| Phoebe bournei(Hemsl.)Yang,a unique local precious tree species in China,has been listed as the second-class protected precious tree species with excellent timber value.It is of great significance and necessity to build and cultivate a plantation of P.bournei for the construction of national reserve forest and the mitigation of wood safety risks in China.In the process of stand transformation and cultivation,it is a key problem to be solved in what kind of woodland environment can the introduced precious tree species P.bournei grow and develop normally,among which stand selection and the intensity of thinning in the cultivation is a key factor.In this study,three kinds of existing forests in the state-owned Zazuo forest farm of Guizhou Province,including the Cryptomeria fortunei forest(L),Quercus acutica forest(M)and mixed forest of C.fortunei cuspidata× Q.acutica cuspidata(H),were divided into three cultivation targets,and three kinds of thinning intensity of tending(1-mild tending: 0.69%-1.49%,2-moderate tending:26.67%-30.56%,and 3-severe tending:53.73% ～ 59.72%),born in seedling underplanting min nan 3 years updated build mixed forest,bare land new creation 1 mu of P.bournei plantation as control(CK),tending thinning intensity on forest canopy structure are analyzed and the influence of the light environment,discusses the P.bournei of sapling growth,physiological,biochemical and organic matter and mineral nutrients absorption effect on reforestation key factor-light response factor.The main results of the study are as follows:(1)With the increase of thinning intensity,gap fraction,canopy opening and leaf inclination of the three stands increased,while leaf area index decreased,and the light environment in the stand was improved.The changes of canopy structure and light environment were different with the change of tree species composition,and the change degree was as severe as that of the pure forest of Q.acutica(>)and mixed forest(>)C.fortunei.The gap fraction and canopy opening of C.fortunei(L3)plantation were the lowest in all the three tests.The light radiation flux under the canopy was significantly positively correlated with canopy opening and negatively correlated with leaf area index.With thinning intensity increasing,the light radiation flux under the canopy increased.Under the same intensity,the far red light in the mixed forest(690～780nm)was higher than that in the pure.In general,the same thinning intensity can improve the light condition under the mixed forest.(2)There were significant differences in the aboveground apparent characteristics among all treatments(P<0.05),and most aboveground apparent parameters were significantly correlated with canopy opening and LAI.Thinning intensity increases,the stand of sapling trees high in total increment,total incremental ground diameter and crown area showed a trend of increase after the first drop,forest light environment is appropriate when the radiation flux under canopy,the young trees of aboveground growth is better,with mixed medium theory best.When light is suitable,saplings tend to consume material to increase the number of branches,branch length,leaf density and leaf area to maximize resources,while when light is too strong or too weak,saplings tend to change the branch Angle,leaf inclination,leaf thickness and leaf area to avoid or tolerate light stress.Compared with theⅠlevel lateral branches,Ⅱlevel lateral branches and leaves of the external circumference of the tree were more significantly in response to the change of light environment,and the difference was gradually obvious with time.(3)With the increase of thinning intensity,the chlorophyll content of young trees in P.bournei decreased,and Pn showed a trend of increasing first and then decreasing.Pn was the highest in the medium tending(H2)of mixed forest for three measurements.Secondly,according to the variation trend of GS and Ci,from mild to severe thinning intensity,the Pn of young trees was firstly restricted by stomatal factors and then by nonstomatal factors.Thinning intensity increases,the young trees Y(Ⅱ),ETR and Fv/Fm are first increased and then drop trend,continue to enhance,light heavy thinning processing(CK,M1)plants under Fv/Fm value less than 0.75,the light protection index Y(NPQ)and light damage index Y(NO)was significantly higher,plants may be light suppressed,the light is bad for the photosynthesis.The increase or decrease of thinning intensity will lead to the decrease of Rubisco and RCA activities in young leaves of P.bournei,which may be one of the key factors limiting the Pn of young tree.(4)Between the groups of sapling soluble protein content,NSC content and C: N: P ratio significant difference(P < 0.05),and raise intensity increased,soluble protein content and C: N: P ratio increase with the decrease of the first measurement and NSC content increased,C,N,P,K content first increased after decreased.Under the same tending intensity,the N content of saplings in the mixed forest was higher than that of the other two pure forests,and the tending intensity was too high or too low,the soluble protein content of the plants increased,N:P decreased,and the growth and development were inhibited to a certain extent.The moderate tending intensity was helpful to the material accumulation and nutrient absorption of P.bournei,forests.When the light condition is too strong or too weak,the C:N and C:P values of young leaves of P.bournei,tree increase,and the plants can resist or adapt to adversity by enhancing the utilization efficiency of N and P elements.(5)The results showed that the mixed forest of C.fortunei × Q.acutica was more suitable for the establishment and growth of young trees in P.after thinning,and the growth and development of young trees were the best under medium thinning intensity,while the effect of bare land afforestation was the worst.The growth of saplings in the pure forest of Q.acutica was slightly better than that in the pure forest of C.fortunei under light and medium thinning,and the growth of saplings in the pure forest of C.fortunei under heavy thinning was better than that in the pure forest of Q.acutica.All in all,after the existing forest tending thinning,forest canopy structure change,understory light environment difference,forest light intensity and light qualitative change affects their forests replanting complement P.bournei,of sapling morphological and physiological situation,choose suitable forest types and thinning strength helps national reserve forest construction change existing forest culture in P.bournei,mixed cultivation. |
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