How do plants respond to nutrient shortage by biomass allocation?

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.     

How do vertebrates respond to mast seeding?

Mast‐seeding is the synchronized and intermittent production of a large seed crop by a population of plants. The cascading effects of masting on wildlife have been well documented in granivorous rodents. Yet, the effects of mast‐seeding are potentially further reaching, since a number of generalist species can take advantage of mast years. We employed a full‐text search algorithm to identify all papers that discussed effects of mast‐seeding on wildlife, in addition to typical searches of titles and abstracts. We aimed to evaluate the breadth of wildlife species for which mast years are thought to be important drivers. In addition, we tested three hypotheses derived from past reviews: 1) species with lower reproductive potential (lower average litter size) are more likely to show aggregative responses to mast‐seeding, 2) species with lower body sizes (lower mobility) are more likely to show reproductive responses, and 3) indirect consumers of mast (predators) are more likely to show aggregative responses than direct consumers. We found 186 articles including reports of response of 122 species of vertebrates to mast‐seeding. Expectations were partly confirmed: relationships 1) and 2) held for mammals, but not for birds. However, 3) direct consumers were more likely than indirect consumers to show aggregative responses. Our tests of the first two hypotheses question the generality of past predictions for taxa other than mammals. Our test of the third hypothesis suggests that responses of direct and indirect consumers might depend on the type of resource pulse. Many of the examples in our analysis come from systems in which wildlife responses to mast have been less rigorously documented than the examples in past reviews. They suggest the range of wildlife responses to mast‐seeding are more taxonomically and ecologically diverse than past reviews have widely recognized and point to directions for future research. Synthesis Mast seeding is a pulsed resource with numerous cascading effects on wildlife. Yet, because masting is largely unpredictable, it is inherently difficult to study. We developed a full‐text search algorithm to identify incidental reports as well as deliberate studies of vertebrate reactions to masting. We found that the type of response to mast seeding (reproductive or through immigration) varies predictably as a function of life history traits (litter size and body mass) in mammals, but not in birds. Our literature search also shows that responses to mast‐seeding are more taxonomically and ecologically diverse than past reviews have recognized.     

How do plants achieve tolerance to phosphorus deficiency? Small causes with big effects

Genotypic differences in phosphorus (P) uptake from P-deficient soils may be due to higher root growth or higher external root efficiency (micrograms of P taken up per square centimeter of root surface area). Both factors are highly interrelated because any additional P provided by externally efficient roots will also stimulate root growth. It will be necessary to separate both factors to identify a primary mechanism to formulate hypotheses on pathways and genes causing genotypic differences in P uptake. For this purpose, a plant growth model was developed for rice (Oryza sativa) grown under highly P-deficient conditions. Model simulations showed that small changes in root growth-related parameters had big effects on P uptake. Increasing root fineness or the internal efficiency for root dry matter production (dry matter accumulated per unit P distributed to roots) by 22% was sufficient to increase P uptake by a factor of three. That same effect could be achieved by a 33% increase in external root efficiency. However, the direct effect of increasing external root efficiency accounted for little over 10% of the 3-fold increase in P uptake. The remaining 90% was due to enhanced root growth as a result of higher P uptake per unit root size. These results demonstrate that large genotypic differences in P uptake from a P-deficient soil can be caused by rather small changes in tolerance mechanisms. Such changes will be particularly difficult to detect for external efficiency because they are likely overshadowed by secondary root growth effects.     

How do aphids respond to elevated CO2?

The performance of herbivore insects is determined directly by the quality of host plants. Elevated CO₂ induced a decline in foliar nitrogen, which reduced the growth of chewing insects. Phloem-sucking insects (i.e. aphid), however, had species-specific responses to elevated CO₂ and were the only feeding guild to respond positively to elevated CO₂. Although many studies attempt to illuminate the interaction between aphids and plants under elevated CO₂, few studies can explain why some aphids are more successful than other chewing insects in elevated CO₂. Elevated CO₂ leads to a re-allocation of the carbon and nitrogen resources in plant tissue, which increases the thickness of the microscopic structures of leaves, reduces amino acids content of leaf phloem sap and increases the secondary metabolites. Considering the complexity of aphid–plant interactions, it is difficult and unreasonable to predict the general response of aphids to elevated CO₂ using a single plant component. Instead, it is more likely that aphids are able to overcome the disadvantages of the indirect effects of elevated CO₂ by reducing developmental times and increasing fecundity under elevated CO₂ conditions. Our results provide several clues to why some aphids are successful in elevated CO₂ conditions. We review recent studies of the effects of elevated CO₂ on aphids and discuss the effects of elevated CO₂ on aphid performance on crops using cotton and cereal aphids as examples.     

How do cyanobacteria sense and respond to light?

Cyanobacteria exhibit numerous responses to changes in the intensity and spectral quality of light. What sensors do cyanobacteria use to detect light and what are the mechanisms of signal transduction? The publication in 1996 of the complete genome sequence of the cyanobacterium Synechocystis 6803 provided a tremendous stimulus for research in this field, and many light‐sensors and signal transducers have now been identified. However, our knowledge of cyanobacterial light‐signal transduction remains fragmentary. This review summarizes what we know about the ways in which cyanobacteria perceive light, some of the ways which they respond to light signals and some recent achievements in elucidating the signal transduction mechanisms. Some problems in characterizing cyanobacterial signal transduction pathways are outlined and alternative experimental strategies are discussed.     

How do plants make mitochondria?

