Abstract Introduction The management of complex anal fistulae remains a topical surgical problem. The choice and success of surgical management are based on the balance between healing and continence. Although porcine dermal collagen (Permacol Collagen Paste [PCP]- Covidien plc, Gosport, Hampshire, UK) represents a new generation of non-solid biomaterials, its results in anal fistulae are mixed. Methods A multicenter observational retrospective analysis of consecutive patients with cryptoglandular anal fistula treated in four colorectal surgery units was performed between 2015 and 2020. Clinical cure of the fistula was the main outcome measure. Adverse events and alterations in anal continence were secondary outcomes. Results The study included 119 patients (87 males, 71.1%), with a mean age of 53 years (IR 44-65). Most patients had complex (80.6%) and recurrent (91.6%) fistulae. With the first PCP treatment, the overall cure rate was 41.2% (49 patients) and 45.4% with the second treatment (5 out of 17 patients). The mean follow-up period was 17 months (IR 5-25). Healing was not affected by the location and type of fistula, the existence or not of a cavity, the number of tracts, or the administration of prophylactic antibiotics. After the PCP treatment, no patient in the series had worsening of continence. Morbidity affected 22.7% of the patients (27), with postoperative abscesses being the most frequent adverse event. There were no statistical differences between the four hospitals studied. Conclusions Permacol collagen paste is a safe and easily reproducible therapy for complicated anal fistulae that has moderate efficacy. The overall success rate is slightly over 40%, with no detriment to fecal continence.

Abstract Background Epilepsy is the most common major neurological disorder that affects people of all ages. The prevalence varies from one country to another and even between different areas, due to a lack of access to medical care for reasons related to limited resources. Objective Epilepsy is a worldwide public health problem that affects more deeply populations living in developing countries such as Mexico, where more aggressive health policies based on epidemiological data are needed; however, this information is scarce and the evolution of this data over time remains unclear. The aim of the present study is to provide an overview of the epidemiology of epilepsy in Mexico from 1970 to 2020. Methods We searched descriptive epidemiological studies on epilepsy in rural and urban regions of Mexico from 1970 to 2020. Available data on the sociodemographic characteristics, prevalence, and incidence data were extracted. Finally, the abstract, full-text review, and data abstraction were conducted in duplicate and reported using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Descriptive statistics was also used. Results Overall, 11 underrepresented and heterogeneous epidemiological studies were included. In total, the prevalence of epilepsy in Mexico is 3.9 to 41:1,000 inhabitants; 3.9 to 41 per 1,000 persons in rural regions, and 3.49 to 44.3 per 1,000 persons in urban regions. None of these studies addressed the incidence of epilepsy. The prevalence of epilepsy in Mexico has remained unchanged during the last 5 decades. Conclusions Our results confirm a high prevalence of epilepsy in both urban and rural settings in Mexico that remain unchanged during the last 5 decades. All studies included in the present review showed multiple methodological limitations. New and robust epidemiological studies are needed to delineate the epidemiological profile of epilepsy in Mexico.

