Arbuscular mycorrhizas and their role in plant growth, nitrogen interception and soil gas efflux in an organic production system

Background and aims

Roots and mycorrhizas play an important role in not only plant nutrient acquisition, but also ecosystem nutrient cycling.

Methods

A field experiment was undertaken in which the role of arbuscular mycorrhizas (AM) in the growth and nutrient acquisition of tomato plants was investigated. A mycorrhiza defective mutant of tomato (Solanum lycopersicum L.) (named rmc) and its mycorrhizal wild type progenitor (named 76R) were used to control for the formation of AM. The role of roots and AM in soil N cycling was studied by injecting a ¹⁵N-labelled nitrate solution into surface soil at different distances from the 76R and rmc genotypes of tomato, or in plant free soil. The impacts of mycorrhizal and non-mycorrhizal root systems on soil greenhouse gas (CO₂ and ¹⁴⁺¹⁵N₂O and ¹⁵N₂O) emissions, relative to root free soils, were also studied.

Results

The formation of AM significantly enhanced plant growth and nutrient acquisition, including interception of recently applied NO ₃ ^? . Whereas roots caused a small but significant decrease in ¹⁵N₂O emissions from soils at 23?h after labeling, compared to the root-free treatment, arbuscular mycorrhizal fungi (AMF) had little effect on N₂O emissions. In contrast soil CO₂ emissions were higher in plots containing mycorrhizal root systems, where root biomass was also greater.

Conclusions

Taken together, these data indicate that roots and AMF have an important role to play in plant nutrient acquisition and ecosystem N cycling.     

Changes in soil hyphal abundance and viability can alter the patterns of hydraulic redistribution by plant roots

Background and aims

We conducted a mesocosm study to investigate the extent to which the process of hydraulic redistribution of soil water by plant roots is affected by mycorrhizosphere disturbance.

Methods

We used deuterium-labeled water to track the transfer of hydraulically lifted water (HLW) from well-hydrated donor oaks (Quercus agrifolia Nee.) to drought-stressed receiver seedlings growing together in mycorrhizal or fungicide-treated mesocosms. We hypothesized that the transfer of HLW from donor to receiver plants would be enhanced in undisturbed (non-fungicide-treated) mesocosms where an intact mycorrhizal hyphal network was present.

Results

Contrary to expectations, both upper soil and receiver seedlings contained significantly greater proportions of HLW in mesocosms where the abundance of mycorrhizal hyphal links between donor and receiver roots had been sharply reduced by fungicide application. Reduced soil hyphal density and viability likely hampered soil moisture retention properties in fungicide-treated mesocosms, thus leading to faster soil water depletion in upper compartments. The resulting steeper soil water potential gradient between taproot and upper compartments enhanced hydraulic redistribution in fungicide-treated mesocosms.

Conclusions

Belowground disturbances that reduce soil hyphal density and viability in the mycorrhizosphere can alter the patterns of hydraulic redistribution by roots through effects on soil hydraulic properties.     

Plant neighbor effects mediated by rhizosphere factors along a simulated aridity gradient

Aims

We investigated how rhizosphere factors (total rhizosphere, roots, arbuscular mycorrhizal fungal hyphae [AMF], and soil solution) and water availability affect interactions between neighboring Medicago sativa plants.

Methods

A three-compartment mesocosm was used to test the effects of rhizosphere factors on plant–plant interactions. A relative interaction index (RII) was calculated to indicate whether effects of neighbor plant on target plant were positive or negative (facilitative or competitive). Isotope tracers were used to test whether AMF hyphae mediated competition for nitrogen (N) between target and neighbor plants.

Results

The effects of rhizosphere factors on the interactions between neighboring M. sativa plants depended on water availability. The effects of total rhizosphere shifted RII from negative to positive as water availability increased. Interaction with the roots and rhizosphere soil solution of neighbor plants shifted RII from negative to positive as water availability increased but the opposite was true for AMF hyphae. AMF hyphae helped neighbor plants compete for ¹⁵N when water was available but not when water was limiting.

Conclusions

The effect of total rhizosphere on plant–plant interaction of M. sativa shifted from competitive to facilitative as water availability increased. Competition was reduced by neighboring soil solution and roots but was increased by AMF hyphae.     

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.     

