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Nitrogen Workshop 2012
Effects of arbuscular mycorrhizal symbiosis on the nitrogen uptake of three durum wheat genotypes from two different organic sources Saia, S.a, Ruisi, P.a, García-Garrido, J.M.b, Amato, G.a, Giambalvo, D.a a Dipartimento dei Sistemi Agro-Ambientali, Università degli Studi di Palermo, Palermo, Italy b Departamento de Microbiología, Estación Experimental de Zaidín, CSIC, Granada, Spain
1. Background & Objectives Arbuscular mycorrhizal (AM) fungi are obligate symbionts of the majority of terrestrial plants. By enhancing nutrient and water uptake, AM symbiosis improves the host plant’s growth, nutrient status, and response to biotic and abiotic stress. The role of AM fungi in nitrogen (N) acquisition remains unclear. Although several studies have shown that AM symbiosis enhances N uptake from inorganic sources (Cliquet et al., 1997), its effects on N uptake from organic sources remains unclear, particularly when both AM hyphae and plant roots can utilize the same source (Hodge, 2003; Hodge et al., 2000). These disparate results may result from the different plant species and genotypes used in the experiments, as well as the type and complexity of the added organic material (e.g., the carbon:nitrogen ratio), the different AM fungus species and strains, and the amount and quality of the bacterial populations. The present study tested the hypothesis that AM symbiosis enhances the N uptake of durum wheat (Triticum durum) from organic sources and examined whether N uptake varies with the type of organic material and the wheat genotype.
2. Materials & Methods A pot experiment was conducted in a climate-controlled glasshouse (25/19°C day/night temperature; 16 h photoperiod). A complete randomized factorial design with four replicates was adopted. Treatments were: i) AM symbiosis, inoculation with Glomus mosseae (+Myc) and uninoculated control (Myc); ii) organic matter (OM), the addition of 4.6 g 15N-enriched maize biomass per kg of soil in the form of maize leaves (+ML: 1.90% N content, 4.78 15N atom%) or maize roots (+MR: 1.56% N content, 3.94 15N atom%); and iii) wheat genotype, Cappelli (an old Italian cultivar), Scorsonera (a Sicilian landrace), and Simeto (the most widely grown cultivar in Italy). Each pot was filled with 600 g of a quartz sand:soil mixture (2:1). Soil properties were: clay 20% and sand 37%; pH 8.1 (soil:water 1:2); 1.04% organic C; 1.05‰ total N. The soil mixture was steam-sterilised. Before starting the experiment, a soil filtrate was inoculated to normalise the microbial community. Three wheat plants per pot were grown. During the experiment, each pot received 5 ml of a modified Hoagland’s solution (with no phosphorus and 10% N) once every 5 days. The dry weights of wheat shoots and roots were recorded 9 weeks after the emergence of the crop and both fractions were analyzed for total N and 15N enrichment using an elemental analyzer– isotope ratio mass spectrometer. Wheat roots were stained with 0.05% trypan blue in lactic acid and AM infection was measured using the grid intersect method (Giovannetti and Mosse, 1980). The recovery of the applied 15N in wheat was calculated according to Allen et al. (2004). An analysis of variance was performed according to the experimental design.
3. Results & Discussion No AM root infection was observed in the –Myc treatment. In the +Myc treatment, AM root infection varied weakly but significantly with the genotype (Simeto Scorsonera = Cappelli) and with the type of organic matter (+ML +MR) added (Table 1). Inoculation with AM fungi (+Myc treatment) significantly increased both plant growth and total N uptake compared to Myc treatments (+15% and +22%, respectively). However, AM inoculation significantly decreased the
Nitrogen Workshop 2012
fraction of 15N recovered from the added OM (–34% on average compared to Myc) with differences among the genotypes but not between +ML and +MR. This decrease was lower in Cappelli and Scorsonera than in Simeto. Moreover, the latter genotype showed the highest 15N recovery fraction when grown without AM symbiosis and the lowest benefit of AM symbiosis in terms of total N uptake. The lower fraction of 15N recovered from the added OM (independently from the type of OM) observed in +Myc treatments is difficult to explain but may depend on the capacity of the fungus to take up N from decomposing OM in the form of amino acids and other products. Thus, fungal uptake of dissolved organic N is greater than host plant uptake (Rains and Bledsoe, 2007); the fungus could utilize this element primarily for its own growth and metabolism.
