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**LEGAL DISCLAIMER: Desert King Mountain High Seed Co does not endorse, encourage, or recommend growing these seeds. We provide our genetic treasures only as a novelty souvenir. Desert King Mountain High Seed Co is in no way responsible for the actions of our customers. It is your responsibility to follow all local, state, and federal laws. We reserve the right to refuse service to ANYONE without explanation. We also reserve the right to refuse service to any person we have reason to believe will use our seeds to break any applicable law. You are responsible for your own actions.

Desert King Mountain High Seed Co.

Choose from any of our 50+ strains

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Our 10 packs are perfect for the average small scale medical or recreational grower in legal states, or for someone looking to keep our seeds as a souvenir of our genetics.

prices starting at $74.99

**LEGAL DISCLAIMER: Desert King Mountain High Seed Co does not endorse, encourage, or recommend growing these seeds. We provide our genetic treasures only as a novelty souvenir. Desert King Mountain High Seed Co is in no way responsible for the actions of our customers. It is your responsibility to follow all local, state, and federal laws. We reserve the right to refuse service to ANYONE without explanation. We also reserve the right to refuse service to any person we have reason to believe will use our seeds to break any applicable law. You are responsible for your own actions.

***In areas where cultivation is legal: All seeds we carry are tested to ensure proper germination rates, however due to the possibility of YOUR OWN human error we cannot guarantee germination rates. All Heights, yields, and listed THC/CBD contents, are based off of the results achieved by experienced outdoor growers unless otherwise stated.

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Packs of 25: $149.99

Packs of 50: $249.99

Packs of 100: $449.99

*Large quantity orders unavailable on some strains.

**LEGAL DISCLAIMER: Desert King Mountain High Seed Co does not endorse, encourage, or recommend growing these seeds. We provide our genetic treasures only as a novelty souvenir. Desert King Mountain High Seed Co is in no way responsible for the actions of our customers. It is your responsibility to follow all local, state, and federal laws. We reserve the right to refuse service to ANYONE without explanation. We also reserve the right to refuse service to any person we have reason to believe will use our seeds to break any applicable law. You are responsible for your own actions.

***In areas where cultivation is legal: All seeds we carry are tested to ensure proper germination rates, however due to the possibility of YOUR OWN human error we cannot guarantee germination rates. All Heights, yields, and listed THC/CBD contents, are based off of the results achieved by experienced outdoor growers unless otherwise stated.

Custom Breeder Packs:

We offer Custom Breeder Packs in both quantities of 50 and 100. You choose any strains and mix and match how many you want of each strain, and we will make you a custom variety pack with your name or business logo right on the packaging.

(Available in legal states ONLY)

50 seed breeder packs: $249.99

100 seed breeder packs: $449.99

*Large quantity orders unavailable on some strains.

**LEGAL DISCLAIMER: Desert King Mountain High Seed Co does not endorse, encourage, or recommend growing these seeds. We provide our genetic treasures only as a novelty souvenir. Desert King Mountain High Seed Co is in no way responsible for the actions of our customers. It is your responsibility to follow all local, state, and federal laws. We reserve the right to refuse service to ANYONE without explanation. We also reserve the right to refuse service to any person we have reason to believe will use our seeds to break any applicable law. You are responsible for your own actions.

***In areas where cultivation is legal: All seeds we carry are tested to ensure proper germination rates, however due to the possibility of YOUR OWN human error we cannot guarantee germination rates. All Heights, yields, and listed THC/CBD contents, are based off of the results achieved by experienced outdoor growers unless otherwise stated.

Desert king mountain high seed co.
Linear correlation of soil variables with DCA axes and seed bank density of the most abundant species in the seed bank indicates significant associations between the floristic composition of the seed bank and the edaphic factors such as CaCO3, electrical conductivity, organic carbon and soil texture. It was reported previously that edaphic factors influence soil seed banks. The contribution of edaphic factors as soil texture (Chambers et al., 1991; Rundel and Gibson, 1996; Goodson et al., 2002), moisture (Leckie et al., 2000) and fertility (Kitajima and Tilman, 1996) to seed bank composition has been reported.

