| Global warming exerts a profound impact on the transformation and cycle of elements in agro-ecosystem. Previous studies have been largely conducted on effect of warming on the aboveground part of agro-ecosystem based on the increase of the averaged temperature of the whole daytime. In addition, no tillage, a protective agronomic measure, has a positive influence on crop growth and carbon and nitrogen transformation of soils. Therefore, it is generally concerned whether no tillage could stimulate soil carbon and nitrogen transformation, maintain the sustainability of agro-ecosystem productivity, and then alleviate the issue of food security in China. In this study, warming experiments were conducted using open field nighttime warming system to investigate the impacts of nighttime warming and no tillage on soil C and N mineralization as well as related enzymatic activities, clarify the response soil C and N transformation to exogenous C and N. Four treatments were included in the study: normal nighttime temperature with traditional tillage ?CK?, nighttime warming with traditional tillage ?W?, normal nighttime temperature with no-tillage ?NT?, and nighttime warming with no-tillage ?WNT?. The main results are as follows:?1? Aerobic incubation were conducted under three N addition treatments ?no addition, NH4+-N and NO3--N? at 5?,10?, 15?, 20?,25? and 30?. Compared to CK, mineralization rates of the soil organic carbon remarkably increased by 5.3%-18.4% under W treatment, and 14.6%-36.7% and 19.5%-56.7% for NT and WNT treatment, respectively. There were different responses of temperature sensitivity of organic carbon mineralization under N addition. The Q10 value of different four treatments increased by 3.9%?4.7% under NH4+-N addition,whereas NO3--N addition did not obviously affect on the Q10 value.?2? Compared to CK, the nitrogen mineralization rate and nitrification rate were increased by 31% and 8.5%, respectively, under the W treatment. The nitrogen mineralization rate of NT treatment was higher than that of W treatment,which were increased by 33.9%, but the nitrification rate was reduced by 23.7%. The nitrogen mineralization rates under the WNT treatment were increased by 73.8%, while the nitrification rate was decreased by 17%. In addition, ammonium nitrogen addition increased N mineralization amount by 4.2?17.7 mg·kg-1 and the nitrification amount by 8.1?25 mg·kg-1. Accordingly, ammonium addition increased N mineralization rates by 18.3%, 26.3%, 54.6% and 53.4%, respectively, and nitrification rates by 84.2%,161.7%, 207.0% and 140.0%.?3? Aerobic incubation were conducted under two C addition treatments ?no addition, glucose? at 5?,10?,15?,20?, 25? and 30?.C addition decreased net mineralization rates of four treatment soils by 38.9%, 38.9%, 43.1% and 46.7%,respectively, and nitrification rates by 39.8%, 38.0%, 40.5% and 43.5%, respectively.?4? The responses of soil enzyme activities were different to nighttime temperature and no tillage treatments. The enzyme activities of urease? catalase and dehydrogenase increased with incubation temperature from 5? to 30?. Compared to CK treatment, W treatment increased urease activity by 11.5%, and NT and WNT treatment by 17.7% and 21.2%, respectively. The dehydrogenase activities under CK treatment ranged from 0.08?L g-1 h-1 to 0.98?L g-1 h-1 at 5? to 30?. It enhanced by 18.2% under W treatment, 9.1% under NT treatment and 22.7% under WNT treatment. Catalase activities ranged from 5.0 mg g-1 h-1 to 5.4 mg g-1 h-1 at 5? to 30? . There was obvious difference in averaged catalase activities among the four treatment soils.In summary, no tillage stimulated mineralization processes of soil organic carbon and nitrogen,and hence increased mineralization rates, but significantlyreduced soil nitrification rates. Hence, under the background of future global warming, no-tillage not only guarantees crop demand for nitrogen, but also reduce the risk of nitrogen loss, which could be a sustainable agricultural measure in response to climate warming. |
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