Understanding understory seedling regeneration mechanisms is important for the sustainable development of temperate primary forests in the context of increasingly intense climate warming events.The poor regeneration o...Understanding understory seedling regeneration mechanisms is important for the sustainable development of temperate primary forests in the context of increasingly intense climate warming events.The poor regeneration of dominant tree species,however,is one of the biggest challenges it faces at the moment.Especially,the regeneration of the shade-intolerant Quercus mongolica seedling is difficult in primary forests,which contrasts with the extreme abundance of understory seedlings in secondary forests.The mechanism behind the interesting phenomenon is still unknown.This study used in-situ monitoring and nursery-controlled experiment to investigate the survival rate,growth performance,as well as nonstructural carbohydrate (NSC) concentrations and pools of various organ tissues of seedlings for two consecutive years,further analyze the understory light availability and simulate the foliage carbon (C) gain in the secondary and primary forest.Results suggested that seedlings in the secondary forest had greater biomass allocation aboveground,height and specific leaf area (SLA) in summer,which allowed the seedling to survive longer in the canopy closure period.High light availability and positive C gain in early spring and late autumn are key factors affecting the growth and survival of understory seedlings in the secondary forest,whereas seedlings in the primary forest had annual negative carbon gain.Through the growing season,the total NSC concentrations of seedlings gradually decreased,whereas those of seedlings in the secondary forest increased significantly in autumn,and were mainly stored in roots for winter consumption and the following year's summer shade period,which was verified by the nursery-controlled experiment that simulated autumn enhanced light availability improved seedling survival rate and NSC pools.In conclusion,our results revealed the survival trade-off strategies of Quercus mongolica seedlings and highlighted the necessity of high light availability during the spring and autumn phenological periods for shade-intolerant tree seedling recruitment.展开更多
The most important process before leaf senescence is nutrient resorption,which reduces nutrient loss and maximizes plant fitness during the subsequent growth period.However,plants must retain certain levels of nitroge...The most important process before leaf senescence is nutrient resorption,which reduces nutrient loss and maximizes plant fitness during the subsequent growth period.However,plants must retain certain levels of nitrogen(N)in their leaves to maintain carbon assimilation during hardening.The objective of this study was to investigate the tradeoffs in N investment between leaf N resorption and N for photosynthesis in seedlings with increased soil fertility during the hardening period.A field experiment was conducted to determine if and how soil fertility treatments(17,34,or 68 mg N seedling−1)affected N resorption and allocation to the photosynthetic apparatus in Quercus mongolica leaves during the hardening period.Seedlings were sampled at T1(after terminal bud formation),T2(between terminal bud formation and end of the growing period),and T3(at the end of the growing period).Results showed that photosynthetic N content continued to rise in T2,while N resorption started from non-photosynthetic N.Leaf N allocation to the photosynthetic apparatus increased as soil fertility increased,delaying N resorption.Additionally,soil fertility significantly affected N partitioning among different photosynthetic components,maintaining or increasing photosynthetic traits during senescence.This study demonstrates a tradeoff in N investment between resorption and photosynthesis to maintain photosynthetic assimilation capacity during the hardening period,and that soil fertility impacts this balance.Q.mongolica leaves primarily resorbed N from the non-photosynthetic apparatus and invested it in the photosynthetic apparatus,whereas different photosynthetic N component allocations effectively improved this pattern.展开更多
基金supported by the Ministry of Science and Technology of China (No.2019FY101602)。
文摘Understanding understory seedling regeneration mechanisms is important for the sustainable development of temperate primary forests in the context of increasingly intense climate warming events.The poor regeneration of dominant tree species,however,is one of the biggest challenges it faces at the moment.Especially,the regeneration of the shade-intolerant Quercus mongolica seedling is difficult in primary forests,which contrasts with the extreme abundance of understory seedlings in secondary forests.The mechanism behind the interesting phenomenon is still unknown.This study used in-situ monitoring and nursery-controlled experiment to investigate the survival rate,growth performance,as well as nonstructural carbohydrate (NSC) concentrations and pools of various organ tissues of seedlings for two consecutive years,further analyze the understory light availability and simulate the foliage carbon (C) gain in the secondary and primary forest.Results suggested that seedlings in the secondary forest had greater biomass allocation aboveground,height and specific leaf area (SLA) in summer,which allowed the seedling to survive longer in the canopy closure period.High light availability and positive C gain in early spring and late autumn are key factors affecting the growth and survival of understory seedlings in the secondary forest,whereas seedlings in the primary forest had annual negative carbon gain.Through the growing season,the total NSC concentrations of seedlings gradually decreased,whereas those of seedlings in the secondary forest increased significantly in autumn,and were mainly stored in roots for winter consumption and the following year's summer shade period,which was verified by the nursery-controlled experiment that simulated autumn enhanced light availability improved seedling survival rate and NSC pools.In conclusion,our results revealed the survival trade-off strategies of Quercus mongolica seedlings and highlighted the necessity of high light availability during the spring and autumn phenological periods for shade-intolerant tree seedling recruitment.
基金supported by the National Natural Science Foundation of China(No.32171764,No.32101503)the 5·5 Engineering Research&Innovation Team Project at the Beijing Forestry University(BLRC2023B08).
文摘The most important process before leaf senescence is nutrient resorption,which reduces nutrient loss and maximizes plant fitness during the subsequent growth period.However,plants must retain certain levels of nitrogen(N)in their leaves to maintain carbon assimilation during hardening.The objective of this study was to investigate the tradeoffs in N investment between leaf N resorption and N for photosynthesis in seedlings with increased soil fertility during the hardening period.A field experiment was conducted to determine if and how soil fertility treatments(17,34,or 68 mg N seedling−1)affected N resorption and allocation to the photosynthetic apparatus in Quercus mongolica leaves during the hardening period.Seedlings were sampled at T1(after terminal bud formation),T2(between terminal bud formation and end of the growing period),and T3(at the end of the growing period).Results showed that photosynthetic N content continued to rise in T2,while N resorption started from non-photosynthetic N.Leaf N allocation to the photosynthetic apparatus increased as soil fertility increased,delaying N resorption.Additionally,soil fertility significantly affected N partitioning among different photosynthetic components,maintaining or increasing photosynthetic traits during senescence.This study demonstrates a tradeoff in N investment between resorption and photosynthesis to maintain photosynthetic assimilation capacity during the hardening period,and that soil fertility impacts this balance.Q.mongolica leaves primarily resorbed N from the non-photosynthetic apparatus and invested it in the photosynthetic apparatus,whereas different photosynthetic N component allocations effectively improved this pattern.
