Cynodon dactylon: An efficient perennial grass to revegetate sodic lands

Ecological Engineering 54 (2013) 32–38

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Cynodon dactylon: An efficient perennial grass to revegetate sodic lands Kripal Singh a,b,∗ , Vimal Chandra Pandey b , Rana P. Singh b a b

Restoration Ecology Group, CSIR-National Botanical Research Institute, Rana Pratap Marg, Lucknow 226 001, Uttar Pradesh, India Department of Environmental Science, Babasaheb Bhimrao Ambedkar (Central) University, Raibarelly Road, Lucknow 226 025, Uttar Pradesh, India

a r t i c l e

i n f o

Article history: Received 17 July 2012 Received in revised form 3 January 2013 Accepted 16 January 2013 Keywords: Cynodon dactylon Enzyme activities Microbial quotient, Rhizosphere sodic soils

a b s t r a c t Sodic soils are wide-spread in semi-arid subtropical regions and characterized by high level of sodium and pH with poor physical, microbial and enzyme activities. In this study frequency (F), density (D), abundance (Ab) and important value index (IVI) of grasses naturally growing on abandoned sodic land were observed to assess sodicity tolerance ability of these grasses. The greatest IVI and visual observations showed that Cynodon dactylon (Bermuda grass) has maximum ability to grow on severely sodic lands and can be identified as an ecological tool in rehabilitation of degraded lands. Besides vegetation analysis, this further would be confirm by analysis of microbial and enzyme activities of rhizosphere soils. Therefore, we also observed the changes in microbial and enzyme activities of rhizosphere soils (RS) of C. dactylon and compared with non-rhizosphere (adjacent non-vegetated area) sodic soils (NRS) to assess its ecological suitability for reclamation of sodic soils. We collected 135 random soil samples from C. dactylon rhizosphere as well as adjacent non-rhizosphere bulk soil. Soil pH, exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), electrical conductivity (EC) and carbon nitrogen ratio (C:N) were significantly lower in rhizosphere soils in comparison to non-rhizosphere soils, while organic carbon (OC), total nitrogen (T-N), available phosphorus (P), microbial biomass carbon (MBC), soil respiration (SR), microbial quotient (Cmic :Corg ), dehydrogenase, protease and alkaline phosphatase activities were significantly higher in rhizosphere soils. Decreases in soil sodicity (pH, ESP and SAR) and increases in soil nutrients, microbial biomass and enzyme activities suggest that C. dactylon can be used to restore and enhance the biological activities of abandoned sodic lands and to facilitate the further vegetation establishment. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Sodic soils are wide-spread (436 million ha) in semi-arid subtropical regions of the world (Wong et al., 2009) and occupy about 249 Mha in Asia. In India sodic soils are estimated to be about 6.9 Mha and 1.63 Mha sodic soils occur only in Uttar Pradesh, a state of the country. High level of sodium and soil pH, poor nutrient availability, dispersion and swelling of clay particles, poor water infiltration rate and impeded microbial activities are the characteristics of these soils which adversely affect plant growth (Qadir et al., 2007; Shukla et al., 2011; Singh et al., 2012a). Therefore, rehabilitation of such degraded lands is important which would increase soil fertility and contribute in mitigation of global warming through sequestration of carbon in aboveground and belowground habitats (Pandey et al., 2011; Singh et al., 2012b). However, the main objective of any restoration/rehabilitation project is amelioration

∗ Corresponding author at: Restoration Ecology Group, CSIR-National Botanical Research Institute, Rana Pratap Marg, Lucknow 226 001, Uttar Pradesh, India. Tel.: +91 0522 2297962; fax: +91 0522 2205836/2205839. E-mail addresses: [email protected], gill [email protected] (K. Singh). 0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.01.007

