Growth, N-2 fixation, and transpiration in soybean plants as affected by humidity

Soybean plants were grown from seeds (in soil culture or hydroponically) and exposed for 38 days to similar humidity conditions in greenhouse during the day and ''dry'' (50-65%) of ''wet'' (95%) relative humidity (RH) regimes during the night. Growth (shoot fresh/dry weight, pod number, and their fresh/dry weight) was significantly favored by the dry RH regime. N-2-fixation capacity (nodule number and dry weight, nitrogen concentration, and total nitrogen amount per plant, and nitrogenase activity) were significantly enhanced by the dry RH regime. An opposite growth/N-2 fixation response was apparent under the wet RH regime. The dark transpiration rate was negatively correlated with the RH, being closely correlated to growth/N-2 fixation parameters (R-2 ranged between 0.64 and 0.80). Similar patterns of growth/N-2 fixation responses to the RH environment in the dark as related to the water dynamics should be emphasized.