Effects Of Shading On Phenotypic Plasticity And Photosynthetic Physiological Characteristics Of Leaves In Ribes Nigrum L. And Ribes Ussuriense Jancz

Ribes nigrum L.and Ribes ussuriense Jancz have high nutritional value,which are mostly for field cultivation at home and abroad.Ribes（Ribes L.）as a small shrub under the forest is covered by tall arbor,and what kind of shade is more suitable for two kinds of Ribes’ cultivation and breeding has not been reported.In order to determine the suitable light environment of two kinds of Ribes,there are three light environments for Ribes nigrum L.through artificial shade.The leaf shape,anatomical structure,photosynthetic pigment,photosynthetic characteristics,chlorophyll fluorescence parameters and kinetics of leaves in Ribes nigrum L.under three shading degrees(full sunlight（Z₀）,20%(Z₂₀),60%（Z60）)and different shading time 35 days（T₁）,74 days（T₂）,106 days（T3）ware carried using pot experiments.In same way,the leaf shape,anatomical structure,photosynthetic pigment,physiological indexes,chlorophyll fluorescence parameters and kinetics of leaves in Ribes ussuriense Jancz were studied under five shading degrees(full sunlight（Z₀）,20%(Z₂₀),40%（Z40）,60%（Z60）,80%（Z80）).The results were as following:（1）Shading treatment relieved the extent of burns in Ribes nigrum L.leaves.plant height,diameter of stems,leaf water content,leaf area and specific leaf area were increased in order to absorb light energy better.（2）Leaf thickness（LT）,palisade tissue thickness（PT）and spongy tissue thickness（ST）were much more thinner,and the ratio of palisade tissue to spongy tissue（PT/ST）was decreased in two kinds of Ribes under shading treatment in order to improve the efficiency of light energy.（3）The contents of chlorophyll a（Chla）,chlorophyll b（Chlb）,total chlorophyll（ChlT）and carotenoid（Chlx·c）were increased in two kinds of Ribes.The maximum value was reached at 60%（Z60）and 80%（Z80）shading treatment in Ribes nigrum L.and Ribes ussuriense Jancz respectively.But the ratio of Chla to Chlb was decreased and reached the minimum value at Z60 and Z40 respectively,which indicated that the strong adaptability in two kinds of Ribes under shading environment.However,with the extending of shading treatment,the contents of Chla,Chlb,Chl T and Chlx·c were decreased（T₁>T₂>T3）,the ratio of Chla to Chlb increased（T₁<T₂<T3）,wihch resulted from the gradual senility of leaves in the late shading treatment.（4）The daily average of net photosynthetic characteristics（Pn）,stomatal conductance（Gs）,stomata limitation（Ls）and water use efficiency（WUE）of full sunlight（Z₀）and 20% shading treatment(Z₂₀)were more higher than 60% shading treatment（Z60）during shading 35 days（T₁）and 74 days（T₂）in Ribes nigrum L.,while the intercellular carbon dioxide concentration（Ci）and vapor pressure deficit（Vpdl）were much higher at 60% shading treatment（Z60）.When shading 106 days（T3）,Pn and Gs at 60% shading treatment（Z60）were more higher than full sunlight（Z₀）and 20% shading treatment(Z₂₀),WUE was significantly higher than full sunlight treatment（Z₀）,while Ci was lower than full sunlight（Z₀）and 20% shading treatment(Z₂₀),which indicated that the appropriate shading treatment can alleviate the damage caused by the light on the leaves of Ribes nigrum L.and promoted the photosynthesis.Excessive shading can reduce light damage,but will also limit leaf photosynthesis.（5）Photochemical maximum efficiency of PSⅡ（Fv/Fm）,efficiency of excitation captured by open PSII centers（Fv’/Fm’）,potential photochemical efficiency（Fv/Fo）,photochemical quenching coefficient（qP）and the electron transport rate（ETR）were increased,while nonphotochemical quenching coefficient（NPQ）was decreased in two kinds of Ribes,which at 20% shading treatment of 35 days（T₁）and 74 days（T₂）,and at 60% shading treatment of 106 days（T3）.The same circumstances occurred in Ribes ussuriense Jancz,however,the electron transport rate（ETR）was followed the rules of Z₀<Z80<Z60<Z₂₀<Z40,which indicated that photochemical efficiency was much higher at 40% shading treatment,what’s more,shading treatment induced photosynthetic reaction center vitality and electron transport rate,then the production of photosynthesis was enhanced.（6）Using Z₂₀ as control,The effects of shading on PSⅡ functions of Ribes nigrum L.and Ribes ussuriense Jancz leaves were investigated by taking the chlorophyll fluorescence kinetics.The results showed that the value of VJ was decreased and lower than Z₂₀,which showed that QA to QB electronic transmission ability of PSⅡelectronic receptor side were not impeded in standardization of OJIP curve;The value of VI,VK and VL was increased,which indicated that PQ electronic library and electron-accepting ability of QB could be decrease and increased QA-accumulation;Meanwhile,the activity of oxygen complexes（OEC）was restrained in the donor side,which resulted in photosynthetic capacity decline;Shading treatment effectively increased the dissociation degree of chloroplast thylakoid,the stability of the PSⅡinstitutions had decreased,and decreased its adhesion of PSⅡprotein complex to maintain photochemical activity of PSⅡ.The main factors of PSⅡreaction center partly inactivation were the limitation of the electron transfer process.Above all,electronic transmission ability was declined under excessive shading treatment.Therefore,the Ribes nigrum L.and Ribes ussuriense Jancz should be shadowed in 20% and 40% shading treatment respectively.In summary,Ribes nigrum L.and Ribes ussuriense Jancz are shade plants,after shading treatment,a series of adaptive adjustments were made to illustrated the shade-tolerance.The Ribes nigrum L.should be shadowed in different degrees（20% shading treatment in 35 days（T₁）,74 days（T₂）,60% shading treatment in 106 days（T3））during the different shading days,and Ribes ussuriense Jancz should be shadowed in 40% shading treatment.