Mitigation of alkaline stress

Summary: In a greenhouse experiment conducted during the spring-summer of 2009, researchers aimed to investigate two hypotheses concerning arbuscular-mycorrhizal (AM) inoculation and fertilization regimes on zucchini plants (Cucurbita pepo L.). The first hypothesis proposed that AM inoculation using a biofertilizer containing Glomus intraradices could mitigate alkalinity issues, while the second hypothesis suggested that mineral fertilization might negatively affect AM development compared to organic fertilization on an equivalent nutrient basis.

The experiment involved growing both AM and non-AM zucchini plants in sand culture under two pH conditions in the nutrient solution (pH 6.0 or 8.1) and two fertilization methods (organic or mineral). The high-pH nutrient solution contained additional NaHCO3 and CaCO3. Results indicated that increasing NaHCO3 concentration in the nutrient solution led to decreased yield, plant growth, SPAD index, net assimilation of CO2 (ACO2), and concentrations of various nutrients in leaf tissue.

Under alkaline conditions, AM-inoculated plants exhibited higher total and marketable yield as well as total biomass compared to non-AM plants. The enhanced yield and biomass were attributed to the ability of AM-inoculated plants to maintain higher SPAD index, net ACO2, and better nutritional status, including higher levels of P, K, Fe, Mn, and Zn, and lower accumulation of Na in response to bicarbonate stress.

Interestingly, while organic-fertilized plants exhibited significantly higher root colonization by AM fungi compared to mineral-fertilized plants, the latter displayed the highest yield and biomass production. This outcome was attributed to the better nutritional status, including higher levels of N, P, Ca, and Mg, as well as larger leaf area, SPAD index, and ACO2 in mineral-fertilized plants.

In summary, the experiment demonstrated the potential of AM inoculation to mitigate alkalinity stress and enhance plant growth and yield, while also highlighting the complex interactions between fertilization methods, AM colonization, and plant nutrient uptake and performance.