Phosphate-solubilizing bacteria were isolated from the rhizosphere of corn,and 38 strains of inorganic phosphate-solubilizing bacteria and 35 strains of organic phosphate-solubilizing bacteria were screened by using traditional method of isolation and culture of microorganisms.The number of both total bacteria and phosphate-solubilizing bacteria in the rhizosphere soil was higher than that in the bulk soil.Major bacterial colony was milky or yellow,irregular or roughly round,smooth,thick,flat,non-transparent with ragged edge.Furhter study on phosphorus solubilizing capacity of the strains by Mo-Sb colorimetry method indicated that pH was significantly correlated with the content of available P of inorganic phosphate-solubilizing bacteria strains,but not correlated with that of organic phosphate-solubilizing bacteria strains.There were great differences between solubilizing calcium phosphate by inorganic phosphate-solubilizing bacteria and solubilizing lecithin by organic phosphate-solubilizing bacteria.Their phosphate-solubilizing capacity ranged from 8.88 to 108.31 and 0.51 to 3.53 mg/L,respectively.The strain SWJ1-4 and SWJ3-1 had a higher ability in solubilizing inorganic phosphate than other strains and strain RYJ1-6 had a higher capacity in solubilizing organic phosphate.The three strains had great potential in further development of microbiological fertilizer because of their stronger phosphate-solubilizing ability,faster growth rate and better growing state.
Soil erosion is a severe environmental problem on the Loess Plateau, China. Vegetation restoration is the most efficient method to control soil erosion and introducing late-successional plant species may accelerate natural succession. However, the progress is affected by soil conditions and the appropriate thresholds of soil condition for seed addition are needed. Our objectives were to identify the vegetation types, examine the key soil factors affecting the vegetation variation, and determine the thresholds of the soil factors for each vegetation type. Five vegetation types in secondary succession were identified: association (assoc.) Artemisia scoparia assoc. Bothriochloa ischaemum assoc. Artemisia gmelinii Artemisia giraldii assoc. Ostryopsis davidiana Rubus parvifolius L., Syringa oblate and assoc. Sophora viciifolia Years since abandonment (YEAR), alkali-hydrolysable nitrogen (AHN), soil water content (SW), and total phosphorus (TP) were the key factors used to discriminate among vegetation types. Assoc. A. scoparia developed in croplands that had been abandoned for less than 11 years. Assoc. B. ischaemum developed in croplands abandoned for more than 11 years with lower soil nutrient levels (0.30 ≤ TP ≤ 0.646 g kg−1 and 16.72 ≤ AHN ≤ 32.62 mg kg−1). Assoc. A. gmelinii + A. giraldii always required greater TP (0.646 ≤ TP ≤ 0.79 g kg−1) to develop. When soil water content was lower (6.6 ≤ SW ≤ 8.4%), the assoc. S. viciifolia developed; otherwise, other associations, such as assoc. O. davidiana, developed. These soil thresholds can be used as references for guiding restoration, such as specifying proper soil conditions for seed sowing.
Abstract In the Loess Plateau, China, arable cultivation of slope lands is common and associated with serious soil erosion. Planting trees or grass may control erosion, but planted species may consume more soil water and can threaten long‐term ecosystem sustainability. Natural vegetation succession is an alternative ecological solution to restore degraded land, but there is a time cost, given that the establishment of natural vegetation, adequate to prevent soil erosion, is a longer process than planting. The aims of this study were to identify the environmental factors controlling the type of vegetation established on abandoned cropland and to identify candidate species that might be sown soon after abandonment to accelerate vegetation succession and establishment of natural vegetation to prevent soil erosion. A field survey of thirty‐three 2 × 2–m plots was carried out in July 2003, recording age since abandonment, vegetation cover, and frequency of species together with major environmental and soil variables. Data were analyzed using correspondence analysis, classification tree analysis, and species response curves. Four vegetation types were identified and the data analysis confirmed the importance of time since abandonment, total P, and soil water in controlling the type of vegetation established. Among the dominant species in the three late‐successional vegetation types, the most appropriate candidates for accelerating and directing vegetation succession were King Ranch bluestem ( Bothriochloa ischaemum ) and Lespedeza davurica (Leguminosae). These species possess combinations of the following characteristics: tolerance of low water and nutrient availability, fibrous root system and strong lateral vegetative spread, and a persistent seed bank.
