Sink Competition Research Articles

Release characteristics of arsenic from sediments and its source or sink competition with phosphorus: A case of a great lake with grass-algae alternation

The arsenic (As) release from sediments in great lakes is affected by various factors. In this study, the characteristics of As release from sediments was investigated, and the As sources and sinks with the strengths in sediments from different areas (grass-type, algae-type, and grass-algae alternation areas) in great shallow lakes (Taihu Lake, China) were analyzed, and the influence of P competition in the process of As release was also studied. The results showed that changing trend of the values of equilibrium As concentration in sediments were consistent with the regional changes (0 to 28.12 µg/L), and the sediments from algae-type areas had the higher values. The sediments from western lake and northwest lake bay were a strong As and a weak P source, and the north lake bay had the opposite trend of these two regions. Intense P source competition with As from the sediments occurred in algae-type areas. The grass-type areas had strong As and P retention capacities, indicating a sink role of sediment with high As and P sorption capacities. The degree of As and P saturation had similar trend in sediments, and the grass-type areas had the higher values, 18.3%-21.4% and 15.31%-20.34%, respectively. Contribution analysis results showed that most of As release contribution was from the bottom (30-50 cm) sediments, and the surface (0-10 cm) sediments from algae-type areas contributed more to the overlying water than other region.

Fine root mortality under severe drought reflects different root distribution of Quercus robur and Ulmus laevis trees in hardwood floodplain forests

Key messageExtremely high fine root mortalities were observed under drought in 2018, increasing fine root mortality in young trees could be explained by differences in root distribution compared to old trees.Juvenile trees in floodplains are prone to high mortality leading to a low success in reforestation in these habitats. One of the reasons contributing to high mortality of juvenile trees could be limited water and nutrient uptake due to a high level of fine root mortality, especially during summer droughts on higher terraces of floodplains. Strategies of different tree species in hardwood floodplain forests (HFFs) on keeping fine roots alive are still poorly understood. During the record-breaking summer drought of 2018, we examined the relationship between tree age and fine root dynamics of Quercus robur and Ulmus laevis along the Elbe River in Germany. Root area index (RAI), live root density (LRD) and relative root mortality (RRM) of young and old Q. robur and U. laevis were analysed by taking soil cores three times during the progression of a summer drought. Old oaks had a lower RAI in the upper soil than young oaks, while RAI of elms did not differ between young and old trees. RRM was very high during summer reaching more than 100% on average. RRM of young trees of both species increased with increasing drought during summer, while RRM of old trees did not change. We argue that differences in the response of RAI between oaks and elms reflect the sink competition between growing deep roots and shallow roots, which is pronounced in oaks due to their characteristic tap root system. Differences in root distribution patterns and the ability to perform hydraulic redistribution may explain the differences in RRM between trees of different species and ages.

Transcriptomic Analysis of the Pistacia vera (L.) Fruits Enable the Identification of Genes and Hormone-Related Gene Linked to Inflorescence Bud Abscission.

Pistacia vera (L.) is an alternate bearing species. The tree produces axillary inflorescence buds every year. Still, they abscise in “ON” overloaded shoots, causing a limited production in the following “OFF” year, causing a significant and unfavorable production fluctuation. In this work, we carried out de novo discovery and transcriptomic analysis in fruits of “ON” and “OFF” shoots of the cultivar Bianca. We also investigated whether the fruit signaling pathway and hormone biosynthesis directly or indirectly linked to the premature fall of the inflorescence buds causing alternate bearing. We identified 1536 differentially expressed genes (DEGs) in fruits of “ON” vs. “OFF” shoots, which are involved primarily in sugar metabolism, plant hormone pathways and transcription factors. The premature bud abscission linked to the phenomenon is attributable to a lack of nutrients (primarily sugar) and the possible competition between the same branches’ sinks (fruits vs. inflorescence buds). Hormone pathways are involved as a response to signals degradation and remobilization of carbon and nutrients due to the strengthening of the developing embryos. Genes of the secondary metabolism and transcription factors are also involved in tailoring the individual branches response to the nutritional stress and sink competition. Crosstalk among sugar and various hormone-related genes, e.g., ethylene, auxin, ABA and cytokinin, were determined. The discovery of putative biomarkers like callose synthase 5, trehalose-6-phosphate synthase, NAD(P)-linked oxidoreductase and MIOX2, Jasmonate, and salicylic acid-related genes can help to design precision farming practices to mitigate the alternate bearing phenomenon to increase farming profitability. The aim of the analysis is to provide insight into the gene expression profiling of the fate of “ON” and “OFF” fruits associated with the alternate bearing in the pistachio.

