| Competition is ubiquitous in plant growth.It is of great importance to plant individual morphology,growth and development and population construction.Light competition is the main competition in the above ground.Under the condition of sufficient water and fertilizer,light competition even plays a decisive role in the growth and development of plants.In natural habitats,higher plants will compete for light competition by covering shorter plants,but the dwarf plants still maintain a relatively stable state,and natural selection does not make the higher plants grow infinitely higher.This may be because the individual will weigh the high growth investment and benefit when it becomes a competitive advantage in the light competition.At the same time,at the same time,we should balance the growth of high growth with other components,and ultimately choose the best growth mode,so as to maintain their optimal fitness in the community.Chinese fir(Cunninghamia lanceolata(Lamb.)Hook.)is one of the most important fast-growing timber species in South China.It has many advantages such as good quality,fast growing and high yield.With the increase of the demand for Chinese fir wood,the area of Chinese fir plantation has been actively constructed,and the area of Chinese fir plantation has expanded rapidly.At the same time,the value of the small diameter timber of Chinese fir is recognized by people.The density of Chinese fir is increasing,which leads to the early closure of the plantation of Chinese fir plantation and the enhancement of the light competition in Chinese fir species.However,most of the researches on Chinese fir are focused on intraspecific competition of Chinese fir,but there are few studies on light competition.At the same time,the high growth of Chinese fir is the key point of the study.In the state of community growth,in addition to the competition of density effect,the study of light competition formed by the difference of individual size has been neglected.How to rationally adjust the stand structure under the dense planting management model is still a difficult problem for the management of Chinese fir plantation,and can Chinese fir adapt to the growth environment of the high density stand by the plastic change of the upper part of the tree under the light competition condition?The research reveals that the internal adaptation mechanism of Chinese fir to light competition has important practical significance for maintaining sustainable management of Chinese fir plantations.In view of this,in view of the present situation of the change of Chinese fir light competitive environment caused by close planting of Chinese fir,this study selects the "020" clones of Chinese fir seedlings with high growth advantages as experimental materials.Through the field simulation test,the pattern of competition and group competition is set up,and the different intensities are constructed by artificially adjusting the height of the adjacent plants.The competition between light and local light competition environment forms the neighborhood effect of Chinese fir under different light competition conditions.By measuring the growth index,photosynthetic index and physiological index of the target tree,the morphological and physiological response mechanism of Chinese fir to the light competitive environment was studied,and the scientific basis for the rational allocation of Chinese fir seedlings in the actual production and the improvement of the productivity of Chinese Fir Plantation in the dense planting state were provided.The main results are as follows:(1)the effect of light competition on the light environment under the crown of Cunninghamia lanceolata shows that the light environment of the two planting patterns is different,the color temperature of the pattern is between 4745.25 K-6102.44 K,the color temperature of the group pattern is between 4949.42 K-6602.39 K,and the PPFD of the pattern is 171.15μmol·m-2·s-1-301.86 μmol·m-2·s-1,group pattern PPFD between 187.21μmol·m-2·s-1-374.27 μmol·m-2·s-1,the illuminance of the pattern is between 7443.29 Lux-17548.72 Lux,and the illuminance of the group pattern is between 8564.52 Lux-15563.68 Lux,and the leaf area index of the two planting patterns is both highly competitive and moderately competitive.The difference was not significant(P>0.05),while the leaf area index of mild competition was significantly higher than that of the former two,indicating that mild competition promoted the growth of plant leaves.The maximum red and far red ratio of the row pattern appeared in the moderate competition treatment(H2)in February(H2),which was 1.04.The red light and far red light ratio in the group pattern appeared in the October highly competitive treatment(Q1),reaching 1.19,but with the passage of time,the red light and far red light ratio under the 2 planting patterns did not show obvious regularity.(2)The response of the canopy structure of Chinese fir to the light competition environment is mainly reflected in the corresponding plasticity changes in the canopy structure of Chinese fir.The leaf area index of Cunninghamia lanceolata seedlings exhibited the same pattern in both row and group mode,and both were mild competition<moderate competition<intensity competition.In general,the sky opening degree of Chinese fir seedlings in the row mode is greater than that in the group mode.The performance of the Chinese fir seedlings in the row mode and the group mode was the same,and they were both mild competition,intensity competition,and moderate competition.The row-type and group-type patterns of the Chinese fir seedlings showed the same diverging angle,and they were mild competition<moderate competition<intensity competition.