Symbiotic nitrogen fixation in plants is the main source of nitrogen input to most natural ecosystems. Observations suggest that N2-fixing plants can play an important role in water-limited ecosystems, and can become especially abundant after disturbances. This pattern is consistent with what we know about fixation in mesic ecosystems. However, central questions remain unresolved, such as: How does the costly strategy of symbiotic fixation survive in water-limited ecosystems? and, Why is it not more abundant?
Specific research projects:
Study symbiotic fixation in the shrub Calicotome villosa (קידה שעירה), a shrub typically abundant after disturbance and in nitrogen poor habitats. The research will evaluate whether C. villosa uses symbiotic N2 fixation as a competitive plant strategy and in what conditions; and how it influences the ecosystem. We will evaluate the nitrogen budget of dominated vegetation in the field and measure rates and timing of symbiotic nitrogen fixation.
Study the nitrogen nutrition and water acquisition in Acacia trees and how it influences the ecosystem nitrogen cycle, under different environmental conditions.
A study of the evolutionary stability of annual N2-fixing legumes in hyper-diverse Mediterranean herbaceous communities. Legumes constitute ~25% of the species diversity (total 300-600 species) of herbaceous plant communities in the Mediterranean region of Israel. The relative abundance of these legumes, however, is much smaller. Our research will evaluate the puzzle of the large diversity and low abundance of legumes and how they survive in competition with abundant grasses. Using controlled pot experiments we will explore the controls and consequences of symbiotic fixation by herbaceous annuals.
The ecological and evolutionary value of symbiotic dinitrogen (N2) fixation in dry environments
Regeneration and dispersal strategies for forest succession in a changing world
Woody plant strategies of regeneration, and specifically seed dispersal, usually are adapted for the plant to reach its appropriate successional stage. Early successional trees typically have small seeds with long-distance dispersal, and late-successional ones are long-lived with local regeneration. Regeneration processes in Mediterranean woody communities challenge these assertions in two ways: (1) Oaks in late-successional Mediterranean forests (Maquis, Matorral, חורש) appear to be unable to self-regenerate; and (2) Massive land-use changes and human exploitation in Mediterranean Basin have changed these landscape dramatically, altering seed sources (e.g., afforestation), and disturbance regimes.
We will study how the regeneration of natural and planted forests and woodlands in Israel are influenced by humans, via climate change and land-use change (agriculture, restoration and forest plantation). This project will involve field work, analysis of historical data and remote sensing.
Specific research projects will be developed with students