Quantification of Arbuscular Mycorrhizal Fungi Colonization Rate in the Study of Invasive Alien Plants

Arbuscular mycorrhizal fungi (AMF) are widely distributed soil fungi in ecosystems and can form symbiotic associations (mycorrhizae) with the roots of ...

Chinese Academy of Agricultural Sciences

Eutrophication and climate warming, induced by anthropogenic activities, are simultaneously occurring worldwide and jointly affecting soil carbon stability. Therefore, it is of great interest to examine whether and how they interactively affect soil microbial community, a major soil carbon driver. Here, we showed that climate warming, simulated by southward transferring Mollisol soil in agricultural ecosystems from the cold temperate climate zone (N) to warm temperate climate (C) and subtropical climate zone (S), decreased soil organic matter (SOM) by 6%-12%. In contrast, amendment with nitrogen, phosphorus and potassium enhanced plant biomass by 97% and SOM by 6% at the N site, thus stimulating copiotrophic taxa but reducing oligotrophic taxa in relative abundance. However, microbial responses to nutrient amendment were overridden by soil transfer in that nutrient amendment had little effect at the C site but increased recalcitrant carbon-degrading fungal Agaricomycetes and Microbotryomycetes taxa derived from Basidiomycota by 4-17 folds and recalcitrant carbon-degrading genes by 23%-40% at the S site, implying a possible priming effect. Consequently, SOM at the S site was not increased by nutrient amendment despite increased plant biomass by 108%. Collectively, we demonstrate that soil transfer to warmer regions overrides microbial responses to nutrient amendment and weakens soil carbon sequestration.

Microbial responses to inorganic nutrient amendment overridden by warming: Consequences on soil carbon stability.

Both fungi and bacteria play essential roles in regulating soil carbon cycling. To predict future carbon stability, it is imperative to understand their responses to environmental changes, which is subject to large uncertainty. As current global warming is causing range shifts toward higher latitudes, we conducted three reciprocal soil transplantation experiments over large transects in 2005 to simulate abrupt climate changes. Six years after soil transplantation, fungal biomass of transplanted soils showed a general pattern of changes from donor sites to destination, which were more obvious in bare fallow soils than in maize cropped soils. Strikingly, fungal community compositions were clustered by sites, demonstrating that fungi of transplanted soils acclimatized to the destination environment. Several fungal taxa displayed sharp changes in relative abundance, including Podospora, Chaetomium, Mortierella and Phialemonium. In contrast, bacterial communities remained largely unchanged. Consistent with the important role of fungi in affecting soil carbon cycling, 8.1%-10.0% of fungal genes encoding carbon-decomposing enzymes were significantly (p < 0.01) increased as compared with those from bacteria (5.7%-8.4%). To explain these observations, we found that fungal occupancy across samples was mainly determined by annual average air temperature and rainfall, whereas bacterial occupancy was more closely related to soil conditions, which remained stable 6 years after soil transplantation. Together, these results demonstrate dissimilar response patterns and resource partitioning between fungi and bacteria, which may have considerable consequences for ecosystem-scale carbon cycling.

Dissimilar responses of fungal and bacterial communities to soil transplantation simulating abrupt climate changes.

Invasive plant species may alter soil nutrient availability to facilitate their growth and competitiveness. However, the roles and functional mechanisms of plant-associated microbes that mediate these soil biogeochemical cycles remain elusive. Here, we studied how soil microorganisms and their functional processes differed between soils invaded by Ageratina adenophora and adjacent non-invaded soils in a region of China with heavy invasion. Our results indicated that soil nitrogen contents were over 4.32 mg/kg higher (p < 0.05) in both rhizosphere soils and bulk soils dominated by A. adenophora as compared with those in soils dominated by non-invaded plants. Concurrently, soil microbial-mediated functional processes, i.e. nitrogen fixation rate, nitrification rate and ammonification rate, were also significantly (p < 0.05) higher in either rhizosphere soils or bulk soils of invasive A. adenophora. Using a functional gene microarray, we found higher relative abundances of soil microbial genes involved in N cycling processes in A. adenophora soils, e.g. nifH, required for nitrogen fixation, which significantly correlated with ammonia contents (r = 0.35 in bulk soils, r = 0.37 in rhizosphere soils, p < 0.05) and the nitrogen fixation rate (r = 0.44, p < 0.05). We also found that the relative abundances of labile carbon decomposition genes were higher in invasive A. adenophora soils, implying a potential higher availability of carbon. These results suggest that the soil surrounding the invasive plant A. adenophora is a self-reinforcing environment. The plant litter and rhizosphere environment of the invasive may influence soil microbial communities, promoting self-supporting soil processes. Alternatively, the regions invaded by A. adenophora may have already had properties that facilitated these beneficial microbial community traits, allowing easier invasion by the exotics. Both scenarios offer important insights for the mitigation of plant invasion and provide an ecosystem-level understanding of the invasive mechanisms utilized by alien plants.

