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1.
A decisive set of steps in the terrestrial carbon (C) cycle is the fixation of atmospheric C by plants and the subsequent C‐transfer to rhizosphere microorganisms. With climate change winters are expected to become milder in temperate ecosystems. Although the rate and pathways of rhizosphere C input to soil could be impacted by milder winters, the responses remain unknown. To address this knowledge‐gap, a winter‐warming experiment was established in a seminatural temperate grassland to follow the C flow from atmosphere, via the plants, to different groups of soil microorganisms. In situ 13CO2 pulse labelling was used to track C into signature fatty acids of microorganisms. The winter warming did not result in any changes in biomass of any of the groups of microorganisms. However, the C flow from plants to arbuscular mycorrhizal (AM) fungi, increased substantially by winter warming. Saprotrophic fungi also received large amounts of plant‐derived C—indicating a higher importance for the turnover of rhizosphere C than biomass estimates would suggest—still, this C flow was unaffected by winter warming. AM fungi was the only microbial group positively affected by winter warming—the group with the closest connection to plants. Winter warming resulted in higher plant productivity earlier in the season, and this aboveground change likely induced plant nutrient limitation in warmed plots, thus stimulating the plant dependence on, and C allocation to, belowground nutrient acquisition. The preferential C allocation to AM fungi was at the expense of C flow to other microbial groups, which were unaffected by warming. Our findings imply that warmer winters may shift rhizosphere C‐fluxes to become more AM fungal‐dominated. Surprisingly, the stimulated rhizosphere C flow was matched by increased microbial turnover, leading to no accumulation of soil microbial biomass.  相似文献   

2.
Two key plant adaptations for phosphorus (P) acquisition are carboxylate exudation into the rhizosphere and mycorrhizal symbioses. These target different soil P resources, presumably with different plant carbon costs. We examined the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on amount of rhizosphere carboxylates and plant P uptake for 10 species of low‐P adapted Kennedia grown for 23 weeks in low‐P sand. Inoculation decreased carboxylates in some species (up to 50%), decreased plant dry weight (21%) and increased plant P content (23%). There was a positive logarithmic relationship between plant P content and the amount of rhizosphere citric acid for inoculated and uninoculated plants. Causality was indicated by experiments using sand where little citric acid was lost from the soil solution over 2 h and citric acid at low concentrations desorbed P into the soil solution. Senesced leaf P concentration was often low and P‐resorption efficiencies reached >90%. In conclusion, we propose that mycorrhizally mediated resource partitioning occurred because inoculation reduced rhizosphere carboxylates, but increased plant P uptake. Hence, presumably, the proportion of plant P acquired from strongly sorbed sources decreased with inoculation, while the proportion from labile inorganic P increased. Implications for plant fitness under field conditions now require investigation.  相似文献   

3.
While the biochemical function of calcium and calmodulin‐dependent protein kinase (CCaMK) is well studied, and plants impaired in the expression of CCaMK are known not to be infected by arbuscular mycorrhizal fungi (AMF) in glasshouse studies, the whole‐plant and ecological consequences of CCaMK silencing are not well understood. Here we show that three independently transformed lines of Nicotiana attenuata plants silenced in CCaMK (irCCaMK) are neither infected by Rhizophagus irregularis in the glasshouse nor by native fungal inoculum in the field. The overall fungal community of field‐grown roots did not differ significantly among empty vector (EV) and the transgenic lines, and the bacterial communities only showed minor differences, as revealed by the alpha‐diversity parameters of bacterial OTUs, which were higher in EV plants compared with two of the three transformed lines, while beta‐diversity parameters did not differ. Furthermore, growth and fitness parameters were similar in the glasshouse and field. Herbivory‐inducible and basal levels of salicylic acid, jasmonic acid and abscisic acid did not differ among the genotypes, suggesting that activation of the classical defence pathways are not affected by CCaMK silencing. Based on these results, we conclude that silencing of CCaMK has few, if any, non‐target effects.  相似文献   

