Effects Of Experimental Warming On Growth And Reproduction Of Brasenia Schreberi

The global surface temperature has increased about 0.85 ℃ since the industrial revolution due to the sharp rise of carbon emissions caused by human activities.Global warming increases the average temperature,and also reduces the diurnal temperature variation.Most plants’ photosynthesis occurs in the daytime,and is more sensitive to the highest temperature.While plant respiration occurs all day and is affected by both the highest and the lowest temperature.The effect of average temperature warming on plants has been well-studied.While researches on the climate change sometimes ignore the phenomenon asymmetric warming due to the decrease of diurnal temperature range.Brasenia schreberi J.F.Gmel.is a perennial aquatic floating leaf plant,which is usually distributed in China and Southeast Asia,North America,Australia and other countries and regions.It is an aquatic vegetable with high economic value in China.This study chose B.schreberi as the research object.Three treatments were set up: laying white plastic film as the control treatment(CK),laying black plastic film as the warming treatment 1(W1),and adding the open-top chamber on top of the black plastic film as the warming treatment 2(W2).W1 and W2 simulated the phenomenon of mean temperature rise and diurnal asymmetric warming,respectively.Effects of global changes on B.schreberi were explored from three aspects: growth,sexual and asexual reproduction.The main results are as follows:(1)The results of chlorophyll fluorescence showed that the maximum quantum yield of PSⅡ decreased in W1 and W2.The photochemical and non-photochemical quenching in W2 were the highest among three treatments.Under the short-term heat stress,the chlorophyll fluorescence of B.schreberi in W2 was most affected.In terms of the pigment content,the total chlorophyll content and carotenoids content of floating leaves in W2 were the highest among three treatments.The chlorophyll a/b value in CK was higher than that in the other two treatments,while the chlorophyll/carotenoid value in W2 was the highest.The results showed that the dry/fresh ratio of floating leaves was the highest in CK,and the thickness of floating leaves in W2 was lower than that in the other two treatments.In summer,the floating leaf area,single bud weight and length of rolled-leaves in W2 were the highest,and the length of rolled-leaves in CK was the same as that in W1 treatment.In autumn,the leaf area of three treatments was lower than that in summer.The mucilage content of W1 and W2 was lower than that in summer,while the mucilage content of CK was slightly higher than that in summer.(2)The results of sexual reproduction showed that W2 treatment advanced the flowering time of B.schreberi by 5 days,and reduced the flowering density.The length of flowering time of three treatments were almost the same.The height and diameter of B.schreberi flowers followed the order from high to low as W2 > W1 > CK.At the same time,the vitality of pistil and stamen of B.schreberi decreased in W2,and the seed setting rate in W2 was the lowest.In terms of seed quality,although W2 had the highest thousand seed weight,its germination rate and germination potential were lower than those of W1 and CK.Meanwhile,the leaf number,seedling height and the dry matter accumulation in W2 were lower than those of the other two treatments.(3)In terms of overwinter buds of B.schreberi,the single bud weight of W1 was the highest in January.The bud length,leaf number,leaf length,leaf width and leaf area of W2 were the highest.In February,the single bud weight of W2 was slightly higher than that of W1.The bud length of CK was lower than that of W1 and W2.In March,the bud length of CK was lower than that of W2.Compared with January and February,the single bud weight,leaf length,leaf width and leaf area of the largest leaf of all three treatments in March were significantly decreased.The results showed that the single bud weight of the three treatments of submerged overwinter buds was higher than that of the floating ones.The leaf number of the submerged overwinder buds in W2 was higher than that in W1 and CK.The above results showed that the effect of average temperature warming on B.schreberi differed from the effect of asymmetric warming.In plant growth,both warming methods affected photosynthesis unfavourably,while asymmetric warming increased the disturbance of photosynthesis under short-term heat stress.The effects of two warming methods on the accumulation of photosynthetic products of B.schreberi were different in summer and autumn.In sexual reproduction,the reduced diurnal water temperature variation advanced the flowering phenology,reduced flowering density,and unfavourably affected B.schreberi floral syndrome and seed germination,whereas the average temperature warming had a slight effect on sexual reproduction.In asexual reproduction,both warming methods improved the quality of overwintering buds of B.schreberi,and the asymmetric warming had a greater effect than that of the average temperature warming.In conclusion,asymmetric warming had a large impact on B.schreberi than average temperature warming.