Resumen Antecedentes La epilepsia es el trastorno neurológico más común que afecta a individuos de todas las edades. La prevalencia varía entre paises e incluso entre diferentes áreas del mismo pais debido a la falta de acceso a la atención médica. Objectivo La epilpesía es un problema de salud pública mundial que afecta de manera más importante a los países en desarrollo como México, donde hacen falta políticas en salud y datos epidemiológicos, para conocer el impacto real de esta enfermedad. El objetivo de este estudio es brindar una visión general de la epidemiología de la epilepsia en México (1970-2020). Métodos Se realizo unas búsquedas bibliografica de estudios epidemiológicos descriptivos sobre epilepsia en regiones rurales y urbanas de México desde 1970 a 2020. Se extrajeron los datos disponibles sobre las características sociodemográficas, prevalencia e incidencia. Finalmente, el resumen, la revisión completa del texto y la extracción de datos se realizaron por duplicado y se informaron utilizando PRISMA. Se utilizo estadística descriptiva. Resultados Se incluyeron 11 estudios epidemiológicos heterogeéneos. En total la prevalencia de epilepsia en México es 3.9-41: 1000 habitantes; 3,9 a 41 por 1000 personas en las regiones rurales y 3,49 a 44,3 por 1000 personas en las regiones urbanas. Ninguno de estos estudios abordó la incidencia de epilepsia. La prevalencia de la epilepsia en México se ha mantenido sin cambios durante las últimas cinco décadas. Conclusiones Nuestros resultados confirman una alta prevalencia de epilepsia en las areas urbanas y rurales de México que se mantiene sin cambios durante las últimas cinco décadas. Todos los estudios incluidos en esta revisión mostraron múltiples limitaciones metodológicas. Se necesitan estudios epidemiológicos nuevos y sólidos para delinear el perfil epidemiológico de la epilepsia en México.

ABSTRACT Environmental surveillance of water sources is important to monitoring viral hepatitis transmission in clinical settings. This study investigated the circulation of hepatitis A (HAV) and E (HEV) viruses in sewage and clinical samples from Argentina. Between 2016 and 2017, 80 raw sewage samples and 86 clinical samples (stool and serum) from suspected cases of hepatitis A and hepatitis E were obtained. HAV and HEV were tested by both real-time and nested PCR. Positive samples were sequenced for genotype determination and phylogenetic analysis. Overall, HAV was recovered in 39% of sewage samples and 61.1% of clinical samples. HEV was detected in 22.5% of sewage samples and 15.9% of clinical samples. HAV was found more frequently in sewage during the winter and in clinical samples in spring; HEV was more prevalent in sewage during summer and in clinical samples in autumn. All HAV isolates belonged to genotype IA and HEV isolates belonged to genotype 3, the most prevalent genotypes in South America. High prevalence of HAV and HEV in environmental and clinical samples in Mendoza, Argentina was observed. These findings reinforce the importance of environmental surveillance and implementation of health strategies to control the spread of HAV and HEV in developing countries.

ABSTRACT Fused deposition modeling (FDM) has gained popularity recently due to its versatility and low cost. Considering that the quality of printed parts depends on many variables, a 3^3 factorial design of experiments was conducted, where three influential parameters in the process were studied: layer height (0.15, 0.2, and 0.25 mm), infill percentage (30%, 60%, and 90%), and shell count (2, 3, and 4), using polylactic acid as the material. Their effects on tensile strength, flexural strength, printing time, and interactions were measured. The maximum tensile and flexural stress obtained were 33.5 MPa and 87.3 MPa, respectively, at a 90% infill percentage. It was found that layer height does not significantly affect mechanical strength, while infill percentage has the most significant influence, followed by the number of shells. The latter two factors show a meaningful interaction. Furthermore, all the studied parameters have a significant impact on printing time.

ABSTRACT Purpose: Peribulbar injection of triamcinolone is an alternative treatment for thyroid eye disease; however the safety profile of this therapeutic option remains controversial. The aim of this study was to describe the occurrence of local and systemic adverse effects after peribulbar injection of triamcinolone in patients with thyroid eye disease. Methods: This was a retrospective case series. Medical records of patients with thyroid eye disease treated with peribulbar injections of triamcinolone at a single academic institution between 2007 and 2019 were analyzed. Local and systemic complications were documented. Results: A total of 123 patients were treated. Only 11 patients (8.9%) developed local complications. The most frequent complication was the presence of superficial eyelid ecchymosis (nine patients; 7.3%). Notably, systemic complications (hyperglycemic and suprarenal inhibition after stop treatment) occurred in two patients (1.6%). All complications were transient, and the patients did not have any long-term sequelae. Conclusions: Peribulbar injection of triamcinolone for the treatment of thyroid eye disease is linked to a very low rate of local or systemic complications. Prospective studies are warranted to delve into this topic.

