Sink Ratio Research Articles

Dry matter, nitrogen and phosphorus accumulation, partitioning and remobilization as affected by N and P fertilization and source–sink relations

Durum wheat ( Triticum turgidum subsp. durum L.) is being increasingly grown in many areas of the world, but there is a lack of information about the physiological processes limiting grain yield. In this study, different rates of N and P fertilization were applied and the source:sink ratio was manipulated to examine the factor(s) limiting grain filling under rainfed conditions. Plants exposed to four fertilization treatments (control, 80 kg N ha −1 (N), 50 kg P ha −1 (P) and 80 kg N ha −1 and 50 kg P ha −1 (N–P)) and were artificially modified to obtain a range of different source:sink ratios. The treatments were (I) control; (II) half of the spike was removed; (III) all the spike was removed. The cultivar Cosmodur was used, which is widely grown in Greece and other Mediterranean countries and is quite productive especially under rainfed conditions. The distribution of dry matter, N and P among grains, stems and leaves was analyzed at anthesis and harvesting. Dry matter accumulation and partitioning into different plant parts was different between the fertilization treatments and the control. At anthesis, leaf + culm dry matter was higher than the chaff dry matter. Total aboveground biomass increased after anthesis in both years and at all fertilization treatments. N fertilization affected N concentration at the whole plant level at anthesis and at maturity. There was an average increase of 20% in N concentration with N application at anthesis in both years relative to the control. N content was affected by the fertilization treatments and it was increased by 33% over the 2 years of the study compared with the control. In addition, P fertilization affected P concentration both at anthesis and maturity in every plant organ, and there was also a significant effect of the change of P concentration at the two different growth stages. P accumulation was also affected by the fertilization regime and by the spike halving treatment. Dry matter translocation was an average of 22% higher at the fertilized treatments compared with the control, which indicates that fertilization led plants to translocate higher amount of dry matter. N and P translocation were affected by the fertilization treatment and in some treatments by the sink reduction. The spike reduction treatment increased the pre-anthesis contribution to seed indicating that the N and P remobilization from vegetative tissues were very important for grain development. The present study indicates that N and P fertilization and sink size can affect dry matter, N, and P accumulation, partitioning, and retranslocation of durum wheat which can affect seed yield.

Carbon autonomy of peach shoots determined by 13C-photoassimilate transport

We used (13)CO(2) tracing and source-sink manipulation to determine if fruiting shoots of peach (Prunus persica (L.) Batsch) trees are autonomous or if they import carbon from neighboring shoots, and if the degree of shoot autonomy is influenced by the source-sink relationship of the shoot. In three experiments, leaf to fruit ratio (L:F) of selected fruiting shoots was moderately (2005 and 2006) or strongly (complete sink removal, 2006) altered to either enhance or inhibit movement of carbon from (13)C-labeled fruiting shoots (LFS) to adjacent non-labeled shoots (NLFS), both located within 10 cm on the same main scaffold of V-shaped peach trees. At Stages I and III of fruit growth, fruit and shoot tips were sampled from LFS and NLFS to determine (13)C percentage on the day of labeling and after one week. Factors that differed among the three experiments in the two years were cultivar, tree age, source:sink ratios and labeling time. In all cases but one, no (13)C was found in fruits or shoot tips of NLFS. Only at Stage III of 'Redhaven' peach fruit growth (2005) was (13)C detected in fruits of NLFS, but only in the treatment favoring movement, and on the day of labeling. When L:F was altered to the maximum extent possible and branches were girdled at their base (complete sink removal, 2006), a detectable concentration of (13)C was recovered in fruits of NLFS at both growth stages, indicating that (13)C movement across adjacent shoots is possible, and detectable by (13)C tracing. According to our results, peach branches are relatively autonomous even at the fruiting-shoot level. However, conditions of strong imbalance between source supply and sink demand, either experimentally imposed or during periods of strong sink competition, may cause some movement of carbon among neighboring shoots.

