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Light plays a dominant role in the biosynthesis and accumulation of photosynthetic products. However, the metabolism and translocation of photosynthetic products in plants under different light spectra remain elusive. In this study, tomato (Solanum lycopersicum L.) seedlings were treated with different light spectra delivered by light-emitting diodes (LEDs) with the same photosynthetic photon flux density at 300 μmol m−2 s−1, including monochromatic red (660 nm, R), blue (450 nm, B), sun-like white (W, 380–780 nm), or a combination of R and B lights (R:B = 1:1, RB). Compared with W, the biomass distribution ratio for leaves under R, B, and RB decreased by 5.01–9.53%, while the ratio for stems and roots increased by 3.71–6.92% and 0.14–2.81%, respectively. The photosynthetic carbon distribution expressed as 13C enrichment was higher in stems and roots under RB and R, while B led to more 13C transported from leaves and enriched in stems when compared with W. Meanwhile, RB led to significant increases in the activities of phosphate synthase (SPS), sucrose synthase (SS), vacuolar acid invertase (VI), and neutral invertase (NI). The R was more efficient in increasing the activity of SPS and SS, while B was more effective in promoting the activity of VI and NI. The transcript levels of SPS, SS3, NI6, and VI were upregulated under R, B, and RB. However, the transcript patterns of SPS, SS3, NI6, and VI were not consistent with the changes in their encoded enzymes, especially the transcript patterns of SPS and SS3. Our study suggests that the red- and blue-light-induced long-distance and short-distance transport of photosynthetic products in plants, respectively, might result from different regulation of sucrose-metabolizing enzymes from transcriptional and post-transcriptional levels. [ABSTRACT FROM AUTHOR]

We developed a phenology-based growth model(PG model) for Spartina alterniflora that incorporates the effects of light, temperature, and salinity on plant production. The PG model is the first to quantify carbon translocation between both above- and below-ground biomass across three phenological periods: growth, senescence, and dormancy periods. This model, fitted to field data from short, medium, and tall S. alterniflora types, estimates physiological parameters such as mass-specific rates of carbon translocation. Once parameterized, the model is applied in forward mode to predict whole-plant production, growth, respiration, mortality, and translocation. Model results reveals that short forms allocate 82 % of photosynthate to below-ground biomass during the growing season, compared to tall (52 %) and medium (22 %) types. However, tall forms, with extensive above-ground biomass, show the highest absolute carbon translocation to below-ground tissues during growth(ave. 3940 g dry weight m−2) and senescence(ave. 265 g dry weight m−2) period. An average mortality rate of 52 % of net production in the tall form below-ground biomass throughout the year indicates a substantial contribution to organic carbon sequestration within the habitat sediment. Model results also reveal that the carbon translocation from below- to above-ground tissues may not be required for survival during winter in milder climate like Sapelo Island, Georgia. • The first Phenology-based Growth model(PG model) for Spartina incorporates salinity effects. • The short form allocating the most photosynthate below-ground during growing season. • High below-ground biomass mortality in the tall form implies significant carbon sequestration. • Carbon translocation from below- to above-ground tissues negligible in all forms in Georgia. • Spartina in milder climates may not rely on below-ground reserves for winter survival. [ABSTRACT FROM AUTHOR]

This study investigated the effect of transient submergence on the recovery of photosynthetic activity and translocation of photosynthate in IR67520 (Sub1A genotype) and IR72442 (non-Sub1A genotype) using 13C-labeled tracer, coupled with some photosynthetic physiological assessments. Plant growth, photosynthetic capacity, and photosynthetic recovery were studied by treating the two rice genotypes without or completely submerged for 7 days in transparent acrylic tanks filled with water to a depth of 80 cm, followed by 7 days of reaeration. Results revealed that the IR67520 was able to obtain new carbon source for assimilation during at 7 days of recovery periods. The IR72442 genotype partitioned 13C to the newly developed upper leaves more than the IR67520 genotype did. This was due to its inability to obtain CO2 from other source during post submergence. Recovery of chlorophyll content, ability to retain higher biomass, and ability to grow faster at 7 days of recovery periods also indicated the ability of Sub1A genotype to reactivate its photosynthetic capacity. [ABSTRACT FROM AUTHOR]

Aims: Livestock grazing is one of the most common utilization methods and exerts a significant effect on the carbon allocations between the above- and belowground components of a grassland ecosystem. The major aim of this study were to evaluate the proportions of 13C allocation to various C pools of the plant-soil system of a meadow steppe ecosystem in response to changes of stocking rate. Methods: In situ stable 13C isotope pulse labeling was conducted in a long-term grazing experiment with 4 stocking rate. Plant materials and soil samples were taken at eight occasions (0, 3, 10, 18, 31, 56 and 100 days after labeling) to analyze the decline in 13C over time, and their composition signature of 13C were analyzed by the isotope ratio mass spectrometer technique. Results: We found a significantly greater decline in assimilated 13C of shoot and living root for the heavily grazed swards compared to other stocking rates, with the highest relocation rate of 13C into soil C pool compared to other fractions. In addition, light grazing significantly allocated 13C assimilates in the belowground pool compared to other stocking rates, especially in the live root and topsoil C-pools. Conclusions: In this study, the effects of grazing on the carbon transfers and stocks within the plant-soil system of the meadow steppe were highly grazing pressure dependent. Plant-soil system in light stocking rate presented the highest C utilization efficiency, however, plants allocated more C to soil C pools with heavily stocking rate. [ABSTRACT FROM AUTHOR]

