Seasonal fluctuation in germination of short and long-term stored Norway spruce (Picea abies [L.] Karst.) seeds

Routine laboratory testing is done throughout the year to determine the quality of forest seeds. This raises the question of how the results are affected by possible seasonal effects on germination energy and germination capacity of seeds. To answer this question, fluctuations in germination energy (GE) and germination capacity (GC) of Norway spruce (Picea abies [L.] Karst.) seed was determined throughout the year. The test seeds had been stored for either a short time (2 months and 1 year) or a long time (12 and 13 years). Seed testing was done according to ISTA rules two times (in the first year T1 and the second year T2) in each month during a year. Ten seed lots from five Norway spruce seed zones in Slovakia were used for each treatment. Obtained data were processed by analysis of covariance (independent factors - T and months, covariate - altitude of seed origin). The monthly germination indicators were compared to annual average (using absolute differences and relative seasonal indexes). The results showed that GE and GC of short-term stored seeds were 59% and 92%, and 35% and 81% for long-term stored seeds. Compared to the annual average, the monthly germination indicators fluctuated very differently: for GE three times more than for GC, for long-term stored seeds 2-3 times more than for short-term stored seeds. For GE, significant deviations were found in six months during a year (in the range 11-23%), for both variants of seed storage. In contrast, for GC values such deviations were confirmed only for short-term stored seeds in February and March, but the differences (-2%) were very small and can be neglected. For use in forestry practice, three methods that eliminate existing seasonal fluctuations are proposed. Seasonal indexes seem promising since they enable converting the observed germination indicators at any one time to a value characterising the entire year average (formula 3).