Mycorrhizal Response Research Articles

Mycorrhizal responsiveness of maize (Zea mays L.) genotypes as related to releasing date and available P content in soil

The aim of this study was to compare the mycorrhizal responsiveness among old and recent Chinese maize genotypes (released from 1950s to 2008) in low- and high-Olsen-P soils and to identify parameters that would indicate the relationships between the mycorrhizal responsiveness and the functional traits related to P uptake of maize. A greenhouse factorial experiment was conducted. The factors were maize genotype [Huangmaya (HMY), Zhongdan 2 (ZD2), Nongda 108 (ND108), and NE15], inoculation with or without arbuscular mycorrhizal fungi (AMF) (Rhizophagus irregularis), and Olsen-P levels (4, 9, 18, 36, or 60mg P kg(-1)). Old and recently released genotypes differed in their response to AMF under low- and high-P supply. Three kinds of responses (in terms of shoot growth) were observed: the response was positive if the soil P content was low, but negative if the soil Olsen-P content was high (HMY and ND108); the response was neutral regardless of soil P content (ZD2); and the response was positive regardless of soil P content (NE15). Principle component (PC) analysis showed that the first PC comprised morphological and physiological traits of maize roots, and the second PC comprised mycorrhizal traits. The opposite was the case, however, in high-P soil. It is concluded that maize breeding selection from 1950s to 2000s is not always against the AM association and that AMF play positive roles in promoting the growth of some maize genotypes in high-P soil. The root length colonization by efficient AMF might be a useful parameter for breeding varieties with increased mycorrhizal responsiveness.

Mycorrhizal response to experimental pH and P manipulation in acidic hardwood forests.

Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e., <pH 5) are particularly vulnerable to P limitation. Results from previous studies in these systems are mixed with evidence both for and against P limitation. We hypothesized that shifts in mycorrhizal colonization and community structure help temperate forest ecosystems overcome an underlying P limitation by accessing mineral and organic P sources that are otherwise unavailable for direct plant uptake. We examined arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) communities and soil microbial activity in an ecosystem-level experiment where soil pH and P availability were manipulated in mixed deciduous forests across eastern Ohio, USA. One year after treatment initiation, AM root biomass was positively correlated with the most available P pool, resin P, while AM colonization was negatively correlated. In total, 15,876 EcM root tips were identified and assigned to 26 genera and 219 operational taxonomic units (97% similarity). Ectomycorrhizal richness and root tip abundance were negatively correlated with the moderately available P pools, while the relative percent of tips colonized by Ascomycetes was positively correlated with soil pH. Canonical correspondence analysis revealed regional, but not treatment, differences in AM communities, while EcM communities had both treatment and regional differences. Our findings highlight the complex interactions between mycorrhizae and the soil environment and further underscore the fact that mycorrhizal communities do not merely reflect the host plant community.

Vesicular-arbuscular (VA) mycorrhizae improve salinity tolerance in pre-inoculation subterranean clover (Trifolium subterraneum) seedlings

Effects of the mycorrhizal fungus Glomus intraradices on establishment of subterranean clover (Trifolium subterraneum L.) seedlings in saline conditions were studied in a glasshouse experiment. Growth and nutrient uptake were determined 10, 20 and 30 days after transplanting of mycorrhizal and nonmycorrhizal matched seedlings into soils with five different levels of salinity. Mycorrhizal plants had greater shoot and root dry weight than nonmycorrhizal plants. The enhancement in seedling dry weight due to mycorrhizal fungi was greater under high salinity levels. The detrimental effects of salinity stress on plant growth were appeared immediately after application low salinity stress to nonmycorrhizal plants (3.5 dS/m), but it was only observed in mycorrhizal plants at 7.5 dS/m and above. Mycorrhizal fungi increased P concentrations in shoots and roots compared with nonmycorrhizal plants particularly at 12 dS/m. Root K/Na ratio was also increased in mycorrhizal plants, possibly contributing to salinity tolerance. Calculation of mycorrhizal responses in terms of plant dry weight, P and K contents showed that the beneficial effects of mycorrhizal fungi on seedling salinity tolerance are due to different mechanisms at different stage of growth: increased P uptake during early growth and increased K uptake at the later stages. Results are discussed in the context of application of mycorrhizal inoculation to revegetation of salt affected lands.