4.
Interactions between plants and root‐associated fungi can affect the assembly, diversity, and relative abundances of tropical plant species. Host–symbiont compatibility and some degree of host specificity are prerequisites for these processes to occur, and these prerequisites may vary with host abundance. However, direct assessments of whether specificity of root‐associated fungi varies with host abundance are lacking. Here, in a diverse tropical forest in Los Tuxtlas, Mexico, we couple DNA metabarcoding with a sampling design that controls for host phylogeny, host age, and habitat variation, to characterize fungal communities associated with the roots of three confamilial pairs of host species that exhibit contrasting (high and low) relative abundances. We uncovered a functionally and phylogenetically diverse fungal community composed of 1,038 OTUs (operational taxonomic units with 97% genetic similarity), only 14 of which exhibited host specificity. Host species was a significant predictor of fungal community composition only for the subset of OTUs composed of putatively pathogenic fungi. We found no significant difference in the number of specialists associating with common versus rare trees, but we found that host abundance was negatively correlated with the diversity of root fungal communities. This latter result was significant for symbiotrophs (mostly arbuscular mycorrhizal fungi) and, to a lesser extent, for pathotrophs (mostly plant pathogens). Thus, root fungal communities differ between common and rare trees, which may impact the strength of conspecific negative density dependence. Further studies from other tropical sites and host lineages are warranted, given the role of root‐associated fungi in biodiversity maintenance.  相似文献   

5.
The strength of species interactions influences strongly the structure and dynamics of ecological systems. Thus, quantifying such strength is crucial to understand how species interactions shape communities and ecosystems. Although the concepts and measurement of interaction strength in food webs have received much attention, there has been comparatively little progress in the context of mutualism. We propose a conceptual scheme for studying the strength of plant–animal mutualistic interactions. We first review the interaction strength concepts developed for food webs, and explore how these concepts have been applied to mutualistic interactions. We then outline and explain a conceptual framework for defining ecological effects in plant–animal mutualisms. We give recommendations for measuring interaction strength from data collected in field studies based on a proposed approach for the assessment of interaction strength in plant–animal mutualisms. This approach is conceptually integrative and methodologically feasible, as it focuses on two key variables usually measured in field studies: the frequency of interactions and the fitness components influenced by the interactions.  相似文献   

6.
The arbuscular mycorrhizal (AM) symbiosis is widespread throughout the plant kingdom and important for plant nutrition and ecosystem functioning. Nonetheless, most terrestrial ecosystems also contain a considerable number of non‐mycorrhizal plants. The interaction of such non‐host plants with AM fungi (AMF) is still poorly understood. Here, in three complementary experiments, we investigated whether the non‐mycorrhizal plant Arabidopsis thaliana, the model organism for plant molecular biology and genetics, interacts with AMF. We grew A. thaliana alone or together with a mycorrhizal host species (either Trifolium pratense or Lolium multiflorum) in the presence or absence of the AMF Rhizophagus irregularis. Plants were grown in a dual‐compartment system with a hyphal mesh separating roots of A. thaliana from roots of the host species, avoiding direct root competition. The host plants in the system ensured the presence of an active AM fungal network. AM fungal networks caused growth depressions in A. thaliana of more than 50% which were not observed in the absence of host plants. Microscopy analyses revealed that R. irregularis supported by a host plant was capable of infecting A. thaliana root tissues (up to 43% of root length colonized), but no arbuscules were observed. The results reveal high susceptibility of A. thaliana to R. irregularis, suggesting that A. thaliana is a suitable model plant to study non‐host/AMF interactions and the biological basis of AM incompatibility.  相似文献   

