Mineral Content and Root Respiration of In Vitro Grown Kiwifruit Plantlets Treated with Two Humic Fractions

ABSTRACT

In vitro grown kiwifruit (Actinidia deliciosa, Liang and Ferguson) plantlets were treated with two humic fractions distinguished by two different relative molecular mass and characterized through their elemental composition and ¹³Carbon (C) nuclear magnetic resonance. The effects exerted on plant growth, root morphology, and nutrition were evidenced by means of leaves and roots mineral content, root respiration, and nitrate reductase activity. The two humic substances differentially influenced the studied parameters. The lower molecular fraction humic substance, endowed with a higher content of phenolic and carboxylic groups, caused an enhanced content of micro- and macro-elements, together with a higher root respiration at lower concentrations (0.5–1 mg C L^{− 1}). The high molecular fraction humic substance, needed higher concentrations (> 5 mg C L^{− 1}) in order to achieve similar effects. This fraction also caused major changes on root morphology. The ability to improve micronutrient assimilation, in particular iron, confirmed the agronomic importance of humic substances on soil fertility.

Keywords:

• ¹³C NMR
• humic substances
• in vitro
• Kiwifruit
• mineral nutrition

ACKNOWLEDGMENTS

The research was supported by funds from the Italian Ministry of Education, University and Research (RFO ex 60%) of G. Marino, S. Nardi, and C. Gessa. The Authors thank Professor Bruno Marangoni, Dipartimento di Colture Arboree, Bologna, for critically reviewing the manuscript, and Azienda Battistini, Cesena (FC), Italy, for providing plant material.

Notes

^x Means ± standard errors (n = 4).

∗

∗∗∗

∗.Means associated to different letters are statistically different (Duncan's test).

^x CO₂ production was detected in roots of 35-d old plantlets after incubation in a 1 mM CaSO₄+ 5 mM MES solution.

^y Values for CO₂ fixation were detected in 28-d old plantlets after 3 h exposure to ligth (120 μ mol m⁻² s^{− 1} PAR).