(3)The response of Chinese fir seedling growth to light competition environment showed that:under different competitive intensities,Cunninghamia lanceolata had different response mechanisms,and in the row mode,moderate competition treatment could promote the growth of seedling height of shorter plants.It can increase the diameter and branch number of higher plants.In the two competition models,the response of the Chinese fir seedlings to light competition was stronger than that of the group pattern under the row-pattern treatment.Due to the large difference in the number of wood samples under competition in the group mode,it is difficult for higher plants to compete for shorter plants.In the row mode,with moderate competition and mild competition,with the increase of time,from June to August,the seedling height of the shorter plants began to exceed the higher plants,and maintained the lead in the later period;Under these two treatments,the number of branches and diameter of taller plants basically maintained the leading position within one year of growth cycle.In the group mode,the difference in morphology between the taller and shorter plants was not significant,and even the phenomenon that the diameter was smaller than that of the shorter plants was not evident.(4)The biomass and nutrient allocation of Chinese fir seedlings responded to the light competition environment as follows:In the two planting modes,the biomass of the Chinese fir showed a certain pattern:in the row mode,the biomass showed high competition>moderate competition>mild Competition occurs,and the biomass of the shorter plants is higher than that of the higher plants,whereas the biomass performance is opposite in the group mode,and the biomass of the higher plants is significantly higher than that of the shorter plants.The intensity of different light competition environments had a certain effect on the nutrient content of Chinese fir seedlings.In the two planting patterns,the C content of each organ of Chinese fir was ranked as follows:leaf>stem>root.The N content was ranked as follows:leaf>stem>root.The P content was ranked as follows:leaf>root>stem.The K content was ranked as follows:leaf>stem>root.The nutrient rankings of various organs basically conformed to the general laws.Comparing dominant wood and competitive wood,higher plants did not have higher C content than dwarf plants,while lower N,P,and K plants appeared higher than higher plants,indicating that shorter plants face competitive pressure.Improve its own resource utilization efficiency.(5)The response of photosynthetic capacity of Chinese fir seedlings to the light competition environment is as follows:With the passage of planting time,the basic fluorescence F0 of each treatment gradually increases and then tends to be stable,and the maximum fluorescence value of FM shows a slight decrease after rising.As the trend toward stabilization,the maximum photochemical efficiency of PSII shows a trend of gradual stabilization.F0 of the row-mode moderate competition(H2)and mild competition(H3)experienced a trough in October and then slowly recovered.The SPAD value of the two cropping patterns generally showed an upward trend.The moderate competition(H2)in the row mode had a low value in April and then quickly recovered.The other two intensity competitions(H1,H3)showed a steady growth trend..In the group mode,low competition occurred in April due to highly competitive and light competition.There was no significant difference in chlorophyll a content between the non-competitive and competitive surfaces of Chinese fir(P>0.05).However,in the moderate competition(H2),the content of chlorophyll a in the competitive surface of Chinese fir showed significant differences(P<0.05).The competition surface has higher chlorophyll a content.Under the group mode,the content of chlorophyll a on the competitive surface of Chinese fir was significantly different(P<0.05)under the highly competitive(Q1)and moderately competitive(Q2)treatments,and the chlorophyll a content of the non-competitive surface was higher.There was no significant difference in the chlorophyll b of the competitive surface of Chinese fir under two cropping patterns.(6)The response of antioxidant system of Chinese fir seedlings to the light competition environment was as follows:In the row mode,the MDA content among the three treatments ranked as follows:intensity competition(H1)>moderate competition(H2)>mild competition(H3);However,in the group mode,the MDA content among the three treatments was ranked as follows:intensity competition(Q1)<moderate competition(Q2)<minor competition(Q3).In the row mode,the POD activity among the three treatments ranked as follows:intensity competition(H1)>moderate competition(H2)>mild competition(H3);but in the group mode,the POD activity among the three treatments ranked as follows:intensity competition(Q1)<moderate competition(Q2)<slight competition(Q3).In the row mode,the SOD activity among the three treatments ranked as follows:intensity competition(H1)>mild competition(H3)>moderate competition(H2);but in the group mode,the SOD activity among the three treatments ranked as:mild competition(Q3)<moderate competition(Q2)<intensity competition(Q1).(7)In summary,the Chinese fir seedlings of different competition sites have obvious response mechanisms to different light competition environments.Morphologically,the competitive dominant species will maintain the stability of their own structures through the growth of branches and ground diameters,and the competitive disadvantages.The species will increase their light harvesting ability through the high growth and biased growth of the crown and ensure their own growth needs.They are not eliminated by dominant species.Morphologically,Chinese fir seedlings regulate its internal stability through its antioxidant enzyme system,chlorophyll fluorescence system,and nutrient partitioning system,so that its own growth can reach its optimal fitness. |
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