7.
It is believed that climate change will influence most of interactions that sustain life on Earth. Among these, the recruitment exerted by plants in their roots vicinity can change, leading to differential assemblages of microbiomes in the rhizosphere. We approached this issue analyzing the variations in the composition of bacterial communities in the rhizosphere of sugarcane cultivated under two concentrations of atmospheric CO2 (350 or 700 ppm). In addition to the analysis of bacterial community, the use of DNA‐SIP allowed the comparison of bacterial groups assimilating roots exudates (based on 13C‐labeled DNA) in both conditions, in a period of 8 days after the CO2 pulse. The separation of 13C‐DNA indicated the low but increasing frequency of labeling in the rhizosphere, as averages of 0.6, 2.4 and 5.0% of total DNA were labeled after 2, 4, and 8 days after the 13CO2 pulse, respectively. Based on large‐scale sequencing of the V6 region in the gene 16S rRNA, we found an increase in the bacterial diversity in the 13C‐DNA along the sampling period. We also describe the occurrence of distinct bacterial groups assimilating roots exudates from sugarcane cultivated under each CO2 concentration. Bacilli, Gammaproteobacteria, and Clostridia showed high affinity for the C‐sources released by sugarcane under 350 ppm of CO2, while under elevated concentration of CO2, the assimilation of roots exudates was prevalently made by members of Bacilli and Betaproteobacteria. The communities became more similar along time (4 and 8 days after CO2 pulse), in both concentrations of CO2, electing Actinobacteria, Sphingobacteriia, and Alphaproteobacteria as the major cross‐feeders on sugarcane exudates. In summary, we described the bacterial groups with higher affinity to assimilate roots exudates in the rhizosphere of sugarcane, and also demonstrated that the rhizosphere community can be differentially assembled in a future scenario with increased contents of CO2.  相似文献   

8.
土壤微生物量磷(Microbial Biomass Phosphorus, MBP)是土壤磷组分中最为活跃的形态,在土壤磷素的形态转化与生物地球化学循环过程中起着关键作用,是植物可利用磷的重要来源。研究土壤MBP库容的大小对于充分认识微生物的固磷潜力和掌握土壤磷素循环与转化能力意义重大。以我国北方农田3种典型的土壤-作物体系为研究对象,基于定点采样,通过分析测定采集的362个表层(0—30 cm)土壤样品来量化不同土壤-作物体系MBP库容的大小。结果表明:黑土-春玉米、潮土-冬小麦/夏玉米、灰漠土-棉花体系表层土壤MBP平均含量分别为17.36、14.45、8.75 mg/kg,且不同土壤-作物体系间MBP含量存在显著差异;3种土壤-作物体系表层土壤(0—30 cm)MBP库容的大小分别为83.60、54.26、39.80 kg P/hm~2,其储存的磷在数量上相当于当季作物需磷量的1.10—2.73倍,表明土壤MBP库是农田生态系统中一个不容忽视的巨大有效养分磷储库。其库容的大小受土壤性质和气候因素的共同影响,土壤pH、有机碳、年均气温和年均降雨量是我国北方农田土壤MBP库容大小的主...  相似文献   

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12.
We present a simple and effective high‐throughput experimental platform for simultaneous and continuous monitoring of water relations in the soil–plant–atmosphere continuum of numerous plants under dynamic environmental conditions. This system provides a simultaneously measured, detailed physiological response profile for each plant in the array, over time periods ranging from a few minutes to the entire growing season, under normal, stress and recovery conditions and at any phenological stage. Three probes for each pot in the array and a specially designed algorithm enable detailed water‐relations characterization of whole‐plant transpiration, biomass gain, stomatal conductance and root flux. They also enable quantitative calculation of the whole plant water‐use efficiency and relative water content at high resolution under dynamic soil and atmospheric conditions. The system has no moving parts and can fit into many growing environments. A screening of 65 introgression lines of a wild tomato species (Solanum pennellii) crossed with cultivated tomato (S. lycopersicum), using our system and conventional gas‐exchange tools, confirmed the accuracy of the system as well as its diagnostic capabilities. The use of this high‐throughput diagnostic screening method is discussed in light of the gaps in our understanding of the genetic regulation of whole‐plant performance, particularly under abiotic stress.  相似文献   

