分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
摘要： In this article, the belowground and aboveground biomass production in bioenergy buffers and biogeochemical N removal processes along the soil–groundwater continuum was assessed. In a sandy loam soil with shallow groundwater, bioenergy buffers of miscanthus and willow (5 and 10 m wide) were planted along a ditch of an agricultural field (AF) located in the Po valley (Italy). Mineral N forms and dissolved organic C (DOC) were monitored monthly over an 18-month period in groundwater before and after the bioenergy buffers. Soil samples were measured for inorganic N, DOC, microbial biomass C (MBC) and N (MBN), and potential nitrate reductase activity (NRA). The results indicated that bioenergy buffers are able to efficiently remove from groundwater the incoming NO3-N (62% – 5 m and 80% – 10 m). NO3-N removal rate was higher when nitrate input from AF increased due to N fertilization. Willow performed better than miscanthus in terms of biomass production (17 Mg DM ha−1 yr−1), fine root biomass (5.3 Mg ha−1) and N removal via harvesting (73 kg N ha−1). The negative nonlinear relationship found between NO3-N and DOC along the soil–groundwater continuum from AF to bioenergy buffers indicates that DOC:NO3-N ratio is an important controlling factor for promoting denitrification in bioenergy buffers. Bioenergy buffers promoted soil microbial functioning as they stimulated plant–microbial linkages by increasing the easily available C sources for microorganisms (as DOC). First, willow and miscanthus promoted high rates of biological removal of nitrate (NRA) along the soil profile. Second, rhizosphere processes activated the soil microbial community leading to significant increases in MBC and microbial N immobilization. Herbaceous and woody bioenergy crops have been confirmed as providing good environmental performances when cultivated as bioenergy buffers by mitigating the disservices of agricultural activities such as groundwater N pollution.
分类： 生物学 >> 植物学 >> 植物生物化学、植物生物物理学 提交时间： 2016-05-04
Jianli Lu
Leichen Zhang
Ramsey S. Lewis
Lucien Bovet
Simon Goepfert
Anne M. Jack
James D. Crutchfield
Huihua Ji
Ralph E. Dewey
摘要： Burley tobaccos (Nicotiana tabacum) display a nitrogen-use-deficiency phenotype that is associated with the accumulation of high levels of nitrate within the leaf, a trait correlated with production of a class of compounds referred to as tobacco-specific nitrosamines (TSNAs). Two TSNA species, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N-nitrosonornicotine (NNN), have been shown to be strong carcinogens in numerous animal studies. We investigated the potential of molecular genetic strategies to lower nitrate levels in burley tobaccos by overexpressing genes encoding key enzymes of the nitrogen-assimilation pathway. Of the various constructs tested, only the expression of a constitutively active nitrate reductase (NR) dramatically decreased free nitrate levels in the leaves. Field-grown tobacco plants expressing this NR variant exhibited greatly reduced levels of TSNAs in both cured leaves and mainstream smoke of cigarettes made from these materials. Decreasing leaf nitrate levels via expression of a constitutively active NR enzyme represents an exceptionally promising means for reducing the production of NNN and NNK, two of the most well-documented animal carcinogens found in tobacco products.
分类： 生物学 >> 植物学 >> 植物生物化学、植物生物物理学 提交时间： 2016-05-03
摘要： OsNRT1.1a is a low-affinity nitrate (NO3 ) transporter gene. In this study, another mRNA splicing product, OsNRT1.1b, putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated 15N levels to about half as compared to OsNRT1.1b-expressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25mM NO3 confirmed 15N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen (N) deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type (WT). The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25mM NH4NO3 and 2.5mM NO3 – or NH4 þ treatments, but not in 0.125mMNH4NO3. However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125mM NH4NO3, suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.(NO3) transporter gene. In this study, another mRNA splicing product, OsNRT1.1b, putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated 15N levels to about half as compared to OsNRT1.1b-expressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25mM NO3 confirmed 15N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen (N) deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type (WT). The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25mM NH4NO3 and 2.5mM NO3 or NH4+ treatments, but not in 0.125mM NH4NO3. However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125mM NH4NO3, suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.
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