Category Archives: AoB PLANTS

CO2 stimulation of photosynthesis in Liquidambar styraciflua is not sustained during a 12-year field experiment

Sweetgum tree canopy during leaf expansion in early spring 2009 at Oak Ridge National Laboratory. Towers hold pipes that deliver Free Air CO2 Enrichment (FACE) to the canopy. Photo: Jeff Warren

Sweetgum tree canopy during leaf expansion in early spring 2009 at Oak Ridge National Laboratory. Towers hold pipes that deliver Free Air CO2 Enrichment (FACE) to the canopy. Photo: Jeff Warren

Atmospheric carbon dioxide levels have increased by ~ 25% over the last 50 years. While more carbon dioxide can initially stimulate plant photosynthesis, in a new study published in AoB PLANTS, Warren et al. found that long-term (12 years) exposure of sweetgum trees to elevated carbon dioxide resulted in no stimulation of photosynthesis. The loss of initial increases in photosynthesis was due to low leaf nitrogen levels, which suggests other limiting resources may moderate future impacts of elevated carbon dioxide on photosynthesis.

Host tree phenology affects vascular epiphytes at the physiological, demographic and community level

Tree phenology imposes an imprint on epiphyte assemblages from leaf physiology to community composition (Photo credit: Helena Einzmann)

Tree phenology imposes an imprint on epiphyte assemblages from leaf physiology to community composition (Photo credit: Helena Einzmann)

The processes that govern diverse tropical plant communities have rarely been studied in life-forms other than trees. Structurally dependent vascular epiphytes, a major part of tropical biodiversity, grow in a three-dimensional matrix defined by their hosts, but these host trees differ in many ways, not least in leaf phenology. In a recent study published in AoB PLANTS, Einzmann et al. hypothesized that differences in microclimatic conditions in evergreen vs. deciduous trees would affect epiphytes at various levels, from organ physiology to community structure. Indeed, they found that deciduous tree species hosted less abundant and species-poorer epiphyte assemblages. Physiologically, epiphyte assemblages differed in the proportion of CAM species and individuals, and in SLA and δ13C values. Effects were also detectable at a demographic level, i.e. in growth and survival rates. Their results thus suggest a cascading effect of tree composition and associated differences in tree phenology on the diversity and functioning of epiphyte communities in tropical lowland forests.

Differential drought tolerance in tree populations from contrasting elevations

Pinus tabuliformis, reproduced with permission from http://www.cfh.ac.cn

Pinus tabuliformis, reproduced with permission from http://www.cfh.ac.cn

To predict the ecological consequences of climate change for a widely distributed tree species, it is essential to develop a deep understanding of the ecophysiological responses of populations from contrasting climates to varied soil water availabilities. In a new study published in AoB PLANTS, Ma et al. investigated the differential drought tolerance between populations of Pinus tabuliformis from high elevation (HP) and low elevation (LP). Seedlings of these two populations were subjected to a gradual depletion of soil water availability with a series of traits related to growth and water use efficiency being measured. They found that all the measured variables from the HP were affected less by drought compared to those of the LP, and most aspects of the HP were canalized against drought stress. They concluded that the two populations responded differentially to drought stress with the HP showing higher drought tolerance than the LP.

Extrafloral nectar fuels ant life in deserts

Dorymyrmex planidens ants on an EFN secreting cladode bud of the desert cactus Tephrocactus articulatus.

Dorymyrmex planidens ants on an EFN secreting cladode bud of the desert cactus Tephrocactus articulatus.

Many ant–plant associations are mediated by extrafloral nectaries (EFNs): nectar-producing structures not related to pollination and commonly found on leaves and inflorescences. These sweet secretions represent a critical energy resource for many ant species and constitute the basis for protective mutualisms: by providing ants with food, ants protect plants from herbivores. Although EFN-bearing plants occur in a wide range of habitats and climates worldwide, interactions mediated by EFN-bearing plants are poorly documented in deserts. In a recent article published in AoB PLANTS, Aranda-Rickert et al. show that, in a seasonal desert of northwestern Argentina, biotic interactions between EFN-bearing plants and ants are ecologically relevant components of deserts, and that EFN-bearing plants are crucial for the survival of desert ant communities.

Light-dark O2 dynamics in submerged leaves of C3 and C4 halophytes under increased dissolved CO2: Clues for saltmarsh response to climate change

Salt marshes undergo periodic flooding being subjected to the carbonate chemistry of the water column twice per day. Predicted CO2 rising will change this carbonate chemistry and thus affect differentially C3 and C4 halophytes.

Salt marshes undergo periodic flooding being subjected to the carbonate chemistry of the water column twice per day. Predicted CO2 rising will change this carbonate chemistry and thus affect differentially C3 and C4 halophytes.

