Response Of Of Camellia Oleifera(Abel.) Physiology And Twigs Development To Understory Light Environment

In order to explore the response of Camellia oleifera leaf phenotype,structure and function,and twigs development characteristics to the understory light environment,analyzed four understory light environments,namely CK(control,no shade,1302.0μmol·m^–2 s^–1),75%light intensity understory habitat(976.5μmol m^–2 s^–1),50%light intensity understory habitat(651.0μmol m^–2 s^–1),30%light intensity understory habitat(390.6μmol·m^–2 s^–1),revealing the changing laws and interrelationships of the leaf phenotype,structure and function,and twigs development of C.oleifera under different light intensities,and using the membership function method to comprehensively evaluate the growth adaptability of C.oleifera.The relevant conclusions can provide scientific guidance for the understory growth and compound management of C.oleifera.The main findings are as follows:（1）With the increase of light intensity under forest,C.oleifera leaves tended to thicken.The width（LW）,leaf thickness（LT）and leaf biomass（LB）of C.oleifera in 75%understory were higher than those under CK,50%and 30%light intensity.And with the decrease of understory light intensity,leaf length（LL）,leaf length/leaf width（LL/LW）,leaf area（LA）,leaf perimeter（LP）and specific leaf area（SLA）decreased.Among them,LL was significantly positively correlated with SLA.（2）The anatomical structure and stomatal structure of C.oleifera leaf changed with the light intensity under forest.With the increase of understory light intensity,the upper cuticle thickness（UCT）and the lower cuticle thickness（LCT）,the upper epidermal thickness（UET）and the lower epidermal thickness（LET）,and the palisade tissue/sponge tissue thickness（PT/ST）showed a significant change.The stomatal axis（HAS）and the vertical stomatal axis（VAS）showed an upward trend with the increase of the understory light intensity.The stomatal density（SD）of 75%understory light intensity was significantly higher than that of other light intensities,while the stomatal area（SA）was significantly lower than other light intensities,and the stomata perimeter（SP）increased with the increase of understory light intensity.Correlation analysis showed that VAS was extremely significantly or significantly negatively correlated with SA,LCT and PT,and UET,LET,PT and ST（p<0.01;p<0.05）.（3）With the increase of light intensity under forest,the contents of chlorophyll a（Chl a）,chlorophyll b（Chl b）and total chlorophyll（Chl T）in C.oleifera leaves showed a decreasing trend,while chlorophyll a/b（Chl a/b）decreased with Decrease with the decrease of light intensity under forest.Among the main environmental factors,the diurnal variation of photosynthetically active radiation（PAR）,air-water pressure deficit(VPD_air)and air temperature(T_air)showed a"single-peak"curve,reaching the maximum at 12:00 noon;The light intensity under CK and 75%of the forest showed a"V"-shaped curve,and the 50%and30%of the forest showed a"U"and"W"-shaped curve.The diurnal variation of net photosynthetic rate（P_n）and transpiration rate（T_r）of the four light intensities showed a"single peak"curve,while the stomatal limit value（L_s）and stomatal conductance（G_s）showed a"single peak"type".The water use efficiency（WUE）showed no obvious regularity,and the intercellular CO₂ concentration（C_i）showed a"double peak"curve.Under 75%light intensity,the light saturation point（LSP）and maximum net photosynthetic rate(P_n-max)of C.oleifera leaves were higher than other understory light intensity conditions,apparent quantum efficiency（AQY）,light compensation point（LCP）),and the dark respiration rate（R_d）decreased to fully adapt to the lower light intensity under forest.The initial fluorescence（F₀）,the maximum photochemical efficiency of PSII（F_v/F_m）,and the apparent electron transfer rate（ETR）showed the maximum values under 75%forest light intensity.Correlation analysis showed that there was a significant negative correlation between PAR,P_n,Chl a,Chl b and Chl T in C.oleifera leaves（p<0.05）,and there was a significant positive correlation between P_n and Chl a/b（p<0.05）.Tair had extremely significant negative correlation（p<0.01）;PAR,P_n,T_r,G_s,AQY had significant or extremely significant correlation（p<0.05;p<0.01）.（4）The contents of total carbon（TC）,total nitrogen（TN）,total phosphorus（TP）,potassium（K）,calcium（Ca）,and magnesium（Mg）in C.oleifera leaves showed different changes with the increase of light intensity under the forest.Among them,the content of TN,TP,K,and Ca showed higher light intensity under 75%forest light intensity,and Mg content showed higher light intensity under 30%forest light intensity.The ratios of TC/TN,TC/TP and TN/TP in leaves were limited by N and P contents.The TN/TP ratio was 17.8 and 18.5under 50%and 30%understory,respectively,which was P-limited,and the CK and 75%understory light intensity were 15.5 and 14.5,respectively,which showed N and P limitation.Correlation analysis showed that TC and Mg,TN and TC/TN,TP and TC/TP were extremely significantly or significantly negatively correlated（p<0.01;p<0.05）.（5）With the increase of understory light intensity,twigs diameter（TD）,twigs length（TL）,leaf number（LN）,and twigs biomass（TB）under CK and 75%light intensity were significantly higher than those under 30%and 50%light intensity.Fruit diameter（FD）,fruit longitudinal diameter（FLD）,twigs diameter（TD）,and twigs biomass（TB）were significantly correlated（p<0.05）;fruit diameter（FD）,fruit longitudinal diameter（FLD）,fruit number（FN）and fruit biomass（FB）were significantly or significantly correlated（p<0.01,p<0.05）,and fruit appeared under CK and 75%light intensity,but not under 30%and 50%light intensity.（6）The comprehensive evaluation of the membership function value method showed that the membership function value of C.oleifera was the highest under 75%light intensity,indicating that the C.oleifera grows and develops better in this habitat.According to the above conclusions,the phenotype,structure and function of C.oleifera leaves and the developmental characteristics of twigs were the best under 75%light intensity,indicating that C.oleifera plants grew more vigorously under forest edge.In the under-forest management,the focus is on the cultivation of C.oleifera with greater than or equal to 75%of the under-forest light intensity.At the same time,by improving the stand structure,a favorable environment for the development of C.oleifera leaves and twigs is created to promote the growth of C.oleifera.