Scholarly article on topic 'Seasonal variation in productivity, water relations and ion contents of Atriplex halimus spp. schweinfurthii grown in Chott Zehrez wetland, Algeria'

Seasonal variation in productivity, water relations and ion contents of Atriplex halimus spp. schweinfurthii grown in Chott Zehrez wetland, Algeria Academic research paper on "Biological sciences"

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{" Atriplex halimus " / "Arid salt steppes" / "Chott Zehrez wetland" / Halophyte / Population / Productivity}

Abstract of research paper on Biological sciences, author of scientific article — Bouzid Nedjimi

Abstract A population of Atriplex halimus spp. schweinfurthii, a perennial halophyte of Algerian saline steppes, was studied for one year under field conditions in chott Zehrez wetland of Djelfa, Algeria. During the one year, the population was exposed to great variations in soil salinity, pH varied from 7.0 to 8.2, soil conductivity was highest (4.47dSm−1) in summer and lowest (1.99dSm−1) in autumn. Soil moisture was relatively low and varied from 7.66% in summer to 21.45% in winter. Plants in the winter and spring seasons showed better growth than the other two seasons. The contents of Na+ and K+ in plant were highest during the summer, however Ca2+ ion content in A. halimus tissues remained constant throughout most of the seasons. The high N was recorded in winter and spring seasons. The succulence remained unaffected during winter, spring and summer seasons and then declined during autumn. This indicates that plants minimize their water uptake during stress to achieve osmotic adjustment, which helps them to survive in chott ecosystem.

Academic research paper on topic "Seasonal variation in productivity, water relations and ion contents of Atriplex halimus spp. schweinfurthii grown in Chott Zehrez wetland, Algeria"

Journal of the Saudi Society of Agricultural Sciences (2012) 11, 43-49

King Saud University Journal of the Saudi Society of Agricultural Sciences

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Seasonal variation in productivity, water relations and ion contents of Atriplex halimus spp. schweinfurthii grown in Chott Zehrez wetland, Algeria

Bouzid Nedjimi *

Laboratoire d'Exploration et Valorisation des Ecosystèmes Steppiques, Université de Djelfa, Faculté des Sciences de la Nature et de la Vie, Cite Ain Chih, BP 3117, Djelfa 17000, Algeria

Received 25 May 2011; accepted 21 August 2011 Available online 28 August 2011

KEYWORDS

Atriplex halimus; Arid salt steppes; Chott Zehrez wetland; Halophyte; Population; Productivity

Abstract A population of Atriplex halimus spp. schweinfurthii, a perennial halophyte of Algerian saline steppes, was studied for one year under field conditions in chott Zehrez wetland of Djelfa, Algeria. During the one year, the population was exposed to great variations in soil salinity, pH varied from 7.0 to 8.2, soil conductivity was highest (4.47 dSm"1) in summer and lowest (1.99 dSm 1) in autumn. Soil moisture was relatively low and varied from 7.66% in summer to 21.45% in winter. Plants in the winter and spring seasons showed better growth than the other two seasons. The contents of Na+ and K + in plant were highest during the summer, however Ca2+ ion content in A. halimus tissues remained constant throughout most of the seasons. The high N was recorded in winter and spring seasons. The succulence remained unaffected during winter, spring and summer seasons and then declined during autumn. This indicates that plants minimize their water uptake during stress to achieve osmotic adjustment, which helps them to survive in chott ecosystem.

© 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

* Tel.: +213 662 128 131; fax: +213 279 002 01. E-mail address: bnedjimi@yahoo.fr

1658-077X © 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

Peer review under responsibility of King Saud University. doi:10.1016/j.jssas.2011.08.002

1. Introduction

Many semi-arid regions in the world contain soils and water resources that are too saline for most common economic crops (Nedjimi, 2009). The utilization of halophytic plants in saline soils for pasture and fodder production is the only economic solution presently available (Khan and Duke, 2001; Nedjimi, 2011a,b). These groups of plants not only tolerate high level of salinity but display optimal growth in saline conditions (Flowers, 2004). Some succulent halophytes grow larger and benefit from a NaCl concentration that is above the minimal amount required as micronutrients in plants (Nedjimi and Daoud 2009c; Slama et al., 2008; Yang et al., 2008).