Soybean seed weight responds to increases in assimilate supply during late seed-fill phase

ABSTRACT The understanding of source-sink dynamics during reproductive stages is essential to increase crop productivity and to describe yield component determination in eco-physiological models. Previous studies in soybean (Glycine max [L.] Merr.) evaluated the effect of changes in assimilate supply from the beginning of rapid seed growth but not at different times during the seed-filling phase or at the single-pod level. Two source-sink manipulation experiments were conducted in the greenhouse to quantify the effect of assimilate supply during the seed-filling phase on final seed weight of soybean. One pod on each node containing 3 mm seeds was marked in all plants, and pods not marked were removed at weekly intervals to avoid sink competition for assimilates. Removing pod competition on the day of marking and up to 21 days later increased final seed weight in marked pods by 25% relative to the control and by 18% when pod competition was removed 28 days after marking. Pods acquired mature color 33–35 days after marking. At 21 and 28 days after marking of individual pods, seeds had achieved 73% and 97% of their final seed weight and had 67 and 62% moisture, respectively. Our study provides new evidence that the final seed weight can still respond to increases in assimilate supply applied by the end of the seed-filling phase. These results highlight the potential to increase soybean yield through management practices and breeding efforts that extend the duration of a photosynthetically active canopy and increase assimilate supply to developing seeds during late seed-fill.

Underlying mechanism on source-sink carbon balance of grazed perennial grass during regrowth: Insights into optimal grazing regimes of restoration of degraded grasslands in a temperate steppe

Overgrazing is the main driver of grassland degradation and productivity reduction in northern China. The restoration of degraded grasslands depends on optimal grazing regimes that modify the source–sink balance to promote best carbon (C) assimilation and allocation, thereby promoting rapid compensatory growth of the grazed plants. We used in situ13CO2 labeling and field regrowth studies of Stipa grandis P.A. Smirn.to examine the effects of different grazing intensities (light, medium, heavy, and grazing exclusion) on photosynthetic C assimilation and partitioning, on reallocation of non-structural carbohydrates during regrowth, and on the underlying regulatory mechanisms. Light grazing increased the sink demand of newly expanded leaves and significantly promoted 13C fixation by increasing the photosynthetic capacity of the leaves and accelerating fructose transfer from the stem. Although C assimilation decreased under medium and heavy grazing, S. grandis exhibited a tolerance strategy that preferentially allocated more starch and 13C to the roots for storage to balance sink competition between newly expanded leaves and the roots. Sucrose phosphate synthase (SPS), sucrose synthase (SS), and other plant hormones regulated source–sink imbalances during regrowth. Abscisic acid promoted accumulation of aboveground biomass by stimulating stem SPS activity, whereas jasmonate increased root starch synthesis, thereby increasing belowground biomass. Overall, S. grandis could optimize source–sink relationships and above- and belowground C allocation to support regrowth after grazing by the regulating activities of SPS, SS and other hormones. These results provide new insights into C budgets under grazing and guidance for sustainable grazing management in semi-arid grasslands.

Effects of the fruiting period and growing seasons on market quality in goji berry (Lycium barbarum L.)