Anisohydric behaviour in grapevines results in better performance under moderate water stress and recovery than isohydric behaviour

Aims

Arbuscular mycorrhizal fungi (AMF) can control root-knot nematode infection, but the mode of action is still unknown. We investigated the effects of AMF and mycorrhizal root exudates on the initial steps of Meloidogyne incognita infection, namely movement towards and penetration of tomato roots.

Methods

M. incognita soil migration and root penetration were evaluated in a twin-chamber set-up consisting of a control and mycorrhizal (Glomus mosseae) plant compartment (Solanum lycopersicum cv. Marmande) connected by a bridge. Penetration into control and mycorrhizal roots was also assessed when non-mycorrhizal or mycorrhizal root exudates were applied and nematode motility in the presence of the root exudates was tested in vitro.

Results

M. incognita penetration was significantly reduced in mycorrhizal roots compared to control roots. In the twin-chamber set-up, equal numbers of nematodes moved to both compartments, but the majority accumulated in the soil of the mycorrhizal plant compartment, while for the control plants the majority penetrated the roots. Application of mycorrhizal root exudates further reduced nematode penetration in mycorrhizal plants and temporarily paralyzed nematodes, compared with application of water or non-mycorrhizal root exudates.

Conclusions

Nematode penetration was reduced in mycorrhizal tomato roots and mycorrhizal root exudates probably contributed at least partially by affecting nematode motility.     

Seasonal carbon allocation to arbuscular mycorrhizal fungi assessed by microscopic examination, stable isotope probing and fatty acid analysis

Background and Aim

Climate change models are limited by lack of baseline data, in particular carbon (C) allocation to – and dynamics within – soil microbial communities. We quantified seasonal C-assimilation and allocation by plants, and assessed how well this corresponds with intraradical arbuscular mycorrhizal fungal (AMF) storage and structural lipids (16:1ω5 NLFA and PLFA, respectively), as well as microscopic assessments of AMF root colonization.

Methods

Coastal Hypochoeris radicata plants were labeled with ¹³CO₂ in February, July and October, and ¹³C-allocation to fine roots and NLFA 16:1ω5, as well as overall lipid contents and AM colonization were quantified.

Results

C-allocation to fine roots and AMF storage lipids differed seasonally and mirrored plant C-assimilation, whereas AMF structural lipids and AM colonization showed no seasonal variation, and root colonization exceeded 80 % throughout the year. Molecular analyzes of the large subunit rDNA gene indicated no seasonal AMF community shifts.

Conclusions

Plants allocated C to AMF even at temperatures close to freezing, and fungal structures persisted in roots during times of low C-allocation. The lack of seasonal differences in PLFA and AM colonization indicates that NLFA analyses should be used to estimate fungal C-status. The implication of our findings for AM function is discussed.     

The role of the external mycelial network of vesicular-arbuscular mycorrhizal fungi: a study of carbon transfer between plants interconnected by a common mycelium

The transfer of ¹⁴C from Lolium perenne (the donor) to Plantago lanceolata (the receiver), mediated by vesicular-arbuscular (VA) mycorrhizal fungi, was examined when the two species were grown together or separately. The VA mycorrhizal infection led to a significant increase, relative to that in uninfected plants, in the ¹⁴C transferred from donor to receiver plants, not only when the roots of the two plants were growing in intimate mixture, but also when they were separated by a root-free zone of 2.33 cm. The majority of isotope transfer between the two plant species was along the direct pathway via VA mycelium.     

Arbuscular mycorrhizal symbiosis alleviates drought stress imposed on Knautia arvensis plants in serpentine soil

Background and Aims

Plants growing on serpentine bedrock have to cope with the unique soil chemistry and often also low water-holding capacity. As plant-soil interactions are substantially modified by arbuscular mycorrhizal (AM) symbiosis, we hypothesise that drought tolerance of serpentine plants is enhanced by AM fungi (AMF).

Methods

We conducted a pot experiment combining four levels of drought stress and three AMF inoculation treatments, using serpentine Knautia arvensis (Dipsacaceae) plants as a model.

Results

AMF inoculation improved plant growth and increased phosphorus uptake. The diminishing water supply caused a gradual decrease in plant growth, accompanied by increasing concentrations of drought stress markers (proline, abscisic acid) in root tissues. Mycorrhizal growth dependence and phosphorus uptake benefit increased with drought intensity, and the alleviating effect of AMF on plant drought stress was also indicated by lower proline accumulation.

