| UV-B radiation enhancement has become an important global environmental problems because of human activities which caused the ozone layer thinning in the atmosphere. At present, domestic and foreign scholars have done extensive research on the biological effects of UV-B radiation. However, the experiments are mostly carried out in indoor and short-cycle, there are some differences on the results. In the study, the materials of Xin Lu Zao number 13 were imposed on different UV-B radiations (R1:0.5W/m2,R2:1.0W/m2,R3:1.5W/m2) by natural light intensity in the manual condions. The materials were treated 8h everyday until the end of the cotton harvest. At the same time, natural light as the control(RO). Based on the research of enhanced UV-B radiation on cotton growth, physiology, biochemistry, yield and quality, the study hoped to lay a certain foundation for resilience of cotton cultivation techniques.This study obtained the following results:(1) Plant growth:As the extension of irradiation time and enhancement of radiation, the visible injury symptoms of cotton leaves become more serious. R1,R2 and R3 processing cotton plant height and stem diameter reached a significant difference compared with the control (P<0.05). The differences in leaf area of the various treatment reached a significant level. And plant dry weight reached a very significant level (P<0.01)(2)Chlorophyll:Following the enhancement of UV-B, cotton leaf chlorophyll a, chlorophyll b and total chlorophyll content all presented the trends of first increasd and then decreased. This illustrates that the UV-B radiation inhibits the synthesis of photosynthesis pigment or accelerated the decomposition of photosynthesis pigment. And the photosynthetic capacity decreased. Among of this, the chlorophyll a content was significantly lower than the content of chlorophyll b. It indicated that the leaves can reduce the absorption of light energy to avoid or mitigate harm of photoinhibition in a certain extent.(3) Pro and soluble protein:Following the enhancement of UV-B, free proline content increased, and soluble protein content was first increasd and then decreased. This is the cotton itself an adaptive protection mechanisms. (4) Active oxygen scavenging system:In the UV-B radiation, cotton leaf SOD, CAT and POD activity showed the first increase after the reduction trends. The initial increase of SOD, CAT and POD activity in cotton leaf is a strategy to adapt to radiation stress. However, with the extension of irradiation time the plants are still unable to maintain the balance between production and scavenging of reactive oxygen species. And antioxidant enzyme activity started to decline. Greater the degree of hurt the decrease in the level will be greater. The maximum time of SOD activity reached to be later than the CAT and POD activity. This is mainly because SOD is an inducible enzyme. The accumulation of reactive oxygen species is not sufficient to induce a significant change in SOD activity in the early stages of radiation stress treatment.(5) MDA and plasma membrane permeability:In the UV-B radiation, with the extension of irradiation, the MDA content and the plasma membrane permeability (RPMP) increasd. The rate of increase is R3>R2>R1>R0. This shows that the longer the radiation time and dose the damage to cotton leaf will be greater.(6) Blade microstructure:UV-B radiation enhancement have important impact on cotton leaves, such as leaf thickening, specifically palisade cell layers and spongy mesophyll cells increased, tissues thickening and intercellular spaces larger. These are considered to be adaptive changes for the enhanced UV-B radiation of cotton.(7) Root growth:With the extension of irradiation time and radiation enhanced, the three treatment group have taken place obvious changes on root morphology compared with the control. In Rl, roots become blended, lateral roots reduced and some lateral roots have the development direction to the main root. R2 taproot has significantly smaller in diameter that equivalent to lateral roots and lateral roots are also reduced accordingly. R3 taproot has developed into lateral roots, lateral roots evenly distributed and the number of roots decreased significantly. Respectively, the root length, root surface aera, average diameter of the root, root density and root volume of Rl, R2, R3 have all reduced compared with the control.(8) Yield and Quality:Increased UV-B radiation reduced cotton production, mainly due to lower cotton boll number, but also reduced the quality of cotton. |
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