REDUCED DROUGHT TOLERANCE DURING DOMESTICATION AND THE EVOLUTION OF WEEDINESS RESULTS FROM TOLERANCE-GROWTH TRADE-OFFS

The increased reproductive potential, size, shoot allocation, and growth rate of weedy plants may result from reduced resource allocation to other aspects of plant growth and defense. To investigate whether changes in resource allocation occurred during domestication or the evolution of weediness, we compared the mycorrhizal responsiveness, growth, and drought tolerance of nine native ruderal, nine agriculturally weedy (four U.S. weedy and five Australian weedy), and 14 domesticated populations (eight ancient landraces and six improved cultivars) of the common sunflower (Helianthus annuus). Domesticated sunflower cultivars were less drought tolerant, but had higher plant growth and fecundity and coarser roots than wild populations. There were no changes in level of drought tolerance between improved cultivars and ancient landrace plants, but there was an increase in allocation to flowers with recent selection. Weedy populations were intermediate between domesticated cultivars and native ruderal populations for plant growth rate, root architecture, and drought tolerance. Weedy populations benefited most from mycorrhizal inoculation by having fewer wilted leaves and wetter soil. Overall, we found that trade-offs between drought tolerance and several aspects of plant growth, including growth rate, allocation to flowering, and root architecture, govern evolution during sunflower domestication and the invasion of disturbed habitat.

Plant species differ in their ability to reduce allocation to non‐beneficial arbuscular mycorrhizal fungi

Theory suggests that cheaters threaten the persistence of mutualisms, but that sanctions to prevent cheating can stabilize mutualisms. In the arbuscular mycorrhizal symbiosis, reports of parasitism suggest that reductions in plant carbon allocation are not universally effective. I asked whether plant species differences in mycorrhizal responsiveness would affect both their susceptibility to parasitism and their reduction in allocation to non-beneficial arbuscular mycorrhizal fungi (AMF) in high-phosphorus soils. In a greenhouse experiment, I found that two C3 grasses, Bromus inermis and Elymus repens, effectively suppressed root colonization and AMF hyphal abundance. Increases in soil phosphorus did not reduce the degree to which AMF increased plant biomass. In contrast, two C4 grasses, Andropogon gerardii and Schizachyrium scoparium, more weakly reduced root colonization and failed to suppress AMF hyphal abundance. Consequently, they experienced strong declines in their response to AMF, and one species suffered parasitism. Thus, species differ in susceptibility to parasitism and their reduction in allocation to non-beneficial AMF. These differences may affect the distribution and abundance of plants and AMF, as well as the stability of the mutualism.

English

With a prime motive to confirm the high quality of Arbuscular Mycorrhizal (AM) inoculum that is widely used as an important bioferti- lizer, an effort was taken to standardize the per cent colonized root bits that have to be present in an AM inoculum. Initial analysis on AM coloni- zation for the effectivity of the AM inoculum revealed that 80 per cent to 100 per cent root colonization enhanced the growth performance of the host plant with better mycorrhizal responses which were assessed in terms of per cent root colonization and viable spore count of Glomus intraradices when the substrate vermiculite was amended with 10 per cent soil compared to vermiculite alone at 60 days. Thus, presence of > 80 per cent colonized root bits in AM inoculum was standardized as one of the quality control parameter of AM inoculum which can be adopted to certify a high quality AM product commercially .

Nuclear-localized and deregulated calcium- and calmodulin-dependent protein kinase activates rhizobial and mycorrhizal responses in Lotus japonicus.

The common symbiosis pathway is at the core of symbiosis signaling between plants and soil microbes. In this pathway, calcium- and calmodulin-dependent protein kinase (CCaMK) plays a crucial role in integrating the signals both in arbuscular mycorrhizal symbiosis (AMS) and in root nodule symbiosis (RNS). However, the molecular mechanism by which CCaMK coordinates AMS and RNS is largely unknown. Here, we report that the gain-of-function (GOF) variants of CCaMK without the regulatory domains activate both AMS and RNS signaling pathways in the absence of symbiotic partners. This activation requires nuclear localization of CCaMK. Enforced nuclear localization of the GOF-CCaMK variants by fusion with a canonical nuclear localization signal enhances signaling activity of AMS and RNS. The GOF-CCaMK variant triggers formation of a structure similar to the prepenetration apparatus, which guides infection of arbuscular mycorrhizal fungi to host root cells. In addition, the GOF-CCaMK variants without the regulatory domains partly restore AMS but fail to support rhizobial infection in ccamk mutants. These data indicate that AMS, the more ancient type of symbiosis, can be mainly regulated by the kinase activity of CCaMK, whereas RNS, which evolved more recently, requires complex regulation performed by the regulatory domains of CCaMK.

