Critical periods for impact of climate warming on early seedling establishment in subarctic tundra

Climate warming is expected to shift bioclimatic zones and plant species distribution. Yet, few studies have explored whether seedling establishment is a possible bottleneck for future migration and population resilience. We test how warming affects the early stages of seedling establishment in 10 plant species in subarctic tundra. To zoom into the life phases where the effects of warming actually take place, we used a novel approach of breaking down the whole‐season warming effect into full factorial combination of early‐, mid‐, and late‐season warming periods. Seeds were sown in containers placed under field conditions in subarctic heath and were exposed to 3 °C elevation of surface temperature and 30% addition of summer precipitation relative to ambient. Heating was achieved with Free Air Temperature Increase systems. Whole‐season heating reduced germination and establishment, significantly in four out of 10 species. The whole‐season warming effect originated from additive effects of individual periods, although some of the periods had disproportionally stronger influence. Early‐germinating species were susceptible to warming; the critical phases were early summer for germination and mid summer for seedling survival. Graminoids, which emerged later, were less susceptible although some negative effects during late summer were observed. Some species with intermediate germination time were affected by all periods of warming. Addition of water generally could not mitigate the negative effects of whole‐season heating, but at individual species level both strengthening and amelioration of these negative effects were observed. We conclude that summer warming is likely to constrain seedling recruitment in open micro sites, which is a common seed regeneration niche in tundra ecosystem. Importantly, we described both significant temporal and species‐specific variation in the sensitivity of seedling establishment to warming which needs to be taken into consideration when modelling population dynamics and vegetation transitions in a warmer climate.     

The dependence of respiration on photosynthetic substrate supply and temperature: integrating leaf, soil and ecosystem measurements

Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO₂ concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week‐to‐week changes in temperature. All three respiration rates responded to the CO₂ concentration‐induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short‐term changes in canopy photosynthesis. The short‐term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q₁₀ was lower in leaves that developed at high CO₂, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short‐ and medium‐term changes in temperature may affect net carbon storage in terrestrial ecosystems.     

Nicotiana plumbaginifolia plants silenced for the ATP-binding cassette transporter gene NpPDR1 show increased susceptibility to a group of fungal and oomycete pathogens

The behaviour of Nicotiana plumbaginifolia plants silenced for the ATP-binding cassette transporter gene NpPDR1 was investigated in response to fungal and oomycete infections. The importance of NpPDR1 in plant defence was demonstrated for two organs in which NpPDR1 is constitutively expressed: the roots and the petal epidermis. The roots of the plantlets of two lines silenced for NpPDR1 expression were clearly more sensitive than those of controls to the fungal pathogens Botrytis cinerea , Fusarium oxysporum sp., F. oxysporum f. sp. nicotianae , F. oxysporum f. sp. melonis and Rhizoctonia solani , as well as to the oomycete pathogen Phytophthora nicotianae race 0. The Ph gene-linked resistance of N. plumbaginifolia to P. nicotianae race 0 was totally ineffective in NpPDR1 -silenced lines. In addition, the petals of the NpPDR1 -silenced lines were spotted 15%–20% more rapidly by B. cinerea than were the controls. The rapid induction (after 2–4 days) of NpPDR1 expression in N. plumbaginifolia and N. tabacum mature leaves in response to pathogen presence was demonstrated for the first time with fungi and one oomycete: R. solani , F. oxysporum and P. nicotianae . With B. cinerea , such rapid expression was not observed in healthy mature leaves. NpPDR1 expression was not observed during latent infections of B. cinerea in N. plumbaginifolia and N. tabacum , but was induced when conditions facilitated B. cinerea development in leaves, such as leaf ageing or an initial root infection. This work demonstrates the increased sensitivity of NpPDR1 -silenced N. plumbaginifolia plants to all of the fungal and oomycete pathogens investigated.     

Systematic within-tree variation in mountain birch leaf quality for a geometrid, Epirrita autumnata

Abstract.

• 1 We studied within-tree variation in leaf quality of the mountain birch, Betula pubescens ssp. tortuosa, for larvae of the autumnal moth, Epirrita autumnata.
• 2 The purpose of the study was to determine the possible occurrence of systematic differences in larval growth on short shoot leaves (i.e. leaves of the same age): among leaves facing in different compass directions, between leaves of lower and upper branches, among leaves on different positions within a branch and among leaves of different sizes within a short shoot. We also measured larval growth between short shoot and long shoot leaves (i.e. between leaves of different age).
• 3 The larvae grew best on leaves on the north side of trees and most poorly on south side leaves, the east and west sides being intermediate. Leaves from the upper branches supported larval growth better than leaves from the lower ones. The larvae grew better on the smallest leaf of each short shoot and were able to utilize it more efficiently than the two larger leaves. Short shoot leaves from the basal and middle parts of the upper branches of the trees were of better quality for the larvae than short shoot leaves from the tip part of the branches. The larval growth rate did not differ between short shoot and long shoot leaves. In general, within-tree variation in the larval growth rate was lower than variation among different trees.
• 4 Damage to leaves can decrease leaf quality for herbivores in the same year (rapidly inducible responses) or the following year(s) (delayed inducible responses). Our results show that systematic within-tree variation in larval growth can be as great as the effects of rapidly inducible responses and that variation among individual trees can be as great as the mean effects of delayed inducible responses.

