1,721,110 research outputs found
Nitrogen metabolism of two contrasting poplar species during acclimation to limiting nitrogen availability
No full textTo investigate N metabolism of two contrasting Populus species in acclimation to low N availability, saplings of slow-growing species (Populus popularis, Pp) and a fast-growing species (Populus alba × Populus glandulosa, Pg) were exposed to 10, 100, or 1000 μM NH4NO3. Despite greater root biomass and fine root surface area in Pp, lower net influxes of NH4+ and NO3– at the root surface were detected in Pp compared to those in Pg, corresponding well to lower NH4+ and NO3– content and total N concentration in Pp roots. Meanwhile, higher stable N isotope composition (δ15N) in roots and stronger responsiveness of transcriptional regulation of 18 genes involved in N metabolism were found in roots and leaves of Pp compared to those of Pg. These results indicate that the N metabolism of Pp is more sensitive to decreasing N availability than that of Pg. In both species, low N treatments decreased net influxes of NH4+ and NO3–, root NH4+ and foliar NO3– content, root NR activities, total N concentration in roots and leaves, and transcript levels of most ammonium (AMTs) and nitrate (NRTs) transporter genes in leaves and genes involved in N assimilation in roots and leaves. Low N availability increased fine root surface area, foliar starch concentration, δ15N in roots and leaves, and transcript abundance of several AMTs (e.g. AMT1;2) and NRTs (e.g. NRT1;2 and NRT2;4B) in roots of both species. These data indicate that poplar species slow down processes of N acquisition and assimilation in acclimation to limiting N supply
Vegetation restoration stimulates soil carbon sequestration and stabilization in a subtropical area of southern China
No full textA Critical Analysis of the Carbon Neutrality Assumption in Life Cycle Assessment of Forest Bioenergy Systems
Full text linkThis study presents a critical analysis regarding the assumption of carbon neutrality in life cycle assessment (LCA) models aimed at assessing climate change impacts of bioenergy usage. We identified a complex of problems in the carbon neutrality assumption, especially regarding bioenergy derived from forest residues. In this study, we summarized several issues related to carbon neutral assumptions, with particular emphasis on possible carbon accounting errors at the product level. We analyzed errors in estimating emissions in the supply chain, direct and indirect emissions due to forest residue extraction, biogenic CO2 emission from biomass combustion for energy, and other effects related to forest residue extraction. Various modeling approaches are discussed in detail. We concluded that there is a need to correct accounting errors when estimating climate change impacts and proposed possible remedies. To accurately assess climate change impacts of bioenergy use, greater efforts are required to improve forest carbon cycle modeling, especially to identify and correct pitfalls associated with LCA accounting, forest residue extraction effects on forest fire risk and biodiversity. Uncertainties in accounting carbon emissions in LCA are also highlighted, and associated risks are discussed.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Anatomical, physiological and transcriptional responses of two contrasting poplar genotypes to drought and re-watering
No full textPopulus × euramericana (Pe) displays higher stable carbon isotope composition (δ13C) and intrinsic water use efficiency (WUEi) than Populus cathayana (Pc) under unlimited water conditions, rendering us to hypothesize that Pe is better acclimated to water deficiency than Pc. To examine this hypothesis, saplings of Pc and Pe were exposed to drought and subsequently re‐watered. Pc and Pe exhibited distinct anatomical, physiological and transcriptional responses in acclimation to drought and re‐watering, mainly due to stronger responsiveness of transcriptional regulation of genes encoding plasma membrane intrinsic proteins (PIPs), higher starch accumulation, δ13C, stable nitrogen isotope composition (δ15N) and WUEi, and lower reactive oxygen species (ROS) accumulation and scavenging in Pe. In acclimation to drought, both poplar genotypes demonstrated altered anatomical properties, declined height growth, differential expression of PIPs, activation of ABA signaling pathway, decreased total soluble sugars and starch, increased δ13C, δ15N and WUEi, and shifted homeostasis of ROS production and scavenging, and these changes can be recovered upon re‐watering. These data indicate that Pe is more tolerant to drought than Pc, and that anatomical, physiological and transcriptional acclimation to drought and re‐watering is essential for poplars to survive and grow under projected dry climate scenarios in the future
Changes in carbon, nutrients and stoichiometric relations under different soil depths, plant tissues and ages in black locust plantations