Ageratina adenophora invasions are associated with microbially mediated differences in biogeochemical cycles.

Mikania micrantha is one of the top 100 worst invasive species that can cause serious damage to natural ecosystems and substantial economic losses. Here, we present its 1.79 Gb chromosome-scale reference genome. Half of the genome is composed of long terminal repeat retrotransposons, 80% of which have been derived from a significant expansion in the past one million years. We identify a whole genome duplication event and recent segmental duplications, which may be responsible for its rapid environmental adaptation. Additionally, we show that M. micrantha achieves higher photosynthetic capacity by CO absorption at night to supplement the carbon fixation during the day, as well as enhanced stem photosynthesis efficiency. Furthermore, the metabolites of M. micrantha can increase the availability of nitrogen by enriching the microbes that participate in nitrogen cycling pathways. These findings collectively provide insights into the rapid growth and invasive adaptation.

Mikania micrantha genome provides insights into the molecular mechanism of rapid growth.

Soil microorganisms play important roles in the ecosystem functioning of subtropical broad-leaved forests (SBFs). However, the patterns and environmental indicators of soil microbial functional structure remain unclear in SBFs. In the present work, we used a functional microarray (GeoChip 4.0) to examine the soil microbial functional structure of three types of SBFs, including a deciduous broad-leaved forest (DBF), a mixed evergreen-deciduous broad-leaved forest (MBF), and an evergreen broad-leaved forest (EBF). We found that microbial functional structure was significantly different among SBFs (P < 0.05). Compared to the DBF and the EBF, the MBF had higher functional α-diversity (P = 0.001, F = 12.55) but lower β-diversity (P < 0.001, F = 61.09), and showed more complex functional gene networks. Besides, the MBF had higher relative abundances of functional genes for carbon (C) decomposition, C fixation, nitrogen (N) cycling, sulfur (S) cycling, and phosphorus (P) cycling (P < 0.05), indicating stronger microbial functional capabilities of nutrient cycling processes. Edaphic variables (i.e., soil pH and soil nutrient content) were revealed as better indicators of soil microbial functional structure than plant-related ones (i.e., vegetation type and plant diversity) in SBFs. For example, functional gene structure of the DBF was significantly related to soil total S (P = 0.041), that of the MBF was significantly related to soil organic C (P = 0.027) and plant available P (P = 0.034), and that of the EBF was significantly related to soil pH (P = 0.006) and total potassium (K) (P = 0.038). Overall, through the analysis of microbial functional gene profiles, this study yields unique insights into the environmental indicators of patterns and mechanisms of soil microbial functional structure in SBFs.

Mengxin Zhao

State Key Laboratory for Biology of Plant Diseases and Insect Pests,
Institute of Plant Protection,
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection

Chinese Academy of Agricultural Sciences

Quantification of Arbuscular Mycorrhizal Fungi Colonization Rate in the Study of Invasive Alien Plants

Mengxin Zhao

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}State Key Laboratory for Biology of Plant Diseases and Insect Pests,Institute of Plant Protection,State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection

Chinese Academy of Agricultural Sciences

Quantification of Arbuscular Mycorrhizal Fungi Colonization Rate in the Study of Invasive Alien Plants

State Key Laboratory for Biology of Plant Diseases and Insect Pests,
Institute of Plant Protection,
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection