Belowground Tissues Research Articles

A comparison of physiological, morphological and growth responses of 13 hybrid poplar clones to flooding

Summary Effects of a 30-day fl ooding period on some morphological and physiological changes and on relative growth rate (RGR) of 13 hybrid poplar clones, belonging to four different parentages i.e. T × N, T × D, D × N and N × E (with T = Popolus trichocarpa , N = P. nigra , D = P. deltoids and E = P. euramericana ) were studied under controlled conditions. Responses of the 13 clones to fl ooding differed, and they varied with duration of fl ooding period. Stomatal conductance was not reduced in any of the plants during the fi rst few days of fl ooding. However , in trees of some clones , stomata opened and then closed as fl ooding was prolonged. Net photosynthesis rates (Pn) of fl ooded trees of some clones decreased during fl ooding, but in some fl ooded clones it returned to the value of the control following a period of decrease. RGR was reduced by fl ooding in 10 clones and was correlated with reduction of Pn. Other responses to fl ooding included formation of adventitious roots and relative amount of carbon allocated to the aboveand below-ground tissues. Based on the dendrogram from the hierarchical cluster analysis, the 13 clones tested could be divided into two groups. Clones 58-280, DN-34, 311-93, DN-70, Simplot, R-419 and OP-367 were grouped into a cluster with high tolerance to fl ooding; clones 309-74, PC-1, DN-14273, 195-529, NE-353 and R-247 into a cluster with low tolerance to fl ooding.

Role of different salt marsh plants on metal retention in an urban estuary (Lima estuary, NW Portugal)

The aim of the present work was to understand the role different salt marsh plants on metal distribution and retention in the Lima River estuary (NW Portugal), which to our knowledge have not been ascertained in this area yet. The knowledge of these differences is an important requirement for the development of appropriate management strategies, and is poorly described for Eurosiberian estuaries, like the one selected. In addition it is important to understand the difference among introduced and native salt marsh plants. In this work, metal levels (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were surveyed (by atomic absorption spectrometry) in sediments from sites vegetated with Juncus maritimus, Spartina patens, Phragmites australis and Triglochin striata (rhizo-sediments), in non-vegetated sediments and in the different tissues of the plants (roots, rhizomes and aerial shoots). In general, rhizo-sediments had higher metal concentrations than non-vegetated sediments, a feature that seems common to sediments colonized by salt marsh plants of different estuarine areas. All plants concentrated metals, at least Cd, Cu and Zn (and Pb for T. striata) in their belowground structures ([ M] belowground tissues/[ M] non-vegetated sediment > 1). However, when considered per unit of salt marsh area, the different selected plants played a different role on sediment metal distribution and retention. Triglochin striata retained a significant metal burden in it belowground structures (root plus rhizomes) acting like a possible phyto-stabilizer, whereas P. australis had an higher metal burden in aboveground tissues acting as a possible phyto-extractor. As for J. maritimus and S. patens, metal burden distribution between above and belowground structures depended on the metal, with J. maritimus retaining, for instance, much more Cd and Cu in the aboveground than in the belowground structures. Therefore, the presence of invasive and exotic plants in some areas of the salt marsh may considerably affect metal distribution and retention in the estuarine region.

Effects of CO2 Enrichment on Photosynthesis, Growth, and Biochemical Composition of Seagrass Thalassia hemprichii (Ehrenb.) Aschers