Plant mitochondria can differ in size, shape, number and protein content across different tissue types and over development. These differences are a result of signaling and regulatory processes that ensure mitochondrial function is tuned in a cell-specific manner to support proper plant growth and development. In the last decade, the processes involved in mitochondrial biogenesis are becoming clearer, including; how dormant seeds transition from empty promitochondria to fully functional mitochondria with extensive cristae structures and various biochemical activities, the regulation of nuclear genes encoding mitochondrial proteins via regulators of the diurnal cycle in plants, the mitochondrial stress response, the targeting of proteins to mitochondria and other organelles and connections between the respiratory chain and protein import complexes. All these findings indicate that mitochondrial function is a part of an integrated cellular network, and communication between mitochondria and other cellular processes extends beyond the known exchange or transport of metabolites. Our current knowledge now needs to be used to gain more insight into the molecular components at various levels of this hierarchical and complex regulatory and communication network, so that mitochondrial function can be predicted and modified in a rational manner.     

How do herbivorous insects respond to drought stress in trees?

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant–insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon‐based and nitrogen‐based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap‐sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought‐induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO₂ levels. There is a need for larger, temperate and tropical forest‐scale drought experiments to look at herbivorous insect responses and their role in tree death.     

Q&A: How do plants respond to cytokinins and what is their importance?

Cytokinins comprise a family of signaling molecules essential for regulating the growth and development of plants, acting both locally and at a distance. Although much is known about their biosynthesis and transport, important open questions remain.     

How do plants feel the heat?

In plants, the heat stress response (HSR) is highly conserved and involves multiple pathways, regulatory networks and cellular compartments. At least four putative sensors have recently been proposed to trigger the HSR. They include a plasma membrane channel that initiates an inward calcium flux, a histone sensor in the nucleus, and two unfolded protein sensors in the endoplasmic reticulum and the cytosol. Each of these putative sensors is thought to activate a similar set of HSR genes leading to enhanced thermotolerance, but the relationship between the different pathways and their hierarchical order is unclear. In this review, we explore the possible involvement of different thermosensors in the plant response to warming and heat stress.     

How do trees respond to species mixing in experimental compared to observational studies?

For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships.     

How do rats respond to playing radio in the animal facility?

In the animal facility, a range of different sounds are present. On the one hand, rats and humans will regard sound and noise differently even within the audible range, but on the other hand mice and rats being very adaptable to the environment may adapt to living in a noisy facility with e.g. a radio playing. It was the aim of the present study to investigate whether two different strains of rats had different preferences for different kinds of sound patterns, including radio, and to get an indication of whether they are able to distinguish between different sound patterns. The present preference study revealed that rats were able to distinguish between different sound patterns. They showed a clear preference for silence to anything else, which may be taken as an indication that they feel disturbed by the sound from the speaker.     

How do soil fauna and soil microbiota respond to beech forest growth?

The dynamics and performance of soil biota during forest rotation were studied in monoculture beech stands forming a chronosequence of four different age-classes(30,62,111,153 yr).Biomass was monitored in major groups of microflora,microfauna,mesofauna,and macrofauna.Resource availability(litter layer,soil organic mater),biomass of the two dominant decomposer groups(microflora,earthworms)as well as the biomass of mesofauna and microfauna were found to remain quite stable during forest succession.Nevertheles...     

How do visual neurons respond in the real world?

Natural visual stimuli have been reported to evoke neural responses with brief, intense firing events. This has important implications for how visual information is encoded. A recent experiment measured the responses of visual neurons in the natural environment, circumventing many limitations of laboratory simulations while still retaining tight experimental control. Under these conditions, neurons fired intensely at precise, discrete times, validating that this firing regime is relevant to natural vision.     

How do beetle assemblages respond to cyclonic disturbance of a fragmented tropical rainforest landscape?

There are surprisingly few studies documenting effects of tropical cyclones (including hurricanes and typhoons) on rainforest animals, and especially insects, considering that many tropical forests are frequently affected by cyclonic disturbance. Consequently, we sampled a beetle assemblage inhabiting 18 upland rainforest sites in a fragmented landscape in north-eastern Queensland, Australia, using a standardised sampling protocol in 2002 and again 12 months after the passage of Severe Tropical Cyclone Larry (March 2006). The spatial configuration of sites allowed us to test if the effects of a cyclone and those from fragmentation interact. From all insect samples we extracted 12,568 beetles of 382 species from ten families. Beetle species composition was significantly different pre-and post-cyclone although the magnitude of faunal change was not large with 205 species, representing 96% of all individuals, present in both sampling events. Sites with the greatest changes to structure had the greatest changes in species composition. At the site level, increases in woody debris and wood-feeding beetle (Scolytinae) counts were significantly correlated but changes in the percent of ground vegetation were not mirrored by changes in the abundance of foliage-feeding beetles (Chrysomelidae). The overall direction of beetle assemblage change was consistent with increasing aridity, presumably caused by the loss of canopy cover. Sites with the greatest canopy loss had the strongest changes in the proportion of species previously identified in the pre-cyclone study as preferring arid or moist rainforest environments. The magnitude of fragmentation effects was virtually unaltered by the passage of Cyclone Larry. We postulate that in the short-term the effects of cyclonic disturbance and forest fragmentation both reduce the extent of moist, interior habitat.     

How to characterize meiotic functions in plants?

Our understanding of plant meiosis is rapidly increasing thanks to the model Arabidopsis thaliana. Here we present the results of a screening for meiotic mutants carried out with a library containing 30,719 T-DNA insertion lines. An average of one mutant per 1000 lines was recovered. Several phenotypic classes could be distinguished and are presented. In parallel, 39 proteins known to be involved in meiosis in non-plant organisms were chosen and a search was performed for homologue sequences in the completed Arabidopsis thaliana genome. Approximately 30% of the meiotic related sequences showed similarities with one or several Arabidopsis putative genes. The relevance of forward versus reverse genetics in order to characterize meiotic functions is discussed.