| Lumnitzera littore(Jack.) Voigt, a kind of Endangered mangrove plant, Combretaceae,Lumnitzera wild., which is recorded as the 2nd endangered species for conservation in China and the endangered species of International Convention on wetlands. Due to the natural growth in the high-tide zone is vulnerable to human disturbance, the distribution of Lumnitzera littorea in the world is not optimistic. In China, it distributed only in Hainan island. Because of the habitat destruction and human disturbance, the number of wild Lumnitzera littorea has declined sharply from 359(2007) to now 14. They distributed respectively in Sanya Tielu Bay(9) and Lingshui Dadun Village(5). And most of them have already in aging or close to aging, although they could flower and fruit normally, but the germination rate is extremely low and embryo abortion is serious.In our country, Lumnitzera littorea have serious reproductive barriers. By using reproductive biology principle and method, we studyed the biological characteristics, floral syndrome, flowering phenology,breeding system and nutrition elements and other aspects of Lumnitzera littorea. The main results are as follows:1. The distribution of Lumnitzera littorea in China: In our country, Lumnitzera littorea, now only 14 strains, all distribute in Hainan island, and 9 strains is in Sanya Tielu Port and 5strains is in Dadun Village of Lingshui.2. The community characteristics of Lumnitzera littorea: The plants, in Sanya Tielu Port,associated with Lumnitzera littorea, are all the thermophilic and stenotopic species. There are18 kinds of true mangrove such asRhizophora apiculata Blume., Lumnitzera racemosa Willd.and Bruguiera sexangula(Lour.) Poir. and six kinds of semi-mangrove such as Cerbera manghas, Pongamia pinnata(L.) Pierre and Hibiscus tiliaceus. Lumnitzera littorea is dispersed and mainly in the low water belt.3. The biological characteristics of Lumnitzera littorea: In addition to some basic characteristics recorded in the Flora of China, the description is more detailed and accurate and new features was found: The height of Lumnitzera littorea actual is about 8.5 m;Branches gradually change from light green to red then taupe with growth; The leaves are waxy and smooth with visible main veins; Racemes are composed of 10 to 15 flowers; The simple fruits are green when matured with slight red around ovary; After the seeds shed from the tree, the pericarps gradually become dark-brown and rotted after soaked in the seawater for a long time, then the top of the seeds is with burr; The seeds shoot out roots after stems,then cotyledons unfold fully. The back of hypocotyl and cotyledon are red. These findings can be used to supplement and perfect the flora of China.4. The floral integration features of Lumnitzera littorea: In addition to some basic characteristics recorded in the Flora of China, the new founds of floral integration features Actinomorphic are as flows: The corolla with radial symmetry; 10 stamens; 2 anthers,longitudinal crack, dorsifixed anther; Petals, filaments and styles were red; single carpel,ovary 1-loculed, inferior ovary, 4-5 ovules.5. The pollen and stigma morphology of Lumnitzera littorea: Under the scanning electron microscope(SEM), the pollen is long spherical or nearly spherical, actinomorphic, equatorial view is oval, 3 germinal apertures with colpus membrane and 3 false ditch, belonging to the N3P4C5 pollen type, namely equator tricolporate pollen; pollen exine has false ditch and wrinkled wavy shaped ornamentation, irregular in shape. Column-shaped stigma, nonbranched, middle-sunken, surface is dry and free from secretions, dry stigma, without Papilla cell.6. The flowering phenology of Lumnitzera littorea: Single flower florescence is 10-14 days,and the open process can be divided into budding period, flower opening, full blooming,flower withering. The florescence lasts 60-140 days. Florescence of groups is from January to August, without double flowering. Single flowering period is of about 12.60 ±0.80 days, the single inflorescence flowering period is of about 29.70±1 days, the flowering period is of about 115.20±6 days, flowering is not synchronized. The average number of flowering of per plant is 9.60±0.03 thousands and the average flowering amplitude of per plant in one day is83.47±1.50.7. The vitality of pollen and stigma of Lumnitzera littorea: The highest pollen viability is less than 10%, lasted about 5 days. The stigma has receptivity in the day before powder; the highest activity ocurred in first 2 days after pollination, lasts about 4 days.8. The breeding system of Lumnitzera littorea: Facultative outcrossing, partially self-compatibility and need pollinators. Pollen-ovule ratio(P/O) is 21649.08, outcrossing index(OCI) is 4,cross-pollination could effectively improve the seeding rate and reduce the empty embryo rate.Embryo abortion is serious, and pest is serious.9. The distribution characteristics of nutrient elements of Lumnitzera littorea during the reproductive period: The content of N, P, K, Na, Ca, Mg, Fe, Cu, Zn, B in Lumnitzera littorea in the different organs and the corresponding organs have significant difference compared with Lumnitzera racemosa. In addition to N, P, Na and B, the remaining elements of Lumnitzera littorea flowers is lower than Lumnitzera racemosa.In conclusion, the factors resulting in the endangering of Lumnitzera racemosa are as follows:(1) small population size, few mating, selfing rate increased;(2) Lack of fragrance and pollen competition of associated species reduced the attract to pollinators;(3)The evolutional stage is more primitive;(4) Flowers are not synchronized;(5) Low pollen vitality;(6) Since the stigma receptivity and the pollen vitality duration have overlapped space, they may have space for selfing which lead to recession;(7) Embryo abortion;(8) Insect pests;(9) Selfing affinity;(10) Low contents of K, Mg, Ca, Fe, Cu and Zn may have inhibition on development of the flowers. |
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