What We Learned About Roots in 2023

• Most studies in 2023 focused on root responses to agricultural practices to improve yield using fewer resources.
• Research into the basic science of roots and the influence of biotic and abiotic factors are the second significant areas of study.
• Fine roots are a particular area of focus, given their importance in nutrient and water uptake and carbon sequestration.

Minirhizotrons allow non-destructive repeat observations of the underground root systems’ morphology, growth, and dynamics. Basic and applied agriculture and ecology research are profiting from this novel technique. 2023 saw many novel discoveries about roots and confirmed several emerging trends. The research findings reported in twenty peer-reviewed papers published in 2023 have been grouped into significant areas of interest in the article.

Growth

Root growth is influenced by soils, the gender of plants, and genetics, with temporal variations arising due to temperature and stress.

Sugarcane roots developed mainly in the 0-0.20 m layer in homogeneous Ferralsol soils and climate. Sugarcane genetics was also essential, and one variety outperformed others by producing higher economic returns by growing more roots in deeper soils.

The choice of rootstocks can alter root production patterns in grapevines. The depth at which new roots are formed is influenced by rootstocks. However, regardless of when new root formation starts, it peaks during flowering in all rootstocks. Warmer temperatures can encourage more root formation in late autumn and winter. This is a typical example of a root response to agricultural practices.

A provenance and its soil type can influence pine root traits such as root volume, surface area, length, specific root length, and biomass. Soil bulk density, total soil potassium, soil organic carbon, and soil particle composition were the factors that influenced root morphology.

The female Idesia polycarpa’s fine roots were more well developed with higher total root length, volume, surface area, root tip numbers, and total average diameter than male plants, and the difference was the most in the fruit material accumulation stage, see Figure 1. Soil carbon, nitrogen, and potassium utilization differed between the genders.

Female plant rhizosphere secretes more carbohydrates to facilitate greater microbial abundance for better plant nutrient availability. During ripening, soil nitrogen and potassium were significantly different. Though the dominant bacteria and fungi were the same in the rhizosphere around the roots of the two genders, the fungi numbers differed at some stages.

Resistance to Stress

Roots are essential for plant adaptation and resistance to drought and waterlogging. Root morphological features are found to be an essential consideration. In normal moisture conditions, cotton roots grow unaffected. However, in waterlogged conditions, roots with diameters less than <2.0 mm, especially <1.0 mm, were stimulated, but larger roots’ growth was unaffected. Also, cotton plants grow more roots in 24-60 cm soil depth instead of the usual 0-24 cm soil depth, indicating they found a way to avoid waterlogging and potential rotting.

Figure 1: “Characteristics of fine roots in male and female plants at different periods (D1: flowering stage; D2: fruit accumulation stage; and D3: fruit maturity stage). (A) Total length, (B) total surface area, (C) total volume, (D) total average diameter, and (E) root tip number,” Li et al. 2023. ( Image credits: https://doi.org/10.3390/f15020234)

Fine Roots

Many novel studies of fine roots were conducted in 2023, with more natural ecosystems from the tropics to the boreal being covered to reveal more about underground root dynamics.

Tropics have the highest fine root production, and globally, fine roots contribute 30% of net primary production, yet fine roots have never been estimated in tropical peatlands. The first-ever fine root production estimates were made in two kinds of tropical peatlands (palm-dominated and hardwood-dominated swamps) and terra firme in Central Congo with repeat scanning using the minirhizotron system. Fine root production in peatlands decreased with soil depth, and more growth was seen during dry months. The fine root production in the three peatlands was similar to global averages.

Microcosm studies of wild roots are rare, but a high frequency of observations with minirhizotrons in a Mediterranean tree-grass ecosystem site allowed scientists a glimpse. Fine root properties were affected by moisture availability and time of day, which could also be connected to soil moisture. Root growth continues during autumn and winter, unlike above-ground parts when no canopy exists. An early season spurt in root growth is attributed to underground stored sugars rather than photosynthesis.

