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.
Sex allocation can vary widely among flowers on a plant and among plants within a population. Austen and Weis develop a numerical model and use it to demonstrate that the widespread tendency towards declining fruit set from first to last flowers on plants may contribute to temporal variation in allocation optima. Temporal trends in relative pollen and ovule investment measured in Brassica rapa, however, do not match the predicted trends in functional gender, but some findings of the model, namely decreasing male reproductive success with later flowering onset, may nonetheless apply in this taxon.
Accuracy in prediction of the growth and development of annual crops depends specifically on the ability to predict the time of the change from vegetative to reproductive growth. This determines the weather conditions in which the crop grows so has a major impact on yield. For wheat, the point that marks the transition from growing vegetative to growing reproductive structures occurs at anthesis, the period during which a flower is open and functional. Accurate anthesis models would simulate the underlying processes that lead to anthesis and provide quantitative estimates of occurrence in any specified environment for any specified genotype by linking genetic information to environmental response coefficients. This would enable rapid characterization of the anthesis behaviour of specific genotypes. It would also enable rapid screening of the adaptive fitness of progeny in a breeding programme by linking molecular markers for development genes/alleles to model coefficients and running simulations to determine the range of anthesis times that will occur in the location for which it is being selected. A model that is suitable for these purposes is yet to be created.
A recent paper in Annals of Botany develops a quantitative model of the expression of specific developmental genes and combines it with physiological models that predict anthesis time in response to the environment. This new model provides a framework to test the current genetic models of floral transition in wheat, and will ultimately inform the development of genotypes adapted to specific environments.
Brown, H.E., Jamieson, P.D., Brooking, I.R., Moot, D.J., & Huth, N.I. (2013) Integration of molecular and physiological models to explain time of anthesis in wheat. Annals of botany, 112(9), 1683-1703.
Background: A model to predict anthesis time of a wheat plant from environmental and genetic information requires integration of current concepts in physiological and molecular biology. This paper describes the structure of an integrated model and quantifies its response mechanisms.
Methods: Literature was reviewed to formulate the components of the model. Detailed re-analysis of physiological observations are utilized from a previous publication by the second two authors. In this approach measurements of leaf number and leaf and primordia appearance of near isogenic lines of spring and winter wheat grown for different durations in different temperature and photoperiod conditions are used to quantify mechanisms and parameters to predict time of anthesis.
Conclusions: The analysis integrates molecular biology and crop physiology concepts into a model framework that links different developmental genes to quantitative predictions of wheat anthesis time in different field situations.
In recent years, research in invasion biology has focused increasing attention on understanding the role of phenology in shaping plant invasions. Multiple studies have found non-native species that tend to flower distinctly early or late in the growing season, advance more with warming or have shifted earlier with climate change compared to native species. In a new article published in AoB PLANTS, Wolkovich and Cleland review recent evidence that non-native and invasive plant species may have distinct timings of their seasonal life history characteristics (such as date of leaf out or flowering, that is, their phenology) that allow them to establish in new communities. In particular they examine how invasions may be bolstered by the longer growing seasons associated with climate change. Based on current knowledge of plant phenology and growth strategies—especially rapid growing, early-flowering species versus later-flowering species that make slower-return investments in growth—they project optimal periods for invasions across three distinct systems under current climate change scenarios.
The cambium is the secondary meristem of plants that produces layers of phloem and xylem cells that envelope the wood cylinders of stem, branches and roots, and results in seasonal radial growth. In temperate, boreal and some tropical ecosystems, the cambium undergoes winter dormancy, producing annual tree rings. During development, the xylem undergoes several different biochemical processes throughout its sequential stages of maturation. Secondary growth represents an intriguing model of complex processes of single cells that gradually and successively proliferate during a growing season. In contrast to the primary meristems (leaf and flower buds), cambial activity (e.g. cell division and differentiation) occurs within the plants and cannot be directly observed during the growing season.
Species native to colder climates are associated with a short growing season and low growth and productivity. At higher latitudes and altitudes, growth has to be completed within a limited time period and in less favourable conditions than in temperate climates. Species adjust their phenology with shifted or compressed growth and reproduction phases, according to specific regional environmental drivers, local adaptations and individual plasticity to climate. It is unclear if and how this pattern applies to the cambium and its phenology across taxonomic groups and locations.
A recent paper in Annals of Botany examines whether phases of xylem production and differentiation occur independently of each other. If any relationships exist among the cambial phenological timings, what is their form (e.g. linear or not) and what does this imply about cambial and growth processes? Answers to these questions could contribute to a more complete understanding of the growth dynamics of forest ecosystems and their possible large-scale responses to climate change.
