BIOMASS ALLOCATION, PHOSPHORUS-NUTRITION AND VESICULAR-ARBUSCULAR MYCORRHIZAL INFECTION IN CLONES OF YORKSHIRE FOG, HOLCUS-LANATUS L (POACEAE) THAT DIFFER IN THEIR PHOSPHATE-UPTAKE KINETICS AND TOLERANCE TO ARSENATE

Biomass and phosphorus allocation were determined in arsenate tolerant and non-tolerant clones of the grass Holcus lanatus L. in both soluti on culture and in soil. Arsenate is a phosphate analogue and is taken up by the phosphate uptake system. Tolerance to arsenate in this grass is achieved by suppression of arsenate (and phosphate) influx. When c lones differing in their arsenate tolerance were grown in solution cul ture with a range of phosphate levels, a tolerant clone did not fare a s well as a non-tolerant at low levels of phosphate nutrition in that it had reduced shoot biomass production, increased biomass allocation to the roots and lower shoot phosphorus concentration. At a higher lev el of phosphate nutrition there was little or no difference in these p arameters, suggesting that differences at lower levels of phosphate nu trition were due solely to differences in the rates of phosphate accum ulation. In experiments in sterile soil (potting compost) the situatio n was more complicated with tolerant plants having lower growth rates but higher phosphorus concentrations. The gene for arsenate tolerance is polymorphic in arsenate uncontaminated populations. When phosphorus concentration of tolerant phenotypes was determined in one such popul ation, again tolerants had a higher phosphorus status than non-toleran ts. Tolerants also had higher rates of vesicular-arbuscular mycorrhiza l (VAM) infection. The ecological implications of these results are th at it appears that suppression of the high affinity uptake system, is at least in part, compensated by increased mycorrhizal infection.