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Influence of salinity and water content on soil microorganisms


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Salinization is one of the most serious land degradation problems facing world. Salinity results in poor plant growth and low soil microbial activity due to osmotic stress and toxic ions. Soil microorganisms play a pivotal role in soils through mineralization of organic matter into plant available nutrients. Therefore it is important to maintain high microbial activity in soils. Salinity tolerant soil microbes counteract osmotic stress by synthesizing osmolytes which allows them to maintain their cell turgor and metabolism. Osmotic potential is a function of the salt concentration in the soil solution and therefore affected by both salinity (measured as electrical conductivity at a certain water content) and soil water content. Soil salinity and water content vary in time and space. Understanding the effect of changes in salinity and water content on soil microorganisms is important for crop production, sustainable land use and rehabilitation of saline soils. In this review, the effects of soil salinity and water content on microbes are discussed to guide future research into management of saline soils.
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International Soil and Water Conservation Research 3 (2015) 316 323
Inuence of salinity and water content on soil microorganisms
Nan Yan
, Petra Marschner
, Wenhong Cao
, Changqing Zuo
, Wei Qin
Department of Sediment Research, China Institute of Water Resources and Hydropower Research, Beijing 100048, China
Research Centre on Soil and Water Conservation of the Ministry of Water Resources, Beijing 100048, China
School of Agriculture, Food & Wine, The Waite Research Institute, The University of Adelaide, Adelaide, SA 5005, Australia
Received 10 October 2015; received in revised form 30 November 2015; accepted 30 November 2015
Available online 2 December 2015
Salinization is one of the most serious land degradation problems facing world. Salinity results in poor plant growth and low soil
microbial activity due to osmotic stress and toxic ions. Soil microorganisms play a pivotal role in soils through mineralization of organic
matter into plant available nutrients. Therefore it is important to maintain high microbial activity in soils. Salinity tolerant soil microbes
counteract osmotic stress by synthesizing osmolytes which allows them to maintain their cell turgor and metabolism. Osmotic potential is a
function of the salt concentration in the soil solution and therefore affected by both salinity (measured as electrical conductivity at a certain
water content) and soil water content. Soil salinity and water content vary in time and space. Understanding the effect of changes in salinity
and water content on soil microorganisms is important for crop production, sustainable land use and rehabilitation of saline soils. In this
review, the effects of soil salinity and water content on microbes are discussed to guide future research into management of saline soils.
& 2015 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and
HostingbyElsevierB.V.Thisisanopenaccess article under the CC BY-NC-ND license
( ).
Keywords: Salinity; Water content; Soil microorganism
1. Introduction .......................................................................317
2. The importance of soil microorganisms for nutrient cycling ....................................... 317
3. Soil salinity .......................................................................317
3.1. Soil salinity denition . . ..........................................................317
3.2. Effects of salinity on microorganisms .................................................318
4. The effects of soil water availability on microorganisms .........................................319
4.1. Forms of water in soils . ..........................................................319
4.2. Effect of water content on microbes ..................................................319
4.3. Effect of uctuating water content on soil microorganisms . . .................................320
2095-6339/& 2015 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Production and
Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (
Corresponding author at: China Institute of Water Resources and Hydropower Research, Beijing 100048, PR China. Fax: +86 68416371.
E-mail address: (N. Yan).
Peer review under responsibility of IRTCES and CWPP.
5. Conclusion. . . .....................................................................320
Acknowledgments. .....................................................................320
References ...........................................................................320
1. Introduction
It is predicted that the human population will reach 8 billion in 2025. To avoid or minimize food shortage, saline
soils have to be rehabilitated and managed to meet the food demand of an ever growing human population (Ladeiro,
2012). Soil microorganisms constitute less than 0.5% (w/w) of the soil mass, but they play a key role in soil
properties and processes. Salinity affects plants and microbes via two primary mechanisms: osmotic effect and
specic ion effects (Oren, 1999; Chhabra, 1996). Another factor inuencing plants and microbes is soil water
content. Soil water potential which relates to the energy level by which the water is held in the soil also closely
related to soil salinity, it is inuenced by osmotic potential in the soil solution.
2. The importance of soil microorganisms for nutrient cycling
Soil microorganisms constitute less than 0.5% (w/w) of the soil mass, but they play a key role in soil properties
and processes. Soil microbes include bacteria, archaea, fungi, protozoa and viruses (Tate, 2000). Microorganisms
participate in oxidation, nitrication, ammonication, nitrogen xation, and other processes which lead to
decomposition of soil organic matter and transformation of nutrients (Amato & Ladd, 1994), they can also store
C and nutrients in their biomass which are mineralized after cell death by survi ving microbes (Anderson & Domsch,
1980). Our understanding of these processes increased considerably in recent years with advances in molecular and
analytical methodologies which have led to more successful strategies to modify them for a range of ecosystem
services (Frey, Six, & Elliott, 2003; Gessner et al., 2010; Rillig & Mummey, 2006).