     

Genetic and morphological variation in a Mediterranean glacial refugium: evidence from Italian pygmy shrews,Sorex minutus (Mammalia: Soricomorpha)

At the Last Glacial Maximum (LGM), the southern European peninsulas were important refugia for temperate species. Current genetic subdivision of species within these peninsulas may reflect past population subdivision at the LGM, as in ‘refugia within refugia’, and/or at other time periods. In the present study, we assess whether pygmy shrew populations from different regions within Italy are genetically and morphologically distinct. One maternally and two paternally inherited molecular markers (cytochrome b and Y‐chromosome introns, respectively) were analysed using several phylogenetic methods. A geometric morphometric analysis was performed on mandibles to evaluate size and shape variability between populations. Mandible shape was also explored with a functional approach that considered the mandible as a first‐order lever affecting bite force. We found genetically and morphologically distinct European, Italian, and southern Italian groups. Mandible size increased with decreasing latitude and southern Italian pygmy shrews exhibited mandibles with the strongest bite force. It is not clear whether or not the southern Italian and Italian groups of pygmy shrews occupied different refugia within the Italian peninsula at the LGM. It is likely, however, that geographic isolation earlier than the LGM on islands at the site of present‐day Calabria was important in generating the distinctive southern Italian group of pygmy shrews, and also the genetic groups in other small vertebrates that we review here. Calabria is an important hotspot for genetic diversity, and is worthy of conservation attention. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 774–787.     

Linking the planktonic and benthic habitat: genetic structure of the marine diatom Skeletonema marinoi

Dormant life stages are important strategies for many aquatic organisms. The formation of resting stages will provide a refuge from unfavourable conditions in the water column, and their successive accumulation in the benthos will constitute a genetic reservoir for future planktonic populations. We have determined the genetic structure of a common bloom‐forming diatom, Skeletonema marinoi, in the sediment and the plankton during spring, summer and autumn two subsequent years (2007–2009) in Gullmar Fjord on the Swedish west coast. Eight polymorphic microsatellite loci were used to assess the level of genetic differentiation and the respective gene diversity of the two different habitats. We also determined the degree of genetic differentiation between the seed banks inside the fjord and the open sea. The results indicate that Gullmar Fjord has one dominant endogenous population of S. marinoi, which is genetically differentiated from the open sea population. The fjord population is encountered in the plankton and in the sediment. Shifts from the dominant population can happen, and in our study, two genetically differentiated plankton populations, displaying reduced genetic diversity, occurred in September 2007 and 2008. Based on our results, we suggest that sill fjords maintain local long‐lived and well‐adapted protist populations, which continuously shift between the planktonic and benthic habitats. Intermittently, short‐lived and mainly asexually reproducing populations can replace the dominant population in the water column, without influencing the genetic structure of the benthic seed bank.     

Movement and phenology of bees in a subtropical Australian agricultural landscape

Bees are mobile organisms that seek food and nesting opportunities from a range of habitats. It is important to understand the way they move in agricultural landscapes if we are to conserve them and benefit from their activity as pollinators. We surveyed bees using directional flight interception (Malaise) traps over a 1‐year period in two agricultural landscapes in south‐east Queensland, Australia. We placed traps at the ecotone between crops and remnant vegetation to establish the pattern of movement between these habitats. Species richness in these landscapes (70) was high relative to that in comparable studies. Some bees were active year round, but most were caught in the period September to March. Across the whole assemblage there was a significant pattern where more species were detected leaving rather than entering remnant vegetation. The same bias was true for the number of individuals of the two most abundant species (Homalictus urbanus and Apis mellifera). Species exclusively found in crops were smaller on average (and therefore have smaller foraging range) than their non‐crop counterparts. Together, these patterns indicate that while bees are abundant in crop habitat, the remnant vegetation is important as the point of origin for bee movements, and the riparian remnant in particular is richer than the dry native remnant. Compositional similarity among samples was significantly explained by landscape but also movement direction (i.e. to or from the riparian remnant) because different species showed different patterns of response. The landscape with greater native vegetation cover supported more species in and around crops than the landscape with less native vegetation.     

YOU CAN USE MY NAME; YOU DON'T HAVE TO STEAL MY STORY – A CRITIQUE OF ANONYMITY IN INDIGENOUS STUDIES

Our claim in this paper is that not being identified as the data source might cause harm to a person or group. Therefore, in some cases the default of anonymisation should be replaced by a careful deliberation, together with research subjects, of how to handle the issues of identification and confidentiality. Our prime example in this article is community participatory research and similar endeavours on indigenous groups. The theme, content and aim of the research, and the question of how to handle property rights and ownership of research results, as well as who should be in charge of the research process, including the process of creating anonymity, should all be answered, before anonymity is accepted.