Four new phenolic diglycosides from the roots of Illicium oligandrum

Four new phenolic diglycosides (1–4), named illoliganoside A–D, and three known glycosides (5–7), were isolated from the roots of Illiciumoligandrum. The structures of the new diglycosides were determined on the basis of HRMS, NMR spectroscopic, and chemical methods. The anti-inflammatory and cytotoxic activities for 1–7 were evaluated.     

Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

Incorporation of 14CO2 into C4 acids by leaves of C3-C4 intermediate and C3 species of Moricandia and Panicum at the CO2 compensation concentration

Comparative ¹⁴CO₂ pulse-¹²CO₂ chase studies performed at CO₂ compensation ()-versus air-concentrations of CO₂ demonstrated a four-to eightfold increase in assimilation of ¹⁴CO₂ into the C₄ acids malate and aspartate by leaves of the C₃-C₄ intermediate species Panicum milioides Nees ex Trin., P. decipiens Nees ex Trin., Moricandia arvensis (L.) DC., and M. spinosa Pomel at . Specifically, the distribution of ¹⁴C in malate and aspartate following a 10-s pulse with ¹⁴CO₂ increases from 2% to 17% (P. milioides) and 4% to 16% (M. arvensis) when leaves are illuminated at the CO₂ compensation concentration (20 l CO₂/l, 21% O₂) versus air (340 l CO₂/l, 21% O₂). Chasing recently incorporated ¹⁴C for up to 5 min with ¹²CO₂ failed to show any substantial turnover of label in the C₄ acids or in carbon-4 of malate. The C₄-acid labeling patterns of leaves of the closely related C₃ species, P. laxum Sw. and M. moricandioides (Boiss.) Heywood, were found to be relatively unresponsive to changes in pCO₂ from air to . These data demonstrate that the C₃-C₄ intermediate species of Panicum and Moricandia possess an inherently greater capacity for CO₂ assimilation via phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) at the CO₂ compensation concentration than closely related C₃ species. However, even at , CO₂ fixation by PEP carboxylase is minor compared to that via ribulosebisphosphate carboxylase (EC 4.1.1.39) and the C₃ cycle, and it is, therefore, unlikely to contribute in a major way to the mechanism(s) facilitating reduced photorespiration in the C₃-C₄ intermediate species of Panicum and Moricandia.Abbreviations Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase - PEP phosphoenolpyruvate - CO₂ compensation concentration - 3PGA 3-phosphoglycerate - SuP sugar monophosphates - SuP₂ sugar bisphosphates Published as Paper No. 8249, Journal Series, Nebraska Agricultural Research Division     

Expression of the C3-C4 intermediate character in somatic hybrids between Brassica napus and the C3-C4 species Moricandia arvensis

The wild crucifer Moricandia arvensis is a potential source of alien genes for the genetic improvement of related Brassica crops. In particular M. arvensis has a C₃-C₄ intermediate photosynthetic mechanism which results in enhanced recapture of photorespired CO₂ and may increase plant water-use efficiency. In order to transfer this trait into Brassica napus, somatic hybridisations were made between leaf mesophyll protoplasts from cultured M. arvensis shoot tips and hypocotyl protoplasts from three Brassica napus cultivars, Ariana, Cobra and Westar. A total of 23 plants were recovered from fusion experiments and established in the greenhouse. A wide range of chromosome numbers were observed among the regenerated plants, including some apparent mixoploids. Thirteen of the regenerated plants were identified as nuclear hybrids between B. napus and M. arvensis on the basis of isozyme analysis. The phenotypes of these hybrids were typically rather B. napus-like, but much variability was observed, including variation in flower colour, leaf shape and colour, leaf waxiness, fertility and plant vigour. CO₂ compensation point measurements on the regenerated plants demonstrated that 3 of the hybrids express the M. arvensis C₃-C₄ intermediate character at the physiological level. Semi-thin sections through leaf tissues of these 3 plants revealed the presence of a Kranz-like leaf anatomy characteristic of M. arvensis but not found in B. napus. This is the first report of the expression of this potentially important agronomic trait, transferred from Moricandia, in M. arvensis x B. napus hybrids.     

