Phosphate absorption: adaptation of tundra graminoids to a low temperature, low phosphorus environment

Seasonal changes in phosphate absorption rate were examined in three tundra graminoids growing under natural field conditions and in experimentally heated soils in the field at Barrow, Alaska. Although tundra plants exhibited a high optimum temperature for phosphate absorption similar to that of temperate plants, rates were relatively insensitive to short-term temperature change, suggesting that tundra plants routinely absorb phosphate from cold soil and do not depend upon daily or seasonal increases in soil temperature for phosphate acquisition. Variation in the calculated seasonal course of phosphate absorption resulted more from change in phosphate availability and phosphate status than from temperature acclimation. Absorption capacity was highest early in the growing season when root growth began and then decreased to a level which was maintained well into September, long after aboveground plant parts had senesced. Nearly half of the phosphate acquired by the plants investigated was probably acquired after shoots had begun a net translocation of nutrients belowground for winter storage. Plants acclimatized to a warm, anaerobic, nitrogenrich soil had a higher capacity for phosphate absorption but a lower affinity for phosphate than did control plants growing in cold soil. The applicability of laboratory-derived concepts of nutrient absorption to the seasonal dynamics of these processes in the field is discussed.