The Phytolith Morphological Charateristics Of Ten Sympodial Bamboo Species And Exogenous Silicon Effect On Cold Tolerance Of Their Seedlings

Bamboo is a typical Si-accumulating plant species.As an essential element for the growth and development of bamboo plants,silicon is one major factor affecting bamboo utilization.As of today,no systematic research has been carried out concerning the silicon deposition,migration and morphology in bamboo species.This research is a core component of the project Biomineralization of Silicon in Sympodial Bamboo Culm supported by the National Natural Science Foundation of China?No.31460169?.Targeting at Dendrocalamus brandisii distributed in Xinping County,Shiping County and Simao District,Dendrocalamus giganteus distributed in Xinping County,Simao District and Menglian County,we determined and analyzed the silicon content in different organs at different growth stages according to the national standard,extracted the phytolith by traditional dry ashing and wet ashing methods and by observing the phytolith morphology and its parameter with light microscope.Moreover,we also analyzed and compared the silicon content and phytolith morphology of ten typical bamboo species from the genera Bambusa,Dendrocalamus and Neosinocalamus from the Bamboo Garden of Southwest Forestry University.The results could contribute to interpreting the rule of silicon variation and phytolith formation and growth in bamboo and to better understanding the natural attributes of bamboo species.Meanwhile the research enriched the phytolith morphology in Gramineae and provided references for sympodial bamboo species classification.In addition,as a tropical bamboo species,D.brandisii was severely damaged by chilling in winter or uncommon cold spells in spring for several consecutive years.This had caused severe chilling injuries to young seedlings,which decreased the productivity and economic return,and affected the overall sustainable management of bamboo forests.In seeking the solutions to the chilling problem,we further analyzed and discussed the influence of application of different concentrations of sodium silicate on D.brandisii seedlings in terms of silicon content,physiological indexes and leaf anatomical structure under low temperature condition in winter,so as to build the theoretical basis for silicon fertilizer application in the cultivation and management of bamboo plantations.The research results were as follows:1.The silicon content of different tissues and organs of sympodial bamboo differed and increased in the order of leaf>sheath>branch>culm>shoot>root.The silicon content increased significantly with increasing culm ages.Higher Si content was in the outer part of bamboo culm than that in the inner part.The Si content in the top portion of culm was greater than that in the bottom portion and more Si content was found in mature tissues than that in young tissues.2.The morphtypes and numbers of phytolith in different tissues and organs of sympodial bamboo were different.Bamboo leaf contained the highest Si content and morphtypes of phytolith,including elongate,elliptical,dumb-bell with convex end,saddle,dumb-bell with straight end,hair,rectangular and fan,totaling eight types.The saddle-typed phytolith was high in the sheath.The branch held six morphtypes,which were elongate,rectangular,dumb-bell,saddle,elliptical and round,but without fan-typed phytolith.Young bamboo culm contained mainly dumb-bell and saddle-typed phytolith;2-and 3-year mature culms had higher percentages of round,rectangular and elongate-typed phytolith.The shoot and root had few round phytolith and amorphous silicon deposition.Phytolith size increased with increasing culm,branch and leaf age.3.The silicon and phytolith content in sympodial bamboo leaf and branch varied with different phenological stages.The lowest silicon content in leaves was observed in August,the prime season for bamboo shoot and the highest value was observed in November,the ending period for bamboo shooting.The difference of silicon content in leaves from different phenological stages was not significant.The lowest silicon content in branches was observed in the dormant period in January and the highest value was observed in November,which was the same as that in leaf.The maximum amount of phytolith in leaf and branch was both observed in November,the ending period of bamboo shooting,in which the amount of phytolith in May,the period for leafing and branching,was significantly lower than that in other phenological stages.The amount of phytolith in branch in the dormant period of January was the lowest.It would be useful to apply silicon fertilizer during the shooting stage to leaf and branching stage in the management of sympodial bamboo stands.4.Silicon content and the morphological parameters of the phytolith of the ten bamboo species from the genera Bambusa,Dendrocalamus and Neosinocalamus were different.Different bamboo species have their own special type of phytolith.The genera Bambusa,Dendrocalamus and Neosinocalamus could be classified according to the clustering analysis by the average proportions of dumb-bell with convex/straight end and saddle shaped phytolith in leaf,as well as the length and width of phytolith in old leaf.5.Exogenous silicon application to D.brandisii seedlings could enhance the Si content,photosynthetic pigment,proline,soluble sugar and starch content,higher CAT and SOD activities,decrease the MAD and H₂O₂,and produce thicker leaf blades and arm cell thickness.Results indicate that the 1.0mmol/L sodium silicate treatment on D.brandisii seedling leaves exhibited the best tolerance to chilling stress.Therefore,in the practical management of D.brandisii stands,spraying application of an adequate amount of exogenous silicon before temperature drop in winter may enhance the adaptability/tolerance of saplings to low temperature,hence minimizing the potential risks of cold stress.