Abstract
Almost all elevated atmospheric CO2 concentrations (eCO2) studies have not addressed the potential responses of plant growth to different CO2 in daytime and nighttime. The present study was to determine the impact of daytime and/or nighttime eCO2 on growth and quality of mulberry (Morus alba L.), a perennial multipurpose cash plant. Six-month-old mulberry seedlings were hence grown in environmentally auto-controlled growth chambers under four CO2 concentrations: (1) ambient CO2 (ACO2, 410 μmol mol–1 daytime/460 μmol mol–1 nighttime), (2) sole daytime elevated CO2 (DeCO2, 710 μmol mol–1/460 μmol mol–1), (3) sole nighttime elevated CO2 (NeCO2, 410 μmol mol–1/760 μmol mol–1), and (4) continuous daytime and nighttime elevated CO2 (D + NeCO2, 710 μmol mol–1/760 μmol mol–1). Plant growth characteristics, nutrient uptake, and leaf quality were then examined after 120 days of CO2 exposure. Compared to control, DeCO2 and (D + N)eCO2 increased plant biomass production and thus the harvest of nutrients and accumulation of leaf carbohydrates (starch, soluble sugar, and fatty acid) and N-containing compounds (free amino acid and protein), though there were some decreases in the concentration of leaf N, P, Mg, Fe, and Zn. NeCO2 had no significant effects on leaf yield but an extent positive effect on leaf nutritional quality due to their concentration increase in leaf B, Cu, starch, and soluble sugar. Meanwhile, (D + N)eCO2 decreased mulberry leaf yield and harvest of nutritious compounds for silkworm when compared with DeCO2. The reason may be associated to N, P, Mg, Fe, and Zn that are closely related to leaf pigment and N metabolism. Therefore, the rational application of mineral nutrient (especially N, P, Fe, Mg, and Zn) fertilizers is important for a sustainable mulberry production under future atmosphere CO2 concentrations.
Highlights
The increasing atmosphere CO2 concentration has become one of the worldwide hot issues
The 710/460 μmol mol−1 DeCO2 significantly enhanced leaf biomass by 102%, stem biomass by 187%, root biomass by 90%, and total plant biomass by 113%, compared with mulberry plants grown under ACO2 (Figure 2A)
Stem, root, and total plant biomass production in mulberry grown under 710/760 μmol mol−1 (D + N)elevated CO2 (eCO2) was, respectively, increased by 42, 42, 22, FIGURE 2 | Plant biomass production (A) and carbon accumulation (B) of mulberry seedlings grown for 120 days under four different daytime and nighttime CO2 concentrations inside environmentally controlled glass growth chambers
Summary
The increasing atmosphere CO2 concentration has become one of the worldwide hot issues. Sekhar et al (2014, 2015) showed that plant height, leaf numbers, branches, total shoot length, and biomass production in 6 month-old mulberry Selection-13 (S13) and Kanva-2 (K2) genotypes were lower under ambient CO2 than under 550 μmol mol−1 eCO2 for 90 days. Such a 550 μmol mol−1 eCO2 treatment significantly increased net photosynthetic rates, intercellular CO2 concentration, photosynthetic N and water use efficiency, and Rubisco, chlorophyll a, starch, and total sugar concentrations, but significantly decreased stomatal conductance, transpiration rates, and light compensation point in the fully expanded upper third or fourth leaf, respectively (Sekhar et al, 2015). 1https://www.co2.earth relatively less attention has been paid to their changes into leaf nutrition quality of mulberry trees, especially their macro- and micronutrients under eCO2, considering that N, P, K, Ca, Mg, boron (B), zinc (Zn), iron (Fe), copper (Cu), and manganese (Mn) in the mulberry leaves are essential to silkworm and other animals (Radojkovic et al, 2014)
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