of physical and chemical characteristics of the soil and ensuring the building of sustainable ecosystems (Hobbs and Norton, 1996; Costanza, 2012). According to The Society for Ecological Restoration, the definition of ecological restoration is the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed (Harris, 2003). In this context, we identified Cynodon dactylon (Cynodon, thereafter) as an ecological tool to ameliorate degraded lands and can be used to assess recovery status. Cynodon is a perennial grass, colonizing well on sodic lands at irregular intervals, and creates a dense green mats in metres of area. Grass multiplies or propagates through seeds, runners and rhizomes. Seeds of Cynodon when get acclimate to sodic condition they initiate their growth. Furthermore, we observed the growth of other grasses (Desmostachya bipinnata, Eragrostis tenella and Chloris barbata) in the premises of Cynodon, while there was no any grass on adjacent sodic soils. This strikes us to investigate the properties of Cynodon rhizosphere soils and adjacent bare sodic soils (termed non-rhizosphere soils). Several grasses have been used as a bioremediation tool to ameliorate a variety of sodic and saline-sodic soils. Some workers have favoured the inclusion of Cynodon (Qadir et al., 2007) as the first crop to accelerate soil amelioration. In general, grasses are more

K. Singh et al. / Ecological Engineering 54 (2013) 32–38

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Table 1 Definitions and calculation formulas of vegetation indices. Indices

Definition

Frequency (F)

Frequency refers to the degree of dispersion in terms of percentage occurrence.

Density (D)

Density refers to the amount of area available for the spp.

Total number of individuals of species total number of quadrats studied

Abundance (Ab)

Abundance refers to the estimated no. of individuals of a spp. occurring per unit area.

Total number of individuals of species total number of quadrats occurrence

Importance value index (IVI)

IVI refers to the sum of relative frequency, density and abundance to show the importance of a sp. in the location.

Relative frequency + relative density + relative abundance

tolerant of sodic conditions than most field crops. Field and greenhouse studies have shown that Cynodon is highly tolerant of sodic conditions and can be successfully grown in sodic soils (Kumar and Abrol, 1979, 1983; Shukla et al., 2011). In other studies potential of Cynodon for rehabilitation of fly ash landfills (Maiti and Nandhini, 2006), mine spoils (Babu and Reddy, 2011; Osaliya et al., 2011) and heavy metal polluted lands (Wu et al., 2010) have also been discussed. Sultan et al. (2007) reported highest palatable value and crude protein (12%) in Cynodon among the 12 grasses growing on marginal lands. Therefore, Cynodon is an efficient perennial grass for phyto-stabilization of degraded lands than other grass because it occurs throughout the world and grows naturally in several stressful environments. But its potential for rehabilitation of degraded sodic lands was not reported. It is a well-established concept that plant–microbe interactions induce such changes in soil properties during early primary succession to invite followers for development of a vegetation ecosystem (Knelman et al., 2012). Plant roots strongly influence the nutrients availability in the plant rhizosphere through rhizodeposition and uptake of nutrients (Koranda et al., 2011). There is considerable work and widespread agreement that higher microbial turnover and activities occur in the rhizosphere than in the bulk or nonrhizosphere soils, mainly due to high growth and activity of the plant fine roots (Babu and Reddy, 2011; Koranda et al., 2011). But information about plant–soil interactions is still missing for sodic land. Therefore, it would be important to understand the changes in microbial and enzyme activities induced by Cynodon are attributed to alterations in soil sodicity. The main objective of the present study is to prove that Cynodon induces desirable changes in the sodic soils making them appropriate for germination of other grasses. This will be evident from dominance of grass species growing in degraded sodic land and reduction in soil sodicity (pH, ESP and SAR) and increase in nutrients availability and microbial activities of sodic soils.

2. Materials and methods 2.1. Study site, sampling and analysis The study site is located at Ranipur village of Banthra Research Station, National Botanical Research Institute (NBRI), Lucknow (80◦ 45 53 E, 26◦ 40 45 N) India. The study site receives about 800–950 mm total annual rainfall, temperature ranges from minimum 18 ◦ C in winter to maximum 42 ◦ C in summer. The degraded sodic lands which were set aside abandoned after extensive agricultural practices since long back (about five decades) are widely distributed in the study area. About 100 ha of sodic land were acquired by NBRI, Lucknow in 1956 for its ecological restoration or rehabilitation under functioning ecosystems. Out of this area there was a patch (15 ha) of land remained untouched to assess recovery status. The soil is classified as typic halaquepts with poor drainage,

