Age and Species of Eucalyptus Plantations Affect Soil Microbial Biomass and Enzymatic Activities

Seasonal variations affect the ecosystem functioning and microbial assembly processes in plantation forest soils

While afforestation mitigates climate concerns, the impact of afforestation on ecological assembly processes and multiple soil functions (multifunctionality) in afforested areas remains unclear. The Xiong'an New Area plantation forests (Pinus and Sophora forests) in North China were selected to examine the effects of plantation types across four distinct seasons on soil microbiomes. Three functional categories (nutrient stocks, organic matter decomposition, and microbial functional genes) of multifunctionality and the average (net) multifunctionality were quantified. All these categories are directly related to soil functions. The results showed that net soil multifunctionality as a broad function did not change seasonally, unlike other narrow functional categories. Bacterial communities were deterministically (variable selection and homogenous selection) structured, whereas the stochastic process of dispersal limitation was mainly responsible for the assembly and turnover of fungal and protist communities. In Pinus forests, winter initiates a sudden shift from deterministic to stochastic processes in bacterial community assembly, accompanied by decreased Shannon diversity and heightened nutrient cycling (nutrient stocks and organic matter decomposition). This indicates the potential vulnerability of deterministic assembly to seasonal fluctuations, particularly in environments rich in nutrients. The results predicted that protist community composition was uniquely structured with C-related functional activities relative to bacterial and fungal β-diversity variations, which were mostly explained by seasonal variations. Our study highlighted the importance of the protist phagocytosis process on soil microbial interactions through the predicted impact of protist α-diversity on microbial cooccurrence network parameters. This association might be driven by the high abundance of protist consumers as the main predators of bacterial and fungal lineages in our sampling plots. Our findings reveal that the complexity of microbial co-occurrence interactions was considerably higher in spring, perhaps attributing thermal variability and increased resource availability within spring that foster microbial diversity and network complexity. This study contributes to local ecosystem prospects to model the behavior of soil biota seasonally and their implied effects on soil functioning and microbial assembly processes, which will benefit global-scale afforestation programs by promoting novel, precise, and rational plantation forests for future environmental sustainability and self-sufficiency.

Fungal community structure shifts in litter degradation along forest succession induced by pine wilt disease

Fungi play a crucial role in decomposing litter and facilitating the energy flow between aboveground plants and underground soil in forest ecosystems. However, our understanding how the fungal community involved in litter decomposition responds during forest succession, particularly in disease-driven succession, is still limited. This study investigated the activity of degrading enzyme, fungal community, and predicted function in litter after one year of decomposition in different types of forests during a forest succession gradient from coniferous to deciduous forest, induced by pine wilt disease. The results showed that the weight loss of needles/leaves and twigs did not change along the succession process, but twigs degraded faster than needles/leaves in both pure pine forest and mixed forest. In pure pine forest, peak activities of enzymes involved in carbon degradation (β-cellobiosidase, β-glucosidase, β-D-glucuronidase, β-xylosidase), nitrogen degradation (N-acetyl-glucosamidase), and organic phosphorus degradation (phosphatase) were observed in needles, which subsequently declined. The fungal diversity and evenness (Shannon's diversity and Shannon's evenness) dropped in twig from coniferous forest to mixed forest during the succession. The dominant phyla in needle/leaf and twig litters were Ascomycota (46.9%) and Basidiomycota (38.9%), with Lambertella pruni and Chalara hughesii identified as the most abundant indicator species. Gymnopus and Desmazierella showed positively correlations with most measured enzyme activities. Functionally, saprotrophs constituted the main trophic mode (47.65%), followed by Pathotroph-Saprotroph-Symbiotroph (30.95%) and Saprotroph-Symbiotroph (10.57%). The fungal community and predicted functional structures in both litter types shifted among different forest types along the succession. These findings indicate that the fungal community in litter decomposition responds differently to disease-induced succession, leading to significant shifts in both the fungal community structure and function.

The impact of fast-growing eucalypt plantations on C emissions in tropical soil: effect of belowground and aboveground C inputs

Planted forest soils can have great potential for CO2-C sequestration, mainly due to belowground C inputs, which impact deep soil C (DSC) accumulation. However, there are still gaps in understanding the CO2 emission dynamics in eucalypt plantations. Therefore, we used isotopic techniques to investigate the dynamics of the soil surface CO2-C flux and CO2-C concentration with depth for a eucalypt plantation influenced by different C inputs (above- and belowground). The gas evaluations were carried in depth the root to valuation of root priming effect (RPE) was calculated. In addition, measurements of the plant (C-fine root and C-litterfall) and soil (total organic carbon - TOC, total nitrogen - TN, soil moisture - SM, and soil temperature - ST) were performed. After planting the eucalypt trees, there was an increase in the soil surface CO2-C flux with plant growth. Root growth contributed greatly to the soil surface CO2-C flux, promoting greater surface RPE over time. In comparison to the other factors, SM had a greater influence on litterfall decomposition and root respiration. It was not possible to detect losses in TOC and TN in the different soil layers for the 31-month-old eucalypt. However, the 40-month-old eucalypt showed a positive RPE with depth, indicating possible replacement of DSC ("old C") by rhizodeposition-C ("new C") in the soil. Thus, in eucalyptus plantations, aboveground plant growth influences CO2 emissions on the soil surface, while root growth and activity influence C in deeper soil layers. This information indicates the need for future changes in forest management, with a view to reducing CO2 emissions.