RESUMO Objetivo: A injeção peribulbar de triancinolona é um tratamento alternativo para doenças oculares da tireoide; no entanto, a segurança desse procedimento continua controversa. O objetivo deste artigo é descrever os efeitos adversos locais e sistêmicos de injeções peribulbares de triancinolona em pacientes com doença ocular da tireoide. Métodos: Estudo retrospectivo de uma série de casos. Foram analisados os prontuários médicos dos pacientes com doença ocular da tireoide tratados com injeções de triancinolona peribulbar em uma única instituição acadêmica entre 2007 e 2019. Foram documentadas as complicações locais e sistêmicas. Resultados: Um total de 123 pacientes foram tratados. Apenas 11 (8,9%) pacientes apresentaram complicações locais, sendo a mais frequente a presença de equimoses palpebrais superficiais (7,3%), enquanto 2 (1,6%) pacientes apresentaram complicações sistêmicas (hiperglicemia e inibição da suprarrenal após a interrupção do tratamento). Todas estas complicações foram transitórias e nenhum paciente apresentou sequelas de longo prazo. Conclusões: As injeções peribulbares de triancinolona nas doenças oculares da tireoide têm uma taxa muito baixa de complicações, tanto locais quanto sistêmicas. São necessários estudos prospectivos para aprofundar este tópico.

Abstract Coronary artery disease (CAD) and ischemic heart disease (IHD) are often indistinctly used terms. Both combined have generated, over the past years, concerns about sex disparities in their presentation. From an epidemiological perspective, females have several disadvantages regarding the prevention, diagnosis, and treatment of CAD. Most of the general cardiovascular risk factors affect women more frequently, or with a higher morbidity and mortality association. Besides, atypical manifestations of the disease and uncommon forms of CAD represent a diagnostic challenge for clinicians. Even if current treatments for CAD have no apparent sex bias, women representation in clinical trials and treatment patterns analyzed in clinical practice refuse this statement. Several disparities are caused by inevitable sex-particularities, but many of them are more social, cultural, and dogmatic beliefs that have to be addressed and overhaul. (CAD IHD (IHD terms generated years presentation perspective prevention diagnosis frequently association Besides clinicians bias statement sexparticularities, sexparticularities particularities, particularities sex-particularities social cultural overhaul

Resumen Desde la identificación del virus Junin en la década del 50, se realizaron numerosos estudios en roedores silvestres dentro del área endémica de la Fiebre Hemorrágica Argentina (FHA) que per mitieron registrar, además, actividad del virus de la coriomeningitis linfocitaria (LCMV) y del virus Latino (LATV). La ausencia de casos confirmados de FHA desde la década del 90 en el departamento Río Cuarto, provincia de Córdoba, promovió la vigilancia ecoepidemiológica y de infección del Calomys musculinus (reservorio del virus Junin) y la búsqueda de reservorios e infección de los otros mammarenavirus. Durante dos años de muestreo estacional, con un sistema de captura, marcación y liberación capturamos 857 roedores, que correspondieron 57.3% a los reservorios: C. musculinus (especie más abundante), C. venustus y Mus musculus. Detectamos anticuerpos y caracterizamos molecularmente los tres agentes virales. Observamos una prevalencia de infección de 3.5% (9/254) para virus Junin, 100% (3/3) para LCMV y 24.1% (21/87) para LATV. En conclusión, demostra mos circulación de virus Junin en su roedor reservorio, en una región considerada histórica para FHA con riesgo potencial para la población y cocirculación espacio-temporal de los tres mammarenavirus en la región central de Argentina.

