Effects of freeze–thaw cycles on soil N_2O concentration and flux in the permafrost regions of the Qinghai–Tibetan Plateau

Nitrous oxide(N_2 O) is one of the most important greenhouse gases in the atmosphere; freeze–thaw cycles(FTCs) might strongly influence the emission of soil N_2 O on the Qinghai–Tibetan Plateau(QTP). However, there is a lack of in situ research on the characteristics of soil N_2 O concentration and flux in response to variations in soil properties caused by FTCs.Here, we report the effect of FTC-induced changes in soil properties on the soil N_2 O concentration and flux in the permafrost region of the higher reaches of the Shule River Basin on the northeastern margin of the QTP. We measured chemical properties of the topsoil, activities of soil microorganisms, and air temperature(AT), as well as soil N_2 O concentration and flux, over an annual cycle from July 31, 2011, to July 30, 2012. The results showed that soil N_2 O concentration was significantly affected by soil temperature(ST), soil moisture(SM), soil salinity(SS), soil polyphenol oxidase(SPO), soil alkaline phosphatase(SAP), and soil culturable actinomycetes(SCA), ranked as SM>SS>ST>SPO>SAP>SCA, whereas ST significantly increased soil N_2 O flux, compared with SS. Overall, our study indicated that the soil N_2 O concentration and flux in permafrost zone FTCs were strongly affected by soil properties, especially soil moisture, soil salinity, and soil temperature.

Responses to defoliation and fertiliser,corm development and chemical control of onion grass(Romulea rosea)in the Mediterranean environment of southern Australia

Background:Onion grass(Romulea rosea)is a common weed that infests native and improved pastures in the Mediterranean environments of southern Australia.It is a very challenging weed to control due to its distinctive growth and survival mechanisms involving corms.Methods:Three glasshouse experiments were conducted in Australia to investigate the response of onion grass to defoliation and fertiliser application,the development and growth of onion grass corms and the chemical control of the weed in winter and spring.Results:Defoliating consistently to 1 cm above ground reduced corm weight by 84%compared with the control.Medium or high fertiliser application did not increase herbage mass of onion grass compared with the nonfertilised treatment.The corm weight of onion grass declined from Weeks 1 to 8 after emergence,remained at 53-60 mg dry matter(DM)corm−1 from Weeks 8 to 19 and then declined on average to 37mgDMcorm−1 up to Week 26 after emergence.New corms started to develop at Week 6 after emergence.A small proportion of the onion grass plants(7.5%)developed multiple new corms(3-6 corms)from a single old corm.The most effective herbicide control was a winter application of metsulfuron methyl or imazamox as an alternative product to protect clover.Conclusions:This study has identified the growth and development patterns of onion grass corms,how the plant responded to defoliation and fertiliser application and effective chemical control of this weed.These findings have significant practical implications for the improvement of onion grass-infested pastures.