Arava Research and Development Station YotvataEcophysiology of Citrus treesPapkuilsfonteinDesert succulents with CAM photosynthesisExpedition Namaqualand, Northern Cape, South AfricaBiodiversity hotspot Richtersveld, Northern CapeEcophysiologyGas exchange measurements at WelwitschiaArid sand dunes - Nizzana


Plant functional ecology in deserts

In various research projects I focussed on how desert plants have evolved to maximize photosynthesis when faced with difficult conditions such as drought, extremely warm temperatures, salt stress and other environmental challenges. Three of the main research projects taking place to studied photosynthesis, gas exchange, soil-plant interactions of desert plants in the Succulent Karoo, South Africa, the Namib desert, Nambia and the Negev desert in Israel. Furthermore, we evaluate the water use efficiency and growth of crops using ecophysiological methods in extreme desert environment. 


Ecophysiological of succulents in the Succulent Karoo, South Africa

The southern African Deserts, especially the Succulent Karoo, are characterized by a high biodiversity of succulent plants, in particular taxa in the families of the Mesembryanthemaceae and the Crassulaceae. These succulents have developed various integrated and co-adapted morphological and ecophysiological features that maximise their chances of surviving the detrimental conditions in arid habitats. Most of these succulents are characterised by the development of Crassulacean acid metabolisms (CAM). A case study in the winter rainfall region of southern Africa showed that around 35% of the species and up to 70% of the total vegetation performed the CAM pathway. CAM can be expressed in various ways. Its expression may range from a C3–type pattern of photosynthesis to nearly exclusive night-time CO2 uptake. This range of extremes may be found within one species during progressing plant development and/or as a response to changes in environmental conditions. In CAM-plants transpiration losses is reduced because of nocturnal CO2 uptake and daytime stomata closure, but on the other hand they show low CO2 uptakes in comparison to most C3 plants. However, it is assumed because of the higher water use efficiency that CAM is an important water saving strategy under dry environmental conditions. From the results of numerous long-termed field investigations on the ecophysiology of plants of the Namib desert and the Karoo it could be proposed that the capability to store water is very important adaptational strategy to survive the desert conditions. Several comparative field and lab studies on the ecophysiology CAM- and C3 succlents were carried out in the South African Deserts.


Living in an extreme desert: Welwitschia mirabilis 

One of the most extraordinary and best-known desert plant of the Namib is undoubtedly Welwitschia mirabilis, colonized large parts of the central Namib Desert north of the Kuiseb Rivers to the Nicolau-Rivier in southern Angola. Especially in the barren landscape of the central Namib it is with her size very noticeable. Since its discovery by the Austrian physician and naturalist Friedrich Welwitsch in southern Angola and by Thomas Baines in Swakop Rivier have grown up around this plant many scientific mysteries and myths. In order to better understand the amazing adaptability of this bizarre plant and to gain more detailed information specifically about their water and carbon budget, we conducted a long-term research project led the working group of Prof. Dr. DJ Willert of the Westfälichen Wilhelms-Universität Münster with extensive ecophysiological measurements along a coastal-inland transect of the Welwitschia Vlakte to Brandberg area.


Arid Dune Ecosystems - The Nizzana dunes in the Negev

Sand dunes occur in many parts of the world, not only in deserts and other arid regions but also along many coastlines in humid biomes and environments.  Nowadays, active dune systems are found mainly in the arid and semi-arid regions. The sand dunes of the north-western Negev are the eastern most part of the sand field covering the northern part of the Sinai Peninsula and the northwestern Negev. he climate is determined by a sharp gradient from semi-arid in north to the arid in the south. Average annual rainfall decreases from around 170 mm at the northern edge of the sand field near Yevul to approx. 90 mm near Nizzana.The southern most experimental site Nizzana  is characterized by vegetated linear dunes with mobile crests. The Nizzana Research Site is one of the long-term research sites operated by the Arid Ecosystem Research Centre (AERC) established in 1987 by the Minerva Foundation (Germany) and the Hebrew University of Jerusalem. The Nizzana Sands site offers an excellent example of the structure and functioning of a sandy desert ecosystem and the importance of biological topsoil crusts. Detailed interdisciplinary studies were conducted in the area at different temporal and spatial scales to understanding the ecosystem processes and pattern in in this arid ecosystem. A special focus of the research activities were on the importance of biological soil crusts for ecosystem processes.


Water use efficiency and crop stress physiology in desert agriculture

Substantial land areas used for agriculture are located in arid zones, where large amounts of irrigation water is required fro crop production. Available water sources for agricultural use are often highly saline and may contain levels of toxic substance. An increased input of various elements (e.g. salt constituents, biogenic and nutritional elements, trace and heavy metals, etc.) into the regional water and soil system causes slow but steady deterioration of water and soil quality. Because the determination of exact water requirement, needed for each crop under specific conditions is complicated and expensive, irrigation with excess amounts of water is a common practice, which results with agricultural and environmental problems. In addition to the water and fertilizer costs, the rise in water table frequently followed by salinization, present a major threat to sustainable agriculture. Today, not enough information is available in order to ensure maximum yields and optimal food quality while conserving water resources.

In cooperation with the Arava Research Station in Yotvata and the Gilat Research Center ( Agricultural Research Organization, Israel) we investigated the ecophysiological responce of tomatoes, sunflowers, grape vine,  and citrus to different irrigation regimes, salt stress and high temperture. Lysimeter experiments were carried out to determine the yield-transpiration relations of crops  and to investigate the impact of stress on the plant productivity. These investigations on the plant level were accompanied by comprehensive measurements of leaf transpiration and photosynthesis.


Read more: papers and book chapters

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