INTERACTION OF LIGHT AND MINERAL NUTRIENT SUPPLY IN THE GROWTH OF IMPATIENS PARVIFLORA

Abstract

Summary(1) Plants of Impatiens parviflora were grown on a boulder‐clay woodland soil at four levels of irradiance with and without addition of ammonium nitrate and calcium phosphate.(2) Addition of nitrogen and phosphorus fertilizer increased dry wt yield and relative growth rate at all four levels of irradiance, and there was a true interaction between the level of irradiance and nutrient supply.(3) At the three higher levels of irradiance the increased growth resulted from an increase in unit leaf rate and leaf weight ratio, but at the lowest level an increase in leaf weight ratio alone was found.(4) Evidence was obtained for lower rates of respiration in the leaves of plants grown with fertilizer at high irradiance. Mycorrhizas were absent from all fertilized plants, but were well developed in the unfertilized plants at high irradiance and absent from unfertilized plants at the lowest irradiance.(5) Plants grown at high irradiance with additional phosphate alone responded initially exactly like plants with additional nitrogen and phosphorus but grew poorly later; plants with additional ammonium nitrate alone showed no response initially, but grew about as fast as plants with additional nitrogen and phosphorus later on.(6) Plants grown one per small pot responded only to additional phosphate in the short term, but plants grown 10 per small pot responded only to additional nitrogen.(7) Emphasis is placed on the important effects of the differential mobilities of nitrate and phosphate ions in experiments on the limiting mineral nutrients in soils.(8) The results are discussed in relation to earlier work, and the penetration of deeper shade by herbs on soils of higher pH is tentatively related to a superior supply of nitrate.