13.
In spite of their putative relevance to host functioning, in‐depth knowledge of sponge microbiome stability over time is scarce. This study tackles the temporal maintenance of bacterial and archaeal assemblages in the model host Sarcotragus spinosulus along three successive years. Prokaryotic communities were profiled by polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE) and 454‐pyrosequencing of S. spinosulus‐derived 16S rRNA gene amplicons. Prevailing bacterial phyla were Actinobacteria, Acidobacteria, Proteobacteria, Poribacteria, PAUC34f, Chloroflexi and Bacteroidetes, with Bacteroidetes, Chloroflexi and Poribacteria showing different abundances over the years. At the approximate species level (operational taxonomic units, OTUs, defined at 97% sequence similarity), no major changes in bacterial richness and composition were found through time. Nearly 50% of all detected bacterial symbionts (96 in 205 OTUs) were recovered from all sampling years, whereas a taxonomically equivalent community of less dominant bacteria characterized the transient sponge microbiota. Despite the evidence for temporal symbiont maintenance, an intriguing cumulative degree of variation between individuals was unravelled, with all the surveyed sponge specimens sharing only 27 bacterial OTUs. Archaeal communities were dominated by one single symbiont of the candidate genus Nitrosopumilus (Thaumarchaeota), known for its ability to aerobically oxidize ammonia to nitrite. Only few bacterial ammonia oxidizers consistently occurred in S. spinosulus across the years as documented by PCR‐DGGE fingerprinting. In conclusion, prokaryotic symbionts of S. spinosulus display a state of dynamic stability shaped by the interplay between the maintenance of dominant players and turnover of less prevalent community members, in time and across host individuals, with no apparent consequences to holobiont functioning.  相似文献   

14.
The lithostratigraphy, calcareous nannofossil biostratigraphy, carbon‐ and oxygen‐isotope stratigraphy and gamma‐ray profile are presented for the Skælskør‐1 core, eastern Denmark. The correlation of carbon isotopes to Gubbio (Italy) and ODP Site 762C (Indian Ocean) provides the chronostratigrahical framework of the core through a tie to magnetostratigraphy. Two new carbon‐isotope excursions are defined for the uppermost Maastrichtian of the core and prove useful for long‐distance correlation. Twenty stratigraphic tie‐points are used for correlation of the upper Campanian–Maastrichtian interval by combining carbon‐isotope and gamma‐ray variations. Significant dissimilarities in the gamma‐ray profiles of the Danish Basin cores preclude the sole use of this tool for basin‐scale correlations. Bulk oxygen‐isotopes and semi‐quantitative abundance changes in the warm‐water calcareous nannofossil Watznaueria barnesiae and the cool‐water Kamptnerius magnificus highlight the following past changes in sea‐surface temperatures (SSTs): relatively warm late Campanian SSTs, cooling across the Campanian–Maastrichtian boundary and through the early Maastrichtian, warming across the early–late Maastrichtian transition, cooling in the late Maastrichtian, intense warming in the latest Maastrichtian chron C29r, followed by a very short episode of cooling immediately before the Cretaceous–Palaeogene boundary. The late Campanian–Maastrichtian evolution in sea water temperatures inferred from the Danish Basin is similar to that delineated at tropical latitude oceanic sites.  相似文献   

15.
Aim Hydrological disconnection of floodplains from rivers is among the top factors threatening river‐floodplain ecosystems. To keep enough floodplain area is of great importance to biodiversity conservation. In the Yangtze River floodplain, most lakes were disconnected from the mainstream by dams in 1950–1970s. By analysing fish diversity data, we aim at determining the effects of river‐lake disconnection on fish diversity, at estimating the minimum protected area of river‐connected lakes and at proposing a holistic strategy for fish conservation in the mid‐lower reaches of the river. Location The Yangtze River floodplain, China. Methods We collected recorded data of fish diversity of 30 Yangtze floodplain lakes. Species–area relationships were analysed and compared between river‐connected and river‐disconnected lakes. Cumulative species–area models were constructed to estimate the minimum protected area of river‐connected lakes. Results River‐lake disconnection reduced fish diversity of Yangtze lakes by 38.1%, so that the river‐connected lakes play an important role in maintaining the floodplain biodiversity. The minimum protected area of river‐connected lakes was estimated to be 14,400 km2. Therefore, we should not only protect the existent connected lakes of 5500 km2, but also reconnect disconnected lakes of at least 8900 km2 in the Yangtze basin. Main conclusions Species–area relationships are of importance in reserve design. We suggest that cumulative species–area model might be more suitable for ecosystems with high connectivity among regions such as floodplains. As the Yangtze River floodplain is an integrative ecosystem, we suggest establishing a holistic nature reserve in the mid‐lower basin for effective conservation of biodiversity.  相似文献   