Calculation formula

 Total number of quadrats in which species occurred  total number of quadrats studied

× 100

brownish grey colour, yellowish brown mottles and silty clay or clay texture. Details of this site can also be found in Singh et al. (2012a,b). This sodic land had high pH (9.92 ± 0.16), electrical conductivity (EC ≈ 2.61 dS m−1 ) and exchangeable sodium percentage (ESP ≈ 90%) (Singh et al., 2012a). Currently, this land is covered by patchy vegetation of few grasses. There is no any published information on succession facilitator species and successional chronosequence. However, Chandra and Kapoor (1987) first time reported few species of weeds like Andropogon annulatus, A. squarrosus, C. dactylon, Sporobolus arabicus and S. barani growing on abandoned sodic lands. Authors mentioned in their note that “there is hardly any place where C. dactylon is not growing”. This indicates the ability of Cynodon to serve as succession facilitator. As hundreds of hectare land is abandoned, livestock movement and grazing is a common practice in this area. Livestock grazing is essential to maintain structure and composition of grassland upon which a variety of plants and animals depend for their survival. However, uncontrolled and excessive grazing further results in ecodegradation. Essentially there are two approaches for the ecodevelopment of degraded land; either by improving land and growing value added crop species, or by screening and indentifying potential one among the naturally growing species (Pandey et al., 2012). Therefore, in this study was undertaken to identify dominant species among companion grasses and assess its effects on microbial and enzyme activities of rhizosphere soil. For this purpose, ten 50 cm × 50 cm quadrats were placed randomly to study the frequency, density and abundance of grasses and biomass production of C. dactylon. Quadrat data were used for computation of analytical features such as frequency, density, abundance and importance value index (IVI), following standard phytosociological methods. Importance value index (IVI) was calculated from the vegetation data which aggregates the frequency, density and basal area/cover on summation of relative frequency, relative density and relative dominance (Curtis, 1959). This index is used to determine the overall importance (relative dominance) of each species in the community structure. In calculating this index, the percentage values of the relative frequency, relative density and relative dominance are summed up together and this value is designated as the IVI of the species (Curtis, 1959). Definitions and calculation formulas of each index are given in Table 1. Total (shoot and root) C. dactylon was harvested (20 cm deep) to estimate the standing biomass. Rhizosphere (RS) and non-rhizosphere (NRS) soil samples were collected in August 2011, from abandoned sodic land. In this patch of land, three plots of 10 m × 10 m were demarcated which have levelled topography, uniform grass cover and appropriate water drainage. These plots were further divided in five subplots of 2 m × 2 m. For RS soil samples three mats of Cynodon were selected at each subplot. Three rhizosphere soil samples were collected from each mat of Cynodon of each subplot of three main plots. Thus total 135 (45 from each plot) soil samples were pooled (to

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K. Singh et al. / Ecological Engineering 54 (2013) 32–38

Fig. 1. Livestock grazing on abandoned sodic land [A] of the study site. Inset figure is showing the roots of Cynodon dactylon. Rhizosphere and non-rhizosphere soil are demarcated by circles [B].