Nutrient cycling is the ux of nutrients within and between the various biotic or abiotic pools in which nutrients
occur in the soil environment (Brady & Weil, 2002). Microorganisms have a major impact on the cycling of
elements, most of which are essential for the growth of living organisms. Bacteria, archaea and fungi, in particular,
are crucial for the cycling of several important inorganic nutrients in soils. Through oxidation, ammonication,
nitrogen xation and other processes, organic materials are decomposed, releasing essential inorganic plant nutrients
to the soil. Nitrate (through nitrication), sulfate (through sulfur oxidation), phosphate (through phosphorus
mineralization) are present in soils primarily due to the action of microorganisms. Therefore, microbes are essential
to maintain a productive and valuable soil system. Disturbance of the soil environment, such as land use change or
soil cultivation, can shift microbial communities and can have detrimental effects on soil nutrient cycling (French et
al., 2009).
In addition, the emission of CO
from soils, which includes respiration from soil organisms and roots, contributes
approximately 10% to atmospheric CO
(Raich & Potter, 1995). Microbes also play an essential role in the formation
of humic substances which are stable forms of organic C and critical for organic C sequestration in soils (Burns et al.,
1986). ( Fig. 1).
3. Soil salinity
3.1. Soil salinity denition
A soil that contains excess salts so as to impair its productivity is called a salt-affected soil. Salt in the soil can
inuence soil processes through the salt concentration in the soil solution (salinity) which determines the osmotic
potential and the concentration of sodium on the exchange complex of the soil (sodicity) which inuences soil
structural stability. Salinity can, over time, lead to sodicity. The major soluble salts in soils are the cations Na
(sodium), Ca
2 þ
(calcium), Mg
2 þ
(magnesium) and K
(potassium), and the anions Cl
(chloride), SO
(bicarbonate), CO
(carbonate) and NO
(nitrate) (Shi & Wang, 2005). There are several classication
systems for salt-affected soils in the world, for example the USDA system, the USSR system and the Australian
N. Yan et al. / International Soil and Water Conservation Research 3 (2015) 316323 317
system (Chhabra, 1996). The USDA system classies soils in three distinct categories (saline, sodic and salinesodic
soils). Saline soils have an electrical conductivity of the saturated paste (EC
)4 4dSm
, ESP o 15 or SARo 13
and pHo 8.5. Sodic soils have an ESP 4 15 or SAR4 13. Soils that have both detrimental levels of neutral soluble
salts (EC
4 4dSm
) and a high-proportion of sodium ions (ESP4 15 or SAR 4 13) are classied as salinesodic
soils (Brady & Weil, 2002; CISEAU, IPTRID, AGLL, & FAO, 2005)(Table 1). Salt-affected soils can be classied
according to how the salinity developed: primary salinity which occurs naturally where the soil parent material is rich
in soluble salts, or geochemical processes result in salt-affected soil. Secondary salinity is salinization of land and
water resources due to human activities. Human activities which can induce salinization include poor irrigation
management; insufcient drainage; improper cropping patterns and rotat ions; chemical contamination (Oldeman,
Hakkeling, & Sombroek, 1990; UNEP, 2007).
3.2. Effects of salinity on microorganisms
High-concentrations of soluble salts affect microbes via two primary mechanisms: osmotic effect and specic ion
Soluble salts increase the osmotic potential (more negative) of the soil water, drawing water out of cells which may
kill microbes and roots through plasmolysis. Low osmotic potential also makes it more difcult for roots and
microbes to remo ve water from the soil (Oren, 1999). Plants and microbes can adapt to low osmotic potential by
accumulating osmolytes, however, synthesis of osmolytes requires large amounts of energy and this results in
reduced growth and activity (Oren, 1999; Wichern, Wichern, & Joergensen, 2006). At high-concentrations, certain
ions, including Na
, and HCO
, are toxic to many plants (Chhabra, 1996).
Table 1
Classication of salt-affected soils.
Salt-affected soil
(dS m
pH Sodium
Saline 4 4.0 o 8.5 o 13 Normal
Salinesodic 4 4.0 o 8.5 4 13 Normal
Sodic o 4.0 4 8.5 4 13 Poor
Animal Biomass
Plant Biomass
Soil CO
Microbial Biomass
Abiontic Residues
Humic Substances
Soil CO
Fig. 1. Conceptual model of carbon cycle emphasizing transfers between major soil organic matter pools (Tate, 2000).
