6,669 research outputs found
Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas
Capturing the full growth potential in crops under future elevated CO₂ (eCO₂) concentrations would be facilitated by improved understanding of eCO₂ effects on uptake and use of mineral nutrients. This study investigates interactions of eCO₂, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO₂ effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO₂ were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon Growth of M. truncatula was increased by AM at low P conditions at both CO₂ levels and eCO₂×AM interactions were sparse. Elevated CO₂ had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO₂, but effects were inconsistent across genes and species. The ability of eCO₂ to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO₂-rich climates.Iver Jakobsen, Sally E. Smith, F. Andrew Smith, Stephanie J. Watts-Williams, Signe S. Clausen and Mette Grønlun
Nutrient interactions and arbuscular mycorrhizas: a meta-analysis of a mycorrhiza-defective mutant and wild-type tomato genotype pair
BACKGROUND AND AIMS Arbuscular mycorrhizas (AM) enhance plant uptake of a range of mineral nutrients from the soil. Interactions between nutrients in the soil and plant, are complex, and can be affected by AM. Using a mycorrhiza-defective mutant tomato genotype (rmc) and its wild-type (76R), provides a novel method to study AM functioning. METHODS We present a meta-analysis comparing tissue nutrient concentration (P, Zn, K, Ca, Cu, Mg, Mn, S, B, Na, Fe), biomass and mycorrhizal colonisation data between the 76R and rmc genotypes, across a number of studies that have used this pair of tomato genotypes. Particular attention is paid to interactions between soil P or soil Zn, with tissue nutrients. RESULTS For most nutrients, the difference in concentration between genotypes was significantly affected either by soil P, soil Zn, or both. When soil P was deficient, AM were particularly beneficial in terms of uptake of not only P, but other nutrients as well. CONCLUSIONS Colonisation by AMF significantly affects the uptake of many soil macro- and micro-nutrients. Furthermore, the soil P and Zn status also influences the difference in nutrient concentrations between mycorrhizal and non-mycorrhizal plants. The interactions identified by this meta-analysis provide a basis for future research in this area.Stephanie J. Watts-Williams, Timothy R. Cavagnar
Using mycorrhiza-defective mutant genotypes of non-legume plant species to study the formation and functioning of arbuscular mycorrhiza: a review
A significant challenge facing the study of arbuscular mycorrhiza is the establishment of suitable non-mycorrhizal treatments that can be compared with mycorrhizal treatments. A number of options are available, including soil disinfection or sterilisation, comparison of constitutively mycorrhizal and non-mycorrhizal plant species, comparison of plants grown in soils with different inoculum potential and the comparison of mycorrhiza-defective mutant genotypes with their mycorrhizal wild-type progenitors. Each option has its inherent advantages and limitations. Here, the potential to use mycorrhiza-defective mutant and wild-type genotype plant pairs as tools to study the functioning of mycorrhiza is reviewed. The emphasis of this review is placed on non-legume plant species, as mycorrhiza-defective plant genotypes in legumes have recently been extensively reviewed. It is concluded that non-legume mycorrhiza-defective mutant and wild-type pairs are useful tools in the study of mycorrhiza. However, the mutant genotypes should be well characterised and, ideally, meet a number of key criteria. The generation of more mycorrhiza-defective mutant genotypes in agronomically important plant species would be of benefit, as would be more research using these genotype pairs, especially under field conditions.Stephanie J. Watts-Williams, Timothy R. Cavagnar
A Glass of Milk: The Rocha, Nicaragua Goat Project
This panel will talk about their plans to embark on a goat-gifting project in two rural Nicaraguan communities
Solution of the Unanimity Rule on exponential, uniform and scalefree networks: A simple model for biodiversity collapse in foodwebs
We solve the Unanimity Rule on networks with exponential, uniform and
scalefree degree distributions. In particular we arrive at equations relating
the asymptotic number of nodes in one of two states to the initial fraction of
nodes in this state. The solutions for exponential and uniform networks are
exact, the approximation for the scalefree case is in perfect agreement with
simulation results. We use these solutions to provide a theoretical
understanding for experimental data on biodiversity loss in foodwebs, which is
available for the three network types discussed. The model allows in principle
to estimate the critical value of species that have to be removed from the
system to induce its complete collapse.Comment: 4 pages, 3 fig
Statistical Analysis of Airport Network of China