Another study of natural ecosystems, this time from the boreal, showed that mixed tree stands dominated by Populus tremuloides and Pinus banksiana, had more fine root lengths than monocultures. The effect of tree mixtures increases fine root production, especially as they age. The fine root growth increased net forest productivity, even though total root biomass and root length turnover remained the same in mixed forests. The fine roots boosted productivity work by increasing water and nutrient uptake, improving carbon sequestration too.

Understanding Root Response to Agricultural Practices

By far, most studies were concerned with agriculture crops and finding root responses to agricultural practices, namely nutrition, irrigation, tillage, and intercropping.

Root Effects of Nutrition and Irrigation

Using a minirhizotron, the phenotyping of tomato roots was achieved, where scientists learned of the variations in root development and root zone water content. Root distribution, which was maximum at 6-10 cm depths, decreased at lower levels. Also, as the water depth lowered, the root length became deeper. Observing root zone water near the roots in real time and recording root growth changes to reach water can help in better formulation of irrigation.

Water and nitrogen found that cotton root longevity increased when less water was available. However, at high levels of soil water and moderate amounts of nitrogen, net productivity increased by 30% as the root length was the greatest aided by longevity and productivity. A resultant increase in leaf area and leaf water content increased the photosynthesis rate to a level comparable to that achieved through high nitrogen application; see Figure 2.

Another study on cotton found that drip irrigation and mulch improved root morphophysiology. It increases cotton fibrous root production in the 0-60 cm layer and improves root physiology by reducing MDA in fine roots at flowering and full boll stage. As a result, the leaf water content improved and reduced leaf MDA to increase cotton biomass by 19.64 to 28.24%. Mulched drip irrigation reduced water consumption and boosted yield-level cotton water use efficiency by 20.76 to 30% compared to full flooding.

Figure 2: Effect of water and nutrients on root dynamics, Wu et al. 2023. (Image credits:  https://doi.org/10.1007/s11104-022-05681-1)

Tillage

Ridge tillage increased halophyte root production and lifespan by increasing soil moisture levels. The increases in soil organic matter, soil water content, and soil salt that vary according to seasons also influenced fine root production and root mortality. Soil depth also played a role. Fine root production peaked in May and early September in the topsoil and in July and late September in the subsoil. Fine root production and turnover were higher in the subsoil than in the topsoil. The increased fine root production and turnover increased soil carbon and belowground productivity in the nutrient-poor saline soils in abandoned fields and can facilitate replanting by improving soil fertility.

Subsoil tillage, in combination with organic fertilizers, increased rice yield (3-4%) compared to rotary tillage cum organic fertilization and chemical farming. The organic fertilizers increased root length density in the subsoil (15-30 cm) due to more access to nitrogen. Combining subsoil tillage and manure reduced soil compaction without changing topsoil compaction. Meanwhile, rotary tillage increases the topsoil’s organic matter, nitrogen, phosphorus, and potassium.

Intercropping

Beetroot has red-colored roots used to study competition in intercrops. However, beetroot also has white roots, around 2.5-4.8% of the total roots, but white roots are more in deeper layers, around 6.9-11.6%, and at early crop stages, which must be considered for competition effects.

Perennial intermediate wheatgrass (Thinopyrum intermedium) is helped by alfalfa intercropping starting from the second year when alfalfa has had time to accumulate root biomass and help through nitrogen fixation and turnover. Nitrogen transfer from the legumes to the grass happens through root and nodule decomposition, mycorrhizal transfer, and alfalfa root exudates rich in nitrogenous compounds.

Fine-root decomposition through a vital source of carbon and nutrients still needs to be better understood, especially in mixed plant ecosystems like integrated crop-livestock-forestry sites with trees and annual crops and pastures. Due to competition, eucalyptus trees (3-5 years old) reduced root production of annual crops and pasture plants close to them. Eucalyptus and grass thicker roots’ root lifespan was more than fine roots by over 200 days, so mortality and root decomposition were also lower closer to trees. Most root biomass was added in topsoils (0-28 cm) and decreased with soil depth. Root decomposition was faster after rains and warmer temperatures, especially if dead corn roots were available. Eucalyptus changes microclimate and reduces root production and turnover close to it.