Abstract Progression of the vegetation period and change of year are associated with variations in general climatic parameters, such as temperature, atmospheric pressure, humidity, radiation, precipitation, wind speed and others. Only limited knowledge is available about the effects of these parameters on the characteristics of quality of fruits especially those with successive ripening such as goji berry. In our study, fruits of goji berry were characterised based on physico-chemical properties within four different harvest periods, in two consecutive years. Based on the obtained results, it was found that the pomological characteristics were superior at the beginning of the production season, while the phytochemical properties were better at the end. Fruit length, width and weight characteristics were noted to decrease from the first harvest to the last by 21%, 18% and 33%, respectively, while the total anthocyanin, phenol and antioxidant activity properties increased by 264%, 48% and 105%, respectively. There was a decrease in fruit weight, fruit length and fruit width up to 15.9%, 18.3% and 6%, respectively and were directly associated with yield due to sink competition among fruits. Providing high ripening index that ensures more acceptable fruits, with high soluble solid content (SSC) and titratable acidity (TA) seems to be a very important breeding objective to meet consumer demands thanks to superior organoleptic quality. According to correlations, the synthesis of phenolic compounds increased in parallel with SSC rise and TA, which improved pomological properties too. It is thought that the obtained results may indicate the cultural processes and evaluation methods to be used for the harvested fruits.

A Novel Graft between Pac Choi (Brassica rapa var. chinensis) and Daikon Radish (Raphanus sativus var. longipinnatus)

Vegetable grafting has primarily been used in the commercial production of high-value crops in the Solanaceae and Cucurbitaceae families. In this study, we explored the feasibility of making a novel graft between pac choi (Brassica rapa L. var. chinensis) and daikon radish (Raphanus sativus L. var. longipinnatus) to create a plant with harvestable pac choi leafy vegetable above-ground, and a daikon radish taproot below-ground. ‘Mei Qing Choi’ pac choi (scion) was grafted onto ‘Bora King’ daikon radish (rootstock). Grafted pac choi–daikon radish plants did not show a decrease in SPAD value, canopy size, leaf number, leaf area, or above-ground weight compared with self-grafted pac choi plants. However, taproot formation was reduced in grafted pac choi–daikon radish plants, as shown by decreased taproot length, diameter, fresh weight, and dry weight compared with non- and self-grafted daikon radish plants. Surprisingly, grafting with radish increased the photosynthetic rate of the pac choi. This pilot study demonstrated the potential of creating a new pac choi–daikon radish vegetable product to help save growing space and minimize waste at consumption, as pac choi roots are not eaten and radish leaves are usually discarded. The inter-generic grafting between B. rapa var. chinensis and R. sativus var. longipinnatus could also provide a unique model system to help elucidate scion-rootstock synergy and above- and below-ground sink competition in horticultural crops.

Fruiting and sink competition

Fruiting and sink competition

The effect of carbohydrate availability on postharvest fruit quality in sweet cherry

Major export countries use a matrix of quality attributes of fruit at harvest to support decisions on the travel potential of key cultivars. However there is uncertainty whether levels of firmness and soluble sugars at harvest are indicative of these attributes postharvest. The objective of this study was to determine the effects of manipulating tree carbohydrate availability through girdling or defoliation on fruit quality at harvest and postharvest. Trunk girdling and limb defoliation treatments were applied five weeks after full-bloom in trees of 'Kordia' and 'Lapins' cultivars in order to manipulate carbohydrate supplies to fruit. Fruit were harvested at commercial maturity and analysed for fruit quality and chemistry parameters at harvest and after 28 days of postharvest storage. Girdling in 'Kordia' resulted in fruit that were significantly firmer, higher in TSS, and larger in diameter which was further pronounced after postharvest storage. Defoliation in 'Kordia' resulted in fruit that were softer, had lower TSS, and were smaller in both mass and diameter. The 'Lapins' treatments often didn't respond in the same way that 'Kordia' did and thus the results of this study indicate a distinct carbohydrate source: sink relationship in 'Kordia' relative to 'Lapins', which may be due to differences in sink competition. Therefore this study indicates that girdling can lead to increased carbohydrate availability resulting in higher quality fruit, particularly following postharvest storage which could improve outcomes when exporting.