Soil seed bank in different habitats of the Eastern Desert of Egypt

Abstract

The floristic composition and species diversity of the germinable soil seed bank were studied in three different habitats (desert salinized land, desert wadi, and reclaimed land) in the Eastern Desert of Egypt. Moreover, the degree of similarity between the seed bank and the above-ground vegetation was determined. The seed bank was studied in 40 stands representing the three habitats. Ten soil samples (each 25 × 20 cm and 5 cm depth) were randomly taken per stand. The seed bank was investigated by the seedling emergence method. Some 61 species belonging to 21 families and 54 genera were identified in the germinable seed bank. The recorded species include 43 annuals and 18 perennials. Ordination of stands by Detrended Correspondence Analysis (DCA) indicates that the stands of the three habitats are markedly distinguishable and show a clear pattern of segregation on the ordination planes. This indicates variations in the species composition among habitats. The results also demonstrate significant associations between the floristic composition of the seed bank and edaphic factors such as CaCO3, electrical conductivity, organic carbon and soil texture. The reclaimed land has the highest values of species richness, Shannon-index of diversity and the density of the germinable seed bank followed by the habitats of desert wadi and desert salinized land. Motyka’s similarity index between the seed bank and the above-ground vegetation is significantly higher in reclaimed land (75.1%) compared to desert wadi (38.4%) and desert salinized land (36.5%).

1. Introduction

Soil seed banks are the aggregations of viable seeds in the soil potentially capable of replacing adult plants (Baker 1989; Thompson and Grime, 1979). Most of the seeds in the seed bank come from the nearby parent plants, while the remaining seeds are contributed by plant communities a long distance away from the parent plants (Solomon, 2011). Thompson and Grime (1979) recognized two main seed bank strategies: transient types in which no seeds remain viable for more than one year and persistent types in which seeds remain viable for longer than one year. The capacity to perform persistent seed bank allows species to survive episodes of disturbance and destruction (Thompson, 2000). Many species have this capacity and many do not (Thompson et al., 1997). Seed banks play a critical role in vegetation maintenance, succession, ecosystem restoration, differential species management and conservation of genetic variability (Harper, 1977; McGraw et al., 1991; Hills and Morris, 1992).

Desert seed banks are usually composed of very small seeds that usually lack dispersal structures (Harper, 1977; Thompson and Grime, 1979; Fenner, 1985; Chambers and MacMahon, 1994; Gutterman, 1994) and are characterized by temporal and spatial fluctuations in seed density (Kemp, 1989; Marone and Horno, 1997; Guo et al., 1998, 1999). Seed banks are a crucial component in desert ecosystems and other stressful habitats where favorable conditions for seed germination and seedling establishment are quite unpredictable both in space and time (Kemp, 1989; Nathan and Muller-Landau, 2003; Meyer and Pendleton, 2005; Koontz and Simpson, 2010). Although the seed bank is an important element in desert ecosystems, little is documented on the diversity of the soil seed bank and its relations to the above-ground vegetation in arid regions (Kemp, 1989; Al-Faraj et al., 1997; Zaghloul, 2008) and in particular in Egyptian deserts. Such information is crucial for developing programs for the conservation and habitat restoration in arid regions and in particular in the Eastern Desert of Egypt where the natural vegetation has been degraded in some areas as a result of several factors as overgrazing and excessive collection of economically important plants (Hegazy et al., 2007). Desert wadi and desert salinized land represent the main habitats that harbor the natural vegetation in the present study area.

The increase in the human population of Egypt necessitates the expansion of the cultivated land. This was achieved by the reclamation of many desert areas during the past few decades. Some studies were concerned with the vegetation of the reclaimed land in Egypt (e.g., El-Bakry, 1982; Shehta and El-Fahar, 2000), but knowledge on the soil seed bank and its relation with the above-ground vegetation in this habitat is very limited.

Seed distribution and storage in soil are related to soil conditions such as particle sizes, structure, and soil chemistry (Harper, 1977; Silvertown, 1981; Coffin and Lauenroth, 1989; Chambers and MacMahon, 1994).

The objectives of this study are to determine (1) the floristic composition and diversity of the germinable soil seed bank in relation to different habitats (desert salinized land, desert wadi and reclaimed land) in Eastern Desert of Egypt, (2) the similarity between the composition of the germinable soil seed bank and the above-ground vegetation in the different habitats, and (3) the associations between the edaphic factors and the composition of the soil seed bank.

