Nitrogen Partitioning During Early Development of Supernodulating Soybean (Glycine max [L.] Merrill) Mutants and their Wild-Type Parent

The relative importance of fixed N², cotyledonary N, and nitratefor growth of seedlings of soybean cv. Bragg and two of itsnitrate tolerant supernodulating (nts) mutants (intermediatents 1116 and extreme nts1007) was investigated during symbioticdevelopment in the presence of nitrate (3.0 mol m^–3) using¹⁵N techniques. Newly-fixed N₂ and nitrate were both major sourcesof N for nodule development and nitrate principally supportedearly shoot and root growth in Bragg. In the nts mutants, however,all plant parts and nodules in particular, relied more on Nstored in the cotyledons. This resulted in later nodule maturityand a period of prolonged N-starvation for the seedlings ofthe extreme supernodulator, and could be responsible for theirsubsequently lowered biomass accumulation compared to the parentcultivar. Key words: Nodules, N partitioning, supernodulating soybeans     

Constructed Wetland Habitat for American Avocet and Black-Necked Stilt Foraging and Nesting

Abstract In 1994, a 117-ha wetland was designed, constructed, and operated by the Tulare Lake Drainage District (TLDD), California, USA, to provide foraging and nesting habitat for American avocets (Recurvirostra americana) and black-necked stilts (Himantopus mexicanus). The wetland was operated seasonally in compliance with regulatory requirements to compensate for impacts to stilts, avocets, and other wildlife exposed to elevated selenium concentrations, fluctuating water levels resulting in nest flooding, and high nest-predation rates at the TLDD agricultural drainage evaporation basins. Water supply for the wetland was from low-selenium (typically <2 μg/L) saline agricultural drainage water, although the facility also had capability to blend and use freshwater and saline supplies. Coincident with wetland construction, 2 evaporation basins totaling 1,174 ha were physically modified and operated to discourage their use by shorebirds. In the first year of wetland operation (1995), American avocet and black-necked stilt nest construction at the wetland was 17.6 nests/ha. This compares to a preproject (1994) combined density of 1.9 nests/ha at the evaporation basins. From 1995 through 2004, annual nesting attempts by American avocets and black-necked stilts at the wetland averaged 2,896 per year (24.8 nests/ha). American avocets and black-necked stilts represented 91% of the nests observed at the wetland. Over the 10-year monitoring period, nest success at the wetland averaged 82% for American avocets and 75% for black-necked stilts. We estimated nest predation rates at the constructed wetland to be <1%. During the same period, American avocet and black-necked stilt nesting at the evaporation basins declined from 2,266 in 1994 to 9 in 2004. The constructed wetland has proven to be effective in attracting and providing suitable nesting habitat for large numbers of avocets and stilts. Results of this long-term study confirm the validity of management recommendations for American avocets and black-necked stilts and suggest that agricultural drainage can be successfully managed to provide highly productive managed wetlands.