Global warming and climate change, as driving forces of sea level rise, tend to increase marsh submersion periods and also modify the carbonate chemistry of the water column due to the increased concentration of CO2 in the atmosphere. In a study published in AoB PLANTS, Duarte et al. found photosynthetic enhancement due to increased dissolved CO2 for both C3 and C4 halophytes. Transposing these findings to the ecosystem, and assuming increased dissolved CO2 concentration scenarios, these results demonstrated a new ecosystem function for the halophyte community, by increasing the water column oxygenation, thus reinforcing their role as principal primary producers of the estuarine system.

Maintenance of self-incompatibility in peripheral populations of a circumboreal woodland subshrub

A flowering individual of Linnaea borealis (twinflower) in Xinjiang, northwestern China, noting its clonal production by stolons.  Photo credit: Shuang-Quan Huang

A flowering individual of Linnaea borealis (twinflower) in Xinjiang, northwestern China, noting its clonal production by stolons. Photo credit: Shuang-Quan Huang

Compared with self-incompatible (SI) species, species that shift to self-compatibility (SC) are more likely to colonize a new habitat. Linnaea borealis, named after Carl Linnaeus and commonly known as twinflower, is an undershrub of woods with a circumpolar distribution in boreal forests. Twinflower is SC at the eastern edge of the species distribution in North America, and SI in populations from Canada through Britain to central Sweden. In a new study in AoB PLANTS, Zhang et al. observed that twinflower was strictly SI in northwestern China, the eastern margin of the species’ distribution in Eurasia. Generalist pollinators and clonal reproduction may help L. borealis to colonize in marginal areas without the shift from SI to SC, but with fruit-set failure resulting from self-plant pollination within clones.

More closely related plants have more distinct mycorrhizal communities

14090R1Neighbouring plants are known to vary from having similar to dissimilar arbuscular mycorrhizal fungal (AMF) communities. One possibility is that closely related plants have more similar AMF communities than more distantly related plants, an indication of phylogenetic host specificity. However, in a new study published in AoB PLANTS, Reinhart and Anacker observed that mycorrhizal communities were more divergent among closely related plant species than among distantly related plant species. This was counter to the observation that plant mutualists (e.g. pollinators, seed dispersers) are often shared among closely related host plant species. Since mycorrhizae may affect nutrient competition among neighbouring plants, closely related plant neighbours that associate with unique mycorrhizae may have greater functional complementarity and a greater capacity to coexist.

Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes

14082-TDuring winter dormancy, temperate trees are capable of only a restricted response to wounding. Depending on the ambient temperature during winter dormancy, wounded trees may start compartmentalization, e.g. by producing inhibitory compounds, but it is thought that processes involving cell proliferation, such as the formation of callus and wound xylem, are delayed until the next growing season. In a recent study published in AoB PLANTS, Copini et al. investigated the effect of wounding on Acer palmatum trees during winter-bud dormancy and found that in the cold (4 °C) treatment, wound reactions were virtually absent. In the warm (15 °C) treatment, however, trees reacted actively to wounding within a three-week period by, e.g., forming callus and local wound xylem. They conclude that temperature is an important factor in wound reactions during winter dormancy and may even induce the formation of callus and wound xylem within a three-week period.

Rapid divergence of ecotypes of an invasive plant

14058S1R2Invasive species represent examples of rapid evolutionary change in a relatively short time period. Lantana camara, a well known invasive plant in the tropics and sub-tropics that has expanded its range and successfully established almost throughout India, is a suitable model system to study the mechanisms underlying its rapid spread and evolution. In a new study in AoB PLANTS, Ray and Ray employed population genetics tools and found differential spread of two genetic varieties across the Indian landscape. Varieties also differ in terms of their climatic adaptation and gene flow, indicating possible local adaptation. Together, this may suggest that these varieties are divergent ecotypes at very early stages of differentiation.

Belowground legacies of Pinus contorta invasion and removal result in multiple mechanisms of invasional meltdown

14095R1 Ian Dickie thumbnailInvasive plants alter plant communities and transform landscapes aboveground, but also have strong belowground effects that are potentially even more important to ecosystem outcomes. In a new study published in AoB PLANTS using management treatments of the widespread invasive tree, Lodgepole Pine, Dickie et al. found that pines and pine removal transform belowground ecosystems, increasing ectomycorrhizal inoculum and driving a change from slow-cycling fungal-dominated soils to fast-cycling bacterial-dominated soils with increased nutrient availability. This results in increased growth of graminoids, particularly exotic grasses, and facilitation of Douglas-fir establishment, hindering ecosystem restoration. The results highlight the importance of considering multiple species interactions in invasion, particularly in terms of belowground legacies.