Conclusions

We documented the role of AM symbiosis in plant drought tolerance under serpentine conditions. However, the potential of AMF to alleviate drought stress was limited beyond a certain threshold, as indicated by a steep decline in mycorrhizal growth dependence and phosphorus uptake benefit and a concomitant rise in proline concentrations in the roots of mycorrhizal plants at the highest drought intensity.     

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.     

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.     

The extent of mycorrhizal colonization of roots and its influence on plant growth and phosphorus content

Aims

The most common metric of arbuscular mycorrhizal fungal (AMF) abundance is percent root length colonized (PRLC) by mycorrhizal structures. Frequently, plants with greater PRLC are assumed to receive more nutrients (such as phosphorus, P) from their mycorrhizal symbionts, leading to greater plant growth. Nevertheless, the functional significance of this metric remains controversial. In this review, I discuss whether manipulations of PRLC generally led to changes in plant biomass and P content, and whether AMF taxa and plant functional groups influence these relationships.

Methods

I conducted a meta-analysis of laboratory- and field-based trials in which mycorrhizal colonization was directly altered compared to unmanipulated controls. For each trial, I calculated (1) the difference in PRLC (ΔPRLC) between the treatments, and (2) the response ratio of plant biomass. In a subset of these studies, the response ratio of P content of host plants could also be calculated.

Results

The response ratio of plant biomass and P content rose significantly and exponentially as ΔPRLC increased. Nevertheless, ΔPRLC explained only a fraction of the variation in response ratios in each case. Moreover, AMF taxa varied in their effects on biomass per unit ΔPRLC. In addition, plant functional groups differed in effects on plant P content per unit ΔPRLC, with C4 grasses responding most strongly.

Conclusions

It appears that as the extent to which plant roots are colonized by AMF increases, plant growth and P content often increase, although substantial variability exists among trials. As others have found, a likely mechanism for this relationship is increased transfer of P (and perhaps other nutrients) through the more-prevalent mycorrhizal structures.     

Plant-soil feedbacks between invasive shrubs and native forest understory species lead to shifts in the abundance of mycorrhizal fungi

Aims

Non-native shrubs are important invaders of the Eastern Deciduous Forest, dramatically altering forest structure and functioning. Study of invasion mechanisms in this system has emphasized aboveground processes, and plant-soil feedbacks are relatively unexplored as a mechanism of shrub dominance. We tested whether plant-soil feedback in this habitat is affected by competition and whether arbuscular mycorrhizal fungi (AMF) are involved in plant-soil feedback.

Methods

We used a standard two-phase plant-soil feedback experiment run concurrently for each of three invasive shrub species, measuring feedback effects on AMF colonization, aboveground biomass, and the responses of native plant species in greenhouse mesocosms.

Results

Lonicera maackii and Ligustrum vulgare reduced AMF colonization of native roots, both with legacy effects (prior growth in soil) and direct effects (current growth in soil). Elaeagnus umbellata grown with natives left a legacy of increased AMF colonization of native communities.

Conclusions

Our results suggest that woody invasive species can alter the AMF associations of native plants even after the invasive is no longer present. Such consequences merit study with other native species and where environmental factors, such as light availability, might be expected to compound the effects of changes in AMF.     

Effects of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia spec.) on soil chemical properties in a mixed deciduous forest

Background and aims

We investigated the genetic diversity of arbuscular mycorrhizal fungi (AMF) in soils and the roots of Phalaris aquatica L., Trifolium subterraneum L., and Hordeum leporinum Link growing in limed and unlimed soil, the influence of lime application on AMF colonization and the relationship between AMF diversity and soil chemical properties.

Methods

The sampling was conducted on a long-term liming experimental site, established in 1992, in which lime was applied every 6 years to maintain soil pH (in CaCl₂) at 5.5 in the 0–10 cm soil depth. Polymerase chain reaction, cloning and sequencing techniques were used to investigate the diversity of AMF.

Results

Altogether, 438 AMF sequences from a total of 480 clones were obtained. Sequences of phylotypes Aca/Scu were detected exclusively in soil, while Glomus sp. (GlGr Ab) and an uncultured Glomus (UnGlGr A) were detected only in plant roots. Glomus mosseae (GlGr Aa) was the dominant AMF in the pastures examined; however, the proportion of G. mosseae was negatively correlated with soil pH, exchangeable Ca and available P. Generally, diversity of the AMF phylotypes was greater in the bulk unlimed soil and plants from this treatment when compared to the limed treatments.