Abstract Since the identification of Junin virus in the 1950s, many studies were carried out in wild rodents within the endemic area of the Argentine Hemorrhagic Fe ver (AHF) that recorded also the activity of the lymphocytic choriomeningitis virus (LCMV) and the Latino virus (LATV). The absence of confirmed cases of AHF since the 1990s in the department of Rio Cuarto, Córdoba province, promoted ecoepidemiological surveillance of infection of Calomys musculinus (Junin virus reservoir) and the search of reservoirs of the other mammarenaviruses. During two years of seasonal sampling, with a capture, mark and release system, 857 rodents were captured, corresponding 57.3% to the rodent reservoirs: C. musculinus, C. venustus and Mus musculus, being the first the most abundant species. Antibodies were detected and the three viral agents were molecularly characterized, showing a prevalence of infection of 3.5% (9/254) for Junin virus, 100% (3/3) for LCMV and 24.1% (21/87) for LATV. In conclusion, we demonstrated Junin virus circulation in its rodent reservoir in a region considered historic for AHF with potential risk for the population and the spatio-temporal co-circulation of the three mammarenaviruses in the central region of Argentina.

Resumen Objetivo: Evaluar el valor añadido de los niveles de glucosa en el líquido sinovial (LS) y otros parámetros bioquímicos en el diagnostico de artritis séptica (AS). Material y métodos: Análisis prospectivo de pacientes adultos con AS. Pacientes con articulaciones no infectadas fueron incluidos como grupo control. Se tomaron muestras de LS y sangre para la realización de análisis microbiológicos y bioquímicos en los pacientes y controles. Resultados: Incluimos 8 sujetos con lesión ligamentosa de rodilla, 6 con lesiones meniscales y 5 con osteoartritis como grupo control, así como 20 pacientes con AS. El cultivo de LS fue positivo en 60%. Los niveles de glucosa en LS de pacientes con AS fueron más bajos que los controles (P = 0.0018) con la concentración más baja en pacientes con cultivo positivo (p = 0.0004). La relación de glucosa en sangre y LS de pacientes con cultivo positivo se vio afectada (p < 0.0001). La esterasa leucocitaria presentó valores más altos en pacientes con cultivo positivo (p < 0.0001); se encontró un pH más ácido en comparación con el grupo control (p < 0.0001). Conclusión: Estos parámetros bioquímicos podrían ser un valor agregado útil, rápido y económico para distinguir entre enfermedad articular infecciosa y no infecciosa.

Abstract Objective: The objective of the study was to determine the added value of synovial fluid (SF) glucose levels and other biochemical parameters as possible biomarkers of bacterial septic arthritis (SA). Materials and methods: We prospectively examined adult patients with SA. As a control group, adults with uninfected joints were enrolled. SF samples were obtained, and microbiological analyses were made. SF glucose levels, pH, and leukocyte esterase were measured using a glucometer and colorimetric test strips. Blood samples were collected from both groups to determine glucose levels. Results: We included eight subjects with knee ligaments lesions, six with meniscus lesions, and five with osteoarthritis as the control group, as well as 20 patients with SA. SF culture was positive in 60%. SF glucose levels from patients were lower than the controls (p = 0.0018) with the lowest concentration in patients with a positive culture (p = 0.0004). Blood and SF glucose concentration from the positive culture patients were compared (p < 0.0001). Leukocyte esterase presented the highest values in patients with a positive culture (p < 0.0001) and a more acidic pH was found compared to the control group (p < 0.0001). Conclusion: These biochemical parameters might be a quick and inexpensive added value for distinguishing between infective and non-infective joint disease.