A meta-analysis of cambium phenology and growth: linear and non-linear patterns in conifers of the northern hemisphere. (2013) Annals of Botany, 112(9), 1911-1920.
Background: Ongoing global warming has been implicated in shifting phenological patterns such as the timing and duration of the growing season across a wide variety of ecosystems. Linear models are routinely used to extrapolate these observed shifts in phenology into the future and to estimate changes in associated ecosystem properties such as net primary productivity. Yet, in nature, linear relationships may be special cases. Biological processes frequently follow more complex, non-linear patterns according to limiting factors that generate shifts and discontinuities, or contain thresholds beyond which responses change abruptly. This study investigates to what extent cambium phenology is associated with xylem growth and differentiation across conifer species of the northern hemisphere.
Methods: Xylem cell production is compared with the periods of cambial activity and cell differentiation assessed on a weekly time scale on histological sections of cambium and wood tissue collected from the stems of nine species in Canada and Europe over 1–9 years per site from 1998 to 2011.
Results: The dynamics of xylogenesis were surprisingly homogeneous among conifer species, although dispersions from the average were obviously observed. Within the range analysed, the relationships between the phenological timings were linear, with several slopes showing values close to or not statistically different from 1. The relationships between the phenological timings and cell production were distinctly non-linear, and involved an exponential pattern
Conclusions: The trees adjust their phenological timings according to linear patterns. Thus, shifts of one phenological phase are associated with synchronous and comparable shifts of the successive phases. However, small increases in the duration of xylogenesis could correspond to a substantial increase in cell production. The findings suggest that the length of the growing season and the resulting amount of growth could respond differently to changes in environmental conditions.
Following from yesterday, do pollinators act as selectors for evolution? A pollinator shift explains floral divergence in an orchid species complex in South Africa by Peter and Johnson tests this idea.
The orchid in question is Eulophia parviflora. This is a deceptive orchid found in Africa, and deceptive means it doesn’t offer a reward to pollinators, it merely looks like it does. The aim is to entice insects in when they look for food and hit them with their pollinaria to carry to other orchids. To do this they need to look and smell convincing, but they also need to make things as easy as possible for the pollinators. The orchid’s problem is that there are so many insects that it could build its flowers in all sorts of ways.
This is indeed what happens.
Peter and Johnson identified two forms of Eulophia parviflora. In the image above, the one on the left is the short-spur morph. This grows tall from the ground with plenty of flowers. The one on the right is the long-spur version. This opens when the stalk is barely out of the ground. They look different and they smell different, but they’re both E. parviflora. So what is it that makes the same plant grow long or short spurs?
The answer seems to be the pollinators. The short-spur plants are pollinated by the beetle Cyrtothyrea marginalis who can get in close to the orchid. The long-spur orchid is pollinated the bee Amegilla fallax. However, simply watching and seeing that the plant has two forms pollinated by two different creatures isn’t enough. There might be some other cause, like local climate that explains the spurs and the presence or lack of an insect. So Peter and Johnson have done some experiments.
Are bees deliberately picking long-spurs in flowers? If they are then that would show the bees are selecting flowers and helping drive the morphological change. The experiment is simple. Reduce the size of the spurs in some of the long-spur flowers. If the spurs matter, then the bees will pick the long-spur plants and ignore the short spur plants. Sure enough, the bees went for the long-spur flowers.
Another experiment was to see how the scent attracted insects. They tried it with both beetles and bees, but found the bees weren’t cooperating, so there were just results from beetles. The experiment is simple and elegant. You have a Y shape. At the top of each arm of the Y you have a fan pushing out the scent of a flower. Put a beetle at the bottom and where does it go to? In this case, it picks the scent of the short-spur plant.
In fact the paper notes the experiment wasn’t quite as simple as I made out. It wasn’t just the scent that attracted beetles, they’d also pick a tunnel depending on the position of the sun, so they found they had to calibrate the tunnels properly before they could sensibly test the beetles.
Peter and Johnson also show that the two forms of the plant are not just diverging in shape but also in time. It makes sense to flower when the pollinators are about. The short-spur flower doesn’t start till after the winter frosts in October (remember South Africa is in the southern hemisphere). This is when the beetles emerge. In contrast the long-spur flower can get going sooner in July when A. fallax starts getting active.
The isolation in time for exchanging pollen, and the specificity of the pollinators means that the pollinators seem to be definitely acting as selectors for the plants. Peter and Johnson say that the two forms might already be considered two sister species given the genetic differences.