The most characteristic types of wetland in Algeria are endorheic wetlands. They consist of chotts and sebkhas, as known in Arabic, also referred to as Athalassic salt lakes. The term athalassic denotes saline waters which are isolated from the sea, or which were once connected to the sea, but which have dried out before being re-flooded by water of non-marine origin (Khaznadar et al., 2009). The chotts and sebkhas are typically seasonal wetlands which dry out in summer and re-flood in winter. According to Pouget (1980), seb-kha is the central zone of saline lake dominated by water and devoid of vegetation due to high salt concentrations. The chott is the surrounding zone which forms a vegetation ring around the water. This vegetation is mainly composed of halophytic, succulent and perennial species. In these environments the main factors controlling vegetation are water salinity in the growing season and the depth and period of flooding. Vegetation at the edges of the chotts comprises mainly members of the Chenopodiaceae family (such as Atri-plex spp., Salsola spp., Suaeda spp. and Salicornia spp.) Among the most important chotts in Algeria are Chott Zehrez, the second largest chott in North Africa (Khaznadar et al., 2009). However, as far as we know, there has not been a lot of research conducted on these systems.

Under pasture systems, animals depend on forages to satisfy all of their nutritional requirements. Seasonal variability can markedly affect the dietary intake of minerals as a result of changes in composition, stage of growth and availability of pasture and to changes in the moisture content and salinity of the soil (Ahmad et al., 2008).

Demographic studies of many halophytic populations show that halophytes exhibit both interspecific and intraspecific variation in resistance to salinity stress based on their location. Generally, salinity, water, and temperature are critical environmental factors that determine the vegetation pattern in a region (Boer 1996). However, populations are predominantly affected by specific overriding physical factors such as pulsed changes in substrate salinity and rainfall fluctuations (Zia et al., 2007; Tariq et al., 2009).

Atriplex halimus (Chenopodiaceae) is a perennial spontaneous shrub of the Algerian salt steppes with an excellent tolerance to drought and salinity (Fig. 1). This species is very palatable and is a preferred fodder shrub of livestock during dearth periods. Endowed with a complex root system and a considerable

Figure 1 A. halimus spp. schweinfurthii (Chenopodiaceae).

biomass, A. halimus is an efficient and a relatively cheap barrier against erosion and desertification. Its ligneous wood is an interesting source of energy. It has been divided into two subspecies: halimus and schweinfurthii. The subspecies are based on differences in morphology, with respect to habit, size, leaf shape and fruit morphology. However, the existence of intermediate morphotypes complicates the designation of plants as one or the other subspecies. A. halimus spp. halimus is found in semiarid and sub-humid areas of the western Mediterranean and on the Atlantic coasts of France and Spain, while spp. schweinfurthii occurs in arid zones with milder winters (e.g. North Africa and the eastern Mediterranean) (Walker et al., 2005).

A. halimus spp. schweinfurthii is best suited to Mediterranean climates, however it is a hardy species that is able to tolerate a variety of harsh environmental conditions. A. halimus is cold-tolerant plants, having average minimum temperatures in the coldest month of-10 0C and -12 0C (Aouissat et al., 2009). Le Houerou (1992) indicates that A. halimus can survive under rainfalls of 100-400 mm year-1, but has been reported to survive between one and several years without rainfall. Native populations are found in loam or clay depressions containing moderately saline soils and a temporary water-table, and also on outcrops of gypso-saline marls. The species grow in the soil where electric conductivity reaches 05-100 dSm-1 in surface horizons.

