Proteolytic activity of wild fruits of Bromelia karatas L. of Yucatán, Mexico
Actividad proteolítica de frutos silvestres de Bromelia karatas L. de Yucatán, México
Available online: 2019-04-02
/ pages 157-168
Introduction: Bromeliads are a source of proteases that have not been fully studied.
Objectives: To evaluate the proteolytic activity of wild fruits of Bromelia karatas L. under different temperature, pH and NaCl conditions, and to estimate the thermal stability of their proteases.
Materials and methods: The effect of pH (6, 7, 8, 9, 10 and 12), incubation temperatures (30, 40, 50, 60 and 70 °C) and NaCl concentrations (5, 10 and 20 %) on the proteolytic activity of the fruits was compared. The thermal stability of the proteases was assessed at 30, 50 and 70 °C for 240 minutes. The molecular weights and isoelectric points of the proteases were estimated by non-reducing two-dimensional zymography. The data were analyzed using a one-factor ANOVA and Tukey's test (α = 0.05).
Results and discussion: The proteolytic activity of B. karatas fruit extract (8.59 U·mg-1) was greater than that of Ananas comosus [L.] Merr. variety comosus (3.42 U·mg-1). The activity was higher at pH 6 and 7 and in concentrations lower than 5 % NaCl. Proteases were stable at 30 and 50 °C for 210 minutes. The two-dimensional zymogram, under non-reducing conditions, showed at least 40 light zones with apparent molecular weights between 27.3 and 290 kDa, potentially representing proteases.
Conclusion: The proteases of B. karatas have potential for application in the food industry.
Soil carbon and nitrogen in tropical montane cloud forest, agroforestry and coffee monoculture systems
Carbono y nitrógeno del suelo en los sistemas bosque mesófilo de montaña, agroforestal y monocultivo de café
Available online: 2019-04-02
/ pages 169-184
Introduction: In natural systems and agroecosystems, the study of soil carbon and nitrogen as a function of the type and magnitude of their plant cover is important because the concentration and content of these elements are related to soil fertility and quality and environmental impact.
Objectives: To determine the carbon and nitrogen in the soil as a function of the type and magnitude of the plant cover of tropical montane cloud forest (TMCF) systems, full sun coffee monoculture (FSCM), coffee agroforestry system as a traditional polyculture (CASTP) and coffee agroforestry system as a commercial polyculture (CASCP).
Materials and methods: Plant covers were characterized and quantified. Soil samples were taken at depths of 0 to 10, 10 to 20 and 20 to 30 cm to determine the concentrations and contents of soil organic carbon (SOC) and nitrogen in its total (Nt), organic (Norg), nitrate (NO3-), ammonium (NH4+) and mineral (Nmin) forms.
Results and discussion: The order of magnitude of plant cover was TMCF>CASTP>CASCP>FSCM. The same order was found in SOC (TMCF: 229.33 Mg·ha-1, CASTP: 211.03 Mg·ha-1, CASCP: 90.95 Mg·ha-1 and FSCM: 92.56 Mg·ha-1), Nt (TMCF: 16.10 Mg·ha-1, CASTP:14.21 Mg·ha-1, CASCP: 7.89 Mg·ha-1 and FSCM: 6.50 Mg·ha-1) and Norg (TMCF: 16.02 Mg·ha-1, CASTP:14.16 Mg·ha-1, CASCP: 7.82 Mg·ha-1 and FSCM: 6.44 Mg·ha-1) stocks. The C:N ratio was similar in the systems.
Conclusions: The TMCF and CASTP had the largest organic carbon and Nt stocks in the soil. Agroforestry systems with coffee were better than coffee monoculture.
Spatial analysis of phenotypic variables in a clonal orchard of Pinus arizonica Engelm. in northern Mexico
Análisis espacial de las variables fenotípicas en un huerto clonal de Pinus arizonica Engelm. en el norte de México
Available online: 2019-04-03
/ pages 185-199
Introduction: Seed orchards provide germplasm genetically suitable for use in forest restoration. Knowledge of the spatial distribution of attributes is crucial for their management.
Objective: To model cone production and tree size variables in a clonal orchard of Pinus arizonica Engelm. from a geospatial perspective in order to determine their behavior and distribution.
Materials and methods: The spatial pattern of tree size variables and cone production of 126 ramets were determined through a geospatial analysis, using the Getis-Ord G statistic. A Pearson correlation analysis (P ≤ 0.05) determined the variables best associated with cone production and these were examined with stepwise regression. In terms of cone production, the best combination was modeled through a geographically weighted regression.
