Elevated atmospheric CO₂ concentration (eCO₂) has been the most important driving factor and characteristic of climate change. To clarify the effects of eCO₂ on the soil microbes and on the concurrent status of soil carbon and nitrogen, an experiment was conducted in a typical summer maize field based on a 10-year mini FACE (Free Air Carbon Dioxide Enrichment) system in North China. Both rhizospheric and bulk soils were collected for measurement. The soil microbial carbon (MBC), nitrogen (MBN), and soil mineral N were measured at two stages. Characteristics of microbes were assayed for both rhizospheric soil and bulk soils at the key stage. We examined the plasmid copy numbers, diversities, and community structures of bacteria (in terms of 16s rRNA), fungi (in terms of ITS-internal transcribed spacer), ammonia oxidizing bacteria (AOB) and denitrifiers including nirK, nirS, and nosZ using the Miseq sequencing technique. Results showed that under eCO₂ conditions, both MBC and MBN in rhizospheric soil were increased significantly. The quantity of ITS was increased in the eCO₂ treatment compared with that in the ambient CO₂ (aCO₂) treatment, while the quantity of 16s rRNA in rhizospheric soil showed decrease in the rhizospheric soil in the eCO₂ treatment. ECO₂ changed the relative abundance of microbes in terms of compositional proportion of some orders or genera particularly in the rhizospheric soil-n particular, Chaetomium increased for ITS, Subgroups 4 and 6 increased for 16s rRNA, Nitrosospira decreased for AOB, and some genera showed increase for nirS, nirK, and nosZ. Nitrate N was the main inorganic nitrogen form at the tasseling stage and both quantities of AOB and denitrifiers, as well as the nosZ/(nirS+nirK) showed an increase under eCO₂ conditions particularly in the rhizospheric soil. The Nitrosospira decreased in abundance under eCO₂ conditions in the rhizospheric soil and some genera of denitrifiers also showed differences in abundance. ECO₂ did not change the diversities of microbes significantly. In general, results suggested that 10 years of eCO₂ did affect the active component of C and N pools (such as MBC and MBN) and both the quantities and relative abundance of microbes which are involved in carbon and nitrogen cycling, possibly due to the differences in both the quantities and component of substrate for relevant microbes in the rhizospheric soils.

Agriculture production has been found to be the most sensitive sector to climate change. Northeast China (NEC) is one of the world’s major regions for spring maize production and it has been affected by climate change due to increases in temperature and decreases in sunshine hours and precipitation levels over the past few decades. In this study, the CERES-Maize model-v4.7 was adopted to assess the impact of future climatic change on the yield of spring maize in NEC and the effect of adaptation measures in two future periods, the 2030s (2021 to 2040) and the 2050s (2041 to 2060) relative to the baseline (1986 to 2005) under RCP4.5 and RCP8.5 scenarios. The results showed that increased temperatures and the decreases in both the precipitation level and sunshine hours in the NEC at six representative sites in the 2030s and 2050s periods based on RCP4.5 and RCP8.5 climate scenarios would shorten the maize growth durations by (1–38 days) and this would result in a reduction in maize yield by (2.5–26.4%). Adaptation measures, including altered planting date, supplemental irrigation and use of cultivars with longer growth periods could offset some negative impacts of yield decrease in maize. For high-temperature-sensitive cultivars, the adoption of early planting, cultivar change and adding irrigation practices could lead to an increase in maize yield by 23.7–43.6% and these measures were shown to be effective adaptation options towards reducing yield loss from climate change. The simulation results exhibited the effective contribution of appropriate adaptation measures in eliminating the negative impact of future climate change on maize yield.

The elevated atmospheric CO₂ concentration (eCO₂) is expected to increase the labile C input to the soil, which may stimulate microbial activity and soil N₂O emissions derived from nitrification and denitrification. However, few studies studied the effect of eCO₂ on N₂O emissions from maize field under the free-air CO₂ enrichment (FACE) conditions in the warm temperate zone. Here, we report a study conducted during the 12th summer maize season under long-term eCO₂, aiming to investigate the effect of eCO₂ on N₂O emissions. Moreover, we tested zero and conventional N fertilization treatments, with maize being grown under either eCO₂ or ambient CO₂ (aCO₂). We hypothesized that N₂O emissions would be increased under eCO₂ due to changes in soil labile C and mineral N derived from C-deposition, and that the increase would be larger when eCO₂ was combined with conventional N fertilization. We also measured the activities of some soil extracellular enzymes, which could reflect soil C status. The results showed that, under eCO₂, seasonal N₂O and CO₂ emissions increased by 12.4–15.6% (p < 0.1) and 13.8–18.5% (p < 0.05), respectively. N fertilization significantly increased the seasonal emissions of N₂O and CO₂ by 33.1–36.9% and 17.1–21.8%, respectively. Furthermore, the combination of eCO₂ and N fertilization increased the intensity of soil N₂O and CO₂ emissions. The marginal significant increase in N₂O emissions under eCO₂ was mostly due to the lower soil water regime after fertilization in the study year. Dissolved organic C (DOC) and microbial biomass C (MBC) concentration showed a significant increase at most major stages, particularly at the tasseling stage during the summer maize growth period under eCO₂. In contrast, soil mineral N showed a significant decrease under eCO₂ particularly in the rhizospheric soils. The activities of C-related soil extracellular enzymes were significantly higher under eCO₂, particularly at the tasseling stage, which coincided with concurrent increased DOC and MBC under eCO₂. We conclude that eCO₂ increases N₂O emissions, and causes a higher increase when combined with N fertilization, but the increase extent of N₂O emissions was influenced by environmental factors, especially by soil water, to a great extent. We highlighted the urgent need to monitor long-term N₂O emissions and N₂O production pathways in various hydrothermal regimes under eCO₂.

In the past century, climate change has become more significant, which has a great impact on crop growth, especially food security. Based on the regional climate model PRECIS, high-precision grid climate data in China under RCP4.5 and RCP8.5 scenarios were output, and the high-precision amplification and calibration of crop model DSSAT were calibrated and verified in combination with data of maize planting from 2005 to 2015, including observation data of agrometeorological stations, ecological networking experiment data and maize survey data of agricultural demonstration counties. The impact of climate change on maize production in 2030s and 2050s was evaluated; and the effect of main adaptation strategies to climate change is put forward which could support macro strategies of layout adjustment for the maize production system. The results show that if no countermeasures are taken in the future, the risk of maize yield reduction in China will gradually increase, especially under the RCP8.5 scenario. The risk of maize yield reduction in each main production area will be very prominent in the 2050s under the RCP8.5 scenario, which would be between 10–30%. Compared with a delayed sowing date, an early sowing date would be more conducive to maize production, but there would be some differences in different regions. The heat in the growing season of maize would increase significantly. If the growth time of maize from silking to maturity could be prolonged and the accumulated temperature could be raised, the dry matter accumulation of maize would effectively increase, which would have an obvious effect on yield. Improving grain filling rate is also significant, although the effect of yield increase would be smaller. Therefore, sowing in advance, full irrigation and cultivating varieties with a long reproductive growth period could effectively alleviate the yield reduction caused by climate change. Adjusting maturity type and grain harvest strategy would have a more obvious mitigation effect on yield reduction in northeast China and northern China, and plays a positive role in ensuring future maize yield.