Diversity and Distribution of Calonectria Species in Soils from Eucalyptus urophylla × E. grandis, Pinus massoniana, and Cunninghamia lanceolata Plantations in Four Provinces in Southern China

The species of Calonectria include many notorious plant pathogens and are widely distributed around the world. Leaf blight caused by Calonectria species is considered one of the most prominent diseases in Eucalyptus plantations in China. Some Calonectria species isolated from soils in Eucalyptus plantations are highly pathogenic to inoculated Eucalyptus genotypes. In southern China, the plantation trees Cunninghamia lanceolata, Eucalyptus spp., and Pinus massoniana are always adjacently planted, especially in FuJian, GuangDong, GuangXi, and YunNan Provinces. The aim of this study was to understand the diversity and distribution of Calonectria in soils from plantations of different tree species in different geographic regions. Soil samples were collected from 12 sampling sites in Eucalyptus urophylla × E. grandis, P. massoniana, and C. lanceolata plantations in FuJian, GuangDong, GuangXi, and YunNan Provinces. Approximately 250 soil samples were collected from each sampling site, and a total of 2991 soil samples were obtained. A total of 1270 Calonectria isolates were obtained from 1270 soil samples. The 1270 isolates were identified based on DNA sequence comparisons of the partial gene regions of act, cmdA, his3, rpb2, tef1, and tub2. These isolates were identified as 11 Calonectria species: Calonectria aconidialis (69.50%), C. kyotensis (13.10%), C. hongkongensis (10.80%), C. ilicicola (2.50%), C. asiatica (2.36%), C. curvispora (0.31%), C. chinensis (0.24%), C. pacifica (0.24%), C. yunnanensis (0.16%), and C. canadiana (0.08%) in the C. kyotensis species complex and C. eucalypti (0.71%) in the C. colhounii species complex. The three dominant species, C. aconidialis, C. kyotensis, and C. hongkongensis, were widely distributed. The richness of Calonectria (percentage of soil samples that yielded Calonectria) in soils in the eastern regions (relatively humid regions) was higher than that in the western regions. The Calonectria richness of E. urophylla × E. grandis, P. massoniana, and C. lanceolata plantations decreased gradually. For each of the three dominant species, its richness in the eastern regions was generally higher than that in the western regions; the species richness was highest in E. urophylla × E. grandis plantations for C. aconidialis, while for each of C. kyotensis and C. hongkongensis, its species richness was highest in P. massoniana plantations. The genetic variation in C. aconidialis, C. kyotensis, and C. hongkongensis was more greatly affected by geographic region than by plantation tree species. This study expanded our understanding of the richness, species diversity, and distribution characteristics of Calonectria in soils from the plantations of different tree species in different geographic regions in southern China. Results in this study enhanced our understanding of the influencing characteristics of geographic region and tree species on the species and genetic diversity of soilborne fungi.

Soil Fungal Community Structure and Function Shift during a Disease-Driven Forest Succession

Forest succession is important for sustainable forest management in terrestrial ecosystems. However, knowledge about the response of soil microbes to forest disease-driven succession is limited. In this study, we investigated the soil fungal biomass, soil enzyme activity, and fungal community structure and function in forests suffering succession processes produced by pine wilt disease from conifer to broadleaved forests using Illumina Miseq sequencing coupled with FUNGuild analysis. The results showed that the broadleaved forest had the highest fungal biomass and soil enzyme activities in C, N, and S cycles, whereas the conifer forest had the highest enzyme activity in the P cycle. Along the succession, the fungal diversity and richness significantly increased (P < 0.05). The fungal communities were dominated by Ascomycota (42.0%), Basidiomycota (38.0%), and Mortierellomycota (9.5%), among which the abundance of Ascomycota significantly increased (P < 0.05), whereas that of Basidiomycota and Mortierellomycota decreased (P < 0.05). The abundance of species Mortierella humilis, Lactarius salmonicolor, and Russula sanguinea decreased, whereas that of Mortierella minutissima increased (P < 0.05). The forests in different succession stages formed distinct fungal communities and functional structures (P < 0.05). Functionally, the saprotrophs, symbiotrophs, and pathotrophs were the dominant groups in the conifer, mixed, and broadleaved forests, respectively. Soil pH and soil organic carbon were the key factors influencing the fungal community and functional structures during the succession. These findings provide useful information for better understanding the plant-microbe interaction during forest succession caused by forest disease. IMPORTANCE The studies on soil fungal communities in disease-driven forest succession are rare. This study showed that during the disease-driven forest succession, the soil enzyme activity, soil fungal diversity, and biomass increased along succession. The disease-driven forest succession changed the soil fungal community structure and function, in which the symbiotrophs were the most dominant group along the succession. These findings provide useful information for better understanding the plant-microbe interaction during forest succession caused by forest disease.