N. Yan et al. / International Soil and Water Conservation Research 3 (2015) 316323318
Many studies showed that salinity reduces microbial activity, microbial biomass and changes microbial
community structure (Andronov et al., 2012; Batra & Manna, 1997; Pathak & Rao, 1998; Rousk, Elyaagubi,
Jones, & Godbold, 2011; Setia, Marschner, Baldock, Chittleborough, & Verma, 2011 ). Salinity reduces microbial
biomass mainly because the osmotic stress results in drying and lysis of cells (Batra & Manna, 1997; Laura, 1974;
Pathak & Rao, 1998; Rietz & Haynes, 2003; Sarig, Fliessbach, & Steinberger, 1 996; Sarig & Steinberger, 1994;
Yuan, Li, Liu, Gao, & Zhang, 2007a). Some studies showed that soil respiration decreased with increasing soil EC
(Adviento-Borbe, Doran, Drijber, & Dobermann, 2006; Wong, Dalal, & Greene, 2009; Yuan et al., 2007b). Setia,
Marschner, Baldock, and Chittleborough (2010) found that soil respiration was reduced by more than 50% at
Z 5.0 dS m
. However, Rietz and Haynes (2003) reported that soil respiration was not signicantly correlated
with EC, but as EC increased, the metabolic quotient (respiration per unit biomass) increased. The sensitivity of soil
enzyme activities to salinity varies: activities of urease, alkaline phosphatase, β-glucosidase were strongly inhibited
by salinity (Frankenberger & Bingham, 1982; Pan, Liu, Zhao, & Wang, 2013), whereas dehydrogenase and catalase
were less affected (Garcia & Hernandez, 1996).
As explained above, microorganisms have the ability to adapt to or tolerate stress caused by salinity by
accumulating osmolytes (Del Moral, Quesada, & Ramos-Cormenzana, 1987; Quesada, Ventosa, Ramoscormenzana,
& Rodriguezvalera, 1982; Sagot et al., 2010; Zahran, Moharram, & Mohammad, 1992). Proline and glycine betaine
are the main organic osmolytes and potassium cations are the most common inorganic solutes used as osmolyte s
accumulated by salinity tolerant microbes (Csonka, 1989). However, the synthesis of organic osmolytes requires
high-amounts of energy (Killham, 1994; Oren 2001). Accumulation of inorganic salts as osmolytes can be toxic
therefore it is conned to halophytic microbes which evolved salt tolerant enzymes to survive in highly saline
environments. Fungi tend to be more sensitive to salt stress than bacteria (Gros, Poly, Monrozier, & Faivre, 2003;
Pankhurst, Yu, Hawke, & Harch, 2001; Sardinha, Muller, Schmeisky, & Joergensen, 2003; Wichern e t al., 2006),
thus the bacteria/fungi ratio can be increased in saline soils. Differences in salinity tolerance among microbes results
in changes in community structure compared to non-saline soils (Gros et al., 2003; Pankhurst et al., 2001 ).
4. The effects of soil water availability on microorganisms
4.1. Forms of water in soils
Substantial volumes of water are commonly stored in soils. For example, 1ha of medium textured soil (1 m deep)
with a water content at eld capacity of 20% can store 8.0 10
L water (Or & Wraith, 2000). Plants and organisms
rely heavily on water in soils and water is essential for nutrient cycling. However, soil water content varies both in
time and in space which not only inuences water availability to plants and microbes but also has a major effect on
the rate of diffusion of solutes and gases (Adl, 2003).
The status of soil water can be described in two ways: the soil water content, which indicates how much water is
present, and soil water potential, which relates to the energy level by which the water is held in the soil. The water
potential is the amount of pressure that needs to be applied to transport a solution of known molarity from a
referenced elevation to that of pure water (McKenzie, 2002), mainly including matric, osmotic and gravitational
potential. Processes dealing with water balance are usually more related to water content; whereas processes related
to water movement are mainly related to soil water potential (Warrick & Or, 2007).
4.2. Effect of water content on microbes
Water is not only an essential transport medium for substrates, it is also an important participant in hydrolysis
processes. Therefore soil water content controls microbial activity and is a major factor that determines the rates of
mineralization (Paul et al., 2003). However, excess soil water content results in limited O
diffusion because O
diffusion in water is much lower (about 10
times) than in air which will reduce the activity of aerobic
microorganisms (Kozlowski, 1984; Skopp, Jawson, & Doran, 1990), but could increase the activities of anaerobes.
Lack of water reduces microbial activity and growth (Bottner, 1985; Kieft, Soroker, & Firestone, 1987), C and N
mineralization (Pulleman & Tietema, 1999; Sleutel et al., 2008) and shifts microbial community structure (Hueso,
Garcia, & Hernandez, 2012; Sorensen, Germino, & Feris, 2013). Cells retain sufcient water for cell turgor and
metabolism by maintaining a higher osmotic potential (more negative) in the cytoplasm than that of the surrounding
N. Yan et al. / International Soil and Water Conservation Research 3 (2015) 316323 319
environment (Martin, Ciulla, & Roberts, 1999). At low water content (high water potential), soil microbes c an
accumulate organic and inorganic compounds which increases the osmotic potential inside their cells. Therefore the
principal tolerance mechanism for low water conten t and high-salinity is the same: accum ulation of osmolytes.
Further as soils dry out, substrate supply becomes incre asingly limited because the pores drain and water lms
around aggregates become thinner and disconnected (Ilstedt, Nordgren, & Malmer, 2000; Stark & Firestone, 1995).
