Future global warming is expected to increase carbon (C) losses from terrestrial ecosystems to the atmosphere through soil respiration (SR). However, the underlying mechanisms involving microbial communities and enzymatic responses remain unclear. A long-term field experiment was started in October 2009 to assess intensively cultivated soil in the North China Plain with an infrared-heated warming system. Soil physic–chemical and microbial properties and absolute and specific activities of enzymes were measured in 2019 (the ninth year). Compared to the control, nine years of warming increased the annual average soil temperature at a 5 cm depth by approximately 1.5 °C, with soil water contents decreasing by about 3%. Long-term warming decreased the total contents of phospholipid fatty acid (PLFA) biomarkers by up to 40%. Microbial communities utilizing recalcitrant C were more sensitive to long-term warming compared to those targeting labile C, as indicated by the increased ratio of Gram-positive to Gram-negative bacteria in May and the increased ratio of fungi to bacteria in August. Long-term warming caused similar absolute activity of oxidase but higher absolute and specific activities of C-, nitrogen-, and phosphorus-acquiring hydrolase, reflecting high microbial nitrogen, phosphorus, and energy demands. We conclude that a nine-year warming period relatively enriched the oligotrophic communities and raised the nitrogen, phosphorus and energy requirements. Co-limitation of multiple nutrients and water inhibits the biomass of microbial communities, which may finally promote microbial acclimation to long-term warming.
Zhang et al. (Sat,) studied this question.