Plant Carbon Content Research Articles

Plant performance and soil–plant carbon relationship response to different biochar types

Biochar (BC) applications in soil has positive effects on plant performance, particularly for loose soil in agricultural context. However, how biochar types affect plant performance of non-crop species and soil–plant carbon relationships is not clear. We selected five different BC types and three plant species to investigate the responses of plant performance and the soil–plant carbon relationship to BC effects. The result demonstrated that peanut shell BC led to the death of both R. tomentosa and C. edithiae, due to a reduction in nutrient uptake caused by higher soil electricity conductivity (2001.7 and 976.3 µS cm−1). However, the carbon content of S. arboricola increased by 57% in peanut shell BC-amended soil, suggesting that S. arboricola has a higher tolerance for soil salinity. Wood BC-amended soil led to better stomatal conductance (gs) and leaf area index (LAI) of both R. tomentosa and C. edithiae due to the higher water retention in the soil (22.68% and 20.79%). This illustrated that a higher amount of water retention brought by wood BC with a great amount of pore volume might be the limited factor for plant growth. The relationship between gs and LAI suggested that gs would not increase when LAI reached beyond 3. Moreover, wood and peanut shell BC caused a negative relationship between soil organic carbon and plant carbon content, suggesting that plants consume more carbon from the soil to store it in the plant. Overall, wood BC is recommended for plant growth of R. tomentosa and C. edithiae, and peanut shell BC is suggested for S. arboricola carbon storage.Graphical

Biomass allocation and carbon storage in the major cereal crops: A meta‐analysis

AbstractCrop biomass is the reservoir of carbon (C), a valuable input to the soil, thus supporting the soil fauna and enhancing soil health. There are limited studies that compared the major cereal crops for C storage for regenerative agriculture and to optimize C sequestration strategies. The objective of this study was to quantify the extent of variation in biomass allocation and C storage between maize (Zea mays L.), sorghum (Sorghum bicolor [L.] Moench), and wheat (Triticum aestivum L.) for crop production, and C sequestration potential. The study used metadata from 40 global studies that reported on the allocation of plant biomass and C between roots and shoots of the major cereal crops. Key statistics were computed to determine the variability between genotypes for total plant biomass (Pb), shoot biomass (Sb), root biomass (Rb), root‐to‐shoot biomass ratio (Rb/Sb), total plant carbon content, shoot carbon content, root carbon content, total plant carbon stock (PCs), shoot carbon stock, root carbon stock, and root‐to‐shoot carbon stock ratio (RCs/SCs). Maize exhibited the highest variability for Pb (with a coefficient of variation [CV] of 31.2% and a mean of 4.2 ± 1.3 Mg ha−1 year−1), followed by wheat (CV of 24.2% and a mean of 1.5 ± 0.4 Mg ha−1 year−1) and sorghum (CV of 16.8% and a mean of 2.0 ± 0.8 Mg ha−1 year−1), respectively. A similar trend was observed for PCs, with maize (CV of 40.1% and mean of 1.6 ± 0.7 Mg ha−1 year−1) showing the highest total plant C stock variability, followed by wheat (24.4% and 0.2 ± 0.1 Mg ha−1 year−1) and sorghum (16.3% and 0.9 ± 0.3 Mg ha−1 year−1), respectively. Maize (with a CV of 24.4% and mean of 0.1 ± 0.03 Mg ha−1 year−1) exhibited the highest variability for Rb/Sb, while wheat (30.92% and 0.2 ± 0.05 Mg ha−1 year−1) exhibited the highest variability for RCs/SCs. Correlation analysis revealed the following significant associations: Pb and mean annual temperature (MAT) (r = −0.47), and Sb and MAT (r = −0.43), and Pb and mean annual precipitation (MAP) (r = −0.34), and Sb and MAP (r = −0.30). Rb had a strong, significant positive correlation with MAT (r = 0.72) and MAP (r = 0.85). The meta‐analysis revealed that maize and sorghum have the highest variability for Pb and plant carbon stocks, while wheat exhibited the highest variability for the below‐ground biomass and carbon stocks. The data aided in crop selection and suggested that the best cultivars could be developed and identified for production and C sequestration potential for cultivation by farmers, land rehabilitation, and climate change mitigation.

