Nature And Properties Of Soils

The potential disease suppressiveness of arbuscular mycorrhizal (AM) fungi of various origins on Bipolaris sorokiniana in barley has been investigated. Firstly, a survey considering the occurrence of AM fungi in arable fields in Sweden were conducted with the aim to exploit site specific genetic resources in relation to disease suppressiveness. Arbuscular mycorrhizal fungi were present at all 45 sampling sites surveyed all over Sweden at densities ranging from 3 up to 44 spores per gram air dried soil. The highest spore density was found in a semi-natural grassland and the lowest were found in a cereal monoculture. The AM fungi were then multiplied in trap cultures in the greenhouse with the aim to use these for studying potential disease suppressiveness. Thus, the effects of the AM fungi trap cultures on the transmission of seed-borne B. sorokiniana in barley were investigated, using the trap culture inocula, but also including inocula consisting on spore mixtures. The arbuscular mycorrhizal fungi were able to suppress the transmission of B. sorokiniana in aerial parts of barley plants. The degree of suppression varied with the origin of the AM fungal trap cultures. The trap culture inoculum with the highest suppression of the B. sorokiniana transmission originated from an organically managed barley field with undersown ley. The two spore-inocula with the best suppression of the pathogen originated from fields with winter wheat and spring barley, respectively. Eventually, an in vitro method was developed for studying the effect of AM fungal colonisation of roots on the development of foliar diseases and the reaction of the actual host plant of the disease causing organism. Using the developed method, it was indicated that AM fungal colonisation of barley plant suppressed the development of leaf necroses due to B. sorokiniana. Further in vitro studies on the interaction between B. sorokiniana and arbuscular mycorrhizal fungi showed that B. sorokiniana decrease the germination of the AM fungal spores. In conclusion, AM fungi suppress the development of B. sorokiniana in barley. My data suggest that for biocontrol of B. sorokiniana AM fungi should be considered.

Arbuscular mycorrhizal fungi

Enzymes in the Environment: Activity, Ecology and Applications Soil Biology and Biochemistry

The crucial biogeochemical processes such as carbon and nutrient cycling are increasingly altered at the ecosystem scale by global environmental changes. Although soil extracellular enzyme activities (EEAs) play a critical role in biogeochemical processes, the global patterns of soil EEAs in a changing world remain elusive. Here, we synthesized eight EEAs involved in carbon (C), nitrogen (N) and phosphorus (P) acquisition in response to seven global change factors based on 132 peer-reviewed papers. Our results showed that elevated CO2 concentration had no significant effects on soil EEAs. Nitrogen addition stimulated C-acquisition (9.1%) and P-acquisition (9.9%) EEAs, but suppressed oxidase activity (−6.8%). Phosphorus addition decreased P-acquisition EEA (−19.8%), while combined N and P addition increased C-acquisition EEA (30.7%). Moreover, decrease in precipitation dramatically suppressed oxidase activity (−47.2%), increase in precipitation marginally stimulated N-acquisition EEA (16.7%), while warming significantly decreased oxidase activity (−10.9%) and had minor positive effect on hydrolytic enzymes. Overall, our results provide some evidence (with exceptions) for the resource allocation theory of microbial enzyme production, and indicate that EEAs are generally more sensitive to nutrient addition than to atmospheric and climate change. We have shown that global environmental changes can alter EEAs, which have implications for soil carbon storage, nutrient cycling, and plant productivity. Further research is needed to elucidate the underlying mechanisms driving the responses of EEAs to global change and to collect data from particularly non-forest ecosystems (e.g., wetland, tundra and desert) and global-change drivers (other than N addition) that lack of EEA data. Our synthesis of the responses of soil enzyme activities to global-change drivers can be used to develop better representations of microbial processes in ecosystem and earth system models.

A meta-analysis of soil extracellular enzyme activities in response to global change

Soils: An Introduction to Soils and Plant Growth

Soil influences human health in a variety of ways, with human health being linked to the health of the soil. Historically, emphasis has been placed on the negative impacts that soils have on human health, including exposures to toxins and pathogenic organisms or the problems created by growing crops in nutrient-deficient soils. However, there are a number of positive ways that soils enhance human health, from food production and nutrient supply to the supply of medications and enhancement of the immune system. It is increasingly recognized that the soil is an ecosystem with a myriad of interconnected parts, each influencing the other, and when all necessary parts are present and functioning (ie, the soil is healthy), human health also benefits. Despite the advances that have been made, there are still many areas that need additional investigation. We do not have a good understanding of how chemical mixtures in the environment influence human health, and chemical mixtures in soil are the rule, not the exception. We also have sparse information on how most chemicals react within the chemically and biologically active soil ecosystem, and what those reactions mean for human health. There is a need to better integrate soil ecology and agronomic crop production with human health, food/nutrition science, and genetics to enhance bacterial and fungal sequencing capabilities, metagenomics, and the subsequent analysis and interpretation. While considerable work has focused on soil microbiology, the macroorganisms have received much less attention regarding links to human health and need considerable attention. Finally, there is a pressing need to effectively communicate soil and human health connections to our broader society, as people cannot act on information they do not have. Multidisciplinary teams of researchers, including scientists, social scientists, and others, will be essential to move all these issues forward.

