Investigations into the root:shoot relationship of sugarcane, and some implications for crop productivity in the presence of sub-optimal soil conditions

The relationship between root and shoot growth of sugarcane was studied under favourable conditions, and also using experimental treatments that reduced the growth and effectiveness of the root system. A simple generic relationship was seen between the pattern of above and below ground growth under favourable conditions, with root:shoot ratio of all varieties declining through ontogeny. When root pruning or defoliation treatments were imposed to alter this relationship, there was a change in the relative growth of the roots and shoot towards the re-establishment of the original trend in root:shoot ratio development. Drying down half of the root system promoted a similar response, with an increase in root growth relative to shoot growth suggesting a re-establishment of the equilibrium between the root system and shoot. The apparently conservative nature of the root:shoot relationship was further demonstrated by the growth response of sugarcane plants to restricted rooting volume. In this study, physically limiting root growth significantly reduced total plant weights, but did not influence biomass partitioning between the roots and shoot. These findings are consistent with existing models of root:shoot relations, and suggest that shoot growth is directly related to the functional capacity of the root system

Functional manganese requirement and its use as a critical value for diagnosis of manganese deficiency in subterranean clover (Trifolium subterraneum L. cv. Seaton park)

The effects of manganese supply on plant growth and on photosynthesis and manganese concentrations in young leaves were examined in Seaton Park subterranean clover in three glasshouse water culture experiments.Plants werc grown initially with a copious supply of manganese, and transferred to solutions either with or without manganese. Sequential harvests were taken to determine the effects of developing manganese deficiency on dry matter (DM) yield of whole plants and selected characteristics [manganese, chlorophyll and photosynthetic oxygen evolution (POE)] of youngest open leaf blades (YOL). In addition, the deffect of leaf age and iron supply on POE werc examined.Manganese concentrations and POE in YOL declined markedly and rapidly in plants transferred to solutions without manganese, while chlorophyll concentrations of YOL and plant DM yield responded more weakly and more slowly. As a result, a level of manganese deficiency which depressed POE in young leaves by more than 50 per cent had no effed on DM production.In youngleaves (YOL, YOL + 1, YOL-1), POE declined when their manganese concentrations were < 20 μg g -1 DM. Iron supply did not affect this rdationship. When learn with < 20 μg Mn g -1 DM were detached and incubated for 24 h in solutions containing high concentrations of manganese, their POE increased to normal rates; leaves with higher manganese concentrations did not respond. It is suggested that the value of 20 μg Mn g -1 DM is the functional manganese requirement for POE in young subterranean clover leaves It is also suggested that this value may be used as a critical value for indicating manganese deficiency in subterranean clover.Functional nutrient requirements determined in this way by correlation of nutrient concentrations in young leaves with their biochemical or physiological activities appear to offer more accurate and consistent standards for use an critical values for diagnosis of plant nutrient status than do the critical values determined in the usual way by correlation with plant dry weight

The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)

Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity.Eun-Young Choi, Peter Kolesik, Ann McNeill, Helen Collins, Qisen Zhang, Bao-Lam Huynh, Robin Graham, James Stangouli