Identification and Quantification of Cause and Effects in Symbiosis of Corn with Arbuscular Mycorrehiza Fungus using Structural Equation Modeling Approach

پژوهشهای زراعی ایران

Article 21, Volume 13, Issue 2 - Serial Number 38, July 2015, Pages 420-433   

Document Type: Research Article

DOI: 10.22067/gsc.v13i2.40356

Authors

M Jahan^* ; M Nasiri mahalati

Ferdowsi University of Mashhad

Abstract

Considering to necessity and importance of determining mycorrhizal symbiosis level and its effects on crop agroecological characteristics as well as other related factors affecting this relationship, beside, the lack of an assured method for this purpose, the present study designed based on new perspectives and insights for determining cause and effects relations, latent variables using structural equation modeling (SEM) approach. A field experiment was conducted during 2 years. A split plots arrangement based on randomized complete block design (RCBD) with three replications was used. Treatments consisted four cropping systems (high, medium, and low input conventional as well as ecological system) and four inoculations (mycorrhizae fungus: Glomus intraradices, plant growth promoting rhizobacteria (PGPR): (Azospirillum brasilense, Azotobacter paspali, dual inoculation: (fungus plus bacteria), and no-inoculation (control), which were allocated to main plots and sub plots, respectively. At the first step, a confirmatory factor analyzing was conducted resulted to two distinguished factors, and then the variables which had the most loads (weight) on one of these two factors were determined. At the second step, considering ecophysiological basis of crops growth and development, in order to continue analyzing, the first factor (including: leaf area index (LAI), root length colonization percent (RLCP), dry matter (DM), stem diameter (D), SPAD readings) and the second factor (including: maximum photosynthesis (Amax), specific root length (SRL), canopy temperature (CT), plant height (H), soil respiration rate (SRR), variable chlorophyll fluorescence to maximum chlorophyll fluorescence (Fv/Fm), plant tissue phosphorus content (%P) determined resource capture latent construct and resource utilization latent construct, respectively. Correlation coefficients, squared multiple correlation coefficients, covariance matrices, direct and indirect path coefficients were calculated. Finally, RMSE and other validity tests applied to evaluate the model efficacy. The results showed the variables including LAI, D, DM, SPAD readings, H and CT had the most causality effect on corn yield production under field conditions associated with mycorrhizal fungus. At a glance, it seems the direct advantages of mycorrhizal symbiosis revealed by 35 percent cooperation in resource capture.

Keywords

Cause and effect relationship; Direct effect; Factor analysis; Path analysis; Path coefficient

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