<p>Reproductive phenology plays a key role in the life cycle of plants. Exposure to late spring frost during flowering can result in the complete loss of seed crops in forest tree species. Siberian stone pine (<i>Pinus sibirica</i> Du Tour) is one of the most important species in Eurasian boreal forests. However, its cone yield is vulnerable to late spring frosts during the flowering year. To explore the range of intraspecific variation in reproductive phenology for Siberian stone pine, cone initiation, flowering time, and cone maturation were monitored over a 12-year period in a clonal common garden experiment established in 1996 in the southern part of the species’ natural range. To evaluate the impact of late spring frost on the species’ provenances, the relationship between the cone survival rate and naturally occurring frost characteristics was analyzed. Intraspecific variation in flowering abundance among the provenances exhibited complex annual dynamics. Provenances from warmer locations had the lowest proportion of flowering clones, which also displayed the least abundant flowering. Provenances from the central part of the species’ range showed the most abundant female flowering, while the same central provenances and those from cold locations exhibited the most abundant male flowering. Flowering started and ended 2–3 days earlier in the provenances from cold locations compared to those from warm locations. Cold-climate provenances required 260 °C of accumulated sum of effective temperatures (SET) above 5 °C to trigger cone bud opening, followed by pollen shedding at 280 °C SET. In contrast, the local provenance and the provenance from the warmest location required the SET accumulation of 300 °C to onset the flowering and pollen shedding. The timing of male and female flowering overlapped to varying degrees across all provenances. The negative impact of late spring frost on the cone survival rate depended on both the SET and the accumulated number of days with a mean daily temperature above 5 °C at the time of the frost. Frosts occurring when the accumulated SET exceeded 138 °C and more than 30 days with a mean daily temperature above 5 °C at date of LSF had accumulated led to total cone crop failure in all provenances, except for the northern ones and those from the central part of the species’ range, which retained up to 18% of their cones. This suggests that northern provenances are more frost-resistant despite their earlier flowering. Frosts at high accumulated SET above 5 °C were damaging even at the early phenological stage of cone bud development, before any visible changes occurred.</p>

Flowering intraspecies variation in Pinus sibirica ex situ: abundance, phenology, and frost survival

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发表日期：

2025年5月10日

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Evgeniya Zhuk

摘要

Reproductive phenology plays a key role in the life cycle of plants. Exposure to late spring frost during flowering can result in the complete loss of seed crops in forest tree species. Siberian stone pine (Pinus sibirica Du Tour) is one of the most important species in Eurasian boreal forests. However, its cone yield is vulnerable to late spring frosts during the flowering year. To explore the range of intraspecific variation in reproductive phenology for Siberian stone pine, cone initiation, flowering time, and cone maturation were monitored over a 12-year period in a clonal common garden experiment established in 1996 in the southern part of the species’ natural range. To evaluate the impact of late spring frost on the species’ provenances, the relationship between the cone survival rate and naturally occurring frost characteristics was analyzed. Intraspecific variation in flowering abundance among the provenances exhibited complex annual dynamics. Provenances from warmer locations had the lowest proportion of flowering clones, which also displayed the least abundant flowering. Provenances from the central part of the species’ range showed the most abundant female flowering, while the same central provenances and those from cold locations exhibited the most abundant male flowering. Flowering started and ended 2–3 days earlier in the provenances from cold locations compared to those from warm locations. Cold-climate provenances required 260 °C of accumulated sum of effective temperatures (SET) above 5 °C to trigger cone bud opening, followed by pollen shedding at 280 °C SET. In contrast, the local provenance and the provenance from the warmest location required the SET accumulation of 300 °C to onset the flowering and pollen shedding. The timing of male and female flowering overlapped to varying degrees across all provenances. The negative impact of late spring frost on the cone survival rate depended on both the SET and the accumulated number of days with a mean daily temperature above 5 °C at the time of the frost. Frosts occurring when the accumulated SET exceeded 138 °C and more than 30 days with a mean daily temperature above 5 °C at date of LSF had accumulated led to total cone crop failure in all provenances, except for the northern ones and those from the central part of the species’ range, which retained up to 18% of their cones. This suggests that northern provenances are more frost-resistant despite their earlier flowering. Frosts at high accumulated SET above 5 °C were damaging even at the early phenological stage of cone bud development, before any visible changes occurred.