Ectomycorrhizal fungi enhance pine growth by stimulating iron-dependent mechanisms with trade-offs in symbiotic performance.

Iron (Fe) is crucial for metabolic functions of living organisms. Plants access occluded Fe through interactions with rhizosphere microorganisms and symbionts. Yet, the interplay between Fe addition and plant-mycorrhizal interactions, especially the molecular mechanisms underlying mycorrhiza-assisted Fe processing in plants, remains largely unexplored. We conducted mesocosms in Pinus plants inoculated with different ectomycorrhizal fungi (EMF) Suillus species under conditions with and without Fe coatings. Meta-transcriptomic, biogeochemical, and X-ray fluorescence imaging analyses were applied to investigate early-stage mycorrhizal roots. While Fe addition promoted Pinus growth, it concurrently reduced mycorrhiza formation rate, symbiosis-related metabolites in plant roots, and aboveground plant carbon and macronutrient content. This suggested potential trade-offs between Fe-enhanced plant growth and symbiotic performance. However, the extent of this trade-off may depend on interactions between host plants and EMF species. Interestingly, dual EMF species were more effective at facilitating plant Fe uptake by inducing diverse Fe-related functions than single-EMF species. This subsequently triggered various Fe-dependent physiological and biochemical processes in Pinus roots, significantly contributing to Pinus growth. However, this resulted in a greater carbon allocation to roots, relatively reducing the aboveground plant carbon content. Our study offers critical insights into how EMF communities rebalance benefits of Fe-induced effects on symbiotic partners.

Weeds in the Alfalfa Field Decrease Rhizosphere Microbial Diversity and Association Networks in the North China Plain.

The competition between weeds and crops for soil nutrients is affected by soil microorganisms, which drive diverse ecological processes and are critical in maintaining the stability of agroecosystems. However, the effects of plant species identity, particularly between forage and weed, on soil microbial diversity, composition, and association are not well understood. Here, we investigate the soil physicochemical properties and bacterial/fungal communities in an agroecosystem with native alfalfa [Medicago stativa (Ms)] and five common weed species (Digitaria sanguinalis, Echinochloa crusgalli, Acalypha australis, Portulaca oleracea, and Chenopodium album) in the North China Plain. The five weeds had a lower plant carbon content than Ms. while the opposite was true for plant nitrogen and phosphorus concentrations. The Shannon diversity of bacterial and fungal communities of the five weeds were significantly lower than in Ms. Soil pH and PO43−-P were identified as the most important factors in shaping the relative abundances of bacteria (Sphingomonadaceae) and fungi (Pleosporaceae), respectively. Importantly, the weeds greatly inhibited the growth of pathogenic fungi (Nectriaceae and Pleosporaceae). Bacterial co-occurrence networks depended on specific species, indicating that Ms. harbored co-occurrence networks that were more complex than those in the bacterial communities of other weed groups. Our study examines how soil nutrients and the soil microbial community structure of five weed species changed in an Ms. field. This analysis of the microbial ecological network enhances our understanding of the influence of weeds on the soil microbiome in agroecosystems.

Effects of organic fertilizer application on accumulation and distribution of assimilates in winter wheat

To understand the effects of organic fertilizer addition on accumulation and distribution of winter wheat assimilates, we compared organic carbon content in soil and wheat plants, photosynthetic characteristics and assimilation transformation under two different fertilizer treatments, CF (chemical fertilizer only) and OF (organic fertilizer with chemical fertilizer), using 13CO2 pulse labeling method. The results showed that OF increased soil organic carbon content and wheat photosynthetic parameters, resulting in higher organic carbon content and total dry biomass accumulation in wheat plants compared with CF treatment. Compared marking to maturity with that on the 7th day after the same marking, the content and distribution rate of 13C in leaves and stems of two treatments decreased; the 13C content in spikes increased at jointing stage and filling stage, decreased at anthesis stage, and the 13C distribution rate increased at all stages. OF treatment was more beneficial for the transportation of photosynthetic product from leaves to spikes at filling stage, with higher 13C distribution rate in spikes compared with CF treatment. The results of correlation analysis showed that dry matter accumulation was significantly positively correlated with the net input of 13C content and its distribution rate, but negatively correlated with organic carbon content in plants. The net input of 13C content was significantly positively correlated with its distribution rate, and negatively correlated with Fv/Fm and Pn. In conclusion, organic fertilizer application could increase the content of organic carbon in soil, improve wheat plants photosynthetic capacity and transportation of photosynthetic product to spikes, and ultimately increase dry matter accumulation in wheat spikes.

