Date of Award

2-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Agricultural Education

First Advisor

Dr. Elke Neuman

Second Advisor

Dr. Shyam Kurup

Third Advisor

Dr. Kenneth B. Marcum

Abstract

In semi-arid parts of the world such as the U A E, salinity is a major constraint to plant growth and development. More than 80 % of a land plants live in symbiosis with soil fungi of the Glomeromycota. These are also called arbuscular mycorrhizal fungi (AMF), and have been shown to contribute to growth and nutrient uptake of a broad range of agricultural plants. A positive effect of the AM symbiosis on plant performance under salinity has often been observed, but the precise mechanisms behind this effect are unknown to date. Mycotrophic plants common I) grown on saline sandy so i l s of the UAE might benefit from inoculation with symbiotic AM fungi, but the development and functioning of mycorrhizae under these conditions has not yet been investigated in much detail . The aim of this study was to illustrate some of these knowledge gaps

The ground cover Wedelia trilobata ( L ) was selected as experimental plant for this study.Stem cuttings were rooted and precultivated for six weeks in cell trays containing soil that was either mixed with AM fungal propagules, or not. After that 48 plants were transferred to compartmented planting pots filled with soil . The planting pots were round, and a smaller pot was placed into the centre of a larger one, in order to create two soil compartments. The inner pot had a latticed wall that was covered either with a nylon net with 2 mm mesh width, or a membrane that had a mesh width of 30 μm . The plants were transferred to the inner pots and could access the outer compartment either with their roots (2 mm mesh), or only via symbiotic AM fungal mycelium ( 3 0 μm mesh). Nutritional elements were fertilized mainly to the outer compartment. Two different levels of NaCI contamination (1200 mg/kg and 2200 mg/kg dry soil) were established in the so i l in the outer compartment. Non- contaminated treatments served as control s . The aim of this experimental set-up was to estimate to which extent AM fungal hyphae would assist plants in uptake of nutritional elements from saline soil , and whether the symbiotic fungus might help plant roots to proliferate in saline soil .

The plants were grown for 6 1 days after transplanting (DAP). A t the harvest date the following data was collected: fresh and dry weight of root and shoot, stem length, the number of fully developed leaves, shoot/root ratio, the dry weight of roots in the outer compartment, A M colonize at ion rate, EC of the soil extract in the inner and outer

compartments, evapotranspiration and water use efficiency ( W U E ), as well as the P. Na, K and Ca concentrations in the shoots, and a l so water extractable N a and Ca in the inner compartments. The results indicated that salinity had a negative effect on AM fungal root colonization and root growth in outer compartments. Never the less. The AM symbiosis contributed to growth and survival of plants under salinity and also increased the water use efficiency. The precise reasons for the positive effect of the AM symbiosis on plant growth remain speculative. Against expectation, the AM symbiosis did apparently not contribute to net Pup take of the plants. However, A M plants contained more cations (Ca and K ) in their shoots compared with non mycorrhizal controls . Different from several previous studies. the A M plants also contained more Na in their shoots compared with non-AM controls. The results of our study do not support the thesis that A M fungal root colonization can assist root proliferation in saline soil or protect plants from the uptake of Na +. To which extent other mechanisms such as an increased level in antioxidants or compatible solutes in response to AM fungal root colonization can explain the beneficial effects of the symbiosis on plant growth under saline conditions, deserves further investigation




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