2. Materials and methods

2.1. Study area

The study area is located in the Eastern Desert of Egypt between latitudes 28° 30′ N to 29° 26′ N and longitudes 30° 50′ E to 31° 21′ E. ( Fig. 1 ). The area includes three main habitats: desert salinized land, desert wadi and reclaimed land. The habitat of desert salinized land is represented by areas with saline soil supporting the growth of halophytic species such as Juncus rig >

Map of the study area showing the locations of stands: desert salinized land (■), desert wadi (▴) and reclaimed land (●).

The area of the present study is situated within a region of dry climate. The total annual rainfall is 7.8 mm with the rainy season occurring from November to April. The mean monthly air temperature ranges between 12.2 °C during January and 29.1 °C during July. The mean relative humidity varies between 35% during May and 57% during December. The mean monthly evaporation ranges from 5.5 mm day −1 during January to 20.1 mm day −1 during June (data from Ministry of Civil Aviation, 1975).

2.2. Vegetation sampling

The standing vegetation was sampled in order to compare its floristic composition with that of the soil seed bank. A total of 40 stands were identified to represent the three habitats in the study area and cover the within-habitat variations in vegetation. Some ten stands were sampled in desert salinized land, while 15 stands were sampled in each of desert wadi and reclaimed land habitats. For every stand, a floristic list was taken. Plant nomenclature and identification followed Boulos (1999, 2000, 2002, 2005, 2009). Species were categorized in terms of their life form according to Raunkiaer (1934) into therophytes, hemicryptophytes, geophytes, chamaephytes and phanerophytes.

2.3. Seed bank sampling

Ten soil samples (each 25 × 20 cm and 5 cm depth) were randomly taken per each of the 40 stands used for the determination of the floristic composition of the above-ground vegetation. To characterize the persistent seed bank, soil samples were collected in late March 2009 after seeds of most species had germinated but before the beginning of seed dispersal for most species (Thompson and Grime, 1979). The soil samples were passed through a 4 mm sieve to exclude coarse stones and plant fragments. The excluded material was examined manually for seeds and fruits. A known volume of sieved soil samples was spread as a 1 cm deep layer overlying sterilized coarse sand in 25 × 20 × 8 cm germination trays. The germination trays were placed in a greenhouse and regularly watered with tap water. Emergent seedlings were identified, counted and discarded. The seedlings which were difficult to be identified were counted, transplanted and grown separately until identification. For each stand, the species composition, mean density (number of seeds/m 2 ) and mean relative density of the species that constitute the germinable soil seed bank were determined. After six months (December–May), the experiment was stopped as no more seedlings appeared for several consecutive weeks.

2.4. Soil analysis

Three soil samples were taken per stand, from a depth of 0to 50 cm. The samples were pooled together, forming one composite sample for each stand. The samples were air dried and sieved through a 2 mm sieve before analysis. For soil texture analysis, the soil fractions were separated by sieves. 100 g of each soil sample was passed through a series of sieves to separate gravels (>2 mm), coarse and medium sand (2–0.25 mm), fine and very fine sand (0.25–0.05 mm), and silt and clay ( Species Richness = S Shannon – index of diversity : H ′ = – ∑ i = 1 S pi ln pi Evenness index : E = – ∑ i = 1 S pi ln pi lnS

where pi = Ni/N, Ni is the number of seeds of species i, N is the total number of seeds of all species present, and S is the number of species present.

3. Results

3.1. Floristic composition of above-ground vegetation

A total of 77 species belonging to 22 families and 66 genera were recorded in the standing vegetation. Asteraceae has the highest contribution to the total flora (14 species) followed by members of Poaceae (13 species), Fabaceae (10 species) and Brassicaceae (8 species). The recorded species include 42 annuals (54%) and 35 perennials ( Table 1 ).

Table 1

A list of species recorded in the standing vegetation and seed bank as well as the mean density of seed bank of species (number of seeds/m 2 ) in the different habitats. Th, therophytes; H, hemicryptophytes; G, geophytes; Ch, chamaephytes; Ph, phanerophytes; +, present; −, absent.