The effects of CO₂ enrichment on various ecophysiological parameters of tropical seagrass Thalassia hemprichii (Ehrenb.) Aschers were tested. T. hemprichii, collected from a seagrass bed in Xincun Bay, Hainan island of Southern China, was cultured at 4 CO₂ (aq) concentrations in flow-through seawater aquaria bubbled with CO₂ . CO₂ enrichment considerably enhanced the relative maximum electron transport rate (RETR(max) ) and minimum saturating irradiance (E(k) ) of T. hemprichii. Leaf growth rate of CO₂ -enriched plants was significantly higher than that in unenriched treatment. Nonstructural carbohydrates (NSC) of T. hemprichii, especially in belowground tissues, increased strongly with elevated CO₂ (aq), suggesting a translocation of photosynthate from aboveground to belowground tissues. Carbon content in belowground tissues showed a similar response with NSC, while in aboveground tissues, carbon content was not affected by CO₂ treatments. In contrast, with increasing CO₂ (aq), nitrogen content in aboveground tissues markedly decreased, but nitrogen content in belowground was nearly constant. Carbon: nitrogen ratio in both tissues were obviously enhanced by increasing CO₂ (aq). Thus, these results indicate that T. hemprichii may respond positively to CO₂ -induced acidification of the coastal ocean. Moreover, the CO₂ -stimulated improvement of photosynthesis and NSC content may partially offset negative effects of severe environmental disturbance such as underwater light reduction.

Growth Response and Tissue Accumulation Trends of Herbaceous Wetland Plant Species Exposed to Elevated Aqueous Mercury Levels

The impacts of elevated aqueous mercury levels (0, 2, and 4 ppm) on the growth status and mercury tissue concentrations of Eleocharis parvula, Saururus cernuus, Juncus effuses, Typha latifolia, and Panicum hemitomon were determined. Both short-term (net CO2 assimilation) and long-term (biomass) indicators of plant growth status suggest that Eleocharis parvula, Saururus cernuus, and Juncus effuses were relatively unimpacted by elevated mercury levels, whereas Typha latifolia and Panicum hemitomon were somewhat impacted at elevated mercury levels. Eleocharis parvula, Panicum hemitomon, and Typha latifolia generally had the greatest overall belowground tissue concentrations of mercury (2 ppm treatment: 7.21, 7.32, and 9.64 ppm respectively; 4 ppm treatment: 16.23, 18.23, and 13.98 ppm, respectively) and aboveground tissue concentrations of mercury (2 ppm treatment: 0.01, 0.04, 0.02; 4 ppm treatment: 0.26; 0.11; 0.17 ppm, respectively). However, the species investigated in this study demonstrated lower levels of mercury accumulation into tissues when compared with similar investigations of other aquatic plants, suggesting that the above species are not optimal for phytoremediation efforts.

Absorption and Translocation of Aminocyclopyrachlor and Aminocyclopyrachlor-Methyl Ester in Canada Thistle (Cirsium arvense)

Laboratory studies were conducted using14C-aminocyclopyrachlor (DPX-MAT28) and its14C-methyl ester formulation (DPX-KJM44) to (1) determine the adjuvants' effects on absorption, (2) compare the absorption and translocation of aminocyclopyrachlor free acid with the methyl ester, and (3) determine the rate at which aminocyclopyrachlor-methyl ester is metabolized to the free acid in Canada thistle. Canada thistle plants were grown from root cuttings and treated in the rosette growth stage. The effect of different adjuvants on absorption was determined by treating individual leaves with formulated herbicide plus14C-herbicide alone or with methylated seed oil (MSO), crop oil concentrate, or nonionic surfactant with and without urea ammonium nitrate and ammonium sulfate. Plants were harvested 96 h after treatment (HAT). For absorption and translocation experiments, plants were oversprayed with aminocyclopyrachlor or its methyl ester at a rate of 0.14 kg ae ha−1in combination with 1% MSO. Formulated herbicide plus14C-herbicide was then applied to a protected leaf, and plants were harvested 24 to 192 HAT. Plants were harvested and radioactivity was determined in the treated leaf and in aboveground and belowground tissues. Metabolism of aminocyclopyrachlor-methyl ester to the free acid was determined 2, 6, and 24 HAT. All aboveground biomass was analyzed by high-performance liquid chromatography to establish the ratio of methyl ester to free acid. MSO applied with either herbicide formulation resulted in the highest absorption compared with no surfactant. Significantly greater aminocyclopyrachlor-methyl ester was absorbed, compared with the free acid, which was reflected in the greater aboveground translocation for the methyl ester. Both formulations had similar amounts of translocation to the roots, with 8.6% (SE ± 3.3) for the methyl ester compared with 6.2% (SE ± 2.5) for the free acid. Approximately 80% of the methyl ester was converted to the free acid at 6 HAT. Based on this conversion rate, aminocyclopyrachlor translocated as the free acid in Canada thistle.