Fungi, Gram-positive bacteria and archaea can better tolerate high matric potential than Gram-negative bacteria
because they have stronger cell walls (Fierer, Schimel, & Holden, 2003; Martin et al., 1999; Schimel, Balser, &
Wallenstein, 2007; Vasileiadis et al., 2012).
4.3. Effect of uctuating water content on soil microorganisms
Soil moisture and the distribution of water within a soil prole vary with seasonal cycles of rainfall, irrigation
periods (farm lands) and temperat ure. In semi-arid and Mediterranean ecosystems, surface soils frequently experience
long dry periods followed by a relat ively rapid wetting (Fierer & Schimel, 2002). The effects of drying and rewetting
on soil microbial processes have been studied (Grifths, Whiteley, O'Donnell, & Bailey, 2003; Herron, Stark, Holt,
Hooker, & Cardon, 2009; Ilstedt et al., 2000; Schimel et al., 2007; Xiang, Doyle, Holden, & Schimel, 2008). The
concentration of available substrate and microbial activity peak in the rst 24 h after rewetting (Fierer & Schimel,
2003). This is because, upon rewetting, cells of sensitive microbes lyse, whilst other microbial genotypes release the
organic solutes they accumulated during the dry phase (Halverson, Jones, & Firestone, 2000). Furthermore, soil
aggregates break down and their previously protected organic matter is exposed and can then be decomposed.
Microbial biomass, activity and nitrication decrease with increasing number of dry and rewetting cycles (Mikha,
Rice, & Milliken, 2005; Nelson, Ladd, & Oades, 1996; Wu & Brookes, 2005). The decrease in microbial biomass
with increasing number of drying and rewetting cycles may be due to the higher microbial biomass turnover (Van
Gestel, Merckx, & Vlassak, 1993) and the loss of C during the ush in respiration upon rewetting (Fierer & Schimel,
2003). However, the response of microbial activity to drying and rewetting varies with soil type (Jin, Haney, Fay, &
Polley, 2013 ) which may be due to the interaction of soil moisture and soil type, aggregation and the concentration of
potentially bioavailable soil organic matter (Anderson & Ingram, 1993). However, drying and rewetting can also kill
some microbes and change microbial community structure which, in turn, could inuence nutrient cycling (Fierer et
al., 2003; Schimel et al., 2007). Butterly, Bunemann, McNeill, Baldock, and Marschner (2009) found that drying and
rewetting induced a reduction in fungi and an increase in Gram-positive bacteria (Butterly et al., 2009).
5. Conclusion
Soil salinity is a threat world-wide to agricultural production and ecosystems because it reduces plant growth and
microbial functioning. The effects of salinity and soil water content on soil microbes have been studied extensively, but
usually separately, in saline soils, the water content also inuences the salt concentration in the soil solution (osmotic
potential), the study of interaction between soil water content and salinity on soil microbes is needed. Further in the eld,
soil salinity and water conten t are not constant in time and space. Therefore, experiments are needed to better understand
the effect of uctuating salinity and so il water content on soil microbe s. Synthesis of osmolytes requires large amounts of
energy. Therefore addition of organic materials such as plant residues or manures as nutrient sources for microbes may be
an important strategy to ameliorate saline soils. Future research could investigate the effect the properties of organic
materials such as decomposability and nutrient content on microbial tolerance to osmotic stress.
This project was funded by the Non-Prot Special Fund of the Ministry of Water Resources, China (Grant no.
201501045) and the Special Fund of the China Institute of Water Resources and Hydropower Research.
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... Salinization is a process of soil degradation that causes desertification and arable land loss in arid and semiarid regions [1,2]. In addition, osmotic stress and toxic ions are important factors in the suppression of plant growth [3], and salinization threatens agricultural production and soil ecosystems [2]. The saline-sodic soil on the Songnen Plain has excess exchangeable Na + and soluble Na + [4]. ...
... Additionally, EEAs were inhibited by low soil organic matter (SOM) content and poor structure and decomposed under high salt concentrations [7][8][9]. Yan reported that soil BG and alkaline phosphatase (ALP) were inhibited by salinity, while the microbial community structure changed with salinity [3]. This resulted in enzyme production and aggregate formation affected by microorganisms 2 of 15 being further suppressed [10,11]. ...