RESUMEN El afrecho de arroz es un subproducto de las industrias que posee importantes valores nutricionales, por lo que puede considerarse como alternativa para incluirlas dentro de un programa alimenticio de ovinos. El objetivo del trabajo fue evaluar el efecto de la sustitución parcial del maíz molido por afrecho de arroz sobre los parámetros productivos de borregas en confinamiento. El diseño experimental fue completamente al azar con cuatro tratamientos y tres repeticiones, cada repetición estuvo compuesta por 2 borregas, totalizando así 12 unidades experimentales (24 animales de 26 ± 2kg PV y en promedio). Los tratamientos consistieron en la sustitución parcial del maíz molido por afrecho de arroz en la dieta. Los niveles fueron 0% para T1, 15% para T2, 30% para T3 y 45% para T4. Las raciones contenían además expeller de soja, sal mineral, urea, carbonato de calcio y heno de Pangola (Digitaria decumbens) como fuente de voluminoso. La duración del experimento fue de 56 días. Los pesajes y ajuste de ración fueron realizados cada 14 días. Los datos recabados fueron sometidos a un análisis de varianza (ANAVA) al 5% probabilidad de error. Los resultados obtenidos indican que no existieron diferencias estadísticas significativas en las variables ganancia diaria de peso, ganancia total de peso, consumo y conversión alimenticia, con valores promedios de 200 g.dia-1, 10,8 kg, 4,7% y 7,4 respectivamente. Por lo tanto, se puede inferir que es factible la utilización de afrecho de arroz en sustitución del maíz molido hasta un 45% sin afectar los parámetros productivos evaluados.

ABSTRACT The rice bran is a by-product of the rice industries that has important nutritional values and can therefore be considered as an alternative to include them in a sheep's food program. The objective of the work was to evaluate the effect of partial replacement of ground corn by rice bran on productive parameters of sheep in feedlot. The experimental design was completely randomized with four treatments and three repetitions, each repetition was composed of 2 ewes, thus totaling 12 experimental units (24 animals of 26 ± 2kg PV on average). The treatments consisted of the partial substitution of ground corn for rice bran in the diet. The levels were 0% for T1, 15% for T2, 30% for T3 and 45% for T4. The rations also contained soybean expeller, mineral salt, urea, calcium carbonate and Pangola hay (Digitaria decumbens) as a voluminous source. The duration of the experiment was 56 days. The weightings and ration adjustment were made every 14 days. The data collected were subjected to an Analysis of variance (ANOVA) at 5% error probability. The results obtained indicate that there were no significant statistical differences in the variables daily weight gain, total weight gain, intake and feed conversion ratio, with average values of 200 g.dia-1, 10.8 kg, 4.7% and 7.4 respectively. Therefore, it can be inferred that it is feasible to use rice bran instead of ground corn up to 45% without affecting the productive parameters evaluated.

Abstract Background: Esophagojejunal anastomotic leakage (EJAL) is among the most feared complications after gastric cancer surgery; they entail an uncertain prognosis and relate with increased morbidity and mortality. Factors associated with their development are not well determined, and their diagnosis and treatment vary between institutions. Material and methods: Retrospective case-control study of patients operated of total gastrectomy with Roux-en-Y esophagojejunostomy from January 2002 to December 2018. We divided our sample into two groups based on the presence of EJAL, and compared demographic, clinical, and histologic variables. We performed a logistic regression model to search risk factors associated with EJAL and described the management offered in our center. Results: We included 58 patients of which 8 (13.7%) presented clinically relevant EJAL. On the comparative analysis, albumin levels and diffuse histology presented a statistically significant difference between groups and presented association with EJAL in the logistic regression model. Regarding treatment of EJAL, ten patients (55.5%) required only conservative measures, whereas eight patients (44.4%) warranted an endoscopic or surgical intervention. Conclusion: Our retrospective analysis identified some factors that may be associated with the development of EJAL after gastric cancer surgery. High suspicion and prompt identification of this complication is essential to improve postoperative outcomes in this group.