4. Conclusion Our results show that AM symbiosis benefits the host plant in terms of both growth and total N uptake. Further analyses of the N content and the relative 15N concentration of the AM extra-radical mycelium are needed to elucidate the complex symbiotic relationships between plants and fungi and their influence on the acquisition of N from different sources.
References Allen S.C., Jose S., Nair P.K.R., Brecke B.J. and Ramsey C.L. 2004. Competition for 15N-labeled fertilizer in a pecan (Carya illinoensis K Koch)-cotton (Gossypium hirsutum L) alley cropping system in the southern United States. Plant and Soil 263, 151-164.
Cliquet J.B., Murray P.J. and Boucaud J. 1997. Effect of the arbuscular mycorrhizal fungus Glomus fasciculatum on the uptake of amino nitrogen by Lolium perenne. New Phytologist 137, 345-349.
Giovannetti M. and Mosse B. 1980. An evaluation of techniques for measuring vesicular-arbuscular mycorrhizal infection roots. New Phytologist 84, 489-500.
Hodge A. 2003. N capture by Plantago lanceolata and Brassica napus from organic material – the influence of spatial dispersion, plant competition and an arbuscular mycorrhizal fungus. Journal of Experimental Botany 54, 2331–2342.
Hodge A., Robinson D. and Fitter A.H. 2000. An arbuscular mycorrhizal inoculum enhances root proliferation in, but not nitrogen capture from, nutrient-rich patches in soil. New Phytologist 145, 575-584.
Rains K.C. and Bledsoe C.S. 2007. Rapid uptake of 15N-ammonium and 13C- glycine, 15N by arbuscular and ericoid mycorrhizal plants native to a Northern California coastal pygmy forest. Soil Biology and Biochemistry 39, 1078-1086.
Nitrogen Workshop 2012
Effects of integrated weed management in cropping systems on soils, microbial activity and N2O fluxes Vermue, A.a, Philippot, L.b, Munier-Jolain N.a, Bizouard, F.b, Bru, D.b, Coffin A.a, Hénault, C.c, Nicolardot, B.a a UMR 1210 Biologie et Gestion des Adventices, INRA-AgroSup Dijon-UB, Dijon, France b UMR 1229 Microbiologie et Science du Sol, INRA-UB, Dijon, France c UR 0272 Science du Sol, INRA, Orléans, France
1. Background & Objectives Cultivated soils have been widely highlighted as a major source of nitrous oxide (N2O) emissions.
This suggests that greenhouse gas emissions should be taken in account when evaluating the impact of new cropping systems. The development of integrated weed management in cropping systems introduces new agricultural practices (combinations of crop rotation, soil management, fertilization, and mechanical and chemical weed control, etc.), which may affect the microbial processes responsible for N2O production in soils. However, the effect of those practices remains to be assessed. Thus, the main objectives of our study is to provide (i) an accurate estimation of the intensity of N2O emissions from an integrated weed management system and (ii) a monitoring of soil chemical, physical, and biological parameters likely to affect N2O emissions over one year.
2. Materials & Methods This study focuses on two 10 year old cropping systems at the experimental site of Dijon-Epoisses (Eastern France). The first is a conventional system (CS) with local practices used for herbicide treatment frequency index and the second is an integrated weed management system (IWM) with halved herbicide treatment frequency index. The soils of both studied plots were described as calcareous clayey soils. Due to the unpredictable nature of N2O emissions from soils, the study of continuous data series is recommended. Nitrous oxide fluxes were measured using 12 automatic chambers coupled with an IR analyzer (Megatec 46i). The chambers were all setup in both plots in a 25 m radius from the analyzer. Soils water content and temperature were continuously measured using probes (respectively Campbell Scientific TDR CS616 and CS107, respectively). A monthly monitoring of the microbial communities was provided from the analyses of composite samples of 3 sub-samples taken around each chamber at two depths: 0-10 cm and 10-30 cm. The sizes of denitrifier, ammonia-oxidizing and total communities were assessed by quantitative PCR of selected genes (respectively nirK, nirS, nosZ; bacterial and crenarchaeal amoA, and 16S rRNA).These composite samples were also used for the determination of inorganic N soil contents by KCl extraction and colorimetric analyses. Data were statistically analysed using two-way ANOVA.
