The rhizomatous species Coriaria sarmentosa and C. angustissima bear coralloid clusters of root nodules which actively fix atmospheric nitrogen. Using rooted cuttings, comparative measurements were made of growth, net photosynthesis, dark respiration and nitrogen fixation in the two species. In both, the optimum temperatures for growth and net photosynthesis are 16-18¡C. Over a range of temperature and light intensity C. sarmentosa possesses a higher rate of net photosynthesis than its more diminuitive sister species C. angustissima.
Before European settlement, most of the 750,000 ha of land comprising the Canterbury Plains was under native tussock grassland with pockets of podocarp forest. The dominant land use today is mixed cropping in which cereals and cash crops are grown for 2 to 4 years followed by grass-clover pasture for 2 to 4 years. These cropping rotations are generally too short for either a substantial build-up in soil organic matter under pasture or its breakdown under arable cropping to occur.
An approach is outlined for synthesising current understanding of nitrogen dynamics in natural grasslands and extensively managed grassland systems. The increasing complexity of models is illustrated from recent literature, first conceptualising and eventually process-simulating the dynamics of nitrogen, especially in the soil sub-systems of grasslands. Some comparisons are made between New Zealand and North American grasslands in the magnitude of some N pools and fluxes and some of the principal features of soil biological studies are noted.