Resumen Introducción: Las fugas de la anastomosis esófago-yeyunal se encuentran entre las más temidas complicaciones de la cirugía para cáncer gástrico. Estas conllevan un mal pronóstico con una alta mortalidad y morbilidad. Los factores asociados a su desarrollo no están bien determinados y su diagnóstico, y tratamiento varían ampliamente entre instituciones. Material y métodos: Estudio retrospectivo de casos y controles en pacientes operados de gastrectomía total con esófago-yeyuno anastomosis en Y de Roux en el periodo de enero 2002 a diciembre 2018. Nuestra muestra fue dividida en dos grupos con base al desarrollo de fuga de anastomosis en el postoperatorio. Se realizó un análisis comparativo de características demográficas, clínicas y histológicas. Se realizó además una regresión logística para identificar factores de riesgo asociados al desarrollo de fuga de anastomosis en nuestra serie. Resultados: Incluimos a 58 pacientes de los cuales 8 (13.7%) presentaron fuga de anastomosis clínicamente relevante. En el estudio comparativo: Niveles disminuidos de albúmina e histología difusa fueron significativamente mayores en el grupo de fuga y se asociaron en el modelo de regresión logística. En cuanto al tratamiento, diez pacientes (55%) requirieron únicamente tratamiento conservador, mientras que ocho pacientes (44.4%) fueron sometidos a maniobras endoscópicas o quirúrgicas. Conclusión: Nuestro análisis retrospectivo identifico factores asociados al desarrollo de fuga de anastomosis posterior a cirugía de cáncer gástrico. Una alta sospecha diagnóstica es esencial para mejorar el pronóstico de estos pacientes.

Abstract Background: In Latin America, research in neuroscience and psychology has had a continuous development; however, the magnitude of this development and its impact on the comparison to other regions or countries has not been well studied. Objective: The objective of the study was to carry out a bibliometric analysis of scientific productivity in neuroscience and psychology in Latin America. Methods: We consulted the Scimago Journal and Country Rank database to obtain the classification of the Latin American countries in these knowledge disciplines, during the period from 2015 to 2020. Results: We found 32 Latin American countries with citable documents in these disciplines. Notably, 90% of Latin American scientific productivity is concentrated in five countries: Brazil, Mexico, Argentina, Chile, and Colombia, with Brazil being the leading country in all cases. Conclusions: Research in neuroscience and psychology in Latin America has had a sustained and moderate growth. However, it is highly circumscribed in these five countries.

Resumen Antecedentes: En América Latina, la investigación en neurociencias y psicología ha tenido un desarrollo continuo; sin embargo, hasta el momento la magnitud de dicho desarrollo y su impacto en comparación a otras regiones o países no ha sido bien estudiada. Objetivo: Realizar un análisis bibliométrico de la productividad científica en neurociencias y psicología en Latinoamérica. Material y métodos: Se consultó la base de datos Scimago Journal and Country Rank para obtener la clasificación de los países de Latinoamérica en estas disciplinas del conocimiento, durante el periodo comprendido del 2015 a 2020. Resultados: Encontramos 32 países latinoamericanos con documentos citables en estas disciplinas. Notablemente, el 90% de la productividad científica latinoamericana está concentrada en cinco países: Brasil, México, Argentina, Chile y Colombia, siendo Brasil el país líder en todos casos. Conclusión: La investigación en neurociencias y psicología en América Latina ha tenido un crecimiento sostenido y moderado, pero ésta se encuentra muy circunscrita a estos cinco países.

ABSTRACT The current work presents a new algorithm to detect bursts in water pipes automatically, focused on its implementation in low-power embedded devices. The algorithm was implemented in an MSP430FR5994 microcontroller and it does not require computer devices with the processing capability to execute high-complexity mathematical operations, unlike most of the existing algorithms. The developed algorithm uses the approach of detecting bursts by enhancing the singularities they create and making decisions based on the application of thresholds. Instead of applying a single mathematically-complex threshold, two simpler ones are used that are compatible with the processing capability of low-power embedded devices. Two implementations for the convolution operation were tested using the microcontroller’s Low Energy Accelerator module; it was found that the convolution in the time domain is faster than the FFT-based method in an average of 65.3%. The algorithm detects bursts with a detection probability of 100% and a probability of false positives of 0.13% on the performed tests.

