Rhizosphere is commonly defined as the soils where the root activity significantly
affects the biological properties of soil. Due to the special environment, the rhizosphere
micro-zone has become one of hot topic for the plant nutrition, plant physiology, ecology
and soil science. Because the lack of the available and comprehensive work on the
rhizosphere soils in the hilly loess region, the present study chose the different revegetation
types and the vegetation community in the natural succession on the abandoned cropland
to analyze the response of rhizosphere soil microorganism to the revegetation using
phospholipid fatty acids and BIOLOG carbon utilization technology. The study mainly
investigated the effect of revegetation types on rhizosphere soil microbial biomass,
enzymes activities, microbial community structure diversity and metabolic functional
diversity as well as the dynamic of microbial community structure diversity during the
abandoned cropland for natural succession. The results could provide scientific basis for
the understanding of microbial function during the vegetation restoration. The main results
are as follows:
1. The characteristic of rhizosphere microbial properties under different
Six vegetation types with 8-year-old were evaluated: two artificial (i.e. planted by
humans) shrublands (Caragana korshinskii and Hippophae rhamnoides) species, two
artificial grasslands (Astragalus adsurgens and Panicum virgatum) and two species from
croplands that were abandoned for natural recovery (Artemisia capillaries and
Heteropappus altaicus). The results showed the higher value of organic C, total N,
available Mn, available Cu, available Zn, microbial biomass C, microbial biomass N,
enzymes activities, microbial community structure diversity and carbon resource metabolic
functional diversity was record for the natural grassland compared to the artificial shrublands and artificial grassland.
Among the microbial properties, metabolic quotient (BR/MBC), BR, urease,
water-soluble C and cellulase were found to be most important for assessing rhizosphere
soil biological quality. Results of rhizosphere soil microbial index indicated that natural
grasslands are most effective for the improvement of rhizosphere soil biological quality in
the hilly loess region, followed by the artificial grassland and artificial shrubland.
A significant difference was found on the rhizosphere effect under the different
vegetation types. Natural grassland species have the significant rhizosphere effect than the
artificial shrubland and artificial grassland.
2. The dynamic of rhizosphere microbial properties during the abandoned
cropland for natural succession.
During the natural succession, the significant rhizosphere effect was only found in
organic C, total N, microbial biomass C, microbial biomass N, basal respiration, enzymes
activities and microbial community structure.
Not all the microbial properties in the rhizosphere soil of dominant species were
higher than those of companion species. The higher value in the rhziosphere of dominant
species was found in organic C, total N, microbial biomass C, microbial biomass N as well
as the metabolic on carbohydrate resources than that of companion species, while in the
enzymes activities and the metabolic on carboxylic acids, the dominant species did not
showed the higher value.
The successional stage of the ecosystem can significantly affect the microbial
properties in the plant rhizosphere. In the current study, the pioneer species, A. capillaries,
exhibited significant fluctuations in the microbial properties, whereas the middle-late
species, A. sacrorum, presented an increasing trend.
3. The characteristics of rhizosphere microbial community structure in the
natural succession simulation
Three community dominant species of the succession, A. capillaries, A. sacrorum and
S. bungeana showed the significant microbial rhizosphere effect in G-negative bacterial,
bacterial and total microbial biomass, their contents decreased with the increase of distance
from root surface.
At the same soil conditions, the middle-late successional species, A. sacrorum and S. bungeana had a higher rhizosphere effect of bacterial and total microbial biomass while
had the lower G-positive bacterial and fungi rhizosphere effect than that of the pionner
species, A. capillaries,
In the successional vegetation competition, the microbial community structure
rhizosphere soil of A. capillaries and A. sacrorum and S. bungeana responded differently
to the competition. In the competition between A. capillaries and A. sacrorum, as well as
between A. capillaries and S. bungeana, the number of microbial PLFA of A. capillaries
did not change, while that of A. capillaries and S. bungeana decreased significantly.
Furthmore, the microbial contents in the rhizopshere soil of A. capillaries was greatly
higher than that of A. capillaries and S. bungeana.
4. Allelopathic effect of dominant plants of vegetation commnutiy during the
abandoned cropland for natural succession
In the seed germination experiment, an inhibition was found on the seed germination
of A. capillaries, A. sacrorum and S. bungeana with each other in their high concentration
of aqueous extracts. Furthermore, a self-allelopathic effect was observed for the seed
germination of A. capillaries. In conclusion, there is a significant alleopathic effect
between vegetation communities during the abandoned cropland for natural succession,
this effect maybe the one of the reseaons for promoting the vegetation succession in the
loess hilly region.
Keywords: Rhizosphere; Vegetation types; Abandoned cropland for natural succession;
Microbial community structure; Loess hilly region