Growth, Phosphate Absorption, and Phosphorus Chemical Fractions in Two Chionochloa Species

Abstract

SUMMARY (1) Seedlings of two New Zealand alpine grasses were grown in solution culture with three rates of phosphate supply. One species, Chionochloa pallens, typically grows in soils in which more phosphate is available than is in soils occupied by the other species, C. crassiuscula. (2) Relative to C. pallens, plants of C. crassiuscula from the low phosphate habitat grew more slowly with all rates of phosphate supply, and their growth was less responsive to changing phosphate supply. Differences in shoot weight between species and treatments were due to both differences in leaf size and number of tillers per plant. The number of leaves per tiller was nearly constant. (3) In both species plants with a small phosphate supply had a large root: shoot ratio. However, the change in root: shoot ratio with changing phosphate supply was greater in C. pallens from the high-phosphate habitat than it was in C. crassiuscula. (4) Both species had similar phosphate absorption capacities when grown with low or moderate rates of phosphate supply. Phosphate absorption rate declined in both species as tissue phosphorus concentration increased, particularly in the high-phosphorusadapted C. pallens. (5) The low-phosphorus-adapted C. crassiuscula had higher tissue phosphorus concentrations (lower efficiency of phosphorus utilization) than did C. pallens because it grew more slowly but absorbed phosphate at a similar rate to C. pallens. (6) With low phosphate supply both species were similar in their distribution of phosphorus into inorganic phosphorus (34-40% of total), nucleic acid phosphorus (34-40%), ester phosphorus (12-15%) and lipid phosphorus (9%). All phosphorus fractions, particularly inorganic phosphorus, increased with increasing phosphate supply. Chionochloa crassiuscula had higher concentrations of most phosphorus fractions than had C. pallens when grown with intermediate and high phosphate supply, but this was due to its higher tissue phosphorus concentration (due to slower growth) rather than to major interspecific differences in the pattern of phosphorus distribution among chemical fractions. (7) The distribution of phosphorus among chemical fractions was similar between shoots and roots. (8) We conclude that a low phosphorus requirement associated with slow growth is more important than between-species differences in phosphorus metabolism, phosphate absorption, or efficiency of phosphorus utilization in explaining the success of C. crassiuscula and other low-phosphorus-adapted species on infertile soils.