| Dwarf bamboo,a dominant understory clonal plant in subalpine and subtropical mountain broad-leaved forests,is recognized to be a key factor for forest regeneration.Most of studies were focused on the effects of special gaps canopy environment on the population characteristics of dwarf bamboo.However the effects of canopy structures of typical forests and the heterogeneity light environment on them were less considered.In November 2016,we selected three typical forest types(deciduous broad-leaved forest,DBF;evergreen and deciduous broad-leaved mixed forest,MBF;evergreen broad-leaved forest,EBF)in Jinfo Mountain National Nature Reserve,southwest China.Three sample plot of the area 300 m2 were set in each forest type,and then three photo points were randomly set in each sample plot.Then we used the Hemi View digital canopy analysis system to quantize the canopy structures(canopy openness,CO;leaf area index,LAI;mean leaf angle,MLA)and light conditions(direct solar radiation under canopy,diffuse solar radiation under canopy,total solar radiation under canopy),and took seasonal dynamic monitoring for canopy structures and light conditions.Meanwhile,clone propagation,clonal morphological plasticity and clonal growth characteristics of Fargesia decurvata were measured under the different canopies.The main results were as follows:(1)With the development of forest succession,canopy structures of each forest type have been significantly changed,which showed that the CO and MLA decreased,LAI increased and canopy extinction ability enhanced,resulting the decrease of light intensity under the canopy.Moreover,the canopy structure was significantly correlated with light condition in the forest,and influenced the composition of light.The effect of canopy structure on diffuse light was greater than that of direct light.(2)With the coming of the growth season,the CO and understory light conditions were decreased,while LAI showed an increase,and the maximum values of them appeared in June or July in the three forest types.The maximum value of MLA appeared in spring,minimum in summer.The seasonal dynamic changes of canopy structures and light conditions were most obvious in DBF,and the EBF was most stable,with little changed.(3)The clonal growth of F.decurvata was closely related to the canopy structures and light conditions.With the decrease of light intensity,the culm height,basal diameter and leaf area of ramets of F.decurvata trended to be smaller,the clone propagation ability and biomass accumulation decreased,but increasing the specific culm length,leaf area ratio,specific leaf area,specific spacer length and branch angle of spacer to improve the utilization of light and effectively adapt to low light environment.Moreover,in the low light environment,F.decurvata reduced the investment on reproductive organs,then allocated more biomass for culms growth.And in the good light environment,F.decurvata reduced the investment on branch and leaf,but increased the investment on rhizome growth,which considering a foraging behavior for water resources.(4)Fargesia decurvata in different forest communities had different time for new bamboo shoot sprouting,but all of them sprouted in March.The shooting periods of F.decurvata could be divided into three stages: early,peak and late stage.And the shooting time go into each period of F.decurvata was different in each forest type.In the EBF,the time for new bamboo shoot sprouting was latest,while the time for the new bamboo shoot stopping was earliest,and the shooting numbers were least,but the shoot degradation rate was low.In the DBF and MBF,the time for new bamboo shoot sprouting or stopping was similar.The MBF had the highest shooting numbers and shoot degradation rate.Besides,the shoot degradation rate increased and the height of degraded shoot decreased with the shooting periods coming.(5)With the different shooting periods coming,the basal diameter of bamboo shoots of F.decurvata had little change in the same forest community.But basal diameter of bamboo shoots in EBF was significantly smaller than those of in the DBF and MBF(P < 0.05).The height growth of bamboo shoots finished about 80 days,and the correlation between height growth and time of bamboo shoots was significant(P < 0.001).The height growth curves of bamboo shoots emerged in early,peak and late stage were ?S-shaped? in each forest communities,which exhibited a tendency of ?slow ? fast ? slow?.The height growth rate of bamboo shoots of F.decurvata was: MBF > DBF > EBF.(6)There was a close relationship between clonal propagation and bamboo density of F.decurvata.With the increase of bamboo density,the shooting numbers increased and mature of bamboo shoot number decreased.This relationship could be considered as a self regulating in bamboo clone propagation.Results indicated that the forest canopy structures had changed in the process of forest succession,and tended to be stable.The change of canopy structures significantly affected the composition of the understory light condition.Low light environment limited the population renewal and development of F.decurvata.And F.decurvata have significant change in morphological plasticity under different forest canopies.These morphological plasticity changes were the result of adaptive response to different forest canopy structures and light conditions,and benefit to enhance the ability of plants to acquire and utilize the light resources in heterogeneous light environments.Moreover,the communities may be able to coordinate and control the development of dwarf bamboo by controlling the canopy structures and light conditions.That made it possible to form a stable coexisting relationship between canopy tree species and dwarf bamboo. |
PDF Full Text Request