https://journals.sagepub.com/doi/pdf/10.1177/1178622120934441

Soil and Human Health: Current Status and Future Needs:

The total area of greenhouse crop production is increasing in China. However, this adversely influences soil physical and chemical properties due to special environmental conditions and agricultural management in greenhouse production. In this study, we evaluated soil properties of greenhouse vegetable systems with different planting years, a long-term greenhouse strawberry system, and an open-field wheat-maize rotation system in a typical agricultural production area of North China. The annual fertilizer application rates of nitrogen (N), phosphorus (P), and potassium (K) in the greenhouse vegetable system were 842.15, 809.14, and 931.55 kg ha−1, respectively, which were 3 times more than those in the wheat-maize rotation system and led to great changes of soil properties. Bulk density and soil pH gradually declined with increased cultivation time from new to 15 years in the greenhouse vegetable system. Bulk density declined from 1.58 g/cm3 in the new greenhouse fields to 1.25 g/cm3 in the 15-year greenhouse fields, and pH decreased from 5.72 to 4.55 with a rate of 0.08 unit per year. The contents of soil organic carbon (SOC), soil soluble salts, total NPK, and available NPK rose steadily until the 10th or 11th year, then decreased. By comparison with another two cropping systems, the greenhouse vegetable fields showed the lowest bulk density and pH, but the highest contents of SOC, soil soluble salts, total NPK, and available NPK due to heavy fertilizer inputs. The contents of soil N, P, and K in greenhouse vegetable fields were imbalanced, as indicated by C:N (11.58), C:P (16.06), and N:P (1.71) molar ratios in soils, which were significantly lower than the level in China and the rest of the world. In addition, the C:P and N:P ratios of greenhouse vegetable fields were also lower than those of wheat-maize rotation fields and greenhouse strawberry fields. Regression analysis indicated that the contents of SOC and soluble salts were positively correlated with pH, while available N and P contents showed negative linear relationships. These results demonstrate dramatic adverse changes of soil properties in intensive greenhouse vegetable fields in China. Our results also emphasize the need to regulate appropriate fertilizer application for intensive greenhouse vegetable management.

Changes in soil physical and chemical characteristics in intensively cultivated greenhouse vegetable fields in North China

Seasonal effects stronger than three-year climate manipulation on grassland soil microbial community.

Cool season grasses host multiple fungal symbionts, such as aboveground Epichloe endophytes and belowground arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSEs). Asexual Epichloe endophytes can influence root colonization by AMF, but the type of interaction—whether antagonistic or beneficial—varies. In Schedonorus arundinaceus (tall fescue), Epichloe coenophiala can negatively affect AMF, which may impact soil properties and ecosystem function. Within field plots of S. arundinaceus that were either E. coenophiala-free (E−), infected with the common, mammal-toxic E. coenophiala strain (CTE+), or infected with one of two novel, non-toxic strains (AR542 NTE+ and AR584 NTE+), we hypothesized that (1) CTE+ would decrease AMF and DSE colonization rates and reduce soil extraradical AMF hyphae compared to E− or NTE+, and (2) this would lead to E− and NTE+ plots having greater water stable soil aggregates and C than CTE+. E. coenophiala presence and strain did not significantly alter AMF or DSE colonization, nor did it affect extraradical AMF hypha length, soil aggregates, or aggregate-associated C and N. Soil extraradical AMF hypha length negatively correlated with root AMF colonization. Our results contrast with previous demonstrations that E. coenophiala symbiosis inhibits belowground AMF communities. In our mesic, relatively nutrient-rich grassland, E. coenophiala symbiosis did not antagonize belowground symbionts, regardless of strain. Manipulating E. coenophiala strains within S. arundinaceus may not significantly alter AMF communities and nutrient cycling, yet we must further explore these relationships under different soils and environmental conditions given that symbiont interactions can be important in determining ecosystem response to global change.

Lindsey C. Slaughter

Papers

Soil and Human Health: Current Status and Future Needs:

Changes in soil physical and chemical characteristics in intensively cultivated greenhouse vegetable fields in North China

Seasonal effects stronger than three-year climate manipulation on grassland soil microbial community.

Aboveground Epichloë coenophiala–Grass Associations Do Not Affect Belowground Fungal Symbionts or Associated Plant, Soil Parameters

Soil physiochemical properties and carbon sequestration of Urban landscapes in Lubbock, TX, USA