Conclusions

Long-term lime application changed soil nutrient availability and increased AMF colonization, but decreased AMF phylotype diversity, implying that soil chemistry may determine the distribution of AMF in acid soils. Future studies are required to explore the functions of these AMF groups and select the most efficient AMF for sustainable farming in acid soils.     

Importance of native arbuscular mycorrhizal inoculation in the halophyte Asteriscus maritimus for successful establishment and growth under saline conditions

Background and aims

The biological restoration of saline habitats could be achieved by using halophyte plant species together with adapted arbuscular mycorrhizal fungi (AMF). An interesting plant to be used in restoration of saline environments, Asteriscus maritimus, is highly mycotrophic. The aim of this study was to assess the effectiveness of native and allochthonous AMF to enhance the establishment and growth of the halophyte A. maritimus under saline conditions.

Methods

We studied the symbiotic effectiveness of four AMF strains (three native fungal isolates from a saline soil and one allochthonous, from collection) in A. maritimus subjected to increasing salinity stress. We measured plant physiological parameters by which AMF may ameliorate the detrimental effects of salinity stress.

Results

A. maritimus plants showed a high mycorrhizal dependency, even in absence of salt stress. Plants inoculated with native AMF had higher shoot dry weight, efficiency of photosystem II, stomatal conductance and accumulation of glutathione than those inoculated with the collection AMF at the highest level of salinity. Moreover, at this salt level, only 30 % of A. maritimus plants inoculated with the collection AMF survived, while with the three native AMF, the rate of survival was 100 %.

Conclusions

Results points out the importance of native AMF inoculation in the establishment, survival and growth of A. maritimus plants. Inoculation with these native AMF enhanced A. maritimus salt tolerance by increasing efficiency of photosystem II, stomatal conductance and glutathione content and by reducing oxidative damage. Thus, the use of adequate native AMF inocula could be a critical issue for success in recovering saline degraded areas.     

Transport of nitrogen and zinc to rhodes grass by arbuscular mycorrhiza and roots as affected by different nitrogen sources (NH<Subscript>4</Subscript><Superscript>+</Superscript>-N and NO<Subscript>3</Subscript><Superscript>−</Superscript>-N)

We investigated the effect of mineral nitrogen forms on transfer of nitrogen (N) and zinc (Zn) from attached compartments to rhodes grass (Chloris gayana) colonised with arbuscular mycorrhizal fungi (AMF). After being pre-cultivated in substrates with adequate nutrient supply and either AMF inoculated (+AM) or left non-inoculated (?AM), rhodes grass was positioned adjacent to an outer compartment holding a similar substrate but applied with labelled nitrogen (¹⁵N) either as ammonium (NH₄ ⁺) or nitrate (NO₃ ^?), and a high supply of Zn (150 mg kg^?1 DS). Plant roots together with fungal mycelium were either allowed to explore the outer compartment (with root access) or only mycorrhizal hyphae were allowed (without root access). Within each access treatment, biomasses of rhodes grass were not significantly affected by AMF inoculation or N form. AMF contribution to plant ¹⁵N uptake was about double in NH₄ ⁺ compared with NO₃ ^?-supplied treatments while the mycorrhizal influence on plant Zn uptake was insignificant. Without root access, the shoot ¹⁵N/Zn concentration ratio was up to ten-fold higher in +AM than –AM treatments and this ratio increase was clearly more pronounced in NH₄ ⁺ than NO₃ ^?-supplied treatments. In conclusion, rhodes grass in symbiosis with the tested AMF acquired more N when supplied with ammonium. Moreover, there is clear indication that although the AMF have transported both nutrients (N and Zn), N was preferentially transferred as compared to Zn. We confirmed that, while rhodes grass is not able to prevent excessive Zn uptake via roots under conditions of high Zn, mycorrhiza is able to avoid excessive Zn supply to the host plant when the fungus alone has access to contaminated patches.     

Arbuscular mycorrhizal fungi affect seedling recruitment: a potential mechanism by which N deposition favors the dominance of grasses over forbs

Background and aims

Nitrogen (N) deposition usually alters plant community structure and reduces plant biodiversity in grasslands. Seedling recruitment is essential for maintaining species richness and determines plant community composition. Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic fungi and could facilitate seedling establishment. Here we conducted an experiment to address whether the influence of AMF on seedling recruitment depends on N addition and plant species.