reduce the spatial heterogeneity of soil, if any) and then total 5 replicate samples from this pooled sample were analyzed for each soil property. It has been common practice to separate rhizosphere soil from non-rhizosphere soil to assess the effect of growing plant roots on the microbial activities in the surrounding soils (Steer and Harris, 2000). Therefore, in this study we separated rhizosphere soil from Cynodon roots. Soil adhering to roots of C. dactylon and within the space explored by the roots was considered as rhizosphere soil (Koranda et al., 2011). Similarly, soil was collected from adjacent non-rhizosphere soils (non-vegetated area) of each mat of Cynodon (Fig. 1B). Spatial heterogeneity of soil influences plant community composition and diversity in natural succession and it may be argued that the Cynodon growing only in the areas where soil sodicity values were lower in the first place. Therefore, soil samples were selected from edge of the Cynodon mat where the grass is of very young stage and close non-vegetated land. Furthermore, experimental plots (100 m2 each) have uniform grass cover which indicates that development of vegetation cover on sodic soil is due to changes in soil properties induced by growth of grasses itself not due to spatial heterogeneity of the soil. Soil pH, electrical conductivity (EC; dS m−1 ), organic carbon (OC; g kg−1 ), total nitrogen (T-N; g kg−1 ) and available phosphorus (P; ␮g g−1 ) were analyzed using standardized protocols described in Kalra and Maynard (1991). The measurement of exchangeable sodium percent (ESP) and sodium adsorption ratio was calculated from extractable and exchangeable cations (sodium; Na, potassium; K, calcium; Ca, and magnesium; Mg). The fumigationextraction method was used to determine soil microbial biomass carbon (MBC; ␮g g−1 ) using kEC of 0.45 (Vance et al., 1987). Soil respiration of fresh moist soil was determined by alkali (NaOH) absorption method (Yao et al., 2009). Soil dehydrogenase was analyzed using 2,3,5-triphenyltetrazolium chloride as the substrate, protease using tyrosine as substrate and alkaline phosphaatse using p-nitrophenyl phosphate as substrate (Tabatabai, 1994). Microbial quotient (Cmic :Corg ) and metabolic quotient (qCO2 ) were derived as described by Wong et al. (2009).

2.2. Statistical analysis The results are expressed as mean ± standard deviation. Differences between rhizosphere soil (RS) and non-rhizosphere soil (NRS) were analyzed using paired t-test.

3. Results and discussion 3.1. Floristic analyses and biomass production of C. dactylon Frequency, density, abundance and IVI of all grass species growing on sodic land are presented in Table 2. The IVI calculated for the individual species encountered in field revealed Cynodon was the most important species followed by the Ceratophyllum verticillatum, Cyperus sp., Cyperus kyllingia and other grasses. This indicates ability of Cynodon to compete with stressful conditions and survive in low-resource environment. Cynodon emerged as a pioneer species in abandoned sodic land with a basal cover higher than 50% (unpublished data) and an IVI about 35%. This is consistent with study of Zhang et al. (2012). They reported 34% IVI of dominant grass Artemisia capillaries on abandoned land when other grass became an important companion species. Furthermore, two surveys, one in 1956 and second in 1974, were undertaken to identify weed flora on same sodic land by Chandra and Kapoor (1987). They tabulated 43 species in the first survey and 71 species in second with dominance of Cynodon in each survey. After 38 years of succession, in 2012, the grassland was also dominated by Cynodon along with companion species such as C. verticillatum and Cyperus sp. This indicates that more tolerant species, Cynodon, created favourable ecological conditions for the less tolerant ones to gradually establish themselves with success and creating multiple-species competitive community. Several plants engage in interactions with rhizosphere and root associated microbes to survive in inhospitable and nutrient limited conditions (Abhilash et al., 2012). In previous study, however, we found less frequency

Table 2 Frequency (F), density (tillers m−2 ), abundance (Ab) and importance value index (IVI) of grasses growing on sodic soils. Grasses

F (%)

Cynodon dactylon Ceratophyllum verticillatum Cyperus sp. Paspalum vaginatum Cyperus kyllingia Sporobolous diander Cyperus triceps Cyperus rotundus Desmostachya bipinnata Chloris barbata Eragrostis tenella

70 20 60 50 30 50 40 20 20 20 20

D (m−2 ) 36.8 16.13 20.13 12.93 12.13 5.6 6.4 4.8 4 0.8 0.8

Ab 13.14 20.17 8.39 6.47 10.11 2.8 4 6 5 1 1

IVI 35.17 25.18 23.03 17.14 16.99 11.15 11.11 9.34 8.22 3.75 3.75

Biomass production (g m-2)

K. Singh et al. / Ecological Engineering 54 (2013) 32–38

83 82 81 80 79 78 77 76 75

NS

Shoot

Root

Fig. 2. Biomass production of C. dactylon (shoot and root) on sodic soil. Error bars indicate standard deviation of the mean (N = 5). NS = not significant.