Interleukin-37 (IL-37), a novel member of the IL-1 family, plays fundamental immunosuppressive roles by broadly reducing both innate inflammation and acquired immunity, but whether it is involved in the pathogenesis of tuberculosis (TB) has not been clearly elucidated. In this study, single nucleotide polymorphism (SNP) analysis demonstrated an association of the genetic variant rs3811047 of IL-37 with TB susceptibility. In line with previous report, a significant elevated IL-37 abundance in the sera and increased expression of IL-37 protein in the peripheral blood mononuclear cells (PBMC) were observed in TB patients in comparison to healthy controls. Moreover, release of IL-37 were detected in either macrophages infected with Mycobacterium tuberculosis (Mtb) or the lung of BCG-infected mice, concurrent with reduced production of proinflammatory cytokines including IL-6 and TNF-α. Furthermore, in contrast to wild-type mice, BCG-infected IL-37-Tg mice manifested with reduced mycobacterial burden and tissue damage in the lung, accompanied by higher frequency of Th1 cell and less frequencies of regulatory T cells and Th17 cells in the spleen. Taken together, our findings demonstrated that IL-37 conferred resistance to Mtb infection possibly involving suppressing detrimental inflammation and modulating T cell responses. These findings implicated that IL-37 may be employed as a new molecular target for the therapy and diagnosis of TB.
The two-way indicator species analysis and the correspondence analysis were adopted to classify and rank the forae naturally recuperating on 33 sample sites distributed in Ansai county standing in the hilly and gully regions of the loess plateau.The results revealed that in the forty-year evolution,the vegetations on the farming-withdrawn lands successfully experienced Artemisia scoparia-,Lespedeza davurica-,Stipa bungeana-,Artemisia gmelinii-,Bothriochloa ischaemun- dominated forae which displayed relatively strong continuation and transmission capacities.The correlation analysis between ranking and ambient factors indicated that soil organic matter,nitrogen,phosphorus,potassium and moisture as well as landforms strongly or weakly affected the changes of the forae naturally growing on the farming-withdrawn lands and of these factors,soil organic matter,nitrogen,phosphorus,potassium and moisture,and slopeland gradients closely related to the changes of vegetation forae.
Based on the observation in the typical hilly and gully region on the Loess Plateau-Wuqi county, the changes of soil water-stable aggregates of different abandoned times? different types of vegetation and different restoration measures during vegetation restoration in abandoned lands were studied. The results showed that the content of 0.25 mm soil water-stable aggregates increases with the increasing of the abandoned time within the depth of 0~60 cm; the content of arbor lands is relatively higher and grassland is relatively lower, bush land is in the middle; For the restoration types, the content of natural restoration is bigger than that of natural restoration with artificial measures, and that of artificial restoration is lower, the cropland is the lowest. The increasing degree of the content of soil water-stable aggregates at the depth of 0~20 cm is bigger in the first stage of vegetation restoration, and lower in the later stage; the changes at the depth of 40~60 cm are on the contrary; The content of 0.25 mm soil water-stable aggregates of the same vegetation land is decline with the depth, the decreasing degree of shrub lands is relatively bigger in shallow layer, and the decreasing degree of arbour lands is relatively bigger in deep layer; soil water-stable aggregates are transformed from bigger particles to smaller ones by means of human interference, and this transformation is more obvious in deeper layer; soil anti-erodibility of arbour lands with longer restoration time is stronger;the natural with artificial restoration not only shorten the restoration time, but also increase the content of soil water-stable aggregates,so the soil structure is improved.