Symbiosis between reef-building corals and unicellular algae (Symbiodiniaceae) fuels the growth and productivity of corals reefs. Capacity for Symbiodiniaceae to fix inorganic carbon (Ci) and translocate carbon compounds to the host is central to coral health, but how these processes change for corals thriving in environmental extremes remains largely unresolved. We investigate how a model coral—Pocillopora acuta—persists from a reef habitat into an adjacent extreme mangrove lagoon on the Great Barrier Reef. We combine respirometry and photophysiology measurements, Symbiodiniaceae genotyping, and 13C labelling to compare P. acuta metabolic performance across habitats, in relation to the Ci uptake and translocation capacity by symbionts' autotrophy. We show that differences in P. acuta metabolic strategies across habitats align with a shift in dominant host-associated Symbiodiniaceae taxon, from Cladocopium in the reef to Durusdinium in the mangroves. This shift corresponded with a change in "photosynthetic strategy", with P. acuta in the mangroves utilising absorbed light for photochemistry over non-photochemical quenching. Mangrove corals translocated similar proportions of carbon compared to the reefs, despite a lower Ci uptake. These trends indicate that coral survival in mangrove environments occurs through sustained translocation rate of organic compounds from coral symbionts to host. [ABSTRACT FROM AUTHOR]

The coral symbiosis is the linchpin of the reef ecosystem, yet the mechanisms that promote and maintain cooperation between hosts and symbionts have not been fully resolved. We used a phylogenetically controlled design to investigate the role of vertical symbiont transmission, an evolutionary mechanism in which symbionts are inherited directly from parents, predicted to enhance cooperation and holobiont fitness. Six species of coral, three vertical transmitters and their closest horizontally transmitting relatives, which exhibit environmental acquisition of symbionts, were fragmented and subjected to a 2-week thermal stress experiment. Symbiont cell density, photosynthetic function and translocation of photosynthetically fixed carbon between symbionts and hosts were quantified to assess changes in physiological performance and cooperation. All species exhibited similar decreases in symbiont cell density and net photosynthesis in response to elevated temperature, consistent with the onset of bleaching. Yet baseline cooperation, or translocation of photosynthate, in ambient conditions and the reduction in cooperation in response to elevated temperature differed among species. Although Porites lobata and Galaxea acrhelia did exhibit the highest levels of baseline cooperation, we did not observe universally higher levels of cooperation in vertically transmitting species. Post hoc sequencing of the Symbiodinium ITS-2 locus was used to investigate the potential role of differences in symbiont community composition. Interestingly, reductions in cooperation at the onset of bleaching tended to be associated with increased symbiont community diversity among coral species. The theoretical benefits of evolving vertical transmission are based on the underlying assumption that the host-symbiont relationship becomes genetically uniform, thereby reducing competition among symbionts. Taken together, our results suggest that it may not be vertical transmission per se that influences host-symbiont cooperation, but genetic uniformity of the symbiont community, although additional work is needed to test this hypothesis.

The symbiosis between cnidarian hosts and microalgae of the genus Symbiodinium provides the foundation of coral reefs in oligotrophic waters. Understanding the nutrient-exchange between these partners is key to identifying the fundamental mechanisms behind this symbiosis, yet has proven difficult given the endosymbiotic nature of this relationship. In this study, we investigated the respective contribution of host and symbiont to carbon and nitrogen assimilation in the coral model anemone Aiptaisa. For this, we combined traditional measurements with nanoscale secondary ion mass spectrometry (NanoSIMS) and stable isotope labeling to investigate patterns of nutrient uptake and translocation both at the organismal scale and at the cellular scale. Our results show that the rate of carbon and nitrogen assimilation in Aiptasia depends on the identity of the host and the symbiont. NanoSIMS analysis confirmed that both host and symbiont incorporated carbon and nitrogen into their cells, implying a rapid uptake and cycling of nutrients in this symbiotic relationship. Gross carbon fixation was highest in Aiptasia associated with their native Symbiodinium communities. However, differences in fixation rates were only reflected in the δ13C enrichment of the cnidarian host, whereas the algal symbiont showed stable enrichment levels regardless of host identity. Thereby, our results point toward a “selfish” character of the cnidarian—Symbiodinium association in which both partners directly compete for available resources. Consequently, this symbiosis may be inherently instable and highly susceptible to environmental change. While questions remain regarding the underlying cellular controls of nutrient exchange and the nature of metabolites involved, the approach outlined in this study constitutes a powerful toolset to address these questions.

