Field evaluation of switchgrass seedlings divergently selected for crown node placement

Excessive crown node elevation of warm-season grass seedlings is a major limitation to successful establishment. Crown node placement at or above the soil surface limits the opportunity for adventitious root development at the crown node. Switchgrass (Panicum virgatum L.) germplasm selected for low- (LC) and elevated- (EC) crown node placement (at 1.5 (μmol m−1 s−1 photosynthetic photon flux density), has been developed from ‘Alamo’ Switchgrass. The objective of this study was to determine if differences in crown node placement and other seedling morphological traits exist among Alamo (nonselected, parental), LC, and EC germplasm and if these differences affect seedling establishment in the field. Seeds were planted during April and May at Beeville, Stephenville, and College Station, TX. Each location was established with six blocks each consisting of a 2-m row of Alamo, LC, or EC seed. Seeds were planted at a 1-cm depth. Three to 10 seedlings were marked at soil level, then dug for detailed seedling measurements. There were no genotype by location interactions for any trait measured. Emergence was more rapid at Beeville for all entries because of prewatering and better soil conditions. Averaged for the three locations, final emergence was 47, 37, and 30% for LC, EC, and Alamo. Mesocotyl length of LC germplasm averaged 5.9 mm compared with 8.4 and 9.1 mm for Alamo and EC germplasm, respectively. Even though LC seedlings had shorter mesocotyles and consequently lower crown node placement than EC or Alamo seedlings, these traits may not be directly responsible for greater establishment success

Livestock selective behaviour in natural grasslands challenges the concept of plant preference in the elaboration of a successful diet.

Conciliating livestock production and conservation of grassland biodiversity is now an imperative. We propose that a way to reach that goal is to take advantage of the natural tendency of herbivores to exploit environmental heterogeneity. However, it would go against the well-rooted concept that mammalian herbivores have invariable preference for some plants. Preference was defined as being “what the animal select when given the minimum of physical constraints” (Parsons et al. 1994). But after decades of studies, the concept of preference remains particularly inefficient in predicting observed patterns of selection by herbivores (e.g. Newman et al. 1992; Parsons et al. 1994; Provenza 2006). We performed detailed descriptions of cattle diet composition and foraging strategy in highly diversified natural pasture of South Brazil. We present here preliminary results that seriously question the concept of plant preference

Continuous bite monitoring: a method to assess the foraging dynamics of herbivores in natural grazing conditions

International audienceAccurate estimates of bite mass and variations in the short-term intake rate of grazing herbivores has been historically considered as a fundamental methodological difficulty, a difficulty that increases with the complexity of the feeding environment. Improving these methodologies will help understand foraging behaviours in natural grazing conditions, where habitat structure and interactions among different forages influence feeding decisions and patterns. During the past 30 years, we have been developing the ‘continuous bite-monitoring’ method, an observational method that allows continuous assessment of foraging behaviours, including bite mass, instantaneous intake rate and food selection, in simple to complex feeding environments. The centrepiece of the method is a ‘bite-coding grid’ where bites are categorised by structural attributes of the forage to reflect differences in bite masses. Over the years, we have been using this method with goats, sheep, llamas and cattle across a range of different habitats. After reviewing the development of the method, we detail its planning and execution in the field. We illustrate the method with a study from southern Brazilian native Pampa grassland, showing how changes in the forages consumed by heifers strongly affect short-term intake rate during meals. Finally, we emphasise the importance of studying animals grazing in their natural environments to first identify the relevant processes that can later be tested in controlled experiments

Asymmetric azidohydroxylation of styrene derivatives mediated by a biomimetic styrene monooxygenase enzymatic cascade

Enantioenriched azido alcohols are precursors for valuable chiral aziridines and 1,2-amino alcohols, however their chiral substituted analogues are difficult to access. We established a cascade for the asymmetric azidohydroxylation of styrene derivatives leading to chiral substituted 1,2-azido alcohols via enzymatic asymmetric epoxidation, followed by regioselective azidolysis, affording the azido alcohols with up to two contiguous stereogenic centers. A newly isolated two-component flavoprotein styrene monooxygenase StyA proved to be highly selective for epoxidation with a nicotinamide coenzyme biomimetic as a practical reductant. Coupled with azide as a nucleophile for regioselective ring opening, this chemo-enzymatic cascade produced highly enantioenriched aromatic α-azido alcohols with up to >99% conversion. A bi-enzymatic counterpart with halohydrin dehalogenase-catalyzed azidolysis afforded the alternative β-azido alcohol isomers with up to 94% diastereomeric excess. We anticipate our biocatalytic cascade to be a starting point for more practical production of these chiral compounds with two-component flavoprotein monooxygenases.BT/Biocatalysi