Species
Life form Vegetation Seed bank
Desert salinized land Desert wadi Reclaimed land Desert salinized land Desert wadi Reclaimed land
Acacia tortilis (Forssk.) Hayne (Fabaceae) Ph +
Achillea fragrantissima (Forssk.) Sch. Bip. (Asteraceae) Ch + 1.3
Alhagi graecorum Boiss. (Fabaceae) H + 0.7
Ammi majus L. (Apiaceae) Th + 1.3
Anabasis setifera Moq. (Chenopodiaceae) Ch +
Anagallis arvensis L. (Primulaceae) Th + 7.3
Anastatica hierochuntica L. (Brassicaceae) Th v 0.7
Artemisia judaica L. (Asteraceae) Ch +
Avena fatua L.(Poaceae) Th +
Avena sativa L. (Poaceae) Th + 2.0
Avena sterilis L. (Poaceae) Th +
Beta vulgaris L. (Chenopodiaceae) Th + 5.3
Brassica nigra (L.) Koch. (Brassicaceae) Th + 7.3
Brassica tournefortii Gouan (Brassicaceae) Th + 1.3
Capsella bursa-pastoris (L.) Medik. (Brassicaceae) Th + 2.1
Centaurea scoparia Sieber ex Spreng. (Asteraceae) Ch +
Chenopodium album L. (Chenopodiaceae) Th + 12.7
Chenopodium murale L. (Chenopodiaceae) Th + 136.7
Cichorium endivia L. (Asteraceae) Th + 0.7
Citrullus colocynthis (L.) Schrad. (Cucurbitaceae) H + v− 1.3
Convolvulus arvensis L. (Convolvulaceae) Th + 1.3
Coronopus squamatus (Forssk.) Asch. (Brassicaceae) Th + 0.7
Cotula cinerea Delile (Asteraceae) Th + 0.7
Cynodon dactylon (L.) Pers. (Poaceae) G +
Cyperus laevigatus L. (Cyperaceae) H +
Deverra tortuosa (Desf.) DC. (Apiaceae) Ch +
Deverra triradiata Hochst. ex Boiss. (Apiaceae) Ch + 1.4
Diplotaxis acris (Forssk.) Boiss. (Brassicaceae) Th +
Echinops spinosus L. (Asteraceae) H +
Emex spinosa (L.) Campd. (Polygonaceae) Th + 24.7
Erodium oxyrhynchum M. Bieb. (Geraniaceae) Th 0.7
Euphorbia helioscopia L. (Euphorbiaceae) Th + 14.0
Euphorbia peplis L. (Euphorbiaceae) Th + 2.0
Fagonia arabica L. (Zygophyllaceae) Ch +
Farsetia aegyptia Turra (Brassicaceae) Ch + + 0.7
Haloxylon salicornicum (Moq.) Bunge ex Boiss. (Chenopodiaceae) Ch +
Heliotropium digynum (Forssk.) C. Chr. (Boraginaceae) Ch +
Hippocrepis multisiliquosa L. (Fabaceae) Th + 1.3
Hordeum murinum L. (Poaceae) Th 1.3
Ifloga spicata (Forssk.) Sch. Bip. (Asteraceae) Th + 0.7
Juncus rigidus Desf. (Juncaceae) H + 1
Lactuca serriola L. (Asteraceae) Th + 1.3
Lasiurus scindicus Henrard (Poaceae) H +
Launaea nudicaulis (L.) Hook. F. (Asteraceae) H + + 6.0 2.7
Lolium temulentum L. (Poaceae) Th + 6.0
Lycium shawii Roem. & Schult. (Solanaceae) Ph + v
Malva parviflora L. (Malvaceae) Th + + 3.3 6.0
Medicago polymorpha L. (Fabaceae) Th + 17.3
Melilotus indicus (L.) All. (Fabaceae) Th + v 86.7
Nauplius graveolens (Forssk.) Wiklund (Asteraceae) Ch + 0.7
Ochradenus baccatus Delile (Resedaceae) Ph + 1.3
Oligomeris linifolia (Vahl ex Hornem.) J. F. Macbr. (Resedaceae) Th + 0.7
Panicum turgidum Forssk. (Poaceae) Ch + 1.3
Pennisetum divisum (Forssk. ex J.F. Gmel.) Henrard (Poaceae) Ch +
Pergularia tomentosa L. (Asclepiadaceae) Ch +
Phalaris paradoxa L. (Poaceae) Th + 1.3
Phragmites australis (Cav.) Trin.ex Steud. (Poaceae) G +
Plantago amplexicaulis Cav. (Plantaginaceae) Th 1.3
Poa annua L. (Poaceae) Th + 4.7
Polygonum equisetiforme Sm. (Polygonaceae) H +
Polypogon monspeliensis (L.) Desf. (Poaceae) Th + 2.2
Pulicaria undulata (L.) C.A. Mey. (Asteraceae) Ch + 0.7
Reichardia tingitana (L.) Roth. (Asteraceae) Th + + 0.7 2.0
Retama raetam (Forssk.) Webb & Berthel. (Fabaceae) Ph + 0.7
Rumex dentatus L. (Polygonaceae) Th + 0.7 2.7
Rumex vesicarius L. (Polygonaceae) Th +
Schismus barbatus (L.) Thell. (Poaceae) Th + 11.3
Senecio glaucus L. (Asteraceae) Th + 2.7 1.3
Sisymbrium irio L. (Brassicaceae) Th + 7.3
Sonchus oleraceus L. (Asteraceae) Th + + 0.7 77.3
Tamarix aphylla (L.) H. Karst. (Tamaricaceae) Ph +
Tamarix nilotica (Ehrenb.) Bunge (Tamaricaceae) Ph + + 8.0 0.7
Trichodesma africanum (L.) R. Br. (Boraginaceae) Ch + 2.7
Trifolium resupinatum L. (Fabaceae) Th + 5.3
Trigonella hamosa L. (Fabaceae) Th + + 17.1
Trigonella stellata Forssk. (Fabaceae) Th + 4.0
Vicia sativa L. (Fabaceae) Th + 1.3
Zilla spinosa (L.) Prantl (Brassicaceae) Ch + + 12.7 0.7
Zygophyllum album L. F. (Zygophyllaceae) Ch + 3.3
Zygophyllum coccineum L. (Zygophyllaceae) Ch + + + 12.0 102.0 11.3
Zygophyllum simplex L. (Zygophyllaceae) Th + 2.2 6.7 0.7

