The Shape of Roots Affects the Activity of Soil Ferments, Says a RUDN Agrochemist

A RUDN agrochemist demonstrated that the activity of soil ferments depends on the shape of a plant's root and increases with its growth. The discovery will lead to a better understanding of the chemical processes involved in plant development and improve the productivity of cultivated lands. The article was published in the Biology and Fertility of Soils journal.

RUDN pedologists made an experiment to find out how the shape of roots and stages of plant growth influenced the activity of ferments in rhizosphere—the soil around the roots. To do so, they grew legumes in small-sized pots. The pots were placed not vertically, but at 45° to the surface causing the roots to grow along their lower walls. The concentration of ferments was measured using the method of zymography. It involves fluorescent substances that start to glow when they come in contact with a certain ferment. The agrochemists made their measurements in the period of active plant growth, i.e. 1, 4, and 8 weeks after planting the seeds.

The experiment showed the distribution of the main ferments emitted by the plants (β-glycosidase, cellobiohydrolase, acidic phosphomonoesterase, and leucine aminopeptidase) in different parts of the root on all stages of its development. Lentil showed stable but slow growth of ferment activity on the surface of the root during all periods of vegetation. In lupine the activity of the main ferments increased by 50-100% on the 8th week of growth compared to weeks 1 and 4. This fact is explained by different shapes of their root systems. Lentil has one central root that is the thickest of all and has poorly developed offshoots. Lupine, on the contrary, doesn't have a main root, but the area of its side roots is 1.5-3.5 times bigger than in lentil. According to the researchers, the growth of its side roots is associated with 6 to 14 times increase of ferment activity in the soil around them.

Using a zymosphere, the researchers visualized the spatial distribution of ferment activity in situ on different growth stages. Lupine entered its reproductive stage during week 7 after planting and showed a radical increase in ferment activity thanks to rapid growth of side roots. In the case of lentils both vegetative growth and the expansion of rhizosphere remained on the same level, and the activity of ferments on the surface of its roots demonstrated stable growth.

"The stage of plant growth and the shape of the roots affected the activity of ferments in the rhizosphere. It increases while the plant growth and until it reaches the reproductive stage. Side roots take a much bigger volume of rhizosphere than root crops and have higher ferment activity on their surface. The effects of plant development and root shape should be taken into account in future studies of ferment activity of rhizosphere,"said Yakov Kuzyakov, a co-author of the work, Ph.D. in Biology, and a research associate at RUDN.

More information:
Xiaomin Ma et al. Spatiotemporal patterns of enzyme activities in the rhizosphere: effects of plant growth and root morphology, Biology and Fertility of Soils (2018). DOI: 10.1007/s00374-018-1305-6

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