Methods

Leymus chinensis were cultivated for 5 months in the microcosms that were inoculated with or without AMF at five N addition rates. Seeds of three main species (two C₃ grasses and one non-N₂-fixing forb) of the Eurasian steppe were sown to the 5-month-old microcosms. Seedling establishment was estimated by shoot biomass, N and P contents 7 weeks after seedling germination.

Results

AMF promoted seedlings recruitment of two C₃ grasses at addition rates above 0.5 g N m^?2. In contrast, seedling recruitment of the non-N₂-fixing forb was increased by AMF at addition rates below 0.5 g N m^?2 but was decreased above 2.5 g N m^?2.

Conclusions

These results partly explain why N addition favored the dominance of grasses over forbs in perennial grassland communities. Our study indicates that AMF have the potential to influence plant community composition by mediating revegetation in the face of N deposition.     

Differences in the AMF diversity in soil and roots between two annual and perennial gramineous plants co-occurring in a Mediterranean, semiarid degraded area

Aims

In the present study, we analysed the diversity of indigenous arbuscular mycorrhizal fungi (AMF) colonising both the roots and rhizosphere soil of an annual herbaceous species, Bromus rubens, and a perennial herbaceous species, Brachypodium retusum, co-occurring in the same Mediterranean, semiarid degraded area. The intention was to study whether these two species promoted the diversity of AM fungi in their rhizospheres differently and to ascertain whether the AMF community harboured by an annual plant species differed from that harboured by a perennial species when both grew in the same place.

Methods

The AMF large subunit ribosomal RNA genes (LSU) were subjected to nested PCR, cloning, sequencing and phylogenetic analysis.

Results

Twenty AMF sequence types belonging to Glomus group A, Glomus group B and Diversispora were identified. The two plant species differed in the AMF community composition in their roots, B. rubens showing a higher diversity of AMF than B. retusum. However the composition of the AMF communities associated with the two rhizosphere soils was similar.

Conclusions

These results suggest that the management of these Mediterranean, semiarid degraded areas should include the promotion of annual herbaceous plant communities in order to maintain the sustainability and productivity of these ecosystems.     

A comparison of phosphorus and nitrogen transfer between plants of different phosphorus status

Summary This study has two objections: (1) to compare transfers of phosphorus (³²P) with nitrogen (¹⁵N) from undefoliated and defoliated mycorrhizal P-rich plants to an adjacent mycorrhizal plant and (2) to determine whether the improved nutrient status of a plant growing with a nutrient-rich plant is due primarily to movement of nutrients from roots of its nutrient-rich neighbor (= nutrient transfer) or to reduced nutrient uptake by its nutrient-rich neighbor (=shift in competition). Two plants of Plantago lanceolata were grown in a three-pot unit in which each of their root systems were split, with part in the central shared pot and part by themselves in an outside pot. There were three treatments: (1) no added P; (2) P added in the outer pot to only plant, termed the donor plant, since it might provide P to the companion plant, acting as a receiver; and (3) as in the previous treatment but the P-fertilized donor plant was also clipped. To encourage the formation of hyphal links between roots of the different plants, transfers were determined when root length densities were high (90 to 130 cm cm^-3 soil) and when 56 to 85% of the root length was infected with vesicular-arbuscular mycorrhizae. Phosphorus fertilization enhanced P but not N movement within donor plants. Regardless of treatment, N transfer from donor to receiver plants was an order of magnitude greater than P transfer and in amounts that could potentially affect plant nutrition in very infertile soils. Phosphorus transfer was very small in any of the treatments. Although P fertilization and clipping improved P status of receiver plants, P transfer was not indicated as the main reason for the improved nutrition. A shift in competition between donor and receiver plants was likely the major factor in the shift in nutrition of the receiver plants.     

Is nitrogen transfer among plants enhanced by contrasting nutrient‐acquisition strategies?

Nitrogen (N) transfer among plants has been found where at least one plant can fix N₂. In nutrient‐poor soils, where plants with contrasting nutrient‐acquisition strategies (without N₂ fixation) co‐occur, it is unclear if N transfer exists and what promotes it. A novel multi‐species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non‐mycorrhizal cluster‐rooted plants in nutrient‐poor soils with mycorrhizal mesh barriers. We foliar‐fed plants with a K¹⁵NO₃ solution to quantify one‐way N transfer from ‘donor’ to ‘receiver’ plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient‐acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N₂ fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM‐only plants. We demonstrate N transfer between plants of contrasting nutrient‐acquisition strategies, and a preferential enrichment of cluster‐rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient‐poor soils.