Showing papers by "Peter E. Mortimer published in 2008"

The role of arbuscular mycorrhizal colonization in the carbon and nutrient economy of the tripartite symbiosis with nodulated Phaseolus vulgaris

Abstract: In the tripartite symbiosis between nodulated legume roots and arbuscular mycorrhizal (AM) fungi, symbiont sink strength may depend upon developmental stage and the nutrient benefits to the host plant The cost-benefits of the tripartite symbiosis were investigated in terms of C-economy and nutrition Nodulated Phaseolus vulgaris seedlings, with and without AM, were hydroponically grown under high (2 mM) and low (1 μM) P conditions in an N-free Long Ashton nutrient solution Plants were sequentially harvested at 17, 24 and 31 days after emergence At each harvest, measurements for biomass, N 2 -fixation, photosynthesis, root respiration, calculated C and nutritional economy were taken Nodular growth was suppressed by the early development of AM colonization This coincided with higher photosynthetic and respiratory rates in AM plants These effects were most pronounced under low P when AM colonization peaked Once AM levels reached the plateau phase, the efficiency of P nutrition increased This was followed by improved nodular and host growth and enhanced N 2 -fixation This indicates that the AM was the dominant symbiont for host C in the tripartite symbiosis, due to its rapid development and subsequent role in supplying P more effectively to both host and nodules

Nutritional and photosynthetic performance of invasive and indigenous legumes in a mediterranean ecosystem

Abstract: Exotic plant invasions have large impacts on native species and ecosystems (Richardson et al., 2000). Invasions often reduce native species diversity or alter species composition (Richardson, 2001), but the mechanisms underlying these impacts are rarely elucidated. Better understanding of mechanisms underlying these impacts is critical to restoring native ecosystems and in understanding why some invaders have larger impacts than others. In the nutrient-poor soil of the Cape Floristic Region (CFR), the success of the invasive legume Acacia cyclops may depend on improved N and P nutrition. This work aims: (i) to identify the traits that make Acacia cyclops a better coloniser than the native Virgilia oroboides; and (ii) to relate invasive ability to the photosynthetic and nutritional physiology of A. cyclops as compared to that of the indigenous V. oroboides.