Soil respiration in wheat fields in North China was studied to see how it changes throughout the day. They found that total soil respiration and microbial respiration peaked around 2:00 PM, while plant respiration did not show a clear pattern. The amount of plant respiration compared to total respiration stayed fairly constant during the day but changed between growth stages. Microbial respiration was more affected by air temperature than soil temperature, and it decreased when humidity increased. Plant respiration depended on how much sunlight the plants were getting, but there was a delay in the response. Overall, soil respiration in the field was mainly influenced by air temperature, humidity, and how much sunlight the plants were getting.