Olive fruit growth, tissue development and composition as affected by irradiance received in different hedgerow positions and orientations

Incident radiation strongly influences fruit development, but little is known regarding the specific responses to the radiation differences found at different canopy heights and orientations in the new intensive hedgerow orchards. We tested the effect of position-determined solar microenvironment on olive fruit size, composition, and cellular development among positions at successive heights along both faces of N–S and E–W oriented olive hedgerows (cv. Arbequina). Total incident irradiance over the fruit growth period at each canopy position was modeled, and the relationships of all fruit parameters to irradiance and amongst each other were tested. Fruit and mesocarp weight and oil increased from canopy base to top and were linearly related to irradiance, while water content showed the opposite pattern, suggesting that priorities for distribution among different sinks are strongly influenced by irradiance level. Similar patterns of fruit size and composition in relation to irradiance were also observed among hedgerow orientations. Endocarp weight and composition varied little among irradiance levels, reflecting the conservative nature of this tissue as an active sink. Greater fruit size, mesocarp weight, and oil in positions of higher irradiance, even when fruit number was higher, indicating that those yield components were primarily affected by source supply and not limited by sink competition. Fruit exposed to light developed larger mesocarp cells than shaded fruit but cell number was not affected, and mesocarp oil content was highly associated with mesocarp cell size.

Useful insights from evolutionary biology for developing perennial grain crops.

Annual grain crops dominate agricultural landscapes and provide the majority of calories consumed by humanity. Perennial grain crops could potentially ameliorate the land degradation and off-site impacts associated with annual grain cropping. However, herbaceous perennial plants with constitutively high allocation to harvestable seeds are rare to absent in nature. Recent trade-off theory models suggest that rugged fitness landscapes may explain the absence of this form better than sink competition models. Artificial selection for both grain production and multiyear lifespan can lead to more rapid progress in the face of fitness and genetic trade-offs than natural selection but is likely to result in plant types that differ substantially from all current domestic crops. Perennial grain domestication is also likely to require the development of selection strategies that differ from published crop breeding methods, despite their success in improving long-domesticated crops; for this purpose, we have reviewed literature in the areas of population and evolutionary genetics, domestication, and molecular biology. Rapid domestication will likely require genes with large effect that are expected to exhibit strong pleiotropy and epistasis. Cryptic genetic variation will need to be deliberately exposed both to purge mildly deleterious alleles and to generate novel agronomic phenotypes. We predict that perennial grain domestication programs will benefit from population subdivision followed by selection for simple traits in each subpopulation, the evaluation of very large populations, high selection intensity, rapid cycling through generations, and heterosis. The latter may be particularly beneficial in the development of varieties with stable yield and tolerance to crowding.

The Influence of Plant Growth Regulators and Inflorescence Removal on Plant Growth, Yield, and Skin Color of Red LaSoda Tubers

Foliar applications of the synthetic auxin compound 2,4-dichlorophenoxyacetic acid (2,4-D) have been used to enhance skin color of red potato cultivars for many years. Relatively, little is known about the mode of action of this compound, but it has been proposed that 2,4-D stimulates ethylene production and enhances the activity of enzymes involved in anthocyanin biosynthesis. The objective of this study was to compare several other plant growth regulators to 2,4-D for their effect on plant growth, tuber yield, and skin color of the light red-skinned cultivar “Red Lasoda.” Trials were conducted in 2010 and 2011 to evaluate the effects of foliar applications of the ethylene-stimulating growth regulator ethephon, the ethylene-inhibitor 1-methylcyclopropene (1-MCP), and 2,4-D. Manual inflorescence removal was also included as a treatment to determine the influence of anthocyanin sink competition between tubers and flowers on tuber skin color. Ethephon application caused floral abscission in treated plants and reduced plant height compared to other treatments and the non-treated control. While 2,4-D caused foliar injury and ethephon slightly increased the yield of <56 g tubers, neither growth regulator affected total and marketable yield. Both ethephon and 2,4-D increased tuber skin color at harvest compared to the non-treated control. In contrast, 1-MCP and inflorescence removal had no effect on yield, tuber size, and skin color. The results indicate that ethephon and 2,4-D foliar applications have similar effects on skin color and appearance, supporting the hypothesis that 2,4-D works by stimulating ethylene production within the plant.