Modelling variety-dependent dynamics of soluble solids and water in berries ofVitis vinifera

Background and Aims: We modelled the dynamics of soluble solids, largely sugars, and water in 12 Vitis vinifera varieties. Emphasis was placed on maximum concentration of soluble solids (S(max)) and time of maturity for their viticultural importance.Methods and Results: We measured the concentration of soluble solids and water at weekly intervals during berry ripening. The dynamics of concentration of soluble solids was characterised with a sigmoid model, whereas water concentration was characterised with a concentration-response type curve. Scaling exponents for soluble solids (alpha(s)) and water (alpha(w)) were calculated as the slope of the log-log regression between amount of soluble solids or water per berry and berry fresh mass. S(max) ranged from 27.1% in Shiraz to 21.2% in Riesling, was associated with both alpha(w) and alpha(s), and was largely unrelated to source size (leaf area, pruning weight, light interception), source activity (stomatal conductance), sink size (yield components) and source : sink ratios. The time of maturity ranged from 26 January in Verdelho to 27 February in Crimson Seedless, and was an inverse function of the rate of change in concentration of soluble solids, which was in turn a direct function of stomatal conductance.Conclusions: Traits related to carbon assimilation influenced time of maturity, but their link with maximum concentration of soluble solids in berries was not evident.Significance of the Study: Quantitative models of accumulation of soluble solids are presented that provide a baseline for comparisons among varieties.

Seed yield determination of peanut crops under water deficit: Soil strength effects on pod set, the source–sink ratio and radiation use efficiency

Peanut ( Arachis hypogaea L.) production in Argentina is affected by frequent and unpredictable periods of water deficit that usually overlap the critical period for pod set of early sown crops. An indirect effect of water deficit is reduced pegging due to increased soil strength promoted by surface soil desiccation. There is no knowledge on the associated effects determined by peg production dynamics and variable plant water status. We evaluated the responses of these traits by means of field experiments (Exp 1: 2002–2003; Exp 2: 2005–2006) that included two peanut cultivars (ASEM 485 INTA and Florman INTA) cropped at different sowing dates and water regimes (IRR: irrigated; WS: water stress). Treatments allowed exploring a range of: (i) evaporative demands, (ii) surface soil strength levels, and (iii) soil water contents ( θ). We computed leaf area index (LAI), intercepted photosynthetically active radiation (IPAR), surface soil strength, degree of leaf folding, degree days of stress (SDD), crop (CGR) and pod growth rates (PGR) at critical periods, and radiation use efficiency (RUE). Seed yield and seed yield components (pod number per m 2, seed number per m 2 and individual seed weight) were determined at final harvest. WS promoted a significant decline (average of 73%) in seed yield ( P ≤ 0.022), which was better explained ( r 2 = 0.98) by the decline in seed and pod numbers than by the decline in individual seed weight ( r 2 = 0.67). Seed number responded chiefly to CGR between R 3 and R 6.5, but WS plots of Exp 1 departed from the general model fitted to IRR plots (40–53% decrease respect to predicted values). Biomass partitioning to reproductive sinks was also affected in WS plots. Enhanced soil strength promoted by soil drying reduced normal pegging pattern, and a generic bilinear model indicated a soil strength threshold of ca. 2.23 ± 0.10 MPa ( θ = 0.119 cm 3 cm −3) above which peg penetration decreased dramatically ( r 2 = 0.57, P < 0.001). WS reduced IPAR accumulation (10–30% reduction) and biomass production (34–67% reduction). The former was affected only by direct WS effects (i.e., tissue expansion, leaf movements). The latter was affected additionally by indirect effects (i.e., those determined by reproductive sink activity). The larger response of biomass production than of cumulative IPAR to WS determined a significant ( P < 0.05) decline in RUE with increased water deficit.

