Discrimination ofPicea chihuahuanaMartinez populations on the basis of climatic, edaphic, dendrometric, genetic and population traits

Abstract

BackgroundPicea chihuahuana, which is endemic to Mexico, is currently listed as “Endangered” on the Red List. Chihuahua spruce is only found in the Sierra Madre Occidental (SMO), Mexico. About 42,600 individuals are distributed in forty populations. These populations are fragmented and can be classified into three geographically distinct clusters in the SMO. The total area covered by P. chihuahuana populations is less than 300 ha. A recent study suggested assisted migration as an alternative to the ex situ conservation of P. chihuahuana, taking into consideration the genetic structure and diversity of the populations and the predictions regarding the future climate of the habitat. However, detailed background information is required to enable development of plans for protecting and conserving species and for successful assisted migration. Thus, it is important to identify differences between populations in relation to environmental conditions. The genetic diversity of populations, which affect vigor, evolution and adaptability of the species, must also be considered. In this study, we examined 14 populations of P. chihuahuana, with the overall aim of discriminating the populations and form clusters of this species.MethodsEach population was represented by one 50 × 50 m plot established in the center of its respective location. Climate, soil, dasometric, density variables and genetic and species diversities were assessed in these plots for further analyses. The putatively neutral and adaptive AFLP markers were used to calculate genetic diversity. Affinity Propagation (AP) clustering technique and k-means clustering algorithm were used to classify the populations in the optimal number of clusters. Later stepwise binomial logistic regression was applied to test for significant differences in variables of the southern and northern P. chihuahuana populations. Spearman’s correlation test was used to analyze the relationships among all variables studied.ResultsThe binomial logistic regression analysis revealed that seven climate variables, the geographical longitude and sand proportion in the soil separated the southern from northern populations. The northern populations grow in more arid and continental conditions and on soils with lower sand proportion. The mean genetic diversity using all AFLP studied of P. chihuahuana was significantly correlated with the mean temperature in the warmest month, where warmer temperatures are associated to larger genetic diversity. Genetic diversity of P. chihuahuana calculated with putatively adaptive AFLP was not statistically significantly correlated with any environmental factor.DiscussionFuture reforestation programs should take into account that at least two different groups (the northern and southern cluster) of P. chihuahuana exist, as local adaptation takes place because of different environmental conditions.

Provenance Trials of the Mexican Spruces in Nursery Conditions: Three Species Endangered by Climatic Variation

“…Our results suggest that there are significant quantitative genetic differences among the three analyzed Picea species and that these differences are correlated with two climate variables (the mean minimum temperature in the coldest month and the summer/spring precipitation balance), supporting the hypothesis of adaptation to local conditions [6]. However, a proportion of phenotypical plasticity cannot be ruled out because the provenance trial experiment was not reciprocally carried out.…”

“…P. mexicana has only three locations, above 3000 m elevation [2,3], P. martinezii is in four populations between 1800 and 2500 m [4] and P. chihuahuana has been found at 40 sites between 2311 and 2700 m [2,5]. The Mexican spruces' distributions are fragmented in isolated populations, which could lead to phenological, morphological and genetic differentiations, partially caused by local adaptation to different soil types and climatic variables [6]. Therefore, it is important to identify the main factors responsible for such adaptation, which could be helpful in assisted migration programs, as an option for ex situ conservation.…”

Recent evidence of Mexican temperate forest decline and the need for ex situ conservation, assisted migration, and translocation of species ensembles as adaptive management to face projected climatic change impacts in a megadiverse country

“…Jaramillo-Correa et al (2006) reported that chloroplast DNA (cpDNA) diversity in Picea chihuahuana increases from southern to northern populations. The higher level of genetic diversity in northern populations can probably be explained by the smaller spatial distances among them and, thus, the potential for higher genetic exchange and lower tendency of genetic drift and inbreeding (Dominguez-Guerrero et al 2017). Populations at the southern distribution limit, which are more fragmented and isolated from each other, are therefore probably at greater risk.…”

“…] tions more severely and eventually causing an extinction vortex at the population level (inbreeding causes reduced seed set and germination potential, which leads to lower seedling recruitment, which subsequently reduces the effective population size and promotes even more inbreeding, thus repeating the cycle) (Gilpin and Soulé 1986;Menges 1991aMenges , 1991bFrankham et al 2002). Moreover, the predicted decline and eventual disappearance of suitable habitat for this species due to possible climatic change imposes a further extinction risk (Ledig et al 2010;Dominguez-Guerrero et al 2017;Pinedo-Alvarez et al 2019).…”

Influence of Environmental Factors on Forest Understorey Species in Northern Mexico

“…To study the effect of soil properties on understory species, a sample of 1000 g was collected from the centre of each of the 20 subplots at 15 cm depth (four samples by plot); a total of 11 soil samples were obtained from the canopy cover and 9 from the gaps. In total, 25 soil variables were analyzed according to the methodology described by Dominguez-Guerrero et al [48]: concentrations (ppm) of potassium (K), magnesium (Mg), sodium (Na), copper (Cu), iron (Fe), zinc (Zn), calcium (Ca), manganese (Mn) and phosphorus (P), concentration of nitrate (NO3, kg/ha), pH, cation exchange capacity (CEC, meq/100 g soil), organic matter (%) and texture (%), among others (Table S1). The organic matter (OM) content ranged from 0.66-14.2% and the percentage water saturation from 29.5 to 80%.…”