Factors Affecting the Seed Production of Teesdalia Nudicaulis: II. Soil Moisture in Spring

Abstract

The winter annual Teesdalia nudicaulis (Cruciferae) was studied in the Breckland region of eastern England. Evidence is presented that in most years Teesdalia experiences periods during the time of its flower production (April-June) when the soil becomes very dry throughout its rooting zone. Results are presented from two pot experiments in which soil moisture conditions were varied during the spring. The following conclusions are drawn. (1) Rosette senescence is hastened by a prolonged drought, or by a short drought at the peak of flower production. (2) A short drought can delay flower production, without altering the final total number of flowers produced. (3) A prolonged drought can cause earlier cessation of flowering; this is probably due to more rapid senescence. (4) The percentage of flowers which form fruits, and the number of seeds formed in each fruit are both closely linked to the state of the rosette; hence a drought which hastens rosette senescence also reduces fruit and seed production. With the aid of these results, and results from a previous paper, it is shown that much of the variation in seed production between 1958, 1959 and 1960 can be attributed to differences in autumn and spring weather.