16.
Fas binding to Fas‐associated death domain (FADD) activates FADD–caspase‐8 binding to form death‐inducing signaling complex (DISC) that triggers apoptosis. The Fas–Fas association exists primarily as dimer in the Fas–FADD complex, and the Fas–FADD tetramer complexes have the tendency to form higher order oligomer. The importance of the oligomerized Fas–FADD complex in DISC formation has been confirmed. This study sought to provide structural insight for the roles of Fas death domain (Fas DD) binding to FADD and the oligomerization of Fas DD–FADD complex in activating FADD–procaspase‐8 binding. Results show Fas DD binding to FADD stabilized the FADD conformation, including the increased stability of the critical residues in FADD death effector domain (FADD DED) for FADD–procaspase‐8 binding. Fas DD binding to FADD resulted in the decreased degree of both correlated and anticorrelated motion of the residues in FADD and caused the reversed correlated motion between FADD DED and FADD death domain (FADD DD). The exposure of procaspase‐8 binding residues in FADD that allows FADD to interact with procaspase‐8 was observed with Fas DD binding to FADD. We also observed different degrees of conformational and motion changes of FADD in the Fas DD–FADD complex with different degrees of oligomerization. The increased conformational stability and the decreased degree of correlated motion of the residues in FADD in Fas DD–FADD tetramer complex were observed compared to those in Fas DD–FADD dimer complex. This study provides structural evidence for the roles of Fas DD binding to FADD and the oligomerization degree of Fas DD–FADD complex in DISC formation to signal apoptosis. Proteins 2013. © 2012 Wiley Periodicals, Inc.  相似文献   

17.
Applying scientific knowledge to confront societal challenges is a difficult task, an issue known as the science–practice gap. In Ecology and Conservation, scientific evidence has been seldom used directly to support decision‐making, despite calls for an increasing role of ecological science in developing solutions for a sustainable future. To date, multiple causes of the science–practice gap and diverse approaches to link science and practice in Ecology and Conservation have been proposed. To foster a transparent debate and broaden our understanding of the difficulties of using scientific knowledge, we reviewed the perceived causes of the science–practice gap, aiming to: (i) identify the perspectives of ecologists and conservation scientists on this problem, (ii) evaluate the predominance of these perspectives over time and across journals, and (iii) assess them in light of disciplines studying the role of science in decision‐making. We based our review on 1563 sentences describing causes of the science–practice gap extracted from 122 articles and on discussions with eight scientists on how to classify these sentences. The resulting process‐based framework describes three distinct perspectives on the relevant processes, knowledge and actors in the science–practice interface. The most common perspective assumes only scientific knowledge should support practice, perceiving a one‐way knowledge flow from science to practice and recognizing flaws in knowledge generation, communication, and/or use. The second assumes that both scientists and decision‐makers should contribute to support practice, perceiving a two‐way knowledge flow between science and practice through joint knowledge‐production/integration processes, which, for several reasons, are perceived to occur infrequently. The last perspective was very rare, and assumes scientists should put their results into practice, but they rarely do. Some causes (e.g. cultural differences between scientists and decision‐makers) are shared with other disciplines, while others seem specific to Ecology and Conservation (e.g. inadequate research scales). All identified causes require one of three general types of solutions, depending on whether the causal factor can (e.g. inadequate research questions) or cannot (e.g. scientific uncertainty) be changed, or if misconceptions (e.g. undervaluing abstract knowledge) should be solved. The unchanged predominance of the one‐way perspective over time may be associated with the prestige of evidence‐based conservation and suggests that debates in Ecology and Conservation lag behind trends in other disciplines towards bidirectional views ascribing larger roles to decision‐makers. In turn, the two‐way perspective seems primarily restricted to research traditions historically isolated from mainstream conservation biology. All perspectives represented superficial views of decision‐making by not accounting for limits to human rationality, complexity of decision‐making contexts, fuzzy science–practice boundaries, ambiguity brought about by science, and different types of knowledge use. However, joint knowledge‐production processes from the two‐way perspective can potentially allow for democratic decision‐making processes, explicit discussions of values and multiple types of science use. To broaden our understanding of the interface and foster productive science–practice linkages, we argue for dialogue among different research traditions within Ecology and Conservation, joint knowledge‐production processes between scientists and decision‐makers and interdisciplinarity across Ecology, Conservation and Political Science in both research and education.  相似文献   

