A common contaminant shifts impacts of climate change on a plant-microbe mutualism: effects of temperature, CO2 and leachate from tire wear particles

Anthropogenic stressors, such as climate change or chemical pollution, affect individual species and alter species interactions. Moreover, species interactions can modify effects of anthropogenic stressors on interacting species - a process which may vary amongst stressors or stressor combinations. Most ecotoxicological work focuses on single stressors on single species. Here, we test hypotheses about multiple stressors (climate change and tire wear particles) and interacting species, and whether species interactions modify responses. We use duckweed and its microbiome to model responses of plant-microbe interactions. Climate change is occurring globally, and with increasing urbanization, tire wear particles increasingly contaminate road runoff. Their leachate is associated with zinc, PAHs, plastic additives, and other toxic compounds. We crossed perpendicular gradients of temperature and CO2 in a well plate with factorial manipulation of leachate from tire wear particles and presence of duckweed microbiomes. We measured duckweed and microbial growth, duckweed greenness, and plant-microbe growth correlations. We found that tire leachate and warmer temperatures enhanced duckweed and microbial growth, but microbes diminished positive responses in duck-weed, meaning microbiomes became costly for duckweed. These costs of microbiomes were less-than-additive with warming and leachate, and might be caused by leachate-disrupted endocrine signaling in duckweed. We observed reduced greenness at higher CO2 without tire leachate, suggesting a relative increase in plant nutrient demand, and possibly underlying positive plant-microbe growth correlations in these conditions, as microbes presumably increase nutrient availability. However, with tire leachate, growth correlations were never positive, and shifted negative at lower CO2, further suggesting leachate favors mutualism disruption. In summary, while individual stressors of global change can affect individual species, in ecology we know species interact; and in ecotoxicology, we know stressors interact. Our results demonstrate this complexity: multiple stressors can affect species interactions, and species interactions can alter effects of multiple stressors.

Shifts in Climate–Growth Relationships of Sky Island Pines

Rising temperatures and changes in precipitation may affect plant responses, and mountainous regions in particular are sensitive to the impacts of climate change. The Santa Catalina Mountains, near Tucson, Arizona, USA, are among the best known Madrean Sky Islands, which are defined by pine-oak forests. We compared the sensitivity and temporal stability of climate–growth relationships to quantify the growth responses of sympatric taxa of ponderosa pine to changing climate. Three taxa (three-needle, mixed-needle, and five-needle types) collected from southern slopes of two contact zones (Mt. Lemmon, Mt. Bigelow) were evaluated. Positive climate–growth correlations in these semiarid high-elevation pine forests indicated a seasonal shift from summer- to spring-dominant precipitation since 1950, which is a critical time for reproduction. Mixed- and five-needle types responded to winter precipitation, and growth was reduced for the five-needle type when spring conditions were dry. Growth trends in response to temperature and specific to site were observed, which indicated the climate signal can be weakened when data are combined into a single chronology. Significant fluctuations in temperature–growth correlations since 1950 occurred for all needle types. These results demonstrated a dramatic shift in sensitivity of annual tree growth to the seasonality of the limiting factor, and a climatic trend that increases local moisture stress may impact the stability of climate–growth relationships. Moreover, output from temperature–growth analyses based on ring-width data (for example from semiarid sites) that does not account for positive and negative growth trends may be adversely affected, potentially impacting climate reconstructions.

Political Institutions, Economic Liberty, and the Great Divergence

I argue that Europe's political fragmentation interacted with her political innovations—self-governing cities and national parliaments—to facilitate “economic liberty,” which in turn unleashed faster and more inter-connected urban growth. Examining urban growth over the period 600–1800 ce throughout Eurasia, I show that inter-city growth correlations were positive and significant only in Western Europe after 1200 ce. Within Western Europe, I show that growth correlations were greatest in the most fragmented and parliamentary areas, individual cities became significantly more tied to urban growth when their realms became parliamentary, and spillover effects (due to competition between rulers) were significant.

«On the Origin of Species»: Didactic transposition to the curriculum and Portuguese science textbooks (1859-1959)

This research aimed to contribute to the history of the teaching of Darwinism in the Portuguese curriculum from 1859 to 1959. To this end, it was analysed the didactic transposition of the book On the Origin of Species for the standards and textbooks of Natural Sciences of secondary education. This study showed that some standards did not address Darwinism (Standards of 1856, 1872, 1880, 1886, 1926 and 1929), while others only prescribed the study of some subjects of Darwinism (Standards of 1889 and 1905). The standards of 1895 were the ones that addressed more Darwinists ideas in the 19th century. In the 20th century, the overall approach to Darwinism was related to the study of transformist ideas (Standards of 1919) or evolution (Standards of 1936 and 1954). However, even when the respective standards did not make that prescription, the major part of textbooks addressed the mechanisms of Darwinian evolution: adaptation, variability, growth correlations, heredity, natural selection, vital competition, geographic isolation and sexual selection.