Genetic variation in plant morphology contributes to the species‐level structure of grassland communities

It is becoming apparent that genetic diversity can influence the species diversity and structure of ecological communities. Here, we investigated the intraspecific trait variation responsible for this relationship. We grew 10 genotypes of the sedge Carex caryophyllea, as monocultures, under standardized conditions and measured traits related to morphology, growth, and life history. The same genotypes had been prominent in determining the structure of multispecies experimental communities, equivalent in species diversity, in which the genetic diversity of the constituent plant species had been varied in parallel. The trait measurements revealed substantial phenotypic variation among Carex genotypes, related predominantly to differences in physical size and to the spatial deployment of above- and belowground tissue. Genotypes successful in experimental communities were larger in size and tended to adopt a "guerrilla" clonal growth strategy. In general, multivariate trait summaries of genotype size (and to a lesser extent, variation along a linear discriminant axis) predicted genotype and species abundance in experimental communities. However, one genotype exhibited a large disparity in this respect. The performance of this genotype lay closer to prediction when it was growing with a highly competitive grass genotype. The strength of the relationship between genotype size and performance within communities decreased with decreasing community genetic diversity. These results indicate that intraspecific trait measurements are useful for predicting and understanding community structure. They also imply that competitive interactions between the genotypes of different species play an increased role in determining phenotype in genetically impoverished communities.

Does the invader Hieracium lepidulum have a comparative growth advantage over co-occurring plants? High leaf area and low metabolic costs as invasive traits

High leaf area has been associated statistically with plant invasiveness, but few studies have quantified metabolic costs of this trait. We have little information on whether high leaf area provides a universal growth advantage or an advantage only under limited conditions. We ask, do invasive Hieracium lepidulum and co-occurring aliens in New Zealand have higher leaf area and lower metabolic tissue costs than co-occurring native species? Invasive and co-occurring plants were grown under standard conditions across a resource availability gradient and leaf area ratio (LAR) estimated. To quantify metabolic costs of above- and below-ground plant tissues, construction costs based on heat of combustion (Wg), plant ash, and nitrogen content (Vg) were measured. Leaf longevity was measured as an index of nutrient use and metabolic efficiency. Hieracium lepidulum and invaders overall did have higher LAR than cooccurring native plant species. Tissue construction costs overlapped among invaders and native species; however, unlike in native species, tissue construction costs in both invaders were reduced at lower nutrient resource levels. This suggests that there would not be a universal growth advantage for invaders, rather there would be more pronounced growth advantage at lower nutrient resource levels. This is discussed in terms of the ecological context within which H. lepidulum and its co-occurring species are found.

Effects of Organic-Rich Sediment and Below-Ground Sulfide Exposure on Submerged Macrophyte, Hydrilla verticillata

The effects of organic-rich sediment and sulfide exposure on Hydrilla verticillata were investigated. The organic richness of sediment was simulated by adding sucrose into sediments, and sulfide exposure was conducted by adding sodium sulfide to plant roots. The length, biomass and density of shoot reduced in the sucrose-amended sediments, and the largest reduction occurred in the highest 1.0% addition treatment by 84.2%, 56.7% and 92.4%, respectively. However, the 0.1% addition treatment stimulated the growth of root. The effects of below-ground sulfide exposure on the physiological activities of H. verticillata were determined by adding sulfide to the below-ground tissue. Significantly inhibitory effects of sulfide were observed on plant photosynthesis, root carbohydrate and nitrogen synthetic reserves. The net photosynthetic rates, soluble carbohydrate and soluble protein contents in root were reduced by 104%, 71.8% and 49.8%, respectively, in the 0.6 mM sulfide treatment.