3.2. Floristic composition and structure of seed bank

At seed bank level, some 61 species belonging to 21 families and 54 genera were recorded ( Table 1 ). The largest families were Asteraceae (12 species) followed by Fabaceae (9 species), Poaceae and Brassicaceae (8 species for each). The recorded species include 43 annuals (70%) and 18 perennials. The most frequent life forms in the seed bank are therophytes (70%) and chamaephytes (18%), while hemicryptophytes and phanerophytes represent only 7% and 5%, respectively ( Table 1 ).

The most abundant species in the germinable soil seed bank of salinized land are Zygophyllum coccineum, T. nilotica and Z. album (mean seed bank density = 12.0, 8.0 and 3.3 m −2 , respectively, Table 1 ). Z. coccineum, Schismus barbatus and Zilla spinosa are the most abundant species in the soil seed bank of desert wadi (102.0, 11.3 and 12.7 m −2 , respectively), while Chenopodium murale, Melilotus indicus and Sonchus oleraceus are the most abundant species in the soil seed bank of the reclaimed land (136.7, 86.7 and 77.3 m −2 , respectively) ( Table 1 ).

Ordination of the 40 stands by DCA ( Fig. 2 ) indicates that the stands of the three habitats show a clear pattern of segregation on the ordination planes. The stands of the habitats are clearly distinguished and distributed mainly along axis 1 from left to right in the order: desert salinized land (A), desert wadi (B) and reclaimed land (C). The eigenvalues for the first two DCA axes are 0.919 and 0.574, respectively. The high eigenvalue for DCA axis 1 indicates that it captures the greater proportion of the variation in species composition among stands.

DCA ordination of the 40 stands based on the mean relative density of seed bank of species. A = desert salinized land, B = desert wadi, C = reclaimed land.

3.3. Seed bank-soil relationships

Table 2

Linear correlation coefficients (r) between edaphic factors and the first two DCA axes.