Comparing growth phenology of co-occurring deciduous and evergreen conifers exposed to drought

Plant phenological events are influenced by climate factors such as temperature and rainfall. To evaluate phenological responses to water availability in a Spring Heath-Pine wood (Erico-Pinetum typicum), the focus of this study was to determine intra-annual dynamics of apical and lateral growth of co-occurring early successional Larix decidua and Pinus sylvestris and late successional Picea abies exposed to drought. The effect of reduced plant water availability on growth phenology was investigated by conducting a rainfall exclusion experiment. Timing of key phenological dates (onset, maximum rate, end, duration) of growth processes were compared among species at the rain-sheltered and control plot during 2011 and 2012. Shoot and needle elongation were monitored on lateral branches in the canopy at c. 16m height and radial growth was recorded by automatic dendrometers at c. 1.3 m height of >120 yr old trees. Different sequences in aboveground growth phenology were detected among the three species under the same growing conditions. While onset of radial growth in April through early May was considerably preceded by onset of needle growth in Larix decidua (5–6 weeks) and shoot growth in Pinus sylvestris (c. 3 weeks), it occurred quite simultaneously with onset of shoot growth in Picea abies. Low water availability had a minor impact on onset of aboveground growth, which is related to utilization of stored water, but caused premature cessation of aboveground growth. At the control plot mean growing season length was 130 days in Pinus sylvestris, 95 days in Larix decidua and 73 days in Picea abies, supporting the hypothesis that early successional species are resource expenders, while late successional species are more efficient in utilizing resources and develop safer life strategies. High synchronicity found in culmination of radial growth in late spring (mid-May through early June) prior to occurrence of more favourable environmental conditions in summer might indicate sink competition for carbohydrates to belowground organs. This is supported by completion of apical growth in mid June in all species, except for needle growth of Pinus sylvestris which lasted until early August. Phenological observations of conifers exposed to drought revealed that tree water status early during the growing season determines total annual aboveground growth and, besides temperature, species-specific endogenous and/or environmental factors (most likely photoperiod and/or different threshold temperatures) are involved in controlling apical and lateral growth resumption after winter dormancy.

Toward a mechanistic understanding of competition in vascular-feeding herbivores: an empirical test of the sink competition hypothesis

Recent evidence suggests that competitive interactions among herbivores are mostly indirect and mediated by plant responses to herbivory. Most studies, however, emphasize chewing insects and secondary chemistry, thus ignoring the diverse group of vascular-parasites that may be more likely to compete through induced changes in phytonutrients. Using an aboveground phloem-feeding aphid (Myzus persicae) and a belowground gall-forming nematode (Meloidogyne incognita) on tobacco plants, we assessed the importance of competition via induced host-plant sinks. In a series of experimental trials, nematode root herbivory caused 55 and 72% declines in the growth and fecundity of aphids, respectively. Aphids, on the other hand, did not impact nematode performance. Therefore, we predicted that nematodes out-compete M. persicae by attenuating the magnitude of aphid-induced sinks. Through a combination of invertase enzyme measurements and stable isotope ((13)C and (15)N) enrichment, we found evidence that both herbivores act as mobilizing sinks. Aphids attracted photoassimilates to feeding aggregations on leaves and nematode galls accumulated resources in the roots. Levels of invertase enzymes, for example, were more than fourfold higher in nematode galls than in surrounding root tissue. Yet we found no evidence supporting a sink competition model for aphid-nematode interactions. The strength of aphid-induced leaf sinks was entirely unaffected by nematode presence, and vice versa. Thus, induced host-plant sinks appear to be a common strategy employed by vascular parasites to manipulate the physiology of their host, but multi-sink competition may be limited to herbivores that co-occur on the same tissue type and/or plants under growth-limited abiotic conditions.

