Is nitrogen transfer among plants enhanced by contrasting nutrient‐acquisition strategies?

Nitrogen (N) transfer among plants has been found where at least one plant can fix N₂. In nutrient‐poor soils, where plants with contrasting nutrient‐acquisition strategies (without N₂ fixation) co‐occur, it is unclear if N transfer exists and what promotes it. A novel multi‐species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non‐mycorrhizal cluster‐rooted plants in nutrient‐poor soils with mycorrhizal mesh barriers. We foliar‐fed plants with a K¹⁵NO₃ solution to quantify one‐way N transfer from ‘donor’ to ‘receiver’ plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient‐acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N₂ fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM‐only plants. We demonstrate N transfer between plants of contrasting nutrient‐acquisition strategies, and a preferential enrichment of cluster‐rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient‐poor soils.     

Phylogenetic signal in the evolution of body colour and spicule skeleton in calcareous sponges

Some of the morphological characters used in Porifera taxonomy have often been shown to be inconsistent. In the present study, we tested the phylogenetic coherence of currently used taxonomic characters of the calcarean genus Clathrina. For this, 20 species of Clathrina and three other calcinean genera (Ascandra, Guancha, and Leucetta) were sequenced for the ITS and D2 region of the 28S ribosomal DNA. Maximum‐likelihood and maximum‐parsimony algorithms were used to reconstruct phylogenetic trees. Deep divergences were observed in our tree and Clathrina was shown to be paraphyletic. The major split in our topology showed a clear‐cut distinction between sponges with and without tetractine spicules. Moreover, a group of yellow‐coloured Clathrina was clearly separated from the remaining white‐coloured species. Our results show that the presence of diactines, water‐collecting tubes, the degree of cormus anastomosis, and actine shapes do not correlate with the major clades of the calcinean phylogeny. On the other hand, the presence of tripods, the absence of tetractines, and the presence of spines in the apical actine of tetractines seem to be good synapomorphies for clades in our tree. Our results demonstrate that skeleton characters can be reliably used in higher level taxonomy in Clathrinida. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 1026–1034.     

CONSUMER INVOLVEMENT AND EVALUATION OF GREEN PEAS1

This paper reports the effect of consumer involvement on overall acceptance of frozen peas used in green salad and the effect of consumer involvement on the consumer's ability to perceive variations in a set of physical/chemical characteristics such as AIS (Alcohol Insoluble Solids) and color. The results reveal that consumers with high involvement evaluate 16 experimentally varied pea samples more in accordance with quality indicators used in the industry than consumers with low involvement. In our study 61% of the consumers were highly involved. For low involved consumers there was no relation between average acceptance and the quality indicators used by producer/retailer and retailer/consumer. High involved consumers could identify more of the physical/chemical variation in the pea samples than the low involved consumers. The results stress the importance of a preliminary segmentation of consumers. The low involved consumers do not seem to have any specific preferences for any of the samples included in the study although samples are varied considerably with respect to size, color and amount of sucrose. It may be considered as indifference. An obvious conclusion to draw from the results of this study is to concentrate on the highly involved consumers in further product development.     

Flight during oviposition reduces maternal egg provisioning and influences offspring development in Pararge aegeria (L.)

As a result of increased habitat fragmentation in anthropogenic landscapes, flying insects may be required to travel over larger distances in search of resources such as suitable host plants for oviposition. The oögenesis–flight syndrome hypothesis predicts that physiological constraints caused by an overlap in the resources used by thoracic muscles during flight and during oögenesis (e.g. carbohydrates, lipids and water) result in a resource trade‐off, with any resources used during flight no longer available for reproduction. Increased flight costs could therefore potentially result in a decrease in maternal provisioning of eggs. In the present study, the speckled wood butterfly Pararge aegeria (L.) is used to investigate whether increased flight during oviposition results in changes in maternal investment in eggs and whether this contributes to variation in the development of offspring in subsequent life stages. Forcing females to fly during oviposition directly influences egg size and embryonic development time, and indirectly influences (through changes in egg size) egg hatching success and larval development time. These effects are mediated through ‘selfish maternal effects’, with mothers forced to fly maximizing their fecundity at the expense of investment to individual egg size. The present study demonstrates that a change in maternal provisioning as a result of increased flight during oviposition has the potential to exert nongenetic cross‐generational fitness effects in P. aegeria. This could have important consequences for population dynamics, particularly in fragmented anthropogenic landscapes.     

