Nitrogen and water addition reduce leaf longevity of steppe species

Background and aims

Changes in supplies of resources will modify plant functional traits. However, few experimental studies have addressed the effects of nitrogen and water variations, either singly or in combination, on functional traits.

Methods

A 2-year field experiment was conducted to test the effects of nitrogen and water addition on leaf longevity and other functional traits of the two dominant (Agropyron cristatum and Stipa krylovii) and three most common species (Cleistogenes squarrosa, Melilotoides ruthenica and Potentilla tanacetifolia) in a temperate steppe in northern China.

Key Results

Additional nitrogen and water increased leaf nitrogen content and net photosynthetic rate, and changed other measured functional traits. Leaf longevity decreased significantly with both nitrogen addition (–6 days in 2007 and –5·4 days in 2008; both P < 0·001) and watering (–13 days in 2007 and –9·9 days in 2008; both P < 0·001), and significant differences in leaf longevity were also found among species. Nitrogen and water interacted to affect leaf longevity and other functional traits. Soil water content explained approx. 70 % of the shifts in leaf longevity. Biomass at both species and community level increased under water and nitrogen addition because of the increase in leaf biomass production per individual plant.

Conclusions

The results suggest that additional nitrogen and water supplies reduce plant leaf longevity. Soil water availability might play a fundamental role in determining leaf longevity and other leaf functional traits, and its effects can be modified by soil nitrogen availability in semi-arid areas. The different responses of species to resource alterations may cause different global change ramifications under future climate change scenarios.     

Stem growth habit affects leaf morphology and gas exchange traits in soybean

Backgrounds and Aims

The stem growth habit, determinate or indeterminate, of soybean, Glycine max, varieties affects various plant morphological and developmental traits. The objective of this study is to identify the effect of stem growth habit in soybean on the stomatal conductance of single leaves in relation to their leaf morphology in order to better understand the ecological and agronomic significance of this plant trait.

Methods

The stomatal conductance of leaves on the main stem was measured periodically under favourable field conditions to evaluate g_max, defined as the maximum stomatal conductance at full leaf expansion, for four varieties of soybean and their respective determinate or indeterminate near isogenic lines (NILs). Leaf morphological traits including stomatal density, guard cell length and vein density were also measured.

Key Results

The value of g_max ranged from 0·383 to 0·754 mol H₂O m⁻² s⁻¹ across all the genotypes for both years. For the four pairs of varieties, the indeterminate lines exhibited significantly greater g_max, stomatal density, numbers of epidermal cells per unit area and total vein length per unit area than their respective determinate NILs in both years. The guard cell length, leaf mass per area and single leaf size all tended to be greater in the determinate types. The variation of g_max across genotypes and years was well explained by the product of stomatal density and guard cell length (r = 0·86, P < 0·01).

Conclusions

The indeterminate stem growth habit resulted in a greater maximum stomatal conductance for soybean than the determinate habit, and this was attributed to the differences in leaf structure. This raises the further hypothesis that the difference in stem growth habit results in different water use characteristics of soybean plants in the field. Stomatal conductance under favourable conditions can be modified by leaf morphological traits.Key words: Soybean, Glycine max, stem growth habit, stomatal conductance, stomatal density, guard cell length, near isogenic lines     

No divergence in Cassiope tetragona: persistence of growth response along a latitudinal temperature gradient and under multi-year experimental warming

Background and Aims

The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate reconstructions, the reliability of which depends on the existence of a linear climate–growth relationship. This relationship was examined over a high-arctic to sub-arctic temperature gradient and under multi-year artificial warming at a high-arctic site.