The coral symbiosis is the linchpin of the reef ecosystem, yet the mechanisms that promote and maintain cooperation between hosts and symbionts have not been fully resolved. We used a phylogenetically controlled design to investigate the role of vertical symbiont transmission, an evolutionary mechanism in which symbionts are inherited directly from parents, predicted to enhance cooperation and holobiont fitness. Six species of coral, three vertical transmitters and their closest horizontally transmitting relatives, which exhibit environmental acquisition of symbionts, were fragmented and subjected to a 2-week thermal stress experiment. Symbiont cell density, photosynthetic function and translocation of photosynthetically fixed carbon between symbionts and hosts were quantified to assess changes in physiological performance and cooperation. All species exhibited similar decreases in symbiont cell density and net photosynthesis in response to elevated temperature, consistent with the onset of bleaching. Yet baseline cooperation, or translocation of photosynthate, in ambient conditions and the reduction in cooperation in response to elevated temperature differed among species. Although Porites lobata and Galaxea acrhelia did exhibit the highest levels of baseline cooperation, we did not observe universally higher levels of cooperation in vertically transmitting species. Post hoc sequencing of the Symbiodinium ITS-2 locus was used to investigate the potential role of differences in symbiont community composition. Interestingly, reductions in cooperation at the onset of bleaching tended to be associated with increased symbiont community diversity among coral species. The theoretical benefits of evolving vertical transmission are based on the underlying assumption that the host-symbiont relationship becomes genetically uniform, thereby reducing competition among symbionts. Taken together, our results suggest that it may not be vertical transmission per se that influences host-symbiont cooperation, but genetic uniformity of the symbiont community, although additional work is needed to test this hypothesis. [ABSTRACT FROM AUTHOR]

Studies suggest that intensively tilled soils have lost 25–75% of their original soil organic C (SOC) content. No tillage (NT) can restore SOC in response to increased C inputs and reduced soil disturbance. Organic amendments provide faster recovery of SOC, ultimately promoting the saturation of soil layers. Here we present evidence of additional SOC accrual through translocation of SOC after saturation of the topsoil layer in a NT soil. Both processes were observed in a long-term (25 yr.) experiment comparing soil tillage systems (chisel tillage − CT, and NT) in central Kansas. Plots with continuous corn were amended with mineral (MF) and organic N (OF), in addition to a control treatment without N fertilization (CO). Accumulation of SOC was limited to the surface layer (0–5 cm) of the NT soil amended with MF. Organic fertilization increased SOC in the 0–5 cm soil layer from 9.5 Mg C ha −1 to a level of 16.2 and 30.2 Mg C ha −1 in CT and NT, respectively. Further analysis confirmed the saturation of physically protected SOC in the surface of NT soil under organic amendments. After saturation, significant SOC accrual (1.3 Mg C ha −1 yr −1 ) was observed in the 5–15 cm soil layer. Isotopic assessment confirmed the occurrence of SOC translocation between saturated and C-depleted NT soil layers. No evidence of SOC translocation was observed between non-saturated soil layers. Further research is needed to elucidate the mechanisms regulating this process. Nonetheless, SOC translocation and subsequent SOC accrual suggests a greater C sink potential for NT soils than previously thought. [ABSTRACT FROM AUTHOR]

Insufficient leaf photoassimilation could allow mobilized carbohydrate reserves to contribute to berry sugar accumulation. However, the extent of this contribution during rapid and slow berry sugar accumulation is undefined. The potential effect of leaf-to-fruit ratio and water availability on carbohydrate reserve distribution in potted Tempranillo grapevines was examined during berry maturation. Within each leaf-to-fruit ratio treatment (full and 50% leaves), vines were grown under full or 50% reduced irrigation regimes. Dry biomass development, and the starch and soluble sugar concentrations were determined in the roots, trunks, stems and leaves. Berry sugar and anthocyanin accumulation were also assessed. Under full irrigation, no starch remobilization from roots was observed, regardless of the leaf-to-fruit ratio. Under reduced water supply, starch remobilization from roots was concurrent with rapid berry sugar accumulation, especially in grapevines with low leaf-to-fruit ratio. Soluble sugar accumulation coincided with starch depletion in the roots of grapevines under reduced water availability. When berry sugar accumulation slowed, an increase in carbohydrates was observed in the roots. Sustained water constraints during rapid berry sugar accumulation resulted in a forced reliance on stored carbohydrates to support berry sugar accumulation, but did not significantly alter the tempo of berry sugar and anthocyanin accumulation. A reduced leaf-to-fruit ratio intensified the reliance of fruit sugar accumulation on stored carbohydrates. Besides the importance of post-harvest carbohydrate reserve replenishment when root carbohydrate reserves are depleted during berry maturation, the reserves are also refilled during maturation when berry sugar accumulation slows. This study showed distinctly that root carbohydrate replenishment could already start a few weeks before harvest, and this replenishment could be important when the post-harvest carbon assimilation period is ineffective. [ABSTRACT FROM AUTHOR]

Northern red oak (Quercus rubra L.) seedlings are frequently planted on suboptimal sites in their native range in North America, subjecting them to environmental stresses, such as flooding, for which they may not be well adapted. Members of the genus Quercus exhibit a wide range of responses to flooding, and responses of northern red oak to flooding remain inadequately described. To better understand the physiological effects of root system inundation in post-transplant northern red oak seedlings and the effects of flooding on endogenous patterns of resource allocation within the plant, we observed the effects of short-term flooding initiated at the linear shoot growth stage on net photosynthetic rates, dark respiration, chlorophyll fluorescence (Fv/Fm) and translocation of 13C-labeled current photosynthate. Downward translocation of current photosynthate declined after 4 days of flooding and was the first measured physiological response to flooding; net photosynthetic rates decreased and dark respiration rates increased after 7 days of flooding. Short-term flooding did not affect maximal potential efficiency of photosystem II (Fv/Fm). The finding that decreased downward translocation of 13C-labeled current photosynthate preceded reduced net photosynthesis and increased dark respiration during flooding suggests the occurrence of sink-limited photosynthesis under these conditions. [ABSTRACT FROM AUTHOR]

