Tropical Rainforest Restoration Plantations Are Slow to Restore the Soil Biological and Organic Carbon Characteristics of Old Growth Rainforest

The Heterogeneous Habitat of Taiga Forests Changes the Soil Microbial Functional Diversity

The soil contains abundant and diverse microorganisms, which interrelate closely with the aboveground vegetation and impact the structure and function of the forest ecosystem. To explore the effect of vegetation diversity on soil microbial functional diversity in taiga forests, we selected significantly different important values of Larix gmelinii as experimental grouping treatments based on plant investigation from fixed plots in Da Xing'anling Mountains. Following that, we collected soil samples and applied the Biolog-ECO microplate method to investigate differences in carbon source utilization, features of functional diversity in soil microorganisms, and factors influencing them in taiga forests. The AWCD decreased as the important value of Larix gmelinii grew, and soil microorganisms preferred carboxylic acids, amino acids, and carbohydrates over polymers, phenolic acids, and amines. The Shannon and McIntosh indexes decreased significantly with the increase of the important value of Larix gmelinii (p < 0.05) and were positively correlated with soil SOC, MBC, C/N, and pH, but negatively with TN, AP, and AN. Redundancy analysis revealed significant effects on soil microbial functional diversity from soil C/N, SOC, AP, MBC, TN, pH, AN, and WC. To sum up, heterogeneous habitats of taiga forests with different important values altered soil microbial functional diversity.

Insights into the deriving of rhizosphere microenvironments and its effects on the growth of authentic Angelica sinensis seedlings under continuous monoculture

Purpose

Continuous monoculture leads to deterioration of soil microenvironment, which can severely threat the quality and efficiency of Angelica sinensis (A. sinensis), especially for seedlings production. However, little attention has been paid to investigate how continuous monocropping affects the growth of A. sinensis seedling, rhizosphere microbial populations, and nutrient status.

Methods

A field experiment consisting of two different planting patterns — raising A. sinensis seedlings in reclamation alpine uncultivated meadow (RW) and 1-year continuous monoculture (CC), was carried out at Min County, Gansu province, China.

Result

The results showed that compared with RW, the growth rate and valid quantity of A. sinensis seedlings were significantly reduced by 195.4% and 36.7% in CC, respectively. Continuous monocropping significantly increased the rhizosphere soil pH value during the growing season, ranging from 6.18 to 7.10, while reducing the content of SOM, total N, and available P and K. Glomalin, AMF spore densities, and the number of actinomycetes, ammonifiers, and azotobacter were also decreased by CC. The CC treatment significantly increased the abundance of fungi. The diversity and richness of bacteria in CC were lower than RW. Furthermore, the composition and structure of bacterial and fungal flora also changed and that the abundance of beneficial bacteria decreased, while the abundance of pathogens increased in CC. Thus, CC appeared to completely upend the relationship between soil nutrient availability and microbial activity.

Conclusion

The results illustrated that continuous monoculture led the flora of bacteria and fungi to changed dramatically, with the abundance of beneficial bacteria decreased and the abundance of harmful microbes, such as Lasiosphaeriaceae, Vishniacozyma, Myrmecridium, and Hypocreales, increased. The function of microbial population has changed from “beneficial bacteria dominated” to “harmful microbes dominant.” We concluded that continuous monoculture significantly reduced the growth and the efficiency of A. sinensis seedlings and deteriorated the rhizosphere soil microenvironment by increasing pH and decreasing nutrient availability, as well as altering the function of interactions between soil nutrients and microbial populations, thereby resulting in an unsuitable microenvironment for A. sinensis seedlings growth.