Grain Filling and Dry Matter Translocation Responses to Source–Sink Modifications in a Historical Series of Durum Wheat

To understand yield limitations imposed by the source–sink relationship and the effects that breeding had on it, the source–sink ratio was modified on 24 durum wheat cultivars released in different periods. Field experiments were conducted during 3 yr, with treatments consisting of removing the flag‐leaf blade, degraining half of the spike, and intact checks. Grains from near‐basal spikelets tended to be the most sensitive to source–sink modifications. Degraining increased grain weight up to 15% in modern cultivars, which were more source limited and more responsive to source–sink modifications than the old ones. Our results suggest a source–sink colimitation for grain filling in Mediterranean environments. Translocation of preanthesis assimilates was responsible for 25, 27, and 33% of grain weight in old, intermediate, and modern cultivars, respectively. Defoliation did not alter dry matter translocation (DMT) from the main stem, as the reduction in translocation of leaf blades was compensated with translocation increases from the chaff. Sink demand determined DMT that was mostly regulated by the stem. Our results indicate that future yield improvements may be achieved by strengthening the source capacity.

Source–sink balance of wheat determines responsiveness of grain production to increased [CO 2] and water supply

Manipulation of source (flag-leaf removal) and sink (ear trimming) was conducted in a factorial CO 2-irrigation field chamber experiment with spring wheat ( Triticum aestivum L.) in south-west Sweden to test the hypothesis that responsiveness of grain production and biomass partitioning to CO 2 concentration ([CO 2]) and water supply is dependent on the source–sink balance of the plant. Negative effects of doubled [CO 2] on both individual grain mass (IGM) and harvest index (HI) were strongly related to decreasing relative sink strength (i.e. increasing source:sink ratio), probably as a result of feedbacks from sink limitation on source activity under elevated [CO 2] being relatively more important as relative sink strength decreases. Substantial down-regulation of photosynthetic capacity in elevated [CO 2], resulted in lack of significant stimulation of grain yield (GY) of unmanipulated shoots growing under elevated [CO 2]. GY was even reduced by elevated [CO 2] in sink-manipulated shoots, implying that high source:sink ratio may result in a down-regulation of photosynthetic capacity that more than offsets the direct stimulating effect of elevated [CO 2]. High irrigation positively affected IGM and HI in source-manipulated shoots only, probably as a result of the timing of irrigation treatment effects on soil moisture during, but not before, grain filling. Irrigation thus probably affected source activity during grain filling rather than potential sink capacity determined before and around anthesis, an effect that should be more pronounced for shoots with low source:sink ratio. We conclude that effects of [CO 2] and irrigation on grain production and biomass partitioning of wheat are strongly modified by source–sink balance of the plant, and that sink limitation is a major constraint on CO 2-induced GY enhancement of spring wheat under Scandinavian climatic conditions. These findings may explain earlier observations of decreased CO 2 responsiveness of GY in modern wheat cultivars, with lower whole-plant sink strength before and around anthesis compared to old cultivars, and call into question current attempts of molecular plant breeding to maximise photosynthetic activity before and around anthesis in order to enhance GY in a world with rising atmospheric [CO 2].

Are temperature effects on weight and quality of barley grains modified by resource availability?

Under field conditions the occurrence of brief periods of moderately high (30–32°C) and very high temperatures (&gt;35°C) is quite common during grain filling in small-grain cereals. These events occur under a wide range of different management and environmental conditions, such as different nitrogen supplies and source–sink ratios after flowering. The objective of the present work was to study whether the effect of a brief heat stress is modified by resource availability for the growing grains. We subjected spikes of barley 10 days after flowering to a heat treatment in factorial combination with different nitrogen availabilities and source–sink ratios during post-flowering to determine effects on grain weight and major malting quality attributes. Grain weight and screening percentage (proportion of grains &lt;2.5 mm) were reduced by the mild heat stress. However, the magnitude of the effect was dependent on the nitrogen fertilisation and the source–sink treatments in which the heat stress was imposed. Grain protein and β-glucan percentages were increased by both nitrogen fertilisation and heat stress. Again, the magnitude of the increase was dependent upon the availability of resources. There was a trend to reduce malt extract in all treatments with respect to the control, but the reduction was only statistically significant with heat stress.