Field-to-farm gate greenhouse gas emissions from corn stover production in the Midwestern U.S.

Measured field data were used to compare two allocation methods on life cycle greenhouse gas emissions from corn (Zea mays L.) stover production in the Midwest U.S. We used publicly-available crop yield, nitrogen fertilizer, and direct soil nitrous oxide emissions data from the USDA-ARS Resilient Economic Agricultural Practices research program. Field data were aggregated from 9 locations across 26 site-years for 3 stover harvest rates (no removal; moderate removal – 3.1 Mg ha−1; high removal – 7.2 Mg ha−1) and 2 tillage practices (conventional; reduced/no-till). Net carbon uptake by crops was computed from measured plant carbon content. Monte Carlo simulations sampled input distributions to assess variability in farm-to-gate GHG emissions. The base analysis assumed no change in soil organic carbon stocks. In all cases, net CO2 uptake during crop growth and soil-respired CO2 dominated system emissions. Emissions were most sensitive to co-product accounting method, with system expansion emissions ∼15% lower than mass allocation. Regardless of accounting method, lowest emissions occurred for a moderate removal rate under reduced/no-till management. The absence of correlations between N fertilization rate and stover removal rate or soil N2O emissions in this study challenges the use of such assumptions typically employed in life cycle assessments Storage of all carbon retained on the field as SOC could reduce emissions by an additional 15%. Our results highlight how variability in GHG emissions due to location and weather can overshadow the impact of farm management practices on field-to-farm gate emissions.

Carbon Sequestration of Soil and Plants along IH-35 in Bexar County, Texas

Soil and vegetation were evaluated along IH-35 within Bexar County for carbon content. The objectives of this study were to evaluate the vegetative composition and carbon sequestration potential of vegetation along IH-35. Three 20 m transects were placed at each site and percent vegetative cover was estimated and above ground plant biomass and soil was collected from three 0.25 m2 subplots along each transect. Plant and soil samples were analyzed for carbon content using the loss-on-ignition method. Two non-native grasses, bermudagrass and King Ranch bluestem, were the dominant cover. Bermudagrass was more efficient in absorbing CO2 compared to King Ranch bluestem. The top 10 cm of soil in all samples contained more organic carbon than the lower 10 cm. Collection of field data has been completed and the soil and plant carbon content is being analyzed with the final results presented at the conference.

Functional coordination between leaf traits and biomass allocation and growth of four herbaceous species in a newly established reservoir riparian ecosystem in China.

The flood‐dry‐flood cycle in the reservoir riparian zone (RRZ) of the Three Gorges Dam has dramatically altered the riparian ecosystem structure and composition. Previous field studies have shown that leaf traits varied greatly and were restricted to the lower‐investment and faster‐return end of the global leaf spectrum, which are typical characteristics of fast‐growing species. However, it is unclear as to the mechanism underpinning the growth potential of these species and how it will respond to soil nutrient availability and temperature. Here, we linked the plant functional traits of four representative dominant C4 herbaceous species (Setaria viridis, Echinochloa crusgalli, Cynodon dactylon and Hemarthria altissima) to their relative growth rates (RGR) under ambient and elevated temperatures, with different nitrogen and phosphorus levels, to explore the potential mechanism of species growth in the newly established reservoir riparian ecosystem in the Three Gorges Reservoir Area, China. We grew seedlings of these species in four open‐top chambers, with three levels of nutrient supplies under two temperature gradients (ambient temperature and an elevated temperature of 4°C). We found that the responses of the RGR and plant traits to soil N and P supply levels and temperature varied considerably among studied species. E. crusgalli displayed the lowest RGR associated with relatively low specific leaf area (SLA), leaf nitrogen content (LN), stem mass ratio (SMR), and high leaf mass ratio (LMR) and was less affected by soil N and P supply levels and temperature. C. dactylon and H. altissima showed the highest RGR compared to the other two species grown at the substrate of N = 0.4 mg/g, P = 0.2 mg/g at ambient air temperature, associated with a relatively high SMR, low LMR and low plant carbon content (PCC). However, the RGR advantage of the two species was diminished at elevated temperatures, while S. viridis showed the highest RGR compared to the other species. Across all datasets, the RGR had no association with the leaf area ratio (LAR) and SLA. The RGR also showed no significant relationships with the LN and leaf phosphorus content (LP). On the other hand, the RGR was captured adequately by the SMR, which can therefore be considered as a powerful functional marker of species’ functioning in this newly established reservoir riparian ecosystem. Our study provides some insight into the underlying mechanisms of species growth in reservoir riparian ecosystems.