Edaphic parameter
DCA axis
1 2
CaCO3 (%) −0.652 ⁎⁎⁎ −0.323 ⁎
HCO 3 – (%) 0.209 −0.093
pH 0.267 0.032
Electrical conductivity (mS/cm) −0.653 ⁎⁎⁎ −0.378 ⁎
Organic carbon (%) 0.459 ⁎⁎ −0.110
Gravels (%) 0.542 ⁎⁎⁎ 0.015
Coarse and medium sand (%) −0.444 ⁎⁎ 0.331 ⁎
Fine and very fine sand (%) 0.039 −0.421 ⁎⁎
Silt and clay (%) 0.449 ⁎⁎ −0.021

P ⁎⁎ P ⁎⁎⁎ P Table 3 . With the exception of HCO 3 – , pH, fine and very fine sand, the measured soil parameters show significant differences among habitats. The correlations of the seed bank density of the most abundant species in the seed bank with soil variables are shown in Table 4 . Except, S. oleraceus, all the tested species show significant correlations with at least one of the measured edaphic parameters. C. murale and M. indicus are negatively correlated with CaCO3 (r = −0.653, P Desert salinized land Desert wadi Reclaimed land CaCO3 (%) 18.4 a ± 3.0 22.2 b ± 3.1 12.5 c ± 2.1 HCO 3 – (%) 0.06 a ± 0.01 0.05 a ± 0.01 0.06 a ± 0.01 pH 7.8 a ± 0.1 7.7 a ± 0.2 7.8 a ± 0.3 Electrical conductivity (mS/cm) 3.02 a ± 0.18 0.78 b ± 0.17 0.74 b ± 0.07 Organic carbon (%) 0.59 a ± 0.14 0.29 b ± 0.11 0.65 a ± 0.14 Gravels (%) 5.6 a ± 1.8 8.3 a ± 3.6 11.3 b ± 3.5 Coarse and medium sand (%) 45.9 ab ± 10.5 45.7 a ± 10.4 35.9 b ± 5.6 Fine and very fine sand (%) 39.6 a ± 9.9 36.7 a ± 7.0 37.4 a ± 3.7 Silt and clay (%) 9.9 a ± 3.7 8.6 a ± 4.6 19.0 b ± 8.0

Values in a raw sharing the same letter are not significantly different at the 0.05 level of probability.

Table 4

Linear correlation coefficients (r) between edaphic factors and the seed bank density of the most abundant species in the different habitats.

Species
Edaphic variable
CaCO3 HCO 3 – pH Electrical conductivity Organic carbon Gravels Coarse and medium sand Fine and very fine sand Silt and clay
Chenopodium murale −0.653 ⁎⁎⁎ 0.261 0.371 ⁎ −0.375 ⁎ 0.492 ⁎⁎ 0.294 −0.253 −0.088 0.374 ⁎
Melilotus indicus −0.499 ⁎⁎ 0.095 0.358 ⁎ −0.302 0.364 ⁎ 0.245 −0.324 ⁎ 0.030 0.396 ⁎
Schismus barbatus 0.389 ⁎ −0.344 ⁎ −0.268 −0.168 −0.224 0.148 −0.031 0.131 −0.165
Sonchus oleraceus 0.231 0.066 −0.009 −0.120 −0.156 0.039 0.044 −0.023 −0.073
Tamarix nilotica 0.165 −0.072 0.207 0.780 ⁎⁎⁎ 0.206 −0.515 ⁎⁎ 0.028 0.454 ⁎⁎ −0.228
Zygophyllum album 0.042 0.183 0.117 0.531 ⁎⁎⁎ −0.012 −0.181 0.124 −0.100 −0.035
Zygophyllum coccineum 0.580 ⁎⁎⁎ 0.072 −0.515 ⁎⁎ −0.278 −0.568 ⁎⁎⁎ −0.032 −0.075 −0.013 0.007
Zygophyllum simplex 0.223 −0.201 −0.253 −0.091 −0.380 ⁎ −0.057 0.304 −0.157 −0.263

Table 5

Means ± SD of diversity indices and density of seed bank as well as the similarity between seed bank and the above-ground vegetation in the different habitats.