Methods

Growth chronologies of annual shoot length, as well as total leaf length, number of leaves and average leaf length per year, were constructed for three sites. Cassiope tetragona was sampled near its cold tolerance limit at Ny-Ålesund, Svalbard, at its assumed climatic optimum in Endalen, Svalbard, and near its European southern limit at Abisko, Sweden. Together these sites represent the entire temperature gradient of this species. Leaf life span was also determined. Each growing season from 2004 to 2010, 17 open top chambers (OTCs) were placed near Ny-Ålesund, thus increasing the daily mean temperatures by 1·23°C. At the end of the 2010 growing season, shoots were harvested from OTCs and control plots, and growth parameters were measured.

Key Results

All growth parameters, except average leaf length, exhibited a linear positive response (R² between 0·63 and 0·91) to mean July temperature over the temperature gradient. Average leaf life span was 1·4 years shorter in sub-arctic Sweden compared with arctic Svalbard. All growth parameters increased in response to the experimental warming; the leaf life span was, however, not significantly affected by OTC warming.

Conclusions

The linear July temperature–growth relationships, as well as the 7 year effect of experimental warming, confirm that the growth parameters annual shoot length, total leaf length and number of leaves per year can reliably be used for monitoring and reconstructing temperature changes. Furthermore, reconstructing July temperature from these parameters is not hampered by divergence.     

Anatomical and physiological plasticity in Leymus chinensis (Poaceae) along large-scale longitudinal gradient in northeast China

Background

Although it has been widely accepted that global changes will pose the most important constrains to plant survival and distribution, our knowledge of the adaptive mechanism for plant with large-scale environmental changes (e.g. drought and high temperature) remains limited.

Methodology/Principal findings

An experiment was conducted to examine anatomical and physiological plasticity in Leymus chinensis along a large-scale geographical gradient from 115° to 124°E in northeast China. Ten sites selected for plant sampling at the gradient have approximately theoretical radiation, but differ in precipitation and elevation. The significantly increasing in leaf thickness, leaf mass per area, vessel and vascular diameters, and decreasing in stoma density and stoma index exhibited more obvious xerophil-liked traits for the species from the moist meadow grassland sites in contrast to that from the dry steppe and desert sites. Significant increase in proline and soluble sugar accumulation, K⁺/Na⁺ for the species with the increasing of stresses along the gradient showed that osmotic adjustment was enhanced.

Conclusion/Significance

Obvious xerophytic anatomical traits and stronger osmotic adjustment in stress conditions suggested that the plants have much more anatomical and physiological flexibilities than those in non-stress habitats along the large-scale gradient.     

Is leaf dry matter content a better predictor of soil fertility than specific leaf area?

Background and Aims

Specific leaf area (SLA), a key element of the ‘worldwide leaf economics spectrum’, is the preferred ‘soft’ plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?

Methods

SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.

Key Results

Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.

Conclusions

Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.     

High temperature triggers latent variation among individuals: oviposition rate and probability for outbreaks

Background

It is anticipated that extreme population events, such as extinctions and outbreaks, will become more frequent as a consequence of climate change. To evaluate the increased probability of such events, it is crucial to understand the mechanisms involved. Variation between individuals in their response to climatic factors is an important consideration, especially if microevolution is expected to change the composition of populations.

Methodology/Principal Findings

Here we present data of a willow leaf beetle species, showing high variation among individuals in oviposition rate at a high temperature (20°C). It is particularly noteworthy that not all individuals responded to changes in temperature; individuals laying few eggs at 20°C continued to do so when transferred to 12°C, whereas individuals that laid many eggs at 20°C reduced their oviposition and laid the same number of eggs as the others when transferred to 12°C. When transferred back to 20°C most individuals reverted to their original oviposition rate. Thus, high variation among individuals was only observed at the higher temperature. Using a simple population model and based on regional climate change scenarios we show that the probability of outbreaks increases if there is a realistic increase in the number of warm summers. The probability of outbreaks also increased with increasing heritability of the ability to respond to increased temperature.

Conclusions/Significance

If climate becomes warmer and there is latent variation among individuals in their temperature response, the probability for outbreaks may increase. However, the likelihood for microevolution to play a role may be low. This conclusion is based on the fact that it has been difficult to show that microevolution affect the probability for extinctions. Our results highlight the urge for cautiousness when predicting the future concerning probabilities for extreme population events.     