A remote sensing-based model of tidal marsh aboveground carbon stocks for the conterminous United States

Remote sensing based maps of tidal marshes, both of their extents and carbon stocks, have the potential to play a key role in conducting greenhouse gas inventories and implementing climate mitigation policies. Our objective was to generate a single remote sensing model of tidal marsh aboveground biomass and carbon that represents nationally diverse tidal marshes within the conterminous United States (CONUS). We developed the first calibration-grade, national-scale dataset of aboveground tidal marsh biomass, species composition, and aboveground plant carbon content (%C) from six CONUS regions: Cape Cod, MA, Chesapeake Bay, MD, Everglades, FL, Mississippi Delta, LA, San Francisco Bay, CA, and Puget Sound, WA. Using the random forest machine learning algorithm, we tested whether imagery from multiple sensors, Sentinel-1 C-band synthetic aperture radar, Landsat, and the National Agriculture Imagery Program (NAIP), can improve model performance. The final model, driven by six Landsat vegetation indices and with the soil adjusted vegetation index as the most important (n = 409, RMSE = 310 g/m2, 10.3% normalized RMSE), successfully predicted biomass for a range of marsh plant functional types defined by height, leaf angle and growth form. Model results were improved by scaling field-measured biomass calibration data by NAIP-derived 30 m fraction green vegetation. With a mean plant carbon content of 44.1% (n = 1384, 95% C.I. = 43.99%–44.37%), we generated regional 30 m aboveground carbon density maps for estuarine and palustrine emergent tidal marshes as indicated by a modified NOAA Coastal Change Analysis Program map. We applied a multivariate delta method to calculate uncertainties in regional carbon densities and stocks that considered standard error in map area, mean biomass and mean %C. Louisiana palustrine emergent marshes had the highest C density (2.67 ± 0.004 Mg/ha) of all regions, while San Francisco Bay brackish/saline marshes had the highest C density of all estuarine emergent marshes (2.03 ± 0.004 Mg/ha). Estimated C stocks for predefined jurisdictional areas ranged from 1023 ± 39 Mg in the Nisqually National Wildlife Refuge in Washington to 507,761 ± 14,822 Mg in the Terrebonne and St. Mary Parishes in Louisiana. This modeling and data synthesis effort will allow for aboveground C stocks in tidal marshes to be included in the coastal wetland section of the U.S. National Greenhouse Gas Inventory. With the increased availability of free post-processed satellite data, we provide a tractable means of modeling tidal marsh aboveground biomass and carbon at the global extent as well.

Direct Electricity Generation from Dissolved Cellulosic Biomass in an Alkaline Fuel Cell

AbstractCellulose, which accounts for more than half of the carbon content in plants, has become a popular feedstock for biofuel production. In this work, direct electricity generation from dissolved cellulosic biomass in an alkaline fuel cell is explored without energy‐intensive process. The effect of different cellulose dissolution solvents on the electricity production is investigated. Results show dissolution treatment can remarkably affect the fuel cell performance. When NaOH/urea/thiourea is chosen as a solvent, the specific capacity of cellulose is about sixfold higher than that using only NaOH as solvent. The limiting current density and the maximum power density reach 0.85 mA cm−2 and 0.07 mW cm−2, respectively. This power density surpasses those of any existing biotic or abiotic designs. Electrochemical characterizations demonstrate that the remarkable activity improvement towards the cellulose oxidation reaction in NaOH/urea/thiourea aqueous solution is due to the lower charger transfer resistance and higher energy transfer efficiency.