Effects of leaf-applied potassium, gibberellin and source–sink ratio on potassium absorption and distribution in grape fruits

Rb has similar characteristics as K, and is often used as a substitute of K due to either no suitable K isotope or having almost the same absorption and distribution traits by plants for both K and Rb. Thus, both 86Rb as a substitute of K and 3-year-old grapevines ( Vitis vinifera L. × V. labrusca L. cv. Jingyou) as the plant materials were used in the experiment to explore potassium (K) absorption and distribution. After 86Rb was daubed on the leaves, much of it was absorbed into fruits, while small proportions were transported into grapevines and non-daubed leaves. Based on stages of fruit development, the distribution of 86Rb in fruits of bearing grapevines varied remarkably in the order: third stage (26.86%) > first stage (15.44%) > second stage (11.40%) > veraision (9.06%). The absorption of 86Rb by fruits was also influenced by nutritional level, gibberellin (GA) application and source–sink ratio. Either 0.5 or 1% KCl significantly suppressed transportation of 86Rb from leaves to grape fruits. At full bloom, both 50 and 100 mg L −1 GA applications resulted in high 86Rb influx into fruits, but 50 mg L −1 GA had a stronger effect. More leaves resulted in less partitioning of 86Rb from treated leaves into grape fruits, while more of 86Rb from the treated leaf was translocated into fruits by reducing the total number of fruits.

Defoliation and nitrogen effects on photosynthesis and growth of Eucalyptus globulus

Plant responses to defoliation are complex. We established a field experiment in a nine-month-old Eucalyptus globulus Labill. plantation to examine the effects of pattern (upper crown versus lower crown removal), frequency (single, double or triple defoliation within a 12-month period) and severity (25 versus 38% of leaf area removed) of defoliation and the effect of soil nitrogen (N) on photosynthetic processes and stem growth. The photosynthetic responses observed following defoliation could be attributed to changes in source:sink ratios. Light-saturated CO(2) uptake (A(max)) increased with increasing severity and frequency of defoliation irrespective of defoliation pattern. Seedlings defoliated in autumn did not exhibit increases in A(max) until the following spring, whereas there was no such delay in photosynthetic responses associated with spring defoliation. Application of N before defoliation allowed trees to compensate for the effect of defoliation on stem diameter growth, which could not be explained simply in terms of increases in A(max). The observed increases in stem diameter increment following N fertilization of defoliated trees suggested increases in leaf area development, and there were changes in the leaf area:leaf dry mass ratio that may have increased light absorption by the crown. Nitrogen fertilization also increased partitioning of dry mass to branches at the expense of main stems, suggesting that N supply was important in rebuilding crowns following a defoliation event.

Maize Kernel Moisture at Physiological Maturity as Affected by the Source–Sink Relationship during Grain Filling

ABSTRACTA wide range of values reported in the literature has precluded the use of grain moisture (GM) as an estimate of physiological maturity (PM) in maize (Zea mays L.). The reason for this variability in GM values remains unclear. Previous evidence suggests that the source–sink ratio could affect the dynamics of kernel water relations during grain filling and thus, GM at PM. To test this possibility, treatments were applied to manipulate the reproductive sink capacity or the assimilate availability during grain filling. Kernel dry weight, water content, and the dry weight to water content (D–W) ratio, were monitored throughout grain filling. A bilinear model relating dry weight and GM was used to estimate GM at PM for each treatment. Severely restricting source capacity during grain filling increased GM at PM. When the source capacity per kernel during grain filling was increased, however, GM at PM was not affected. A single model (r2 = 0.99, p &lt; 0.001) described the relationship between relative dry weight and GM for all hybrids and treatments without source reduction during grain filling. The estimated value of GM at PM for this model was 34.9%. These results suggest that calculating GM late in grain filling can provide a reliable estimate of PM when the source capacity has not been severely restricted. A value of 35% moisture would be adequate in these situations. The D–W ratio of developing kernels was similar across all source–sink treatments until PM. Premature cessation of grain filling caused by defoliation increased the D–W ratio as the kernels continued to desiccate.

