The Responses And Regional Differences Of Winter Wheat Root Syetem And Soil Environment To Passive Nighttime Warming

Climate warming is an indisputable fact, which is one of the major characteristics of global climate change. The global surface temperature has increased in the past100years by about0.74℃and is recently predicted to increase1.4-5.8℃within this century. The temperature has increased, most obviously in the higher latitudes of the northern hemisphere. China’s warming trend is consistent with the global, but much higher than the global average temperature increased amplitude, and is expected to continue warming in the future. Global climate will further warm with a greater level of daily maximum temperature than daily minimum temperature, be warmer in the north than the south, in winter and spring than in summer and autumn. At present, researches on the responses of terrestrial ecosystems to experimental warming mostly focus on all day temperature increased effects and aboveground of natural ecosystems, while responses and adaptation on different latitudes of belowground biological processes to passive nighttime warming are relatively scarce. Meanwhile, the main research approaches are base on modeling and the greenhouse/open-top warming methods, they cannot truly reflex crop biological processes above and below ground under the global warming. Wheat, as one of the most important food crops in China, produced22.5%of total grain yield. Winter wheat is the major part of China’s wheat, occupying more than80%of countrywide wheat planting area. In the context of global warming, to learn the responses of crop production in different main cropping areas of winter wheat in China to passive nighttime warming and the belowground biological mechanisms, not only conducive to provide technical choice for wheat production in response to climate change, but also has important theoretical reference value to the scientific evaluation of climate warming on food security in China. Therefore, based on the technique of passive nighttime warming (PNW), a four-year field nighttime warming experiment was conduced for crop entire growth period in the main cropping areas of winter wheat in China, including four locations of Shijiazhuang, Xuzhou, Xuchang and Zhenjiang. Soil moisture,0-5cm soil temperature, soil microbial characteristics, winter wheat roots characteristics and soil chemical properties were determined under field conditions in2008-2010.1. This passive nighttime waming (PNW) facility can provide a reliable warmed system for field warming experiment.In the entire growth period of winter wheat in2008-2010, the corresponding temperatures of0-5cm soil layer in the experimental sites of Shijiazhuang, Xuzhou, Xuchang and Zhenjiang, were significantly higher by1.2℃,0.7℃,0.7℃and0.7℃in the warmed plots than the non-warmed, respectively. Although soil moisture was correspondingly8.8%,3.7%,3.8%and2.9%lower in the warmed plots than the non-warmed, these decrements were not significant. The increase of soil temperature and the decrease of soil moisture were larger in the higher latitudes region than in the lower latitudes region, and gradually narrowed with winter wheat growth period in the whole warming area. Warming at nighttime also advanced initial flowing period of winter wheat. The passive nighttime warming facility adopts in the experiment accorded with climate warming mechanism, and basically satisfies the conditions which were required in the field warming research on the responses and adoption of winter wheat to nighttime warming scenarios.2. Warming at nighttime decreased soil microbial biomass carbon and nitrogen, dissolved organic carbon and nitrogent and microbial respiration rate.In2008-2010, nighttime warming significantly decreased soil microbial biomass C and N and dissolved organic C and N, as well as microbial activity in the entire growth period of winter wheat. Compared to the ambient, warming at nighttime reduced soil microbial biomass C on average by11.4%,7.8%,10.9%and8.5%, soil microbial biomass N by15.2%,16.7%,13.8%and8.4%, soil dissolved organic C by8.3%,10.8%,6.7%and15.5%, soil dissolved organic N by8.0%,11.0%,17.3%and17.6%, and microbial respiration rates by6.6%,9.6%,7.0%and11.1%in the experimental sites of Shijiazhuang, Xuzhou, Xuchang and Zhenjiang, respectively. Soil microbial biomass C and N, dissolved organic C and N, and microbial activity of different latitude have a consistent response tendency to nighttime warming treatment. Among them, the responses of soil microbial biomass N and dissolved organic N to warming treatment were most obvious, reduced the amplitude of the most, followed by soil microbial C and dissolved organic C, the response of the soil microbial respiration was the least. The response trends of soil microbial biomass C and N in different latitudes to nighttime warming treatment were consistent with the range of increased temperature in the different latitudes, i.e. showed a trend of gradual increase with the increasing latitudes in general.3. Warming at nighttime increased wheat root biomass, root/shoot ratio and root length etc.Elevated nighttime temperature treatment increased winter wheat root dry weight, root/shoot ratio and roots morphology indexes in heading stage of winter wheat in2009-2010. Nighttime warming increased dry matter weight of winter wheat root on average by31.5%,27.0%and14.5%, and root length by32.5%,26.9%and11.2%in the experimental sites of Shijiazhuang, Xuzhou and Zhenjiang, respectively. Warming increased root/shoot ratio in the experimental sites of Shijiazhuang, Xuchang and Zhenjiang on average by23.8%,13.7%and9.7%, respectively. Compared to the ambient, warming at nighttime increased winter wheat root surface area on average by30.9%,20.4%,11.6%and11.5%, root average diameter by2.1%,1.8%,4.3%and2.5%, root volume by25.0%,10.5%,3.8%and11.3%in the experimental sites of Shijiazhuang, Xuzhou, Xuchang and Zhenjiang in heading stage, respectively. The order of warming treatment effects on the winter wheat root indexes was root surface area> the root dry weight> root length> root volume> root/shoot ratio> average root diameter. The effects of nighttime warming on dry matter weight of winter wheat root and root shoot/ratio increased with the increase of latitudes, had a large value at higher latitudes. The response of root length and root surface area to nighttime warming also exhibited a latitudinal rising trend, although there was no significant latitude difference of warming treatment effects on root volume, it was showed a greater increase trend at higher latitudes.4. Warming at nighttime significantly decreased soil pH and available nutrient contents.In2009-2010, nighttime warming significantly decreased soil pH and soil available nutrient contents. Compared to the ambient, warming at nighttime reduced soil pH on average by0.35%,0.38%,0.73%and0.91%, soil alkaline nitrogen by8.1%,8.1%,7.1%and6.0%, soil available phosphorus by15.7%,12.1%,19.6%and25.8%, and soil available potassium by11.5%,7.6%,7.6%and10.1%in the experimental sites of Shijiazhuang, Xuzhou, Xuchang and Zhenjiang, respectively. Among them, the response of soil available phosphorus on warming treatment was most obvious, followed by soil available potassium and nitrogen. The decrease amplitude of soil pH and available phosphorus content in warming treatment decreased with the increasing latitude, i.e. warming treatment had a larger influence on soil pH and soil available phosphorus in lower latitudes. While, the decrease amplitude of soil alkaline nitrogen changed greater at higher altitudes.