Removal of the testa during germination or establishment increases germinant mortality, decay and water loss

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Abstract
By means of direct manipulation, this study showed that the testa protects the germinating seed and germinant from decay (an advantage in moist soils) and desiccation (an advantage in periodically dry soils) in four species, all of which retain their testas until the cotyledons are lifted above the soil. Furthermore, the testa prevents early spreading of the cotyledons (an advantage when elongating through soil and litter). Almost all germinants ofBanksia hookerianaandLeucadendron eucalyptifolium, with their testas removed, died and rotted away after being sown on the soil surface or at a range of depths.Hakea cyclocarpaandH. strumosashowed only minor losses compared with the intact germinants. All naked germinants were smaller than the controls at any depth, except amongH. cyclocarpa. Absence of the testa did not differentially affect the length of the hypocotyl in the dark or light, but lateral spread of the cotyledons was accelerated, especially in the dark. Removal of a small fraction of the testa was sufficient to cause general mortality ofB. hookerianagerminants but not ofH. cyclocarpaorH. strumosa. After imbibition, water content of the naked embryos ofB. hookerianareverted to the air-dry state within 24 h of sowing in air-dry sand, while intact seeds were still moist even after 7 days of drying. Compared with intact seeds, drying periods of 3–7 days decreased the amount of germination and root growth of naked embryos after rewetting, and increased microbial infection of the survivors. Removal of the testa from germinants was sufficient to cause general mortality after only 6 h in air-dry sand. In contrast, most intact germinants with short radicles recovered after drying for 2 days.