Changes in seed size and oil accumulation in Brassica napus L. by manipulating the source - sink ratio and excluding light from the developing siliques

Most of the oil in canola seed is contained in the cotyledons and so an increase in cotyledon size may lead to increased oil concentration in the whole seed, provided compensatory changes in non-oil bearing tissues are minimised. In addition, in in vitro studies, light has been shown to affect fatty acid synthesis. In two glasshouse experiments, we manipulated seed size in 3 cultivars of canola by increasing the source–sink ratio through removal of lateral inflorescences, restricting the plants to flowering on the main axis. We manipulated the ability of the growing seed to use light for the synthesis of fatty acids for oil by shading the siliques at different stages of seed development. The growth of ovules and embryos in the first experiment was assessed by evaluating changes in the projected area of the organs during growth and the final seed weight. We examined the pattern of organ development in the embryo by fitting appropriate curves and comparing the effect of the treatments on the coefficients. Pruning axillary branches increased seed weight by 14–43% but did not change the pattern of development of the cotyledons or radicle in the seed. Embryo growth over time was sigmoid in form with the most rapid growth occurring 12–27 days after flowering (daf). The removal of axillary branches and inflorescences reduced oil concentration in the larger seeds by 2.6–4.5% but only in one experiment. Light was excluded from the siliques from 2, 10, or 30 daf or not at all. Excluding light from 2 or 10 daf reduced ovule weight at maturity by 63% and excluding light from 30 daf reduced ovule weight by 20%. Excluding light reduced the number of seeds per silique by up to 90%, especially when excluded from 2 daf. Excluding light slightly reduced oil concentration, suggesting that, provided maternal substrates are available to the seed, it can use these to obtain energy for oil synthesis, even in the dark. We conclude that manipulation of the canopy of canola to change the source–sink ratio or the distribution of light within the canopy may have large effects on seed size, but little effect on the accumulation of oil in the seeds. This conclusion assumes that the relationships found in our glasshouse experiments apply in the field.

Is barley yield in the UK sink limited?: I. Post-anthesis radiation interception, radiation-use efficiency and source–sink balance

Source or sink limitation of grain filling in cereals is often inferred from experiments in which the source:sink ratio is manipulated by shading, defoliation or grain removal. However, interpretation of this type of experiment is usually qualitative rather than quantitative in nature and the extent of any imbalance between the source and sink is not known. The objectives of the current work were: (1) to provide a detailed analysis of radiation interception, radiation-use efficiency (RUE) and carbohydrate storage reserves in winter barley in order to quantify the potential supply of photosynthates for grain filling; (2) to estimate the variation in source–sink balance between environments. Field experiments were conducted on cv Pearl at six sites in the UK and over 3 years. Crops were grown under a comparable husbandry regime at each site and received a full fertilizer and crop protection programme. When the cumulative interception of post-anthesis photosynthetically active radiation (PAR) was plotted against the increase in biomass to determine RUE, the pattern of response differed between sites and years; for some site/years the response was linear, for others it was non-linear where RUE decreased during the latter stages of grain filling. The extent and statistical significance of non-linearity was determined from the quadratic term of fitted 2nd order polynomials. There was no significant association between climatic variables, such as temperature, radiation or rainfall, and the value of the quadratic term of RUE. Neither could non-linearity of RUE be explained in terms of the shedding of leaf tissue during canopy senescence. There were weak associations ( r 2 < 0.3) between the extent of non-linearity and green area index (GAI), above-ground biomass, and specific leaf N, at ear emergence (Zadoks GS 59). A much stronger relationship ( r 2 = 0.63) was found between the source:sink ratio (green area per grain) at GS 59 and non-linearity of RUE. These results suggest that a major factor leading to the reduction in RUE during the second half of grain filling at some sites was feedback inhibition from a limited sink capacity. This conclusion is supported by a fairly strong positive association between RUE non-linearity and the apparent contribution of stem carbohydrate reserves to grain yield ( r 2 = 0.47). The potential assimilate supply for grain filling was estimated as (maximum post-anthesis RUE × PAR intercepted) + stem soluble carbohydrate reserves at GS 59. The potential supply exceeded the measured yield at all sites except one implying that crops were predominantly sink limited. The size of the excess, which is a measure of the relative source–sink balance during grain filling, differed widely between site/years.