Aims: Rice fields are an important source for the greenhouse gas methane. Plants play an essential role in carbon supply for soil microbiota, but the influence of the microbial community on carbon cycling is not well understood. Methods: Microcosms were prepared using sand-vermiculite amended with different soils and sediments, and planted with rice. The microcosms at different growth stages were pulse-labeled with CO followed by tracing C in plant, soil and atmospheric carbon pools and quantifying the abundance of methanogenic archaea in rhizosphere soil. Results: Overall, >85 % of the freshly assimilated carbon was allocated in aboveground plant biomass, approximately 10 % was translocated into the roots and < 2 % was recovered in soil organic matter, independently from soil type. Only about 0.3 % was transformed to CH, but emission of C-labeled CH started immediately and C enrichment revealed that plant-derived carbon was an important source for methanogenesis. The results further demonstrated that carbon assimilation and translocation processes, microbial abundance and gas emission were not only affected by the plant growth stage, but also by the content and type of soil in which the rice plants grew. Conclusions: The study illustrates the close ties between plant physiology, soil properties and microbial communities for carbon turnover and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Background: It was recently discovered that symbiotic algae in the eggs of the salamander Ambystoma maculatum translocate fixed carbon from photosynthesis to developing embryos. Fixed carbon translocation was shown in embryos at one time point during development, however, it was unknown if fixed carbon translocation occurs throughout all developmental stages. Findings: In this study, fixed carbon translocation was measured in salamander eggs at six time points over the latter half of development. Fixed carbon translocation did not occur until the middle tailbud portion of development (stages 26-30), and translocation was measured in 20% or less of eggs sampled. Peak carbon translocation occurred during the late tailbud phase of development (stages 31-35), where as much as 87% of eggs sampled showed translocation, and average percent translocation was 6.5%. During the final stages of development, fixed carbon translocation declined, and translocation was not detected in embryos five days prior to hatching. Conclusions: The onset of fixed carbon translocation from Oophila to A. maculatum embryos during the second half of embryonic development is likely due to the corresponding settlement and concentration of Oophila in the inner egg envelope. In addition, carbon translocation ceases in late stage embryos as the inner egg envelope thins and ruptures in preparation for hatching. [ABSTRACT FROM AUTHOR]

Each spring, North American spotted salamander (Ambystoma maculatum) females each lay hundreds of eggs in shallow pools of water. Eggs are surrounded by jelly layers and are deposited as large gelatinous masses. Following deposition, masses are penetrated by a mutualistic green alga, Oophila amblystomatis, which enters individual egg capsules, proliferates and aggregates near the salamander embryo, providing oxygen that enhances development. We examined the effects of population density of intracapsular O. amblystomatis on A. maculatum embryos and show that larger algal populations promote faster embryonic growth and development. Also, we show that carbon fixed by O. amblystomatis is transferred to the embryos, providing the first evidence of direct translocation of photosynthate from a symbiont to a vertebrate host. [ABSTRACT FROM AUTHOR]

Background Carbon assimilation and leaf-to-fruit sugar transport are, along with plant water status, the driving mechanisms for fruit growth. An integrated comprehension of the plant water and carbon relationships is therefore essential to better understand water and dry matter accumulation. Variations in stem diameter result from an integrated response to plant water and carbon status and are as such a valuable source of information. Methods A mechanistic water flow and storage model was used to relate variations in stem diameter to phloem sugar loading and sugar concentration dynamics in tomato. The simulation results were compared with an independent model, simulating phloem sucrose loading at the leaf level based on photosynthesis and sugar metabolism kinetics and enabled a mechanistic interpretation of the ‘one common assimilate pool’ concept for tomato. Key Results Combining stem diameter variation measurements and mechanistic modelling allowed us to distinguish instantaneous dynamics in the plant water relations and gradual variations in plant carbon status. Additionally, the model combined with stem diameter measurements enabled prediction of dynamic variables which are difficult to measure in a continuous and non-destructive way, such as xylem water potential and phloem hydrostatic potential. Finally, dynamics in phloem sugar loading and sugar concentration were distilled from stem diameter variations. Conclusions Stem diameter variations, when used in mechanistic models, have great potential to continuously monitor and interpret plant water and carbon relations under natural growing conditions. [ABSTRACT FROM AUTHOR]

Summer-green herbs inhabiting deciduous forests often put out aerial shoots under bright conditions before tree-canopy closure and grow until late summer under the closed canopy. Some of them produce leaves continuously even after the initiation of canopy closure, indicating an exploitation of the low light period. The manner of carbon assimilation during bright and shade periods within a growth season should reflect the seasonal patterns of vegetative growth and reproductive allocation of individual species. We examined the seasonal patterns of assimilation, partitioning of photosynthate between reproduction and storage, and the budget of reproduction of a perennial understory herb, Parasenecio auriculata. Although photosynthetic rates per unit leaf area decreased with the seasonal reduction in light level, net assimilation at the whole-plant level was maintained at a high level even after canopy closure owing to the increase in the total leaf area. Stored resource in tubers contributed to the rapid development of aerial shoots in the early season, and annual tuber growth was completed before flowering. Instant photosynthetic products considerably contributed to the maintenance of flowers but not to fruit development because of low assimilation rate during fruiting. These findings indicated that carbon assimilation during flowering contributes to sexual reproduction without influencing the development of storage organs. Stable carbon assimilation over summer by shade-acclimatized leaves enabled the maintenance of high productivity associated with high sexual reproduction. [ABSTRACT FROM AUTHOR]

