Karst rocky desertification does not erode ectomycorrhizal fungal species richness but alters microbial community structure
Overview: Why is this paper important in the context of organic land management, whether for the landowner with acreage or the homeowner with a neglected patch of ground? Because it shows that we can extrapolate from this study that there is lots of biological activity in the soil, whether the land is a well-established forest or, in the case of this study, karst rocky desertification (a landscape generally of limestone, dolomite, or gypsum, that has been impacted by erosion). In this study, the stage of "rocky desertification" with scrub plants and shrubs instead of forest is due to human activities such as agriculture or clear cut forestry. This particular study was conducted in a karst region of Yunnan province, China, near the city of Mengzi.
The article introduction explains that soil degradation has impacted many areas of the planet, "particularly in the Mediterranean area and southwest China" where human activity and changes in the climate have reduced areas of the landscape to desert or desert-like conditions. They note that in by studying soil properties and comparing biological activity in undisturbed land and land that was used for agriculture or logging in karst landscapes (in particular) they can show that these human activities led to desertification. But they can also show a means for improvement.
This study examined three aspects of the soil microbiome in a region that has both old established forests and lands that have been impacted by logging and agriculture. Soil samples were taken in an equal number of plots in two separate areas near small towns, to compare forest (non-KRD) versus karst rocky desertification (KRD). The "soil fertility decreases along with processes of urbanization [such as] conversions of primary forest to agricultural field" (p. 384). The three types of soil biology examined in this study of microbial diversity were the bacterial community, the fungal community structure, and within the fungal community, the effect on a sub-group called the ectomycorrhizal fungi (ECM).
In the context of studying the levels and health of the microbiome the researchers also carefully documented the soil acidity and total amounts of carbon (TC), nitrogen (TN), phosphorus (TP) and potassium (TK). Only potassium levels remained relatively equal, unchanged between the two types of land that were studied. "Interactions between soil microbial communities and soil conditions determine the functions, resilience and stability of ecosystems . . . . Plant diversity is usually positively correlated with soil microbial diversity in various environments. . . " (384).
The gist of this study is that there were higher levels of biological and fungal diversity in the degraded lands because there were so many small niches with different levels of disturbance or surface plants over the region. The one area with stronger representation in the undisturbed forest was the ectomycorrhizal fungi (ECM), that thrived in the deeply established and better hydrated soil of the forest floor and trees it was associated with.
So how does this study from China, examining limestone landscapes, help the landowner who has purchased a bunch of scrub land in a dry part of North Texas who wants to improve the land? It suggests that the microbiome is there, waiting for a shift in the surface conditions. When Howard Garrett tells landowners to spread a layer of shredded native tree trimmings, he is giving them the information that will lead to kick-starting the microbiome into using the carbon in the trimmings for unlocking the NPK for the soil to host a higher level of plants. When he tells the homeowner to spread a layer of compost over the bare soil, they will be doing the same thing – making nutrients available to the plants that will eventually grow in that environment. And when the plants are there, the fungus will go to work carrying nutrients to where they are needed.
This is the part we can publish on the Dirt Doctor site. See below for information on how to get the full text version. At the very bottom of the page is a figure from the article showing the position of samples taken for the study and inset two small photos of the landscape types.
Backgrounds: There are growing concerns regarding the restoration of karst rocky desertification (KRD) areas. However, the soil conditions and its residing microorganisms, which are essential for the plants, remain largely unclear.
Methods: We studied soil characteristics and microbial communities in natural forests (non-KRD) and shrubs with eroded soil and surface soil run-off, using Illumina Miseq sequencing.
Results: Our results showed that despite KRD reduced soil fertility and altered microbial community structures, microbial diversity did not diminish. Interestingly, bacterial OTU richness and diversity were greater in the KRD areas than in the non-KRD areas, which had relatively greater plant density and diversity. Fungal OTU richness and diversity remained unchanged by KRD. Although the KRD areas had been clear-cut and trees were mostly absent, ectomycorrhizal fungi did not differ in diversity and relative abundance between the two land types, indicating that the KRD shrubs hosted surprisingly diverse and abundant ectomycorrhizal fungi.
Conclusions: Our results highlight the highly diverse microbes under environmental and anthropogenic stresses in KRD areas. Despite the fact that degraded soil properties and an altered microbial community structure remain, KRD did not erode ectomycorrhizal fungal species richness, which is crucial in the revegetation of trees in KRD areas.
Keywords: Karst rocky desertification. Microbial community, Primary forests, Secondary shrubs, Mycorrhizae, Soil degradation.
The paper is by Nan Hui, Ningxiao Sun, Hongmei Du, Muhammad Umair, Hongzhang Kang, Xinxin Liu, Martin Romantschuk, and Chunjiang Liu
It was published in Plant Soil in 2019. This research paper was supported by the National Key R&D Program in China. The journal is under the Springer Nature Switzerland umbrella of publications (behind a paywall – go to your local library to see if they have access to the full text). The durable link to this article is https://doi.org/10.1007/s11104-019-04319-z
Distribution of sampling sites near the city of Mengzi, China. KRD = karst rocky desertification.