Manganese uptake and Mn efficiency of wheat cultivars explained by root growth and Mn uptake kinetics

摘要

Wheat cultivars differ widely in Mn efficiency. To investigate the mechanisms underlying different Mn efficiencies, a pot culture experiment with soil, a solution culture experiment and model calculations were carried out. The pot experiment was carried out in a screen house in India using wheat (Triticum aestivum L. cv. PBW 373, PBW 154, PBW 343, PBW 138 and Triticum durum L. cv. PBW 34 and PDW 233). The soil was loamy sand, pH 8.1, DTPA-extractable Mn 1.62 mg kg~(-1) soil, soil solution Mn concentration (C_(Li)) 0.19 μM and when fertilized with 50 mg Mn kg~(-1) soil, C_(Li) increased to 0.32 μM. At C_(Li) 0.19 μM, wheat cv. PBW 373 produced 74% of its maximum shoot dry weight (SDW) with 64% of its maximum root length (RL), while cv. PDW 233 produced only 25%of its maximum SDW with 11% of its maximum RL. The other wheat cultivars were in between these extremes. The low Ma efficiency of durum cv. PDW 233 was mainly due to the strong depression of its root growth, while the Mn influx was similar for all cultivars, varying between 2.7x10~(-7) and 4.0x10~(-7) nmol cm~(-2) s~(-1). In solution culture, under controlled growth chamber conditions, Mn influx was linearly related to Mn concentration in the concentration range of interest i.e. below 1 μM. Efficient cv. PBW 343 and inefficient cv. PDW 233 had a similar influx of about 2.0x10~(-7) nmol cm~(-2) s~(-1) at a solution concentration of 0.2 μM. Uptake kinetic parameters from the solution experiment together with soil Mn parameters were used in a mechanistic computer model. Values of Mn influx calculated for wheat grown in soil were close to measured values. This indicates that Mn transport to roots by mass flow and diffusion and root uptake kinetics properly described Mn uptake from soil. A sensitivity analysis showed that increasing Mn solution concentration, as for example by chemical mobilization, would proportionately increase Mn uptake. The results indicate that Mn uptake and Mn efficiency of wheat cultivars can be explained by Mn uptake kinetics and root growth.