(F), density (D), abundance (Ab), and importance value index (IVI) and total biomass of Cynodon on sodic lands when compared to two other land use systems with low sodicity levels (Shukla et al., 2011). This indicates that growth of Cynodon further can be facilitated with application of organic and chemical amendments as applied in earlier study. Cynodon, growing on sodic soils, produces about 134 g total biomass m−2 (roots contribute about 40%) (Shukla et al., 2011) and 158 g m−2 (contribution of roots was 78 g m−2 ) in the present study (Fig. 2). High values of root biomass production in the present study might be due to grazing. 3.2. Chemical properties of rhizosphere and non-rhizosphere soil of C. dactylon The effect of the rhizosphere and non-rhizosphere on soil pH, ESP (%), SAR (%), EC (dS m−1 ), OC (g kg−1 ), C:N, T-N (g kg−1 ) and P (␮g g−1 ) are presented in Table 3. The rhizosphere is a biologically active zone with high microbial growth and activities because it is around the plant roots. In this study, soil pH, EC, ESP, SAR and C:N were significantly (P < 0.05) lower in rhizosphere soils than nonrhizosphere soils (Table 3). This was most likely due to the growth of Cynodon and accumulation organic carbon in the root zone. Phytoremediation of sodic soils involves the alleviation of sodicity through plant–microbe interactions. As a result of this interaction, partial pressure of CO2 increases which results in production of H+ ions corresponding to reduction in soil pH (Qadir et al., 2007). Organic acids produced by microorganisms and present in root exudates may also play an important role in reduction of soil pH (Hamilton et al., 2008; Babu and Reddy, 2011; Koranda et al., 2011). Table 3 Chemical properties of rhizosphere and non-rhizosphere soil of C. dactylon. Values are mean ± standard deviation (N = 5). Soil properties

Rhizospheric (RS)

Soil pH Electrical conductivity (dS m−1 ) Exchangeable sodium percent (%)b Sodium adsorption ratio (%)b Organic carbon (g kg−1 ) Total nitrogen (g kg−1 ) C:N Available phosphorus (␮g g−1 )

8.52 1.61 24.2 6.22 2.20 0.29 7.52 21.2

a

± ± ± ± ± ± ± ±

0.25a 0.15a 2.25a 0.79a 0.07a 0.05a 1.15a 1.03a

Nonrhizospheric (NRS) 9.50 2.30 82.0 25.6 1.68 0.15 11.6 15.6

± ± ± ± ± ± ± ±

0.09 0.14 5.29 0.82 0.20 0.03 3.31 1.52

Significant difference between RS and NRS soil (paired t-test, P < 0.05). Values were calculated from extractable and exchangeable cations (Na, K, Ca and Mg) not presented here. b