Diversity index
Habitat
Desert salinized land Desert wadi Reclaimed land
Species richness 2.2 a ± 0.4 4.7 b ± 1.4 9.3 c ± 2.3
Shannon index 0.74 a ± 0.16 1.12 a ± 0.36 1.57 b ± 0.49
Evenness 0.95 a ± 0.06 0.73 b ± 0.18 0.71 b ± 0.20
Density of seed bank (seeds m −2 ) 28.0 a ± 9.2 174.7 b ± 83.6 471.3 c ± 177.0
Motyka’s similarity index 36.5 a ± 3.7 38.4 a ± 10.3 75.1 b ± 5.0

Values in a raw sharing the same letter are not significantly different at the 0.05 level.

3.5. Similarity between seed bank and above-ground vegetation

Of the 77 species recorded in the standing vegetation, only 57 species (74%) were present in the seed bank ( Table 1 ). Four species Anastatica hierochuntica, Erodium oxyrhynchum, Hordeum murinum and Plantago amplexicaulis were recorded only in the seed bank and not found in the standing vegetation. The species that were present only in the standing vegetation are mainly perennials (85%), whereas all the species which were recorded only in the seed bank are annuals.

4. Discussion

4.1. Floristic composition and structure of seed bank

A total of 77 species were found in the above-ground vegetation including 42 annuals and 35 perennials, while some 61 species were recorded in the germinable soil seed bank including 43 annuals and 18 perennials. The separation of the stands of the different habitats on the ordination planes of DCA analysis demonstrates that the species composition of the seed bank differs among the habitats. Such variations in floristic composition can be explained by variation in environmental conditions among habitats. Environmental variations among habitats are indicated by differences in soil characteristics among the different habitats demonstrated in the present study. The variations among habitats also include differences due to the crop management practices applied in the reclaimed land. The stands of salinized soil are scattered along DCA axis one while those of the desert wadi are scattered along axis two. This pattern can be related to the within-habitat variations in species composition among stands. These differences are not major but this pattern appears due to the low species richness per stand in these habitats. So, any difference even in only one species between two stands will result in a significant distance between them in the ordination plot.

4.2. Seed bank-soil relationships

Linear correlation of soil variables with DCA axes and seed bank density of the most abundant species in the seed bank indicates significant associations between the floristic composition of the seed bank and the edaphic factors such as CaCO3, electrical conductivity, organic carbon and soil texture. It was reported previously that edaphic factors influence soil seed banks. The contribution of edaphic factors as soil texture (Chambers et al., 1991; Rundel and Gibson, 1996; Goodson et al., 2002), moisture (Leckie et al., 2000) and fertility (Kitajima and Tilman, 1996) to seed bank composition has been reported.

4.3. Diversity and density of seed bank

Significant differences were found in species diversity and density of seed bank among habitats. The reclaimed land has the highest diversity (as measured by species richness and Shannon index) and density of the seed bank. This may be related to the fact that the seed bank of reclaimed land consists of a mixture of desert plants seeds already present in the soil before land reclamation and the seeds dispersed from surrounding natural desert vegetation in addition to the seeds of weeds which grow associated with the cultivated crops in the reclaimed land. In general, weeds are characterized by the production of large numbers of long-lived seeds. This allows the presence of the large and relatively constant weed seed bank in cultivated land (Radosevich et al., 1997). The mean ± SD density of the seed bank varies between 28.0 ± 9.2 seeds m −2 in salinized land and 471.3 ± 177.0 seeds m −2 in reclaimed land. These values are comparable to those reported by Zaghloul (2008) in his study on soil seed banks of Sinai (overall mean ± SD = 118.4 ± 226.4 seeds m −2 ).

