Population dynamic and management of <Emphasis Type="Italic">Pinus oocarpa</Emphasis> and <Emphasis Type="Italic">Tabebuia rosea</Emphasis> within silvopastoral systems in Central America

Silvopastoral systems—the management of trees within pastures from natural regeneration or planting—are a strategy to promote sustainable livestock systems and ecosystems services. Timber is one of the products from these systems with potential to increase family revenues. The management of natural regeneration and population dynamics of trees is a feasible way to harvest timber and maintain environmental services. In this research, we modeled the population dynamics of Pinus oocarpa and Tabebuia rosea, two important timber species of silvopastoral systems in Central America. The results showed that farmers manage a significant density of different tree species from natural regeneration. However, only the species with well-known uses or desired services are allowed to remain. The natural regeneration is more impressive in silvopastoral systems with natural grass than those with exotic grass. Farming practices, for instance use of fire for weed control, are the main reasons for low rates of natural regeneration in pastures with exotic grass. The models of population dynamics for both species showed that the sustainable timber harvest plans are a viable activity in pasturelands under natural-regeneration management plans. Innovative farmers are willing to adopt silvicultural practices and management of population dynamics to increase timber revenues and sustainability if forestry regulations for sustainable use of trees in farms are simplified.     

Influences of nitrogen fertilization and energy supplementation for growth perfomance of beef cattle on Alexander grass

This study evaluated the influences of nitrogen fertilizer and energy supplementation cattle on the growth performance of beef cattle. This study was conducted at the Federal University of Technology of Paraná, Dois Vizinhos through continuous grazing on 6.3 ha, divided into nine paddocks. The treatments were: Alexander grass +100 kg ha^?1 of N (N100); Alexander grass + 100 kg ha^?1 of N + 0.5 kg per 100 kg of weight live supplementation of wheat bran (N100S); and Alexander grass +200 kg ha^?1 of N (N200), with an average herbage allowance of 10% for all treatments. Crossbred and non-castrated steers with an average weight of 276 ± 41 kg were used for 107 days. The crude protein from entire plant differed (P < 0.05) between treatments, with the greater value (14.8%) occurring in the N200, and the lesser value (13.3%) occurring in the N100S. The herbage accumulation rate was greater (P < 0.05) in the N200 (55.7  DM ha^?1 d^?1) than that in the N100S and N100 (40.0 and 39.7 kg DM ha^?1 d^?1, respectively). The N100S produced greater (P < 0.05) average daily weight gains (0.815 kg animal day^?1) than did the N200 (0.685 kg animal day^?1) and N100 treatments (0.727 kg animal day^?1).

     

Roughage levels impact on performance and carcass traits of finishing Nellore cattle fed whole corn grain diets

This study was carried out to evaluate the effects of chopped hay levels in high-concentrate diets with whole corn grain (WCG) on performance and carcass traits of finishing Nellore cattle. One hundred and eight 24-month-old Nellore intact males (453 ± 75 kg) were fed one of three WCG-based diets that differed in roughage level: without roughage (WCG), with 5% chopped hay included (WCG5), or with 12% chopped hay included (WCG12) in a block design (based on initial body weight) for 86 days. Animals fed WCG5 or WCG12 had significantly improved on final body weight, dry matter intake, average daily gain, feed efficiency, hot carcass weight, and dressing percentage when compared to those fed WCG. The Longissimus muscle area (P = 0.1108), backfat thickness (BFT; P = 0.6089), and rump fat thickness (P = 0.1798) were not affected by roughage levels. Therefore, using WCG diets without roughage negatively affects the performance of feedlot Nellore cattle but does not affect carcass traits and does lead to the minimum BFT required by the industry.     

Total petroleum hydrocarbons and heavy metals in road-deposited sediments in Tijuana,Mexico

Purpose

A study was carried out to evaluate the concentration of heavy metals (Pb, Cu, Cr, Cd, and Hg) and total petroleum hydrocarbons (TPH) in road-deposited sediments (RDS) from Tijuana, Mexico, and identify their possible sources.

Materials and methods

Thirty RDS samples were randomly collected during the dry season using a brush and dustpan and classified according to construction material, traffic intensity, and land use. Soil samples were collected from a nonurban area and their concentrations were used as background values. For TPH, the samples were quantified gravimetrically after Soxhlet extraction, whereas heavy metals were extracted by acid digestion and their concentrations were measured by atomic absorption spectrometry.