Interspecific prediction of photosynthetic light response curves using specific leaf mass and leaf nitrogen content: effects of differences in soil fertility and growth irradiance

Background and Aims

Previous work has shown that the entire photosynthetic light response curve, based on both Mitscherlich and Michaelis–Menten functions, could be predicted in an interspecific context through allometric relations linking the parameters of these functions to two static leaf traits: leaf nitrogen (N) content and leaf mass per area (LMA). This paper describes to what extent these allometric relations are robust to changes in soil fertility and the growth irradiance of the plants.

Methods

Plants of 25 herbaceous species were grown under controlled conditions in factorial combinations of low/high soil fertility and low/high growth irradiance. Net photosynthetic rates per unit dry mass were measured at light intensities ranging from 0 to 700 µmol m⁻² s⁻¹ photosynthetically active radiation (PAR).

Key Results

The differing growth environments induced large changes in N, LMA and in each of the parameter estimates of the Mitscherlich and Michaelis–Menten functions. However, the differing growth environments induced only small (although significant) changes in the allometric relationships linking N and LMA to the parameters of the two functions. As a result, 88 % (Mitcherlich) and 89 % (Michaelis–Menten) of the observed net photosynthetic rates over the full range of light intensities (0–700 µmol m⁻² s⁻¹ PAR) and across all four growth environments could be predicted using only N and LMA using the same allometric relations.

Conclusions

These results suggest the possibility of predicting net photosynthetic rates in nature across species over the full range of light intensities using readily available data.     

Extreme variation in floral characters and its consequences for pollinator attraction among populations of an Andean cactus

Background and aims

A South American cactus species, Echinopsis ancistrophora (Cactaceae), with dramatic among-population variation in floral traits is presented.

Methods

Eleven populations of E. ancistrophora were studied in their habitats in northern Argentina, and comparisons were made of relevant floral traits such as depth, stigma position, nectar volume and sugar concentration, and anthesis time. Diurnal and nocturnal pollinator assemblages were evaluated for populations with different floral trait combinations.

Key Results

Remarkable geographical variations in floral traits were recorded among the 11 populations throughout the distribution range of E. ancistrophora, with flower lengths ranging from 4·5 to 24·1 cm. Other floral traits associated with pollinator attraction also varied in a population-specific manner, in concert with floral depth. Populations with the shortest flowers showed morning anthesis and those with the longest flowers opened at dusk, whereas those with flowers of intermediate length opened at unusual times (2300–0600 h). Nectar production varied non-linearly with floral length; it was absent to low (population means up to 15 µL) in short- to intermediate-length flowers, but was high (population means up to 170 µL) in the longest tubed flowers. Evidence from light-trapping of moths, pollen carriage on their bodies and moth scale deposition on stigmas suggests that sphingid pollination is prevalent only in the four populations with the longest flowers, in which floral morphological traits and nectar volumes match the classic expectations for the hawkmoth pollination syndrome. All other populations, with flowers 4·5–15 cm long, were pollinated exclusively by solitary bees.

Conclusions

The results suggest incipient differentiation at the population level and local adaptation to either bee or hawkmoth (potentially plus bee) pollination.Key words: Pollination, floral biology, Echinopsis ancistrophora, cactus, Cactaceae, hawkmoth, bee     

Ecological correlates of ex situ seed longevity: a comparative study on 195 species

Background and Aims

Extended seed longevity in the dry state is the basis for the ex situ conservation of ‘orthodox’ seeds. However, even under identical storage conditions there is wide variation in seed life-span between species. Here, the effects of seed traits and environmental conditions at the site of collection on seed longevity is explored for195 wild species from 71 families from environments ranging from cold deserts to tropical forests.

