Relative impacts of disturbance and temperature: persistent changes in microenvironment and vegetation in retrogressive thaw slumps

In the Low Arctic, a warming climate is increasing rates of permafrost degradation and altering vegetation. Disturbance associated with warming permafrost can change microclimate and expose areas of ion-rich mineral substrate for colonization by plants. Consequently, the response of vegetation to warming air temperatures may differ significantly from disturbed to undisturbed tundra. Across a latitudinal air temperature gradient, we tested the hypothesis that the microenvironment in thaw slumps would be warmer and more nutrient rich than undisturbed tundra, resulting in altered plant community composition and increased green alder ( Alnus viridis subsp. fruticosa ) growth and reproduction. Our results show increased nutrient availability, soil pH, snow pack, ground temperatures, and active layer thickness in disturbed terrain and suggest that these variables are important drivers of plant community structure. We also found increased productivity, catkin production, and seed viability of green alder at disturbed sites. Altered community composition and enhancement of alder growth and reproduction show that disturbances exert a strong influence on deciduous shrubs that make slumps potential seed sources for undisturbed tundra. Overall, these results indicate that accelerated disturbance regimes have the potential to magnify the effects of warming temperature on vegetation. Consequently, understanding the relative effects of temperature and disturbance on Arctic plant communities is critical to predicting feedbacks between northern ecosystems and global climate change.     

Differential Na2SO4 tolerance in tobacco plants regenerated from Na2SO4-grown callus

Abstract The regenerated shoots from sodium sulphate (Na₂SO₄) grown callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) were evaluated for Na₂SO₄ tolerance based on shoot proliferation and rooting in vitro, and seed germination in vivo in response to Na₂SO₄. An increase in Na₂SO₄ concentration resulted in significantly decreasing shoot fresh weight, number of shoots, shoot length and leaf size, and increasing per cent shoot dry weight of both control and Na₂SO₄-grown cultures. In rooting, shoots of Na₂SO₄-grown cultures exhibited the highest per cent rooting (85%) in the presence of 1% w/v Na₂SO₄. However, per cent rooting, root number per rooted cutting and root fresh weight decreased significantly with increasing Na₂SO₄ concentration when shoots were transferred to the medium in the absence of Na₂SO₄ for 4-monthly passages. Following acclimatization of the rooted shoots of Na₂SO₄-grown cultures, phenotypic variation was observed during growth and development. There were 13.2% sterile plants. Fertile plants were sorted into normal (N), tolerant (T), and sensitive (S) categories and the respective percentages of plants were 31.6, 44.7 and 10.5, based on per cent germination, germination velocity index and seedling survival to Na₂SO₄. The response of N, T and S types to Na₂SO₄ in subsequent shoot proliferation was similar to that of seed germination.     

Predicting the future of forests in the Mediterranean under climate change,with niche‐ and process‐based models: CO2 matters!

Assessing the potential future of current forest stands is a key to design conservation strategies and understanding potential future impacts to ecosystem service supplies. This is particularly true in the Mediterranean basin, where important future climatic changes are expected. Here, we assess and compare two commonly used modeling approaches (niche‐ and process‐based models) to project the future of current stands of three forest species with contrasting distributions, using regionalized climate for continental Spain. Results highlight variability in model ability to estimate current distributions, and the inherent large uncertainty involved in making projections into the future. CO₂ fertilization through projected increased atmospheric CO₂ concentrations is shown to increase forest productivity in the mechanistic process‐based model (despite increased drought stress) by up to three times that of the non‐CO₂ fertilization scenario by the period 2050–2080, which is in stark contrast to projections of reduced habitat suitability from the niche‐based models by the same period. This highlights the importance of introducing aspects of plant biogeochemistry into current niche‐based models for a realistic projection of future species distributions. We conclude that the future of current Mediterranean forest stands is highly uncertain and suggest that a new synergy between niche‐ and process‐based models is urgently needed in order to improve our predictive ability.     

Gnidia (Thymelaeaceae) is not monophyletic: taxonomic implications for Thymelaeoideae and a partial new generic taxonomy for Gnidia

We address the generic limits of Gnidia (Thymelaeaceae) through a phylogenetic analysis of nuclear ribosomal DNA internal transcribed spacer (ITS) and plastid rbcL, trnL intron and trnL‐F intergenic spacer regions. Maximum parsimony and Bayesian inference were used to produce trees and assess internal support. The most significant conclusion drawn from the molecular analysis is that Gnidia is polyphyletic as currently circumscribed, comprising at least four distinct lineages that are each related to other genera within Thymelaeoideae. Gnidia pinifolia and G. racemosa are members of a clade within which Struthiola is embedded; a second group of species allies with Drapetes as sister to Passerina; and a third lineage corresponds to the previously recognized genus Lasiosiphon. The remaining species of Gnidia included in this study are allied with the Australian genus Pimelea. The taxonomic implications of these findings are discussed in relation to the principle of monophyly. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 402–417.     

Population genetic structure of two primary parasitoids of Spodoptera frugiperda (Lepidoptera), Chelonus insularis and Campoletis sonorensis (Hymenoptera): to what extent is the host plant important?

Plant chemistry can strongly influence interactions between herbivores and their natural enemies, either by providing volatile compounds that serve as foraging cues for parasitoids or predators, or by affecting the quality of herbivores as hosts or prey. Through these effects plants may influence parasitoid population genetic structure. We tested for a possible specialization on specific crop plants in Chelonus insularis and Campoletis sonorensis, two primary parasitoids of the fall armyworm, Spodoptera frugiperda. Throughout Mexico, S. frugiperda larvae were collected from their main host plants, maize and sorghum and parasitoids that emerged from the larvae were used for subsequent comparison by molecular analysis. Genetic variation at eight and 11 microsatellites were respectively assayed for C. insularis and C. sonorensis to examine isolation by distance, host plant and regional effects. Kinship analyses were also performed to assess female migration among host‐plants. The analyses showed considerable within population variation and revealed a significant regional effect. No effect of host plant on population structure of either of the two parasitoid species was found. Isolation by distance was observed at the individual level, but not at the population level. Kinship analyses revealed significantly more genetically related—or kin—individuals on the same plant species than on different plant species, suggesting that locally, mothers preferentially stay on the same plant species. Although the standard population genetics parameters showed no effect of plant species on population structure, the kinship analyses revealed that mothers exhibit plant species fidelity, which may speed up divergence if adaptation were to occur.     

Bird migration times, climate change, and changing population sizes

Past studies of bird migration times have shown great variation in migratory responses to climate change. We used 33 years of bird capture data (1970–2002) from Manomet, Massachusetts to examine variation in spring migration times for 32 species of North American passerines. We found that changes in first arrival dates – the unit of observation used in most studies of bird migration times – often differ dramatically from changes in the mean arrival date of the migration cohort as a whole. In our study, the earliest recorded springtime arrival date for each species occurred 0.20 days later each decade. In contrast, the mean arrival dates for birds of each species occurred 0.78 days earlier each decade. The difference in the two trends was largely explained by declining migration cohort sizes, a factor not examined in many previous studies. We found that changes in migration cohort or population sizes may account for a substantial amount of the variation in previously documented changes in migration times. After controlling for changes in migration cohort size, we found that climate variables, migration distance, and date of migration explained portions of the variation in migratory changes over time. In particular, short-distance migrants appeared to respond to changes in temperature, while mid-distance migrants responded particularly strongly to changes in the Southern Oscillation Index. The migration times of long-distance migrants tended not to change over time. Our findings suggest that previously reported changes in migration times may need to be reinterpreted to incorporate changes in migration cohort sizes.