Unilateral ablation of follicles >= 4 mm leads to compensatory follicle response from the contralateral ovary in heifers

In each of two experiments, heifers were assigned to a control group and a unilaterally ablated (UA) group (n = 6/group). In the UA group, follicles >= 4 mm in the left ovary were ablated by transvaginal ultrasound-guided technique at Hour 0 (8:00 AM) on the day of ovulation. Follicles in the CL-bearing right ovary remained intact. In Experiment 1, ablations continued until the next ovulation, and new follicles emerged in the right ovary in 9 of 14 (64%) waves. The number of follicles/wave (combined, 6.4 +/- 0.4) did not differ between groups. In Experiment 2, follicles were counted at Hours 0, 4, 8, 12, and 24; the resistance index (RI) for blood flow in the ovarian pedicle was determined at Hours 0 and 12; and blood samples were collected every hour from Hours 0 to 12 and Hour 24. An increase (P < 0.05) in the number of follicles in the follicle-intact ovary began at Hour 4 with complete compensation by Hour 24. Concentrations of FSH did not change between Hours 0 and 24 in the UA group but decreased (P < 0.05) in the controls by Hour 7. At Hour 12, RI to the right ovary approached being lower (P < 0.06) in the UA group than in the control group. Results indicated that unilateral ablation of follicles >= 4 mm led to compensatory follicle response in the follicle-intact ovary, and initially circulatory FSH concentrations were maintained and blood flow to the follicle-intact ovary increased. (c) 2012 Elsevier Inc. All rights reserved.

Soil-nutrient availability modifies the response of young pioneer and late successional trees to elevated carbon dioxide in a Brazilian tropical environment

The aim of this work was to determine the impact of three levels of [CO2] and two levels of soil-nutrient availability on the growth and physiological responses of two tropical tree species differing in their ecological group: Croton urucurana Baillon, a pioneer (P), and also Cariniana legalis (Martius) Kuntze, a late succession (LS). We aimed to test the hypothesis that P species have stronger response to elevated [CO2] than LS species as a result of differences in photosynthetic capacity and growth kinetics between both functional groups. Seedlings of both species were grown in open-top-chambers under high (HN) or low (LN) soil-nutrient supply and exposed to ambient (380 mu mol mol(-1)) or elevated (570 and 760 mu mol mol(-1)) [CO2]. Measurements of gas exchange, chlorophyll a fluorescence, seedling biomass and allocation were made after 70 days of treatment. Results suggest that elevated [CO2] significantly enhances the photosynthetic rates (A) and biomass production in the seedlings of both species, but that soil-nutrient supply has the potential to modify the response of young tropical trees to elevated [CO2]. In relation to plants grown in ambient [CO2], the P species grown under 760 mu mol mol(-1) [CO2] showed increases of 28% and 91% in A when grown in LN and HN, respectively. In P species grown under 570 mu mol mol(-1) [CO2], A increased by 16% under HN, but there was no effect in LN. In LS species, the enhancement of A by effect of 760 mu mol mol(-1) [CO2] was 30% and 70% in LN and HN, respectively. The exposure to 570 mu mol mol(-1) [CO2] stimulated A by 31% in HN, but was no effect in LN. Reductions in stomatal conductance (g(s)) and transpiration (E), as a result of elevated [CO2] were observed. Increasing the nutrient supply from low to high increased both the maximum rate of carboxylation (V-cmax) and maximum potential rate of electron transport (J(max)). As the level of [CO2] increased, both the V-cmax and the J(max) were found to decrease, whereas the J(max)/V-cmax ratio increased. In the LS species, the maximum efficiency of PSII (F-v/F-m) was higher in the 760 mu mol mol(-1) [CO2] treatment relative to other [CO2] treatments. The results suggest that when grown under HN and the highest [CO2], the performance of the P species C. urucurana, in terms of photosynthesis and biomass enhancement, is better than the LS species C. legalis. However, a larger biomass is allocated to roots when C. legalis seedlings were exposed to elevated [CO2]. This response would be an important strategy for plant survival and productivity of the LS species under drought stresses conditions on tropical environments in a global-change scenario. (C) 2011 Elsevier B.V. All rights reserved.