Arbuscular mycorrhizal fungi enhance photosynthesis, water use efficiency, and growth of frankincense seedlings under pulsed water availability conditions

Under drought conditions, arbuscular mycorrhizal (AM) fungi alter water relationships of plants and improve their resistance to drought. In a factorial greenhouse experiment, we tested the effects of the AM symbiosis and precipitation regime on the performance (growth, gas exchange, nutrient status and mycorrhizal responsiveness) of Boswellia papyrifera seedlings. A continuous precipitation regime was imitated by continuous watering of plants to field capacity every other day during 4 months, and irregular precipitation by pulsed watering of plants where watering was switched every 15 days during these 4 months, with 15 days of watering followed by 15 days without watering. There were significantly higher levels of AM colonization under irregular precipitation regime than under continuous precipitation. Mycorrhizal seedlings had higher biomass than control seedlings. Stomatal conductance and phosphorus mass fraction in shoot and root were also significantly higher for mycorrhizal seedlings. Mycorrhizal seedlings under irregular watering had the highest biomass. Both a larger leaf area and higher assimilation rates contributed to higher biomass. Under irregular watering, the water use efficiency increased in non-mycorrhizal seedlings through a reduction in transpiration, while in mycorrhizal seedlings irregular watering increased transpiration. Because assimilation rates increased even more, mycorrhizal seedlings achieved an even higher water use efficiency. Boswellia seedlings allocated almost all carbon to the storage root. Boswellia seedlings had higher mass fractions of N, P, and K in roots than in shoots. Irregular precipitation conditions apparently benefit Boswellia seedlings when they are mycorrhizal.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2258-3) contains supplementary material, which is available to authorized users.

Mycorrhizal responsiveness trends in annual crop plants and their wild relatives—a meta-analysis on studies from 1981 to 2010

Background and aims Year of release of a cultivar reflects the agricultural and breeding practices of its time; we hypothesize that there are differences in mycorrhizal responsiveness of new high yielding and old crop plants and landraces. We evaluated the importance of the year of release on mycorrhizal responsiveness, arbuscular mycorrhizal (AM) fungal root colonization and P efficiency. We also analyzed the effect of experimental treatments, P efficiency (P acquisition and P utilization efficiency) and AM fungal root colonization on a potential mycorrhizal responsiveness trend for year of release.

Contrasting arbuscular mycorrhizal responses of vascular and non-vascular plants to a simulated Palaeozoic CO2 decline

The arbuscular mycorrhizal (AM) fungal symbiosis is widely hypothesized to have promoted the evolution of land plants from rootless gametophytes to rooted sporophytes during the mid-Palaeozoic (480-360 Myr, ago), at a time coincident with a 90% fall in the atmospheric CO(2) concentration ([CO(2)](a)). Here we show using standardized dual isotopic tracers ((14)C and (33)P) that AM symbiosis efficiency (defined as plant P gain per unit of C invested into fungi) of liverwort gametophytes declines, but increases in the sporophytes of vascular plants (ferns and angiosperms), at 440 p.p.m. compared with 1,500 p.p.m. [CO(2)](a). These contrasting responses are associated with larger AM hyphal networks, and structural advances in vascular plant water-conducting systems, promoting P transport that enhances AM efficiency at 440 p.p.m. [CO(2)](a). Our results suggest that non-vascular land plants not only faced intense competition for light, as vascular land floras grew taller in the Palaeozoic, but also markedly reduced efficiency and total capture of P as [CO(2)](a) fell.

Mutualism breakdown in breadfruit domestication.

During the process of plant domestication, below-ground communities are rarely considered. Some studies have attempted to understand the changes in root symbionts owing to domestication, but little is known about how it influences mycorrhizal response in domesticated crops. We hypothesized that selection for above-ground traits may also result in decreased mycorrhizal abundance in roots. Breadfruit (Artocarpus sp.) has a long domestication history, with a strong geographical movement of cultivars from west to east across the Melanesian and Polynesian islands. Our results clearly show a decrease in arbuscular mycorrhizas (AMs) along a domestication gradient from wild to recently derived cultivars. We showed that the vesicular and arbuscular colonization rate decreased significantly in more recently derived breadfruit cultivars. In addition, molecular analyses of breadfruit roots indicated that AM fungal species richness also responded along the domestication gradient. These results suggest that human-driven selection for plant cultivars can have unintended effects on below-ground mutualists, with potential impacts on the stress tolerance of crops and long-term food security.