Variations and determinants of carbon content in plants: a global synthesis

Abstract. Plant carbon (C) content is one of the most important plant traits and is critical to the assessment of global C cycle and ecological stoichiometry; however, the global variations in plant C content remain poorly understood. In this study, we conducted a global analysis of the plant C content by synthesizing data from 4318 species to document specific values and their variation of the C content across plant organs and life forms. Plant organ C contents ranged from 45.0 % in reproductive organs to 47.9 % in stems at global scales, which were significantly lower than the widely employed canonical value of 50 %. Plant C content in leaves (global mean of 46.9 %) was higher than that in roots (45.6 %). Across life forms, woody plants exhibited higher C content than herbaceous plants. Conifers, relative to broad-leaved woody species, had higher C content in roots, leaves, and stems. Plant C content tended to show a decrease with increasing latitude. The life form explained more variation of the C content than climate. Our findings suggest that specific C content values of different organs and life forms developed in our study should be incorporated into the estimations of regional and global vegetation biomass C stocks.

STUDY ON CARBON CONTENT AND ECOLOGICAL MANGROVE INDEX IN MUARAREJA, TEGAL, CENTRAL JAVA

The accumulation of carbon in the atmosphere causing the greenhouse effect as a result of trapping of short-wave sunlight, which increase the temperature of Earth's atmosphere. One of the forest ecosystems that can reduce the effects of greenhouse gases and to mitigate the climate change is a mangrove forest. The role of mangroves related to the Blue Carbon was emphasized as mangrove efforts to utilize CO₂ for photosynthesis and store it in biomass stock and sediment as a climate change mitigation efforts. The purpose of the research are a) to determine the density, dominance and the importance value of mangroves index, b) to know the Diversity Index and Uniformity Index of mangrove that dominates, c) to determine the content of carbon in the mangrove forests, and d) to determine the relationship of the density of mangrove with a carbon content in the mangrove forest area in the village of Muarareja Tegal. Mangrove areas in the Village of Muarareja was dominated by <em>Rhizophora mucronata</em> with Relative Density (KR) in ponds: 42.11% - 100%, residential homes: 28.57% - 45.45%, the river: 31.58% - 61.90%, the beach : 59.09% - 73.68%. Relative dominance (DR) of ponds station: 34.71% - 100%, residential home stations: 14.24% - 39.61%, river station: 20.46% - 72.95%, coast stations: 64.08% - 92,25%. Importance Value Index (IVI) in ponds station: 76.82% - 200%, residential home stations: 42.81% - 85.07%, the river station: 52.03% - 134.85%, coast stations: 123.17% - 165.93%. Diversity Index (H) mangrove <em>Rhizophora mucronata</em> ranged by 0.000 - 0.692 and Uniformity Index (J) mangrove ranged by 0.000 - 2.107. The largest carbon content (tons / ha) was produced at the coast with the average number of total carbon content of the plot (tons / ha) was 189,942.77 tons / ha, followed by the river with the average number of total carbon content of the plot (tons / ha) was 179,011.49 tons / ha, the average number of total carbon content ot the plot for the ponds (tons / ha) was 176,519.79 tons / ha and with the average number of total carbon content of the plot (tons / ha) for the residential homes was 165,774.82 tons / ha. The density of mangrove has a very close correlation with the total carbon content in liters per hectare of the plot, the total carbon content in plants per hectare of the plot below, the total carbon content in leaves per hectare of the plot, and the total carbon content of soil per hectare of the plot. The total carbon content of the tree biomass per hectare on the plot, the total carbon content of nekromassa per hectare of the plot, and the total carbon content in the roots per hectare of the plots does not have a positive correlation with the density of mangrove.

Greenhouse gas mitigation potential of annual and perennial dairy feed crop systems

Abstract Dairy production constitutes a significant amount of the total global anthropogenic greenhouse gas (GHG) emission. One of the proposed strategies to mitigate GHG emission from dairy production is by enhancing soil carbon sequestration through promoting the growing of perennial over annual dairy feed crop. We determined the net ecosystem carbon budget (NECB) of a hay and corn field grown side-by-side over three years to compare the GHG mitigation potential of perennial over annual feed crops in Elora, Ontario, Canada. The NECB was determined using measurements of net ecosystem exchange (NEE), total plant carbon content, and carbon content in applied dairy manure. The greenhouse gas balance (GHGB) were determined using the NECB plus the total nitrous oxide (N 2 O) fluxes measured by a complementary study at the same site. The effect of plowing of the hay field on the NECB and GHGB was also investigated. Our observations indicate that on average over the three study years, NECB of hay (7 ± 51 g C m −2 yr −1 ) was significantly lower than corn (154 ± 79 g C m −2 yr −1 ) indicating that corn was a larger carbon source than hay. The three-year average GHGB of 796 and 127 g CO 2 -eq m −2 yr −1 for corn and hay, respectively, indicated that corn was a larger emitter of GHG than hay. The NECB was the more dominant factor than N 2 O emissions in influencing the outcome of the annual GHGB. We conclude that hay has a larger potential than corn in sequestering carbon and mitigating GHG emission even when emissions from hay plow-down are included.