Soil seed bank includes all live seeds existed both in litter and in soil,which is simply classified into transient soil seed bank with seeds germinated within a year of initial dispersal,and persistent soil seed bank with seeds remained in soil more than one year.The soil seed bank,as the potential for regeneration,plays an important role in the natural restoration of vegetation.This paper reviewed its research methods,including sampling methods,sampling time and identification of seedling.It suggests that long-term anchor observation is adopted for the dynamics of soil seed bank and seedling specimen bank should be founded to identify seedling correctly.
Abstract Vegetation succession depends on the availability of suitable propagules in the soils, and an understanding of soil seed banks is important for effective vegetation restoration of abandoned croplands. Aims of this study were to identify characteristics of soil seed bank, relationship with standing vegetation, and potential significance of soil seed bank for vegetation restoration in abandoned croplands on the hilly-gullied Loess Plateau. Results of field survey, germination, and correspondence analysis showed that density of soil seed bank ranged from almost 900 through almost 6470 seeds m−2 at 0–5 cm depth and almost 120 through almost 2470 seeds m−2 at 5–10 cm depth, with species richness of 7–14. Early successional species dominated soil seed bank, while later successional species occurred only at low densities. Similarity between soil seed bank and standing vegetation was low (with an average of 0.261). Most important variables contributing to the variation of the standing vegetaion included soil water, extractable P, soil seed bank density, and aspect. Soil seed bank alone explained 32% of vegetation community variation. Potential for vegetation restoration from soil seed banks is limited, and it is recommended to transplant some later successional species into abandoned croplands to accelerate succession. Keywords: community similaritycorrespondence analysisseed germination methodsoil erosion We thank the NSFC projects (40771126; 40571094; 40271074) for funding this research, the assistance of Ansai Ecological Experimental Station of Soil and Water Conservation, CAS. We are also grateful to X. H. Ma, Z. G. Zhang, L. R. Xu, H. Y. Zou, and J. M. Cheng for field survey and experiment suggestions. We would like to thank the three anonymous reviewers for constructive comments. Notes SW0-5, soil water content in 0–500 cm layers; SW2-5, soil water content in 200–500 cm layers; SOM, soil organic matter. CV, Coefficient of variation; SE, Standard Error. Frequency of seeds (%) in the soil seed bank is based on presence in 144 sampling points and in vegetation is based on 72 sampling points; Seed density is the range of the mean value (6 sub-samples) in the plots in which it occurred. CVA, Canonical Variate Analysis; PCVA, Partial Canonical Variate Analysis; ∗P < 0.05; ∗∗P < 0.01; the inertia of CVA is 3.000; "/", "partialling out" the following variable. Bs, species forming a persistent seed bank; V, possessing lateral vegetative spread; VBs, species characterized by Bs and V; W, producing numerous widely dispersed seeds.
Afforestation has been accepted as a key measure for preventing soil erosion on the Chinese Loess Plateau for 40 years. In this study, we assessed the ecological success of afforestation by comparing afforested with pre‐afforested (croplands) and natural recovery sites in a typical watershed on the Loess Plateau. We evaluated the ecosystem response in terms of vegetation structure, plant diversity, and several key ecological processes of soil moisture, soil nutrients, and soil anti‐erodibility. Compared with the croplands, we found that the following indexes were significantly enhanced in afforested sites: vegetation structure and species diversity (species richness, Margalef index, Shannon–Wiener index, and Sorensen's similarity index), soil nutrients (organic carbon, total nitrogen, extractable ammonium nitrogen, available potassium, and available phosphorous), and soil anti‐erodibility indexes (water‐stable soil aggregates, mean weight diameter, and the ratio of soil structure dispersion). Afforestation offered few additional advantages when compared with natural recovery sites. More importantly, afforestation had significant negative effects on soil desiccation, with negative impacts on the long‐term sustainability of these ecosystems. In order to develop self‐sustaining and functional ecosystems, our results suggest that natural revegetation offers a more adaptive and appropriate method of ecological restoration on the Loess Plateau.
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