| Abies beshanzuensis M.H.Wu,belonging to Pinaceae,is an evergreen tree.It is an ancient relict plant native to China,which is also a national first-class key wild protected plant with only three mother trees in the wild.It is very difficult to propagate naturally and artificially.In addition,the seed bearing of A.beshanzuensis is low,and most of seeds are abortive.Because of these reasons,A.beshanzuensis is on the verge of extinction,becoming the most precious species in genus Abies.In order to strengthen the scientific research and effective protection of A.beshanzuensis,the reproductive biology of A.beshanzuensis was studied with the method of developmental anatomy.The determination of chlorophyll fluorescence parameters and chlorophyll content was employed to the research of photosynthetic capacity in A.beshanzuensis.Moreover,the energy accumulation of A.beshanzuensis was studied with organic element analysis and oxygen bomb calorimeter.Therefore,the endangering mechanism of A.beshanzuensis was elaborated from these three perspectives.Through the above research,the main results of this study are as follows:1.The female strobiles,male strobiles and cones of A.beshanzuensis in 2019 were studied by paraffin section method.The results showed that the microspores of A.beshanzuensis formed5-cell mature pollen grains after 4 times of mitosis,and no abnormal development of male gametophytes was found.The megaspores divided to form some free nuclei in May,and then they developed into cellular female gametophytes.At the same time,the degeneration of free nucleus and abnormal development of female gametophytes were found.During the development of seeds,the proportion of fertile seeds was only 0.71 % in 2019,while it was33.17 % in 2020,which means that A.beshanzuensis has big years and small year of seed bearing.Moreover,the abnormal development of female gametophytes led to the abortive endosperm,abnormal embryo and low fertility rate of seeds,which became one of the reasons of endangering A.beshanzuensis.2.Comparing the chlorophyll content and chlorophyll fluorescence parameters of leaves in different types of branches of A.beshanzuensis during different growing periods,the results showed that Chl a content,Chl b content and Chl a+b content of leaves with cones in the branch were significantly lower than those of leaves with no cones in the branch and leaves with no cones in the tree at most of the developmental stages.Yield,ETR and q P of leaves with cones in the branch were lower than those of leaves with no cones in the branch and leaves with no cones in the tree on May 31,June 27,October 12 and October 31.In addition,from May 31 to June 27,Chl a content,Chl b content and Chl a+b content of leaves with cones in the branch were significantly lower than those on July 16,and Yield,ETR and q P of leaves with cones in the branch were lower than those on July 16.These dates showed the development of female gametophytes,embryo and endosperm.Therefore,during this period,the chlorophyll content,electron transfer rate and photochemical utilization efficiency of leaves with cones in the branch decreased,and the ability of photosynthesis and the amount of photosynthate also decreased.These may cause the abnormal development of female gametophytes,and lead to the abortion of endosperm and embryo,and reduce the rate of fertile seeds,which was one of the reasons of endangering A.beshanzuensis.3.Comparing the C content,N content,H content,C/N ratio,C/H ratio,N/H ratio and calorific value of different types of leaves and branches of A.beshanzuensis,the results showed that the N content and N/H ratio of leaves and branches in A.beshanzuensis were significantly positively correlated with the calorific value,and the C/H ratio was positively correlated with calorific value,while the C/N ratio was significantly negatively correlated with the calorific value.Moreover,the N content and N/H ratio of branches and leaves with cones in the branch were significantly lower than those of branches and leaves with no cones in the tree at most of the developmental stages,respectively.However,C/N ratio of branches and leaves with cones in the branch was significantly higher than that of branches and leaves with no cones in the tree at most of the developmental stages,respectively.In addition,the caloric value of branches with cones in the branch was significantly lower than that of branches with no cones in the tree at most of the developmental stages.Therefore,the energy of leaves and branches with cones in the branch was significantly lower than that of leaves and branches with no cones in the tree.At the same time,during the development of female gametophytes,the N content,N/H ratio and calorific value of leaves and branches with cones in the branch were significantly lower than those on June 27 and at most of other developmental stages,making the insufficient energy for reproductive development of cones.It could result in the abnormal development of female gametophytes,the abortion of endosperm and embryo,and decreasing the rate of seed fertility,which was one of the reasons of endangering A.beshanzuensis. |
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