Viability of OPS Vitrified Sheep Embryos After Direct Transfer

The aim of this study was to evaluate the viability in the effect of open pulled straw (OPS) vitrification procedure of sheep embryos after direct transference. Embryos were produced in vivo and cryopreserved in slow freezing or OPS vitrification. The survival rates of cryopreserved embryos were compared to non-frozen standard pattern. In a first set of experiments, embryos at morula and blastocyst stages were dived in ethylene glycol (1.5 M) and frozen in an automatic freezer. After being thawed, they were directly or indirectly transferred to ewes recipient. A second group of embryos were drawn into OPS and plunged into liquid nitrogen after being exposed at room temperature for 1 min and 45 s in 10% EG plus 10% dimethyl sulphoxide (DMSO), then again for 30 s in 20% EG + 20% DMSO + 0.5 M sucrose. After being warmed, embryos were also directly transferred using a French mini straw as the catheter for the transplantation process or after in vitro dilution of cryoprotectants (two-step-process). No significant difference was observed among fresh, frozen or vitrified embryos on pregnancy rate (50.0%, 38.6% and 55.8%). However, when we evaluated only the direct transference, the pregnancy rate of OPS vitrified embryos was higher than that of frozen embryos (57.1% vs 34.8%) (p = 0.07). In addition, vitrified morulae had a higher pregnancy rate than the one with frozen embryos (64.0% vs 38.9%) (p = 0.07). Finally, our results indicate that OPS vitrification technique in association with direct transference improves the viability of sheep embryos with potential applications to field conditions.     

Water limitations to carbon exchange in old-growth and young ponderosa pine stands

We investigated the impact of seasonal soil water deficit on the processes driving net ecosystem exchange of carbon (NEE) in old-growth and recently regenerating ponderosa pine (Pinus ponderosa Doug. ex Laws.) stands in Oregon. We measured seasonal patterns of transpiration, canopy conductance and NEE, as well as soil water, soil temperature and soil respiration. The old-growth stand (O) included two primary age classes (50 and 250 years), had a leaf area index (LAI) of 2.1 and had never been logged. The recently regenerating stand (Y) consisted predominantly of 14-year-old ponderosa pine with an LAI of 1.0. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. By August, soil volumetric water content within the upper 30 cm had declined to a seasonal minimum of 0.07 at both sites. Between April and June, both stands showed similar rates of transpiration peaking at 0.96 mm day(-1); thereafter, trees at the Y site showed increasing drought stress with canopy stomatal resistance increasing 6-fold by mid-August relative to values for trees at the O site. Over the same period, predawn water potential (psi(pd)) of trees at the Y site declined from -0.54 to -1.24 MPa, whereas psi(pd) of trees at the O site remained greater than -0.8 MPa throughout the season. Soil respiration at the O site showed a strong seasonal correlation with soil temperature with no discernible constraints imposed by declining soil water. In contrast, soil respiration at the Y site peaked before seasonal maximal soil temperatures and declined thereafter with declining soil water. No pronounced seasonal pattern in daytime NEE was observed at either site between April and September. At the Y site this behavior was driven by concurrent soil water limitations on soil respiration and assimilation, whereas there was no evidence of seasonal soil water limitations on either process at the O site.