Phenology affects nearly all aspects of ecology and evolution. Virtually all biological phenomena—from individual physiology to interspecific relationships to global nutrient fluxes—have annual cycles and are influenced by the timing of abiotic events. Recent years have seen a surge of interest in this topic, as an increasing number of studies document phenological responses to climate change. Much recent research has addressed the genetic controls on phenology, modelling techniques and ecosystem-level and evolutionary consequences of phenological change. To date, however, these efforts have tended to proceed independently. Here, we bring together some of these disparate lines of inquiry to clarify vocabulary, facilitate comparisons among habitat types and promote the integration of ideas and methodologies across different disciplines and scales. We discuss the relationship between phenology and life history, the distinction between organismal- and population-level perspectives on phenology and the influence of phenology on evolutionary processes, communities and ecosystems. Future work should focus on linking ecological and physiological aspects of phenology, understanding the demographic effects of phenological change and explicitly accounting for seasonality and phenology in forecasts of ecological and evolutionary responses to climate change.

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Toward a synthetic understanding of the role of phenology in ecology and evolution

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

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In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Gibberellins (GAs) function not only to promote the growth of plant organs, but also to induce phase transitions during development. Their involvement in flower initiation in long-day (LD) and biennial plants is well established and there is growing insight into the mechanisms by which floral induction is achieved. The extent to which GAs mediate the photoperiodic stimulus to flowering in LD plants is, with a few exceptions, less clear. Despite evidence for photoperiod-enhanced GA biosynthesis in leaves of many LD plants, through up-regulation of GA 20-oxidase gene expression, a function for GAs as transmitted signals from leaves to apices in response to LD has been demonstrated only in Lolium species. In Arabidopsis thaliana, as one of four quantitative floral pathways, GA signalling has a relatively minor influence on flowering time in LD, while in SD, in the absence of the photoperiod flowering pathway, the GA pathway assumes a major role and becomes obligatory. Gibberellins promote flowering in Arabidopsis through the activation of genes encoding the floral integrators SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), LEAFY (LFY), and FLOWERING LOCUS T (FT) in the inflorescence and floral meristems, and in leaves, respectively. Although GA signalling is not required for floral organ specification, it is essential for the normal growth and development of these organs. The sites of GA production and action within flowers, and the signalling pathways involved are beginning to be revealed.

Gibberellin as a factor in floral regulatory networks

Annual plants grow vegetatively at early developmental stages and then transition to the reproductive stage, followed by senescence in the same year. In contrast, after successive years of vegetative growth at early ages, woody perennial shoot meristems begin repeated transitions between vegetative and reproductive growth at sexual maturity. However, it is unknown how these repeated transitions occur without a developmental conflict between vegetative and reproductive growth. We report that functionally diverged paralogs FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2), products of whole-genome duplication and homologs of Arabidopsis thaliana gene FLOWERING LOCUS T (FT), coordinate the repeated cycles of vegetative and reproductive growth in woody perennial poplar (Populus spp.). Our manipulative physiological and genetic experiments coupled with field studies, expression profiling, and network analysis reveal that reproductive onset is determined by FT1 in response to winter temperatures, whereas vegetative growth and inhibition of bud set are promoted by FT2 in response to warm temperatures and long days in the growing season. The basis for functional differentiation between FT1 and FT2 appears to be expression pattern shifts, changes in proteins, and divergence in gene regulatory networks. Thus, temporal separation of reproductive onset and vegetative growth into different seasons via FT1 and FT2 provides seasonality and demonstrates the evolution of a complex perennial adaptive trait after genome duplication.

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FLOWERING LOCUS T duplication coordinates reproductive and vegetative growth in perennial poplar

Climate Change and Agriculture in the United States: Effects and Adaptation

The intention of this review is to discuss floral initiation of horticultural trees. Floral initiation is best understood for herbaceous species, especially at the molecular level, so a brief overview of the control of floral initiation of Arabidopsis (Arabidopsis thaliana (L.) Heynh.) precedes the discussion of trees. Four major pathways to flowering have been characterized in Arabidopsis, including environmental induction through photoperiod and temperature, autonomous floral initiation, and regulation by gibberellins. Tropical trees are generally induced to flower through environmental cues, whereas floral initiation of temperate deciduous trees is often autonomous. In the tropical evergreen tree mango, Mangifera indica L., cool temperature is the only factor known to induce flowering, but does not ensure floral initiation will occur because there are important interactions with vegetative growth. The temperate deciduous tree apple, Malus domestica Borkh., flowers autonomously, with floral initiation dependent on aspects of vegetative development in the growing season before anthesis, although with respect to the floral initiation of trees in general: the effect of the environment, interactions with vegetative growth, the roles of plant growth regulators and carbohydrates, and recent advances in molecular biology, are discussed.

