Root:shoot ratio

Salinity also interferes with N acquisition and utilisation (Lewis, 1986). Adaptation to salinity and models of salt tolerance have been discussed by Stewart and Ahmad (1983). Hawkins and Lewis (1993) found that in both N03 and NH supplied Triticum aestivum L., the shoot and root morphology of the salinities plants was visibly different from the controls. The salinised shoots were smaller and the stems were less fibrous compared with control plants. Moreover, with increasing NaCl concentrations, there was a concomitant decrease in the shoot root ratio and reduction in the moisture content of both shoots and roots. 

Morphologically this biochemical process manifests itself in the "anti-gibberellin habitus" of the treated plants that corresponds to compact growth with shortened internodes and to a more intensive color of leaves. However, it is also worth mentioning the changes in the shoot-root ratio that lead to a pronounced shift in favor of root growth, especially after treatment with norbornenodiazetines (10). 

Enhanced "harvest index" Improved standing ability Improved light interception Improved shoot/root ratio... 

Ericsson, T. (1995). Growth and shoot root ratio of seedlings in relation to nutrient availability. Plant and Soil, 169, 205-14. 

Vysotskaya, L.B. (2005). Mechanisms Coordinating Wheat Seedling Growth Response as Affected by Shoot/Root Ratio. Russian Journal of Plant Physiology, Vol. 52, No. 5, pp. 679-684, ISSN 1021-4437... 

It is a general observation that seedlings raised under the influence, for instance, of tetcyclacis or triazoles exhibit a shoot-root-ratio which has shifted in favor of the root. In many cases, root growth is stimulated and longer and thicker main roots can be observed, while the formation of adventitious roots and root hairs is initially inhibited [38]. The formation of an improved root system may be one of the reasons why most of these plants show a better performance at later stages of development. 

The evidence, based on the isolation of GS and glutamate synthase mutants, for the role of the glutamate synthase cycle in the photorespiratory nitrogen cycle as discussed in Section III,B,3, mitochondrial GDH-deficient mutant of Zea mays has been isolated and is being investigated by Rhodes et al. (1989). In the absence of MSO, wild-type plants have a higher shoot/root ratio and show a... 

No differences were observed in the Au concentration found in roots of plants treated with lCU40mgAuU (317-350 mg kg dry mass). However, the roots of plants exposed to 80, 160, and 320mgAuU, concentrated (average + SE) 998 + 63, 1779 161, and 5704+109, respectively [75]. On the other hand, it was observed that the translocation of Au from roots to shoots was higher in plants exposed to lOmgAuU (ratio shoot/root of 0.2) and lower in plants exposed to 320mgAuU (ratio of 0.04). 

P is crucial for several aspects of plant metabolism, especially the energy and sugar metabolism, and several enzymatic reactions, including photosynthesis. Plants have therefore developed mechanisms for the uptake and efficient use of P. Maize plants recycled N quicker from old to young tissue when P is deficient, leading to earlier leaf senescence (Usuda 1995). P-deficient plants invest more resources into root development and therefore have an increased root-to-shoot biomass ratio compared to well-nourished plants. Furthermore, they accumulate more carbohydrates in leaves and allocate more carbon to the roots (Hermans et al. 2006). 

The tolerance index of plants was determined as the ratio of the mean length of the shoot (root) of the plant grown on a solution with a certain concentration of metal ions, to the mean length of the shoot (root) control... 

Empirical data describing the extent of chemical uptake by plants roots are generally expressed as ratios of chemical concentrations in the plant compartment of interest (e.g., shoots, roots, xylem sap) to that in the exposure medium (soil, soil pore water, hydroponic solution) measured at the time the samples are collected. These ratios are generally referred to as bioconcentration factors (BCFs) but they may or may not reflect equilibrium conditions. Plant BCF values are widely used to provide direct and approximate estimates of plant tissue concentrations from measured exposure... 

Fig. 8.4 Relationship between root to shoot ratio and the amount of above-ground biomass that can be harvested and still maintain the SOC level at the current level...

Below-ground biomass is typically estimated from the root to shoot ratio (Johnson et al. 2006 Bolinder et al. 2007). Extreme care must be used when using published root to shoot ratios because different scientists define root to shoot ratios differently. For example, Johnson et al. (2006) defined root to shoot ratios for com (Zea mays) as the ratio between root biomass and total above-ground biomass (grain, stover, and cob), whereas Amos and Walters (2006) defined this value as the ratio between root biomass and com stover. In addition, a standardized root to shoot ratio has not been used in maintenance calculations. For example, Barber (1978) used a value of 0.17 for com, Huggins et al. (1998) used a value of 0.53, and Larson et al. (1972) did not consider roots. 

Sensitivity analysis showed that the amount of com stover that could be harvested increased with root to shoot ratio (Fig. 8.4). If roots were not considered in the NHC value, then the estimated amount of above-ground biomass that could be safely harvested was about 35%, whereas if the root to shoot ratio was 1.00 then 70% of the above-ground biomass could be harvested. These findings are attributed to a relative increase in importance of the below-ground biomass. Based on these calculations, underestimating the root to shoot ratio will result in underestimating com stover removal rates, which, while having a positive influence on future... 

