Silica defences in grasses have recently been suggested to be a potential driver of vole population dynamics. However, the ability of grasses to induce silica in response to herbivory has not been tested in northern ecosystems where small rodents are important herbivores. We conducted a large‐scale field experiment in subarctic tundra using three river catchments differing in herbivore densities, and examined the effects of small rodent and/or reindeer exclusion on leaf silica levels in five grass species (Avenella flexuosa, Anthoxanthum nipponicum, Calamagrostis phragmitoides, Deschampsia cespitosa and Phleum alpinum). We also conducted a greenhouse experiment using three of these species (A. flexuosa, A. nipponicum and D. cespitosa) and Festuca ovina to determine whether intraspecific genotypic variation affects baseline silica concentrations and the capacity to induce silica in response to simulated grazing. Baseline leaf silica concentrations and silica induction varied with plant species in both experiments, with catchment in the field experiment and with genotype in the greenhouse experiment. These findings show that the allocation to silica defences in grasses is highly variable, and suggest that the combined effects of grazing pressure, plant species and intraspecific genotypic differences are likely to determine the circumstances under which silica induction may be an optimal defence strategy. A better understanding of the interplay between grazing and other factors influencing silica induction is necessary to interpret the role of silica in plant–herbivore interactions.

Silicon (Si) is one of the most common elements in the earth bedrock, and its continental cycle is strongly biologically controlled. Yet, research on the biogeochemical cycle of Si in ecosystems is hampered by the time and cost associated with the currently used chemical analysis methods. Here, we assessed the suitability of Near Infrared Reflectance Spectroscopy (NIRS) for measuring Si content in plant tissues. NIR spectra depend on the characteristics of the present bonds between H and N, C and O, which can be calibrated against concentrations of various compounds. Because Si in plants always occurs as hydrated condensates of orthosilicic acid (Si(OH)4), linked to organic biomolecules, we hypothesized that NIRS is suitable for measuring Si content in plants across a range of plant species. We based our testing on 442 samples of 29 plant species belonging to a range of growth forms. We calibrated the NIRS method against a well-established plant Si analysis method by using partial least-squares regression. Si concentrations ranged from detection limit (0.24 ppmSi) to 7.8% Si on dry weight and were well predicted by NIRS. The model fit with validation data was good across all plant species (n = 141, R2 = 0.90, RMSEP = 0.24), but improved when only graminoids were modeled (n = 66, R2 = 0.95, RMSEP = 0.10). A species specific model for the grass Deschampsia cespitosa showed even slightly better results than the model for all graminoids (n = 16, R2 = 0.93, RMSEP = 0.015). We show for the first time that NIRS is applicable for determining plant Si concentration across a range of plant species and growth forms, and represents a time- and cost-effective alternative to the chemical Si analysis methods. As NIRS can be applied concurrently to a range of plant organic constituents, it opens up unprecedented research possibilities for studying interrelations between Si and other plant compounds in vegetation, and for addressing the role of Si in ecosystems across a range of Si research domains.

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The critical situation of the European eel (Anguilla anguilla) has urged the development of sperm cryopreservation protocols for reproduction in captivity and cryobanking. In the last years, two research groups have developed their own protocols in Spain and Hungary with positive results, but difficult to compare. Here, a series of experiments were conducted to test the quality of thawed sperm after using both protocols, determining which of them produce the best results and aiming for standardization. The quality of thawed sperm was assessed by studying the motility and kinetic values of thawed sperm from both cryopreservation protocols using a computerassisted sperm analysis (CASA-Mot) system. In addition, a viability analysis was performed using flow cytometry to test if the cryoprotectants or the freezing-thawing process led to a reduction in spermatozoa survival. Furthermore, since during cryopreservation the sperm was treated with methylated cryoprotectants (DMSO or methanol) that may induce epigenetic changes in the sperm DNA (cytosine methylation) and could affect the offspring, we conducted a luminometric methylation assay (LUMA) to study the DNA methylation levels induced by both protocols. In this work, all the above-mentioned parameters were analyzed in fresh and frozen-thawed sperm samples. Our results showed that thawed sperm samples from both protocols presented lower sperm motility and velocity, and lower percentage of live cells than those shown in fresh sperm samples. Furthermore, sperm samples from the methanol based protocol showed significantly higher motility, velocity and percentage of live spermatozoa than the same sperm samples treated with the DMSO based protocol. In addition, the DMSO based protocol induced a hypomethylation of sperm DNA compared to fresh samples whereas the methanol based protocol did not alter sperm DNA methylation level. Our results indicate that the methanol based protocol is a more suitable protocol that preserves better the motility and genetic qualities of the European eel sperm.