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Liu F.C.,Shandong Academy of Forest | Ma H.L.,Shandong Academy of Forest | Du Z.Y.,Shandong Academy of Forest | Ma B.Y.,Shandong Academy of Forest | And 2 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2015

Plant growth-promoting rhizobacteria (PGPR) are rhizosphere inhabitants that promote plant growth and suppress diseases. One of the proposed mechanisms through which PGPR enhance plant growth is the production of plant growth regulators, especially cytokinin. However, little information is available about the effects of cytokinin-producing PGPR inoculation on the drought stress response. Soil water availability is a crucial determining factor of plant yield, because drought stress inhibits stem elongation, leaf expansion, and stomatal movement. Therefore, a strain of rhizobacteria with a high rate of cytokinin production, Bacillus cereus L90, was selected for use in this investigation. The bacteria were obtained from the rhizosphere of a walnut tree, where water is limited and frequent dry periods occur. Serial dilution and a bioassay for the detection of cytokinin production were both used to isolate and screen the bacterial strain from the soil sample. This study investigated how PGPR affects the physiological characteristics of Lonicera japonica Thunb. under different drought stress treatments (light, moderate, severe, and a control). The combined effects of B. cereus L90 inoculation and various levels of drought stress on the photosynthetic characteristics, chlorophyll fluorescence parameters, photosynthetic pigment, cytokinin and ABA(abscisic acid) concentrations, relative water content, and relative electrolyte leakage were studied using the pot method. The results showed that the net photosynthetic rate and stomatal conductance decreased with increasing drought stress. However, B. cereus L90 inoculation was associated with an increase in stomatal conductance and net photosynthetic rate in plants under drought stress. B. cereus L90 inoculation reduced the negative impact of drought stress on the maximum photochemical efficiency of PSII, the actual photochemical efficiency of PSII, and the photochemical quenching coefficient. B. cereus L90 inoculation also prevented the non-photochemical quenching coefficient from increasing. Although no significant difference was observed under well-watered conditions, the leaves of inoculated drought-stressed L. japonica seedlings had higher photosynthetic pigments contents compared to those of non-inoculated seedlings. The roots of inoculated L. japonica seedlings had higher ABA content compared to non-inoculated seedlings. The elevated levels of cytokinins in L. japonica leaves and the higher concentration of ABA are both associated with drought stress. B. cereus L90 inoculation significantly increased the cytokinin content of drought-stressed L. japonica leaves, and improved the rate of transportation of ABA from the roots to the leaves. No significant differences in relative water content and relative electrical conductance were observed between inoculated and non-inoculated seedlings under light drought stress. Compared to the irrigated control, under severe drought stress, the relative water content of non-inoculated seedlings decreased by 20.56%, while that of inoculated seedlings decreased by 10.21%. However, the relative electrical conductance of inoculated and non-inoculated seedlings under severe drought stress increased by 31.42% and 16.08%, respectively. These results demonstrate that inoculation of B. cereus L90 under drought stress increases the cytokinin content of L. japonica leaves, and interferes with the suppression of photosynthetic pigments and net photosynthetic rate. Thus, B. cereus L90 inoculation could improve the adaptability ability of L. japonica seedlings to drought conditions. In conclusion, inoculation of cytokinin-producing PGPR could be used to alleviate drought stress and interfere with the suppression of physiological processes, showing real potential for practical use in arid environments as a drought stress inhibitor. © 2015, Ecological Society of China. All rights reserved. Source


Liu F.,Shandong Academy of Forest | Xing S.,Shandong Academy of Forest | Ma H.,Shandong Academy of Forest | Du Z.,Shandong Academy of Forest | And 3 more authors.
Chinese Journal of Applied and Environmental Biology | Year: 2012

The aim of this research was to determine the effects of plant growth-promoting rhizobacteria (PGPR) fertilizer on the biological characteristics, root activity, growth and construction of Cerasus pseudocerasus (Lindl.) G. Don (sweet cherry). To prepare sweet cherry biological-fertilizer (YMF), dominant bacteria YT-3, a type of PGPR, was extracted from rhizosphere soil of C. pseudocerasus trees by keeping green method and radish cotyledon weight increase method. Sweet cherry biological-fertilizer was prepared by compounding YT-3 and decomposed chicken manure (DCM). The effects of YMF, normal biological fertilizer (NMF) and DCM on biological characteristics of C. pseudocerasus rhizosphere soil were studied in Yiyuan sweet cherry orchards. And the effects of YMF, DCM and NMF on the root activity, growth and construction of C. pseudocerasus were also investigated. The results showed that YMF increased the amount of bacteria and total microorganism amount in rhizosphere soil of C. pseudocerasus, but the fungus amount was decreased significantly. However, YMF had no influence on actinomycetes amount in rhizosphere soil. Root activity in YMF was significantly increased by 15.33%, 22.49% and 13.25% than that in CK, NMF and DCM, respectively. YMF had great influence on the root growth and construction of C. pseudocerasus. Root weight, especially fine root weight in 0-40 soil profile of YMF was significantly increased. Rhizosphere soil pH value in YMF decreased by 8.61% than that in NMF. In addition, YMF significantly enhanced available phosphorus and potassium contents by 17.21% and 9.56%, respectively, compared to that in NMF. However, it had no effects on available nitrogen content in sweet cherry rhizosphere soil. Moreover, PGPR fertilizer increased the cation exchange capacity of rhizosphere soil, which benefited the nutrient retain and uptake of C. pseudocerasus. As a result, plant growth-promoting rhizobactera biological-fertilizer benefited the ecological environment of sweet cherry rhizosphere soil, improved nutrient availability and cation exchange capacity, increased the root activity and benefited the root growth, especially fine root growth in top soil (mainly 0-40 cm). Source