Methods

Seeds were rapidly aged at elevated temperature and relative humidity (either 45°C and 60% RH or 60°C and 60% RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50% (p₅₀) was determined using Probit analysis and used as a measure of relative seed longevity between species.

Key Results

Across species, p₅₀ at 45°C and 60% RH varied from 0·1 d to 771 d. Endospermic seeds were, in general, shorter lived than non-endospermic seeds and seeds from hot, dry environments were longer lived than those from cool, wet conditions. These relationships remained significant when controlling for the effects of phylogenetic relatedness using phylogenetically independent contrasts. Seed mass and oil content were not correlated with p₅₀.

Conclusions

The data suggest that the endospermic seeds of early angiosperms which evolved in forest understorey habitats are short-lived. Extended longevity presumably evolved as a response to climatic change or the invasion of drier areas. The apparent short-lived nature of endospermic seeds from cool wet environments may have implications for re-collection and re-testing strategies in ex situ conservation.Key words: Gene banks, seed ageing, seed longevity, taxonomic trends, climate, seed structure     

Duration of xylogenesis in black spruce lengthened between 1950 and 2010

Background and Aims

Reconstructions have identified the 20th century as being uniquely warm in the last 1000 years. Changes in the phenology of primary meristems converged toward increases in length of the growing season. Has the phenology of secondary meristem changed during the last century, and to what extent?

Methods

Timings of wood formation in black spruce, Picea mariana, were monitored for 9 years on a weekly timescale at four sites in the boreal forest of Quebec, Canada. Models for assessing xylem phenology were defined and applied to reconstruct onset, ending and duration of xylogenesis between 1950 and 2010 using thermal thresholds on chronologies of maximum and minimum temperatures.

Key Results

All sites exhibited increasing trends of both annual and May–September temperatures, with the greatest changes observed at the higher latitudes. Phenological events in spring were more affected than those occurring in autumn, with cambial resumptions occurring 0·5–0·8 d decade⁻¹ earlier. The duration of xylogenesis has lengthened significantly since 1950, although the models supplied wide ranges of variations, between 0·07 and 1·5 d decade⁻¹, respectively.

Conclusions

The estimated changes in past cambial phenology demonstrated the marked effects of the recent increase in temperature on the phenological traits of secondary meristems. In the long run, the advancement of cambial activity could modify the short time window for growth of boreal species and dramatically affect the dynamics and productivity of trees in these temperature-limited ecosystems.     

Independent effects of warming and nitrogen addition on plant phenology in the Inner Mongolian steppe

Background and Aims

Phenology is one of most sensitive traits of plants in response to regional climate warming. Better understanding of the interactive effects between warming and other environmental change factors, such as increasing atmosphere nitrogen (N) deposition, is critical for projection of future plant phenology.

Methods

A 4-year field experiment manipulating temperature and N has been conducted in a temperate steppe in northern China. Phenology, including flowering and fruiting date as well as reproductive duration, of eight plant species was monitored and calculated from 2006 to 2009.

Key Results

Across all the species and years, warming significantly advanced flowering and fruiting time by 0·64 and 0·72 d per season, respectively, which were mainly driven by the earliest species (Potentilla acaulis). Although N addition showed no impact on phenological times across the eight species, it significantly delayed flowering time of Heteropappus altaicus and fruiting time of Agropyron cristatum. The responses of flowering and fruiting times to warming or N addition are coupled, leading to no response of reproductive duration to warming or N addition for most species. Warming shortened reproductive duration of Potentilla bifurca but extended that of Allium bidentatum, whereas N addition shortened that of A. bidentatum. No interactive effect between warming and N addition was found on any phenological event. Such additive effects could be ascribed to the species-specific responses of plant phenology to warming and N addition.

Conclusions

The results suggest that the warming response of plant phenology is larger in earlier than later flowering species in temperate grassland systems. The effects of warming and N addition on plant phenology are independent of each other. These findings can help to better understand and predict the response of plant phenology to climate warming concurrent with other global change driving factors.     