A functional-structural kiwifruit vine model integrating architecture, carbon dynamics and effects of the environment.

Functional-structural modelling can be used to increase our understanding of how different aspects of plant structure and function interact, identify knowledge gaps and guide priorities for future experimentation. By integrating existing knowledge of the different aspects of the kiwifruit (Actinidia deliciosa) vine's architecture and physiology, our aim is to develop conceptual and mathematical hypotheses on several of the vine's features: (a) plasticity of the vine's architecture; (b) effects of organ position within the canopy on its size; (c) effects of environment and horticultural management on shoot growth, light distribution and organ size; and (d) role of carbon reserves in early shoot growth. Using the L-system modelling platform, a functional-structural plant model of a kiwifruit vine was created that integrates architectural development, mechanistic modelling of carbon transport and allocation, and environmental and management effects on vine and fruit growth. The branching pattern was captured at the individual shoot level by modelling axillary shoot development using a discrete-time Markov chain. An existing carbon transport resistance model was extended to account for several source/sink components of individual plant elements. A quasi-Monte Carlo path-tracing algorithm was used to estimate the absorbed irradiance of each leaf. Several simulations were performed to illustrate the model's potential to reproduce the major features of the vine's behaviour. The model simulated vine growth responses that were qualitatively similar to those observed in experiments, including the plastic response of shoot growth to local carbon supply, the branching patterns of two Actinidia species, the effect of carbon limitation and topological distance on fruit size and the complex behaviour of sink competition for carbon. The model is able to reproduce differences in vine and fruit growth arising from various experimental treatments. This implies it will be a valuable tool for refining our understanding of kiwifruit growth and for identifying strategies to improve production.

Competition between fruit and vegetative growth in Hayward kiwifruit

Fruit dry matter content (DM) of kiwifruit, defined as the fruit dry weight (DW) expressed as a percentage of the fresh weight (FW), is used as an indicator of eating quality. A high DM at harvest results in increased consumer satisfaction. To determine the role of carbohydrate availability and sink competition in altering fruit size and DM at commercial harvest, we used an experimental model system based on phloem-girdled shoots to manipulate the number of source leaves, fruit and vegetative sinks on a shoot of ‘Hayward’ kiwifruit. Commercially produced kiwifruit fruits typically weigh 95–115 g and have a DM of 14–17 units (this is a percentage but the % sign has not been shown, to reduce confusion with changes in DM expressed as a % change). With our experimental system, this corresponded to the fruit growth observed with two to three leaves when there was no vegetative competition. With four source leaves and a single fruit, competition from a vegetative regrowth reduced fruit fresh weight by 28% and dry weight by 39%. With two fruit, and no vegetative sink, between-fruit competition had less severe effects on the fruit and dry weight. Doubling the number of fruit on a girdled shoot reduced average fruit fresh weight by 15%, dry weight by 23% and DM by 12%. With a high source supply (seven leaves with no regrowth competition) fruit growth was very high with a fresh weight of 174 g and 18.4 DM, substantially above that of commercial production.