1. The carbon source for reproduction in plants may differ between flowering and fruiting stages. To clarify how spring ephemerals use current photosynthetic products for reproduction, the allocation patterns of photosynthate at flowering and fruiting and the effects of resource limitation on reproductive performance in Corydalis ambigua were assessed. 2. A 13C tracing experiment revealed that about 20% of the current photosynthetic carbon was used for reproduction at both flowering and fruiting. The proportion of 13C allocated to fruits was constant irrespective of the light level. In contrast, 13C translocation to tubers increased at fruiting, and this trend was accelerated when plants were shaded. 3. Defoliation treatment significantly reduced nectar production and tuber mass, while seed production was not affected. Therefore, when carbon assimilation was limited, carbon was preferentially allocated to current reproduction (seeds) rather than to pollinator attraction (nectar) or storage (tuber). 4. If seed production is partly supported by carbohydrate reserved in the old tissue of tubers, nectar and seed production may not compete strongly for carbon sources. In contrast to the ability of high seed production, the susceptibility of nectar production to current photosynthesis indicates that seed production of this species is basically limited by pollen capture. 5. Therefore, temporal separation of resource pool for reproduction may mitigate the joint limitation of seed production between pollinator attraction and resource availability. Temporal variation of the sink–source balance of storage organ is crucial to understand the cost of reproduction in perennial plants. [ABSTRACT FROM AUTHOR]

Background and Aims: Rubus chamaemorus (cloudberry) is a herbaceous clonal peatland plant that produces an extensive underground rhizome system with distant ramets. Most of these ramets are non-floral. The main objectives of this study were to determine: (a) if plant growth was source limited in cloudberry; (b) if the non-floral ramets translocated carbon (C) to the fruit; and (c) if there was competition between fruit, leaves and rhizomes for C during fruit development. [ABSTRACT FROM PUBLISHER]

In Crocus vernus, a spring bulbous species, prolonged growth at low temperatures results in the development of larger perennial organs and delayed foliar senescence. Because corm growth is known to stop before the first visual sign of leaf senescence, it is clear that factors other than leaf duration alone determine final corm size. The aim of this study was to determine whether reduced growth at higher temperatures was due to decreased carbon import to the corm or to changes in the partitioning of this carbon once it had reached the corm. Plants were grown under two temperature regimes and the amount of carbon fixed, transported, and converted into a storable form in the corm, as well as the partitioning into soluble carbohydrates, starch, and the cell wall, were monitored during the growth cycle. The reduced growth at higher temperature could not be explained by a restriction in carbon supply or by a reduced ability to convert the carbon into starch. However, under the higher temperature regime, the plant allocated more carbon to cell wall material, and the amount of glucose within the corm declined earlier in the season. Hexose to sucrose ratios might control the duration of corm growth in C. vernus by influencing the timing of the cell division, elongation, and maturation phases. It is suggested that it is this shift in carbon partitioning, not limited carbon supply or leaf duration, which is responsible for the smaller final biomass of the corm at higher temperatures. [ABSTRACT FROM PUBLISHER]

1. Arid ecosystems are a patch mosaic of plants and biological soil crusts that have been described as islands and mantles of fertility, respectively. To determine whether these patches are metabolically linked by a fungal network of dark septate and arbuscular mycorrhizal fungi (AMF), we measured translocation of nitrogen (N) and carbon (C) in a desert grassland using 15N-NO3 and 13C5, 15N-glutamic acid as substrates. 2. Substrates were applied as point sources to either small patches of biotic crust or to a subset of leaves within a bunch grass tussock. 3. Both substrates were translocated over approximately 1 m2 areas (approximately 20 patches) at rates up to 100 cm day−1 during a 4-day period following a natural rainfall event. Foliar uptake of 15N from glutamate was initially more rapid than 15N uptake from nitrate, and translocation from foliage was initially more rapid than translocation from soil crust. Rates of 15N translocation between patches were similar to rates of atmospheric N deposition and denitrification. 4. 13C from 13C5, 15N-glutamic acid applied to leaves was translocated to crust suggesting that plant C may provide metabolic support to biological soil crusts during periods of active growth. 13C from 13C5, 15N-glutamic acid applied to soil crusts did not enter plants, in contrast to the 15N from this substrate, indicating that glutamate was not translocated intact. 5. The dominant fungi of roots, rhizosphere soil and biological soil crusts are dark septate ascomycetes, most classified as Pleosporales, and AMF are rare. Phylogenetic analyses indicate substantial overlap in fungal community composition between roots and crusts, which may facilitate nutrient transfers. 6. Synthesis. This study supports the hypothesis that the spatial structure of semi-arid ecosystems, a patch mosaic of grasses and biological soil crust described, respectively, by the island of fertility and mantle of fertility paradigms, is functionally integrated by exchanges of C and N through a symbiotic fungal network dominated by dark-septate fungi. [ABSTRACT FROM AUTHOR]

