Effect of seed storage temperature on fine root development and mycorrhizal colonization of young Populus nigra seedlings

KEY MESSAGE: Seed storage temperature influences root anatomy of the endangered Populus nigra, and consequently may alter nutrient absorption. A lower temperature during seed storage (−20 and −196 °C) may preserve the potential for a suitable root system development after germination. CONTEXT: Seed storage conditions can be an important determinant of later seedling growth of Populus nigra L., an endangered tree species. AIMS: We tested whether long-term seed storage temperature, −10, −20 or −196 °C, affects the pattern of seedling root traits responsible for resource acquisition as compared to seedlings of fresh seeds. METHODS: We analysed the morphology, anatomy, degree of mycorrhizal colonization, and biochemical composition of roots developed from seed stored for 24 months at five different temperatures (from 3 to −196 °C) commonly used to preserve genetic resources. RESULTS: Except for root anatomy, we found no relationship between seed storage temperature and the root traits of seedlings. Among the various storage conditions, the proportion of roots with primary development in the first four orders was similar in seedlings developed from fresh seeds of from seeds stored at −196 or −20 °C. Nitrogen content in the roots was positively correlated with the proportion of (i) roots with primary development and (ii) the cortex width in the root diameter. CONCLUSIONS: Higher temperatures during seed storage reduced the proportion of roots with absorptive function (with primary development). Therefore, for preservation of P. nigra seeds we recommend lower temperatures such as −20 and −196 °C.