RESUMEN En este trabajo se presenta un nuevo algoritmo de detección automática de rupturas súbitas orientado a su implementación en dispositivos embebidos de bajo consumo de potencia. El algoritmo fue implementado en un microcontrolador MSP430FR5994 y no necesita dispositivos con suficiente capacidad de procesamiento para ejecutar operaciones matemáticas complejas, contrario a la mayoría de los algoritmos existentes. El algoritmo desarrollado emplea el enfoque de detectar rupturas súbitas mediante la acentuación de las singularidades que ellas crean y tomando decisiones basadas en la aplicación de umbrales. En lugar de aplicar un solo umbral que fuera matemáticamente complejo, se usaron dos umbrales más simples que fueran compatibles con la capacidad de procesamiento de dispositivos embebidos de bajo consumo de potencia. Se probaron dos implementaciones de la operación de convolución usando el módulo Acelerador de Baja Energía del microcontrolador; se obtuvo que la convolución en el dominio del tiempo se ejecuta, en promedio, un 65.3% más rápido que la basada en el uso de la Transformada rápida de Fourier. El algoritmo es capaz de detectar rupturas súbitas con una probabilidad de detección del 100% y una probabilidad de falsos positivos del 0.13% para las pruebas realizadas.

Abstract The litterfall that accumulates in the forest soil and its further decomposition play an important roll in the maintenance of productivity in different terrestrial ecosystems since its constitute the main flow of nutrients to the soil. The objective of this study was to evaluate the production of litterfall, its nutrient return thru litterfall deposition and macronutrient use efficiency. The study was conducted in Linares, Crucitas and Los Ramones, state of Nuevo León, México. Average litterfall deposition was 5 800, 5 270 and 6 596 kg ha−1 year−1 for Linares, Crucitas and Los Ramones, respectively. Total nutrient return thru litterfall followed the sequence: Linares > Crucitas > Los Ramones, with value of 135, 122 and 101 kg ha−1 year−1, respectively. Even though the return of P thru litterfall was the lowest, P nutrient use efficiency was higher with respect to Ca, Mg and K. Greatest nutrient use efficiency in terms of Ca and Mg was observed in Los Ramones, K in Crucitas and P in Linares. The results showed that there exist spatial and temporal variation in the production of litterfall, nutrient return and nutrient use efficiency between studied sites. Thus, litterfall deposition, nutrient return and nutrient use efficiency between sites depend on stand composition and richness, edaphic properties, litterfall quality, and plant phenology.

Resumen La hojarasca que se acumula sobre el piso forestal y su posterior descomposición juegan un papel importante en el mantenimiento de la productividad de los diferentes ecosistemas terrestres al constituir el principal flujo de nutrientes al suelo. El objetivo del estudio fue evaluar la producción de hojarasca y retorno de nutrientes a través de la caída de la hojarasca y la eficiencia en el uso de macro-nutrientes. El estudio se realizó en los sitios de Linares, Crucitas y Los Ramones, en el Estado de Nuevo León, México. El promedio de caída de hojarasca fue de 5 800, 5 270 a 6 596 kg ha−1 año−1 para Linares, Crucitas y Los Ramones, respectivamente. El retorno total de nutrientes siguió la secuencia: Linares > Crucitas > Los Ramones con valores de 135, 122 y 101 kg ha−1 año−1, respectivamente. A pesar de que el retorno de P en la hojarasca fue menor, la eficiencia del uso de este nutriente fue mayor que la presentada por el Ca, Mg ó K. La mayor eficiencia de uso de nutrientes en términos de Ca y Mg se observó en Los Ramones, el K en Crucitas y el P en linares. Existe variación espacial y temporal en la producción de hojarasca, retorno de nutrientes y la eficiencia en su uso entre los sitios evaluados. Por tanto, la caída de hojarasca, retorno de nutrientes y uso eficiente en estos sitios dependen de la riqueza de especies, diferencias edáficas, calidad de la hojarasca y fenología de las diferentes especies.