Do elevated CO2 and temperature affect organic nitrogen fractions and enzyme activities in soil under rice crop?

A study was conducted to quantify the effect of elevated carbon dioxide (CO2) and temperature on soil organic nitrogen (N) fractions and enzyme activities in rice rhizosphere. Rice crop was grown inside the open top chambers in the ICAR-Indian Agricultural Research Institute. The N was applied in four different doses. Grain yield and aboveground N uptake by rice significantly reduced under elevated temperature. However, elevated CO2 along with elevated temperature was able to compensate this loss. Principal component analysis clearly indicated that microbial biomass carbon, microbial biomass N, amino acid N, total hydrolysable N, ammonia N and serine–threonine N contributed significantly to rice grain yield. Combined effect of elevated CO2 and elevated temperature decreased the total hydrolysable N, especially for lower N doses. The N-acetyl-glucosaminidase and leucine aminopeptidase enzyme activities were negatively correlated with the organic N pools. Higher activities of these enzymes under limited N supply may accelerate the decomposition of organic N in soil. When N was applied in super-optimal dose, plant N demand was met thereby causing lesser depletion of total hydrolysable N. Better nitrogen management will alleviate faster depletion of native soil N under future scenario of climate change and thus might cause N sequestration in soil.