The Effects of Salinity on Nitrogen Fixation and Trehalose Metabolism in Mycorrhizal Cajanus cajan (L.) Millsp. Plants

Arbuscular mycorrhizal (AM) fungi exist widely in natural ecosystems as well as in salt-affected soils and are considered suitable candidates for bio-ame- lioration of saline soils. Plants respond to salinity by accumulating sugars and other low-molecular-weight compatible solutes. One such compound is trehalose, which has been found to play an important role as a stress pro- tectant. The aim of the present investigation was to study interactions between an AM fungus and salinity stress on growth, nitrogen fixation, and trehalose metabolism in Cajanus cajan (L.) Millsp. (pigeonpea). Two genotypes (Sel 85N (salt-tolerant) and ICP 13997 (salt-sensitive)) were subjected to saline treatments with and without mycorrhizal inoculations. Salinity reduced plant biomass (shoot and root) in both genotypes and resulted in a decline in shoot-to-root ratio (SRR); however, a smaller decline was observed in Sel 85N than in ICP 13997. AM coloni- zation was reduced with increasing salinity levels but mycorrhizal responsiveness (MR) increased. Genotypic variability in nitrogen fixation and trehalose metabolism in response to salinity and mycorrhization was observed. An increment in nodule number was accompanied by a reduction in dry mass. Subsequently, nodular activity (leghemoglobin, acetylene-reduction activity (ARA), nitrogen content) was reduced under soil salinity, which was more profound in ICP 13997 than in Sel 85N. The symbiotic association with Glomus mosseae led to signif- icant improvement in plant dry mass and nitrogen-fixing potential of nodules under salt stress. Salinity led to an increase in trehalose-6-P synthetase (TPS) and trehalose-6-P phosphatase (TPP) activities resulting in increased treha- lose content in nodules, which was accompanied by inhi- bition of trehalose catabolism (trehalase activity). AM plants had lower trehalase activity under saline and non- saline conditions. Thus, a symbiotic relationship between plant roots and G. mosseae might have resulted in salinity tolerance in a genotype-dependent manner.

Grazing tolerance and mycorrhizal colonization: Effects of resource manipulation and plant size in biennial Gentianella campestris

As herbivory usually leads to loss of photosynthesizing biomass, its consequences for plants are often negative. However, in favorable conditions, effects of herbivory on plants may be neutral or even beneficial. According to the compensatory continuum hypothesis plants can tolerate herbivory best in resource-rich conditions. Besides herbivory, also primarily positive biotic interactions like mycorrhizal symbiosis, bear carbon costs. Tritrophic plant–fungus–herbivore interaction further complicates plant's cost-benefit balance, because herbivory of the host plant is expected to cause decline in mycorrhizal colonization under high availability of soil nutrients when benefits of symbiosis decline in relation to costs. To gain insight into above interactions we tested the effects of plant size and resource manipulation (simulated herbivory and fertilization) on both above-ground performance and on root fungal colonization of the biennial Gentianella campestris. Clipping caused allocation shift from height growth to branches in all groups except in large and fertilized plants. For large plants nutrient addition may have come too late, as the number of meristems was most likely determined already before the fertilization. Clipping decreased the amount of DSE (dark septate endophytic) fungi which generally are not considered to be mycorrhizal. The effect of clipping on total fungal colonization and colonization by arbuscular mycorrhizal (AM) fungal coils were found to depend on host size and resource level. Dissimilar mycorrhizal response to simulated herbivory in small vs. large plants could be due to more intensive light competition in case of small plants. Carbon limited small plants may not be able to maintain high mycorrhizal colonization, whereas large clipped plants allocate extra resources to roots and mycorrhizal fungi at the expense of above-ground parts. Our results suggest that herbivory may increase carbon limitation that leads re-growing shoots and fungal symbionts to function as competing sinks for the limited carbon reserves.