Prenylated anthronoid antioxidants from the stem bark of Harungana madagascariensis

Two new prenylated anthronoids, harunmadagascarins A and B, were isolated from the stem bark of Harungana madagascariensis along with six known compounds including two anthronoids: harunganol B and harungin anthrone, one benzophenone: methyl 3-formyl-2,4-dihydroxy-6-methyl benzoate and three pentacyclic triterpenes: friedelin, lupeol and betulinic acid. Harunmadagascarins A and B were characterized as 8,9-dihydroxy-4,4-bis-(3,3-dimethylallyl)-6-methyl-2,3-(2,2-dimethylpyrano)anthrone and 8,9-dihydroxy-4,4,5-tris-(3,3-dimethylallyl)-6-methyl-2,3-(2,2-dimethylpyrano)anthrone, respectively. The structures of these secondary metabolites were determined by spectroscopic means and comparison with the published data. Methyl 3-formyl-2,4-dihydroxy-6-methyl benzoate was isolated for the first time from a plant. Harunmadagascarins A and B, harunganol B and harungin anthrone exhibited significant antioxidant activity.     

Photorespiratory metabolism and immunogold localization of photorespiratory enzymes in leaves of C3 and C3-C4 intermediate species of Moricandia

Photorespiratory metabolism of the C₃-C₄ intermediate species Moricandia arvensis (L.) DC has been compared with that of the C₃ species, Moricandia moricandioides (Boiss.) Heywood. Assays of glycollate oxidase (EC 1.1.3.1), glyoxylate aminotransferases (EC 2.6.1.4, EC 2.6.1.45) and hydroxypyruvate reductase (EC 1.1.1.29) indicate that the capacity for flux through the photorespiratory cycle is similar in both species. Immunogold labelling with monospecific antibodies was used to investigate the cellular locations of ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), glycollate oxidase, and glycine decarboxylase (EC 2.1.2.10) in leaves of the two species. Ribulose 1,5-bisphosphate carboxylase/oxygenase was confined to the stroma of chloroplasts and glycollate oxidase to the peroxisomes of all photosynthetic cells in leaves of both species. However, whereas glycine decarboxylase was present in the mitochondria of all photosynthetic cells in M. moricandioides, it was only found in the mitochondria of bundle-sheath cells in M. arvensis. We suggest that localized decarboxylation of glycine in the leaves of M. arvensis will lead to improved recapture of photorespired CO₂ and hence a lower rate of photorespiration.Abbreviations kDa kilodalton - RuBP ribulose-1,5-bisphosphate     

Prenylated arylbenzofuran derivatives from Morus mesozygia with antioxidant activity

Five prenylated arylbenzofurans, moracins Q-U, were isolated from Morus mesozygia (Moraceae). Their structures were elucidated on the basis of spectroscopic evidence. Along with these compounds, 3β-acetoxyurs-12-en-11-one, marsformoxide, moracin C, moracin M, moracin K, artocarpesin, cycloartocarpesin, morachalcone A were also isolated. Four of the five compounds, (moracins R-U) displayed potent antioxidant activity.     

C3-C4 intermediate photosynthetic characteristics of cassava (Manihot esculenta Crantz)

Cassava, bean and maize leaves were fed with¹⁴CO₂ in light and the primary products of photosynthesis identified 5 and 10 seconds after assimilation. In maize, approximately three quarters of the labelled carbon was incorporated in C₄ acids, in beans about two thirds in PGA, and in cassava approximately 40–60% in C₄ acids with 30–50% in PGA. These data indicate that cassava possesses the C₄ photosynthetic cycle, however due to the lack of typical Kranz anatomy appreciable carbon assimilation takes place directly through the Calvin-Benson-Bassham cycle.     

Coordination of the cell-specific distribution of the four subunits of glycine decarboxylase and of serine hydroxymethyltransferase in leaves of C3-C4 intermediate species from different genera

The cell-specific distribution of the four subunit proteins (P, L, T and H) of glycine decarboxylase (GDC) and of serine hydroxymethyltransferase (SHMT) has been studied in the leaves of C₃-C₄ intermediate and C₄ species of three genera (Flaveria, Moricandia and Panicum) using immunogold localization. Antibodies raised against these proteins from pea leaf mitochondria were used to probe Western blots of total leaf proteins of F. linearis Lag., M. arvensis (L.) DC and P. milioides Nees ex Trin. (C₃-C₄), and F. trinervia (Spring.) Mohr and P. miliaceum (L.) (C₄). For all species, each antibody recognised specifically a protein of similar molecular weight to that in pea leaves. In leaves of M. arvensis the P protein was present in the mitochondria of the bundle-sheath cells but was undetectable in those of the mesophyll, whereas the L, T and H proteins and SHMT were present in both cell types. The density of immunogold labelling of SHMT on the mitochondria of mesophyll cells was less than that on those of the bundle-sheath cells, which correlates with the relative activities of SHMT in these cell types. These data reveal that the lack of functional GDC in the mesophyll cells of M. arvensis, which is the principal biochemical reason for reduced photorespiration in this species, is due to the loss of a single subunit protein. This lack of coordinate expression of the subunit proteins of GDC within a photosynthetic cell represents a clear difference between M. arvensis and other C₃ and C₃-C₄ species. None of the GDC proteins was detectable in the mesophyll cells of the C₃-C₄ and C₄ Flaveria and Panicum species but all were present in the bundle-sheath cells. The differences in the distribution of the GDC proteins in leaves of the C₃-C₄ species studied are discussed in relation to the evolution of photosynthetic mechanisms.     