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Excess Na+ and high pH result in poor structures in Saline-Sodic soils, which reduces extracellular enzyme activity (EEA) and causes nutrient limitations. The application of manure improved the Physical-Chemical properties of soil and balanced the soil nutrient supply, which was reflected in the soil EEAs and stoichiometry. Five experimental treatments were designed according to the manure application duration as follows: manure application for 11 years (11a), 16 years (16a), 22 years (22a), and 27 years (27a) and a control treatment with no manure application (CK). The results of the redundancy analysis (RDA) showed that physical properties (mean weight diameter (MWD)) and EEA (β–glucosidase (BG)) significantly increased and bulk density (ρb) significantly decreased when the nutrient content increased. Additionally, soil pH, electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR) significantly decreased after manure application. Based on stepwise multiple linear regression models (SMLR), total nitrogen (TN) was the dominant variable that significantly increased EEA, and the Mantel test showed that soil C:N significantly influenced enzyme stoichiometry. Furthermore, RDA showed that pH, soil C:N and TN were the main factors influencing EEAs and enzyme stoichiometry. Soil EEAs significantly increased with TN and decreased with pH and soil C:N, which affected enzyme stoichiometry. The enzyme stoichiometry increased from 1:2.1:1.2 and 1:2.7:1.5 to 1:1.7:1.2, and the vector angle (vector A) increased, which showed that the N limitation was relieved after the application of manure. The vector length (vector L) showed no significant difference in the C limitation at depths of 0–20 cm and significantly increased at depths of 20–40 cm. In conclusion, soil EEAs and stoichiometry improved with changes in TN and soil C:N, and pH decreased with changes in the soil structure after the application of manure, which accelerated the soil nutrient cycle and balanced the soil nutrient supply.
... Soil water availability greatly influences microbial activities, as accessibility of water changes the activity of microbial enzymes (Yan et al., 2015). Nitrification rate is influenced by variation in soil moisture contents, which impact the substrate accessibility of oxygen and NH 4 + by diffusion and through direct effects of dehydration under low water potential. ...
... Controlled increase in water contents increases nitrification rate, but submergence of water reduces nitrification rate, as flooding leads to limited oxygen supply (Norton and Stark, 2011). During dry conditions, thin water layers between successive soil particles inhibit the movement of substrates to microbes (Yan et al., 2015). Production of NO 3 − and availability of soil water are positively interlinked, because water serves as the medium for substrate transportation . ...
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The abundance and structural composition of nitrogen (N) transformation-related microbial communities under certain environmental conditions provide sufficient information about N cycle under different soil conditions. This study aims to explore the major challenge of low N use efficiency (NUE) and N dynamics in aerobic rice systems and reveal the agronomic-adjustive measures to increase NUE through insights into the ecophysiology of ammonia oxidizers. Water-saving practices, like alternate wetting and drying (AWD), dry direct seeded rice (DDSR), wet direct seeding, and saturated soil culture (SSC), have been evaluated in lowland rice; however, only few studies have been conducted on N dynamics in aerobic rice systems. Biological ammonia oxidation is majorly conducted by two types of microorganisms, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). This review focuses on how diversified are ammonia oxidizers (AOA and AOB), whose factors affect their activities and abundance under different soil conditions. It summarizes findings on pathways of N cycle, rationalize recent research on ammonia oxidizers in N-cycle, and thereby suggests adjustive agronomic measures to reduce N losses. This review also suggests that variations in soil properties significantly impact the structural composition and abundance of ammonia oxidizers. Nitrification inhibitors (NIs) especially nitrapyrin, reduce the nitrification rate and inhibit the abundance of bacterial amoA without impacting archaeal amoA. In contrast, some NIs confine the hydrolysis of synthetic N and, therefore, keep low NH4+-N concentrations that exhibit no or very slight impact on ammonia oxidizers. Variations in soil properties are more influential in the community structure and abundance of ammonia oxidizers than application of synthetic N fertilizers and NIs. Biological nitrification inhibitors (BNIs) are natural bioactive compounds released from roots of certain plant species, such as sorghum, and could be commercialized to suppress the capacity of nitrifying soil microbes. Mixed application of synthetic and organic N fertilizers enhances NUE and plant N-uptake by reducing ammonia N losses. High salt concentration promotes community abundance while limiting the diversity of AOB and vice versa for AOA, whereas AOA have lower rate for potential nitrification than AOB, and denitrification accounts for higher N2 production. Archaeal abundance, diversity, and structural composition change along an elevation gradient and mainly depend on various soil factors, such as soil saturation, availability of NH4+, and organic matter contents. Microbial abundance and structural analyses revealed that the structural composition of AOA was not highly responsive to changes in soil conditions or N amendment. Further studies are suggested to cultivate AOA and AOB in controlled-environment experiments to understand the mechanisms of AOA and AOB under different conditions. Together, this evaluation will better facilitate the projections and interpretations of ammonia oxidizer community structural composition with provision of a strong basis to establish robust testable hypotheses on the competitiveness between AOB and AOA. Moreover, after this evaluation, managing soils agronomically for potential utilization of metabolic functions of ammonia oxidizers would be easier.
... Salt stress is a severe abiotic threat that restricts crop plant productivity and is negatively associated with reduced soil organic matter and C:N ratio. It also alters the soil microbial community by decreasing biomass and activity (Yan et al. 2015). Consistent with previous studies by Abou-Zeid et al. (2021) and Ekinci et al. (2022), the findings confirm the negative effects of 150 mM salt stress on wheat plants' growth and physiological characteristics. ...