Results and discussion: Statistically significant (P < 0.01) clustering values were found in the orchard. Correlation analysis showed that all tree size variables, including the moisture index, were statistically related to cone production. Stepwise regression identified a model that presented crown diameter as the variable that best explained cone production. Geographically weighted regression showed that crown diameter moderately influenced cone production.
Conclusion: Tree size variables and cone production presented a tendency towards clustering. The use of a geospatial perspective allowed a better understanding of the spatial dynamics of tree size variables.
Historical and current spatial modeling of the sacred fir (Abies religiosa [Kunth] Schltdl. & Cham.) in the Trans-Mexican Volcanic Belt
Modelado espacial histórico y actual del oyamel (Abies religiosa [Kunth] Schltdl. & Cham.) en la Faja Volcánica Transmexicana
Available online: 2019-04-05
/ pages 201-217
Introduction: Climatic conditions in the Trans-Mexican Volcanic Belt during the middle Holocene were different from today's conditions, which may have an effect on the historical distribution areas of the sacred fir (Abies religiosa [Kunth] Schltdl. & Cham.).
Objective: To determine whether the environmental requirements that delimit the current distribution of the sacred fir in the Trans-Mexican Volcanic Belt have changed since 6,000 years ago.
Materials and methods: A. religiosa records were obtained from the Niche Toolbox platform. The WorldClim version 2.0 variables for the current (1970-2000) and middle Holocene (CNRMCM5 and MIROC_ESM models) periods were downloaded. The distribution models were generated in MaxEnt using 75 % of the data for training and 25 % for validation. The most important variables of each period were determined with the Jackknife test.
Results and discussion: The estimated sacred fir areas were similar in both periods. Approximately 86.5 % of the sacred fir distribution is found in protected natural areas of the zone. The limiting environmental variables of its distribution are: elevation, annual precipitation, summer precipitation, annual mean temperature and diurnal temperature oscillation. Nevado de Toluca and Mexico City had larger sacred fir areas (+2 658.4 ha and +20 129.7 ha, respectively) during the Middle Holocene. Annual precipitation was 80 to 224 mm higher than the current level and the temperature was 1 °C colder.
Conclusion: The most important environmental variables for sacred fir distribution are similar to those reported in the literature, indicating similarity between the current and historical ecological niche of A. religiosa.
Influence of the seed tree method on the diversity of regeneration in a mixed forest in Durango, Mexico
Influencia del método de árboles padres en la diversidad de la regeneración de bosques mixtos de Durango, México
Available online: 2019-04-05
/ pages 219-234
Introduction:Forest managers need to know the impact of regeneration cuts on tree species diversity in order to conserve it.
Objective:To evaluate changes in tree species richness and diversity after applying the seed tree method in six communities.
Materials and methods: The communities of Ciénega Grande, Las Ciénegas, La Colmena, El Venado, Los Bajíos and Pino Gordo of the Pueblo Nuevo ejido, Durango, were divided into three plots called: a) regeneration in seed trees cuttings (RST); b) regeneration in adult trees (RAT); and c) adult trees (AT). Starting from the center of each RST plot, and following the cardinal and subcardinal points, eight sites of 25 m2 and 0.1 ha were located to record the regeneration and adult tree species, respectively. Species richness indicators (Shannon-Wiener, Simpson, Pielou and Sørensen) were estimated to characterize the plots by community and were compared with t-tests and rarefaction analysis.
Results and Discussion. Twelve species were recorded in the study area, of which 11 are found as a renewal of seed trees. Species richness in the RST plots with respect to that of AT was equal in the Ciénega Grande, El Venado and La Colmena communities, and higher in Las Ciénegas and Los Bajíos. The Shannon-Wiener and Simpson indices were higher in Pino Gordo, Los Bajíos and El Venado. The Sørensen index ranges from 0.67 to 1.0, indicating high species similarity among plots.
Conclusions. The seed tree method in a mixed forest ensures the continuity of tree species diversity.
Nutrient input via gross rainfall, throughfall and stemflow in scrubland species in northeastern Mexico
Aporte de nutrientes vía precipitación incidente, directa y escurrimiento fustal en especies de matorral en el noreste de México
Available online: 2019-04-07
/ pages 235-251
Introduction: Precipitation is an important factor in the input of nutrients to ecosystems. In some cases, rainfall can add elements that are not available due to area conditions.
