in the entire root system and in the upper roots were the most varied traits (coefficient of variation CV >0.50). Over 94% of the root system architectural variation determined from the principal components analysis was captured by six components (eigenvalue >1). Five relatively homogeneous groups of genotypes with distinguished patterns of root architecture were separated by k-means clustering analysis.

Conclusions

Variability in the fine-scale features of root systems such as branching behaviour and taproot growth rates provides a basis for modelling root system structure, which is a promising path for selecting desirable root traits in breeding and domestication of wild and exotic resources of L. angustifolius for stressful or poor soil environments.     

Putting the P in Ptilotus: a phosphorus-accumulating herb native to Australia

Background and Aims

Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), ‘Puna’.

Methods

Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg⁻¹ mineral N and 2 mg kg⁻¹ bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0–300 mg P pot⁻¹) and nitrogen (N) (0–270 mg N pot⁻¹) was examined.

Key Results

Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1·7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot⁻¹, respectively. Ptilotus could not downregulate P uptake. Concentrations of P in shoots approached 4 % of dry weight and cryo-scanning electron microscopy and X-ray microanalysis showed 35–196 mm of P in cell vacuoles in a range of tissues from young leaves. Ptilotus had a remarkable tolerance of high P concentrations in shoots. While chicory exhibited symptoms of P toxicity at the highest rate of P addition (300 mg P pot⁻¹), no symptoms were present for ptilotus. The two species responded in a similar manner to addition of N.

Conclusions

In comparison to chicory, ptilotus demonstrated an impressive ability to grow well under conditions of low and high P availability. Further study of the mechanisms of P uptake and tolerance in ptilotus is warranted.Key words: Phosphorus, nitrogen, hyperaccumulation, X-ray microanalysis, cell vacuole, Australian native plant, toxicity, domestication, phytoremediation, Ptilotus polystachyus, Cichorium intybus     

Carbon footprint of spring barley in relation to preceding oilseeds and N fertilization

Purpose

Carbon footprint of field crops can be lowered through improved cropping practices. The objective of this study was to determine the carbon footprint of spring barley (Hordeum vulgare L.) in relation to various preceding oilseed crops that were fertilized at various rates of inorganic N the previous years. System boundary was from cradle-to-farm gate.

Materials and methods

Canola-quality mustard (Brassica juncea L.), canola (Brassica napus L.), sunflower (Helianthus annuus L.), and flax (Linum usitatissimum L.) were grown under the N fertilizer rates of 10, 30, 70, 90, 110, 150, and 200?kg?N?ha^?1 the previous year, and spring barley was grown on the field of standing oilseed stubble the following year. The study was conducted at six environmental sites; they were at Indian Head in 2005, 2006 and 2007, and at Swift Current in 2004, 2005 and 2006, Saskatchewan, Canada.

Results and discussion

On average, barley grown at humid Indian Head emitted greenhouse gases (GHGs) of 1,003?kg?CO₂eq?ha^?1, or 53% greater than that at the drier Swift Current site. Production and delivery of fertilizer N to farm gate accounted for 26% of the total GHG emissions, followed by direct and indirect emissions of 28% due to the application of N fertilizers to barley crop. Emissions due to N fertilization were 26.6 times the emission from the use of phosphorous, 5.2 times the emission from pesticides, and 4.2 times the emission from various farming operations. Decomposition of crop residues contributed emissions of 173?kg?CO₂eq?ha^?1, or 19% of the total emission. Indian Head-produced barley had significantly greater grain yield, resulting in about 11% lower carbon footprint than Swift Current-produced barley (0.28 vs. 0.32?kg?CO₂eq?kg^?1 of grain). Emissions in the barley production was a linear function of the rate of fertilizer N applied to the previous oilseed crops due to increased emissions from crop residue decomposition coupled with higher residual soil mineral N.

Conclusions

The key to lower the carbon footprint of barley is to increase grain yield, make a wise choice of crop types, reduce N inputs to crops grown in the previous and current growing seasons, and improved N use efficiency.     

