Study On Reproductive Characteristics Of Dodonaea Viscosa In Jinsha River Dry-hot Valley

Dodonaea viscosa(Linn.)Jacq is a kind of shrub or small tree,belongs to Dodonaea genous in Sapindaceae family.The growth habits of it are drought tolerance,strong sprouting ability,developed roots and clusters.It is good water-retaining soil-fixing plant and is often used as a pioneering tree species in the dry-hot valley of southwest China.The shrub-grass vegetation formed by the dominant species of the D.viscosa is one of the several important native vegetation in the the Jinsha river dry-hot valley.It plays an important role in soil and water conservation and vegetation restoration,and also has a high ecological value.In order to clarify its reproductive ecological characteristics and impacts on its population renewal,and provide theoretical support for the protection and sustainable use of D.viscosa in the Jinsha river dry-hot valley,we studied the plant community characteristics,flowering phenology,reproductive characteristics,development of microsporogenesis and megasporogenesis,reproductive investment and allocation characteristics,seed germination and early seedling growth characteristics.The main results and conclusions are as follows:(1)The plant species composition of D.viscosa community in the Jinsha river dry-hot valley was simple,and the species richness and diversity were relatively low,inclouding 18 species belonged to 14 families in 17 genera.The D.viscosa was the dominant species in shrub layer;and the important value of Heteropogon contortus was the largest in the herb layer.(2)The initial flowering period of D.viscosa was mid-June,and the final flowering period was mid-to-late September in the Jinsha river dry-hot valley.The flowering period lasted for about 3 months.The flowering periods at the individual,inflorescence,and single flower levels were 26-36 days,20-26 days,and 6-7 days,respectively.The types of flowers were female flowers,male flowers and a few bisexual flowers with male abortion.At the beginning of flowering,the pollen vigor could be as high as 90.8%,and completely lost vigor after 3 days.The stigma was partially accessible in expansion stage,and it was not accessible until thefourth day of flowering.The P/O value were about 30667,and the OCI were 4.The D.viscosa was a typical wind pollination plant.(3)D.viscosa had 4 pollen sac.The anther wall was composed of the epidermis,the endothecium,2-3 middle layers,and tapetum(glandular tapetum)from the outside to the inside.The cytokinesis occurred simultaneously in a microspore mother cell.The tetrad was tetrahedral.The mature pollen was two-celled type.D.viscosa had style canal and placentation was axial.The ovary had 3 locules with two ovules per locule and the ovule without hypostase was amphitropous,bitegmic and crassinucellate.The type of megasporogenesis was monosporogenesis.The mature embryo sac of 7 cells and 8 nuclei was formed by three mitosis of uninucleate embryo sac,and the development type of embryo sac was polygonum type.The results suggested that a few abnormal phenomena such as the embryo sac was not empty and no cellularization of the free nucleus in the development of female gametophyte,abnormal pollen and the empty of pollen sac during the development of stamen.Our researches showed that these abnormal phenomena might be one of the reasons of low natural seed setting rate.(4)D.viscosa population was extremely biased towards female in the Jinsha river dry-hot valley(P ?0.01).The morphological characteristics and biomass allocation traits of the twigs were gender-different.The flower biomass and total biomass of female reproductive twigs were significantly higher than those of male twigs(P ?0.05).There was no trade-off between vegetation growth and reproductive growth,and reproductive allocation was not depent on individual size.This biomass allocation model as reproductive allocation was a fixed value might be an adaptation to the special environment of the Jinsha river dry-hot valley.(5)The seed vigor of D.viscosa was up to 89.1%,the seed swelled and absorbed water quickly,and the seed coat had good water permeability.Temperature,soil moisture and their interaction significantly affected seed germination and seedling growth(P ?0.01).When the temperature was below 20?,the soil moisture was high(50% and above)or low(10% and below),the seeds did not germinate or the initial germination time was significantly delayed(P?0.05).The optimal temperature for the germination was 25-35?,and the optimal soil water content was 15%-40%.The optimal temperature for seedlings was 20-30?,and the optimalsoil moisture content was 15%-30%.When the temperature ?35??the soil moisture ?10%,the seedlings were severely inhibited and even couldnot survive.It concluded that temperature and soil moisture were the main limiting factors for the germination and seedling early growth of D.viscosa in the Jinsha river dry-hot valley.