Critical Leaf Magnesium Thresholds and the Impact of Magnesium on Plant Growth and Photo-Oxidative Defense: A Systematic Review and Meta-Analysis From 70 Years of Research

Abstract

Magnesium (Mg) deficiency in plants is a widespread problem affecting productivity and quality in agricultural systems and forestry. Although numerous studies addressed the effect of Mg deficiency on biomass and photosynthetic CO 2 assimilation, a summary evaluation of the effect of Mg supply on plant growth and photosynthesis is so far missing. We performed a systematic review and meta-analysis to collect and combine all relevant scientifically published data on the relationship between Mg nutrition and parameters that can be related to plant growth such as root and shoot biomass, harvestable yield, net CO 2 assimilation and antioxidant enzyme activities. Moreover, this data pool was used to calculate critical Mg leaf concentrations for biomass and net CO 2 assimilation for various plant species. Summarizing all studies included in our analysis, adequate Mg supply enhances net CO 2 assimilation by 140%, leading to a biomass increase of 61% compared to Mg deficient control plants. Biomass partitioning between shoot and root is not only sensitive to Mg nutrition, but highly affected by the experimental cultivation technique. If plants are grown under adequate Mg supply during initial growth stages before exposing them to Mg deficiency, the shoot-root ratio was not affected. Otherwise, the shoot-root ratio significantly decreased in contrast to Mg deficient control plants. Concentration of reactive oxygen species decreased under adequate Mg supply by 31% compared to Mg deficient plants, resulting in decreased activities of most antioxidant enzymes and metabolites under adequate Mg supply. We combined all published data relating leaf Mg concentrations to growth and found a critical leaf Mg range for dry weight between 0.1 and 0.2% which was valid for numerous crop species such as wheat, potato, rice, maize, sorghum and barley. Critical leaf Mg concentrations for net CO 2 assimilation were higher than for biomass for most species, e.g., potato, rice, citrus, and cotton. In conclusion, our evaluation can be used to identify Mg nutritional status in plants and may help to optimize fertilization strategies. It quantifies the demand of Mg for various crop and tree species for maintaining important physiological processes such as net CO 2 assimilation that is required for optimal plant growth and yield.

Magnesium supply regulate leaf nutrition and plant growth of soilless cultured cherry tomato - interaction with potassium

“…Clear relationships were observed between SPAD reading, photosynthesis rate, plant dry matter accumulation and leaf Mg concentration. It may be explained by the adequate Mg supply during initial growth stages [34]. These results clearly demonstrate the importance of Mg supply in maintaining strong photosynthesis to produce cherry tomato dry matter.…”

“…The plant dry matter accumulation increased first with solution Mg concentration increased but decreased when Mg treatment concentrations over 8 mM and 4 mM at the first and second harvest periods. The positive effects of Mg nutrient supply on plant growth have been discussed extensively [33,34,36], the inhibitive effects observed in this study have rarely been reported due to the difficulty of detecting toxicity symptoms, even at high concentrations [37]. The inhibitive effect of high Mg supply on plant dry matter accumulation was caused by slight decreases in the photosynthetic rate at first and second harvest.…”

“…Which can satisfy the requirements for optimized SPAD, photosynthesis rate and plant dry matter accumulation combined with high fruit yield. Those leaf Mg concentrations are slightly higher than that reported in a previous study, which demonstrated that tomato dry matter accumulation responded best at 3.9 g kg -1 plant Mg concentration [34][35]. However, excessive Mg concentrations (> 8 mM) in solution should be avoided due to the risk of adverse effects on photosynthesis.…”

“…Similarly, dry matter accumulation in Pinus radiata was shown to be inhibited by Mg deficiency [33]. Hauer-Jákli and Tränkner (2019) confirmed 3.9 g kg -1 as the critical leaf Mg concentration for tomato dry matter accumulation [34] based on the results of Kasinath et al (2014), which was lower than this study [35]. The different critical leaf Mg concentrations among SPAD reading, photosynthesis rate and plant dry matter accumulation indicated that sufficient Mg supply can guarantee the chlorophyll concentration and the production of photosynthates, which was consistent with the result that plant growth reduction appears as a later response compared with chlorophyll content decrease to Mg deficiency [14].…”

Sintomas de deficiência de macronutrientes em alface

“…O restante acompanha o Ca na formação da parede celular (Prado, 2008;Gerendás & Führs, 2013). Esse nutriente é essencial para os cloroplastos, sendo o átomo central da molécula de clorofila, sendo a quantidade dessa influenciada por variações no teor de Mg no citossol e no cloroplasto (Ding et al, 2006;Hauer-Jákli & Tränkner, 2019). Assim, na deficiência de Mg, há diminuição na síntese de clorofila e consequentemente, na taxa fotossintética.…”