No full textTo investigate influences of forest plantations on soil nutrient properties, biomass accumulation, major nutrient elements (NPK) and their stoichiometric couplings in different tissues and aged plants, and correlations between major nutrient contents in soils and in foliage of plants, 5-, 10-, 15- and 20-year-old plantations of black locust (Robinia pseudoacacia L.) and farmland were selected. Black locust plantations increased soil organic carbon (SOC) and N stocks by 23–327 and 23–119 %, respectively, in the 0–10 cm top soil layer compared to those in farmland. Soil C:N, C:P, C:K, N:P, N:K and P:K ratios were 10.1, 22.9, 0.7, 2.2, 0.7 and 0.03, respectively. These ratios were higher in the 0–10 cm soil layer than those in the 10–20 cm soil layer and increased under older plantations. Higher C contents in stem, N contents in leaf, the largest C pools in stem and N pools in root in 20-year-old plantation were observed. Correspondingly, the highest C:N, C:P and C:K and the lowest N:P and N:K ratios in stem, decreased C:N and C:P ratios in older trees were found. No strong correlations were observed between element contents in soils and in leaves of black locust trees. These results suggest that black locust plantations can increase soil nutrient concentrations, SOC and N stocks resulting in changes in element stoichiometric relations. CNPK contents and their stoichiometries vary with tissues and tree ages of black locust. No strong coupling relations exist between major nutrient element contents in the top soil and in foliage of black locust
Phosphorus and nitrogen physiology of two contrasting poplar genotypes when exposed to phosphorus and/or nitrogen starvation
No full textPhosphorus (P) and nitrogen (N) are the two essential macronutrients for tree growth and development. To elucidate the P and N physiology of woody plants during acclimation to P and/or N starvation, we exposed saplings of the slow-growing Populus simonii Carr (Ps) and the fast-growing Populus × euramericana Dode (Pe) to complete nutrients or starvation of P, N or both elements (NP). P. × euramericana had lower P and N concentrations and greater P and N amounts due to higher biomass production, thereby resulting in greater phosphorus use efficiency/N use efficiency (PUE/NUE) compared with Ps. Compared with the roots of Ps, the roots of Pe exhibited higher enzymatic activities in terms of acid phosphatases (APs) and malate dehydrogenase (MDH), which are involved in P mobilization, and nitrate reductase (NR), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), which participate in N assimilation. The responsiveness of the transcriptional regulation of key genes encoding transporters for phosphate, ammonium and nitrate was stronger in Pe than in Ps. These results suggest that Pe possesses a higher capacity for P/N uptake and assimilation, which promote faster growth compared with Ps. In both poplars, P or NP starvation caused significant decreases in the P concentrations and increases in PUE. Phosphorus deprivation induced the activity levels of APs, phosphoenolpyruvate carboxylase and MDH in both genotypes. Nitrogen or NP deficiency resulted in lower N concentrations, amino acid levels, NR and GOGAT activities, and higher NUE in both poplars. Thus, in Ps and Pe, the mRNA levels of PHT1;5, PHT1;9, PHT2;1, AMT2;1 and NR increased in the roots, while PHT1;9, PHO1;H1, PHO2, AMT1;1 and NRT2;1 increased in the leaves during acclimation to P, N or NP deprivation. These results suggest that both poplars suppress P/N uptake, mobilization and assimilation during acclimation to P, N or NP starvation
Ectomycorrhizas with Paxillus involutus enhance cadmium uptake and tolerance in Populus × canescens
No full textEctomycorrhizas (EMs), which are symbiotic organs formed between tree roots and certain fungi, can mediate cadmium (Cd) tolerance of host plants, but the underlying physiological and molecular mechanisms are not fully understood. To investigate EMs mediated Cd tolerance in woody plants, Populus × canescens was inoculated with Paxillus involutus (strain MAJ) to establish mycorrhizal roots. Mycorrhizal poplars and non‐mycorrhizal controls were exposed to 0 or 50 μM CdSO4. EMs displayed higher net Cd2+ influx than non‐mycorrhizal roots. Net Cd2+ influx was coupled with net H+ efflux and inactivation of plasma membrane (PM) H+‐ATPases reduced Cd2+ uptake of EMs less than of non‐mycorrhizal roots. Consistent with higher Cd2+ uptake in EMs, in most cases, transcript levels of genes involved in Cd2+ uptake, transport and detoxification processes were increased in EMs compared to non‐mycorrhizal roots. Higher CO2 assimilation, improved nutrient and carbohydrate status, and alleviated oxidative stress were found in mycorrhizal compared to non‐mycorrhizal poplars despite higher Cd2+ accumulation. These results indicate that mycorrhizas increase Cd2+ uptake, probably by an enlarged root volume and overexpression of genes involved in Cd2+ uptake and transport, and concurrently enhance Po. × canescens Cd tolerance by increased detoxification, improved nutrient and carbohydrate status and defence preparedness
