Belowground Biological Responses And Their Mechanisms Of Winter Whera To Three Diurtnal Warming Scenarios

Human activities and the use of fossil fuels had led the earth temperature to increase 0.6～0.9℃from the industrial revolution bingening. IPCC forecasts that the global temperatures will rise by 1.4～5.8℃from 1990 to 2100, and China's average temperature will rise by 2.3～3.3℃from 2000 to 2050 related to Chinese forecast. At present, researches of the responses of terrestrial ecosystems to experimental warming mostly focus on aboveground of natural ecosystems, while responses and adaptation of belowground biological processes to different diurnal warming are relatively scarce. Meanwhile, the main research approaches are base on modeling and the greenhouse/open-top warming methods, they cannot truely reflex crop biological processes above and below ground under the global warming. Winter wheat, as one of the most important food crops of China, produced 22.5% of total grain yield. In the context of global warming, to learn the responses of crop production to different diurnal warming scenarios and the belowground biological mechanisms plays a important role for people to enhance the understanding of relationship between global climate change and terrestrial ecosystems, and to reduce uncertainty of the future climate change prediction. Therefore, based on existing field warming facilities in the world, we designed the first Free Air Temperature Increased system for agroecosystems of China in Nanjing. Jiangsu province. In order to explore the response characteristics and mechanism of the crop belowground biological process to global warming, we conducted three diurnal warming scenarios (AW:All-daytime warming; DW:Daytime warming; NW:Nighttime warming) in the wheat field during 2007-2009. Our objectives are to (1) assess the practicability of the FATI system and effect of warming on winter wheat. (2) investigate the responses of soil physical and chemical characteristics, winter wheat root characteristics and vitality, soil and root respiration, soil enzymology dynamics, microbial biomass. soil nematodes and functional components. The main conclusions are as follows:1 Warming effects of Free Air Temperature Increased (FATI) facilityThe free air temperature increased system could significantly increase the temperature of farmland ecosystem microenvironment within the 4 m2,but did not affect the variation trend of the night field temperature. The soil water decreased slightly under different diurnal warming scenarios, but the difference did not reach significant level. Under the three different diurnal warming scenarios, the days from sowing to the beginning of earing and sowing to maturitying significantly shortened. Therefore, the free air temperature increased system adopts in the experiment accorded with climate warming mechanism, and basically satisfys the conditions which were required in the research on the responses and adaption of winter wheat to different diurnal warming scenarois.2 Responses of soil chemical characteristics to different diurnal warming scenariosThe three diurnsl warming scenarois all reduced the soil pH. The all-day warming treatment, in which the soil pH reduced 0.6%, had the minimum effect, while night warming treatment had maximum effect, in which the difference also reached significant level in booting stage and heading stage. There was no significant effect of warming on the total soil nutrient content. Warming reduced soil alkalined-nitrogen in the whole growth and development period by 3.7%,5.2% and 7.8%. respectively, in the NW, DW and AW. All-daytime warming (AW) and Daytime warming (DW) increased soil available phosphorus by 5.5% and 1.86% respectively, however. Nighttime warming (NW) reduced by 2.9%. All-daytime warming (AW) also increased soil available potassium by average 10.2%, while Daytime warming (DW) and Nighttime warming (NW) increased soil available potassium by 3.3% and 7.5% respectively before heading stage.3 Responses of wheat root to different diurnal warming scenariosAll-daytime warming (DW) treatments increased the root dry matter accumulation. root volume, root surface area, root diameter, root length and root activity, in which the differences of root dry matter and root volume reached significant level. Nighttime warming (NW) significantly increased root dry matter accumulation, root volume, and root activity by 