Non-Peer ReviewedPulses are an important component in crop rotations in southern Saskatchewan. Besides their capability to fix nitrogen, pulse crops establish a symbiotic relationship with arbuscular mycorrhizal fungi, which have been shown to increase nutrient and water uptake through hyphal extensions in the soil. This 2 year study is designed to evaluate the impact of pulses in crop rotations on the biodiversity of AMF communities and their dynamics. Plant N and P uptake and the available soil N and P pools under a durum crop are also measured to assess if there is any correlation with AMF communities. The sampling and analysis is completed on the durum phase of the rotation with preceding crops of pea, lentil, chickpea, canola and durum. The final results will be explained by: (1) the size, nature, and physiological state of the soil microbial community and (2) the nature of the preceding crop residues. Preliminary results from the 2004 season indicate that higher plant P uptake is related to AMF colonization, while no significant change was detected in the soil N and P pools

Clapperton, J.

Fraser, T.

Germida, J.

Hamel, C.

Hanson, K.

Selles, F.

English

eCommons@USASK

Influence of pulse crops on arbuscular mycorrhizal fungi in a durum-based cropping system

University of Saskatchewan Research Archive

Influence of Pulse Crops on Arbuscular Mycorrhizal Fungi ina Durum-Based Cropping SystemT. Fraser1,2, C. Hamel1,2, K. Hanson2, J. Germida1, J. Clapperton3, F. Selles2and B. McConkey21Department of Soil Science, University of Saskatchewan, Saskatoon, SK, S7N 0W02Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada,Swift Current, SK, S9H 3X23Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, T1J4B1.Key Words: arbuscular mycorrhizal fungi, pulse crops, crop rotations, nutrient uptakeAbstractPulses are an important component in crop rotations in southern Saskatchewan. Besidestheir capability to fix nitrogen, pulse crops establish a symbiotic relationship witharbuscular mycorrhizal fungi, which have been shown to increase nutrient and wateruptake through hyphal extensions in the soil.  This 2 year study is designed to evaluatethe impact of pulses in crop rotations on the biodiversity of AMF communities and theirdynamics.  Plant N and P uptake and the available soil N and P pools under a durum cropare also measured to assess if there is any correlation with AMF communities.  Thesampling and analysis is completed on the durum phase of the rotation with precedingcrops of pea, lentil, chickpea, canola and durum.  The final results will be explained by:(1) the size, nature, and physiological state of the soil microbial community and (2) thenature of the preceding crop residues.  Preliminary results from the 2004 season indicatethat higher plant P uptake is related to AMF colonization, while no significant changewas detected in the soil N and P pools.IntroductionPulses are an important component in crop rotations in southern Saskatchewan.Conservation tillage in the brown soil zone of Saskatchewan typically includes acombination of cereals, pulses, and oilseeds in the cycle.  The benefits that pulse cropscontribute to a rotation are not completely understood.  Previously benefits were mostlyattributed to their ability to fix N, but the non-N benefits are not well understood(Stevenson and van Kessel 1996).  Besides their capability to fix nitrogen, pulse cropsestablish a symbiotic relationship with arbuscular mycorrhizal fungi (AMF).Arbuscular mycorrhizal fungi help the plants take up nutrients and water, while the plantsupplies the fungi with carbon derived from photosynthesis.  AM fungi can increaseuptake through hyphal extensions in the soil.  The fungi work by colonizing the root andthen extending hyphae out into the soil.  Hyphae have the ability to increase soil-rootcontact, increase exploration in micropores, extract water, and improve water holdingcapacity (Auge et al. 2003).  The extraradical hyphae provide contact between the AMfungi and the host, thereby contributing to nutrient uptake in the soil (Miller and Jastrow2000).  The fungal hyphae (2-5_m diameter) are smaller than root hairs (10-20_mdiameter) so have the ability to penetrate soil pores that are inaccessible to non-mycorrhizal roots (Marulanda et al. 2003).  