The reported annual productivity of A. halimus communities varied from 0.5 to 05 t DW ha-1. The variability in productivity is related to the growing environment including ecological conditions of soil and climate and management applied. A. halimus plants are relatively high in crude protein (CP) and ash (12.6% DM and 22.7% DM respectively) as a character for halophytic plants. Digestibility of A. halimus species on dry matter may reach 56%. Based on mentioned data, it seems that A. halimus could cover the essential nutrients for maintenance requirements of small ruminants in good rainy seasons according to the recommended nutritional requirements of livestock (El Shaer, 2010).

A. halimus spp. schweinfurthii is found in an environment where halomorphic soil induces extreme osmotic stress, with erratic and low precipitation during the growing seasons (Nedjimi and Daoud, 2009a). This perennial shrub grows in environmental conditions beyond the potential of almost any conventional species in a salt ecosystem (Le Houerou, 2000). Laboratory experiments on seed germination and growth of A. halimus showed it to be a high salt tolerant species (Nedjimi and Daoud, 2009b; 2009c). Knowledge of forage production and species production potential under variable environmental conditions is vital for better utilization and management of chott wetlands of Algeria. Little work has been done on the productivity and growth of local halophytes around Chott Zehrez wetland. The objective of this study was to investigate the growth, water relations, and ionic contents of A. halimus population (endemic chott halophyte) every season during one year. This information will be useful in determining the potential for growing of A. halimus on chott ecosystems.

2. Materials and methods

2.1. Site description

The study was carried out for one year in a salt chott of Zehrez Djelfa, which is located to the North of Algeria (3003'E

longitude, 34°36'N latitude). The chott area is about 50 ha and the altitude ranges from 840 m to 825 m. The geology consists mainly of Cretaceous, with deposits of Quaternary. According to Pouget (1980) principal type of soils in chott Zehrez wetland are the calci-magnesic solontchak and hydromorphic soils (gley). The Sebkha soils are characterised by saline silts, prone to flooding in winter and covered by salty crusts in summer (Boumezbeur and Ben hadj, 2003). The endorheic nature of the area and the flat relief induce water accumulation in the chott from winter rainfall. The saline soils (solontchaks) are poorly developed and contain a high amount of exchangeable sodium and soluble salts. The texture changes from silt-clays to silt-sands (Pouget, 1973). Soil salinity ranges from 1.99 to 4.47 dSm-1. The water table varies from 1 to 3 m below the surface. The climate of chott Zehrez is typically Mediterranean, characterised by wet winters and hot dry summers with a mean annual precipitation of 250 mm year_1(2000-2010). The average minimum winter and maximum summer temperatures are 5 °C in January and 26 °C in July, respectively. The rainy season is generally from mid-October to May (Le Houerou, 2001).

The natural vegetation is represented by halophytes such as A. halimus, Suaeda fruticosa, Salsola vermiculata and Salicornia fruticosa. A number of rare and endemic plant species are found, including: Herniaria mauritanica, Salicornia arabica, Avena bomoides, Hordeum maritimum, Juncus bufonius, Lau-naea resedfolia, Polygonum equisetforme and Reaumuria venni-culata (Quezel and Santa,1963).

The Chott Zehrez wetland is very important for breeding and over-wintering of many bird populations. There is a diversity of species many of which are rare and threatened. These include Outarde (Chlamydotis undulata), different types of ducks: Anas penelope, Anas clypeata, Anas platyrhynchos and other birds such as Falco tinnunculus; Columba livia and Tyto alba. This relatively diverse flora and fauna were a critical factor in the designation of the chott as a RAMSAR site.

2.2. Plant analysis

In 2009/2010, three transects of 100 m were laid across the population. These transects were further divided into three random blocks. Ten plants from each block were randomly harvested each season (during 15th January, 15th April, 15th July and 15th October) to measure the dry weight (DW), water relations and ion contents. Plant samples were clipped with stainless steel scissors and consequently, these samples were packed into paper bags. The DW was measured after the samples had been dried at 65 °C for 72 h.

Plant material (0.5 g) was boiled in 25 ml of distilled water for 2 h at 100 °C using a dry heat bath. This hot water extract was cooled and filtered using Whatman no. 2 filter paper. One milliliter of hot water extract was diluted with distilled water for ion analysis. Cation contents of plant samples were analyzed using a Perkin Elmer (Norwalk, CT, USA) model 360 atomic absorption spectrophotometer. Nitrogen was measured according to Kjeldahl method.

