Growth,Morphology And Physiological Responses Of Different-aged Naturally Regenerated Juglans Mandshurica Saplings To Habitat

The light environments of forests have high heterogeneity in space,which has different effects on naturally regenerating saplings of different ages.This study used natural regeneration of Juglans mandshurica saplings aged 1-3 years,4-6 years and 7-9 years（abbreviated age stage I,II,III）in the experimental forestry farm of Zhuan Shan,Fangzheng County,Harbin City as experimental subjects,determining growth morphology and photosynthetic physiological indicators in different light environments（forest edge,forest gap and understory）,exploring the growth morphology of saplings in different light conditions as they age,nutrient status and its adaptation strategies,to reveal suitable light conditions for Juglans mandshurica saplings of different ages,to provide theoretical basis for developing artificial nurturing measures for Juglans mandshurica saplings in understory naturally regeneration.The results show that:（1）Different habitats have a significant impact on the growth and biomass of saplings at all age stages.The height and ground diameter of saplings at all ages were forest edge>forest gap>understory,with saplings at the forest edge significantly larger than in the forest gap and understory（P<0.05）,and non-significant differences in the forest gap and understory.Root,stem,leaf and whole plant biomass of saplings at all ages increased with increasing light intensity,with the forest edge significantly higher than the forest gap and understory（P<0.05）and the forest gap higher than the understory,but the differences were not significant.（2）Different habitats have significant effects on the photosynthetic physiology of saplings,reflected in photosynthetic parameters,chlorophyll content of saplings.Dark respiration rate（R_d）,light compensation point（LCP）and maximum net photosynthetic rate(P_max)were all forest edge>forest gap>understory,with significant differences（P<0.05）.As light decreases,chlorophyll content rises and chlorophyll a/b decreases.（3）In forest edge,saplings leaves at all ages had the highest net photosynthetic rate and C and N content,as well as increased accumulation of NSC in the roots and stems.In a low light environment,saplings increased the K content of leaves.（4）In forest gap and understory,saplings at age II have the highest maximum net photosynthetic rate,chlorophyll content and dark respiration efficiency,the lowest light compensation point and chlorophyll a/b,higher apparent quantum efficiency（AQY）and NSC content of above-ground parts.In forest edge,as the age growth of saplings,the maximum net photosynthetic rate increases and the light compensation point decreases.（5）The interaction of tree-age and habitat had a significant effect（P<0.05）on leaf morphology,photosynthetic parameters,and C,N and P content in leaves of saplings.In conclusion:optimal growth of Juglans mandshurica saplings appears at the forest edge,but saplings of all ages will also respond positively in low light conditions environment.In the understory and forest gap,saplings at 4-6 years are best able to withstand low light conditions and have higher shade-tolerant,relatively less shade tolerant in years 1-3 and 7-9 that require more light.However,at the forest edge,as saplings age,the requirement of light increases and the shade-tolerant decreases.