Alain Olivier

Soil biochemical properties and microbial resilience in agroforestry systems: Effects on wheat growth under controlled drought and flooding conditions

Agroforestry is increasingly viewed as an effective means of maintaining or even increasing crop and tree productivity under climate change while promoting other ecosystem functions and services. This study focused on soil biochemical properties and resilience following disturbance within agroforestry and conventional agricultural systems and aimed to determine whether soil differences in terms of these biochemical properties and resilience would subsequently affect crop productivity under extreme soil water conditions. Two research sites that had been established on agricultural land were selected for this study. The first site included an 18-year-old windbreak, while the second site consisted in an 8-year-old tree-based intercropping system. In each site, soil samples were used for the determination of soil nutrient availability, microbial dynamics and microbial resilience to different wetting-drying perturbations and for a greenhouse pot experiment with wheat. Drying and flooding were selected as water stress treatments and compared to a control. These treatments were initiated at the beginning of the wheat anthesis period and maintained over 10 days. Trees contributed to increase soil nutrient pools, as evidenced by the higher extractable-P (both sites), and the higher total N and mineralizable N (tree-based intercropping site) found in the agroforestry compared to the conventional agricultural system. Metabolic quotient (qCO2) was lower in the agroforestry than in the conventional agricultural system, suggesting higher microbial substrate use efficiency in agroforestry systems. Microbial resilience was higher in the agroforestry soils compared to soils from the conventional agricultural system (windbreak site only). At the windbreak site, wheat growing in soils from agroforestry system exhibited higher aboveground biomass and number of grains per spike than in conventional agricultural system soils in the three water stress treatments. At the tree-based intercropping site, higher wheat biomass, grain yield and number of grains per spike were observed in agroforestry than in conventional agricultural system soils, but in the drought treatment only. Drought (windbreak site) and flooding (both sites) treatments significantly reduced wheat yield and 1000-grain weight in both types of system. Relationships between soil biochemical properties and soil microbial resilience or wheat productivity were strongly dependent on site. This study suggests that agroforestry systems may have a positive effect on soil biochemical properties and microbial resilience, which could operate positively on crop productivity and tolerance to severe water stress.

Tree-based intercropping systems increase growth and nutrient status of hybrid poplar: A case study from two Northeastern American experiments

Tree-based intercropping is considered to be a potentially useful land use system for mitigating negative environmental impacts from intensive agriculture such as nutrient leaching and greenhouse gas emissions. Rapid early growth of trees is critical for rapidly accruing environmental benefits provided by the trees. We tested the hypothesis that intercropping increases the growth and nutrient status of young hybrid poplars (Populus spp.), compared to a harrowing alley treatment (i.e., no intercrop), in two experimental sites (St-Rémi and St-Edouard) in southern Québec, Canada. Three hybrid poplar clones (TD3230, Populus trichocarpa x deltoides; DN3308, P. deltoides x nigra; and NM3729, P. nigra x maximowiczii) were planted at St-Rémi. Clones DN3333 and DN3570 were planted at St-Edouard. At St-Rémi, intercropping comprised a 4-year succession of three crops of soybean (Glycine max (L.) Merr.) and barley (Hordeum vulgare L.). At St-Edouard, intercropping comprised a 3-year succession of buckwheat (Fagopyrum esculentum Moench), winter rye (Secale cereale L.), and winter wheat (Triticum aestivum L.). At St-Rémi, four years after treatment began, leafless aboveground biomass of hybrid poplars in the intercropping treatment was 37% higher compared to that in the harrowing treatment. At St-Edouard, after the third growing season, leafless aboveground biomass of hybrid poplars in the intercropping treatment was significantly higher by 40%. Vector analysis of foliar nutrient concentrations and comparison with critical concentration values showed that N (both sites) and K (St-Edouard) were the most limiting nutrients. Hybrid poplar clones responded similarly to treatments, with no consistent differences in tree growth observed between clones. We conclude that tree-based intercropping systems may offer an effective means of improving the early growth of hybrid poplars planted to provide both environmental services and high-value timber.

The impact of lime and organic fertilization on the growth of wild-simulated American ginseng

A 5-yr experiment was undertaken in a red maple forest to evaluate the effects of lime and organic fertilizer application on the growth parameters of wild-simulated American ginseng growing on a very acidi c soil. The application of lime had a positive impact on ginseng emergence and survival rate; it also significantly increased soil Ca, as compared to no application (control). During the last years of the experiment, adding lime also increased leaf area, a s well as shoot and root mass of ginseng. Adding lime and organic fertilizer together positively affected ginseng survival rate and root mass, as compared to adding lime alone. These results indicate that liming can improve the growth and survival of Amer ican ginseng during the first 5 yr of its development in this very acidic maple forest soil. The improvement could be due, at least partly, to increased Ca content in the soil. Addition of organic fertilizer would be beneficial as long as sufficient Ca2+is provided to alleviate the Al toxicity of thi...

Growing American ginseng in maple forests as an alternative land-use system in Québec, Canada

American ginseng (Panax quinquefolium) is a medicinal crop which provides tens of millions of dollars in income every year for Canadian farmers. Most of the ginseng roots are produced in open fields under expensive shade structures. Farmers need to plant ginseng at a very high density to achieve profitability. Since high planting densities are related to high disease levels, field-cultivated ginseng requires frequent applications of pesticide. Growing ginseng in forests eliminates the need of a shade structure and may reduce the need for pesticides. Thus, an experiment was performed in a maple (Acer rubrum) forest in Québec to evaluate the effects of nutrient inputs such as lime or compost on ginseng development. Ginseng emergence and survival rates, leaf area and foliar and root weight were evaluated for each treatment. Soil samples were taken in each plot to determine the concentration of various soil nutrients. During the first two years of the experiment, it was noted that the application of lime had a significative positive effect on ginseng growth. This effect could be related to higher calcium concentration and/or lower aluminium toxicity. Liming would be an efficient way to improve the early development of ginseng in maple forests. This practice is also known to improve the health of maple stands.

The Effects of CO2 Enrichment, Increased Light Irradiance, and Reduced Sucrose Concentration on Acclimatization of Micropropagated American Ginseng Plantlets

ABSTRACT American ginseng (Panax quinquefolius L.) plantlets produced by somatic embryogenesis were pre-acclimatized for four weeks inside growth chambers in a factorial design. The three factors of the experiment were CO2 concentration (400 and 3000 μL L−1), photosynthetic photon flux (30 and 50 μmol m−2 s−1) and sucrose concentration (0 and 15 g L−1) in the culture medium. The plantlets were subsequently transferred into a greenhouse where they were acclimatized for two weeks. Regardless of photosynthetic photon flux and sucrose levels, CO2 enrichment during the pre-acclimatization phase significantly increased (6.3%) the fresh mass of American ginseng plantlets in the growth chambers. This positive effect resulted in a 26.4% increase in fresh mass after the acclimatization phase in the greenhouse. CO2 enrichment during the pre-acclimatization phase also significantly increased (32%) leaf area after acclimatization, but had no significant effect on dry mass, height nor survival. Increased light irradiance and reduced sucrose concentration had no significant effects on the growth parameters and survival of American ginseng plantlets. Despite the biological and ecological constraints that limit growth and development of this species, CO2 enrichment could enhance its acclimatization.