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Similarly, Zhang et al. (2012) and studies referred therein also reported significant decrease in soil pH in rhizosphere soils than the bulk soils. Cynodon has a deep root system and roots can grow to a distance of about 2 m deep (Babu and Reddy, 2011). Development of deep root channels leaches the salts out of the surface soils (Garg, 1999), which results in 30%, 61% and 66% decrease in EC, ESP and SAR, respectively. This reduction in sodicity is somewhat similar to the observation made by Singh et al. (2012a). They observed 53% reduction in ESP in surface soil (0–15 cm) of 50 years old forest developed on same sodic land. This clearly indicates that Cynodon has potential equal to that of forest to ameliorate (decrease in soil sodicity) sodic soil environment. The amounts of OC, TN and P in the rhizosphere soil of the Cynodon were significantly higher than those in the non-rhizosphere soils. Increased level of organic carbon in soil is due to rhizodeposition of organic matter transferred from plant roots to soil. Generally, plant succession results in increased soil nutrient pools. In this study, Cynodon greatly enhanced soil nitrogen and phosphorus contents. 3.3. Microbial and enzyme activities of rhizosphere and non-rhizosphere soil of C. dactylon In spite of the significant information on the effects of sodication on microbial and enzyme activities, none has focused on the effects of sodication on microbial and enzyme activities in the rhizosphere. In this study we found that microbial biomass carbon (MBC), soil respiration, microbial quotient (Cmic :Corg ), dehydrogenase, protease and alkaline phosphatase were significantly (P < 0.05) higher in rhizosphere soils (RS), while metabolic quotient (qCO2 ) showed insignificant differences, when compared to nonrhizosphere soils (Fig. 3A–D). This was in agreement with studies on stressed soils (Caravaca et al., 2005; Zhang et al., 2010; Koranda et al., 2011). The increase in substrate (organic matter) availability, via biomass of Cynodon, counters the sodicity stress on microbial population and increases the microbial biomass (Yuan et al., 2007; Wong et al., 2009). It might be likely to that organic matter is generally resistant to sodium adsorption and rarely displays sodic behaviour, mainly due to hydrophobicity caused by the presence of hydrophobic organic compounds (Rengasamy and Olsson, 1991; Wong et al., 2010). Significant increase in soil respiration and microbial quotients has also suggested that primary succession of Cynodon on highly sodic soils induced microbial growth to establish early ecosystem development. Furthermore, functional abilities such as nitrogen fixation, organic matter turnover, rhizodeposition and mycorrhizal associations facilitate the plant establishment on degraded lands (Babu and Reddy, 2011). The metabolic quotient (qCO2 ) was estimated to determine the sodicity stress in the microbial population and has presented as the ratio of respiration to the soil microbial biomass carbon (Anderson and Domsch, 1990; Wong et al., 2008). Insignificant difference between qCO2 of rhizosphere and non-rhizosphere soils suggests that substrate (biomass, root exudates and nutrients) availability do not affects soil respiration (Chowdhury et al., 2011; Setia et al., 2011). Respiration of microbial communities in non-rhizosphere sodic soils, which are more tolerant to sodicity may therefore decreases less than that of less tolerant communities in Cynodon rhizosphere soils. Soil enzymes involved in carbon (dehydrogenase), nitrogen (protease) and phosphorus (phosphatase) cycling (Singh et al., 2012c) were significantly (P < 0.05) higher in rhizosphere soils in comparison to non-rhizosphere soils (Fig. 3E–G). The increase in respective nutrients (C, N, and P) has positive effects on enzyme activities. This indicates the mechanism of positive feedback of microbial enzyme production to the increase in availability of organic matter and nutrients in the rhizosphere soils of Cynodon. Soil MBC and soil respiration indicate that there have

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K. Singh et al. / Ecological Engineering 54 (2013) 32–38

300 [A]

250 MBC (μg g-1)

200 150

*

100 50 0 RS

140 [B]

Microbial quotient (Cmic:Corg)

100

20

*

15 10 5

80

*

60 40 20 0

0 RS

RS

NRS

NRS

30

0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

[D] Dehydrogenase (μgTPF g-1 hr-1)

q CO2 (mg CO2-C dˉ1mg MB-C)

[C]

120

25

25

[E]

20

*

15 10 5 0

RS 80 70 60 50 40 30 20 10 0

[F]

*

NRS

RS

NRS Alkaline phosphatase (μg PNP g-1 hr-1)

Soil respiration (mg CO2 kgˉ1 24hˉ1)

30

Protease (μg Tyrosine g-1 hr-1)

NRS

250

[G]

200

*

150 100 50 0

RS

NRS

RS

NRS

Fig. 3. Microbial biomass carbon (MBC) [A], soil respiration [B], microbial quotient [C], metabolic quotient (qCO2 ) [D], dehydrogenase [E], protease [F] and alkaline phosphatase [G] activities in rhizosphere soil (RS) and non-rhizosphere soil (NRS). Error bars indicate standard deviation of the mean (N = 5). Asterisks indicate significant differences (paired t-test, P < 0.05).

been four times higher microbial population in rhizosphere soil than non-rhizosphere soils. Similarly, Steer and Harris (2000) reported significantly higher basal respiration in rhizosphere soil in comparison to non-rhizosphere of Agrostis stolonifera plant. The rhizosphere soil was expected to contain a larger and more active microbial community and higher soil respiration readings in rhizosphere soil were also indicative of a more active microbial community (Steer and Harris, 2000). But the increase in activities

of dehydrogenase, protease and alkaline phosphatase soil enzymes was similar to that of soil MBC. This might be likely due to negative and positive feedbacks of microbial production of soil enzymes with effect of organic carbon, nutrients availability and microbial resource reallocation in the rhizosphere soils (Shi, 2011). The decomposition of fine roots, leaf litters and root exudates incorporate nutrients into the microbial food chain which enhance the microbial growth and consequently enzyme activities (Koranda