4.4. Similarity between seed bank and above-ground vegetation

Of the 77 species recorded in the standing vegetation, only 57 species were present in the seed bank. Four species were recorded only in the seed bank and not found in the above-ground vegetation. At habitat level, seven species were recorded in the above-ground vegetation in salinized land. Five of them are present in the seed bank. Out of 42 species recorded in the above-ground vegetation of desert wadi, 24 species were found in the seed bank. Some 38 species were recorded in the above-ground vegetation of reclaimed land. Out of these species, 34 are present in the seed bank. The species which were recorded only in the standing vegetation and were absent in the seed bank are mostly long-lived perennials. A similar pattern was reported by Guo et al. (1999) and Marone et al. (1998) who indicated the scarce presence of perennials in the seed bank of desert ecosystems in comparison with the short-lived species. The large seeds of long-lived species are more likely to suffer predation in the soil than are small seeds of short-lived plants (Bertiller, 1998). Additionally, the lower seed production, higher seed retention in the canopy, and scarce presence in the seed rain of long-lived species, may also contribute to their infrequent occurrence in the soil (Kemp, 1989; Jiménez and Armesto, 1992; Bertiller, 1998). The proportion of the annual species in the seed bank is high (70%) when compared to their proportion in the standing vegetation (54%). Moreover, the four species which were present only in the seed bank and absent in the above-ground vegetation are annuals. These results are consistent with those of Assaeed and Al-Doss (2002) who reported that annuals are over-represented in the soil seed bank of desert rangelands in Saudi Arabia. Annuals have only one chance to reproduce, and if an environmental stress such as drought in deserts or weed management practices in reclaimed land results in the death of all individuals before they have a chance to produce seeds, the seed bank will provide the source for recruitment of the species in subsequent years. So, the only way for an annual species to survive in such risky environments is to have a persistent seed bank (Ungar, 1988; Baskin and Baskin, 1998; De Villiers et al., 2003).

The similarity between seed bank and above-ground vegetation is high in the reclaimed land in comparison with the desert wadi and desert salinized land which show little similarity. This agrees with the results of other studies that reported a poor relationship between existing vegetation and underground seed reserves in desert communities (Khan, 1993; Aziz and Khan, 1996). This poor correspondence between seed bank and above-ground vegetation may be due to seed predation (Baskin and Baskin, 1998; Crowley and Garnett, 1999; Marone et al., 2000), reliance on vegetative reproduction (Baker, 1989) and lack of dormancy mechanisms (Esmailzadeh et al., 2011). The high similarity between the seed bank and above-ground vegetation in the reclaimed land agrees with the findings of Shaukat and Siddiqui (2004) who reported high similarity between above-ground vegetation and seed bank in arable land. The similarity between seed bank and above-ground vegetation may be determined by the perennial/annual species ratio (Peco et al., 1998). In annual dominated communities like those of the reclaimed land, there are high similarities between the seed bank and vegetation composition, while in communities dominated by perennials like those of the desert wadi and salinized land in the present study, there are low similarities.

4.5. Implications for conservation

The vegetation of desert wadi and desert salinized land in the present study area suffers from human activities as overgrazing and collection of plants for medicinal purposes. This may lead to habitat degradation and vegetation destruction in some areas. Knowledge of the soil seed bank in natural communities is a useful tool for conservation and restoration efforts (Hegazy, 1996; Bakker and Berendse, 1999; Funes et al., 2001; Wassie and Teketay, 2006; Satterthwaite et al., 2007). In years with severe drought conditions, or following severe disturbance, a persistent seed bank might reduce the chance of extinction for a population on a site (Strykstra et al., 1998; Bakker and Berendse, 1999; Funes et al., 1999). Of the 77 species that constitute the standing vegetation, some 20 species (26%) are not represented in the seed bank (see Table 1 ). So, they are vulnerable to elimination from the standing vegetation and not to be replaced by individuals of their own species (Fenner, 1985; O’Connor, 1991). The restoration of these species would be difficult and slow to accomplish if they are destroyed. Such species must receive attention to protect them. On the other hand, other species such as Z. coccineum, S. barbatus and Z. spinosa have a better chance of recovery since they have relatively large persistent soil seed banks. If there is a high similarity between seed bank and the standing vegetation, the seed bank will be an effective method for the restoration of the vegetation. On the other hand, if the vegetation has low similarity with the soil seed bank, seed bank alone will therefore not be helpful for restoration of the destructed vegetation (Halassy, 2001; De Villiers et al., 2003). The low similarity between seed bank and above-ground vegetation in the desert wadi and salinized land of the present study area suggests that soil seed bank cannot be used effectively for restoration of the degraded vegetation in these habitats.

Acknowledgment

The author appreciates the reviewers for their valuable comments and suggestions which significantly improved the manuscript.