2.3. Soil analysis

Ten soil samples were collected seasonally near the plants along the three transects, using a stainless steel sampling auger at a depth of 15-20 cm (rooting zone). Samples were collected in plastic bags, dried at 65 °C for 72 h and passed through a 2mm sieve.

Soil moisture was measured by weighing each sample, oven dried at 136 °C for 24 h and reweighed to determine the water loss. Percent soil moisture was calculated as percentage weight of water in dry soil. Five grams of soil mixed with 25 ml of distilled water were shaken and filtered using Whatman no. 1 filter paper. Soil conductivity (model 10 portable conductivity meter) and pH (pH meter) were measured. Cation contents of the soil samples were analyzed using a Perkin Elmer (Norwalk, CT, USA) model 360 atomic absorption spectrophotometer.

40 35 30 25 20

" 15 <u

10 5 0

T —•— Precipitation

\ --0-- Temperature 9

\ \ .....of \

\ / \ ° / '■ '

•k. / / Q

Dry period O" \ / \ / c

•D \ Q

\ 1 o-'' \ / 'o

<U i-3

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Months

Figure 2 Seasonal variation in rainfall and temperature recorded during 10 years (2000-2010) at Chott Zehrez wetland.

2.4. Statistical analysis

The experiment was set up as a completely randomised design, with tree replications of each season. Data were analysed statistically, using the SPSS 7.5 software package, by one-way ANOVA and by Tukeys multiple range test, to determine differences between means.

3. Results

The temperatures gradually increased from May to August (Fig. 2), a peak was reached during July, followed by a gradual decrease from August to December. The precipitation was much higher from September to January (Fig. 2).

A one way ANOVA showed a significant effect of season in affecting DW (P < 0.05). A. halimus plants collected in winter and spring were greater DWs than plants collected in other seasons (Fig. 3). The lowest DW was recorded in summer and autumn. Salinity had a significant effect on tissue water of plant (P < 0.05). The succulence remained unaffected during winter, Spring and summer seasons and then declined during autumn (Fig. 3).

A one-way ANOVA of the ion contents showed that seasons significantly affected Na+ (P < 0.01), K+ (P < 0.05)

rn 40-

Autumn Winter Spring Summer Seasons

Figure 3 Seasonal variation in dry weight (DW) and tissue water of A. halimus spp. schweinfurthii community at Chott Zehrez wetland. Values represent means ± SE (n = 3). Different letters above bars indicate significant difference at the 5% level according to the Tukeys multiple range test.

and N (P < 0.05) but not Ca2 + content of plants (P > 0.05). Na+ ion concentration gradually increased from 05.41 mM in autumn to 12.57 mM in summer (Table 1). K+ ion concentration in plants was significantly higher in autumn (Table 1). However, K+ concentration was significantly lower in spring. The K + ions in plant decreased significantly during the seasons of high salinity. The Ca2 + ion content in A. hali-mus tissues remained constant throughout most of the seasons. The high N was recorded in winter and spring seasons (Table 1).

Soil electrical conductivity (EC) varied significantly (P < 0.05), whereas, pH remained more or less same (P 7) throughout the seasons (Table 2). Soil EC increased from 1.99 dSm-1 in autumn to 4.47 dSm-1 in summer but it decreased with a rise in soil moisture content (Table 2). A significant (P < 0.01) increase in soil moisture was observed during autumn and winter accompanied by a lowering of soil salinity (Table 2).

Salinity significantly affected Na+ (P < 0.01), K+ (P < 0.05) and Ca2+ (P < 0.0001) contents of soil. Individual ion analysis of soil samples from sub-surface layers (15-20 cm) showed that Na+ was the ion responsible for most of the salinity of the soil (Tables 3). The concentration of Na+ and K+ was highest during the summer (Tables 3), but the level of Ca2+ was fairly constant throughout all seasons.