In a glasshouse experiment, different tiller categories (main, young primary, and old primary) of two Guinea grass cultivars, Mombacxa and Tanzânia, were 14C-labelled to investigate C translocation between tillers. In both cultivars, young primary tillers retained less radiocarbon (79%) than main (86%) and old primary (87%) labelled tillers, suggesting that the photosynthetic capacity of the young tillers exceeds their capacity either to store or use that photosynthate for growth and maintenance. In cv. Tanzânia the old primary tillers translocated more photoassimilate to their daughter tillers and to the rest of the plant than cv. Mombacxa, suggesting either higher vascular connectivity between tillers or stronger diurnal fluctuations in sink--source balance in Tanzânia than Mombacxa. For unlabelled tillers, specific activities were almost always higher in roots than in shoots, although total radiocarbon uptake by roots was reduced in younger tillers with low root mass. Where young primary tillers were labelled, the largest single repository of exported photoassimilate was the main tiller roots, indicating that daughter tillers may make an important contribution to the maintenance of older roots on mature tillers. [ABSTRACT FROM AUTHOR]

Hybrid winter wheat (cv. XN901) shows a strong hybrid vigor in terms of yield potential and its leaves and stems stay green when its kernels reach maturity. Much of its pre-stored carbon reserve is left unused in its stems and leaves. In this study, photosynthesis and translocation of carbon assimilates of the hybrid wheat were investigated at its late grain-filling stage. Feeding labelled 14CO2 to flag leaves of XN901 showed that its export to grains was much slower than that of an ordinary cultivar (Shaan 229) that is currently used in production. Within 24 h of labelling, Shaan 229 and XN901 exported 59 % and 40 %, respectively, of the 14C from their flag leaves. At the sink side, 52.1 % of the fed 14C in Shaan 229 was exported to its grains within the first 24 h while XN901 deposited only 15.8 % of the fed 14C in the grains at the same period. Photosynthetic rates and chlorophyll contents in the flag leaves declined much more slowly in XN901 than in Shaan 229 during the late grain-filling stage. Hybrid wheat XN901 also had a longer grain-filling period (6 days longer), higher grain yield (15 % more), but lower harvest index (19 % less) than Shaan 229. Its grain-filling rate was lower but declined more slowly at the late grain-filling stage than that of Shaan 229. Results indicate that the strong hybrid vigour of XN901 leads to an unfavourably delayed senescence which results in the much unused carbon reserve in its straws. Raising harvest index should be the key aim to materialize its yield potential. [ABSTRACT FROM AUTHOR]

Comments on the physiology of symbiotic fungi and clonal plants. Effect of biotrophic fungi on plant growth; Association of vascular plant species with arbuscular mycorrhizal fungi; Influences to the clonal growth of plant population.

• Carbon transfer from fungus to plant in the arbuscular mycorrhizal (AM) symbiosis has been reported, but its significance and even its existence have been called into question and the issue remains controversial. We investigated carbon movement from fungus to plant and from one mycorrhizal root system to another via a common AM fungal network in monoxenic cultures to avoid limitations of some previous studies. • 13C and 14C labeled substrates were supplied to functioning in vitro AM mycorrhizas between Ri T-DNA transformed carrot ( Daucus carota) roots and Glomus intraradices to follow carbon movement into and between host and fungal metabolite pools. • Fungal triacylglycerol and trehalose were labeled when permeant substrates were supplied to the extraradical mycelium (ERM), but host-specific compounds in the roots did not become labeled. When labeled glucose was provided to a donor root system, label moved to recipient roots via a common AM fungal network but remained in fungal compounds. • We conclude that carbon flow in the AM symbiosis is normally unidirectional from plant to fungus and that while carbon is translocated by the fungus from one metabolically active root system to another, it remains within the intraradical mycelium (IRM). New Phytologist (2004) 163: 617–627 © New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01152.x [ABSTRACT FROM AUTHOR]

New Zealand is currently identifying and quantifying its carbon sources and sinks to develop a national carbon budget. This will enable it to set policy and targets to reduce greenhouse gas emissions in line with the Kyoto Protocol. While soil is a major carbon sink, New Zealand also has high sediment yields to the ocean, suggesting that erosion has a significant effect on soil carbon fluxes, through CO2 emission during transport of carbon in sediment, carbon burial and recovery of carbon on eroded areas.As a contribution to the national carbon budget, a mass balance approach was used to calculate soil carbon fluxes from landslide and sheetwash erosion in the Tutira catchment in the North Island of New Zealand. This soft rock hill country catchment represents the upper limit for landslide-related soil carbon losses. It contains a lake that acts as a highly efficient trap for sediment and nutrients, and has preserved a high-resolution record of storm-induced erosion. Information from previous studies of erosion and lake sedimentation was used to construct a carbon budget for the 114-year period of European pastoral farming. The budget assumes the gross transfer of carbon by geomorphological processes and does not include biogeochemical exchanges with the atmosphere.Results indicate that 0.94±0.23 Mg C ha-1 per year enter the lake (0.50±0.15 Mg C ha-1 per year from landslide erosion and 0.44±0.17 Mg C ha-1 per year from sheetwash erosion). On a national scale this equates to an anthropogenically induced loss of 2 112 000 Mg C per year from the 10% of similar terrain under pastoral land use. However, the net loss from the landscape is significantly less due to carbon recovery on eroded sites. Landslide scars have a carbon recovery rate (after oxidation) of ∼0.61 Mg C ha-1 per year. Carbon recovery on areas affected solely by sheetwash erosion was not measured, but is significantly lower. This information is being used to constrain models of erosion-related carbon fluxes developed for landslide-prone terrains, as part of the national carbon budget. [Copyright &y& Elsevier]

