Drought is a limiting factor to forest regeneration and restoration, which is likely to increase in intensity and duration under future climates. Nitrogen (N) nutrition is related to drought-resistance mechanisms in trees. However, the influence of chemical N form (inorganic and organic N) on physiological traits related to drought resistance has been sparsely studied in conifer seedlings. We investigated the effect of N forms on morpho-physiological traits of Pinus ponderosa Dougl. ex Laws. seedlings and subsequent influences in drought tolerance and acclimation. One-year-old seedlings were fertilized during 10 weeks at 9 mM N with different N forms [either NH4+, NO3− or organic N (amino acids mixture)] in their second year of growth. After fertilization, we measured traits associated with intrinsic drought tolerance (shoot water relations, osmotic regulation, photosynthesis and cell membrane stability). Seedlings were then subjected to an 8-week drought period at varying drought intensities to evaluate plant acclimation mechanisms. We demonstrated that P. ponderosa seedlings could efficiently use amino acids as a primary N source, showing similar performance to those grown with inorganic N forms. Nitrogen form influenced mainly drought-acclimation mechanisms rather than intrinsic drought tolerance. Osmotic potential at saturation (Ψπsat) was marginally affected by N form, and a significant relationship between proline concentration in needles and Ψπsat was found. During acclimation, seedlings fertilized with organic N minimized needle senescence, retained more nutrients in the oldest needles, had maximum increments in proline concentration and hastened the development of water-use efficiency mechanisms compared with those fertilized with inorganic N sources. Our results suggest an improved physiological drought acclimation of organic N-fertilized seedlings.

Reliable calculations of carbon stocks in forest ecosystems are crucial for proper implementation of global warming mitigation policies. Accurate estimations depend upon applying the correct factor of carbon (C) concentration for different forest species and tissues instead of the often assumed 50% carbon content. Despite the high forest species richness in Mexico and the increasing CO2 emissions, data on carbon concentrations in forest plant tissues are scarce. In this study, we determined variation in C concentration of different tissues for 175 plant species common in Mexican forests. C contents were estimated and contrasted for plant distribution, taxa, and plant structure (main stems, branches, twigs, bark, leaves, buds, fruits, roots and root cuticles). The mean C concentration across species was 44.7%. Species significantly differed in C concentration by tissue, environment and taxa. These multi-species data contribute to improve precision on estimates of C balance in terrestrial ecosystems, reducing the uncertainty in C inventories in Mexico and elsewhere.

Global climate change will alter forests by shifting species ranges, which has implications for their ecological functions. Annual tree-ring widths and wood density are useful proxies for carbon cycle studies across a range of species. Here, using a dendroecological approach we sought to understand the carbon accumulation rates of two representative pine species growing on contrasting wet (P. arizonica) and dry (P. cembroides) sites and reveal how such species cope with climate variability. Although the rate of carbon gain was not significantly different across sites, we found that variations in carbon accumulation responded differently to specific hydroclimate drivers, site conditions, or to functional features of each species, which are still to be explored. Overall, annual carbon accumulation (C) was less sensitive to climate variability than ring width and wood density. Annual C was more sensitive to rainfall in the cold season (P. arizonica) and to the start of spring (both species). Our spe...

Los árboles constituyen un recurso importante en las zonas urbanas debido a los servicios ambientales que brindan. El objetivo de este estudio fue evaluar la composición florística, estructura y diversidad del arbolado urbano del centro de Hualahuises, Nuevo León. Se evaluó el arbolado urbano de los espacios públicos del centro de Hualahuises, abarcando las plazas públicas y aceras. A cada árbol se le midieron su altura total, el diámetro normal y diámetro de copa. Para cada especie se determinó su abundancia, su cobertura, y su frecuencia, para obtener su Índice de Valor de Importancia. También se determinó la riqueza de especies mediante el índice de Margalef, el índice de diversidad de Shannon, y el número de especies efectivas. Se registraron 38 especies de plantas vasculares distribuidas en 35 géneros y 22 familias. El 63.20 % (25 especies) son introducidas y el 36.8 % (21 especies) son nativas. La familia más representativa fue Fabaceae con cuatro especies. Los análisis de clases diamétricas y de altura indican una mayor proporción de individuos con diámetros bajos (d1.303 m y <6 m). La comunidad vegetal presenta valores intermedios-altos de riqueza y altos de diversidad de especies comparado con otras áreas verdes urbanas del noreste de México. Más de la mitad de las especies (63 %) son introducidas, entre las cuales Fraxinus americana y Thuja occidentalis sobresalen por su Índice de Valor de Importancia. La especie nativa con mayor valor de importancia fue Quercus virginiana.

Forest structure and composition have changed rapidly worldwide, presenting tendencies towards an increasing proportion of younger trees. From chronologies of tree-ring indices (TRI) and the reconstruction of the basal area increment (BAI), a dendroecological study was conducted from the perspective of the radial growth of twelve contemporary conifer species in a highly diverse region of the planet. From an elevational perspective, the TRI were associated with climate and the NDVI, while the BAI was also modeled as a potential proxy for forest productivity. Climate affects the species differently according to elevation: at 1900 m asl, Pinus caribaea, P. oocarpa and P. jeffreyi presented the lowest sensitivities to climate and drought. For their part, species occupying the intermediate part of the gradient (1901–3000 m asl), such as P. engelmannii, P. patula, P. johannis and P. maximartinezii, were very sensitive to maximum temperature (TMax), precipitation (PP) and drought during the winter–spring period. Finally, of the species distributed on the upper part of the gradient (>3000 m asl), only Abies religiosa was associated with TMax and drought; Juniperus deppeana, A. hickelii and P. hartwegii did not seem to be vulnerable to drought. Complementarily, we found significant differences in the BAI as a function of elevation, with the sites at 1001–1500 m asl presenting higher BAI. The results suggest that the growth in these forests is impacted by droughts and follows a distinct spatial pattern, with greater restriction found in mid-elevation forests. Consistent implications are also observed in BAI trends. For its part, the NDVI demonstrated a decreasing tendency in greenness from south to north, although no elevation pattern was evident. The combined proxies utilized here produced parameters that improve our understanding of forest growth and should be considered in vegetation dynamics models in order to reduce their uncertainty in the face of climate vulnerability. These forests must be sustainably managed, and it is therefore crucial to determine the influence of ecological variables on their growth.

Currently, assessing carbon content in forest species is considered essential for programs designed to mitigate global warming. Although in Mexico these studies are becoming more numerous, we still do not know the state of the art in this scientific field. To our knowledge there is a lack of a systematic synthesis of the current condition of carbon sequestration from forest species in Mexico. This would be a useful baseline for scientists interested in further developing carbon studies. The aim of the present study is to analyze the variations of carbon uptake in Mexican forest species. From a comprehensive literature review of indexed journals and specialized databases, this study records the efforts made to record carbon storage rates in Mexican forests based on species, tree components, regions and ecosystems. The results identify those areas that are frequently the subject of research, as well as where opportunities exist and where efforts should be targeted, particularly in rainforests that have been the subject of very few research studies. This study to generate the first Mexican data base that summarizes state of the art data on the topic under study and contributes to a better understanding of potential functional relationships between diversity and carbon sequestration in forest ecosystems in Mexico.