In addition to highly variable root to shoot ratios (0.01-1.22) the use of these values is complicated by (1) ratios that are hybrid, variety, and species-specific and (2) below-ground allocations that are impacted by stress (Herbert et al. 2001 Bradford et al. 2005 Amos and Walters 2006 Johnson et al. 2006). For example, Johnson et al. (2006) used root to shoot ratios of 0.82,0.55, and 0.62 for wheat (Triticum aestivum), com, and soybean (Glycine max), respectively whereas Amos and Walters (2006) reported that root to shoot ratios increased with N and P deficiencies and decreased with increasing water stress, population, shade, and soil compaction. 

Drainage class, tile drainage, soil characteristics, and initial SOC levels can also impact SOC maintenance requirements (Arrouays and Pelissier 1994 Zach et al. 2006 Clay et al. 2007). If the SOC maintenance requirement is related to the SOC level, then the range of values reported by Barber (1978), Wilts et al. (2004), Larson et al. (1972), and Frye and Blevins (1997) may be related to these differences. To assess the impact of SOC level on maintenance requirements, data from Barber (1978), Wilts et al. (2004), Larson et al. (1972), and Frye and Blevins (1997) were analyzed using the Clay et al. (2006) approach (Table 8.1). For these calculations, a common soil depth (0-15 cm) and root to shoot ratios suggested by Johnson et al. (2006) were used. Across the sites, located in the central USA, the analysis suggested that in plowed fields, 15.5% of the SOC contained in the surface 15 cm must be returned annually (Fig. 8.5). The 0-15 cm soil zone was selected because soil data from this zone are available in many studies. 

Table 8.1 The calculated percentages of SOC, using the non-isotopic approach, that must be returned annually to maintain SOC. Root to shoot ratios for corn, soybean, and wheat were identical to the values reported in Johnson et al. (2006). SOC was from the 0-15 cm soil depth... 

Fig. 8.5 A comparison of data collected from multiple sites analyzed using Clay et al. (2005). Tillage was conducted at all sites. In this plot NHC was non-harvested biomass, SOC was soil organic C, and dSOC/dt was the annual change in soil organic matter resulting from the imposed treatments. Root to shoot ratios was assumed to be 0.55 and the soil depth considered was the 0-15 cm zone...

Fig. 8.6 The relationship between initial SOC and the net C balance (stover + roots - maintenance requirement), and relative amount of carbon supplied by the roots (maintenance requirement -root biomass carbon) tilled and no-tilled system. Calculations were based on tilled and no-tilled systems with maintenance requirements of 16% and 10% of the SOC, a 11,270 kg grain ha-1 (180 bu acre-1), a harvest index of 0.5, a root to shoot ratio of 0.55, and that non-harvested com stover contained 0.4 g carbon(g plant)-1...

Carbon turnover in production fields can be determined, using non-isotopic techniques, by combining historical soil samples, current soil samples, and whole field yield monitor data. Sensitivity analysis of such data shows that the amount of above-ground biomass that could be harvested decreases with root to shoot ratio (Table 8.1). For example, if root biomass is ignored, analysis suggests that only 20-30% of the above-ground biomass can be harvested, whereas if the root to shoot ratio is 1.0, then between 40% and 70% of the residue could be harvested. 

The impact of the root to shoot ratios on calculated maintenance requirements is important because root to shoot ratios are highly variable and almost always underestimate below-ground biomass. Amos and Walters (2006) reported that the net below-ground C deposition in com at physiological maturity was 29% 13% of the shoot biomass (leaves, stems, and husks) in 41 studies. The use of these values is further complicated by the use of different definitions for root to shoot ratio. Converting Amos and Walters (2006) units to units used by Johnson et al. (2006) would reduce the reported values from 0.29 to 0.15 (harvest index 50%). 

The close agreement between the experimental and calculated (Equation 9) ratios of 18 2/18 3 support exclusion of the 4-hydroxylphenyl analogue from the calculations. Examination of Equation 9 shows an interdependence between the biological activity and the hydrophobic properties of the chemical used, commonly found with many QSAR equations. This interdependent relationship is determined by the and terms, respectively. These terms control phenomena of hydrophobic interactions with receptors and phenomena of transport and distribution within the total biological systems. The occurrence of squared terms of the hydrophobic parameter in structure-activity correlations has been explained on the assumption that the compound has to penetrate several lipophilic-hydrophilic barriers or compartments on its way to the site of action (16, 17). This is consistent with the uptake of pyridazinones by roots and sbsequent translocation to the shoots (chloroplast) as the site of action (13). 

Cloning. Asexual propagation (cloning) of plants ordinarily occurs by virture of the ability of embryonic meristematic tissue to differentiate into roots and shoots. If isolated phloem cells or other more differentiated cells are cultured, the result is often the formation of a callus, a dedifferentiated mass of cells somewhat reminiscent of embryonic cells. Under proper conditions, e.g., in a coconut milk culture and in the presence of the correct auxin-to-cytokinin ratio, some carrot root phloem cells revert to embyronic cells and develop into intact plants.99 This experiment provided proof that the differentiated carrot phloem cells... 

Nicotine biosynthesis is localized in the roots of Nicotiana plants, and the alkaloids are transported to the shoots in the xylem stream,70 mainly to young leaves and stems and the reproductive parts of the plant.72 At first glance, the costly transport mechanisms seem to be a disadvantage, as there is a time lag of 10 hr from time of induction until the increase of nicotine production.73 The roots, however, as the site of synthesis are well protected against herbivory and continue the production, even when up to 88% of the total leave area is removed.74 Optimization of the cost-value ratio seems to be the reason for the inducible defense acting as a cost-saving... 

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