Sorption of cobalt and zinc from single and binary metal solutions by Evernia prunastri

Non-living lichen Evernia prunastri was studied as biosorbent material for zinc and cobalt removal from single and binary metal solutions. Sorption equilibrium of Zn2+ and Co2+ ions was reached within 1 hour. Both cobalt and zinc biosorption was not pH dependent within the range pH 4-6 and negligible at pH 2. The experimental results were fitted to the Langmuir, Freundlich, Redlich-Peterson and Langmuir-Freundlich adsorption isotherms to obtain the characteristic parameters of each model. The Langmuir, Redlich-Peterson and Langmuir-Freundlich isotherms were found to well represent the measured sorption data. According to the evaluation using the Langmuir equation, the maximum sorption capacities of metal ions onto lichen biomass were 112 μmol/g Zn and 97.2 μmol/g Co from single metal solutions. E. prunastri exhibited preferential uptake of zinc from equimolar binary Zn2+ - Co2+ mixtures within the range 50 – 4000 μM. Even thought mutual interference was seen in all Co-Zn binary systems. To evaluate the two-metal sorption system, simple curves had to be replaced by three-dimensional sorption surface. These results can be used to elucidate the behavior of lichens as bioindicators of cobalt and zinc pollution in water and terrestrial ecosystems.

Asymbiotic mass production of the arbuscular mycorrhizal fungus Rhizophagus clarus

Arbuscular mycorrhizal (AM) symbiosis is a mutually beneficial interaction between fungi and land plants and promotes global phosphate cycling in terrestrial ecosystems. AM fungi are recognised as obligate symbionts that require root colonisation to complete a life cycle involving the production of propagules, asexual spores. Recently, it has been shown that Rhizophagus irregularis can produce infection-competent secondary spores asymbiotically by adding a fatty acid, palmitoleic acid. Furthermore, asymbiotic growth can be supported using myristate as a carbon and energy source for their asymbiotic growth to increase fungal biomass. However, the spore production and the ability of these spores to colonise host roots were still limited compared to the co-culture of the fungus with plant roots. Here we show that a combination of two plant hormones, strigolactone and jasmonate, induces the production of a large number of infection-competent spores in asymbiotic cultures of Rhizophagus clarus HR1 in the presence of myristate and organic nitrogen. Inoculation of asymbiotically-generated spores promoted the growth of host plants, as observed for spores produced by symbiotic culture system. Our findings provide a foundation for the elucidation of hormonal control of the fungal life cycle and the development of inoculum production schemes.

The Influence of Residue Mixing on the Decomposition of Pepper Root Residues

(1) Background: Residue degradation plays a very important role in terrestrial ecosystems and residue mixing is the main factor affecting the degradation rates. However, in the agricultural systems, the effect of residue mixing on the degradation of pepper residues and the microbial community in pepper root residues is not clear. (2) Methods: In this study, we added different residues into soil by using double-layered nylon litterbags in culture bottles. The treatments including pepper root (P: Capsicum annuum L.), soybean [S: Glycine max (L.) Merr.] and maize (M: Zea mays L.) residue, as well as mixtures of soybean + pepper (SP), maize + pepper (MP), maize + soybean + pepper (MSP) mixtures. Litterbags were harvested after 7, 14, 28, and 56 days, respectively. Mass loss and nitrogen and phosphorus contents in pepper residue were quantified and bacterial and fungal community levels in pepper residues were analyzed using quantitative PCR and high throughput amplicon sequencing; (3) Results: The study showed that the mass loss and fungal community abundance of pepper root residue in mixtures were higher than P, except day 7. The phosphorus contents in MSP-P and MP-P were significantly lower than that for P at day 28 and day 56. Illumina MiSeq sequencing showed that the presence of maize residue significantly altered the microbial community composition of pepper root pepper. Day 56. (4) Conclusions: Our results suggest that residue mixing changed the microbial community abundance in pepper residue and promoted the degradation of pepper residues compared to pepper residue decomposition alone, especially for mixtures with soybean.

Long-Term Spatiotemporal Variation of Net Primary Productivity and Its Correlation With the Urbanization: A Case Study in Hubei Province, China

Net primary productivity (NPP) is a critical component in terrestrial ecosystem carbon cycles. Thus, quantitatively estimating and monitoring the dynamics of NPP have become key aspects for exploring the carbon cycle of terrestrial ecosystems. Anthropogenic activity, such as urbanization, has significant effects on NPP and increases pressure on the natural resources of a specific region. However, to date, although many studies have focused on the relationship between NPP variation and urbanization, they usually ignored any differences at a long-term spatiotemporal variation of urbanization factors, which led to the insufficient understanding of the urbanization-induced impacts on NPP. As a result, this study effectively explored the spatiotemporal variation of NPP from 2001 to 2012 and its corresponding relationship with urbanization, taking the Hubei Province in China as a case study area. To clarify the degree of urbanization, the spatial distribution and temporal variation of population and gross domestic product (GDP) were simulated based on the elevation-adjusted human settlement index and nighttime lights data. The major results showed that high NPP areas were located in those highlands with widespread woodland, in which the NPP value continued to grow during the period. The low NPP areas were mainly distributed in urban areas, and the NPP value had a continued and visible loss. The population and GDP both had a strong correlation with NPP. The significant negative correlation was concentrated in the center of Hubei, with a dense population and developed economy. In order to further realize their complex relationship, the correlation coefficients between the annual NPP and the two factors from 2001 to 2012 were calculated, and the changing trends were investigated. Overall, the findings of this study may provide a reference for studies on the interaction between ecological environment and socioeconomic processes under the background of global rapid urbanization.

Spatial and temporal models in plant ecology: logic and causality

In the paper, I argue that in order to make credible ecological predictions for terrestrial ecosystems in a changing environment, we need empirical plant ecological models that are fitted to spatial and temporal ecological data. Here, it is advocated to use structural equation models in a hierarchical framework with latent variables. Furthermore, it is an advantage that the proposed hierarchical models are analogous to well-known theoretical epistemological models of how knowledge is obtained.

Model Selection for Ecosystem Respiration Needs to Be Site Specific: Lessons from Grasslands on the Mongolian Plateau

Selecting an appropriate model for simulating ecosystem respiration is critical in modeling the carbon cycle of terrestrial ecosystems due to their magnitude and high variations in time and space. There is no consensus on the ideal model for estimating ecosystem respiration in different ecosystems. We evaluated the performances of six respiration models, including Arrhenius, logistic, Gamma, Martin, Concilio, and time series model, against measured ecosystem respiration during 2014–2018 in four grassland ecosystems on the Mongolian Plateau: shrubland, dry steppe, temperate steppe, and meadow ecosystems. Ecosystem respiration increased exponentially with soil temperature within an apparent threshold of ~19.62 °C at shrubland, ~16.05 °C at dry steppe, ~16.92 °C at temperate steppe, and ~15.03 °C at meadow. The six models explained approximately 50–80% of the variabilities of ecosystem respiration during the study period. Both soil temperature and soil moisture played considerable roles in simulating ecosystem respiration with R square, ranging from 0.5 to 0.8. The Martin model performed better than the other models, with a relatively high R square, i.e., R2 = 0.68 at shrubland, R2 = 0.57 at dry steppe, R2 = 0.74 at temperate steppe, and R2 = 0.81 at meadow. These models achieved good performance for around 50–80% of the simulations. No single model performs best for all four grassland types, while each model appears suitable for at least one type of ecosystem. Models that oil moisture include models, especially the Martin model, are more suitable for the accurate prediction of ecosystem respiration than Ts-only models for the four grassland ecosystems.