Yield stability of hybrids versus lines in wheat,barley, and triticale

Key message

We present experimental data for wheat, barley, and triticale suggesting that hybrids manifest on average higher yield stability than inbred lines.

Abstract

Yield stability is assumed to be higher for hybrids than for inbred lines, but experimental data proving this hypothesis is scarce for autogamous cereals. We used multi-location grain yield trials and compared the yield stability of hybrids versus lines for wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and triticale (×Triticosecale Wittmack). Our study comprised three phenotypic data sets of 1,749 wheat, 96 barley, and 130 triticale genotypes, which were evaluated for grain yield in up to five contrasting locations. Yield stability of the group of hybrids was compared with that of the group of inbred lines estimating the stability variance. For all three crops we observed a significantly (P < 0.05) higher yield stability of hybrids compared to lines. The enhanced yield stability of hybrids as compared to lines represents a major step forward, facilitating coping with the increasing abiotic stress expected from the predicted climate change.     

Do arbuscular mycorrhizas or heterotrophic soil microbes contribute toward plant acquisition of a pulse of mineral phosphate?

Aims

We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microbes in the uptake of phosphorus (P) by Trifolium subterraneum from a pulse.

Methods

Plants were grown in sterilised pasture field soil with a realistic level of available P. There were five treatments, two of which involved AMF: 1) unsterilised field soil containing a community of AMF and heterotrophic organisms; 2) Scutellospora calospora inoculum (AMF); 3) microbes added as filtrate from the field soil; 4) microbes added as filtrate from the S. calospora inoculum; 5) no additions, i.e. sterilised field soil. After 11 weeks, plants were harvested: 1 day before (day 0), 1 day after (day 2) and 7 days after (day 8) the pulse of P (10 mg kg^?1).

Results

There was no difference among treatments in shoot and root dry weight, which increased from day 0 to day 8. At day 0, shoots and roots of plants in the colonised treatments had higher P and lower Mn concentrations. After the pulse, the rate of increase in P concentration in the shoots was slower for the colonised plants, and the root Mn concentration declined by up to 50 % by day 2.

Conclusions

Plants colonised by AMF had a lower rate of increase in shoot P concentration after a pulse, perhaps because intraradical hyphae accumulated P and thus reduced its transport to the shoots.     

Field inoculation with arbuscular-mycorrhizal fungi overcomes phosphorus and zinc deficiencies of linseed (Linum usitatissimum) in a vertisol subject to long-fallow disorder

Background and aims

Long-fallow disorder is expressed as exacerbated deficiencies of phosphorus (P) and/or zinc (Zn) in field crops growing after long periods of weed-free fallow. The hypothesis that arbuscular-mycorrhizal fungi (AMF) improve the P and Zn nutrition, and thereby biomass production and seed yield of linseed (Linum usitatissimum) was tested in a field experiment.

Methods

A factorial combination of treatments consisting of ± fumigation, ±AMF inoculation with Glomus spp., ±P and ±Zn fertilisers was used on a long-fallowed vertisol. The use of such methods allowed an absolute comparison of plants growing with and without AMF in the field for the first time in a soil disposed to long-fallow disorder.

Results

Plant biomass, height, P and Zn concentrations and contents, boll number and final seed yield were (a) least in fumigated soil with negligible AMF colonisation of the roots, (b) low initially in long-fallow soil but increased with time as AMF colonisation of the roots developed, and (c) greatest in soil inoculated with AMF cultures. The results showed for the first time in the field that inflows of both P and Zn into linseed roots were highly dependent on %AMF-colonisation (R²?=?0.95 for P and 0.85 for Zn, P?<?0.001) in a soil disposed to long-fallow disorder. Relative field mycorrhizal dependencies without and with P+Zn fertiliser were 85 % and 86 % for biomass and 68 % and 52 % for seed yield respectively.

Conclusions

This research showed in the field that AMF greatly improved the P and Zn nutrition, biomass production and seed yield of linseed growing in a soil disposed to long-fallow disorder. The level of mycorrhizal colonisation of plants suffering from long-fallow disorder can increase during the growing season resulting in improved plant growth and residual AMF inoculum in the soil, and thus it is important for growers to recognise the cause and not terminate a poor crop prematurely in order to sow another. Other positive management options to reduce long fallows and foster AMF include adoption of conservation tillage and opportunity cropping.     

C and N allocation in soil under ryegrass and alfalfa estimated by 13C and 15N labelling

Background and Aims

Below-ground translocated carbon (C) released as rhizodeposits is an important driver for microbial mobilization of nitrogen (N) for plants. We investigated how a limited substrate supply due to reduced photoassimilation alters the allocation of recently assimilated C in plant and soil pools under legume and non-legume species.

Methods

A non-legume (Lolium perenne) and a legume (Medicago sativa) were labelled with ¹⁵N before the plants were clipped or shaded, and labelled twice with ¹³CO₂ thereafter. Ten days after clipping and shading, the ¹⁵N and ¹³C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the ¹³C in soil CO₂ were analyzed.

Results

After clipping, about 50 % more ¹³C was allocated to regrowing shoots, resulting in a lower translocation to roots compared to the unclipped control. Clipping also reduced the total soil CO₂ efflux under both species and the ¹³C recovery of soil CO₂ under L. perenne. The ¹⁵N recovery increased in the shoots of M. sativa after clipping, because storage compounds were remobilized from the roots and/or the N uptake from the soil increased. After shading, the assimilated ¹³C was preferentially retained in the shoots of both species. This caused a decreased ¹³C recovery in the roots of M. sativa. Similarly, the total soil CO₂ efflux under M. sativa decreased more than 50 % after shading. The ¹⁵N recovery in plant and soil pools showed that shading has no effect on the N uptake and N remobilization for L. perenne, but, the ¹⁵N recovery increased in the shoot of M. sativa.

Conclusions

The experiment showed that the dominating effect on C and N allocation after clipping is the need of C and N for shoot regrowth, whereas the dominating effect after shading is the reduced substrate supply for growth and respiration. Only slight differences could be observed between L. perenne and M. sativa in the C and N distribution after clipping or shading.     

Endogeic earthworms modify soil phosphorus,plant growth and interactions in a legume–cereal intercrop

Background and aims

Intercropping of legumes and cereals appears as an alternative agricultural practice to decrease the use of chemical fertilizers while maintaining high yields. A better understanding of the biotic and abiotic factors determining interactions between plants in such associations is required. Our study aimed to analyse the effect of earthworms on the legume–cereal interactions with a focus on the modifications induced by earthworms on the forms of soil phosphorus (P).

Methods

In a glasshouse experiment we investigated the effect of an endogeic earthworm (Allolobophora chlorotica) on the plant biomass and on N and P acquisition by durum wheat (Triticum turgidum durum L.) and chickpea (Cicer arietinum L.) either grown alone or intercropped. The modifications of the different organic and inorganic P forms in the bulk soil were measured.

Results

There was no overyielding of the intercrop in the absence of earthworms. Earthworms had a strong influence on biomass and resource allocation between roots and shoots whereas no modification was observed in terms of total biomass production and P acquisition. Earthworms changed the interaction between the intercropped species mainly by reducing the competition for nutrients. Facilitation (positive plant–plant interactions) was only observed for the root biomass and P acquisition in the presence of earthworms. Earthworms decreased the amount of organic P extracted with NaOH (Po NaOH), while they increased the water soluble inorganic P (Pi H₂O) content.

Conclusions

In this experiment, earthworms could be seen as “troubleshooter” in plant–plant interaction as they reduced the competition between the intercropped species. Our study brings new insights into how earthworms affect plant growth and the P cycle.