Elsevier

Field Crops Research

Volume 92, Issues 2–3, 14 June 2005, Pages 169-183
Field Crops Research

Growth and function of the sugarcane root system

https://doi.org/10.1016/j.fcr.2005.01.017Get rights and content

Abstract

A literature review was undertaken to assess current knowledge on how root system growth and function influences sugarcane productivity. Sugarcane root systems are commonly depicted as comprising highly branched superficial roots, downward-oriented buttress roots and deeply penetrating agglomerations of vertical roots known as rope roots. It is unclear how common rope systems are in modern sugarcane cultivars. Root distributions for sugarcane show the expected exponential decline with depth, with maximum values for root length density as high as 5 cm cm−3. Observations from the 1930s suggested maximum root depth could exceed 6 m and there is evidence of root activity below 2 m, from use of 32P as a tracer and observed changes in soil water content. There is little information available on root turnover in sugarcane, but evidence shows that the root system is not completely replaced when ratooning occurs. The below-ground C budget for sugarcane is very poorly understood and, consequently, C allocation and the ‘energy cost’ of the sugarcane root system is unknown. Hydraulic properties for root systems have been determined with considerable variation in conductivities found among the few varieties for which measurements have been made. Stomatal and root hydraulic conductances are correlated in sugarcane, for both pot and field-grown crops, resulting in approximately homeostatic regulation of leaf water potential. Available evidence indicates that stomatal response to root water status is achieved by transmission of a chemical signal in xylem sap, suggesting root water status may affect assimilation. Models and management need to acknowledge this, particularly for example where parts of the root system are in compacted or dry soil. Extraction of water and nutrients from depth should also be addressed, to improve utilisation of available resources and reduce the risk of off-site impacts. It is possible that improvements in yield through breeding have come at the expense of roots and capacity for water and nutrient uptake, and therefore old and new cultivars should be compared to determine if selection programs are causing application efficiencies (uptake per unit of resource applied) for water and nutrients to decline.

Introduction

There are many below-ground constraints on crop growth that are of significant concern in commercial sugarcane production. These constraints are both abiotic and biotic, but response of the plant is determined directly and indirectly by the growth and function of the root system. Consequently, gaps in our knowledge and misconceptions about the sugarcane root system may be an impediment to development of improved strategies for overcoming below-ground constraints in sugarcane production. These strategies may relate, for example, to soil and crop management or cultivar selection.

Our objective was to review available information on growth and function of the sugarcane root system, to enable synthesis of current knowledge into efforts to improve sugarcane productivity. The scope of the review was restricted to gross root system characteristics and function and thus cell-level processes have been excluded. This review encompasses: (1) the growth and development, size and distribution of the sugarcane root system; (2) root system effects on partitioning and plant growth; (3) root system effects on whole plant physiology, including control of assimilation and growth in response to changes in the environment.

Section snippets

Root system development

In the commercial sugarcane crop, which is asexually propagated, development of the root system is initiated soon after planting a portion of stem (sett) with at least one lateral bud. The first roots formed are sett roots, which emerge from a band of root primordia above the leaf scar on the nodes of the sett (Fig. 1) (van Dillewijn, 1952, Glover, 1967). Sett roots can emerge within 24 h of planting (Glover, 1967), although differences in the time required for root emergence occur among

Below ground carbon allocation

Little is known about the rate of turnover of sugarcane roots or their lifespan. Pritchard and Rogers (2000) cite a mean lifespan for roots of sugarcane of 14–90 days, but this appears to be derived only from observations of root longevity after harvest (Ball-Coelho et al., 1992). Comparable data from the rest of the crop growth cycle are not available. Data on turnover rates would enable calculation of the rate of biomass loss below ground and therefore help in determining a below-ground C

Hydraulic conductivities for sugarcane roots

Uptake of water by roots is driven by the difference in water potential between the soil and plant, with the transport coefficients for water flow into roots parameterised as hydraulic conductivities using an Ohm's Law analogy. Uptake of water (S) by a root system of root length density Lv and occupying soil volume V is then (van den Honert, 1948, Newman, 1969):S=(ψs−ψp)(1/κs+1/κr)LvVwhere ψs and ψp are the water potentials of soil and xylem at the base of the stem, respectively, κs the soil

Discussion

Considerable knowledge of the sugarcane root system has emerged from research over the last several decades. Root system architecture has been described, although there is uncertainty over how applicable the traditional depiction of the sugarcane root system is to modern cultivars, as data on root depth below approximately 2 m have not been published since the 1930s. The distribution of sugarcane roots is similar to other crops and tropical grasses, with an exponential decline in root biomass

Conclusions

This review indicates that sugarcane productivity may be influenced by root system properties because of their effects on (1) the supply of below-ground resources; (2) gas exchange and assimilation; (3) the C economy of the plant and partitioning of assimilate to yield components. Investigation of the effects of the root system on the supply of below-ground resources has been the traditional focus of root research and thus existing knowledge of root system size, distribution, depth and uptake

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