Liu F.C.,Shandong Academy of Forest | Xing S.J.,Shandong Academy of Forest | Ma H.L.,Shandong Academy of Forest | Chen B.,Shandong Agricultural University | And 2 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2014

Drought stress in soil can be crucial to plant yield because it reduces growth rate, stem elongation, leaf expansion, and stomatal movements. Several microorganisms in the rhizosphere soil are free-living, soil-borne bacteria that aggressively colonize the rhizosphere or plant roots. The efficiency of rhizosphere microorganisms in promoting plant growth has been demonstrated in numerous greenhouse and field studies on different plant species. However, studies on the influences of continuous drought on rhizosphere microbial populations and community diversity are limited. Therefore, a bacterial strain with known positive effects on plant growth, named YT3, was used in the present study to investigate the effect of continuous drought on soil bacteria population. The bacterial strain was isolated and screened using the serial dilution method on the rhizosphere soil of sweet cherry (Cerasus pseudocerasus) growing fields. YT3-gfp was labeled with green fluorescent protein into plant growth-promoting rhizobacteria YT3. A pot experiment was conducted to determine whether continuous drought stress (continuous drought of 7, 14, 21, 28, 35, and 42 d) could benefit YT3-gfp activities in sweet cherry rhizosphere soil. In addition, the effect of continuous drought stress on microbial populations, as well as the community diversity in rhizosphere soil was investigated by plate culture method and terminal restriction fragment length polymorphism (T-RFLP) analysis. The results showed that the YT3-gfp populations in the rhizosphere soil were 8.75 to 28.77 times higher than those in the non-rhizosphere soil of sweet cherry. The YT3-gfp amount increased simultaneously with the continuous drought stress in rhizosphere soil or non-rhizosphere soil; however, a decrease was also observed during the severe drought stress period. YT3-gfp in the rhizosphere was more easily subjected to drought stress than that in non- rhizosphere soil. The maximum YT3-gfp amounts in rhizosphere soil and non-rhizosphere soil were observed on day 21 at 166 ×104 CFU/ g and on day 28 at 6.7 ×104 CFU/ g. Along with continuous drought stress, bacteria and actinomycete populations, as well as the total microorganism amounts, first increased then decreased; however, fungus populations in the rhizosphere soil of sweet cherry decreased continuously. Continuous drought stress significantly influenced the T-RFLP profiles in the rhizosphere soils of sweet cherry seedlings. The T-RFLP profiles showed that some special terminal restriction fragments (T-RFs) decreased, and some T-RFs disappeared with continuous drought stress. However, some T-RFs appeared under certain drought stress conditions. The highest Margalef and Shannon indexes and the lowest Simpson's index were observed on days 21 or 28 after continuous drought stress. Moreover, the principal component analysis for T-RFs of the different treatments showed that an independent group of bacterial community structure was formed during continuous drought stress in 14 days to 35 days, indicative of the diversiform community structure. The other two independent groups were formed on days 7 and 42 after continuous drought, respectively, indicative of the simplified community structure. Consequently, soil bacteria community structure was significantly influenced by continuous drought stress. Certain drought stress can improve the bacteria and actinomycete populations, and increase the microbial community diversity. Therefore, certain drought stress is beneficial to the sustainable microbial community structure in sweet cherry rhizosphere soil. Source


Ma H.,Shandong Academy of Forest | Liu F.,Shandong Academy of Forest | Ma B.,Shandong Academy of Forest | Du Z.,Shandong Academy of Forest | And 2 more authors.
Chinese Journal of Applied and Environmental Biology | Year: 2016

This paper discusses the effects of super-absorbent polymer (SAP) on biological activity in the rhizosphere soil and drought resistance of platycladus orientalis container seedlings to verify the utilization suitability of SAP for container seedlings in arid mountainland afforestation. Acrylamide acrylic acid potassium cross-linked copolymer was used as SAP in this study. Four afforestation treatments were designed, including NS (4.0 g SAP added in the nursery substrate) and AS (4.0 g SAP added during afforestation). The effects of SAP and its utilization on microbial populations, diversity of bacterial community structure in the rhizosphere soil of Platycladus orientalis, and the drought resistance of P. orientalis container seedlings at the initial afforestation stage were studied by the traditional plate culture method and the modern terminal restriction fragment-length polymorphism analysis. The results showed that SAP addition significantly increased bacterial and fungal populations, as well as soil microbial biomass carbon and biomass nitrogen contents in the rhizosphere soil of P. orientalis. The bacterial populations and soil microbial biomass carbon content in the NS treatment were 21.65% and 8.04%, respectively, higher than in the AS treatment. SAP and its utilization was found to significantly affect the bacterial community structure. The diversity of the bacterial community structure in rhizosphere soil of P. orientalis was significantly increased by SAP addition. Among the 3 treatments, the highest Margalef and Shannon indexes and the lowest Simpson index were observed in the NS treatment. SAP addition also increased the survival rate, net photosynthetic rate, and relative water content, but decreased the relative electric conductance of the leaves of P. orientalis container seedlings. The survival rate and relative water content in the AS treatment was 11.64% and 8.33%, respectively, higher than in the NS treatment, whereas the relative electric conductance was 12.19% lower. Therefore, SAP addition and its utilization in arid mountain afforestation has the potential to alleviate drought stress by improving biological activity in the rhizosphere soil of P. orientalis. Addition of SAP is more effective in the nursery substrate than during afforestation. Source

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