Effect of Soil pH, Soil Water, Light Intensity, and Temperature on Perennial Sowthistle (Sonchus arvensisL.)

Abstract

Growth of perennial sowthistle was examined under different levels of soil pH, soil moisture content, light intensity, and temperature. Soil pH ranging from 5.2 to 7.2 had little effect on the number of leaves, rosette diameter, plant height, and number of capitula. However, total dry weight was 30% less in plants grown in soil of pH 5.2 compared to those grown at higher soil pH levels. Perennial sowthistle demonstrated a consistent positive growth response to increasing soil water including saturation. Severe reduction in vegetative and reproductive growth occurred in plants grown in soil below field capacity. Plants grown under full light (1015 μE m−2s−1photosynthetic photon flux density) developed a fourfold increase in the number of capitula per plant and a 50% increase in total dry weight compared to plants grown at 285 μE m−2s−1. Initiation of reproduction was delayed 4 weeks for plants grown at 580 μE m−2s−1and 285 μE m−2s−1. Plants grown under less than full light developed fewer but larger leaves. Plants grown under a day/night temperature of 20/15 C grew more rapidly than those under 30/25 C or 10/5 C. Plants at 30/25 C began to senesce 7 to 8 weeks after planting. Net carbon assimilation, leaf conductance, transpiration, and water use efficiency decreased as soil moisture and light intensity decreased. Plants at 30/25 C had the highest rate of transpiration and the lowest water use efficiency. The observed optimum for perennial sowthistle growth occurred at a soil pH of 6.2 or 7.2, water-saturated soil, high light intensity, and a temperature of 20/15 C, day/night.