Grain weight responses to post-anthesis spikelet-trimming in an old and a modern wheat under Mediterranean conditions

Average grain weight is a major yield component contributing to its variation, especially in Mediterranean regions where grain weight is frequently exposed to terminal stresses affecting grain growth. Most of the literature agrees that wheat grain growth is hardly limited by the source. However, no source–sink ratios studies seem to have been conducted in the Mediterranean region to determine to what degree wheat grain growth is actually limited by the source in these particular regions. We conducted two field experiments in Catalonia (north-eastern Spain), where an old cultivar (Anza) and a more recently released one (Soissons) were sown in a range of different nitrogen and water availabilities and sowing dates. This was to analyse the degree of source limitation for grain growth. Sink size was modified by removing half of the spikelets c. 10 days after anthesis, virtually doubling the availability of assimilates per grain effectively growing. Trimming the spikes did not produce significant changes in grain growth rate or duration of grain filling. Consequently, grain weight did not respond noticeably to the reduction in sink demand and any eventual response has been far from representing a strong competition among grains during grain filling.

Photosynthetic capacity increases in Acacia melanoxylon following form pruning in a two-species plantation

The photosynthetic responses to partial defoliation through pruning were examined in a 5-year-old Acacia melanoxylon plantation grown with a Pinus radiata nurse crop. Form pruning, the removal of large branches or competing leaders, was used to remove either 25 or 50% of tree foliage from throughout individual tree crowns and compare responses to unpruned trees. Photosynthetic capacity, expressed as light-saturated photosynthetic rate ( A max), was measured periodically over a 12-month period. An increase in photosynthetic capacity of phyllodes was observed between 2 and 6 weeks after pruning and the magnitude of the increase was greater in the 50% pruning treatment. The increase in photosynthetic capacity was confined to the upper two-thirds of the crown. While maximum stomatal conductance ( g s) values were generally greater following 50% pruning, there were no pruning-induced changes in photosynthetic water-use efficiency (WUE) ( A max/ g s). Foliar nutrient levels were not altered by pruning treatment. Changes in A max were strongly correlated with phyllode phosphorus content and only weakly correlated with phyllode nitrogen content. The absence of corresponding changes in water-use efficiency, phyllode nutrient content and photosynthetic efficiency suggests that the observed increases in photosynthetic capacity were driven by changes in the carbon source:sink ratio. Form pruning that removes foliage solely from the upper reaches of the crown is likely to reduce the overall magnitude of photosynthetic enhancement in the crown and have the greatest negative effect on the growth of A. melanoxylon.

Hordein composition as affected by post-anthesis source–sink ratio under different nitrogen availabilities

Hordein composition as affected by post-anthesis source–sink ratio under different nitrogen availabilities

Responses of Soya bean Yield and Yield Component Distribution across the Main Axis under Source–Sink Manipulation

AbstractExtensive studies have been conducted regarding the source–sink alterations on soya bean [Glycine max (L.) Merr.] yield, but limited information is available for the seed yield and distribution of yield components across main nodes under whole‐plant light‐enriched conditions. A 2‐year research was conducted at the University of Massachusetts Agronomy Farm under ambient and light‐enriched conditions for two old and two new cultivars planted with a normal density. A randomized block design was used in each year. Light enrichment was initiated at the onset of flowering by installing a 90‐cm tall wire mesh fencing (mesh hole size 4–5 cm) adjacent to the centre row and sloping away at a 45° angle and was left in place for the remainder of the growing season. Five source–sink manipulations were initiated following the establishment of light enrichment. The yield sensitivity of the two old cultivars to the changes in source strength and light‐enriched conditions during reproductive period was much greater than that of the two new cultivars. The increased yield by light enrichment in various manipulations of source–sink treatments was, in part, due to increased branch contribution. Most pods were produced at the nodes in the middle sections of the plants and appeared in higher node position in new cultivars compared with the old cultivars. Seed number per pod and seed size was quite uniform across all node positions. Seed size of both the old and the new cultivars was responsive to changes in the source–sink ratio and changes in the environment during the growth of the soya bean plant. The results suggested that soya bean plants showed several mechanisms to control or realize their excess reproductive potential in a constantly changing environment.

