Martin Venturas

Human-induced changes on fine-scale genetic structure in Ulmus laevis Pallas wetland forests at its SW distribution limit

Human activities have deeply transformed the Mediterranean landscape for millennia. Wetland and riverbed vegetation are among the most affected ecosystems because of the value of these areas for agriculture, due to their rich soil and water availability. This has caused the fragmentation, population reduction, and extinction of many species. We focus our study on Ulmus laevis Pallas, an endangered tree species in the Iberian Peninsula, as an extreme example of these formations. We study the diversity and fine-scale spatial genetic structure of two human disturbed wetland populations with chloroplast markers and nuclear microsatellites. We evaluate their recovery possibilities, and how they will be affected by future aridification and water table depletion. Our results show that although these populations have suffered bottlenecks and have low genetic diversity, they maintain the same diversity levels as the European populations. Despite the low genetic variation that could contribute to inbreeding problems in the future, we discuss that the main threat of the species is habitat destruction. Finally, we propose some management and conservation policies to ameliorate these effects.

Empty Seeds Are Not Always Bad: Simultaneous Effect of Seed Emptiness and Masting on Animal Seed Predation

Seed masting and production of empty seeds have often been considered independently as different strategies to reduce seed predation by animals. Here, we integrate both phenomena within the whole assemblage of seed predators (both pre and post-dispersal) and in two contrasting microsites (open vs. sheltered) to improve our understanding of the factors controlling seed predation in a wind-dispersed tree (Ulmus laevis). In years with larger crop sizes more avian seed predators were attracted with an increase in the proportion of full seeds predated on the ground. However, for abundant crops, the presence of empty seeds decreased the proportion of full seeds predated. Empty seeds remained for a very long period in the tree, making location of full seeds more difficult for pre-dispersal predators and expanding the overall seed drop period at a very low cost (in dry biomass and allocation of C, N and P). Parthenocarpy (non-fertilized seeds) was the main cause of seed emptiness whereas seed abortion was produced in low quantity. These aborted seeds fell prematurely and, thus, could not work as deceptive seeds. A proportion of 50% empty seeds significantly reduced ground seed predation by 26%. However, a high rate of parthenocarpy (beyond 50% empty seeds) did not significantly reduce seed predation in comparison to 50% empty seeds. We also found a high variability and unpredictability in the production of empty seeds, both at tree and population level, making predator deception more effective. Open areas were especially important to facilitate seed survival since rodents (the main post-dispersal predators) consumed seeds mostly under shrub cover. In elm trees parthenocarpy is a common event that might work as an adaptive strategy to reduce seed predation. Masting per se did not apparently reduce the overall proportion of seeds predated in this wind-dispersed tree, but kept great numbers of seeds unconsumed.

Massive sequencing of Ulmus minor's transcriptome provides new molecular tools for a genus under the constant threat of Dutch elm disease

Elms, especially Ulmus minor and U. americana, are carrying out a hard battle against Dutch elm disease (DED). This vascular wilt disease, caused by Ophiostoma ulmi and O. novo-ulmi, appeared in the twentieth century and killed millions of elms across North America and Europe. Elm breeding and conservation programmes have identified a reduced number of DED tolerant genotypes. In this study, three U. minor genotypes with contrasted levels of tolerance to DED were exposed to several biotic and abiotic stresses in order to (i) obtain a de novo assembled transcriptome of U. minor using 454 pyrosequencing, (ii) perform a functional annotation of the assembled transcriptome, (iii) identify genes potentially involved in the molecular response to environmental stress, and (iv) develop gene-based markers to support breeding programmes. A total of 58,429 putative unigenes were identified after assembly and filtering of the transcriptome. 32,152 of these unigenes showed homology with proteins identified in the genome from the most common plant model species. Well-known family proteins and transcription factors involved in abiotic, biotic or both stresses were identified after functional annotation. A total of 30,693 polymorphisms were identified in 7,125 isotigs, a large number of them corresponding to single nucleotide polymorphisms (SNPs; 27,359). In a subset randomly selected for validation, 87% of the SNPs were confirmed. The material generated may be valuable for future Ulmus gene expression, population genomics and association genetics studies, especially taking into account the scarce molecular information available for this genus and the great impact that DED has on elm populations.

Root iron uptake efficiency of Ulmus laevis and U. minor and their distribution in soils of the Iberian Peninsula.

