Morphology and biomass production of prairie cordgrass on marginal lands

Prairie cordgrass (Spartina pectinata Link.) is indigenous throughout most of the continental United States and Canada to 60°N latitude and is well suited to marginal land too wet for maize (Zea mays L.) and switchgrass (Panicum virgatum L.). Evaluations of prairie cordgrass in Europe and North America indicated it has high potential for biomass production, relative to switchgrass, in short‐season areas. Our objective was to describe morphology and biomass production and partitioning in mature stands of ‘Red River’ prairie cordgrass and determine biomass production of natural populations on marginal land. This study was conducted from 2000 to 2008 in eastern South Dakota. Mean biomass production of mature stands of Red River was 12.7 Mg ha^?1. Leaves composed >88% of the biomass, and 60% of the tillers had no internodes. Belowground biomass to a depth of approximately 25 cm, not including roots, was 21 Mg ha^?1. Tiller density ranged from 683 tillers m^?2 for a 10‐year‐old stand to 1140 tillers m^?2 for a 4‐year‐old stand. The proaxis was composed of about eight phytomers, with rhizomes originating at proximal nodes and erect tillers at distal nodes. Vegetative propagation was achieved by both phalanx and guerilla growth. Differences among natural populations for biomass were expressed on gravelly marginal land. However, production, averaged across populations, was low (1.37 Mg ha^?1) and comparable to ‘Cave‐In‐Rock’ switchgrass (1.67 Mg ha^?1) over a 4‐year period. The large carbon storage capacity of prairie cordgrass in proaxes and rhizomes makes it useful for carbon sequestration purposes. Prairie cordgrass should be compared with switchgrass and other C₄ perennial grasses along environmental gradients to determine optimum landscape positions for each and to maximize bioenergy production and minimize inputs.     

The Effect of High Concentrations of Heavy Water on Root Morphogenesis in Zea mays

The effect of high concentrations of heavy water on young rootsof Zea mays was investigated. Submersion for 24 hrs. in solutionsof 80–90 per cent. D₂O will temporarily stop growth ofthe primary root. During the treatment period the root-tip regionswill swell as the result of radial cell enlargement, primarilyin the cortical region. Upon removal from D₂O growth will resume,initially at a slower rate than controls but ultimately at similarmaximum rates. Lateral root production is inhibited in thatportion of the primary root which is the region of elongationat time of treatment. However, in the swollen region lateralroot formation is accentuated. The mitotic index drops sharplyupon introduction of the primary roots into 80 per cent. D₂O.Within 12 hrs. the index drops to zero and remains at this leveluntil the roots are removed from the heavy water. The mitoticindex then rises again, reaching control values within 24 hrs.It is suggested that the gentle, temporary inhibitory actionof D₂O makes this substance a useful tool in morphogenetic investigations.     

Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte,lower Cambrian of North Greenland

Stein, M., Peel, J.S., Siveter, D.J. & Williams, M. 2009: Isoxys (Arthropoda) with preserved soft anatomy from the Sirius Passet Lagerstätte, lower Cambrian of North Greenland. Lethaia, Vol. 43, pp. 258–265. Isoxys volucris is the most commonly occurring species in the lower Cambrian Sirius Passet Lagerstätte of North Greenland. Newly identified material allows a first, limited, account of the ventral morphology of this species, hitherto known only by the morphology of its shield. The antennula is large and robust, composed of about seven articles armed with spines, and was probably not sensorial. The postantennular limbs are serially similar, biramous with a large paddle‐shaped exopod fringed with setae. It is possible that the animal possessed a furca. The inner lamella, lining the ventral surface of the shield is recognised in Isoxys for the first time. Comparisons with other congeneric species of which aspects of the ventral morphology are known, show similarities with Isoxys auritus from China, reconsidered here, but indicate differences in antennular morphology with other species as currently understood. □Cambrian, Greenland, Isoxys, soft anatomy, Sirius Passet, palaeoecology.     

Ecology and genetics of speciation in Ficedula flycatchers

Birds have for long been popular study objects in speciation research. Being easy to observe in the field, they have traditionally been particularly important in studies of behavioural and ecological factors in speciation, whereas the genetic aspects of the process have been studied in other organisms, such as Drosophila. More recently, however, a stronger genetic focus has been placed on speciation research also in birds. Here, we review ecological, behavioural and genetic studies on speciation in the pied flycatcher (Ficedula hypoleuca) and the collared flycatcher (Ficedula albicollis). These well‐studied birds provide among the few proposed examples of the process of reinforcement of premating isolation, and the evidence for reinforcement is strong. They are further characterized by having strong intrinsic postzygotic barriers (female hybrid sterility), yet the two species appear to be very similar ecologically. This is in stark contrast to another well‐studied bird complex, Darwin’s finches, in which the species differ vastly in ecologically important traits but have no developmental problems arising from genetic incompatibilities, and where no evidence for reinforcement is found. In the flycatchers, sex chromosome linkage of genes affecting traits associated with both pre‐ and postzygotic barriers to gene exchange is likely to facilitate reinforcement. We discuss whether such sex‐linkage may be common in birds. The contrast between flycatchers and Darwin’s finches indicate that speciation in birds cannot always be understood mainly as a result of divergent natural selection (‘ecological speciation’), and generalizations from one system may lead us astray. We discuss to what extent insight from research on the flycatchers may point to fruitful avenues for future research on bird speciation and specifically call for a more systematic effort to simultaneously investigate ecology, behaviour and genetics of birds caught in the process of speciation.