Effect of heavy metals on the carbon and nitrogen ratio in Avicennia marina from polluted and unpolluted regions

The accumulation of heavy metals and its impact on the C/N ratio of Avicennia marina of the Patalganga and Amba estuaries were studied. Vadinar was selected as a relatively uncontaminated location for comparison. Cd was accumulated in leaves of the Patalganga and Amba estuarine mangroves; however, at Vadinar it was accumulated and arrested only in roots and stems. Negative correlation of Cr, Cd, Pb and Zn with C in the mangroves suggested that their accumulation may lead to lowered C content in the mangroves. The average C/N ratios in mangroves of the inner Patalganga estuary, Patalganga mouth, and Amba estuary were found to be 80.1±7.3, 105.8±12.5 and 52.4±3.4 respectively, whereas at Vadinar it was well within the expected range (26.4±2.8). The results of the present study suggest: (i) metal accumulation, leading to less carbon content in plants; (ii) heavy metal enrichment in the root zone sediment, affecting the uptake of nitrogen by plants and resulting in altered C/N ratio.

Comparative Performance of Cyanobacterial Strains on Soil Fertility and Plant Growth Parameters in Rice

The diazotrophic cyanobacterial consortium consists of Anabaena variabilis, Aulosira fertilissima, Nostoc muscorum and Tolypothrix tenuis are widely used to supplement chemical N fertilizers for flooded rice cultivation in India. Our present study was undertaken to evaluate the comparative performance of these individual cyanobacterial species on soil fertility and plant growth in rice at three levels of nitrogenous fertilizer. Significant intergeneric differences were observed with respect to nitrogen fixing potential and other N assimilatory parameters under in vitro conditions. Application of individual cyanobacterial species enhanced N uptake and plant carbon content of rice over uninoculated control. Analyses of soil samples after rice harvest revealed significant differences in soil microbial biomass carbon, organic carbon, available N and increase in grain yields with the cyanobacterial inoculants. Yield increase with Anabaena variabilis was comparable with uninoculated control. Correlation coefficient (r) revealed a positive correlation between available nitrogen and soil microbial biomass carbon with N uptake and C content in plants. Our findings revealed functional potential of individual cyanobacterial species in biofertilizer consortia in relation to soil fertility, plant nutrition and yield of rice; however their potential for improving C-N status of flooded rice soils needs to be evaluated at farm level under long-term experimental conditions.

Juncus bulbosus nuisance growth in oligotrophic freshwater ecosystems: Different triggers for the same phenomenon in rivers and lakes?

Since the 1980s nuisance growth of the aquatic macrophyte Juncus bulbosus has been observed in an increasing number of rivers and lakes in Europe. Freshwater acidification, lake liming, as well as the impact of hydropower plants and climate-related parameters have previously been assumed to have caused J. bulbosus mass development, but are unlikely to be the sole reason for today's phenomenon. To explore causalities for J. bulbosus mass development and to assess whether or not different patterns emerge in rivers and lakes, we analyzed macrophyte vegetation, periphyton coverage, water and sediment chemistry, catchment characteristics, and J. bulbosus elemental composition in 17 lakes and 28 river sites in southern Norway. We found that J. bulbosus mass development generally is a phenomenon of the most phosphorus- and calcium-poor rivers and lakes. This likely is a result of increased competition from other macrophyte species in all but the very most oligotrophic and acidic ecosystems. Despite a large number of measured parameters, however, we still lack clear correlations to J. bulbosus success. Nevertheless, our results with respect to changes in water CO2 and plant carbon content were consistent with literature suggesting CO2 as the most likely factor causing J. bulbosus mass development in lakes. While J. bulbosus seems to be carbon-limited in lakes with low J. bulbosus abundance, we have no such indications in high-abundance lakes. For rivers, our study indicates that the factor most closely connected to J. bulbosus success is a slightly enhanced NH4+ supply. We suggest that different factors may be responsible for J. bulbosus nuisance growth in rivers and lakes.

