Earth's climate is changing. Anthropogenic activity, amongst other catalyzers, is responsible for raising atmospheric carbon dioxide (CO2) levels in a way that impact overall climate change effects and dramatically influence plant life and nutrition. Key contributors of essential nutrients for human health, iron (Fe) and zinc (Zn), legumes are also one of most sensitive plant families to elevated concentrations of CO2 (e[CO2]), thus the importance of unraveling the effects and mechanisms underlying e[CO2] responses on biomass yield, photosynthetic processes, nutritional value and soil microbiome communities modulation. In that way, this thesis relied on free air CO2 enriched (FACE) experiments, a unique platform to study the increasing levels of atmospheric CO2 in plants, focusing three genotypes of common bean (Phaseolus vulgaris L.) (G1-G2-G3). The genotypes were grown permanently in ambient [CO2] (control, a[CO2]) or were exposed to a month of e[CO2] (600 pm) during pod-filling stage. Initially, overall plant biomass increased (33-35 %) on e[CO2] group, with G2 presenting the higher increase for the vegetative tissue and G1 the most yield-responsive biomass accumulation in grains, 12%. Active and passive ChlF measurements, respectively with LIFT and FloX instruments, displayed G1, from the three genotypes, as having the lower solar-induced ChlF (SIF) yield and higher efficiency of photosystem II observed at e[CO2], during the end of pod filling. Considering the nutritional value, e[CO2] impact on P. vulgaris was highly dependent on the genotype, mineral and tissue tested. At the foliar level, Fe concentrations were found to be increased in G1 and decreased on G3, whereas considering the edible portion of the plant (grain tissue), the concentration of that same nutrient was higher for G2 and lower for G1 and G3. As these nutrient fluctuations cannot be explained by augmented biomass dilution-effect, legumes response may operate on the molecular level, therefore being important to analyze the expression of genes related to abiotic stress and Fe and Zn metabolism for G1 and G2. Indeed, even considering there was no alteration of ZIP1 expression, e[CO2] conditions appeared to promote a 1.1-fold expression increase of FRO2 in G1 leaf samples. Likewise, bHLH148 expression gene was also up-regulated for the same genotype and conditions. As several bHLH transcription factors are key players on iron homeostasis and act as positive regulators of FRO2, this may indicate an activation of Fe uptake machinery under an e[CO2] environment, eventually contributing for increased iron concentrations. We also conducted a total phenolic content determination for G1 and G2 and found that both genotypes displayed significant reductions (27-28 %) at e[CO2] conditions. Remarkably, the follow-up assessment on antioxidant activity did not show any differences considering ABTS assay and a 28% reduction for G1 with DPPH assay. At last and considering the importance of soil microbial communities to plant development at changing environments, the overall soil microbiota composition was influenced by time, but unaffected by higher levels of [CO2], with significant differences regarding Proteobacteria, Bacteroidetes, Actinobacteria and Chloroflexi phyla. This study contributes in that way to a better understanding on the bilateral responses of legumes to short-term exposure to e[CO2]. Even though a clear biomass increase, P. vulgaris plants have also had their nutritional value impacted, with shifting concentrations of micronutrients and phenolic content reductions.
|Date of Award||15 Feb 2021|
- Universidade Católica Portuguesa
|Supervisor||Marta Vasconcelos (Supervisor) & Célia Manaia (Co-Supervisor)|
- Free-air CO2 enrichment (FACE)
- Nutritional value
- Mestrado em Microbiologia Aplicada