A genetic resource for early-morning flowering trait of wild rice Oryza officinalis to mitigate high temperature-induced spikelet sterility at anthesis

Background and Aims

High temperatures over 32–36 °C at anthesis induce spikelet sterility in rice. The use of a germplasm with an early-morning flowering (EMF) trait has been hypothesized as a way of avoiding this problem. In this study, the effect of the EMF trait on avoiding high temperature-induced sterility at anthesis by flowering at a cooler temperature in the early morning was evaluated.

Methods

The EMF trait was introgressed from wild rice (Oryza officinalis) into the rice cultivar ‘Koshihikari’ (O. sativa). First, spikelets of the EMF line and Koshihikari were subjected to rising temperatures during the daytime in the greenhouse to test for differences in spikelet sterility. Secondly, spikelets of both plants were exposed to 26, 34 and 38 °C at anthesis and to 38 °C beginning at least 1 h after flowering, in the growth chambers at 70 % relative humidity, to test for differences in tolerance to high temperatures.

Key Results

Spikelets of the EMF line started and completed flowering a few hours earlier than Koshihikari. In a greenhouse experiment, spikelets of Koshihikari opened after the air temperature reached 35 °C, but those of the EMF line could open at cooler temperatures. Under these conditions, spikelet sterility significantly increased in Koshihikari, but did not in the EMF line. The number of sterile spikelets increased as their flowering time was delayed in Koshihikari. Furthermore, the chamber experiments revealed that 60 % of the spikelets from both lines were sterile when exposed to 38 °C at anthesis, indicating that tolerance of high temperature was similar in both genotypes.

Conclusions

Reduced sterility in the EMF line subjected to rising temperatures at anthesis in the greenhouse was attributed to an earlier flowering time compared with Koshihikari. The EMF trait of wild rice is effective in mitigating anticipated yield loss due to global warming by escaping high-temperature stress at anthesis during the daytime.     

Simulating the influence of vernalization, photoperiod and optimum temperature on wheat developmental rates

Background and Aims

Accurately representing development is essential for applying crop simulations to investigate the effects of climate, genotypes or crop management. Development in wheat (Triticum aestivum, T. durum) is primarily driven by temperature, but affected by vernalization and photoperiod, and is often simulated by reducing thermal-time accumulation using vernalization or photoperiod factors or limiting accumulation when a lower optimum temperature (T_optl) is exceeded. In this study T_optl and methods for representing effects of vernalization and photoperiod on anthesis were examined using a range of planting dates and genotypes.

Methods

An examination was made of T_optl values of 15, 20, 25 and 50 °C, and either the most limiting or the multiplicative value of the vernalization and photoperiod development rate factors for simulating anthesis. Field data were from replicated trials at Ludhiana, Punjab, India with July through to December planting dates and seven cultivars varying in vernalization response.

Key Results

Simulations of anthesis were similar for T_optl values of 20, 25 and 50 °C, but a T_optl of 15 °C resulted in a consistent bias towards predicting anthesis late for early planting dates. Results for T_optl above 15 °C may have occurred because mean temperatures rarely exceeded 20 °C before anthesis for many planting dates. For cultivars having a strong vernalization response, anthesis was more accurately simulated when vernalization and photoperiod factors were multiplied rather than using the most limiting of the two factors.

Conclusions

Setting T_optl to a high value (30 °C) and multiplying the vernalization and photoperiod factors resulted in accurately simulating anthesis for a wide range of planting dates and genotypes. However, for environments where average temperatures exceed 20 °C for much of the pre-anthesis period, a lower T_optl (23 °C) might be appropriate. These results highlight the value of testing a model over a wide range of environments.Key words: Wheat, Triticum aestivum, T. durum, air temperature, thermal time, shoot apex, phenology, growth stages, anthesis, flowering     

Phenology and growth adjustments of oil palm (Elaeis guineensis) to photoperiod and climate variability

Background and Aims

Oil palm flowering and fruit production show seasonal maxima whose causes are unknown. Drought periods confound these rhythms, making it difficult to analyse or predict dynamics of production. The present work aims to analyse phenological and growth responses of adult oil palms to seasonal and inter-annual climatic variability.