Since water, N and P are often limitingfactors for plant growth on the Brown Chernozemic soils in the semiarid region ofSaskatchewan, increased levels of AMF in the soil may decrease fertilization and diseasemanagement costs.  Increased water infiltration, decreased soil erosion, and better soilaeration stemming from improved soil aggregation are other AMF-derived benefits.The function and abundance of AMF are influenced by a combination of environmentaland plant factors.  The environmental factors include the soil type, temperature, pH,moisture, and dissolved nutrients.  The plant factors comprise of the species, age, andbiomass of the particular plant (Bever et al. 2001).  The soil conditions are constantlychanging, in addition fluctuations in temperature and plant growth result in changes in themicrobial community.  Seasonality also plays a large role in determining the microbialcommunity composition.Crop rotation encourages diversity of the AM fungi community (Douds et al. 1993).Strongly mycorrhizal crops such as pulses with no till cropping systems promote AMFdiversity and increased soil inoculum levels.  Crops that are highly mycorrhizaldependent (i.e. legumes) have shown substantial differences in dry weight of roots andshoots, root length and overall colonization, and P uptake per plot in inoculated plantscompared to non-inoculated (Shibata and Yano 2003).  The use of AM field inoculum isnot currently practical (Saito and Marumoto 2002) since it has not always been beneficialand predictable (Rayan and Graham 2002).  Production of AMF inoculum is complicatedbecause of an inability to grow in a pure culture and its dependency to be multiplied onliving roots (Budi et al. 1998).  The best option for increasing inoculum levels is bymanipulation using plants promoting AMF symbiosis.The objectives of this study are to: 1) assess the impact of pulses in crop rotations on thebiodiversity of AMF communities and their dynamics and 2) measure the plant availableN and P pools in soil under a durum crop, and assess any correlation with AMFcommunities.  It is expected that pulse crops will increase the biodiversity and dynamicsof AMF communities under a subsequent durum crop and there will be an increase inplant N and P uptake which cannot be explained by changes in the soil N and P pools.The effect of pea, lentil and chickpea on soil biological and biochemical factors will beevaluated through microbial community profiling and examination of nutrient inputs ofthe preceding crop of pulses, canola, or a subsequent durum wheat crop.Materials and MethodsThe experiment is a two year field plot study (2004 and 2005), conducted at the SouthFarm of the Semiarid Prairie Agricultural Research Centre, in Swift Current on 5 year oldplots. It is located in the Brown soil zone on a Swinton Silt Loam.  Three repetitions offive treatments: pea-durum, lentil-durum, chickpea-durum, canola-durum and durum-durum are being compared (Table 1) in 5 x 24 m plots1.  The durum monoculture isincluded in the study since it once represented the best management practice underconventional tillage.Table 1.   Crop varieties used in this study are commonly grown in southernSaskatchewan.Crop Variety InoculantDurum cv. Avonlea n/aCanola Argentine n/aLentil Sovereign Nitragin CPea Handel Nitragin CChickpea Myles Nitragin GCCrops are fertilized each year to equalize soil fertility among treatments, as determinedby soil tests.  For durum plots the total N level is equalized to 65 lbs/ac.  This iscalculated as 65 minus amount of N in top 24 inches as determined by fall soil sampling.Phosphorous (11-51-0) is routinely applied with seed at approximately 40lbs/ac.Table 2.  Variables used as indicators of soil quality in this field experiment and methodsused for their evaluation.Experiment Sample Evaluation MethodAnion ExchangeMembranesSoil N and P dynamics Modified from Ziadi et al. 1999NH4/NO3 Soil Point in time available NKCl extraction (Maynard and Karla,1993)Mineralizable N SoilN made available over growingseasonIncubation extraction (Campbell et al.1993)Resin P Soil Point in time available PHedley extraction procedure (Hedleyet al. 1982)NLFA/PLFA SoilSize, nature & physiological stateof soil microbial communityExtracting, purifying and analyzingPLFA from soil (Clapperton andLacey, unpublished)Biodiversity Soil Qualification of AMF populationPolymerase Chain Reaction; GelElectrophoresisInoculumPotentialSoil/RootAMF potential at beginning ofgrowing seasonInfectivity Assay (Brundett 1999)RootColonizationRoot Percent of root colonized by AMFStaining (Vierheilig et al. 1998);Gridline Intersect Method(Giovannetti and Mosse 1980)Plant N & P Plant Nutrient uptake from soilDigestion of tissue on auto analyzer(Thomas et al. 1967)Four soil samples per plot were taken at emergence, five leaf, flag leaf, anthesis, andphysiological maturity.  