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In C3 leaves, the mesophyll conductance to CO2 diffusion, gm, determines the drawdown in CO2 concentration from intercellular airspace to the chloroplast stroma. Both gm and stomatal conductance limit photosynthetic rate and vary in response to the environment. We investigated the response of gm to changes in CO2 in two Arabidopsis genotypes (including a mutant with open stomata, ost1), tobacco and wheat. We combined measurements of gas exchange with carbon isotope discrimination using tunable diode laser absorption spectroscopy with a CO2 calibration system specially designed for a range of CO2 and O2 concentrations. CO2 was initially increased from 200 to 1000 ppm and then decreased stepwise to 200 ppm and increased stepwise back to 1000 ppm, or the sequence was reversed. In 2% O2 a step increase from 200 to 1000 ppm significantly decreased gm by 26–40% in all three species, whereas following a step decrease from 1000 to 200 ppm, the 26–38% increase in gm was not statistically significant. The response of gm to CO2 was less in 21% O2. Comparing wild type against the ost1 revealed that mesophyll and stomatal conductance varied independently in response to CO2. We discuss the effects of isotope fractionation factors on estimating gm. 相似文献
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ROBERT M. BODDEY CLAUDIA P. JANTALIA PAULO C. CONCEIÇÃO JOSILEIA A. ZANATTA CIMÉLIO BAYER JOÃO MIELNICZUK JEFERSON DIECKOW HENRIQUE P. DOS SANTOS JOSÉ E. DENARDIN CELSO AITA SANDRO J. GIACOMINI BRUNO J.R. ALVES SEGUNDO URQUIAGA 《Global Change Biology》2010,16(2):784-795
Conservation agriculture can provide a low‐cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0–100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long‐term experiments (15–26 years) on free‐draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover‐crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha?1 in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha?1. However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha?1 yr?1) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO2 mitigation induced by the change from CT to ZT on the free‐draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow‐release of N from decaying surface residues/roots which favored maize root growth. 相似文献
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Clarifying misunderstandings regarding vegetation self‐organisation and spatial patterns of fairy circles in Namibia: a response to recent termite hypotheses
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NEIL CUMBERLIDGE RICHARD M. VON STERNBERG SAVEL R. DANIELS 《Biological journal of the Linnean Society. Linnean Society of London》2008,93(2):399-413
The higher taxonomy of the 20 known genera of Afrotropical freshwater crabs is revised to reflect the evolutionary relationships revealed by the consensus of a series of recent morphological and molecular phylogenetic studies of the group. The Afrotropical freshwater crab genera fall into two monophyletic groups, one from Socotra with two genera (Potamidae) and another that includes the remaining 18 genera. The latter group, which includes the bulk of the region's freshwater crab fauna, forms a well-supported monophyletic clade. We recognize two monophyletic sister groups (subfamilies) within the Potamonautidae, one for seven genera from Africa (the Potamonautinae) and one for 11 genera from Africa, the Seychelles, and Madagascar (the Deckeniinae). The Deckeniinae includes two monophyletic groups (tribes), one with seven genera from Madagascar (the Hydrothelphusini), and one with four genera from Africa and the Seychelles (the Deckeniini). The Deckeniini is further divided here into two subtribes, the Deckeniina and the Globonautina. The Platythelphusidae is not recognized, and the Deckeniidae and Globonautinae are lowered in rank. There is no phylogenetic support for the continued inclusion of any genus from the Afrotropical region in the Gecarcinucidae which is treated here as an exclusively Oriental family. The Afrotropical freshwater crabs (excluding those from Socotra) form a monophyletic assemblage that has no representatives outside of the region. The wider biogeographical implications of the taxonomic revision are discussed. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 399–413. 相似文献