Methods

Two oil palm genotypes planted in a replicated design at two sites in Indonesia underwent monthly observations during 22 months in 2006–2008. Measurements included growth of vegetative and reproductive organs, morphology and phenology. Drought was estimated from climatic water balance (rainfall – potential evapotranspiration) and simulated fraction of transpirable soil water. Production history of the same plants for 2001–2005 was used for inter-annual analyses.

Key Results

Drought was absent at the equatorial Kandista site (0°55′N) but the Batu Mulia site (3°12′S) had a dry season with variable severity. Vegetative growth and leaf appearance rate fluctuated with drought level. Yield of fruit, a function of the number of female inflorescences produced, was negatively correlated with photoperiod at Kandista. Dual annual maxima were observed supporting a recent theory of circadian control. The photoperiod-sensitive phases were estimated at 9 (or 9 + 12 × n) months before bunch maturity for a given phytomer. The main sensitive phase for drought effects was estimated at 29 months before bunch maturity, presumably associated with inflorescence sex determination.

Conclusion

It is assumed that seasonal peaks of flowering in oil palm are controlled even near the equator by photoperiod response within a phytomer. These patterns are confounded with drought effects that affect flowering (yield) with long time-lag. Resulting dynamics are complex, but if the present results are confirmed it will be possible to predict them with models.     

Pushed to the limit: consequences of climate change for the Araucariaceae: a relictual rain forest family

Background and Aims

Under predicted climate change scenarios, increased temperatures are likely to predispose trees to leaf and other tissue damage, resulting in plant death and contraction of already narrow distribution ranges in many relictual species. The effects of predicted upward temperatures may be further exacerbated by changes in rainfall patterns and damage caused by frosts on trees that have been insufficiently cold-hardened. The Araucariaceae is a relictual family and the seven species found in Australia have limited natural distributions characterized by low frost intensity and frequency, and warm summer temperatures. The temperature limits for these species were determined in order to help understand how such species will fare in a changing climate.

Methods

Experiments were conducted using samples from representative trees of the Araucariaceae species occurring in Australia, Agathis (A. atropurpurea, A. microstachya and A. robusta), Arauacaria (A. bidwilli, A. cunninghamii and A. heterophylla) and Wollemia nobilis. Samples were collected from plants grown in a common garden environment. Lower and higher temperature limits were determined by subjecting detached winter-hardened leaves to temperatures from 0 to –17 °C and summer-exposed leaves to 25 to 63 °C, then measuring the efficiency of photosystem II (F_v/F_m) and visually rating leaf damage. The exotherm, a sharp rise in temperature indicating the point of ice nucleation within the cells of the leaf, was measured on detached leaves of winter-hardened and summer temperature-exposed leaves.

Key Results

Lower temperature limits (indicated by FT₅₀, the temperature at which PSII efficiency is 50 %, and LT₅₀ the temperature at which 50 % visual leaf damage occurred) were approx. –5·5 to –7·5 °C for A. atropurpurea, A. microstachya and A. heterophylla, approx. –7 to –9 °C for A. robusta, A. bidwillii and A. cunninghamii, and –10·5 to –11 °C for W. nobilis. High temperature damage began at 47·5 °C for W. nobilis, and occurred in the range 48·5–52 °C for A. bidwillii and A. cunninghamii, and in the range 50·5–53·5 °C for A. robusta, A. microstachya and A. heterophylla. Winter-hardened leaves had ice nucleation temperatures of –5·5 °C or lower, with W. nobilis the lowest at –6·8 °C. All species had significantly higher ice nucleation temperatures in summer, with A. atropurpurea and A. heterophylla forming ice in the leaf at temperatures >3 °C higher in summer than in winter. Wollemia nobilis had lower FT₅₀ and LT₅₀ values than its ice nucleation temperature, indicating that the species has a degree of ice tolerance.