Through the study of airport network of China (ANC), composed of 128 airports
(nodes) and 1165 flights (edges), we show the topological structure of ANC
conveys two characteristics of small worlds, a short average path length
(2.067) and a high degree of clustering (0.733). The cumulative degree
distributions of both directed and undirected ANC obey two-regime power laws
with different exponents, i.e., the so-called Double Pareto Law. In-degrees and
out-degrees of each airport have positive correlations, whereas the undirected
degrees of adjacent airports have significant linear anticorrelations. It is
demonstrated both weekly and daily cumulative distributions of flight weights
(frequencies) of ANC have power-law tails. Besides, the weight of any given
flight is proportional to the degrees of both airports at the two ends of that
flight. It is also shown the diameter of each sub-cluster (consisting of an
airport and all those airports to which it is linked) is inversely proportional
to its density of connectivity. Efficiency of ANC and of its sub-clusters are
measured through a simple definition. In terms of that, the efficiency of ANC's
sub-clusters increases as the density of connectivity does. ANC is found to
have an efficiency of 0.484.Comment: 6 Pages, 5 figure
Growing Scale-Free Networks with Small World Behavior
In the context of growing networks, we introduce a simple dynamical model
that unifies the generic features of real networks: scale-free distribution of
degree and the small world effect. While the average shortest path length
increases logartihmically as in random networks, the clustering coefficient
assumes a large value independent of system size. We derive expressions for the
clustering coefficient in two limiting cases: random (C ~ (ln N)^2 / N) and
highly clustered (C = 5/6) scale-free networks.Comment: 4 pages, 4 figure
Subgraph Centrality in Complex Networks
We introduce a new centrality measure that characterizes the participation of
each node in all subgraphs in a network. Smaller subgraphs are given more
weight than larger ones, which makes this measure appropriate for
characterizing network motifs. We show that the subgraph centrality (SC) can be
obtained mathematically from the spectra of the adjacency matrix of the
network. This measure is better able to discriminate the nodes of a network
than alternate measures such as degree, closeness, betweenness and eigenvector
centralities. We study eight real-world networks for which SC displays useful
and desirable properties, such as clear ranking of nodes and scale-free
characteristics. Compared with the number of links per node, the ranking
introduced by SC (for the nodes in the protein interaction network of S.
cereviciae) is more highly correlated with the lethality of individual proteins
removed from the proteome.Comment: 29 pages, 4 figures, 2 table
Analytical solution of a model for complex food webs
We investigate numerically and analytically a recently proposed model for
food webs [Nature {\bf 404}, 180 (2000)] in the limit of large web sizes and
sparse interaction matrices. We obtain analytical expressions for several
quantities with ecological interest, in particular the probability
distributions for the number of prey and the number of predators. We find that
these distributions have fast-decaying exponential and Gaussian tails,
respectively. We also find that our analytical expressions are robust to
changes in the details of the model.Comment: 4 pages (RevTeX). Final versio
Uptake of zinc and phosphorus by plants is affected by zinc fertiliser material and arbuscular mycorrhizas
Background and Aims Water solubility of zinc (Zn) fertilisers affects their plant availability. Further, simultaneous application of Zn and phosphorus (P) fertiliser can have antagonistic effects on plant Zn uptake. Arbuscular mycorrhizas (AM) can improve plant Zn and P uptake. We conducted a glasshouse experiment to test the effect of different Zn fertiliser materials, in conjunction with P fertiliser application, and colonisation by AM, on plant nutrition and biomass. Methods We grew a mycorrhiza-defective tomato geno-type (rmc) and its mycorrhizal wild-type progenitor(76R) in soil with six different Zn fertilisers ranging in water solubility (Zn sulphate, Zn oxide, Zn oxide (nano), Zn phosphate, Zn carbonate, Zn phosphate carbonate), and supplemental P. We measured plant biomass, Zn and P contents, mycorrhizal colonisation and water use efficiency. Results Whereas water solubility of the Zn fertilisers was not correlated with plant biomass or Zn uptake, plant Zn and P contents differed among Zn fertiliser treatments. Plant Zn and P uptake was enhanced when supplied as Zn phosphate carbonate. Mycorrhizal plants took up more P than non-mycorrhizal plants; the reverse was true for Zn. Conclusions Zinc fertiliser composition and AM have a profound effect on plant Zn and P uptake.Stephanie J. Watts-Williams, Terence W. Turney, Antonio F. Patti, Timothy R. Cavagnar
- …