K. Singh et al. / Ecological Engineering 54 (2013) 32–38

et al., 2011). Increase in enzyme activities, mainly dehydrogenase, in rhizosphere soils likely are due to microbial as well as plant functions (Singh et al., 2012c). Fig. 1A shows that local cattle from nearby villages are grazing and clipping grass (Cynodon) on sodic land. This is likely that clipping of grass by cattle may induce root exudation. Hamilton et al. (2008) proved that clipping induces the root exudation and triggers positive rhizospheric feedbacks. Root exudates are made up of organic acids, sugars, amino acids, hormones and mucilage which stimulate rhizospheric processes and the availability of nutrients to growing plant (Hamilton et al., 2008; Koranda et al., 2011). Guttation is another important physiological phenomenon occurs in Cynodon grass at night when stomata are closed and soil moisture is high (Kerstetter et al., 1998). Guttation fluids may contain a variety of organic and inorganic compounds, mainly sugar and mineral nutrients (Lindner and Brand, 1989). Kerstetter et al. (1998) reported the presence of peroxidases in droplets of guttation fluid of Cynodon and estimated that peroxidase-catalyzed reactions in soils planted with these grasses may convert about 8 g C m−2 year−1 of soil organic carbon compounds to more persistent oligomers and polymers. Oligomerization and polymerization of organic matter through the catalytic effect of peroxidases in guttation fluid of Cynodon also supports the feasibility of the grass for sodic soils. 4. Conclusion C. dactylon has the tremendous potential to grow on extreme conditions as reported earlier (Maiti and Nandhini, 2006; Wu et al., 2010; Babu and Reddy, 2011; Osaliya et al., 2011). In this study, the gradual establishment of sparse cover of Cynodon on abandoned sodic soils and significant changes in soil sodicity (pH, EC, ESP and SAR), and microbial (MBC, soil respiration, Cmic :Corg and qCO2 ) and enzyme (dehydrogenase, protease and alkaline phosphatase) activities concludes that Cynodon can be used for rehabilitation of sodic soils at minimal inputs. Cynodon extremely tolerant to grazing and is valuable for soil conservation, as a turf, and as a vegetation cover on abandoned sodic lands. Further researches on isolation of sodic tolerant bacteria and arbuscular mycorrhizal fungi from Cynodon rhizosphere soil should be done for effective restoration of sodic soils. Additionally, changes in soil microbial community structure in the rhizosphere soils of companion grasses should be determined through biochemical and molecular tools to scrutinize their potentials to rehabilitate abondoned sodic lands. Acknowledgements Kripal Singh expresses his sincere thanks to Council of Scientific and Industrial Research (31/8/(233)2009/EMR-1) and University Grant Commission (F.4-2/2006(BSR)/13-779/2012(BSR)), New Delhi, India for financial support. We are also thankful to the three anonymous reviewers for their useful comments. References Abhilash, P.C., Powell, J.R., Singh, H.B., Singh, B.K., 2012. Plant–microbe interactions: novel applications for exploitation in multipurpose remediation technologies. Trends Biotechnol. 30, 416–420. Anderson, T.H., Domsch, K.H., 1990. Application of ecophysiological quotients (qCO2 and qD) on microbial biomasses from soils of different cropping histories. Soil Biol. Biochem. 22, 251–255. Babu, G., Reddy, M.S., 2011. Influence of arbuscular mycorrhizal fungi on the growth and nutrient status of bermudagrass grown in alkaline bauxite processing residue. Environ. Pollut. 159, 25–29. Caravaca, F., Alguacil, M.M., Torres, P., Roldan, A., 2005. Plant type mediates rhizospheric microbial activities and soil aggregation in a semiarid Mediterranean salt marsh. Geoderma 124, 375–382. Chandra, V., Kapoor, S.L., 1987. Weed flora. In: Khoshoo, T.N. (Ed.), Ecodevelopment of Alkaline Land, Banthra – A Case Study. CSIR, New Delhi, pp. 21–25.

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