Conclusions

While lower temperature limits in the Australian Araucariaceae are generally unlikely to affect their survival in wild populations during normal winters, unseasonal frosts may have devastating effects on tree survival. Extreme high temperatures are not common in the areas of natural occurrence, but upward temperature shifts, in combination with localized radiant heating, may increase the heat experienced within a canopy by at least 10 °C and impact on tree survival, and may contribute to range contraction. Heat stress may explain why many landscape plantings of W. nobilis have failed in hotter areas of Australia.     

Quantitative trait loci for seed yield and yield-related traits, and their responses to reduced phosphorus supply in Brassica napus

Background and Aims

One of the key targets of breeding programmes in rapeseed (Brassica napus) is to develop high-yield varieties. However, the lack of available phosphorus (P) in soils seriously limits rapeseed production. The aim of this study was to dissect the genetic control of seed yield and yield-related traits in B. napus grown with contrasting P supplies.

Methods

Two-year field trials were conducted at one site with normal and low P treatments using a population of 124 recombinant inbred lines derived from a cross between ‘B104-2’ and ‘Eyou Changjia’. Seed yield, seed weight, seed number, pod number, plant height, branch number and P efficiency coefficient (PEC) were investigated. Quantitative trait locus (QTL) analysis was performed by composite interval mapping.

Key Results

The phenotypic values of most of the tested traits were reduced under the low P conditions. In total, 74 putative QTLs were identified, contributing 7·3–25·4 % of the phenotypic variation. Of these QTLs, 16 (21·6 %) were detected in two seasons and in the mean value of two seasons, and eight QTLs for two traits were conserved across P levels. Low-P-specific QTLs were clustered on chromosomes A1, A6 and A8. By comparative mapping between Arabidopsis and B. napus, 161 orthologues of 146 genes involved in Arabidopsis P homeostasis and/or yield-related trait control were associated with 45 QTLs corresponding to 23 chromosomal regions. Four gene-based markers developed from genes involved in Arabidopsis P homeostasis were mapped to QTL intervals.

Conclusions

Different genetic determinants were involved in controlling seed yield and yield-related traits in B. napus under normal and low P conditions. The QTLs detected under reduced P supply may provide useful information for improving the seed yield of B. napus in soils with low P availability in marker-assisted selection.     

Longevity, lignin content and construction cost of the assimilatory organs of Nepenthes species

Background and Aims

This study examined level of causal relationships amongst functional traits in leaves and conjoint pitcher cups of the carnivorous Nepenthes species.

Methods

Physico-chemical properties, especially lignin content, construction costs, and longevity of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, northern Borneo were determined.

Key Results

Longevity of these assimilatory organs was linked significantly to construction cost, lignin content and structural trait of tissue density, but these effects are non-additive. Nitrogen and phosphorus contents (indicators of Rubisco and other photosynthetic proteins), were poor predictors of organ longevity and construction cost, suggesting that a substantial allocation of biomass of the assimilatory organs in Nepenethes is to structural material optimized for prey capture, rigidity and escape from biotic and abiotic stresses rather than to light interception. Leaf payback time – a measure of net carbon revenue – was estimated to be 48–60 d. This is in line with the onset of substantial mortality by 2–3 months of tagged leaves in many of the Nepenthes species examined. However, this is a high ratio (i.e. a longer minimum payback time) compared with what is known for terrestrial, non-carnivorous plants in general (5–30 d).

