Effects of herbaceous and woody vegetation control on leaf characteristics and seedling growth of Tilia amurensis
[Objective]Tilia amurensis is an endemic tree species in northern China,with crucial ecological and economic values.It is difficult to regenerate T.amurensis under all-light conditions.Vegetation control can promote the growth of target species by changing light conditions and soil quality.As a consequence,identifying the optimal intensity of vegetation control and its impact on leaf characteristics and seedling's growth is crucial for popularizing T.amurensis.[Method]T.amurensis monocultures(five-year-old)with an inter-row and intra-row spaces of 1.5 m×1.5 m were used as experimental materials.Vegetation control treatments with different intensities T30,T50 and T75(clearing vegetation in the radius of 30,50 and 75 cm around T.amurensis seedlings)and control groups(CK)were set as experimental designs.We investigated leaf morphology,gas exchange parameters,the content of chlorophyll and nutrients,and seedling growth.The effects of herbaceous and woody vegetation control on leaf characteristics and seedling growth of T.amurensis were revealed by ANOVA.[Result]The light intensity was linearly positively correlated with the vegetation control intensity(P＜0.05),and reached the maximum under the T75 treatment(84.43±7.30×103 lx).The leaf morphological indices(leaf length,leaf width,single leaf area and specific leaf area)of T.amurensis decreased with the intensity of vegetation control,and reach their maximum and minimum values under CK and T75 treatment,respectively.The leaf net photosynthetic rate was the highest under T30 treatment(12.12±1.28 μmol·m-2·s-1),and the intercellular CO2 concentration was largest under CK treatment(263.14±8.77 μmol·mol-1),both of which decreased with the intensity of vegetation control.The leaf stomatal conductance and transpiration rate increased with the intensity of vegetation control,and reached their maximum values under T75 treatment(0.17±0.02 mol·m-2·s-1 and 7.02±1.21 mmol·m-2·s-1,respectively).Vegetation control had significant effects on the leaf's total carbon,total nitrogen and total phosphorus contents(P＜0.05),but had no significant effect on the stoichiometric ratio of the leaf's carbon,nitrogen and phosphorus(P＞0.05).In addition,vegetation control increased the contents of soluble sugar and starch in leaves but decreased the contents of chlorophyll a and chlorophyll b in leaves,promoting the seedling's growth of ground diameter,but inhibiting the seedling's growth of tree height.[Conclusion]With the change in vegetation control intensity,the morphology,stoichiometry and physiological characteristics of T.amurensis leaves take adaptive changes correspondingly.T.amurensis seedlings can increase the leaf area,specific leaf area,chlorophyll content and the absorption of nutrients to improve the ability to capture light energy,enhance their photosynthesis and promote the seedling's growth under low light conditions.The leaf net photosynthetic rate and seedling ground diameter growth reach their maximum under the T30 treatment,indicating that T.amurensis seedlings are the most competitive under the T30 treatment.Consequently,vegetation control within a radius of 30 cm centered on seedlings is the best way to promote the artificial regeneration of T.amurensis.
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