Greenhouse gas fluxes from tropical peatlands in south‐east Asia

The lowland peatlands of south‐east Asia represent an immense reservoir of fossil carbon and are reportedly responsible for 30% of the global carbon dioxide (CO₂) emissions from Land Use, Land Use Change and Forestry. This paper provides a review and meta‐analysis of available literature on greenhouse gas fluxes from tropical peat soils in south‐east Asia. As in other parts of the world, water level is the main control on greenhouse gas fluxes from south‐east Asian peat soils. Based on subsidence data we calculate emissions of at least 900 g CO₂ m^?2 a^?1 (～250 g C m^?2 a^?1) for each 10 cm of additional drainage depth. This is a conservative estimate as the role of oxidation in subsidence and the increased bulk density of the uppermost drained peat layers are yet insufficiently quantified. The majority of published CO₂ flux measurements from south‐east Asian peat soils concerns undifferentiated respiration at floor level, providing inadequate insight on the peat carbon balance. In contrast to previous assumptions, regular peat oxidation after drainage might contribute more to the regional long‐term annual CO₂ emissions than peat fires. Methane fluxes are negligible at low water levels and amount to up to 3 mg CH₄ m^?2 h^?1 at high water levels, which is low compared with emissions from boreal and temperate peatlands. The latter emissions may be exceeded by fluxes from rice paddies on tropical peat soil, however. N₂O fluxes are erratic with extremely high values upon application of fertilizer to wet peat soils. Current data on CO₂ and CH₄ fluxes indicate that peatland rewetting in south‐east Asia will lead to substantial reductions of net greenhouse gas emissions. There is, however, an urgent need for further quantitative research on carbon exchange to support the development of consistent policies for climate change mitigation.     

The Humidity Response of Stomata and its Measurement

Meidner, H. 1987. The humidity response of stomata and its measurement.—J.exp. Bot. 38:877–882. Using artificial membranes of constant conductance with vapourpressures below the membranes of 2?33 kPa (saturated) and 2?26kPa (97% saturated) it was found that an automated water vapourdiffusion porometer registered a change in conductance. In otherwords, it underestimated the conductance when the vapour pressurebelow the membranes was only 97% saturated. This is becausethe programmed computation of the conductance assumes that thespace below the membrane is at all times saturated. The implicationsfor measuring leaf conductance with these instruments is discussedin connection with the humidity response of stomata to a stepwiseincrease in the vapour pressure difference between the leafinterior and the atmosphere. This response appears to involvea lowering of the vapour pressure in the sub-stomatal spaceand, therefore, a transient opening movement which can be detectedby sensitive mass flow porometry. It is concluded that in cases in which a transient opening movementprecedes partial stomatal closure the humidity response to anincrease in vapour pressure difference cannot be due to vapourloss direct from the guard cells. Key words: Humidity, transients, stomata     

Pressure Effects on Catalysis and Control of Catalysis by Liver Fructose Diphosphatase from an Off-Shore Benthic Fish

SYNOPSIS: At low temperature (2°C), in the absence of FDPand Mg²⁺, the enzyme fructose disphosphatase (FDPase), extractedfrom the liver of an off-shore benthic Coryphaenoides species,is inactivated by exposures to relatively low pressures. Thesubstrate, FDP, and the cofactor, Mg²⁺, protect against thisinactivation, so that catalysis per se is not retarded by pressure.In contrast, at alkaline pH, pressure dramatically acceleratesthe catalytic rate when FDP and Mg²⁺ are saturating. The volumechange of activation, V*, for Coryphaenoides FDPase under theseconditions is about –40 cm³/mole. At low concentrationsof FDP and saturating concentrations of cofactor, the reactionrate at alkaline pH is pressure-independent. Similarly, at lowconcentrations of Mg²⁺ but saturating concentration of FDP,the reaction rate is pressure-independent. The K_m for FDP doesnot change measureably with pressure, while the K_a for Mg²⁺increases slightly with pressure. Under conditions of low (probablephysiological) FDP and Mg²⁺ concentrations, it is evident thatthe reaction rate is determined by the kinetic characteristicsof the enzyme and not by its energy-volume relationships, asituation which would appear to be of functional and selectivesignificance to an organism living under constantly high hydrostaticpressure. AMP is a potent specific inhibitor of CoryphaenoidesFDPase. The K₄ for AMP is essentially pressure-independent bothat neutral and alkaline pH, suggesting that efficiency of AMPcontrol of this enzyme is comparable at all pressures likelyto be encountered in nature.     

Precise Measurements of Carbon Dioxide Exchange by Illuminated Leaves near the Compensation Point

The results of precise measurements of rates of carbon dioxideassimilation at low external concentrations of carbon dioxideand of rates of carbon dioxide output into virtually carbondioxide-freeair show that linear extrapolations of the carbon dioxide intakecurve plotted against the external concentrations of carbondioxide give an exaggerated estimate of the rate of carbon dioxideoutput from illuminated leaves into carbon dioxide-free air. The shape of the exchange curve suggests that the rate of endogenousproduction of carbon dioxide changes at external concentrationsin the region of the carbon dioxide compensation point ().     

Compensation Points and Carbon Dioxide Enrichment for Lettuce Grown Under Glass in Winter

Measurements of , the minimum intercellular-space carbon dioxideconcentration or carbon dioxide compensation point, made attwo temperatures and at light intensities from 15 to 1,500 f.c.,were used to study the relation between the compensation pointsfor light and carbon dioxide. This was found to be hyperbolicand consistent with the Warburg–Maskell model for photosynthesis.The apparently beneficial effects of carbon dioxide enrichmentof the atmosphere at increased temperature, found in practicewith lettuce or other crops grown under glass at light intensitiesthat might be expected to be severely limiting, must be in partdue to the reduction of the light compensation point at highcarbon dioxide concentration.