Fungal Community Changes Amid Salinity and Succession

Primary Source: LIU, Y., FANG, L., YANG, C. (2022). Significant changes in arbuscular mycorrhizal community and soil physicochemical properties during the saline-alkali grassland vegetation succession. BIOCELL, 46(11), 2475–2488.

High concentration of harmful salts can degrade soil, making it appear cracked and dry. While tolerant plants can eventually return and remediate these soils, human contribution of salts has exacerbated this issue beyond many ecosystems’ natural ability to combat this process. Source:Pixahive

From dense forests to flowing fields of grass, vegetation forms the base level of nearly every terrestrial ecosystem. However, various human influences have led to the degradation of soil around the world. Pollutants such as heavy metals prevent plants from accessing necessary nutrients, and water-soluble salts accumulate in human run off and are deposited into the soil in excess. This soil degradation affects not only natural ecosystems in present day, but they also limit the ability that these lands have to be used for agriculture or animal husbandry in the future. While the environment can naturally recover from similar, naturally occurring degradation, this natural recovery is too slow to counteract human disturbances. This process of an ecological community developing (or redeveloping) over time, is known as succession, and it looks different and is understood to different degrees from ecosystem to ecosystem.

In the well understood ecosystem of China’s Songnen Plains, a grassland harmed by soluble salts, three different species of plants have been found in previous studies to be representative of different steps in the succession and recovery of the ecosystem. While this understanding of changing vegetation may be helpful towards noting ecosystem recovery, it does not help to speed up the process. As such, researchers Liu et al. took understanding of this ecosystem’s succession process a step further by examining the mechanisms by which various species of mycorrhizal fungi, a symbiotic partner to over 90% of vascular plants, help to make these degraded soils habitable to each plant species involved in the succession process.

Human influence has led to a global increase in salinization, the process of harmful salts accumulating in and degrading soil. The results of this process can be seen above in the picture of the dried Lake Owen in California, one of the largest sources of dust pollution (via wind borne salt deposits) in America. Credit: Richard Ellis Source: Wikimedia
Studying and Sifting Salty Soils

First, soil was collected from the roots of ten clumps of each plant species (Suaeda glauca, Puccinellia tenuiflora, and Leymus chinensis representing each step of succession, respectively) at three different locations within a 50 square meter quadrant. This was repeated for five quadrants throughout the grasslands. After collecting soil from the roots of these plants, chemical testing was carried out testing for DNA of a variety of common mycorrhizal fungi species, as well as other factors related to soil health such as enzyme activity, pH, electrical conductivity of soil water (which is used as an indication of soluble salts being present in said soil), organic carbon content, phosphorus content, carbonate content, nitrogen content, and ratio of carbon to nitrogen. Through this testing, the researchers were able to determine the general mycorrhizal microbiome for each species of plant, and, by proxy, each step in the succession process. Additionally, by intensively measuring factors related to soil health, the researchers can better understand the mechanisms by which the different species of mycorrhizae present remediate the degraded soil. These measurements also serve to re-confirm the results found in other literature that the plant species being used as spatial proxy for succession over time are truly representative of their respective stages in the redevelopment of the ecosystem.

As expected, factors associated with high concentration of deposited salts, such as pH, electrical conductivity, and carbonate content were at their highest in soils samples from S. glauca, and, conversely, at their lowest in soil samples from L. chinensis. Factors associated with good soil health, such as phosphorus content and enzyme activity of sucrose and catalase, were highest among soil from L. chinensis, and lowest in soil from S. glauca. With these succession proxy species reconfirmed, and information into the exact health of each species’ soils acquired, analysis of the mycorrhizae present in these soils could possibly give insight into the mechanisms behind this improvement in soil quality. To test for mycorrhizal activity, each sample was tested for a number of amplicon sequence variants, inferred DNA sequences recovered from amplification of any present matches to known marker genes of common mycorrhizal species. The results of these tests found that soil taken from L. chinensis contained twice the amount of amplicon sequence variants to either soil from S. glauca or soil from P. tenuiflora, which both had a number of amplicon sequence variants that was not significantly different from one another. This shows that soil from L. chinensis, representing the last stage of succession, had the most mycorrhizal activity from many different species of mycorrhizal symbionts.

Despite degraded soil, tolerant plants such as the above S. glauca can grow in soil with high concentration of harmful salts. As such plants grow, they reduce the impact of these harmful pollutants through enzymatic activity and adding their own organic content to the soil, allowing more plants to grow after them in the process of succession. Credit: Dalgial Source: Wikimedia
As Above, So Below

The presence of diverse activity from many mycorrhizal species in the most recovered soil of this salt-damaged ecosystem lends credence to the multiplicative effect of mycorrhizae to remediate soil. When noted in tandem with the measurements of enzyme activity, this idea is much more likely. Where a single species of mycorrhizal fungi may produce enzymes that alter the chemistry of harmful soil products into more tolerable, sometimes even useful forms, multiple, diverse species of mycorrhizae each altering the surrounding soil to be more tolerable can exacerbate and accelerate this remediation ability, as the semi-tolerable product of one mycorrhizae’s enzymatic activity can be further altered by another fungi’s enzymes, becoming entirely benign or possibly even a source of nutrients for the mycorrhizal fungi’s photosynthetic partners above ground. Further understanding the abilities of these individual fungi, as well as their synergistic benefits, can help to speed up the recovery of highly degraded soils, both in the wild as well as in various industries, such as polluted agricultural lands or grazing lands for farm-raised animals.

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Cypress Novick

Cypress Novick

I am a recent graduate of Occidental College in Los Angeles, California, where I studied for my Bachelor's in Biology. My main research interests are wetlands ecology, mycology, estuary ecosystem interactions, and plant-based trophic interactions. I have always been passionate about making science more available and understandable, and am always trying to improve my writing so I may help myself and others be better understood.

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