Response of Theobroma cacao and Inga edulis seedlings to cross-inoculated populations of arbuscular mycorrhizal fungi

Response of Theobroma cacao L. (cacao) and the shade tree Inga edulis Mart. (inga) seedlings from an organically-grown cacao plantation to inoculation with native arbuscular mycorrhizae forming fungi (AMF) was studied in a cross-inoculation assay under greenhouse conditions. Seedlings of inga and cacao were grown in pots filled with heat-treated soil from the plantation. Control was heat-treated soil without inoculum and roots of cacao and inga from the plantation were applied as AMF inocula. Undisturbed soil blocks were used as a “positive control” of the inoculation potential of untreated soil and roots combined. No AMF structures were observed in the roots of either species in the heat-treated control. All inocula were infective in both hosts and the differences in the total AMF colonization percentage between the hosts were not significant but inga had significantly higher colonization by hyphal coils and arbuscules. Cacao roots but neither inga roots nor soil block inocula stimulated cacao growth. All inocula significantly increased growth of inga, which had higher relative mycorrhizal responsiveness than cacao. Thus, in spite of the strong infectivity of the inocula in both hosts, cacao and inga responded differently to the same AMF populations. The strong conspecific preference of cacao suggests that attention must be paid to the AMF inoculum used for this species. However, the strong response of inga to cacao root inoculum indicates that the two species may share same AMF symbionts, thus enabling positive interactions between them, including formation of common mycelial networks.

Arbuscular mycorrhizas in phosphate-polluted soil: interrelations between root colonization and nitrogen

To investigate whether arbuscular mycorrhizal fungi (AMF) – abundant in a phosphate-polluted but nitrogen-poor field site – improve plant N nutrition, we carried out a two-factorial experiment, including N fertilization and fungicide treatment. Percentage of root length colonized (% RLC) by AMF and tissue element concentrations were determined for four resident plant species. Furthermore, soil nutrient levels and N effects on aboveground biomass of individual species were measured. Nitrogen fertilization lowered % RLC by AMF of Artemisia vulgaris L., Picris hieracioides L. and Poa compressa L., but not of Bromus japonicus Thunb. This – together with positive N addition effects on N status, N:P-ratio and aboveground biomass of most species – suggested that plants are mycorrhizal because of N deficiency. Fungicide treatment, which reduced % RLC in all species, resulted in lower N concentrations in A. vulgaris and P. hieracioides, a higher N concentration in P. compressa, and did not consistently affect N status of B. japonicus. Evidently, AMF had an influence on the N nutrition of plants in this P-rich soil; however – potentially due to differences in their mycorrhizal responsiveness – not all species seemed to benefit from a mycorrhiza-mediated N uptake and accordingly, N distribution.

Arbuscular mycorrhizal fungi associated with Artemisia umbelliformis Lam, an endangered aromatic species in Southern French Alps, influence plant P and essential oil contents

Root colonization by arbuscular mycorrhizal (AM) fungi of Artemisia umbelliformis, investigated in natural and cultivated sites in the Southern Alps of France, showed typical structures (arbuscules, vesicles, hyphae) as well as spores and mycelia in its rhizosphere. Several native AM fungi belonging to different Glomeromycota genera were identified as colonizers of A. umbelliformis roots, including Glomus tenue, Glomus intraradices, G. claroideum/etunicatum and a new Acaulospora species. The use of the highly mycorrhizal species Trifolium pratense as a companion plant impacted positively on mycorrhizal colonization of A. umbelliformis under greenhouse conditions. The symbiotic performance of an alpine microbial community including native AM fungi used as inoculum on A. umbelliformis was evaluated in greenhouse conditions by comparison with mycorrhizal responses of two other alpine Artemisia species, Artemisia glacialis and Artemisia genipi Weber. Contrary to A. genipi Weber, both A. umbelliformis and A. glacialis showed a significant increase of P concentration in shoots. Volatile components were analyzed by GC-MS in shoots of A. umbelliformis 6months after inoculation. The alpine microbial inoculum increased significantly the percentage of E-β-ocimene and reduced those of E-2-decenal and (E,E)-2-4-decadienal indicating an influence of alpine microbial inoculum on essential oil production. This work provides practical indications for the use of native AM fungi for A. umbelliformis field culture.

Genetic analysis of the interaction between Allium species and arbuscular mycorrhizal fungi.