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The production of olive mill solid waste (OMSW) raises concerns due to its toxicity and negative environmental impact. However, by utilizing pyrolysis, OMSW can be converted into biochar, a carbon-rich material that detoxifies the waste and preserves its nutrient content. The OMSW-based biochar possesses alkaline properties (pH 9.6), low electrical conductivity (EC), high cation exchange capacity (CEC), a porous surface morphology, various surface functional groups, and high mineral content. This study assessed the influence of two concentrations (5% and 10%) of OMSW-based biochar on wheat plants' growth biomarkers and physiological characteristics subjected to salt stress conditions (150 mM NaCl). Findings of the study revealed that salt stress had deleterious effects on various parameters, including shoot height, fresh and dry weights of shoots and roots, relative water content (RWC%), membrane stability index (MSI%), photosynthetic pigments, and photosynthetic parameters such as the coefficient of the effective quantum yield of photochemical energy conversion of PSII (ØPSII), photochemical quenching (qP), and photochemical efficiency of PSII (Fo, Fm, Fv/Fo, and Fv/Fm). Furthermore, the levels of lipid peroxidation (MDA), hydrogen peroxide (H2O2), superoxide dismutase (SOD), and peroxidase (POD) activities significantly increased in stressed plants. On the other hand, applying both concentrations of OMSW-based biochar effectively improved the overall performance of wheat plants, irrespective of the presence of salinity. OMSW-based biochar is a promising strategy for promoting wheat growth in salt-stressed soil by improving various growth parameters and mitigating plant oxidative stress.
... It is widely acknowledged that soil electrical conductivity (EC) can affect the number and abundance of soil bacteria [59,60]. The findings also revealed a substantial negative correlation between EC and the Shannon index of soil bacteria ( Figure S1b), which may be because salinity mainly inhibited microbial proliferation through ionic toxicity and high osmotic pressure [61]. ...
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The high salt content in saline–alkaline land leads to insufficient nutrients, thereby reducing agricultural productivity. This has sparked widespread interest in improving saline–alkaline soil. In this investigation, 16S rRNA gene high-throughput sequencing was employed to examine the impacts of three cropping systems (monoculture, rotation, and mixture) on soil bacterial communities. It was found that cropping rotations and mixtures significantly increased soil bacterial α-diversity. Random forest analysis showed a significant linear relationship between AK and EC and bacterial α-diversity. In addition, principal coordinates analysis (PCoA) further confirmed the significant differences in β-diversity between different soil layers. Through co-occurrence network analysis, it was found that cropping rotations and mixtures increased the stability and complexity of co-occurrence networks. By calculating NST to analyze the assembly process of soil bacterial communities in different cropping systems, it was found that the assembly process of soil bacterial communities was dominated by a stochastic process. Functional prediction results showed that a large number of C, N, and S cycling microbes appeared in soil bacterial communities. Our study aims to establish a fresh perspective on the improvement and recovery of saline–alkaline soil.
... The accelerated weathering of minerals The soil salinity effect, driven either by the climate (due to drought conditions) or by irrigation management, is another important issue. The salts cause toxicity phenomena, reduce water plant uptake, and impair soil microorganisms, impacting soil functioning and crop production [32,[51][52][53][54]. Moreover, Na accumulation can degrade the soil structure, affecting the fate of water, nutrients, and carbon in the crop-water-soil-atmosphere matrix. ...
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“Climate” is a complex concept [...]
... Elevated salt levels in saline soils negatively impact soil structure and impede water infiltration. Furthermore, higher salt concentration significantly inhibits the activities of microorganisms necessary for nutrient cycling and breakdown of organic matter [4,5]. Elevated salt concentration exerts negative effects on the hydrological characteristics of the soil, thereby hindering the plants' ability to acquire sufficient moisture necessary for their normal physiological functions and development [6]. ...
Salinity exerts significant negative impacts on growth and productivity of crop plants and numerous management practices are used to improve crop performance under saline environments. Micronutrients, plant growth promoting bacteria and biochar are known to improve crop productivity under stressful environments. Maize (Zea mays L.) is an important cereal crop and its productivity is adversely impacted by salinity. Although boron (B) application, seed inoculation with boron-tolerant bacteria (BTB) and biochar are known to improve maize growth under stressful environments, there is less information on their combined impact in enhancing maize productivity on saline soils. This study investigated the impact of B seed coating combined with seed inoculation with BTB + biochar on maize productivity under saline soil. Four B seed coating levels [0.0 (no seed coating), 1.0, 1.5, 2.0 g B kg⁻¹ seed], and individual or combined application of 5 % (w/w) maize stalk biochar, and seed inoculation with Bacillus sp. MN-54 BTB were included in the study. Different growth and yield attributes and grain quality were significantly improved by seed coating with 1.5 B kg⁻¹ seed coupled with biochar + BTB. Seed coating with 1.5 B kg⁻¹ seed combined with biochar + BTB improved stomatal conductance by 32 %, photosynthetic rate by 15 %, and transpiration ratio by 52 % compared to seed coating (0 B kg⁻¹ seed) combined with biochar only. Similarly, the highest plant height (189 cm), number of grain rows cob⁻¹ (15.5), grain yield (54.9 g plant⁻¹), biological yield (95.5 g plant⁻¹), and harvest index (57.6 %) were noted for B seed coating (1.5 g B kg⁻¹ seed) combined with biochar + BTB inoculation. The same treatment resulted in the highest grain protein and B contents. It is concluded that B seed coating at 1.5 g B kg⁻¹ seed combined with biochar + BTB inoculation could significantly improve yield and quality of maize crop on saline soils. However, further field experiments investigating the underlying mechanisms are needed to reach concrete conclusions and large-scale recommendations.
