Plant homeostasis, growth and development in natural and artificial soils

Abstract

Plant growth and development is dependent on factors internal and external to the plant. The effect of nutrient on root morphology has been widely studied in artificial soils or solution cultures. However, the effect of this experimental procedure has never been assessed by comparing plant response in artificial and natural soils. In a laboratory experiment, plants were submitted to three levels of nitrogen supply, in one artificial substratum made of pure sand and one natural soil. Deep differences in plant homeostasis, growth and development were observed between natural and artificial soils: (i) the chemical composition of plant tissues (%C and %N) was changing according to the nitrogen gradient in the artificial substratum, whereas it remained constant in the natural soil; (ii) the same amount of added nitrogen was responsible for a 17% increase in total plant production in the natural soil as compared with the artificial substratum; (iii) plant development differed deeply in the two substrata: in the artificial substratum, the shoot to root ratio was stable whereas the thick to fine roots ratio was increasing with increasing N supply, suggesting an exploration strategy to found an absent limiting nutrient. Conversely, in the natural soil, the thick to fine roots ratio was stable whereas the shoot to root ratio was decreasing with increasing N supply, suggesting an exploitation strategy dedicated to extract a limiting nutrient present in soil components. Even if mechanisms responsible for changes in homeostasis, growth and development were not elucidated, these results stress the importance to consider substrata with a minimal level of complexity if we expect to understand plant growth and development in natural conditions thanks to laboratory experiments.