The Role of Fluctuating Temperatures in the Germination and Establishment of Sorghum halepense (L.) Pers. Regulation of Germination Under Leaf Canopies

1 The regulation of germination of Sorghum halepense (L.) Pers. under plant canopies, and its relation with temperature fluctuation requirements of these seeds, were studied. 2 Seed germination was depressed under closed leaf canopies and both seedling emergence and soil thermal amplitude were strongly related to canopy height. 3 A similar effect was observed when seed banks were subjected to increasing artificial shading. Heating the soil under dense canopies resulted in the same germination flux as observed in bare soil. 4 Germination responses to different alternating temperature regimes under controlled conditions were in agreement with the results of field experiments where soil temperature was modified either by shading or heating. 5 These results demonstrate that the alternating temperature requirements for germination of S. halepense seeds have a role in regulating seed germination under leaf canopies. Some ecological implications of this mechanism are discussed. Key-words: Sorghum halepense, fluctuating temperatures, germination