The samples were bulked into one composite sample and putthrough 2 mm sieves before analysis (Table 2).  Two plants were taken at four locationsper plot and ground before N and P analysis.  Soil samples and root samples were also                                                 1 Durum following durum was grown in 15 x 24 m plotstaken at intermediate stages for analysis of phospholipids/neutral lipid fatty acids(PLFA/NLFA), biodiversity, and mycorrhizal root colonization.  This sampling schemewill be repeated in 2005.Results and DiscussionSoil N and P was not significantly different between the treatments, as determined byNH4/NO3 and nitrate and phosphate flux measurements (data not shown).  The mostevident results from the 2004 season were the effect of the treatments on mycorrhizalcolonization (Figure 1).  Colonization after the pulse crops was high, especially lentilwhich exhibited the highest colonization between the five leaf and flag leaf stages ofdevelopment.  Using canola as a precrop resulted in no colonization for the first 2sampling times, with a maximum colonization reaching only 6% between anthesis andmaturity.  Since canola is a non-mycorrhizal crop, it was expected that AMFdevelopment would be delayed in the subsequent durum crop, but the treatment effect didnot taper off at the end of the growing season.Durum Root Mycorrhizal Colonization (%)  0 5 10 15 20 25 30 35 Canola Chickpea Lentil Pea Durum Preceding crops  Series1 Series2 Series3 Series4 Between  seeding  and  5  leaf Between  5  leaf and  flag  leaf Between  flag  leaf  and  anthesis  Betwe n  anthesis  and maturity                        Figure 1.  Effect of previous crop on mycorrhizal colonization of durum wheat roots.Error bars are standard errors of the means (3 replicates).00.10.20.30.40.50.60.7Canola Chickpea Durum Lentil PeaPreceding CropsFive leafFlag leafAnthesisFigure 2.  Effect of previous crop on P concentration of durum wheat.  Error bars arestandard errors of the means (3 replicates).The lower colonization levels were also related to lower concentrations of total P in theplants (Figure 2).  Durum P uptake was higher after chickpea and lentil and lower aftercanola and durum.  Canola is lower than all others but an interaction (P=0.02) showedthat differences are greatest at the flag leaf stage and before maturity.  The crop precedingdurum had no significant difference on plant N uptake (data not shown).0500100015002000250030003500400045005000Canola Chickpea Durum Lentil PeaPreceding CropsFigure 3.  Effect of previous crop on grain yield of durum.  Error bars are standard errorsof the means (3 replicates).Previous crop was significant (P=0.06) after lentil and pea, while the other treatmentsresulted in lower yields (Figure 3).  The 2004 season was unusually wet and cool and thelower durum yields may be partially explained by the large incidence of tan spot resultingfrom the durum monoculture.ConclusionsIncreased durum yield following a pulse crop is a result of both the nitrogen and non-Nbenefits, including AMF symbiosis.  The preliminary results of this study indicate thatthe increased plant P uptake cannot be explained by changes in the soil N and P pools,and are related to increased AMF colonization.  The biodiversity of the AMF populationand the changes in microbial community structure over the growing season must still beevaluated.  The possibility that including pulse crops in a durum-based rotation have apositive influence on the soil microbial populations must still be looked into, as well asrepeated sampling and analysis in 2005.ReferencesAuge, R. M., J. L. Moore, K. Cho, J. C. Stutz, D. M. Sylvia, A. K. Al-Agely and A. M.Saxton. 2003. 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Influence of pulse crops on arbuscular mycorrhizal fungi in a durum-based cropping system

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