The occurrence of both C3 and C4 photosynthetic characteristics in a single Zea mays plant

The activities of the carboxylating enzymes ribulose-1,5-biphosphate (RuBP) carboxylase and phosphoenolpyruvate (PEP) carboxylase in leaves of three-week old Zea mays plants grown under phytotron conditions were found to vary according to leaf position. In the lower leaves the activity of PEP carboxylase was lower than that of RuBP carboxylase, while the upper leaves exhibited high levels of PEP carboxylase. Carbon dioxide compensation points and net photosynthetic rates also differed in the lower and upper leaves. Differences in the fine structure of the lowermost and uppermost leaves are shown. The existence of both the C₃ and C₄ photosynthetic pathways in the same plant, in this and other species, is discussed.Abbreviations PEP phosphoenolpyruvate - RuBP ribulose-1,5-biphosphate     

C6-Green leaf volatiles trigger local and systemic VOC emissions in tomato

In response to insect feeding, tomato plants (Lycopersicon esculentum) release elevated levels of volatile organic compounds; that is, monoterpenes and sesquiterpenes are released both locally and systemically with wounding while C(6) green leaf volatiles are released only from damaged leaves. With the exogenous application (100 nmol) of the C(6)-tomato-volatile (E)-2-hexenal, an increase in the release of local and systemic terpenes was observed, while an equimolar amount of methyl jasmonate triggered only local emissions of terpenes. Labeling studies with 13CO(2) showed that de novo synthesis was not required for monoterpene or sesquiterpene release immediately following chemical treatment or insect feeding. Comparative measurements were made between aldehyde doses applied to the plant and levels naturally released from leaves with insect damage.     

Effects of irradiance and temperature on photosynthesis in C3, C4 and C3/C4 Panicum species

Species in the Laxa and Grandia groups of the genus Panicum are adapted to low, wet areas of tropical and subtropical America. Panicum milioides is a species with C₃ photosynthesis and low apparent photorespiration and has been classified as a C₃/C₄ intermediate. Other species in the Laxa group are C₃ with normal photorespiration. Panicum prionitis is a C₄ species in the Grandia group. Since P. milioides has some leaf characteristics intermediate to C₃ and C₄ species, its photosynthetic response to irradiance and temperature was compared to the closely related C₃ species, P. laxum and P. boliviense and to P. prionitis. The response of apparent photosynthesis to irradiance and temperature was similar to that of P. laxum and P. boliviense, with saturation at a photosynthetic photo flux density of about 1 mmol m^-2 s^-1 at 30°C and temperature optimum near 30°C. In contrast, P. prionitis showed no light saturation up to 2 mmol m^-2 s^-1 and an optimum temperature near 40°C. P. milioides exhibited low CO₂ loss into CO₂-free air in the light and this loss was nearly insensitive to temperature. Loss of CO₂ in the light in the C₃ species, P. laxum and P. boliviense, was several-fold higher than in P. milioides and increased 2- to 5-fold with increases in temperature from 10 to 40°C. The level of dark respiration and its response to temperature were similar in all four Panicum species examined. It is concluded that the low apparent photorespiration in P. milioides does not influence its response of apparent photosynthesis to irradiance and temperature in comparison to closely related C₃ Panicum species.Abbreviations AP apparent photosynthesis - I CO₂ compensation point - gl leaf conductance; gm, mesophyll conductance - PPFD photosynthetic photon flux density - PR apparent photorespiration rate - RuBPC sibulose bisphosphate carboxylase     

Algicidal and antifungal compounds from the roots of Ruta graveolens and synthesis of their analogs