3. Results & Discussion N2O fluxes ranged between a flux of -6 to 26 g N-N2O ha-1 day-1 (Figure 1). Emissions were low during the measuring period with respective medians of 0 and 0.45 g N-N2O ha-1 day-1 for the IWM and CS systems. This may be explained by relatively low soil water content which ranged over the study period from 9 to 24 % (mean 15% dry soil) for the top 30 cm soil layer. Without rainfall, soils consumed rather than produced N2O. However, after major rainfall events, significant N2O emissions were observed. Finally over the measurement period, a net production of N2O was recorded on both plots, with average emissions of 2.8 and 1.6 g N-N2O ha-1 day-1 for the CS and IWM systems, N2O emissions from the CS system were significantly higher (P 0.001).
Figure 1. Mean N2O fluxes per system and 6 hours from integrated weed management and conventional systems.
Rainfall histogram corresponds to the sum of precipitation on the last 6 hours and arrows indicate crop harvest dates.
In contrast to the N2O emissions, the temporal variability of the abundances of both the denitrifying and ammonia-oxidizing communities was very low between May and July. The nirK and nirS gene copy numbers, which were used as proxies for the abundance of the denitrifiers, ranged between 3.9 X 10 to 2.5 X 10 copies per gram of dry soil. The abundance of crenarchaeal ammonia-oxidizers was in the same range while bacterial ammonia-oxidizers were less numerous with about 2.5 X 105 to 2.8 X 106 gene copies per gram of dry soil. The abundance of bacterial ammonia-oxidizers was also more affected by the management system than the other microbial guilds, especially in July when the highest N2O emissions were observed.
4. Conclusion This work highlights the potential impacts of new agricultural practices on greenhouses gas emissions with an original approach, which consists in continuous N2O fluxes measurements on site coupled with a long-term monitoring of microbial communities and soils parameters.
Nitrogen Workshop 2012 Effects of new catch crop and tillage systems on nitrogen management in sugar beet production Stavridou, E.a, Nielsen, O.b, Kristensen, H.L.a a Department of Food Science, Aarhus University, Denmark b NBR Nordic Beet Research, Denmark
1. Background & Objectives Tillage and autumn catch crops are two management practices that can influence the nitrogen (N) dynamics and yields of row crop production systems. Catch crops take up N during the autumn and may decrease N losses from agro-ecosystems with benefits for the environment (Kristensen and Thorup-Kristensen, 2004). Tillage treatments may influence N transformations and flows in the soil. Moreover, tillage is important for sugar beet growth, yield and quality (Jabro et al., 2010). The objective of this study was to investigate the effects of new combined catch crop and tillage systems on i) soil N content and ii) the growth and N uptake of a subsequent sugar beet crop.
2. Materials & Methods A two year field experiment comprising six catch crop-tillage treatments were arranged randomly in a split plot design with four replicate blocks with tillage as the main factor giving a total of 24 plots. White mustard (Sinapis alba L. “Accent”) was used as the catch crop. The experiment was located at Halsted (54o50’N, 11o13’E), West Lolland, Denmark on a sandy loam soil.
The tillage methods in combination with white mustard tested were: (i) strip tillage in September, where the catch crops were incorporated in the rows where sugar beets were going to grow in spring; (ii) reduced tillage, where sugar beet was sown directly in spring where catch crops grew during the winter season; (iii) early ploughing and incorporation of catch crops in September, which is the standard time of ploughing; (iv) late ploughing and incorporation of catch crops in November; (v) autumn ridges, where catch crops grew between them during the winter season. The strip tillage and autumn ridge treatments had only half the stand of white mustard compared to the reduced, early and late ploughing treatments. In addition, (vi) a control treatment without catch crop and with late ploughing was included.
Soil was sampled three times (September, December, March) in 0.25 and 0.50 m depth intervals to 2 m depth, extracted by 1 M KCl, and analysed for content of NH4+ and NO3- by continuous flow analysis. Root growth of catch crops was registered by use of minirhizotrons of 1.5 m length every two weeks starting four weeks after sowing. (Kristensen and ThorupKristensen, 2004). Biomass and N content of catch crops and sugar beets as well as sugar content of sugar beets were evaluated by the GLM procedure of the SAS statistical package.
3. Results & Discussion Tillage treatments did not affect the root growth of mustard during autumn and early spring.