4. Discussion

The region of chott Zehrez investigated in this study is a characteristic of the salt marshes (sebkha and chott) situated in the northern part of Djelfa. The halophytic and wet halophytic communities constitute the natural vegetation of the site. The productivity of A. halimus in chott Zehrez wetland is highly variable, depending on the ecological conditions of the soil and climate. The productivity of A. halimus reported in this study showed strong seasonal pattern. Winter and spring rains, associated with reduced ambient temperature and soil conductivity, primarily determines the productivity of A. halimus dominated communities along the chott Zehrez wetland. The maximum DW was observed in winter and spring while substantially decreasing in summer and autumn. Soil salinities and temperature were higher before the rainfall and may have substantially reduced in the aboveground biomass. Halophytes often exhibit stunted growth when found under saline conditions approaching their tolerance limits, indicating that increased salinity stress during the late summer could account for the decreased growth (Malcolm et al., 2003; Nedjimi and Daoud, 2006).

Succulence is an anatomical adaptation which, by increasing the vacuolar volume, permits the accumulation of larger amounts of water (and dissolved ions) in the plants (Munns, 2002). The present work showed that succulence (tissue water) in A. halimus remained unaffected during winter, spring and summer seasons and then declined during autumn. Measurements of plant water status indicated that A. halimus plants adjusted their water potential to more negative levels as salinity increased. There is an adaptive capability of A. halimus to grow better in high salinity areas (Nedjimi et al., 2006). Aziz et al. (2005) also observed similar patterns for water relations in Halopyrum mucronatum growing at the coastal dunes of Arabian Sea. Water potential (Wrn) of plants became extremely

Table 1 Seasonal variation in ion contents of A. halimus spp. schweinfurthii community at Chott Zehrez wetland. Values represent

means ± SE (n = 3).

Seasons Na+ (mM) K+ (mM) Ca2+ (mM) N (%)

Autumn 05.41 ± 0.86 b 2.68 ± 0.95 a 5.51 ± 1.58 b 0.65 ± 0.13 b

Winter 05.49 ± 1.14 b 1.22 ± 0.55 b 7.72 ± 1.64 b 1.20 ± 0.22 a

Spring 06.32 ± 2.18 b 0.44 ± 0.22 c 6.21 ± 1.14 b 1.31 ± 0.11 a

Summer 12.57 ± 0.63 a 1.72 ± 0.85 b 4.51 ± 1.96 b 1.02 ± 0.19 ab

Different letters in the same column indicate significant difference at the 5% level according to the Tukeys multiple range test.

Table 2 Seasonal variation in soil properties of A. halimus spp. schweinfurthii community at Chott Zehrez wetland. Values represent

means ± SE (n = 3).

Seasons pH EC (dSm-1) Moisture (%)

Autumn 7.86 ± 0.15 a 1.99 ± 0.45 b 20.13 ± 2.14 a

Winter 7.84 ± 0.23 a 3.04 ± 1.03 ab 21.45 ± 2.82 a

Spring 8.02 ± 0.23 a 3.63 ± 1.07 ab 10.60 ± 2.77 b

Summer 7.00 ± 0.27 ab 4.47 ± 0.88 a 07.66 ± 2.46 c

Different letters in the same column indicate significant difference at the 5% level according to the Tukeys multiple range test.

Table 3 Seasonal variation in soil ion contents of A. halimus spp. schweinfurthii community at Chott Zehrez wetland. Values represent means ± SE (n = 3).