Results and discussion

The mean TPH concentrations for RDS were 4208 mg kg^?1 and ranged from 1186 to 9982 mg kg^?1. For heavy metals, mean concentrations were 31.8, 50.2, 17.1, 0.1, and 0.1 mg kg^?1 for Pb, Cu, Cr, Cd, and Hg, respectively. The Igeo results showed that RDS from Tijuana are moderately to strongly polluted with Pb and Cu and moderately polluted with Cr. Principal component analysis (PCA) showed that Pb, Cu, and Cr could have their origin in tire wear, brake pads, bearings, and bushings.

Conclusions

The findings of this study revealed that RDS from Tijuana are polluted with TPH and heavy metals and that their principal sources are anthropogenic activities.

     

A restricted selection index method based on eigenanalysis

Selection indices, used in animal and plant breeding to select the best individuals for the next breeding cycle, are based on phenotypic observations of traits recorded in candidate individuals. The restrictive selection index (RSI) facilitates maximizing the genetic progress of some characters, while leaving others unchanged. Recently a selection index (SI) was proposed based on the eigen analysis method (ESIM), in which the first eigenvector (from the largest eigenvalue) is used as the SI criterion, and its elements determine the proportion of the trait that contributes to the SI. However, the current ESIM, which has two main limitations, is based on the assumption that the vector of coefficients of the index is equal to the genotypic variance-covariance matrix among the traits multiplied by the vector of economic weights, and does not allow one to restrict the number of traits. In this study, we develop a more general ESIM that has two main features, namely, it makes no assumption concerning the coefficients of the index and it can be generalized to a restrictive ESIM (RESIM). We use two datasets to illustrate the theoretical results and practical use of ESIM and RESIM, and to compare them with standard unrestrictive and restrictive selection indices. The main advantages of RESIM over traditional unrestrictive and restrictive SIs are that its statistical sampling properties are known; its selection responses are equal to or greater than those estimated from the traditional restrictive SI; and it does not require economic weights and thus can be used in practical applications when all or some of the traits need to be improved simultaneously (traditional SIs cannot improve several traits simultaneously if economic weights are not available). Finally, we prove that the coefficients of the traditional RSI belong to the space generated by the eigenvectors of RESIM.     

Improved parameters of Pinus greggii seedling growth and health after inoculation with ectomycorrhizal fungi

Pinus greggii Engelm. ex Parl. is an endemic pine of Mexico with notorious adaptability to eroded, shallow and poor soils. It is widely used in reforestation programmes worldwide. The purpose of the present study is to develop an ectomycorrhizal fungi (ECM) treatment with different native ectomycorrhizal fungal species (collected in P. greggii and Abies vejarii stands) to improve seedling survival of P. greggii. Four-month-old P. greggii var. greggii seedlings were inoculated with ground fruiting bodies of the ECM species Astraeus spp., Boletus barrowsii, Geastrum minimum, Lactarius deliciosus var. deterrimus, Russula cf. atroglauca, Russula spp., Suillus caerulescens, as well as a mixture of three species (Russula sp., R. lutea and L. deliciosus) and soil litter with mycelium from the base of a fruiting body of L. deliciosus. Agronomic variables, and total phosphorous and glucosamine contents were measured in P. greggii seedlings. Inoculated treatments with B. barrowsii, Geastrum minimum and S. caerulescens showed increases in seedling height and basal diameter as well as dry shoot biomass compared with those of the control plants. Geastrum minimum, B. barrowsii and R. xerampelina significantly increased values of dry weight compared with that of the control. Inoculation of soil litter from the base of a fruiting body of L. deliciosus induced the maximum glucosamine response (40.2 mg g^?1 of dry root biomass). Geastrum minimum, a fungus collected in P. greggii stands, enhanced basal diameter of pine seedlings in the nursery. Fungal species B. barrowsii, Suillus caerulescens, Russula cf. atroglauca and Russula spp. from the Abies forest improved plant quality in terms of the Dickson quality index and root and shoot biomass, compared with those of the control.     

Carbon sequestration and biodiversity of re-growing miombo woodlands in Mozambique