The response of Allium cepa, A. roylei, A. fistulosum, and the hybrid A. fistulosum × A. roylei to the arbuscular mycorrhizal fungus (AMF) Glomus intraradices was studied. The genetic basis for response to AMF was analyzed in a tri-hybrid A. cepa × (A. roylei × A. fistulosum) population. Plant response to mycorrhizal symbiosis was expressed as relative mycorrhizal responsiveness (R′) and absolute responsiveness (R). In addition, the average performance (AP) of genotypes under mycorrhizal and non-mycorrhizal conditions was determined. Experiments were executed in 2 years, and comprised clonally propagated plants of each genotype grown in sterile soil, inoculated with G. intraradices or non-inoculated. Results were significantly correlated between both years. Biomass of non-mycorrhizal and mycorrhizal plants was significantly positively correlated. R′ was negatively correlated with biomass of non-mycorrhizal plants and hence unsuitable as a breeding criterion. R and AP were positively correlated with biomass of mycorrhizal and non-mycorrhizal plants. QTLs contributing to mycorrhizal response were located on a linkage map of the A. roylei × A. fistulosum parental genotype. Two QTLs from A. roylei were detected on chromosomes 2 and 3 for R, AP, and biomass of mycorrhizal plants. A QTL from A. fistulosum was detected on linkage group 9 for AP (but not R), biomass of mycorrhizal and non-mycorrhizal plants, and the number of stem-borne roots. Co-segregating QTLs for plant biomass, R and AP indicate that selection for plant biomass also selects for enhanced R and AP. Moreover, our findings suggest that modern onion breeding did not select against the response to AMF, as was suggested before for other cultivated species. Positive correlation between high number of roots, biomass and large response to AMF in close relatives of onion opens prospects to combine these traits for the development of more robust onion cultivars.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-010-1501-8) contains supplementary material, which is available to authorized users.

Arbuscular mycorrhizal (AM) status and seedling growth response to indigenous AM colonisation of Euryodendron excelsum in China: implications for restoring an endemic and critically endangered tree

It is increasingly evident that the mycorrhizal colonisation of endangered species is of major importance for their restoration. In the present study, the symbiosis of arbuscular mycorrhizal fungi (AMF) and endangered species Euryodendron excelsum was investigated in 10 patches of a remnant population in south China. The presence of arbuscules and vesicles indicates that E. excelsum is a typical arbuscular mycorrhizal plant. Five genera were identified in the rhizosphere of E. excelsum, and the most common and frequent genus was Glomus. Root total colonisation intensity is negatively correlated with the available soil phosphorus and potassium content in the soil. In addition, we find no significant relationship between spore density and soil characteristics, or between spore density and total colonisation intensity. Furthermore, a greenhouse experiment under two soil types (humus: native soil = 3 : 1 ST1; humus: native soil = 1 : 3 ST2) was conducted to evaluate the effects of AMF inoculation on seedling growth. The levels of plant mycorrhizal response of E. excelsum seedlings under the ST1 and ST2 soil types were 136 and 413%, respectively. Although a significant growth enhancement was found in the ST1 soil type, seedling growth and survival rate were improved after AMF colonisation under both soil types. The results suggest that AMF colonisation may have practical implications in establishing effective conservation and restoration strategies for this critically endangered plant.

Influence of Biochar and Azospirillum Application on the Growth of Maize

A pot culture experiment was conducted to assess the influence of different levels of acacia wood based Biochar with Azospirillum strain AZ 204 on the growth of maize variety PEHM5 in the black cotton soil. The results revealed that the addition of biochar to soil with Azospirillum inoculation significantly increased the plant-microbial responses and the nutrient status of both plant and amended soil. Azospirillum and total diazotrophs population in the rhizosphere significantly increased with Biochar application at all the stages of crop growth. Furthermore, a significant increase of the native mycorrhizal response to Biochar with Azospirillum application was also observed in terms of root colonization of maize.

Organic Maize Growth and Mycorrhizal Root Colonization Response to Tillage and Organic Fertilization

The influence of conventional and no-tillage on mycorrhizal root colonization, soil properties and yield, was studied for 2 years in an experimental field of organic maize, fertilized by cattle manure or by seaweed compost. The no-tillage system improved soil macroporosity, increased organic carbon content, and enhanced the mean weight diameter of soil aggregates. Similarly, it had a positive effect on plant growth. Root density, leaf area index, biomass, grain yield and mycorrhizal root colonization were significantly affected by tillage system. Fertilization with manure and compost improved soil structure and aeration, thus favoring a higher mycorrhizal colonization of organic maize. The improved soil physical properties were positively related to mycorrhizal root colonization. High correlation coefficients of determination (r2) were also found between mycorrhizal root colonization and plant characteristics. It is concluded that the no-tillage system can improve the productivity of organic agriculture via pronounced arbuscular mycorrhizal root colonization.