Impact of drought on the temporal dynamics of wood formation in Pinus sylvestris

We determined the temporal dynamics of cambial activity and xylem cell differentiation of Scots pine (Pinus sylvestris L.) within a dry inner Alpine valley (750 m a.s.l., Tyrol, Austria), where radial growth is strongly limited by drought in spring. Repeated micro-sampling of the developing tree ring of mature trees was carried out during two contrasting years at two study plots that differ in soil water availability (xeric and dry-mesic sites). In 2007, when air temperature at the beginning of the growing season in April exceeded the long-term mean by 6.4 degrees C, cambial cell division started in early April at both study plots. A delayed onset of cambial activity of c. 2 weeks was found in 2008, when average climate conditions prevailed in spring, indicating that resumption of cambial cell division after winter dormancy is temperature controlled. Cambial cell division consistently ended about the end of June/early July in both study years. Radial enlargement of tracheids started almost 3 weeks earlier in 2007 compared with 2008 at both study plots. At the xeric site, the maximum rate of tracheid production in 2007 and 2008 was reached in early and mid-May, respectively, and c. 2 weeks later at the dry-mesic site. Since in both study years more favorable growing conditions (i.e., an increase in soil water content) were recorded during summer, we suggest a strong sink competition for carbohydrates to mycorrhizal root and shoot growth. Wood formation stopped c. 4 weeks earlier at the xeric compared with the dry-mesic site in both years, indicating a strong influence of drought stress on cell differentiation. This is supported by radial widths of earlywood cells, which were found to be significantly narrower at the xeric than at the dry-mesic site (P < 0.05). Repeated cellular analyses during the two growing seasons revealed that, although spatial variability in the dynamics and duration of cell differentiation processes in P. sylvestris exposed to drought is strongly influenced by water availability, the onset of cambial activity and cell differentiation is controlled by temperature.

Carbohydrate uptake from xylem vessels and its distribution among stem tissues and buds in walnut (Juglans regia L.)

Bud break pattern is a key determinant of tree architecture. The mechanisms leading to the precedence of certain buds over the others are not yet fully explained, but the availability of soluble sugars may play a significant role, especially those in the xylem sap at the onset of the growing period. Here, we measured carbon availability in the different tissues (bud, xylem and bark). To assess the capacity of buds to use the xylem sap carbohydrates, the fluxes between xylem vessels and parenchyma cells, bark and buds of walnut (Juglans regia cv 'Franquette') were measured during the rest period until bud break. This uptake capacity varies according to the temperature, the sugar and the position on the branch of the fragment studied. Between December and March, in xylem tissues, the active component of sucrose uptake was predominant compared with diffusion (90% of the total uptake), whereas the active component accounted for more moderate amounts in buds (50% of the uptake). The active uptake of hexoses took place belatedly (April) in xylem. The flow rates between xylem vessels and buds increased 1 month before bud break and reached 2000 microg sucrose h(-)(1) g DW(-)(1). Fluxes seemed to depend on bud position on the branch. However, this study strongly suggests that they were mainly dependent on the sink strength of the buds and on the sink competition between bud, xylem parenchyma and bark.

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.

Sink Competition and Desuckering Effects on Field Performance of Triploid and Tetraploid Plantain Genotypes

Reproductive growth in polyarchic Musa spp. varieties occurs by the simultaneous growth of several shoots, resulting in competitive inhibition of fruit development in the individual shoots, particularly under poor soil fertility conditions. Nine plantain genotypes were forced into single-culm growth by continuous sucker removal in the ratoon crop (RC). There were no significant differences among genotypes for days to flowering (DTF) and days to harvest (DTH) in the plant crop (PC), but significant differences occurred in RC for both traits. There was a negative correlation between degree of sucker growth in the PC and DTF or DTH in RC, indicating that early flowering and maturity in the RC occurred as a result of fast sucker development in the PC. Likewise, bunch weight in the RC was positively correlated with sucker growth in the previous crop. However, sucker growth appeared to compete against the development of the bunch in the PC, resulting in a significant reduction in fruit size but not fruit number. Desuckering significantly reduced DTF and DTH in the RC. Bunch weight and fruit size were significantly improved by sucker removal in the RC. Gains were highest for genotypes that normally produce multiple lateral shoots and lowest for those displaying a more hierarchical growth habit. Thus, sucker removal could be recommended as a crop management option for the polyarchic Musa genotypes.