Land management in tropical woodlands is being used to sequester carbon (C), alleviate poverty and protect biodiversity, among other benefits. Our objective was to determine how slash-and-burn agriculture affected vegetation and soil C stocks and biodiversity on an area of miombo woodland in Mozambique, and how C stocks and biodiversity responded once agriculture was abandoned. We sampled twenty-eight 0.125 ha plots that had previously been cleared for subsistence agriculture and had been left to re-grow for 2 to ∼25 years, and fourteen 0.25 ha plots of protected woodlands, recording stem diameter distributions and species, collecting wood for density determination, and soil from 0 to 0.3 m for determination of %C and bulk density. Clearance for agriculture reduced stem wood C stocks by 19.0 t C ha⁻¹. There were significant relationships between period of re-growth and basal area, stem numbers and stem biomass. During re-growth, wood C stocks accumulated at 0.7 t C ha⁻¹ year⁻¹. There was no significant difference in stem C stocks on woodlands and on abandoned farmland 20–30 years old. Soil C stocks in the top 0.3 m on abandoned land had a narrower range (21–74 t C ha⁻¹) than stocks in woodland soils (18–140 t C ha⁻¹). There was no discernible increase in soil C stocks with period of re-growth, suggesting that the rate of accumulation of organic matter in these soils was very slow. The re-growing plots did not contain the defining miombo species, and total stem numbers were significantly greater than in woodland plots, but species richness and diversity were similar in older abandonments and miombo woodlands. Wood C stocks on abandoned farmland were capable of recovery within 2–3 decades, but soil C stocks did not change on this time-scale. Woodland soils were capable of storing >100 t C ha⁻¹, whereas no soil on a re-growing area exceeded 74 t C ha⁻¹, so there is a potential for C sequestration in soils on abandoned farmland. Management should focus on identifying C-rich soils, conserving remaining woodlands to protect soil C and preserve defining miombo species, and on investigating whether fire control on recovering woodland can stimulate accumulation of soil C and greater tree biomass, and restore defining miombo species.     

Decomposition of chestnut litterfall and eight-year soil chemical changes under a no-tillage management system in Northern Portugal

? Chestnut stands (Castanea sativa Mill.) for fruit production, in Northern Portugal, are subjected to frequent soil tillage operations, which is considered a threat for the system sustainability.

? The effects of replacement of conventional tillage by the no-tillage system in chestnut stands on decomposition and nutrient dynamics of leaf litter and burs were evaluated, using the litterbag methodology. Amounts of mass and nutrients in the organic layers, and chemical characteristics of the 0–20 cm top soil layer were assessed after eight years.

? The mass loss and release of N, P, Ca and Mg from both leaves and burs buried in the soil were faster than from those placed on the soil surface. Burs decomposed and released nutrients more slowly than leaf litter. The no-tillage system led to the formation of organic layers, which retained great amounts of N (249.2 kg ha^?1) and Ca (215.5 kg ha^?1). Such a management system increased the concentration of organic C and nutrients in the 0–5 cm top soil layer, but significant differences were only observed for exchangeable Ca.

? The no-tillage system may enhance organic C accumulation regarding the conventional system, due to the increment in both organic and mineral soil layers.

     

Identification of microsatellite markers linked to the blast resistance gene <Emphasis Type="Italic">Pi-1(t)</Emphasis> in rice

The present work was conducted to identify microsatellite markers linked to the rice blast resistance gene Pi-1(t) for a marker-assisted selection program. Twenty-four primer pairs corresponding to 19 microsatellite loci were selected from the Gramene database (www. gramene.org) considering their relative proximity to Pi-1(t) gene in the current rice genetic map. Progenitors and DNA bulks of resistant and susceptible families from F₃ segregating populations of a cross between the near-isogenic lines C101LAC (resistant) and C101A51 (susceptible) were used to identify polymorphic microsatellite markers associated to this gene through bulked segregant analysis. Putative molecular markers linked to the blast resistance gene Pi-1(t) were then used on the whole progeny for linkage analysis. Additionally, the diagnostic potential of the microsatellite markers associated to the resistance gene was also evaluated on 17 rice varieties planted in Latin America by amplification of the specific resistant alleles for the gene in each genotype. Comparing with greenhouse phenotypic evaluations for blast resistance, the usefulness of the highly linked microsatellite markers to identify resistant rice genotypes was evaluated. As expected, the phenotypic segregation in the F₃ generation agreed to the expected segregation ratio for a single gene model. Of the 24 microsatellite sequences tested, six resulted polymorphic and linked to the gene. Two markers (RM1233*I and RM224) mapped in the same position (0.0 cM) with the Pi-1(t) gene. Other three markers corresponding to the same genetic locus were located at 18.5 cM above the resistance gene, while another marker was positioned at 23.8 cM below the gene. Microsatellite analysis on elite rice varieties with different genetic background showed that all known sources of blast resistance included in this study carry the specific Pi-1(t) allele. Results are discussed considering the potential utility of the microsatellite markers found, for MAS in rice breeding programs aiming at developing rice varieties with durable blast resistance based on a combination of resistance genes. Centro Internactional de Agricultura Tropical (CIAT) institute where the research was carried out