10.9%.12.3% and 19.3% respectively. Wheat root morphology had inter-annual differences under All-daytime warming (AW) treatment, but did not reach significant level. All the three diurnal warming scenarois reduced the ratio of root/shoot from booting stage to maturity, in which All-daytime warming (AW) reached significant level.4 Responses of soil respiration to different diurnal warming scenarios Under three diurnal warming scenarios and the control, the average daily soil CO2 efflux, during the whole growth period, reached maximum before wintering period and came up to minimum during the wintering period and shooting stage. All the warming treatments significantly improved soil respiration from sowing to jointing stage, and soil respiration increased 4.9%,14.2%,23.2% for All-daytime warming (AW). Daytime warming (DW), Nighttime warming (NW) respectively. Soil respiration declined slightly for All-daytime warming (AW) and Daytime warming (DW) after jointing stage. During the whole growth period, soil respiration declined by 2.8% and 2.3% respectively for All-daytime warming (AW) and Daytime warming (DW), but did not reached significant level, however, soil respiration of Nighttime warming (NW) increased by 7.2%, and reached significant level. All the warming treatments had no effect on the daily dynamic changes of soil respiration.5 Responses of soil enzymology to different diurnal warming scenariosAll-daytime warming (AW) treatment increased soil urease. protease and sucrase average activities by 6.3%,6.3% and 2.7% respectively. Daytime warming (DW) treatment increased two-year average activities of soil urease and sucrase by 3.8% and 1.2% respectively, but reduced the activity of soil protease. Night warming (NW) treatment yearly reduced the activities of urease, protease and sucrase by 10.9%,16.7% and 5.6% respectively. Nighttime warming (NW). Daytime warming (DW) and All-daytime warming (AW) reduced the activity of soil hydrogen peroxide by 12.3%,3.2% and 6.1% respectively. After comparing the effect of warming treatments to the activity of soil enzyme, we found that the warming effect sizes were All-daytime warming (AW)> Daytime warming (DW)> Nighttime warming (NW).6 Responses of microbial biomass to different diurnal warming scenariosAll the warming treatments reduced the soil microbial biomass carbon and soil soluble carbon, in which Nighttime warming (NW) had maximum impact while All-Daytime warming (DW) showed the minimum effect. All-daytime warming (AW), Daytime warming (DW) and Nighttime warming (NW) treatments reduced the average soil microbial biomass carbon by 8.4%,15.1% and 29.1%, and soil soluble carbon by 7.1%, 19.2% and 27.7%, respectively. The three different diurnal warming scenarios reduced the soil microbial biomass nitrogen and soil soluble nitrogen, in which All-daytime warming (AW) had maximum impact while Nighttime warming (NW) showed minimum effect. Statistic analysis revealed that the impact of Nighttime warming (NW) and Daytime warming (DW) on the soil microbial biomass carbon and soil soluble carbon reached significant level, and only the impact of All-daytime warming (AW) to soil microbial biomass nitrogen and soil soluble nitrogen reached significant level.7 Responses of soil nematode to different diurnal warming scenariosAll-daytime warming (AW) and Daytime warming (DW) treatment reduced the total number of nematodes which inhabited in the 0-25cm soil layer by 19.7%and 12.6% respectively. The impact of All-daytime warming (AW) on nematodes reached significant level. The warming treatments mostly affected nematodes in the 0-10cm soil layers, and All-daytime warming (AW) and Daytime warming (DW) reduced nematodes by 37.5 and 20.4% respectively. In the 10-25cm soil layer. Nighttime warming (NW). Daytime warming (DW) and All-daytime warming (AW) reduced the number of nematodes by 17.6%.14.5% and 11.4% respectively, but all the differences did not reach significant level. Warming increased the bacterivorous nematode and slightly reduced Plant-parasites All-daytime warming (AW). Daytime warming (DW) and Nighttime warming (NW) increased the numbers of nematodes averagely by 13.6%.18.0% and 26.9%. respectivlity. during the four stages, in which the booting stage and heading stage had the maximum impact. The proportions of omnivorous nematodes and other feeding habit nematodes had inconsistent variation, but none reached significant level.