Summary Acknowledgements References All nutrients that plants absorb have to pass a region of intense interactions between roots, microorganisms and animals, termed the rhizosphere. Plants allocate a great portion of their photosynthetically fixed carbon to root-infecting symbionts, such as mycorrhizal fungi; another part is released as exudates fuelling mainly free-living rhizobacteria. Rhizobacteria are strongly top-down regulated by microfaunal grazers, particularly protozoa. Consequently, beneficial effects of protozoa on plant growth have been assigned to nutrients released from consumed bacterial biomass, that is, the ‘microbial loop’. In recent years however, the recognition of bacterial communication networks, the common exchange of microbial signals with roots and the fact that these signals are used to enhance the efflux of carbon from roots have revolutionized our view of rhizosphere processes. Most importantly, effects of rhizobacteria on root architecture seem to be driven in large by protozoan grazers. Protozoan effects on plant root systems stand in sharp contrast to effects of mycorrhizal fungi. Because the regulation of root architecture is a key determinant of nutrient- and water-use efficiency in plants, protozoa provide a model system that may considerably advance our understanding of the mechanisms underlying plant growth and community composition. © New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01066.x [ABSTRACT FROM AUTHOR]

Summary 1. Clonal plants can share resources such as carbon and nitrogen among connected, separately rooted plant units or ramets. In many cases, resource sharing tends to equalize the performance of ramets, suggesting that differences in resource supply drive the sharing process, with resources moving from ramets with high access to resources to those with low access to resources. However, some patterns of apparent C and N sharing in the stoloniferous wild strawberry Fragaria chiloensis make the growth of ramets less equal, which is inconsistent with this model of resource sharing. As hormones are a mechanism by which non-clonal plants can make the growth of the branches of a shoot less equal, we hypothesized that clonal plants might use hormones to modify patterns of resource sharing between ramets. 2. Auxin (IAA) or cytokinin (BA) was applied to the shoot tip of ramets using a non-invasive protocol previously shown to increase internal hormone concentrations. 14 C or 15 N was then fed to connected ramets, and the amounts of 14 C or 15 N imported by the hormone-treated ramets and by suitable controls were measured. 3. Ramets treated with IAA showed greater C import from connected ramets than did control ramets when the IAA-treated and control ramets were shaded and the connected ramets were not. Ramets treated with IAA showed increased N import from connected ramets compared with the controls when the IAA-treated and control ramets were given less N than the connected ramets, and were also younger than the connected ramets. IAA had no consistent effect on C or N sharing between ramets given the same resource treatments as one another and did not affect the direction of N sharing, which is strongly acropetal in F. chiloensis . BA showed little effect on resource sharing. 4. The results supported the hypothesis that hormones can modify patterns of resource sharing between ramets in clonal plants. In F. chiloensis ,... [ABSTRACT FROM AUTHOR]

Experiments were conducted with Echinochloa crus-galli to partition the effects of chilling the leaf vs. chilling the whole plant on subsequent [SUP11]C translocation. The results clearly demonstrated that whole plant chilling was very detrimental whereas chilling only the leaf had no effect on subsequent translocation nor on [SUP11]C uptake. The inhibition of translocation was due to a reduced rate and percentage of export while [SUP11]C fixation rate was not significantly altered. When the leaf of a chilled plant was maintained at 22 °C, there was no impairment of the transport system nor of photosynthesis. The decrease in export with whole plant chilling may have been due to carbon movement into storage carbohydrates, resulting in a low sucrose gradient. [ABSTRACT FROM AUTHOR]

The in vitro specific activity of ribulose‐1,5‐bisphosphate carboxylase (Rubisco; EC 4. 1. 1. 39) and the dark and light in vivo CO2 fixation activities were determined in the cyanobiont of Gunnera. Compared to the free‐living isolate Nostoc PCC 9231, the in vitro Rubisco activity was high, while the in vivo CO2 fixation was very low. Light did not significantly influence CO2 fixation if the cyanobiont was left in the sliced Gunnera tissues, while a small light stimulation was found for CO2 fixation of the freshly‐isolated cyanobiont. The adjacent non‐infected Gunnera tissue showed a very low CO2 fixation. A rapid translocation of fixed 14CO2 from leaves towards apical parts of the plant was apparent, in particular to the symbiotic tissue. The 14C label appeared mainly in soluble form in this tissue and was rapidly catabolised as shown by 14C chase experiments. Also, short‐term experiments revealed that maximum 14C accumulation occurred in the symbiotic tissue showing the highest rates of nitrogen fixation (Söderbäck et al. 1990), about 10–15 mm from the plant apex. The data were taken to indicate that there is a modification in the photosynthetic light reaction of the cyanobiont and that the cyanobiont lives heterotrophically in the dark on photo‐synthate rapidly delivered from nearby leaves of the host plant. [ABSTRACT FROM AUTHOR]