Net fluxes of ammonium and nitrate in association with H+ fluxes in fine roots of Populus popularis
No full textPoplar plants are cultivated as woody crops, which are often fertilized by addition of ammonium (NH4 +) and/or nitrate (NO3 −) to improve yields. However, little is known about net NH4 +/NO3 − fluxes and their relation with H+ fluxes in poplar roots. In this study, net NH4 +/NO3 − fluxes in association with H+ fluxes were measured non-invasively using scanning ion-selective electrode technique in fine roots of Populus popularis. Spatial variability of NH4 + and NO3 − fluxes was found along root tips of P. popularis. The maximal net uptake of NH4 + and NO3 − occurred, respectively, at 10 and 15 mm from poplar root tips. Net NH4 + uptake was induced by ca. 48 % with provision of NO3 − together, but net NO3 − uptake was inhibited by ca. 39 % with the presence of NH4 + in poplar roots. Furthermore, inactivation of plasma membrane (PM) H+-ATPases by orthovanadate markedly inhibited net NH4 +/NO3 − uptake and even led to net NH4 + release with NO3 − co-provision. Linear correlations were observed between net NH4 +/NO3 − and H+ fluxes in poplar roots except that no correlation was found between net NH4 + and H+ fluxes in roots exposed to NH4Cl and 0 mM vanadate. These results indicate that root tips play a key role in NH4 +/NO3 − uptake and that net NH4 +/NO3 − fluxes and the interaction of net fluxes of both ions are tightly associated with H+ fluxes in poplar roots
Cadmium tolerance in six poplar species
No full textSelection of poplar species with greater Cd tolerance and exploiting the physiological mechanisms involved in Cd tolerance are crucial for application of these species to phyto-remediation. The aim of this study is to investigate variation in Cd tolerance among the six poplar species and its underlying physiological mechanisms. Cuttings of six Populus species were cultivated for 10 weeks before exposure to either 0 or 200 μM CdSO4 for 20 days. Gas exchange in mature leaves was determined by a portable photosynthesis system. Cd concentrations in tissues were analyzed by a flame atomic absorbance spectrometry. Subsequently, Cd amount per plant, bio-concentration factor (BCF) and translocation factor (T f) were calculated. Nonenzymatic compounds and activities of antioxidative enzymes in tissues were analyzed spectrophotometrically. Cd exposure caused decline in photosynthesis in four poplar species including Populus cathayana (zhonghua 1). Among the six species, P. cathayana (zhonghua 1) displayed the highest Cd concentrations in tissues, the largest Cd amount in aerial parts, the highest BCF in aerial parts and T f under Cd exposure. Under Cd stress, increases in total soluble sugars in roots but decreases in starch in roots, wood, and leaves of P. cathayana (zhonghua 1) were found. Induced O 2 •− and H2O2 production in roots and leaves, and increases in free proline, soluble phenolics, and activities of antioxidative enzymes were observed in P. cathayana (zhonghua 1). Based on results of this pot experiment, it is concluded that P. cathayana (zhonghua 1) is superior to other five species for Cd phyto-remediation, and its well-coordinated physiological changes under Cd exposure confer the great Cd tolerance of this species
Physiological and transcriptional regulation in poplar roots and leaves during acclimation to high temperature and drought
No full textTo elucidate the physiological and transcriptional regulatory mechanisms that underlie the responses of poplars to high temperature (HT) and/or drought in woody plants, we exposed Populus alba × Populus tremula var. glandulosa saplings to ambient temperature (AT) or HT under 80 or 40% field capacities (FC), or no watering. HT increased the foliar total carbon (C) concentrations, and foliar δ13C and δ18O. HT triggered heat stress signaling via increasing levels of abscisic acid (ABA) and indole‐3‐acetic acid (IAA) in poplar roots and leaves. After perception of HT, poplars initiated osmotic adjustment by increasing foliar sucrose and root galactose levels. In agreement with the HT‐induced heat stress and the changes in the levels of ABA and carbohydrates, we detected increased transcript levels of HSP18 and HSP21, as well as NCED3 in the roots and leaves, and the sugar transporter gene STP14 in the roots. Compared with AT, drought induced greater enhancement of foliar δ13C and δ18O in poplars at HT. Similarly, drought caused greater stimulation of the ABA and foliar glucose levels in poplars at HT than at AT. Correspondingly, desiccation led to greater increases in the mRNA levels of HSP18, HSP21, NCED3, STP14 and INT1 in poplar roots at HT than at AT. These results suggest that HT has detrimental effects on physiological processes and it induces the transcriptional regulation of key genes involved in heat stress responses, ABA biosynthesis and sugar transport and HT can cause greater changes in drought‐induced physiological and transcriptional responses in poplar roots and leaves
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