Sunflower Seed Weight and Oil Concentration under Different Post‐Flowering Source‐Sink Ratios

Sunflower (Helianthus annuus L.) seed weight and oil concentration are commonly related to post‐flowering source of assimilates (e.g., leaf area index duration, LAD). A predictive variable including both the source of assimilates and the sinks (i.e., seed number) would better account for seed weight and seed oil concentration variability of crops with contrasting seed number and canopy size. We established quantitative relationships between oil weight per seed components and post‐flowering source–sink ratio. Field experiments were conducted in Argentina from 1998 to 2001. Four hybrids were cultivated under contrasting plant populations and nutrient supplies. A wide range of LAD (913–3130 m2°Cd m−2), seed number (4270–8880 seeds m−2), and seed weight (41–62 mg) was recorded. In contrast, seed oil concentration was not modified (about 530 mg g−1). Post‐flowering source–sink ratio (LAD per seed) better accounted (r2 = 0.69) for seed‐weight prediction than LAD (r2 = 0.42). Maximum seed weight (60 mg) was attained with source–sink ratios ≥0.33 m2°Cd seed−1 Results from our data set pooled together with others of different agro‐ecological regions reveal that sunflower crops are normally growing under limiting post‐flowering source–sink ratios and a 47% reduction of seed weight occurs when post‐flowering source–sink ratio is dramatically (100%) reduced. Seed weight is only 23% increased at saturated source–sink ratios. In contrast, for the wide range of post‐flowering source–sink ratios analyzed, seed oil concentration did not vary.

The impact of free-air CO 2 enrichment (FACE) and N supply on yield formation of rice crops with large panicle

Because CO 2 is needed for plant photosynthesis, the increase in atmospheric [CO 2] has the potential to enhance the growth and yield of agricultural crops. However, little is known about the interactive effects of elevated [CO 2] and nitrogen (N) supply on grain yield formation of rice ( Oryza sativa L.), and no information is available on the combined effect of these factors on grain yield formation of rice cultivars with large panicles or under high N supply. Therefore we conducted a free-air CO 2 enrichment (FACE) experiment at Wuxi, Jiangsu, China, in 2001–2003. A japonica cultivar with large panicle (Wuxiangging 14) was grown at ambient or elevated (c. 200 μmol mol −1 above ambient) [CO 2] under three levels of N: low (LN, 15 g N m 2), medium (MN, 25 g N m 2) and high N (HN, 35 g N m 2 (2002, 2003)). The MN level was similar to that recommended to local farmers. FACE significantly increased the grain yield by 12.8% across the 3 years. Maximum grain yield was reached by MN-crops under both ambient and FACE treatments. FACE also substantially increased panicle number per square meter (+18.8%) due to the increase in maximum tiller number (+30.0%) being substantially more than the decreases in productive tiller ratio (−7.7%) with FACE: the former was related to significant increases with FACE in tillering occurrence speed from 10 to 30 days after transplanting (DAT), while for the latter the increases in tillering extinction speed after 45 DAT contributed to the decreases. FACE significantly reduced spikelet number per panicle (−7.6%), which was due mainly to the significant increase in degenerated spikelets per panicle (+51.7%) while differentiated spikelets per panicle showed no change. FACE caused a small but significant increase in filled spikelet percentage and grain weight, which may be due to the combined effects of increased proportion of spikelets on primary branches and source–sink ratio at heading under FACE conditions. The year effects were all significant for yield and its components; however, interactions between all treatment variables were hardly detected. For the cultivar and conditions of this experiment, the above results indicate that, in addition to supply proper total amount of N over the whole season, high-yielding cultivation under future elevated [CO 2] conditions need to be focused on regulations after panicle initiation in order to increase the productive tiller ratio, enhance the spikelet formation and raise harvest index.

