Factors affecting the nodulation and growth of tropical woody legume seedlings

This study surveys the occurrence of nodulation in woody legume species in Panamá and Costa Rica, describes nodule and root characteristics, and researches host-bacteria specificity, nodulation potential of soils, and the effects of light, added nitrogen, and rhizobia and VA mycorrhizal fungi inoculation on seedling growth. I examined 83 species in 37 genera and found 80% to be nodulated. Percent nodulated species in the Caesalpinioideae, Mimosoideae, and Papilionoideae was 17, 95, and 86, respectively, with no correlation between nodule morphology and tribal classification. Nodules formed mainly at root branch points which supports epidermal breaks as an important rhizobia infection route. More non-nodulated than nodulated species had root hairs. Several species emitted volatile sulfur-containing compounds, including the toxic compound ethylmercaptan, from roots, germinating seeds, and other tissues. These emissions may have an allelopathic action against pathogens, predators, or other plants. In contrast to the general non-specificity of most legumes for rhizobia, Mimosa pigra L. was highly specific and only nodulated in flooded soils. This species' specificity, combined with a limited occurrence of its root nodule bacteria may limit its natural distribution, but its spread as an invasive weed is facilitated when fill material from rivers is deposited in other areas. ^ An experimental light level of 1.5% of full sun completely inhibited seedling nodulation, as do similar naturally low levels in forest understory. In the forest, trees and seedlings were not nodulated. in some soils with suspected high N content. For six experimental species, added N progressively increased seedling growth while decreasing nodule biomass; at the highest level of added N nodulation was completely suppressed. Species and individuals showed variation in nodule biomass at high N applications which may indicate an opportunity for genetic selection for optimal N acquisition. Rhizobia inoculation had a small positive effect on seedling shoot growth, but VA mycorrhiza inoculation overwhelmingly increased seedling size, biomass, and leaf mineral concentration. In lowland tropical forest, VA mycorrhizal colonization appears indispensable for legume nodulation because of the fungus' ability to supply P in deficient soils. This requirement makes the legume-rhizobia-mycorrhiza association obligately tripartite. ^

A fresh look at decision making in international investment choices: Firm international coherence and home-host country relatedness

Understanding how decisions for international investments are made and how this affects the overall pattern of investments and firm’s performance is of particular importance both in strategy and international business research. This dissertation introduced first home-host country relatedness (HHCR) as the degree to which countries are efficiently combined within the investment portfolios of firms. It theorized and demonstrated that HHCR will vary with the motivation for investments along at least two key dimensions: the nature of foreign investments and the connectedness of potential host countries to the rest of the world. Drawing on cognitive psychology and decision-making research, it developed a theory of strategic decision making proposing that strategic solutions are chosen close to a convenient anchor. Building on research on memory imprinting, it also proposed that managers tend to rely on older knowledge representation. In the context of international investment decisions, managers use their home countries as an anchor and are more likely to choose as a site for foreign investments host countries that are ‘close’ to the home country. These decisions are also likely to rely more strongly on closeness to time invariant country factors of historic and geographic nature rather than time-variant institutions. Empirical tests using comprehensive investments data by all public multinational companies (MNC) worldwide, or over 15,000 MNCs with over half a million subsidiaries, support the claims. Finally, the dissertation introduced the concept of International Coherence (IC) defined as the degree to which an MNE’s network comprises countries that are related. It was hypothesized that maintaining a high level of coherence is important for firm performance and will enhance it. Also, the presence of international coherence mitigates some of the negative effects of unrelated product diversification. Empirical tests using data on foreign investments of over 20,000 public firms, while also developing a home-host country relatedness index for up to 24,300 home-host pairs, provided support for the theory advanced.