Bioassay-guided fractionation of the ethyl acetate extract of Ruta graveolens roots yielded rutacridone epoxide with potent selective algicidal activity towards the 2-methyl-isoborneol (MIB)-producing blue-green alga Oscillatoria perornata, with relatively little effect on the green alga Selenastrum capricornutum. The diol-analog of rutacridone epoxide, gravacridondiol, which was also present in the same extract, had significantly less activity towards O. perornata. Rutacridone epoxide also showed significantly higher activity than commercial fungicides captan and benomyl in our micro-bioassay against the agriculturally important pathogenic fungi Colletotrichum fragariae, C. gloeosporioides, C. acutatum, and Botrytis cineara and Fusarium oxysporium. Rutacridone epoxide is reported as a direct-acting mutagen, precluding its use as an agrochemical. In order to understand the structure-activity relationships and to develop new potential biocides without toxicity and mutagenicity, some analogs containing the (2-methyloxiranyl)-dihydrobenzofuran moiety with an epoxide were synthesized and tested. None of the synthetic analogs showed comparable activities to rutacridone epoxide. The absolute stereochemistry of rutacridone was determined to be 2'(R) and that of rutacridone epoxide to be 2'(R), 3'(R) by CD and NMR analysis.     

Cytotoxic diterpenoid quinonemethides from the roots of Pygmacopremna herbacea

Two new diterpenoid quinonemethides (1 and 2) along with two known compounds (3 and 4) were isolated from the hexane and ethyl acetate extracts of root nodules of Pygmacopremna herbacea. The structures of the new compounds were established by spectroscopic data interpretation. Single crystal X-ray diffraction analysis confirmed the structure of 1. The cytotoxic activities of these compounds were evaluated against A 549, HEPG2, MCF-7, PC-3 and HELA cancer cell lines. Compounds 4, 2 and 1 were shown very good cytotoxic activity.     

Light/dark modulation of phosphoenolpyruvate carboxylase in C3 and C4 species

In this report, the effects of light on the activity and allosteric properties of phosphoenolpyruvate (PEP) carboxylase were examined in newly matured leaves of several C₃ and C₄ species. Illumination of previously darkened leaves increased the enzyme activity 1.1 to 1.3 fold in C₃ species and 1.4 to 2.3 fold in C₄ species, when assayed under suboptimal conditions (pH 7) without allosteric effectors. The sensitivities of PEP carboxylase to the allosteric effectors malate and glucose-6-phosphate were markedly different between C₃ and C₄ species. In the presence of 5 mM malate, the activity of the enzyme extracted from illuminated leaves was 3 to 10 fold higher than that from darkened leaves in C₄ species due to reduced malate inhibition of the enzyme from illuminated leaves, whereas it increased only slightly in C₃ species. The Ki(malate) for the enzyme increased about 3 fold by illumination in C₄ species, but increased only slightly in C₃ species. Also, the addition of the positive effector glucose-6-phosphate provided much greater protection against malate inhibition of the enzyme from C₄ species than C₃ species. Feeding nitrate to excised leaves of nitrogen deficient plants enhanced the degree of light activation of PEP carboxylase in the C₄ species maize, but had little or no effect in the C₃ species wheat. These results suggest that post-translational modification by light affects the activity and allosteric properties of PEP carboxylase to a much greater extend in C₄ than in C₃ species.     

Le vie fotosintetiche C3, C4 e CAM nel contesto ecologico

Abstract

Ecological aspects of C₃, C₄ and CAM photosynthetic pathways. - Three different photosynthetic CO₂ fixation pathways are known to occur in higher plants. However all three pathways ultimately depend on the Calvin-Benson cycle for carbon reduction. The oxygenase activity of RuBP carboxilase is responsible for photorespiratory CO₂ release. Both C₄ and CAM pathways behave as a CO₂ concentrating mechanism which prevent photorespiration. The CO₂-concentrating mechanism in C₄ plants is based on intracellular symplastic transport of C₄ dicarboxylic acids from mesophyll-cells to the adjacent bundle-sheath cells. On the contrary in CAM plants the CO₂-concentrating mechanism is based on the intracellular transport of malic acid into and out of the vacuole.

The C₄ photosynthetic pathway as compared to the C₃ pathway permits higher rates of CO₂ fixation in high light and high temperature environments at low costs in terms of water loss, given the stability of the photosynthetic apparatus under such conditions.

CAM is interpreted as an adaptation to arid environments because it enables carbon assimilation to take place at very low water costs during the night when the evaporative demand is low. Nevertheless many aquatic species of Isoetes and some relatives are CAM, suggesting the adaptive role of CAM to environments which become depleted in CO₂.

The photosynthetic carbon fixation pathway certainly contributes to the ecological success of plants in different environments. However the distribution of plants may also reflect their biological history. On the other hand plants with different photosynthetic pathways coexist in many communities and tend to share resources in time. In any case some generalizations are possible: C₄ plants enjoy an ecological advantage in hot, moist, high light regions while the majority of species in desert environments are C₃; CAM plants are more frequent in semiarid regions with seasonal rainfall, coastal fog deserts, and in epiphytic habitats in tropical rain forests.     