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The rapid decline in soil water affects water resources, plant physiology, and agricultural development. However, the changes in soil drying rate and associated climatic mechanisms behind such changes remain poorly understood. Here, we find that wet regions have witnessed a significant increasing trend in the soil drying rate during 1980−2020, with an average increase of 6.01 − 9.90% per decade, whereas there is no consistent trend in dry regions. We also identify a near-linear relationship between the annual soil drying rate and its influencing factors associated with atmospheric aridity and high temperatures. Further, enhanced evapotranspiration by atmospheric aridity and high temperatures is the dominant factor increasing the soil drying rate in wet regions. Our results highlight the accelerated soil drying in the recent four decades in wet regions, which implies an increased risk of rapidly developing droughts, posing a serious challenge for the adaptability of ecosystems and agriculture to rapid drying.
Reductions in soil moisture due to prolonged episodes of drought can potentially affect whole forest ecosystems, including soil microorganisms and their functions. We investigated how the composition of soil microbial communities is affected by prolonged episodes of water limitation. In a mesocosm experiment with Scots pine saplings and natural forest soil maintained at different levels of soil water content over 2 years, we assessed shifts in prokaryotic and fungal communities and related these to changes in plant development and soil properties. Prolonged water limitation induced progressive changes in soil microbial community composition. The dissimilarity between prokaryotic communities at different levels of water limitation increased over time regardless of the recurrent seasons, while fungal communities were less affected by prolonged water limitation. Under low soil water contents, desiccation‐tolerant groups outcompeted less adapted, and the lifestyle of prokaryotic taxa shifted from copiotrophic to oligotrophic. While the abundance of saprotrophic and ligninolytic groups increased alongside an accumulation of dead plant material, the abundance of symbiotic and nutrient‐cycling taxa decreased, likely impairing the development of the trees. Overall, prolonged episodes of drought appeared to continuously alter the structure of microbial communities, pointing to a potential loss of critical functions provided by the soil microbiome.
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Thoroughly updated and now in full color, the 15th edition of this market leading text brings the exciting field of soils to life. Explore this new edition to find: A comprehensive approach to soils with a focus on six major ecological roles of soil including growth of plants, climate change, recycling function, biodiversity, water, and soil properties and behavior. New full-color illustrations and the use of color throughout the text highlights the new and refined figures and illustrations to help make the study of soils more efficient, engaging, and relevant. Updated with the latest advances, concepts, and applications including hundreds of key references. New coverage of cutting edge soil science. Examples include coverage of the pedosphere concept, new insights into humus and soil carbon accumulation, subaqueous soils, soil effects on human health, principles and practice of organic farming, urban and human engineered soils, new understandings of the nitrogen cycle, water-saving irrigation techniques, hydraulic redistribution, soil food-web ecology, disease suppressive soils, soil microbial genomics, soil interactions with global climate change, digital soil maps, and many others Applications boxes and case study vignettes bring important soils topics to life. Examples include “Subaqueous Soils—Underwater Pedogenesis,” “Practical Applications of Unsaturated Water Flow in Contrasting Layers,” “Soil Microbiology in the Molecular Age,” and "Where have All the Humics Gone?” Calculations and practical numerical problems boxes help students explore and understand detailed calculations and practical numerical problems. Examples include “Calculating Lime Needs Based on pH Buffering,” “Leaching Requirement for Saline Soils,” "Toward a Global Soil Information System,” “Calculation of Nitrogen Mineralization,” and “Calculation of Percent Pore Space in Soils.”
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With the continue increase of the world population the requirements for food, freshwater, and fuel are bigger every day. This way an urgent necessity to develop, create, and practice a new type of agriculture, which has to be environmentally sustainable and adequate to the soils, is arising. Among the stresses in plant agriculture worldwide, the increase of soil salinity is considered the major stress. This is particularly emerging in developing countries that present the highest population growth rates, and often the high rates of soil degradation. Therefore, salt-tolerant plants provide a sensible alternative for many developing countries. These plants have the capacity to grow using land and water unsuitable for conventional crops producing food, fuel, fodder, fibber, resin, essential oils, and pharmaceutical products. In addition to their production capabilities they can be used simultaneously for landscape reintegration and soil rehabilitation. This review will cover important subjects concerning saline agriculture and the crop potential of halophytes to use salt-contaminated resources to manage food requirements.
