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Mistletoes are epiphytic hemiparasitic plants that are known to negatively affect the growth of their hosts, increase tree mortality, and as a consequence change the community dynamics. Mistletoe alters the mineral nutrition of the host and the nutrient cycle in the soil. In the present study, the elemental nutrient status is described for Acacia asak, A. ehrenbergiana, A. gerrardii, and A. tortilis that were infected with the mistletoe Plicosepalus curviflorus, at three levels of infection (no infection, low and high infection). The nutrients of the mistletoe and the soil under the studied acacias were also determined. The elemental contents of the infected Acacia species were significantly reduced compared to non-infected trees, particularly for potassium and sodium. The reduction in the elemental composition was also species-specific and dependent on infection density. Elemental contents of the mistletoe were significantly higher than their Acacia hosts, particularly for nitrogen, phosphorus, and potassium, and the concentrations of minerals in mistletoe tissues were host- and density-dependent. This study revealed a significant increase in nutrients in the soil beneath the canopy of infected Acacia compared to the non-infected trees. Overall, it appears that mistletoe infection has a dual effect. It threatens the health of the Acacia, potentially killing its host tree due to absorption of host nutrients particularly when the infection intense. It also has a positive effect in that it improves the availability of the micro-habitat of nutrients under the canopy, which in turn may contribute to the maintenance of biodiversity.

Wetlands are represented in Saudi Arabia in the form of mangrove, sabkha, and wadi (valleys) systems, and these habitats are considered as a sanctuary for biodiversity. The present study aimed to identify different vegetation groups in a wetland site in Wadi Hargan near Alqurainah, Riyadh, Saudi Arabia, and to relate different plant communities and plant diversity to soil moisture, salinity, and other soil properties. Floristic analysis and vegetation structure were investigated within 15 stands along the wadi and were subjected to correlation analysis with soil factors via multivariate analysis. The floristic survey revealed the presence of 111 plant species belonging to 39 families. The most represented families were Asteraceae, Poaceae, Brassicaceae, Caryophyllaceae, and Papilionaceae, which accounted for the largest proportion (55.4%) of the total species. The therophytes were the dominant life form, where they were represented by 46.9% of the total number of species. The application of cluster analysis (TWINSPAN) to the importance value of each species based on the relative cover and density led to the recognition of four plant communities: (A) Phragmites australis—Tamarix nilotica community, (B) Zygophyllum coccineum—Acacia gerrardii community, (C) Lycium shawii—Zygophyllum coccineum community, and (D) Rhazya stricta community. The soil analysis and correlation test revealed significant variations in the content of salinity, moisture, CO3, Cl, SO4, Ca, Mg, and Na among the plant communities. It can be concluded that soil moisture and salinity factors were the fundamental driving forces for plant community structure in the studied wadi. The wadi was moderately grazed, mainly by camels, thereby, the invasive plant Rhazya stricta dominated the central region of the wadi. Also, human interference was observed at the end of the wadi, where some weeds sprouted such as Malva parviflora. The presence of those two rare wetland species, Adiantum capillus-veneris and Ficus salicifolia, in the study area, showed the unique properties of the studied wadi and necessitate an urgent biodiversity conservation action to protect its natural vegetation from overgrazing and human interference.

[EGU General Assembly 2018, 2018-04-08 - 2018-04-13, Vienna, Austria] EGU General Assembly 2018, EGU 2018, Vienna, Austria, 8 Apr 2018 - 13 Apr 2018; Katlenburg-Lindau : European Geophysical Society, Geophysical Research Abstracts 20, 1 Seite (2018)., Published by European Geophysical Society, Katlenburg-Lindau