Interconversions of different forms of vitamin B6 in tobacco plants

There are six different vitamin B₆ (VB₆) forms, pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN), pyridoxal 5′-phosphate (PLP), pyridoxamine 5′-phosphate (PMP), and pyridoxine 5′-phosphate (PNP), of which PLP is the active form. Although plants are a major source of VB₆ in the human diet, and VB₆ plays an important role in plants, the mechanisms underlying the interconversions of different VB₆ forms are not well understood. In this study, in vitro tobacco plants were grown on Murashige and Skoog (MS) basal media supplemented with 100 mg/L of PM, PL or PN and the abundance of the different B₆ vitamers in leaf tissue was quantified by high performance liquid chromatography (HPLC). The total amount of VB₆ was about 3.9 μg/g fresh weight of which PL, PM, PN, PLP and PMP accounted for 23%, 14%, 37%, 20% and 6%, respectively. Tobacco plants contained a trace amount of PNP. Supplementation of the culture medium with any of the non-phosphorylated vitamers resulted in an increase in total VB₆ by about 10-fold, but had very little impact on the concentrations of the endogenous phosphorylated vitamers. Administration of either PM or PN increased their endogenous levels more than the levels of any other endogenous B₆ vitamers. PL supplementation increased the levels of plant PN and PM significantly, but not that of PL, suggesting that efficient conversion pathways from PL to PN and PM are present in tobacco. Additionally, maintenance of a stable level of PLP in the plant is not well-correlated to changes in levels of non-phosphorylated forms.     

3-Keto-22-epi-28-nor-cathasterone, a brassinosteroid-related metabolite from Cystoseira myrica

Bioassay-guided purification of an ethanolic extract of Cystoseira myrica against HEPG-2 (liver) and HCT116 (colon) human cancer cell lines led to the isolation of 3-keto-22-epi-28-nor-cathasterone, 1 and cholest-4-ene-3,6-dione, 2. This finding allowed us to report for the first time that a brassinosteroid-related metabolite occurs in seaweed. These compounds showed activity in the range of 12.38–1.16 μM with selective activity of compound 2 to liver cancer cell lines.     

Comparison of Belowground Biomass in C3- and C4-Dominated Mixed Communities in a Chesapeake Bay Brackish Marsh

Belowground biomass is a critical factor regulating ecosystem functions of coastal marshes, including soil organic matter (SOM) accumulation and the ability of these systems to keep pace with sea-level rise. Nevertheless, belowground biomass responses to environmental and vegetation changes have been given little emphasis marsh studies. Here we present a method using stable carbon isotopes and color to identify root and rhizomes of Schoenoplectus americanus (Pers.) Volk. ex Schinz and R. Keller (C₃) and Spartina patens (Ait.) Muhl. (C₄) occurring in C₃− and C₄-dominated communities in a Chesapeake Bay brackish marsh. The functional significance of the biomass classes we identified is underscored by differences in their chemistry, depth profiles, and variation in biomass and profiles relative to abiotic and biotic factors. C₃ rhizomes had the lowest concentrations of cellulose (29.19%) and lignin (14.43%) and the lowest C:N (46.97) and lignin:N (0.16) ratios. We distinguished two types of C₃ roots, and of these, the dark red C₃ roots had anomalously high C:N (195.35) and lignin:N (1.14) ratios, compared with other root and rhizome classes examined here and with previously published values. The C₄-dominated community had significantly greater belowground biomass (4119.1 g m⁻²) than the C₃-dominated community (3256.9 g m⁻²), due to greater total root biomass and a 3.6-fold higher C₃-root:rhizome ratio in the C₄-dominated community. C₃ rhizomes were distributed significantly shallower in the C₄-dominated community, while C₃ roots were significantly deeper. Variability in C₃ rhizome depth distributions was explained primarily by C₄ biomass, and C₃ roots were explained primarily by water table height. Our results suggest that belowground biomass in this system is sensitive to slight variations in water table height (across an 8 cm range), and that the reduced overlap between C₃ and C₄ root profiles in the C₄-dominated community may account for the greater total root biomass observed in that community. Given that future elevated atmospheric CO₂ and accelerated sea-level rise are likely to increase C₃ abundance in Atlantic and Gulf coast marshes, investigations that quantify how patterns of C₃ and C₄ belowground biomass respond to environmental and biological factors stand to improve our understanding of ecosystem-wide impacts of global changes on coastal wetlands.