18.
In flowering plants, the interaction of pollen tubes with female tissues is important for the accomplishment of double fertilization. Little information is known about the mechanisms that underlie signalling between pollen tubes and female tissues. In this study, two Arabidopsis pollen tube‐expressed CrRLK1L protein kinases, Buddha's Paper Seal 1 (BUPS1) and BUPS2, were identified as being required for normal tip growth of pollen tubes in the pistil. They are expressed prolifically in pollen and pollen tubes and are localized on the plasma membrane of the pollen tube tip region. Mutations in BUPS1 drastically reduced seed set. Most of the bups1 mutant pollen tubes growing in the pistil exhibited a swollen pollen tube tip, leading to failure of fertilization. The bups2 pollen tubes had a slightly abnormal morphology but could still accomplish double fertilization. The bups1 bups2 double mutant exhibited a slightly enhanced phenotype compared to the single bups1 mutants. The BUPS1 proteins could form homomers and heteromers with BUPS2, whereas BUPS2 could only form heteromers with BUPS1. The BUPS proteins could interact with the Arabidopsis pollen‐expressed RopGEFs in the yeast two‐hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. The results indicated that the BUPSs may mediate normal polar growth of pollen tubes in the pistil.  相似文献   

19.
The performance of a bioreactor in meeting process goals is affected by the microorganism used, medium composition, and operating conditions. A typical bioreactor uses a supervisory control and data acquisition (SCADA) system for control, and a combination of software and hardware tools for real‐time data analysis. However, when the process is disrupted by utility or instrumentation failure, typical process controllers may be unable to reinstate normal operating conditions before the cells in the reactor shift to unfavorable metabolic regimes. The objective of this study is to examine how the response of a controller affects process recovery when disruptive incidences occur under a process analytical technology (PAT) framework. The process used for this investigation is the production of lethal toxin‐neutralizing factor (LTNF) by Escherichia coli (E. coli), which is controlled by a decoupled input–output‐linearizing controller (DIOLC). The performance of the DIOLC is compared to a proportional integral derivative (PID) controller subjected to the same conditions. The disruptions are introduced manually and the effect of controller action on process recovery and LTNF synthesis is measured in terms of peak purity and concentration. It is observed that DIOLC performs better after reinstating operating conditions and results in a meaningful improvement in performance.  相似文献   

20.
Humans are changing the biosphere by exerting pressure on land via different land uses with variable intensities. Quantifying the relative importance of the land‐use composition and intensity for communities may provide valuable insights for understanding community dynamics in human‐dominated landscapes. Here, we evaluate the relative importance of the land‐use composition versus land‐use intensity on the bird community structure in the highly human‐dominated region surrounding Paris, France. The land‐use composition was calculated from a land cover map, whereas the land‐use intensity (reverse intensity) was represented by the primary productivity remaining after human appropriation (NPPremaining), which was estimated using remote sensing imagery. We used variance partitioning to evaluate the relative importance of the land‐use composition versus intensity for explaining bird community species richness, total abundance, trophic levels, and habitat specialization in urban, farmland, and woodland habitats. The land‐use composition and intensity affected specialization and richness more than trophic levels and abundance. The importance of the land‐use intensity was slightly higher than that of the composition for richness, specialization, and trophic levels in farmland and urban areas, while the land‐use composition was a stronger predictor of abundance. The intensity contributed more to the community indices in anthropogenic habitats (farmland and urban areas) than to those in woodlands. Richness, trophic levels, and specialization in woodlands tended to increase with the NPPremaining value. The heterogeneity of land uses and intensity levels in the landscape consistently promoted species richness but reduced habitat specialization and trophic levels. This study demonstrates the complementarity of NPPremaining to the land‐use composition for understanding community structure in anthropogenic landscapes. Our results show, for the first time, that the productivity remaining after human appropriation is a determinant driver of animal community patterns, independent of the type of land use.  相似文献   

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