Soil physical measurements are essential for solving many natural resource management problems. This operational laboratory and field handbook provides, for the first time, a standard set of methods that are cost-effective and well suited to land resource survey. It provides: practical guidelines on the soil physical measurements across a range of soils, climates and land uses; straightforward descriptions for each method (including common pitfalls) that can be applied by people with a rudimentary knowledge of soil physics, and guidelines on the interpretation of results and integration with land resource assessment. Soil Physical Measurement And Interpretation for Land Evaluation begins with an introduction to land evaluation and then outlines procedures for field sampling. Twenty detailed chapters cover pore space relations, water retention, hydraulic conductivity, water table depth, dispersion, aggregation, particle size, shrinkage, Atterburg limits and strength. The book includes procedures for estimating soil physical properties from more readily available data and shows how soil physical data can be integrated into land planning and management decisions.
Cambridge Core - Ecology and Conservation - Soil Ecology - by Ken Killham
Soil salinity, as an increasingly important process of land degradation, is a major threat to microbial communities and thus strongly alters organic matter turnover processes. This study was conducted to determine the influence of salinity on the decomposition of maize and on the response of soil microbial communities. Soil samples were collected from two pasture sites in Heringen (Germany). One of the sites has previously been influenced by salinity caused by saline effluent from a potassium mine. These sandy soils were washed, resulting in equal levels of electrical conductivity. Moist soils were then incubated with 2% incorporated maize straw and at three levels of salinity (0, 15, 50 mg NaCl g− 1 soil) for almost 7 weeks at 25 °C. The amount of recovered maize derived particulate organic matter (POM) increased with increasing salinity, exhibiting reduced decomposition of substrate. Furthermore, inorganic N, which consisted almost exclusively of NH4+, increased with increasing levels of salinity. Corresponding to this, biological indices like soil respiration and microbial biomass decreased with increasing levels of salinity, underlining the detrimental effect of salinity on soil microorganisms. This effect was reduced after addition of maize straw, documenting the importance of organic matter amendment in counteracting the negative effects of salinity on microbial communities and related mineralisation processes. Addition of organic matter also led to a spatial differentiation of the microbial community in the soil, with bacteria dominating the surface of the substrate, indicated by a low glucosamine-to-muramic acid ratio. This ratio, however, was not altered by salinity. On the other hand, the ergosterol-to-microbial biomass C ratio was an evidence of fungal dominance in the soil. The ratio increased with elevated salt content, either showing a shift towards fungi, a change in fungal cell morphology, or accumulation of ergosterol in the soil. The metabolic quotient qCO2 was higher in the soil previously subjected to osmotic stress, showing a physiologically more active population that is using substrate less efficiently. We assume that it might further reflect adaptation mechanisms to the increased osmotic pressure.
Molecular methods were used to study variation in the taxonomic structure of bacterial, archaeal, and fungal communities in soil samples taken along a salinity gradient from a solonchak in the vicinity of Lake Akkol’ (Shingirlau, Kazakhstan). Soils from arable fields located 195 km from the solonchak served as the control. Total DNA was isolated from every sample and analyzed by T-RFLP and real-time PCR. Salinization was found to be the main ecological factor determining the structure of soil microbial community in the study region. The values of Simpson’s index characterizing the diversity of this community proved to be similar in all the samples, which, however, significantly differed in the taxonomic composition of microorganisms. A significantly increased content of archaea was revealed in the sample with the highest salinity. The results of this study show that the structure of soil microbial community reflects specific features of a given soil and can be used as an indicator of its ecological state.
Precipitation amount and seasonal timing determine the duration and distribution of water available for plant and microbial activity in the cold desert sagebrush steppe. In this study, we sought to determine if a sustained shift in the amount and timing of precipitation would affect soil microbial diversity, community composition, and soil carbon (C) storage. Field plots were irrigated (+200 mm) during the dormant or growing-season for 17 years. Microbial community responses were assessed over the course of a year at two depths (15–20 cm, 95–100 cm) by terminal restriction fragment length polymorphism (T-RFLP), along with co-occurring changes in plant cover and edaphic properties. Bacterial richness, Shannon Weaver diversity, and composition in shallow soils (15–20 cm) as well as evenness in deep soils (95–100 cm) differed across irrigation treatments during July. Irrigation timing affected fungal community diversity and community composition during the dormant season and most strongly in deep soils (95–100 cm). Dormant-season irrigation increased the ratio of shrubs to forbs and reduced soil C in shallow soils by 16% relative to ambient conditions. It is unclear whether or not soil C will continue to decline with continued treatment application or if microbial adaptation could mitigate sustained soil C losses. Future changes in precipitation timing will affect soil microbes in a seasonally dependent manner and be coupled to co-varying effects of water content on vegetation and soil C.