Quantifying effects in two-sample environmental experiments using bootstrap confidence intervals

Two-sample experiments (paired or unpaired) are often used to analyze treatment effects in life and environmental sciences. Quantifying an effect can be achieved by estimating the difference in center of location between a treated and a control sample. In unpaired experiments, a shift in scale is also of interest. Non-normal data distributions can thereby impose a serious challenge for obtaining accurate confidence intervals for treatment effects. To study the effects of non-normality we analyzed robust and non-robust measures of treatment effects: differences of averages, medians, standard deviations, and normalized median absolute deviations in case of unpaired experiments, and average of differences and median of differences in case of paired experiments. A Monte Carlo study using bivariate lognormal distributions was carried out to evaluate coverage performances and lengths of four types of nonparametric bootstrap confidence intervals, namely normal, Student's t, percentile, and BCa for the estimated measures. The robust measures produced smaller coverage errors than their non-robust counterparts. On the other hand, the robust versions gave average confidence interval lengths approximately 1.5 times larger. In unpaired experiments, BCa confidence intervals performed best, while in paired experiments, Student's t was as good as BCa intervals. Monte Carlo results are discussed and recommendations on data sizes are presented. In an application to physiological source–sink manipulation experiments with sunflower, we quantify the effect of an increased or decreased source–sink ratio on the percentage of unfilled grains and the dry mass of a grain. In an application to laboratory experiments with wastewater, we quantify the disinfection effect of predatory microorganisms. The presented bootstrap method to compare two samples is broadly applicable to measured or modeled data from the entire range of environmental research and beyond.

Initial observations of increased requirements for light-energy dissipation in ryegrass (Lolium perenne) when source/sink ratios become high at a naturally grazed free air CO2 enrichment (FACE) site.

Although photosynthetic response to long-term elevated CO2 has been extensively studied, little attention has yet been directed at coordinated adjustments between the use of absorbed light for CO2 fixation, and the dissipation of potentially harmful excess light. In this study, we have performed an initial analysis of photosynthetic light use and excess light dissipation in response to grazing-induced variation in the source / sink ratio in ryegrass (Lolium perenne L.) after 6 years' exposure to Free Air CO2 Enrichment (FACE). Before grazing, when the source / sink ratio was relatively large, significant down-regulation of photosynthetic capacity (Amax) was observed in the FACE leaves compared with control leaves at the same stage of maturity. The decrease in Amax partly offset the direct stimulation of elevated CO2 on light-saturated photosynthesis, and was accompanied by a reduction in photochemical electron flow that was accompanied by a large increase in susceptibility to photoinhibition. This was indicated by large increases in both non-photochemical quenching (NPQ) and the de-epoxidised state of xanthophyll cycle (DEPS), and also by changes in the photochemical reflectance index (PRI). However, no significant increase in the xanthophyll pool size in FACE leaves was observed, despite the apparent large increase in requirements for photodissipation in FACE leaves. After grazing, when the source / sink ratio was relatively small, the CO2 fixation rates in both the FACE and control leaves were, as expected, significantly higher compared with those before grazing, and there was no down-regulation of photosynthetic capacity in the leaves under FACE conditions. In addition, the extent of photodissipation in the FACE and control leaves was not significantly different. Overall, the profile of leaf physiological and biochemical responses supports the hypothesis that the effect of long-term elevated CO2 can be significantly influenced by short-term variation in the source / sink ratio. As the xanthophyll pool size does not change significantly, this poses the question of whether the increased photodissipative demand observed here under even moderately elevated CO2 concentrations may lead to increased plant susceptibility to photoinhibition, and thus to an increased risk of damage to plant function, under conditions of low sink demand. This question clearly deserves further study.