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Regulation of floral initiation in horticultural trees

We examined the relationship between shoot growth and temperature and solar radiation in macadamia (Macadamia integrifolia Maiden and Betche, M. integrifolia × tetraphylla Johnson) as an aid to developing pruning strategies for this crop. Trees growing at Alstonville (28.9°S) in northern NSW, Australia, were pruned at various times to promote vegetative flushing under a range of environmental conditions. Flush development in macadamia is cyclic: bud release and stem elongation followed by a period of dormancy, before bud release of the subsequent flush. The rate of bud release after pruning was best correlated with the product of the mean temperature and solar radiation (r2 = 0.75, P < 0.0001), whereas the rate of flush development was best correlated with the mean temperature (r2 = 0.76, P < 0.0001). The number of buds released per pruned stem was greater under higher temperatures and solar radiation (r2 = 0.37, P < 0.001), but the length of the flush after pruning decreased with increasing temperatures (r2 = 0.32, P < 0.01). The descriptive models were combined with long-term weather data to predict the duration and characteristics of flushes following pruning at various times of the year along Australia’s eastern seaboard, from Mareeba (17.0°S) to Coffs Harbour (30.3°S). Flush duration and stem length following June pruning were predicted to be greater than following early autumn or September pruning and to vary from year to year, and with location (latitude). We discuss the implications of the model predictions for productivity and propose pruning times intended to optimise flowering and yield. Further research is required to test these proposed pruning strategies.

A model of vegetative flush development and its potential use managing macadamia (Macadamia integrifolia) tree canopies

Macadamia (Macadamia integrifolia, M. integrifolia × M. tetraphylla) trees were pruned at different times at sites near Alstonville, northern New South Wales, Australia, to examine the effects on vegetative flushing, subsequent flower raceme production and yield. Pruning of cv. 849 and cv. A268 modified the cycle of flush development. Pruning times that resulted in immature flushes on the canopy in late autumn or early winter inhibited raceme production. In contrast, pruning in late May and early June did not generally reduce raceme production relative to production on unpruned trees. The times of pruning that reduced raceme production also reduced yield. The yields of trees pruned in late May were also reduced, presumably because of decreased light interception. In the season after treatment the trees pruned in early April had greater numbers of racemes per unit of tree canopy volume than the trees pruned in late May. The trees of the lighter flowering cv. 849 pruned in early April had higher yield efficiencies than the trees pruned in late May, whereas there was no effect on yield efficiency in the prolifically flowering cv. A268. The differences in raceme production in the season after pruning may have been due to a combination of an alternate bearing response, characteristics of the stems produced after pruning, or maturity of the flushes. In a separate experiment, uniconazole sprays immediately after pruning reduced the length of the new stems, slowed canopy expansion, and increased kernel recovery compared with untreated hedged trees, but did not affect flowering or yield. In another experiment, hedging in early June had no effect on raceme production in cv. 849 trees in consecutive seasons, and no effect on canopy volume or yield in the first season. In contrast, canopy volume and yield were reduced in the second season. Finally, pruning of young, yet-to-flower cv. 849 trees from late winter to spring staggered flush development, with the earliest pruned trees producing more racemes and setting more fruit than the later pruned trees.

The timing of pruning affects flushing, flowering and yield of macadamia

Macadamia (Macadamia integrifolia Maiden and Betche, M. integrifolia × tetraphylla Johnson) flowers are borne on racemes that usually originate from axillary buds in response to cool conditions. In...

John D. Wilkie

Papers

Regulation of floral initiation in horticultural trees

A model of vegetative flush development and its potential use managing macadamia (Macadamia integrifolia) tree canopies

The timing of pruning affects flushing, flowering and yield of macadamia

Characteristics of flowering stems and raceme position in macadamia

The Timing of Pruning Affects Flush Development and Flowering in 'Honey Gold' Mango