Root Response to Pests

Western corn rootworm (WCR), a major North American pest, causes significant yield and quality loss. The root damage by the pest was detected early by imaging even though above-ground attributes like leaf color and area and plant height between infected and uninfected plants remained the same.

Carbon sequestration

Temporal fine root changes contribute more than absolute biomass to soil carbon efflux.

Though fine root turnover is usually a significant contributor to soil carbon flux, contrary results were reported from temperate forests on rocky soils. Here, seasonal fluctuations in fine-root standing biomass and mortality contributed little to soil carbon. Contribution by fine root mortality and turnover to carbon depends on temperature and soil moisture.

In an alpine meadow in Tibet, root length density, specific root length, root branching intensity, and carbon input were not influenced by precipitation changes. However, root turnover, carbon and nitrogen content, and C/N ratio change with rain. So, while root biomass and soil organic carbon remain the same, the soil carbon in subsurface soil is unstable because rain changes the root length density and residue carbon input.

Climate Change Effects on Roots

An experiment to study root response in two soil types (loamy and stony) to climate change followed root dynamics over entire crop seasons using minirhizotrons along with soil temperature and water content data, besídes a study of above around plant physiology. Scientists examined the effect of root architecture response to growing conditions on water and nutrient uptake functions and yield. The resultant data should aid in developing water-efficient cultivars and field management practices.

Minirhizotrons

The CID Bioscience Inc. produces two root scanners that can be used with minirhizotrons – the CI-600 In-Situ Root Imager and the CI-602 Narrow Gauge Root Imager. These devices have been used by scientists globally, and the research findings have been published in scientific journals to better our understanding of roots.

Contact us at CID Bio-Science to learn more about how we can help with your research needs.

Sources

1. Bu, R., Li, M., Cheng, W. et al. Subsoil Tillage and Organic Fertilization Benefit Rice Root Growth and Yield by Ameliorating Soil Compaction and Fertility. J Soil Sci Plant Nutr 23, 6114–6124 (2023). https://doi.org/10.1007/s42729-023-01468-0

1. Bieluczyk, W., Piccolo, M. D. C., Pereira, M. G., Lambais, G. R., Germon, A., Moraes, M. T. D., Soltangheisi, A., Camargo, P. B. D., Bosi, C., Bernardi, A. C. D. C., Pezzopane, J. R. M., Batista, I., & Cherubin, M. R. (2023). Fine root dynamics in a tropical integrated crop-livestock-forestry system. Rhizosphere, 26, 100695. https://doi.org/10.1016/j.rhisph.2023.100695

1. Feng, J., Bai, Y., & Zhou, Y. (2023). Interactive effects of provenance and soil lithology on root dynamics of a young subtropical plantation in China. Plant Soil 490, 93–108. https://doi.org/10.1007/s11104-023-06065-9

1. Gillert, A., Peters, B., von Lukas, U.F., Kreyling, J., & Blume-Werry, G. (2023). Tracking Growth and Decay of Plant Roots in Minirhizotron Images. Proceedings of the IEEE/CVF Winter Conference on Applications of Computer Vision (WACV), 3699-3708.

1. Huang, C., H. Chen, H. Y., Chang, S. X., Cahill, J. F., & Ma, Z. (2023). Species mixtures increase fine root length to support greater stand productivity in a natural boreal forest. Journal of Ecology, 111(5), 1139-1150. https://doi.org/10.1111/1365-2745.14087

1. Lärm, L., Bauer, F.M., Hermes, N. et al. (2023). Multi-year belowground data of minirhizotron facilities in Selhausen. Sci Data 10, 672 (2023). https://doi.org/10.1038/s41597-023-02570-9

1. Li, Z., Yang, Y., Feng, J., Rana, S., Wang, S., Wang, H., Zhang, T., Wang, Y., Guo, G., Cai, Q., Geng, X., Yuan, Q., Miao, C., Dai, L., & Liu, Z. Evaluation of Fine Root Morphology and Rhizosphere Environmental Characteristics of the Dioecious Idesia polycarpa Maxim. Forests, 15(2), 234. https://doi.org/10.3390/f15020234

