Use of ammonium in nutrient solutions

Three experiments were conducted in greenhouse under hydroponic conditions to study the response of wheat to: i) different ammonium/nitrate (NH₄/NO₃) ratios, ii) the application of NH₄ during different phenological states, and iii) the addition of calcium carbonate (CaCO₃) for maximum replacement of NO₃ by NH₄. Small amounts of NH₄ considerably increased yield and grain quality. The best response was observed with a 2/5 ratio NH₄/NO₃ (meq/L). The application of small fractions of NH4 during grain fill increased production. Dry matter (DM) production decreased when large quantities of NH₄ were applied. However, when CaCO₃ was used in amounts similar to those of NH₄, it was possible to neutralize the acidifing effect of reduced nitrogen (N) and to recuperate DM and grain production, thus increasing the harvest index.     

Mango tree pruning hay in substitution of elephant grass in cattle diet

This experiment was conducted to evaluate the effect of different levels of substitution (0, 33.3, 66.7, and 100 %) of elephant grass by hay of mango tree pruning (HMTP) on intake and digestibility in cattle and on the in vitro gas production. Moreover, the effect of tannin in HMTP on the gas production and in vitro degradability of the dry matter was evaluated, using polyethylene glycol (PEG). The intake and digestibility were evaluated in a double 4?×?4 square Latin design, using eight Holstein intact bulls. To evaluate the gas production and degradability, in vitro semi-automated gas production technique was used. The substitution of elephant grass by HMTP decreased the intake (P?<?0.05) and the digestibility (P?<?0.05) of the nutrients and also the gas production (P?<?0.05). Furthermore, the utilization of PEG as a tannin-complexing agent increased the gas production and degradability of the HMTP (P?<?0.05). It was concluded that the high cell wall lignification and the presence of tannin limit the use of HMTP as the only source of roughage in cattle diets.     

Enhanced tolerance of photosynthesis to high-light and drought stress in Pseudotsuga menziesii seedlings grown in ultraviolet-B radiation

We investigated the effects of an ambient dose of ultraviolet-B (UV-B) radiation on chamber-grown Pseudotsuga menziesii var. glauca (Beissn.) Franco (Douglas-fir) seedlings, to determine if the presence of UV-B radiation in the growth light regime induces tolerance to environmental stresses such as high light and drought. Douglas-fir seedlings were grown without UV-B radiation or with 6 kJ m-2 day-1 of biologically effective UV-B, which is ambient for the intermountain regions of Idaho. Non-stressed seedlings grown with UV-B radiation had 35% lower seedling dry mass, 36% higher concentrations of UV-B absorbing compounds per unit leaf area, 30% lower stomatal frequencies, 25% lower light-saturated photochemical efficiencies of Photosystem II and 45% lower light-saturated stomatal conductance than non-stressed seedlings grown without UV-B radiation. After 4 days of high-light stress, seedlings grown with UV-B radiation had 32% higher light-saturated carbon assimilation rates (A(CO2)) than seedlings grown without UV-B radiation. After water was withheld from the seedlings for up to 15 days, seedlings grown with UV-B radiation had 50% higher A(CO2) and 40% higher seedling water potentials than seedlings grown without UV-B radiation. The results support the hypothesis that UV-B radiation can act as an environmental signal to induce tolerance to high-light and drought stress in Douglas-fir seedlings. Possible mechanisms for the enhanced stress tolerance are discussed.     

Chemical composition of lignocellulosic biomass in the wood of <Emphasis Type="Italic">Abies religiosa</Emphasis> across an altitudinal gradient

Tree adaptation to environment has been extensively studied. However, little is known about the variations in structure and chemical composition of lignocellulosic biomass (LB) in relation to altitudinal gradient. We wonder, are there significant variations in the LB in the wood across an altitudinal gradient? To answer this, we carried out a study of Abies religiosa. Wood samples were collected from 36 trees, grown between 3000 and 3500 masl, and then subjected to gravimetric and FTIR (Fourier Transform Infrared) spectroscopic analyses. The gravimetric results showed a proportion of 54.81 ± 2.20 % cellulose, 12.37 ± 1.33 % hemicellulose and 24.68 ± 1.16 % of insoluble lignin. Using the principal components analysis with analysis of variance (ANOVA), significant differences were found at 3100 and 3200 masl in two independent components related to both hemicellulose and lignin, through gravimetry as well as the spectroscopic bands assigned to the carbonyl groups of these polymers, respectively. However, the observed changes in chemical composition of LB did not follow a linear relationship with respect to the altitudinal gradient, which suggests that complex environmental interactions could also be playing an important role. Also, there were significant differences (p < 0.05) in two of the empirical indexes calculated from the FTIR analysis.     

Growth and yield modelling of <Emphasis Type="Italic">Acacia mangium</Emphasis> in Colombia

To study the growth and yield of Acacia mangium in the Caribbean region of Colombia, allometric equations of total volume and aboveground plus coarse roots biomass were fitted as a function of the tree’s diameter at breast height (dbh). The von Bertalanffy’s growth model and 59, 0.1 ha plots (0.55–9.55 years old) were used to develop site index (SI) curves at 6 years base age. Then, using the state-space approach, stand growth and yield models were developed for basal area, volume and biomass. The results show that A. mangium is a very promising species for timber production, atmospheric carbon removal and soil restoration because it grows very fast even in mining degraded soils. On average sites it reaches 15 m in height in 3 years. However, early and reiterated thinning coupled with initial mortality by cattle invasion of the very young understocked plantations are producing relatively low yields.     

Antimicrobial and free radical scavenging activity of Gentianella nitida

The antimicrobial and free radical scavenging activity of the ethanol extract and fractions of Gentianella nitida have been assessed. The most susceptible microorganisms were Candida albicans, Trichophyton mentagrophytes and Microsporum gypseum. The antifungal activity was concentrated in the 90% methanol and nonsoluble fractions, while the radical scavenging activity was stronger in the ethyl acetate and nonsoluble fractions.