Growth and development of seminal and crown root systems in N-limited barley, and their contributions to nitrate acquisition during vegetative and generative growth

Abstract

Barley (Hordeum vulgare L., cvs Golf and Laevigatum) was grown under nitrogen limitation, controlled by the relative rate of nitrate-N addition (RA), in solution culture. The seminal and crown root systems were kept apart, but in contact with the same nutrient solution throughout culturing. Growth, nitrate uptake, and in vitro nitrate reductase (NR) activity in the different root parts were studied at plant ages from 40 (late vegetative stage) to 110 (mid grain-filling) days. The RA was during this time interval stepwise decreased from 0.08 day -1 to 0.005 day -1. The ratio between seminal root dry weight and total plant dry weight decreased drastically during post-anthesis growth, whereas the contribution by crown roots remained unchanged. Tissue nitrogen concentrations in seminal roots did not change with time, but decreased in crown roots after day 80. The NR activity decreased with age in both seminal and crown roots. The Vma x for net nitrate uptake decreased throughout the experiment in the seminal root system, but not in the crown root system. The kinetic properties (Vma x and KM) were used to calculate the nitrate concentration required to maintain a relative rate of nitrate-N uptake that equals the relative addition rate. These concentrations (2 to 5 mmol m -3) were found to closely match actually measured nitrate concentrations in the nutrient solution (1 to 6 mmol m-3). From uptake kinetics, it was deduced that the contribution by seminal roots to total nitrate uptake at these concentrations decreased from more than 50% in vegetative plants, to about 20% just after main shoot anthesis, and to less than 5% during grain-filling.

Soil exploration and resource acquisition by plant roots: an architectural and modelling point of view

“…Nodal roots of maize were able to take up more phosphate from soil than radicle and seminal roots [55]. While the maximum uptake rate of barley for nitrate globally decreases between vegetative and reproductive growth stages, the nitrate uptake rate by nodal roots remains constant [51]. Lazof et al [42] showed that nitrate uptake rates (per unit of dry weight) of the primary axis of young maize plant amount for 68% of the lateral uptake rate.…”

Root Functional Architecture: A Framework for Modeling the Interplay between Roots and Soil

“…Navara (1987) showed that the radicle and seminal roots of maize ( Zea mays L.) play a dominant role in supplying water during a significant part of the plant's lifespan, while the nodal root system seems to be more heavily involved in the uptake of resources such as phosphate (Mistrik and Mistrikova, 1995). In barley ( Hordeum vulgare L.) root systems, although nitrate uptake rates decrease overall between the vegetative and reproductive stages, they tend to remain constant in the nodal root system (Mattson et al, 1993). Lazof et al (1992) showed that nitrate uptake rates (per unit dry weight) of the primary axis of young maize plants was up to 68% of that of the lateral roots.…”

A comparison of the dynamics of root growth and biomass partitioning in wild oat (Avena fatua L.) and spring wheat

“…If roots are randomly distributed through the soil volume, plants with a large root system will capture a greater proportion of a limited pool of nutrients than those with a small root system, when the two are grown in mixtures (Andrews & Newman, 1970;Newman, 1983), The contribution of adventitious roots to the total root length, and hence below-ground competition, may depend on the tiUering capacity of the cultivars involved and its degree of expression in mixtures. Wheat and wild oat seem to vary widely in their ability to tiller in mixtures compared to monoculture (see Martin & Field 1987;Cousens et al, 1991), Rates of ion uptake per unit root length may be greater in adventitious roots than seminals and in barley adventitious roots may contribute over 80% to the total ion uptake from main shoot anthesis onwards (Mattsson et al, 1993). Thus, any factor which influences the development of the adventitious root system is likely to have an impact on competition, particularly in the later growth stages of a crop.…”