1. Mahmud, K.P., Field, S.K.,  Rogiers, S.Y., et al. (2023). Rootstocks Alter the Seasonal Dynamics and Vertical Distribution of New Root Growth of Vitis vinifera cv. Shiraz grapevines. Agronomy, 13, 2355. https://doi.org/10.3390/agronomy13092355

1. Medrado, L.D.C., Santos, G.G., Correchel, V. et al. (2023). Evaluation of Sugarcane Root Growth Through Images Obtained via the Minirhizotron Method in a Ferralsol in the Midwest Region of Brazil. Sugar Tech 25, 638–652. https://doi.org/10.1007/s12355-022-01220-5

1. Nair, R., Strube, M., Hertel,  M., Kolle, O., Rolo, V., & Migliavacca, M.  (2023). High frequency root dynamics: sampling and interpretation using replicated robotic minirhizotrons, Journal of Experimental Botany, 74 (3),  769–786, https://doi.org/10.1093/jxb/erac427

1. Primka, E. J., Adams, T. S., Buck, A., Forsythe, B., Harper, J., Kopp, M., Kaye, J., & Eissenstat, D. M. (2023). Temporal patterns of fine-root dynamics have little influence on seasonal soil CO2 efflux in a mixed, mesic forest. Ecosphere, 14(10), e4670. https://doi.org/10.1002/ecs2.4670

1. Qian, L., Huang, T., Zeng, W., Chen, X., & Wang, X. (2023). Determining the dynamic responses of cotton root morphological characteristics under waterlogging stress using the minirhizotron technique. Irrigation and Drainage, 72(1), 60-74. https://doi.org/10.1002/ird.2752

1. Richmond, G.A.J. (2023). Root Structure, Biomass Allocation, and Legume Intercropping of Intermediate Wheatgrass. Ph.D thesis submitted to the  University of Minnesota. Retrieved from https://www.proquest.com/openview/19c2975c8d10e3247dea636166cc402c/1?pq-origsite=gscholar&cbl=18750&diss=y

1. Sciumbata, M., Wenina, Y.E.M., Mbemba, M. et al. (2023). First estimates of fine root production in tropical peat swamp and terra firme forests of the central Congo Basin. Sci Rep 13, 12315. https://doi.org/10.1038/s41598-023-38409-x

1. Song, X., Wang, C., Liu, D. et al. (2023).  Variation of Root Traits and its Influences on Soil Organic Carbon Stability in Response to Altered Precipitation in an Alpine Meadow. Available at SSRN: https://ssrn.com/abstract=4705712 or http://dx.doi.org/10.2139/ssrn.4705712

1. Song, Z., Zhao, T., & Jin, J. Early Identification of Root Damages Caused by Western Corn Rootworms Using a Minimally Invasive Root Phenotyping Robot—MISIRoot. Sensors, 23(13), 5995. https://doi.org/10.3390/s23135995

1. Wang, J., Gangfeng D., and Jingshan, T., et al. (2023). Mulched Drip Irrigation Increases Water Productivity of Cotton by Regulating Root Morpho-Physiological and Leaf Physiological Characteristics in Arid Area. Available at SSRN: https://ssrn.com/abstract=4409536 or http://dx.doi.org/10.2139/ssrn.4409536
2. Wu, B., Zhang, L., Tian, J. et al. (2023). Fine root dynamics, longevity, and canopy characteristics of cotton under varying water and nitrogen levels. Plant Soil 482, 191–209. https://doi.org/10.1007/s11104-022-05681-1

1. Xie, Y., Shanmugam, S. & Kristensen, H.L. (2023).Dispersed white roots in red beetroot influence the accuracy of root identification based on colours for intercropping studies. BMC Plant Biol 23, 416. https://doi.org/10.1186/s12870-023-04414-5

1. Zheng, X., Chen, C., Li, L., & Wang, J. (2023). Ridge tillage increased halophyte fine root production and turnover rates by altering soil properties in an abandoned farmland in northwest China. Rhizosphere, 27, 100742. https://doi.org/10.1016/j.rhisph.2023.100742