The within-season timing of shoot growth in trees has often been considered independently of shoot growth rate. Schiestl-Aalto et al. study lateral shoot growth in Scots pine (Pinus sylvestris) over 7 years and find that daily maximum growth rate correlates positively with growth duration, expressed as thermal time. Higher July–August temperature of the previous summer also prolongs the growth period. The results suggest that the thermal-time requirement for completion of lateral shoot extension in Scots pine may interact with resource availability to the shoot, both from year to year and among shoots in a crown each year. If growing season temperatures rise in the future, this will affect not only the rate of shoot growth but also its duration.
Brunonia australis and Calandrinia sp. are Australian native herbs with commercial potential as flowering potted or bedding plants. Both species are best grown as annuals and flower naturally during spring and early summer. However, many ornamental plants are grown outside their natural flowering period to align flowering with peak market demand, which requires the capacity to predict flowering date under changing or different environments. Scheduling crop production using quantitative flowering time models can have considerable advantages as they can be tailored for individual requirements, unlike traditional scheduling methods that are typically based on calendar date and have no particular reference to the environment.
Most development rate models for ornamental species predict flowering time in relation to temperature, photoperiod and/or daily light integral as observed for the above models. However, there are few flowering time models for ornamental plants that include a vernalization function. Vernalization is important for early and complete flowering of many traditional herbaceous crops. Plant responses to vernalization have been incorporated into some models for field crops and arabidopsis, which reportedly improved accuracy. A new paper in Annals of Botany quantifies temperature and photoperiod or vernalization responses of B. australis and Calandrinia sp. and model development for the purpose of scheduling year-round flowering. The effects of temperature and photoperiod or vernalization on plant quality characteristics, including flower and branch number, were defined.
Modelling temperature, photoperiod and vernalization responses of Brunonia australis (Goodeniaceae) and Calandrinia sp. (Portulacaceae) to predict flowering time. Ann Bot (2013) 111 (4): 629-639.
Crop models for herbaceous ornamental species typically include functions for temperature and photoperiod responses, but very few incorporate vernalization, which is a requirement of many traditional crops. This study investigated the development of floriculture crop models, which describe temperature responses, plus photoperiod or vernalization requirements, using Australian native ephemerals Brunonia australis and Calandrinia sp.
A novel approach involved the use of a field crop modelling tool, DEVEL2. This optimization program estimates the parameters of selected functions within the development rate models using an iterative process that minimizes sum of squares residual between estimated and observed days for the phenological event. Parameter profiling and jack-knifing are included in DEVEL2 to remove bias from parameter estimates and introduce rigour into the parameter selection process.
Development rate of B. australis from planting to first visible floral bud (VFB) was predicted using a multiplicative approach with a curvilinear function to describe temperature responses and a broken linear function to explain photoperiod responses. A similar model was used to describe the development rate of Calandrinia sp., except the photoperiod function was replaced with an exponential vernalization function, which explained a facultative cold requirement and included a coefficient for determining the vernalization ceiling temperature. Temperature was the main environmental factor influencing development rate for VFB to anthesis of both species and was predicted using a linear model.
The phenology models for B. australis and Calandrinia sp. described development rate from planting to VFB and from VFB to anthesis in response to temperature and photoperiod or vernalization and may assist modelling efforts of other herbaceous ornamental plants. In addition to crop management, the vernalization function could be used to identify plant communities most at risk from predicted increases in temperature due to global warming.
In plants that produce both closed, obligatory self-pollinated (cleistogamous) and open, potentially out-crossed (chasmogamous) flowers, suboptimal conditions typically favour production of cleistogamous flowers. Munguía-Rosas et al. study the effects of shade and drought on Ruellia nudiflora and find that cleistogamous flowers are produced earlier under shaded conditions whilst chasmogamous flowers are produced for shorter periods; however, resources are preferentially allocated to those chasmogamous flowers receiving larger pollen loads. The results demonstrate complex interactions between environment and reproduction in cleistogamous plants.
Genome size is known to affect various plant traits such as stomatal size and seed mass but these associations are not well understood for species with very large genomes, which are largely represented by geophytic plants. Veselý et al. survey genome size across 219 geophytes and find that it is associated with species’ ecology and phenology, and analysis also shows an association with changes in DNA base composition. They suggest that although production of larger cells appears to be an advantageous strategy for fast development in seasonal habitats, the drought sensitivity of large stomata may restrict the occurrence of geophytes with very large genomes to regions not subject to water stress.