A clone of Alnus incana (L.) Moench was grown in symbiosis with a local source of Frankia or with Frankia Ar14. Seven to 9‐week‐old plants were given 20 mM NH4Cl (20 mM KCl = control) for 3 days. Nitrogenase activity of intact plants decreased gradually within the 3 days of treatment to about 10% of the initial rates. Hydrogen evolution in air and total nitrogenase activity responded similarly to the treatment. Relative efficiency of nitrogenase thus remained the same throughout the study period. Control plants were not affected. Measurements of nitrogenase activity in root nodule homogenates (in vitro measurements) indicated loss of active nitrogenase rather than shortage of energy for nitrogenase activity in Frankia from ammonium‐treated plants. Shoots were exposed to 14CO2 and translocation of 14C to Frankia vesicle clusters prepared from root nodules was studied. Frankia vesicle clusters from ammonium‐treated plants contained about half as much 14C as those of control plants during all 3 days studied. One explanation for the observed effects is that a reduced supply of carbon to Frankia vesicles in the root nodules caused a reduced metabolic rate, including reduced protein synthesis and synthesis of nitrogenase. [ABSTRACT FROM AUTHOR]

Wheat (Triticum aestivum L. cv. SUN 9E) was grown in a growth chamber under conditions of low soil nitrogen. Translocation of carbon to the roots and the subsequent utilization of these carbohydrates was determined. In vegetative plants (22 days old), 21.5 mg C day−1 were translocated to the roots. 29% of this was incorporated into dry matter, 32% was respired (28% via the cytochrome and 4% via a SHAM‐sensitive, presumably the alternative nonphosphorylating, pathway) and 39% was translocated back to the shoots, mainly in the form of amino acids. – The rote of root maintenance respiration during the vegetative phase was estimated to be 0.7 mg O2 h−1 (g dry weight of roots)−1 and the root growth respiration to be 0.41 g O2 (g dry weight of roots)−1. Total carbohydrate utilization due to root respiration via the alternative, nonphosphorylating pathway during the major part of the growth period was calculated to be only ca 6% of carbohydrate utilization for grain growth. The rate of specific mass transfer (SMT) of sugars in the sieve tubes was estimated from the data on C‐translocation and data on the total area occupied by sieve tubes in a cross section of the root system. SMT was calculated to be 0.8 mg sucrose s−1 cm−2, which is very similar to the published value on SMT for other organs, except roots. [ABSTRACT FROM AUTHOR]

Translocation of C-labelled carbohydrates between the parent stolon and branches, and among branches, of Trifolium repens plants was investigated in two glasshouse experiments to determine patterns of physiological organisation in this clonal species. Differential defoliation treatments were applied to the parent stolon and/or branches to test the sensitivity of translocation to the short-term carbon needs of defoliated sinks. Strong reciprocal exchange of carbohydrate between the parent stolon and branches was observed, with 18 41% of the C exported from leaves on the parent stolon moving to branches, while branches simulta-neously exported 25% (for old source branches) to 54% (for young source branches) of the C they assimilated to the parent plant, including translocation to other branches. Branch-to-branch translocation occurred both acropetally and basipetally. Parent-to-branch, branch-to-parent and branch-to-branch carbon fluxes all increased in response to defoliation of the sink, at the expense of carbon supply to stolon tissue or roots of the source module. Reduced export to stolon tissue of the parent axis played a major role in facilitating C reallocation from leaves on the parent stolon to defoliated branches. The observed patterns of C allocation and translocation could be adequately explained by accepted source-sink theory, and are consistent with a high degree of intra-plant physiological integration in resource supply and utilisation. This information provides mechanistic explanations for aspects of the growth dynamics and ecological interactions of T. repens in the patchy environment of a grazed pasture. [ABSTRACT FROM AUTHOR]

Cloned plants of Alnus incana (L.) Moench were inoculated and grown without combined nitrogen for seven weeks. The effects of ammonium on the function and structure of the root nodules were studied by adding 20 mM NHCl (20 mM KCl=control) for four days. Nitrogenase activity decreased to ca. 50% after one day and to less than 10% after two days in ammonium treated plants, but was unaffected in control plants. The results were similar at photon flux densities of 200 and 50 μmol m s. At the higher light level the effect was concentration dependent between 2 and 20 mM NHCl. The recovery was slow, and more than 11 d were needed for plants treated with 20 mM ammonium to reach initial activity. The distribution of C to the root nodules after assimilation of CO by the plants was not changed by the ammonium treatment. Microscopical studies of root nodules showed high frequencies of endophyte vesicles being visually damaged in nodules from ammonium-treated plants, but not in nodules from control plants. When nitrogenase activity was restored, visually damaged vesicles were again few, whereas young developing vesicles were numerous. The slow recovery, the C-translocation pattern, and the structural changes of the endophyte indicate a more complex mechanism of ammonium influence than simply a short-term reduction in supply of carbon compounds to the nodules. [ABSTRACT FROM AUTHOR]