Granular Calcite Stimulates Natural Mycorrhization and Growth of White Spruce Seedlings in Peat-Based Substrates in Forest Nursery.

Mohammed S Lamhamedi,Isabelle Auger,Mario Renaud,J André Fortin

doi:10.3390/microorganisms8071088

Mohammed S Lamhamedi, Isabelle Auger + Show 2 more

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https://doi.org/10.3390/microorganisms8071088

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Abstract

The acidity of peat-based substrates used in forest nurseries limits seedling mineral nutrition and growth as well as the activity of microorganisms. To our knowledge, no study has yet evaluated the use of granular calcite as a covering material to increase pH, calcium and CO2 concentrations in the rhizosphere and ectomycorrhizal development. The objective is to compare different covering treatments on early colonization of the roots by ectomycorrhizal fungi, as well as the growth and calcium nutrition of white spruce seedlings in the forest nursery. Three treatments were used to cover the plant cavities (Silica (29 g/cavity; control treatment), Calcite (24 g/cavity) and calcite+ (31 g/cavity)) and were distributed randomly inside each of the five complete blocks of the experimental design. The results show that calcite stimulates natural mycorrhization. Seedlings grown with calcite have significant gains for several growth and physiological variables, and that the periphery of their root plugs are more colonized by the extramatrical phase of ectomycorrhizal fungi, thus improving root-plug cohesion. The authors discuss the operational scope of the results in relation to the tolerance of seedlings to environmental stress and the improvement of their quality, both in the nursery and in reforestation sites.

Highlights

The production of boreal forest seedlings in peat-based substrates presents a significant challenge because of the acidity and variations in the physical properties of these substrates over a production cycle
The main objectives of this study are: (i) to compare the effects of granular calcite and silica on the main physicochemical characteristics of the substrate, on the early extension of the extramatrical phase of ectomycorrhizal fungi and on the growth and calcium nutrition of containerized white spruce seedlings during the second growing season (2+0) in a nursery, and (ii) to compare logistic models of seedling growth based on covering material and the presence or absence of ectomycorrhizal colonization
The presence of ectomycorrhizal fungi improves the plasticity and functional features of planted seedlings, including the acquisition, absorption and transport of water and mineral elements, gas exchanges, and tolerance to different environmental stresses [40,52,77,78]. This is the first assessment of the effects of granular calcite used as covering material on substrate physicochemistry, early root colonization by ectomycorrhizal fungi, growth and calcium nutrition of forest seedlings produced at an operational scale

Summary

Introduction

The production of boreal forest seedlings in peat-based substrates presents a significant challenge because of the acidity and variations in the physical properties of these substrates over a production cycle. These factors limit oxygen availability and affect the absorption kinetics of mineral nutrients, microorganism activity, along with shoot and root growth [1,2,3,4]. The container cavities in which the seedlings are produced are usually covered with silica Due to their chemical composition, the granules or fine particles of silica (SiO2) do not induce variations in the pH of the substrate. Rapid, uncontrolled pH increases of the peat-based substrate (up to values above 7) results in symptoms of mineral deficiency (e.g., iron, boron) and stunted coniferous and deciduous seedlings, which fail to meet morphophysiological quality standards [3,5,8]

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