Role of cytokinins in growth correlations between roots and stems in pea (Pisum sativum L.) seedlings

Pea seeds were swollen in solutions with different concentrations of cytokinin benzyladenine (BA). As compared with controls, a low concentration of BA (0.05 mg/l) did not affect the growth of stems and roots of twelve-day-old seedlings but concentrations of 0.20–4.00 mg/l showed an inhibiting effect; this inhibition was proportional to the concentration of BA. In controls the ratio between the lengths of stems and roots was equal to 1.14, while in seedlings influenced by BA in concentration of 0.20 mg/l its value was significantly lowered to 0.91. Also in six-day-old pea seedlings cultivated under in vitro conditions, BA concentrations of 0.70 and 3.30 mg/l inhibited the growth of roots and epicotyls and significantly increased the production of ethylene (by 150 and 330%, respectively). Three hours after the amputation of the root of five-day-old pea seedlings the level of cytokinin trans-zeatin increased in the apical part of the stem. Within the interval of 48 hours after the amputation of the root the concentration of this plant hormone gradually decreased again. The initial increase in the zeatin level in the stem indicates that the absence of the root induces a reduction of growth-inhibiting effects of roots, which negatively influences the zeatin level in the stem apex at the beginning of germination.

Spatial and temporal variability in forest growth in the Olympic Mountains, Washington: sensitivity to climatic variability

We compared annual basal area increment (BAI) at different spatial scales among all size classes and species at diverse locations in the wet western and dry northeastern Olympic Mountains. Weak growth correlations at small spatial scales (average R = 0.084–0.406) suggest that trees are responding to local growth conditions. However, significant positive growth correlations between geographically adjacent forest types (R = 0.440–0.852) and between watersheds (R = 0.430) indicate that there is a common overarching growth-limiting factor (e.g., climate) that affects tree growth over large areas. The Sitka spruce (Picea sitchensis (Bong.) Carrière) forest type is the most sensitive to environmental change with the highest mean sensitivity (0.345), the highest potential for annual growth change (mean BAI = 0.0047 m2), and the highest growth variability (coefficient of variation = 0.498). In addition, this forest type is most likely to exhibit extreme positive growth responses (4.2% of years have BAI values 2 standard deviations above the mean). Low-elevation coniferous forests are relatively sensitive to changes in growth-limiting factors (in contrast to the traditional view) and may play an important role in storing carbon in a warmer climate.

Modifications expérimentales de la morphogenèse du système racinaire de jeunes semis d'hévéa (Hevea brasiliensis)

Determining factors involved in root polymorphism were studied in young hevea seedlings (Hevea brasiliensis Mull. Arg.) following an experimental block of the tap root in the laboratory, using minirhizotron grown plants. The authors show that this block promotes different morphogenetic modifications in the root system: regrowth of the early secondary roots having the largest external apex, high density of the ramification zone in the taproot apical area, large growth (associated with an important external diameter at the apex), and orthogeotropism of the sequential secondary roots emerging after the treatment in the zone close to the blockage site. The evolution of morphogenetic potentialities of sequential secondary roots following an inhibition of the taproot growth was confirmed using other cultivation set ups, under controlled (aeropinic) or natural (underground observation windows) conditions. Overall results show that the expression of the early morphogenetic potential acquired by the roots can be modulated by the environmental conditions exerting their effect during their development. Notably, the active growth correlations existing between the taproot and the secondary axes confer a high plasticity to the root system which will permit its adaptation to heterogeneous or restricting environments. These correlative influences are discussed in the frame of an hormono-trophic model for the root morphogenetic determinism, essentially based on taproot dominancy.Key words: articial block, growth correlations, root system, morphogenesis, minirhizotron, Hevea brasiliensis.[Journal translation]

Influences foliaires dans le contrôle du développement des « bourgeons anticipés » chez Vitis vinifera

In grapevines, the young leaves play an important role in the control of the growth of anticipated buds. Through a basipetal inhibition, which these young leaves exercise over subjacent buds, they contribute to apical dominance. This inhibitory influence persists as long as the duration of laminar growth of the leaf; it is neither sector-based nor cumulative; it is perceived even by buds very far from young leaves. This foliar inhibition is also one of the causes of the acrotonic character of lateral ramification that develops, in the apical part of the shoot, after shoot tip removal. In the older part of the shoot, this acrotony, consecutive to a shoot section, is mainly determined by correlations between the buds. All these results are analysed and discussed in regard to morphogenesis elements previously established in other species. The contribution of young leaves to apical dominance has been demonstrated previously in many other plants. On the other hand, in grapevine, this morphogenetic character was unknown. The fact that young leaves contribute to the acrotonic development of the lateral ramifications growing after decapitation of the main shoot constitutes a much more original result because it has rarely been described in previous studies relative to other species. Earlier works also lead us to expect that both correlative inhibitions and competitive process are involved in the correlations between anticipated buds released from apical dominance. Concerning the growth correlations between grapevine buds, only thuse correlations relative to latent buds had been, until now, very much studied. New and precise knowledge on correlations that control the development of anticipated buds are supplied by this work. It appears then that correlations between these two sorts of buds have two common features: inhibition of their growth by young leaves and sectorial character of the inhibitions between the buds. A hypothesis on the mechanisms through which young leaves control the growth of anticipated buds is suggested. These mechanisms probably change in relation with the developmental stage of a bud; before the bud develops, the young leaves exercise on it a basipetal polarized inhibition. As soon as the bud begins to grow, nonpolarized competitive relations become established between the lateral ramification and the upper young leaves.Key words: Vitis vinifera, apical dominance, acrotony, leaves, buds, correlations.