Objective: To compare the nutritional contribution in gross rainfall (Pi) and rainwater reaching the soil by throughfall (Pd) and stemflow (Ef) of scrubland species.
Materials and methods: A total of 41 rainfall events were evaluated in northeastern Mexico in the period September 2016-September 2017. Precipitation volumes were recorded and their chemical composition were analyzed: pH, electrical conductivity and contribution of macronutrients (Ca, Mg, K) and micronutrients (Fe, Mn, Zn and Cu).
Results and discussion: Pi accumulated 508.97 mm. Pd is the one that deposits more nutrients to the soil. The net contribution (Pd+Ef) indicated that Fe was the most deposited micronutrient with 2 938.29 g·ha-1·year-1, of which Casimiroa greggii (S. Watson) F. Chiang contributed 31.59 %. The macronutrient with greater presence was Ca with 319.31 kg·ha-1·year-1, being Acacia farnesiana (L.) Willd. the one that achieved greater flow of the mineral (22.66 %). pH and electrical conductivity were similar (Kruskal-Wallis, P > 0.05) in the three types of rainfall.
Conclusion: The precipitation chemistry is modified after passing the canopy of each species, either to enrich or remove nutrient concentrations, playing an important role in the biogeochemical cycles of the ecosystem.
Perception of occupational risk factors in sawmills in the El Salto region of Durango, Mexico
Percepción de factores de riesgo ocupacional en aserraderos de la región de El Salto, Durango, México
Available online: 2019-04-10
/ pages 253-268
Introduction: In the sawmill industry, the identification and assessment of potentially dangerous agents, as well as the worker's attitude towards the perception of risk factors, are important in the prevention of work accidents.
Objective: To measure the level of workers' perception of risk factors during work performance, at 11 sawmills in the El Salto region, Pueblo Nuevo, Durango, Mexico.
Materials and methods: An exploratory questionnaire was applied to 108 workers to determine the frequency of use of personal protective equipment (PPE) and the perception of safety in the face of exposure to noise, lighting, smoke, dust and vibrations.
Results and discussion: The average worker is a 37-year-old married person with 15 years of work experience and a grade six education. Most are overweight. Only 21 % of workers use PPE during the entire working day; gloves and dust masks are the most and least used items, respectively. Noise and vibrations are perceived as the most serious risk factors and, in general, the perception of safety at work goes from fair to good. The use of PPE is significantly related (Chi-square test P < 0.05) to age and sawmill. The perception of risk to the exposed parts of the body and noise depend on the job position (P < 0.05).
Conclusions: Training and supervision of workers in the proper use of PPE is necessary to minimize occupational hazards.
Historical bark beetle outbreaks in Mexico, Guatemala and Honduras (1895-2015) and their relationship with droughts
Brotes históricos de descortezadores en México, Guatemala y Honduras (1895-2015) y su relación con las sequías
Available online: 2019-04-11
/ pages 269-290
Introduction: In the United States of America, forest pests are associated with climate variability. Such studies are scarce in Mexico.
Objectives: To create a data base of historical outbreaks of bark beetles and analyze their relationship with drought.
Materials and methods: Historical records of outbreaks of bark beetles were obtained from official documents in Mexico, Guatemala, and Honduras. Dendroclimatic indices were used as a climate proxy. The relationship between pest outbreaks and climate was analyzed with the Superpose Epoch Analysis (SEA).
Results and discussion: A database of 120 years (1895-2015) of bark beetle outbreaks was created. The most frequent species were Dendroctonus mexicanus Hopkins, Dendroctonus frontalis Zimmermann and Dendroctonus adjunctus Blandford. A total of 106 records of outbreaks in 15 states of Mexico were recorded during the period 1903-2015; 16 outbreaks in Guatemala during the period 1895-2013, and 15 outbreaks in Honduras during the period 1962-2015. Historically, outbreaks were recorded in years with below-average precipitation (550 mm) and have increased since 1970. The SEA determined that bark beetle outbreaks in Mexico, Guatemala and Honduras were recorded during dry years (P < 0.05) with non-significant positive values (P > 0.05) of NIÑO 3 and PDSI (Palmer Drought Severity Index) and significant negative indices (P < 0.01) of NIÑO 3 and PDSI in the year prior to the outbreak, conditions involving intense drought.
Conclusion: A significant relationship was determined between bark beetle outbreaks and drought conditions for the last 120 years.