Lina Cui

Cunninghamia lanceolata is an important species in plantations and is widely planted in sub-tropical regions of China because of its fast-growing and productive characteristics. However, the monoculture planting is carried out in the pursuit of economic value. This planting mode has led to problems such as the exhaustion of soil fertility, decrease in vegetation diversity, and decrease in woodland productivity. In order to restore soil fertility and increase timber production, the introduction of broad-leaved tree species to plantations is an effective transformation model. Understanding how forest age changes and stand structure differences drive the composition and diversity of soil microbial communities is helpful in understanding the trend of soil–microbial changes in plantations and evaluating the effects of the introduction of broad-leaved tree species in soil–plant–microbial ecosystems in plantations. Therefore, the purpose of our study is to investigate the effects of forest age and pure forest conversion on C. lanceolata–P. bournei-mixed forest soil microbial community structure and diversity by detecting soil nutrients, enzyme activities, and soil microbial 16S and ITS rRNA gene sequencing. According to the findings, the diversity and abundance of bacterial communities in C. lanceolata plantations of different ages increased first and then decreased with the increase in forest age, and the max value was in the near-mature forest stage. The fungal abundance decreased gradually with stand age, with the lowest fungal diversity at the near-mature stand stage. During the whole growth process, the bacterial community was more limited by soil pH, nitrogen, and phosphorus. After introducing P. bournei into a Chinese fir plantation, the abundance and diversity of the bacterial community did not improve, and the abundance of the fungal community did not increase. However, soil nutrients, pH, and fungal community diversity were significantly improved. The results of these studies indicate that the introduction of broad-leaved tree species not only increased soil nutrient content, but also had a significant effect on the increase in the diversity of soil fungal communities, making the microbial communities of mixed forests more diverse.

In China, the invasion of Spartina alterniflora is an important driver for the decrease of mangrove area and ecological service functions related to this habitat. In the past few decades, S. alterniflora clearing and mangrove restoration projects have mainly focused on the areas where it is already changed but ignored the potential distribution areas. This study suggested that implementation of mangrove protection prior to the areas with the threat of S. alterniflora invasion could greatly improve protection efficiency and save costs. Thus, using Maximum Entropy Modeling (MaxEnt), we estimated the potential spatial distribution of both mangroves and S. alterniflora in China, considering the current distribution data, topographical, sediments, sea surface temperature and bioclimatic variables. What’s more, we identified and calculated the potential distributed areas in each province. We aimed to explore (i) the key factors determining the distribution of mangrove and Spartina alterniflora along the coastline and (ii) the hotspots of their competitive occurrence, including S. alterniflora invasion areas and mangroves degradation areas, in order to support mangrove conservation. The model showed that the distance to the coastline and the topography play important roles in the distribution of S. alterniflora, while mangroves were more sensitive to the range of the annual sea surface temperature. Our results furthermore confirm that S. alterniflora has a wider potential distribution area (~10,585 km²) than mangroves (~9124 km²) at the coastline of China; and predict the provinces Zhangzhou, Quanzhou, Zhanjiang, Beihai and Wenzhou as hotspots for the competition between mangroves and S. alterniflora. We propose that priority should be given to the protection or restoration of mangrove plants in those areas which are co-suitable for mangroves and S. alterniflora. In these areas, management measures should be conducted that hinder S. alterniflora invasions or clear existing S. alterniflora plants, firstly. This study provides guidance for the management of native species by preventing biological invasion.

Sea level rise (SLR) has a significant impact on the vegetation ecosystem in coastal wetlands. Taking coastal China as the study area, the SLAMM (sea level rise affecting marsh model) was used to simulate the continuous long-term (2015–2100) effects of the spatiotemporal changes in mangrove and Spartina alterniflora in the four shared socioeconomic pathway scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5) of sea level rise by 2100; then, ArcGis was used to assess and compare the impact of SLR on land use. The results are as follows. (1) The dramatic reduction in the vegetation area is positively correlated with the rate of sea level rise. (2) Tidal differences and sedimentation rates affect the response of mangrove and S. alterniflora distribution to sea level rise, as well as interactions between organisms. (3) The reasonable land use of coastal wetlands is important to researchers. Land use is one of the tools for effective mangrove conservation. In conclusion, in scientific research and production practice, it is important to combine the biotic and abiotic factors affecting the distribution of mangroves and S. alterniflora.

It has been reported that the invasion of Spartina alterniflora changed the soil microbial community in the mangrove ecosystem in China, especially the bacterial community, although the response of soil fungal communities and soil microbial ecological functions to the invasion of Spartina alterniflora remains unclear. In this study, we selected three different communities (i.e., Spartina alterniflora community (SC), Spartina alterniflora–mangrove mixed community (TC), and mangrove community (MC)) in the Zhangjiangkou Mangrove Nature Reserve in China. High-throughput sequencing technology was used to analyze the impact of Spartina alterniflora invasion on mangrove soil microbial communities. Our results indicate that the invasion of Spartina alterniflora does not cause significant changes in microbial diversity, but it can alter the community structure of soil bacteria. The results of the LEfSe (LDA Effect Size) analysis show that the relative abundance of some bacterial taxa is not significantly different between the MC and SC communities, but different changes have occurred during the invasion process (i.e., TC community). Different from the results of the bacterial community, the invasion of Spartina alterniflora only cause a significant increase in few fungal taxa during the invasion process, and these taxa are at some lower levels (such as family, genus, and species) and classified into the phylum Ascomycota. Although the invasion of Spartina alterniflora changes the taxa with certain ecological functions, it may not change the potential ecological functions of soil microorganisms (i.e., the potential metabolic pathways of bacteria, nutritional patterns, and fungal associations). In general, the invasion of Spartina alterniflora changes the community structure of soil microorganisms, but it may not affect the potential ecological functions of soil microorganisms.