Water Relations and CO2 Exchange of Tropical Bryophytes in a Lower Montane Rain Forest in Panama

Abstract:For 6 tropical bryophytes, measurements of the diel courses in water status and net CO2 exchange were made in a submontane tropical rain forest in Panama. In addition, the response of gas exchange to changes in photon flux density (PPFD) and thallus water content (WC) was studied under controlled conditions. Diel variation of WC was pronounced, and both low and high WC limited carbon gain considerably. Low PPFD, e.g. during rain storms, was less important in limiting CO2 exchange. More than half of the mean diurnal carbon gain of 2.9 mg C per g thallus carbon was lost during the night as respiration. Assuming that the average 24‐h carbon gain was representative for the entire year, we estimated the net annual primary productivity of the mosses and liverworts to be 45% of the initial plant carbon content.

Genotypic Variation in Transpiration Efficiency, Carbon-Isotype Discrimination and Carbon Allocation During Early Growth in Sunflower

Transpiration efficiency of dry matter production (W), carbon-isotope discrimination (�) and dry matter partitioning were measured on six sunflower (Helianthus annuus L.) genotypes grown for 32 days in a glasshouse. Two watering regimes, one well watered (HW) and the other delivering half the water used by the HW plants (LW), were imposed. Four major results emerged from this study. (1) There was significant genotypic variation in W in sunflower and this was closely reflected in Δ for both watering treatments. (2) The low watering regime caused a decrease in Δ but no change in W; nonetheless the genotypic ranking for either Δ or W was not significantly altered by water stress. (3) A positive correlation between W and biomass accumulation occurred among genotypes of HW plants. (4) Q, the ratio of total plant carbon content to leaf area, was positively correlated with W and negatively correlated with Δ. These results are discussed with reference to the connection between transpiration efficiency and plant growth. In short, Δ can be used to select for W among young vegetative sunflower plants. However, selection for W may be accompanied by changes in other important plant growth characteristics such as Q.

Significance of Photosynthate Produced at Different Stages of Growth as Carbon Source for Fruit Filling and Seed Reserve Accumulation in Lupinus angustifolius L

Growth and reproductive phenology of field-grown, non-irrigated L. angustifolius (cv. Unicrop) were studied by periodic sampling of plants. Anthesis occurred when plant carbon content was only 15% of its final maximum. Flowering and the main periods of pod growth and seed filling took place, respectively, 0-6, 5-9 and 8-12 weeks after anthesis. Over 80% of the plant's gain of carbon in dry matter occurred 0-8 weeks after anthesis, after which drought-induced defoliation curtailed dry matter accumulation. 14CO2 was fed to selected plants at weekly intervals over the period 0-12 weeks after anthesis and time courses of transfer of 14C-labelled assimilates to fruits were assayed non-destructively by periodic sampling of phloem sap from fruits. Average specific radioactivity of carbon of phloem sap samples from primary, secondary and tertiary fruits of each feeding treatment were compared with specific 14C activities of the respective fruits harvested at maturity. The agreement between data was very close with times of 14CO2 feeding up to 8 weeks after anthesis. With later times of feeding, average specific radioactivity of phloem sap was higher than that of fruits as labelled sap was collected for only the latter part of the life of the fruit and before the fruit had accumulated unlabelled carbon. Carbon from photosynthate fed before or during flowering contributed mainly to protein of the seed, that from photosynthate formed during fruiting mainly to non-protein seed components. Distribution of 14C between amino and non-amino compounds of fruit phloem sap of plants fed 14CO2 at anthesis or in late fruiting reflected this effect. Estimates of contributions of carbon of photosynthate to fruits suggested that only 2% of the fruit's carbon came from photosynthesis before flowering and only 3 % from photosynthesis 0-3 weeks after anthesis, while 18, 28 and 23% came from photosynthate formed respectively 3-6, 6-9 and 9-12 weeks after anthesis.