Extracellular Enzyme Stoichiometry Reveals Soil Microbial Carbon and Phosphorus Limitations in the Yimeng Mountain Area, China

Soil extracellular enzymes are considered key components in ecosystem carbon and nutrient cycling, and analysing their stoichiometry is an effective way to reveal the resource limitations on soil microbial metabolism. In this study, the soil and litter of Quercus acutissima plots, Pinus thunbergii plots, Quercus acutissima–Pinus thunbergii mixed-plantation plots, herb plots, and shrub plots in the state-owned Dawa Forest Farm in the Yimeng Mountain area were studied. The total carbon (C), nitrogen (N), and phosphorus (P) contents of litter and the physical and chemical properties of soil were analyzed, along with the activities of four extracellular enzymes related to the soil C, N, and P cycle: β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (AP). The extracellular enzyme stoichiometric model was used to study and compare the metabolic limitations of soil microorganisms in different plots, and the driving factors of microbial metabolic limitations were explored by redundancy and linear regression analyses. The results showed that the values of BG/(NAG + LAP) were all higher than 1, the values of (NAG + LAP)/AP all lower than 1, and the vector angles of the five plots all greater than 45°, which indicated that the soil microorganisms were relatively limited by C and P. Redundancy and linear regression analysis revealed that soil physical properties (e.g., soil moisture) and litter total C make greater contributions to soil extracellular enzymes and stoichiometry than the other investigated soil parameters, whereas soil chemical properties (e.g., soil organic C and available P) predominantly controlled vector properties. Therefore, microbial metabolism limitations are greatly regulated by soil physical and chemical properties and litter total C and N. Compared with the forest plots, the soil microbial C (1.67) and P (61.07°) limitations of herb plots were relatively higher, which means that the soil microbial communities of forest plots are more stable than those of herb plots in the Yimeng Mountain area. Forest plots were more conducive than other plots to the improvement of soil microbial ecology in this area. This study could be important for illuminating soil microbial metabolism and revealing soil nutrient cycling in the Yimeng Mountain area ecosystem of China.

Eucalyptus Plantation Age and Species Govern Soil Fungal Community Structure and Function Under a Tropical Monsoon Climate in China

Fungi perform crucial roles in nutrient cycles, but there is limited information on how soil fungal communities vary with stand age and tree species. Eucalyptus has been extensively planted in China, which has caused severe soil erosion and water deficiency due to short rotation management. In this study, the fungal community structure and potential function in Eucalyptus plantations with different ages (1-5+ years) and species (Eucalyptus urophylla × Eucalyptus grandis, Eucalyptus camaldulens, and Eucalyptus pellita) under a tropical monsoon climate in China were characterized by Illumina Miseq coupled with FUNGuild analysis. The results showed that the fungal alpha diversity decreased with an increase in the age of the plantation. Plantations of different ages and species formed distinct fungal communities and potential functional structures, respectively (p < 0.05), in which the age of the plantation contributed more to the variations. At high taxonomic levels, the soil fungal community changed from the dominance of orders belonging to Ascomycota (Pleosporales, Chaetothyriales, and Eurotiales) to orders belonging to Basidiomycota (Agaricales, Sebacinales, Cantharellales, and Russulales) with increasing plantation age. The community potential function shifted from the dominance of plant pathogens to a higher abundance of saprotrophs and symbiotrophs. The organic carbon of the soil was the key environmental driver to both the fungal community and potential functional structure. The results provide useful information on the importance of fungi for the management of Eucalyptus plantations.

Recent Advances in Applied Microbiology: Editorial

The importance of microbiology has grown exponentially since the development of genomics, transcriptomics, and proteomics, making it possible to clarify microbial biogeochemical processes and their interactions with macroorganisms in both health and disease. Particular attention is being payed to applied microbiology, a discipline that deals with the application of microorganisms to specific endeavors, whose economic value is expected to exceed USD 675.2 billion by 2024. In the Special Issue "Recent Advances in Applied Microbiology", twenty-four papers were published (four reviews and twenty original research papers), covering a wide range of subjects within applied microbiology, including: microbial pathogenesis, the health-promoting properties of microorganisms and their by-products, food conservation, the production of alcoholic beverages, bioremediation and the application of microbiology to several industrial processes.