The calcifuge and calcicole character of wild plants has been related to nutrient availability shortages, including iron (Fe)-deficiency. Surprisingly, just a few studies examined the relation between root Fe uptake and plant distribution in different soil types. We assessed the root Fe acquisition efficiency of two Ulmus species with calcareous (Ulmus minor) and siliceous (U. laevis) soil distribution patterns in the Iberian Peninsula. Seedlings of both elm species were grown hydroponically with different Fe concentrations during 6 weeks. Plant physiological responses to Fe-limiting conditions were evaluated as were the ferric reductase activity and proton (H+) extrusion capacity of the roots. Iron deprived elm seedlings of both species were stunted and suffered severe Fe-chlorosis symptoms. After Fe re-supply leaf chlorophyll concentrations rose according to species-dependent patterns. While U. minor leaves and seedlings re-greened evenly, U. laevis did so along the nerves of new growing leaves. U. minor had a higher root ferric reductase activity and H+-extrusion capability than U. laevis and maintained a better nutrient balance when grown under Fe-limiting conditions. The two elm species were found to have different Fe acquisition efficiencies which may be related to their natural distribution in calcareous and siliceous soils of the Iberian Peninsula.

Surface properties and physiology of Ulmus laevis and U. minor samaras: implications for seed development and dispersal

Plant surface properties influence solid-liquid interactions and matter exchange between the organs and their surrounding environment. In the case of fruits, surface processes may be of relevance for seed production and dispersal. To gain insight into the relationship between surface structure, chemical composition and function of aerial reproductive organs, we performed diverse experiments with the dry, winged fruits, or samaras, of Ulmus laevis Pall. and Ulmus minor Mill. both at the time of full maturity (green samaras) and of samara dispersal (dry samaras). Samaras of both elm species showed positive photosynthetic rates and absorbed water through their epidermal surfaces. The surface wettability, free energy, polarity and solubility parameter were lower in U. laevis than in U. minor and decreased for dry samaras in both species. Ulmus laevis samaras had a high degree of surface nano-roughness mainly conferred by cell wall folds containing pectins that substantially increased after hydration. The samaras in this species also had a thicker cuticle that could be isolated by enzymatic digestion, whereas that of U. minor samaras had higher amounts of soluble lipids. Dry samaras of U. laevis had higher floatability and lower air sustentation than those of U. minor. We concluded that samaras contribute to seed development by participating in carbon and water exchange. This may be especially important for U. minor, whose samaras develop before leaf emergence. The trichomes present along U. laevis samara margin may enhance water absorption and samara floatability even in turbulent waters. In general, U. minor samaras show traits that are consistent with a more drought tolerant character than U. laevis samaras, in line with the resources available both at the tree and ecosystem level for these species. Samara features may additionally reflect different adaptive strategies for seed dispersal and niche differentiation between species, by favoring hydrochory for U. laevis and anemochory for U. minor.

Species selection for reforestations: what happens with historic local extinctions and habitat protection zones? A case study in the Cantabrian Range

Species selection for reforestations can be challenging in habitat protection zones, especially in human transformed landscapes, where nativeness of some species is not easily determined and yet is crucial for knowing whether a species can be used or not. We try to determine whether Pinus uncinata Ramond ex DC was present in the Cantabrian Range (Spain) and whether it could have disappeared recently due to anthropogenic causes. Plant morphology and needle anatomy were characterized in Pinus sylvestris L. and P. uncinata 2-year-old seedlings. An analysis of variance was used for selecting morphological markers capable of discriminating both species. These markers permit the comparison of seedlings coming from the highest zone of Puebla de Lillo relict pinewood (Cantabrian Range) with reference material from Castillo de Vinuesa (Iberian Range). This comparison was firstly made with two multivariate methods, a principal component analysis and a multivariate discriminant analysis. Subsequently, this was corroborated with the detection of a species-specific chloroplast DNA marker. The differences found between both species reflect the better adaptation of P. uncinata to typical highland environment. Several Puebla de Lillo seedlings had P. uncinata type morphology and haplotype, suggesting the presence of this species in the Cantabrian Range until recently. This discovery changes the current interpretation of the zone’s vegetation, enhancing the natural presence of highland open pinewoods. However, human activities (fire and livestock grazing) have driven them to extinction and have favoured the contemporary expansion of heathlands. Based on this P. uncinata case, we discuss how local extinctions can affect management and conservation policies negatively.