Vegetation analysis and seasonal variations among some Xerophytes along Wadi Sudr

Abstract

Wadi Sudr is one of the largest and most developed Wadis of the Sinai’s southern western coast. The Wadi is characterized by rich and variable communities and species which exhibited an economic importance. The objective of the present study was to assess the effects of environmental factors on the distribution of plant communities in Wadi Sudr and the acclimation strategies of some of its prevalent species. The adaptive mechanisms of the chosen dominant species to ecophysiological drought and salinity stresses were also illustrated. Karyotype analysis was performed on some dominant species. The bioactivity of the selected species was assessed on some pathogenic microorganisms. The vegetation analysis along W. Sudr showed the occurrence of 54 species belonging to 44 genera and representing 22 families. The abundant family Zygophyllaceae comprises 15% of the total number of the recorded species. Chamaephytes were the dominant life forms in the studied Wadi (55.56%). Chorological analysis showed the dominance of the monoregional Saharo-Arabian chorotype (46.3%). The TWINSPAN classification separated five vegetation groups including (I) Zygophyllum album, (II) Haloxylon salicornicum, (III) Retama raetam, (IV) Reaumuria hirtella and (V) R. raetam groups representing the up, mid and downstream of Wadi Sudr. However, CCA analysis indicated that the vegetation group representing the downstream of Wadi Sudr was greatly affected by soil chemical properties. But the up and midstream parts of the Wadi were influenced by both CaCO3% and the soil physical properties. The chromosomal features measurements values of chromosome analysis of three studied species which are Reaumaria hirtella, Retama raetam and Zygophyllum dumosum) showed that the chromosomal number of Retama raetam was 2n=48, and the size of chromosome ranged from 4.51 μ2 to 0.93μ2. The chromosomal length ranged from 5.45 μ to 0.96 μ, the arm ratio ranged between 1.88 and 1.41 and the centromeric index ranged between 41.47 and 34.69. On the other hand, it was recorded that, centromeric positions of the chromosomes were submetacentric and acrocentric. While the chromosomal number of Reaumuria hirtella was 2n=22, and the chromosome size ranged from 6.29 μ2 to 4.11 μ2. The chromosomal length ranged from 5.05 μ to 2.95 μ, the centromeric index ranged between 49.50 and 30.00 and the arm ratio ranged between 2.33 and 1.02. Moreover, centromeric positions were metacentric, submetacentric and acrocentric. Finally the chromosomal number of Zygophyllum dumosum was 2n=24, and the size of chromosome ranged from 8.95 μ2 to 5.00 μ2. The chromosomal length ranged from 6.32 μ to 3.6 μ, the centromeric index ranged between 49.53 and 46.02 and the arm ratio ranged between 1.17 and 1.02. Moreover, the centromeric position of all the chromosomes were metacentric. The ecophysiological adaptive responses to seasonal changes and the soil physical and chemical characteristics of four selected xerophytes including Reaumaria hirtella, Retama raetam, Tamarix nilotica and Zygophyllum dumosum showed increments in their succulence during spring which was positively related to soil moisture content.

The photosynthetic pigments and the chlorophyll stability index (CSI) in the studied species increased markedly during spring. However, there was no seasonal remarkable difference in the chlorophyll content in succulent xerophytes Zygophyllum dumosum, besides it showed the lowest CSI. It was also noticed that there was seasonal but no spatial significant difference in chl.b content among all studied species. Moreover, Chl. a to chl. b ratio were more pronounced in crynohalophytic species (Reaumaria hirtella and Tamarix nilotica) particularly during summer.

The present study clearly indicated that the studied plants exposed to adverse environments developed different strategies to adapt and survive the dry arid environments especially during summer. The investigated species tend to enhance the accumulation of osmoregulators and antioxidants including total soluble sugars, sucrose during summer. Meanwhile, the increments in total soluble sugars and sucrose level were more pronounced in the succulent xerophyte Zygophyllum dumosum. While the lowest level was assayed in Reaumuria hirtella during spring. It is of interest to notice that due to sea spray and the presence of underground water and increase in plant succulence osmolytes like sucrose, total soluble sugars and total amino acids reduction was clearly shown in Tamarix nilotica inhibiting downstream, compared with in those inhabiting the Wadi upstream. There is a tendency to accumulate free amino acids and proline during spring in all the investigated species. Retama raetam attained greater levels of free amino acids. It is of interest to notice that generally Z. dumosum attained the highest significant values of proline content, while T.nilotica attained the lowest.