Seasons Na+ (mM) K+ (mM) Ca2+ (mM)

Autumn Winter Spring Summer 34.45± 8.49 b 30.94 ± 8.44 b 20.68 ± 7.14 b 66.60 ± 5.58 a 02.63 ± 1.48 b 04.09 ± 2.17 b 01.17 ± 0.03 b 34.67 ± 1.32 a 14.93 ± 2.55 a 09.62 ± 2.96 a 10.42 ± 3.57 a 09.32 ± 4.95 a

Different letters in the same column indicate significant difference at the 5% level according to the Tukeys multiple range test.

negative with increase in soil salinity; it peaked during the summer season. Khan and Beena (2002) found that species growing in higher salinities had a more negative Wrn than those growing in low saline areas. Gul et al. (2001) showed that Wrn of Allenrolfea occidentalis dropped significantly during the dry seasons. The survival of plants in saline conditions depends on the maintenance of cell turgor mainly by decreasing the osmotic potential Wp thorough osmotic adjustments (Munns, 2002). Plant water status responded immediately to changes in the soil moisture content after rain period that probably correlates with a decrease in salinity. These findings indicate that reduced leaf Wrn with increasing salinity was associated with decreases in both osmotic and pressure potential during the dry season.

It is a common observation that EC increased with temperature (Halitim, 1988) and finding of present study are in agreement. The enhancement in EC may be due to seasonal variation because in summer evapotranspiration rate of soil was very high and all soluble salts accumulated in the upper layers of the soil (Pouget, 1980).

A higher concentration of Na + in soil during summer was observed as compared to other seasons. The salt concentration of the soil surface layers was considerably higher during the hot summer months. Autumn and winter rain reduces the salt

concentration in the soil surface layer. During the hot summer months, soil surface layers were often encrusted with deposits of white salt, which gave the impression that the plants were surrounded by extremely high concentrations of salt (Pouget, 1980).

Sodium (Na+) and K+ were the two principal ions responsible for increases in osmotic potential of soil samples (Pouget, 1980). In most saline environments, including chott zehrez wetland, external Na + and K + concentrations far exceed those of Ca2 + . Calcium concentrations changed little during all seasons. These values of soil Ca+2 were higher than those already reported by Khan et al. (2004) in southern Punjab, Pakistan. Similar to Agha et al. (2009), there was very little variation in soil Ca + 2 concentrations due to seasons in Arabian Sea coast.

Chott wetland plants establish and persist in an environment where halomorphic soils induce extreme osmotic stress, and atmospheric precipitation is very low and erratic, occurring largely during the winter and spring when temperatures are too low for growth (Le Houerou, 2001). Many species in the Chenopodiaceae accumulate a large amount of Na+ when the external salinity is high (Khan et al., 2000; Ramos et al., 2004). High substrate Na + , in addition to any direct toxic effects, presents both water relations and a nutritional challenge for plants (Niu et al., 1995). Na+ uptake, necessary for osmo-regulation in halophytes, could start as soon as the seed germinates, and allow the seedling to maintain water uptake, turgor and growth (Koyro and Eisa, 2008). In saline and alkaline soils, availability of the cations like Ca + 2 may also be limited (Halitim, 1988).

Plants growing on salt chott were prone to a variety of common stresses like water and nutrient deficiencies, extreme pH values and high soil salinity (Barrett-Lennard, 2003). Many halophytes control high Na+ concentrations either through ion exclusion at the root or secretion of ions from the leaves through salt glands (Malcolm et al., 2003; Barhoumi et al., 2007). Other halophytes accumulate salts in their tissues for osmotic adjustment and compartmentalize ions in the vacuole

(Parida and Das, 2005). Ion accumulation data showed that A. halimus, like most halophytes (Flowers 2004), accumulated high concentrations of Na+ in leaves as an osmoticum. It appears that under saline period, plants tend to gradually increase their N content. This result shows that A. halimus can maintain a good nutritive value under stress conditions and represents an interesting indicator in predicting the quality of the fodder shrub.

5. Conclusion

In conclusion, a chott Zehrez wetland population of A. halimus was found to be high salt tolerant. A. halimus employs an osmo-conformer strategy during the summer period and appears to use osmotic adjustment during the dry and saline periods. A. halimus could be considered as a low cost for salt steppe rehabilitation, this species could also be raised as a supplementary fodder shrub for livestock during dearth periods.

Acknowledgments

This research was financially supported by Algerian Ministry of Higher Education and Scientific Research (Project CNE-PRU no. F-02820100012). The author also thanks Hassani S. for her help in chemical analysis.

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