Effects Of Phyllostachy Heterocycla Expansion On Root Morphological Plasticity And Rhizosphere Denitrifying Bacterial Community Structure Of Alsophila Spinulosa

Alsophila spinulosa belongs to Alsophila of Cyatheaceae.It is a living fossil of scientific research,which witnesses the changes of the earth’s history.It is of great value to the study of plant origin,evolution and geographical flora.A.spinulosa is endangered due to climate change and the destruction of its growth environment.It has been listed as a national second-level key protected wild plant.Chishui Alsophila Natural Reserve takes A.spinulosa and its living environment as its main protection object.There are more than 40,000 A.spinulosa trees in Chishui National Nature Reserve.It has the largest number and the widest area of A.spinulosa forest in the world.The prohibition of harvesting in the reserve caused a large expansion of P.heterocycla,and quickly invaded the A.spinulosa forest.The original habitat of A.spinulosa growth was damaged to varying degrees.The original pure A.spinulosa forest has disappeared in recent years.The competition between P.heterocycla and A.spinulosa in space,sunshine and nutrients seriously threatens the survival and reproduction of A.spinulosa.In this paper,the carp community in the Chishui Alsophila Natural Reserve was disturbed by different degrees of P.heterocycla.The root-drilling method was used to study the morphological plasticity of the roots in the horizontal and vertical directions.Based on the principle of interaction between rhizosphere microorganisms and plant roots,Illumina Genome Analyzer IIx technology was used to analyze the diversity of qnorB-type denitrifying bacteria in the rhizosphere soil of three disturbances(mild,moderate and severe).In order to provide a theoretical basis for the protection of A.spinulosa population from the perspective of underground micro-ecology.The specific research results are as follows:1.The vertical distribution pattern of root system of P.heterocycla and A.spinulosa showed that the total root biomass density of P.heterocycla increased significantly with the increase of disturbance intensity,while that of A.spinulosaincreased first and then decreased.The biomass density of roots of 0-10 cm soil layer was the largest,which was 951.95 g/m~2,accounting for 39.09%of the total.The roots of the P.heterocycla with a diameter>5 mm are only distributed in the severe disturbed 10-20 cm soil layer.In addition,with the increase of soil depth,the root biomass density of A.spinulos increased gradually,that is,the root system of A.spinulos mostly concentrated in 20-30 cm soil layer.2.The horizontal distribution of the root system of P.heterocycla and A.spinulos was less than 2 mm.The root system of P.heterocycla decreased gradually with the increase of the distance from the P.heterocycla in the three soil layers.The variation trend of 2-5 mm root system in most soil layers is the same as that of<2 mm root system of P.heterocycla.The root biomass of A.spinulosa decreased with the increase of disturbance degree,moderate disturbance decreased by 47.62%,severe disturbance decreased by 37.53%,and the root biomass of A.spinulosa increased with the increase of distance from P.heterocycla.3.Under severe disturbance,the specific root length of P.heterocycla increased significantly,with an average increase of 66.9%.Overall,the fine root length of A.spinulosa decreased by 28.71%under severe disturbance.The distance between primary and secondary lateral roots of P.heterocycla is the smallest under severe disturbance,and the distance between nodes is the smallest in 0-10 cm soil layer,which indicates that the number of lateral roots of P.heterocycla is the largest.4.With the increase of disturbance degree of P.heterocycla,soil alkali-hydrolyzed nitrogen content increased significantly,available phosphorus content decreased significantly(P<0.05),while pH,water content and soil organic matter did not change significantly.5.The results of high throughput sequencing showed that a total of 201641 valid sequences and 119600 optimized sequences were obtained from three different interference levels of A.spinulosa rhizosphere soil samples.There were 4-5 phyla,11-13 classes,19-20 orders,23-25 families,25-28 genera and 33-37 species of denitrifying bacteria identified.Among them,the denitrifying bacteria under mild disturbance had the least composition and the bacterial species under severe disturbance were the richest.6.The abundance of Shewanella in all plots is greater than 6.5%,which is the dominant flora.Except for Anaeromyxobacter,the abundance of the other genera increased with the increase of interference intensity.The samples with moderate and severe disturbance of P.heterocycla had higher Ace and Chao values,and the qnorB denitrifying bacteria community with severe disturbance had the highest Shannon index and the lowest Simpson index.Both UPGMA and PCoA analyses showed that communities under severe and mild disturbance belonged to two different branches.