Effect of Cultivated Pastures on Soil Bacterial Communities in the Karst Rocky Desertification Area

Soil bacteria play an important role in regulating the process of vegetation restoration in karst ecosystems. However, the effects of vegetation restoration for different cultivated pastures on soil bacterial communities in the karst rocky desertification regions remain unclear. Therefore, we hypothesized that mixed pasture is the most effective for soil bacterial communities among different vegetation restorations. In this study, we systematically studied the soil properties and soil bacterial communities in four vegetation restoration modes [i.e., Dactylis glomerata pasture (DG), Lolium perenne pasture (LP), Lolium perenne + Trifolium repens mixed pasture (LT), and natural grassland (NG)] by using 16S rDNA Illumina sequencing, combined with six soil indicators and data models. We found that the vegetation restoration of cultivated pastures can improve the soil nutrient content compared with the natural grassland, especially LT treatment. LT treatment significantly increased the MBC content and Shannon index. The vegetation restoration of cultivated pastures significantly increased the relative abundance of Proteobacteria, but LT treatment significantly decreased the relative abundance of Acidobacteria. Soil pH and MBC significantly correlated with the alpha diversity of soil bacterial. Soil pH and SOC were the main factors that can affect the soil bacterial community. FAPROTAX analysis showed LT treatment significantly decreased the relative abundance of aerobic chemoheterotrophs. The results showed that the bacterial communities were highly beneficial to soil restoration in the LT treatment, and it confirmed our hypothesis. This finding provides a scientific reference for the restoration of degraded ecosystems in karst rocky desertification areas.

Natural Recovery from Fire Disturbance is More Favorable than Assisted Recovery for the Restoration of Soil Nematode-trapping Fungi

Fire is usually considered a severe disturbance factor in environment. Globally, rising temperatures and increasing human activities have intensified the severity and frequency of fire incidents; research on postfire recovery has inevitably become an important focus for ecologists. In terms of the restoration of burned areas, there are usually two primary approaches: natural recovery and assisted recovery. However, there are very few relevant studies that systematically compared these recovery alternatives suggesting which one is more favorable to the overall restoration of an ecosystem, especially to the soil microbes that function as indispensable components of ecosystems. In this study, the restoration of soil nematode-trapping fungi (NTF) was compared between natural and assisted recovery environments. Results showed that although the NTF community structures differed among the sample sites, the counts and diversity of the NTF communities in the upper and lower soil layers in the natural recovery area were higher than those in the assisted recovery and the unburned control areas. These findings suggests that artificial efforts to help ecosystem recovery after fire produce negative effects on the speed and quality of soil NTF community recovery. Instead, natural recovery appears to be the more suitable land management choice after fire disturbance.

Effect of Different Grain for Green Approaches on Soil Bacterial Community in a Karst Region

Soil bacteria participate in nutrient cycling above and below ground to promote ecosystem stability and health. However, the relationship of soil bacteria and environmental factors following the Grain for Green (GfG) program remains poorly understood in southwest China. Soil samples were collected from seven Grain for Green sites that had been revegetated for 15 years. Four of these sites were afforested with a different tree species: Zenia insignis (ZI), Toona sinensis (TS), Castanea mollissima (CM), and Citrus reticulate (CR). One site was revegetated with Zenia insignis and Guimu-1 elephant grass (ZG), and one with only Guimu-1 elephant grass (GM). The remaining site, abandoned cropland (AC), was left to regenerate naturally. Here, we used Illumina sequencing of 16S rRNA genes to explore how the Grain for Green project affected soil bacterial community. We found that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in these soils. The dominant genera at each revegetation site were also different. The CM, ZI, TS, and AC sites were dominated by Micromonospora, ZG was dominated by Streptomyces, and CR and GM were dominated by Subgroup 6. The bacterial structure was most similar in AC and TS. Correlation analysis showed that the ratio of C:P had positive effects on KD4-96, Intrasporangiaceae, and Gaiella. The ratio of soil N:P was significantly positively correlated with Cupriavidus and Kribbella. The combination of planting Zenia insignis and Guimu-1 elephant grass had the best edaphic benefits, and the approach of planting Citrus reticulate and Toona sinensis needs to be improved. Redundancy analysis (RDA) revealed that plant Simpson index, and soil N:P contributed to 16 and 15.7% of the total variations in the soil bacterial community composition, respectively. Our results suggested that plant diversity (Simpson index) and soil stoichiometric ratio (N:P) were the important factors affecting the bacterial community, and phosphorus was the limiting factor of the bacterial community in the Grain for Green karst region. In the future, revegetation should be accompanied with phosphorus fertilizer and polycultures should be considered.