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MARIA HELENA PEREIRA‐PEIXOTO GESINE PUFAL MICHAEL STAAB CELSO FEITOSA MARTINS ALEXANDRA‐MARIA KLEIN 《Ecological Entomology》2016,41(3):241-252
1. Urbanisation and agricultural intensification cause the replacement of natural ecosystems but might also create novel habitats in urban and rural ecosystems promoting some insect communities by providing food and nesting resources. 2. This study investigated how host–natural enemy communities change in urban and rural landscapes and their transitional zone, the urban–rural interface, by using trap nests for cavity‐nesting Hymenoptera in gardens and rapeseed fields that were either isolated or paired in the urban–rural interface. 3. Host dynamics were important for natural enemy occurrence, species richness and parasitism rates, and landscape effects were evident for natural enemy variables except for the richness of bee natural enemies. The number of parasitised brood cells was at its highest in the urban–rural interface, but the highest parasitism rates of bees were observed in isolated gardens. Parasitism rates of bees were negatively affected by host abundance, while parasitism rates of wasps were positively affected. 4. Higher specialisation and lower connectivity of host–natural enemy interactions were found in paired habitats than in isolated habitats. This indicates that paired habitats comprise more specific natural enemies and vulnerable interactions, while isolated habitats comprise more generalist natural enemies, and thus interactions appear more stable. 5. These results confirm that host dynamics play an essential role in the abundance and richness of natural enemies and drive parasitism. However, high habitat heterogeneity found in the urban–rural interface can also have an effect on host–natural enemy communities. This highlights that the provisioning of resources in the urban–rural interface can benefit insect communities in these areas. 相似文献
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CELSO VATARU NAKAMURA MANUEL JOSE GIL ESTEVES ARNALDO FEITOSA BRAGA ANDRADE CELUTA SALES ALVIANO WANDERLEY DE SOUZA JAYME ANGLUSTER 《The Journal of eukaryotic microbiology》1992,39(2):303-309
ABSTRACT. Cell surface carbohydrates of three phytoflagellates, Phytomonas francai. Phytomonas serpens and Phytomonas sp. from different hosts including cassava, coreid insect Phthia picta and the milkweed plant Euphorbia hyssopifolia, respectively, were analysed by agglutination assays employing a battery of highly purified lectins with affinity for receptor molecules containing N-acetylglucosamine (d-GlcNAc), N-acetylgalactosamine (D-GalNAc), galactose, mannose-like (D-Man-like) residues and fucose, and by binding assay using radiolabeled [125I]-wheat germ agglutinin (WGA) and fluorescent WGA lectin, as well as glycosidases of known sugar specificity, Escherichia coli K with mannose-affinity fimbrial lectin was also used as an agglutination probe. In general, the presence of D-GlcNAc. D-GalNAc and D-Man-like residues was detected in the phytomonads' plasma membrane. These sugar moieties were confirmed in whole cell hydrolysates as assessed by gas-liquid chromatography (GLC) which in addition, also showed the presence of galactose and xylose. However, marked differences in cell surface carbohydrate structures were observed. Wheat germ agglutinin, which binds to sialic acid and/or d-GlcNAc-containing residues, shows selective agglutinin activities for P. francai and Phytomonas sp., while Bandeiraea simplicifolia II agglutinin (which recognizes d-GlcNAc units) specifically bound to Phytomonas sp. Helix pomatia agglutinin which binds to D-GalNAc-containing residues reacted preferentially with Phytomonas sp. and P. serpens. Con A, which recognizes D-Man-like receptors, agglutinates all the phytomonads; however, the higher interaction was observed with Phytomonas sp. P. francai was selectively agglutinated in the presence of E. coli fimbrial lectin. Fluorescence WGA binding was significantly decreased by N-acetylglucosaminidase activities and the cell agglutination was not altered by neuraminidase treatment, suggesting the presence of an exposed D-GlcNAc moiety on the P. francai and Phytomonas sp. surfaces. Binding studies with [125I]-WGA essentially confirmed the fluorescence WGA binding and agglutination assays. 相似文献