Conclusions

It is concluded that the leaf trait bivariate relationships within the Nepenthes genus, as in other carnivorous species (e.g. Sarraceniaceae), is substantially different from the global relationship documented in the Global Plant Trait Network.Key words: Botanical carnivory, carbon gain, functional traits, leaf chemistry, leaf lifespan, leaf mass per unit area, Nepenthes, pitcher, payback time     

Spider-fed bromeliads: seasonal and interspecific variation in plant performance

Background and Aims

Several animals that live on bromeliads can contribute to plant nutrition through nitrogen provisioning (digestive mutualism). The bromeliad-living spider Psecas chapoda (Salticidae) inhabits and breeds on Bromelia balansae in regions of South America, but in specific regions can also appear on Ananas comosus (pineapple) plantations and Aechmea distichantha.

Methods

Using isotopic and physiological methods in greenhouse experiments, the role of labelled (¹⁵N) spider faeces and Drosophila melanogaster flies in the nutrition and growth of each host plant was evaluated, as well as seasonal variation in the importance of this digestive mutualism.

Key Results

Spiders contributed 0·6 ± 0·2 % (mean ± s.e.; dry season) to 2·7 ± 1 % (wet season) to the total nitrogen in B. balansae, 2·4 ± 0·4 % (dry) to 4·1 ± 0·3 % (wet) in An. comosus and 3·8 ± 0·4 % (dry) to 5 ± 1 % (wet) in Ae. distichantha. In contrast, flies did not contribute to the nutrition of these bromeliads. Chlorophylls and carotenoid concentrations did not differ among treatments. Plants that received faeces had higher soluble protein concentrations and leaf growth (RGR) only during the wet season.

Conclusions

These results indicate that the mutualism between spiders and bromeliads is seasonally restricted, generating a conditional outcome. There was interspecific variation in nutrient uptake, probably related to each species'' performance and photosynthetic pathways. Whereas B. balansae seems to use nitrogen for growth, Ae. distichantha apparently stores nitrogen for stressful nutritional conditions. Bromeliads absorbed more nitrogen coming from spider faeces than from flies, reinforcing the beneficial role played by predators in these digestive mutualisms.     

Variation in the functioning of autonomous self-pollination, pollinator services and floral traits in three Centaurium species

Background and Aims

Reproductive assurance through autonomous selfing is thought to be one of the main advantages of self-fertilization in plants. Floral mechanisms that ensure autonomous seed set are therefore more likely to occur in species that grow in habitats where pollination is scarce and/or unpredictable.

Methods

Emasculation and pollen supplementation experiments were conducted under laboratory conditions to investigate the capacity for, and timing of autonomous selfing in three closely related Centaurium species (Centaurium erythraea, C. littorale and C. pulchellum). In addition, observations of flower visitors were combined with emasculation and pollen addition experiments in natural populations to investigate the degree of pollinator limitation and pollination failure and to assess the extent to which autonomous selfing conferred reproductive assurance.

Results

All three species were capable of autonomous selfing, although this capacity differed significantly between species (index of autonomous selfing 0·55 ± 0·06, 0·68 ± 0·09 and 0·92 ± 0·03 for C. erythraea, C. littorale and C. pulchellum, respectively). The efficiency and timing of autogamous selfing was primarily associated with differences in the degree of herkogamy and dichogamy. The number of floral visitors showed significant interspecific differences, with 1·6 ± 0·6, 5·4 ± 0·6 and 14·5 ± 2·1 floral visitors within a 2 × 2 m² plot per 20-min observation period, for C. pulchellum, C. littorale and C. erythraea, respectively. Concomitantly, pollinator failure was highest in C. pulchellum and lowest in C. erythraea. Nonetheless, all three study species showed very low levels of pollen limitation (index of pollen limitation 0·14 ± 0·03, 0·11 ± 0·03 and 0·09 ± 0·02 for C. erythraea, C. littorale and C. pulchellum, respectively), indicating that autonomous selfing may guarantee reproductive assurance.

Conclusions

These findings show that limited availability of pollinators may select for floral traits and plant mating strategies that lead to a system of reproductive assurance via autonomous selfing.