Manganese is an essential nutrient and plays key roles in photosynthetic processes, including in NAD‐malic enzyme (NAD‐ME)‐type C4 plants as an activator of NAD‐ME. However, little is known about the Mn requirements of switchgrass (Panicum virgatum L.). To study Mn requirements for optimum growth and biomass production, a lowland (‘Alamo’) and an upland (‘Cave‐in‐Rock’) switchgrass ecotype were grown with either washed sand, vermiculite, or perlite and fertilized with nutrient solutions ranging in [Mn] from 0 to 200 μM. In the perlite experiment, pearl millet [Pennisetum glaucum (L.) R. Br. ‘KGraze’] was also grown. Shoot [Mn] was highly responsive to increasing Mn in the nutrient solution. When grown in washed sand and vermiculite, tissue [Mn] remained above those normally considered deficient, even in the 0 μM Mn treatment, and no Mn treatment effects on biomass production were found. In perlite, end‐of‐season shoot [Mn] were <5 mg kg−1 in all entries when no Mn was supplied, and a decrease in biomass production compared with 10–25 μM Mn treatments was observed for Alamo and KGraze, but not for Cave‐in‐Rock. Relative chlorophyll contents of switchgrass were lower in the 0 μM Mn treatment than in other treatments late in the season, but in KGraze, they were low early in the season and increased throughout the season, resulting in less pronounced (but still significant) differences at late stages. Overall, results indicated that switchgrass and pearl millet respond differently to low Mn availability and that even low levels of shoot tissue [Mn] allow switchgrass to maintain biomass production.

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Manganese (Mn) is an essential micronutrient and has a broad range of functions for all plant growth and reproduction. It plays a crucial role in NAD-ME C4 photosynthesis, including as a constituent of the water splitting protein of photosystem II (PSII) and as an activator of NAD-ME which catalyzes the release of CO2 from malate in bundle sheath cells (BSC). Switchgrass (Panicum virgatum L.), a perennial NAD-ME C4 grass, is native to much of the United States. Switchgrass is also considered as a promising biofuel species for sustainable production of bioenergy feedstock. As a NADME C4 species, switchgrass may have a high requirement for Mn for optimum growth. However, little is known about switchgrass responses to Mn availability at present. To study the influence of Mn on biomass production and photosynthetic characteristics, one lowland ('Alamo') and one upland ('Cave-in-Rock') switchgrass ecotype were grown in 19-L pots filled with either washed sand, vermiculite, or perlite, and fertilized with nutrient solutions with Mn concentrations ranging from 0 to 200 [micro]M under field conditions in three consecutive years. In the last year (perlite), pearl millet (Pennisetum glaucum L. R. Br.) ('KGraze') was also grown. Shoot Mn concentration was highly responsive to increasing Mn in the nutrient solution in all experiments and for all entries. When grown in washed sand and vermiculite, no Mn treatment effects on biomass production were found for either switchgrass ecotype. In perlite, a significant decrease in biomass production grown in the 0 [micro]M Mn treatment compared to 10-25 [micro]M Mn treatments was only observed for Alamo and KGraze, and not for Cave-in-Rock. Late in the season, relative chlorophyll contents of both switchgrass ecotypes were significantly lower in the 0 [micro]M Mn treatment than other treatments, but, in KGraze, relative chlorophyll content was low early in the season, increased throughout the season, resulting in a less pronounced, but still significant Mn treatment effect, at late stages. Leaf Mn concentration of all entries increased with increasing Mn concentration in the nutrient solution. In switchgrass, leaf Mn concentration was significantly greater early compared to late in the season in the absence of Mn in the nutrient solution; however, this was not the case for pearl millet. In switchgrass, the absence of Mn in the nutrient solution significantly decreased photosynthetic rates and maximum PSII efficiency (Fv/Fm) late in the season. In contrast, in pearl millet the effect of 0 ë_M Mn in the nutrient solution on net photosynthesis and Fv/Fm was more pronounced early in the season. Chloroplast ultrastructure in mesophyll and bundle sheath cells were only affected by Mn availability in the lowland switchgrass ecotype. Manganese availability did not influence NAD-ME, NADP-ME and PEPCK activities in switchgrass, but NADME and PEPCK activities were reduced in pearl millet early in the season in the absence of Mn in the nutrient solution. Based on these results, Mn limitation for the oxygen evolving compex of PSII rather than for NAD-ME was the primary limitation of low Mn availability on net photosynthesis. Overall, switchgrass and pearl millet exhibited distinct temporal responses to limited Mn availabillity.

With the development of global warming, the carbon pool in the degraded permafrost zone around the Arctic will gradually be disturbed and enter the atmosphere in the form of methane gas. The frequency and intensity of forest fires will gradually increase, and the release of geological methane will become important factors affecting wildfires in permafrost regions. The northwestern section of China's Xiao Xing'an Mountains, which is located in the degradation zone of the southern edge of the permafrost region of Eurasia, was selected as the research area. Monitoring equipment such as atmospheric electric field, air temperature, methane concentration, soil temperature and pore water pressure were deployed to monitor relevant data changes for a long time. Through indoor soil ventilation tests, it was verified that the friction between gas and soil particles caused the difference in soil electric potential, and the analysis revealed the mechanism of seasonal wildfires in the study area. The results show that the gradual decomposition of metastable methane hydrate and stable methane hydrate stored in the permafrost in the northern part of the Xiao Xing'an Mountains in Northeast China is the main source of high-concentration methane gas entering the atmosphere from the surface. In spring, as the frozen layer on the surface of the study area thaws and the snow gradually melts, the high-concentration, high-pressure methane gas accumulated under the frozen layer will be quickly released into the atmosphere. The study area has the annual maximum value of methane concentration on the surface every spring (March to May), and the rapid rise of gas molecules during the decomposition of underground methane hydrate will cause friction with soil particles, causing methane molecules to be positively charged. Under the action of soil pore pressure and the negative charge at the bottom of the near-surface cloud layer, positively charged methane gas enters the atmosphere. The positively charged methane gas in the air contacts the negative charge in the near-surface cloud layer to form a discharge channel to enhance the discharge phenomenon. With the gradual accumulation of positive charges in the air, the positively charged methane in the air near the ground and the water molecules in the air form positively charged aerosols, and contact with the negative charges near the ground will also form a discharge channel to produce a discharge phenomenon, which will lead to high concentrations of methane gas near the surface were ignited. In addition, the mixed gas with higher pressure and concentration will reduce the thermal spontaneous combustion temperature of methane gas, and when methane aerosol is formed, it will further increase the impact on the air temperature, thereby increasing the risk of wildfires. The electric potential difference between the ground and the near-surface and the flammability of methane aerosols caused by the methane gas emission process in the permafrost degraded area will become an important factor in inducing wildfires.