Passive Pathogen Movement via Open Xylem Conduits in Grapevine Graft Unions

In grapevines, scion-rootstock grafting is a common practice to impart pathogen resistance and to manipulate aspects of grapevine physiology, including vigor, yield, and fruit composition. Successful grafting requires the integration of the scion and rootstock vascular networks. The nature and extent of this integration was evaluated to determine the impacts of the graft union on the movement of vascular pathogens between scion and rootstock. Using both xylem-mobile dyes and the xylem-limited bacterial pathogen <i>Xylella fastidiosa</i>, we demonstrate that the graft union contains open xylem conduits providing for passive pathogen movement. These open conduits may facilitate bacteria overwintering in below-ground vine tissues of grafted vines and systemic infection in subsequent growing seasons.

Nutrient Bioaccumulation in Phragmites australis: Management Tool for Reduction of Pollution in the Mar Menor

We studied nutrient removal by Phragmites australis in the Albujon rambla, the main drainage system that discharges into the Mar Menor, a Mediterranean coastal lagoon of high conservation interest, but highly threatened by point and nonpoint pollution derived from tourism and agricultural activities. We measured aerial biomass and N and P concentrations in both aboveground and belowground tissues of common reed during an annual cycle that included two cutting events and two periods of reed growth (one at the end of summer after cutting and another at the beginning of spring, following their natural cycle). The temporal variation of N and P concentrations was related to the phenology of the plant and cutting events. The maximum nutrient concentrations were recorded in young stems in the initial stages of the autumn growing season (35.86 mg N g−1 and 2.38 mg P g−1). The phosphorus dynamics showed evidence of translocation processes related with growth activity, although no evidence of N translocation was found. In November and in summer, when aerial growth ceases because of the hard conditions, the P concentration in rhizomes was higher than in stems, while in spring and in September, the period of maximal growth, the reverse relation was found. The highest total amounts of the two elements in the aboveground biomass (0.54 Tm N ha−1 and 0.25 Tm P ha−1) were reached in July, coinciding with the highest biomass (3.72 kg DW m−2), which then decreased to approximately half in August. Nutrient content in the aboveground tissues was highly dependent on the ammonium and nitrate water concentrations. In addition, the N content was inversely related to the Corg/N of sediments, while the P content was influenced positively by the phosphorous concentration of the water. Common reed of the Albujon rambla corresponds to the assimilation type, adapted to nutrient-rich habitats, which is characterized by a pronounced external N cycle and P internal reserves. Based on the results obtained, we propose a management plan for common reed to help control eutrophication of the Mar Menor lagoon. This would bring forward reed cutting to the beginning of summer, instead of August, coinciding with the time of maximum aerial biomass, greater nutrient retention, and lower risk of strong precipitation.

Phragmites australis and Typha orientalis in removal of pollutant in Taihu Lake, China

Two plant populations of Phragmites australis and Typha orientalis grown in gravel and sediment substrate were studied to assess their capabilities for purifying polluted water in Taihu Lake, China. The substrate displayed most significant effects on the suspended matter (P < 0.01), with the reduction of 76%-87% and 52%-63% for P. australis, and 83%-86% and 45%-62% for T. orientalis in gravel substrate and sediment substrate, respectively. Both species and substrates significantly decreased the N and P concentrations of water body (P < 0.01). P. australis showed higher total N and P concentrations in tissues than T. orientalis and had a greater potential to remove nutrients from the lake. Phosphate was easily to concentrate in the belowground tissues, while nitrate concentration was higher in leaf and stalk. Therefore, harvesting the aboveground tissues could take most of nitrate out of the sediment. The saturate photosynthetic rate (Asat) of P. australis was higher than that of T. orientalis when grown in sediment substrate. But instance water-use-efficiency (WUEi) (A/E) and intrinsic water use efficiency (A/gs) showed the maximum values of two species grown in river water. With significant difference in gs, however, intercellular CO2 concentration (Ci) had no obvious difference in two species which indicated that high Asat value of P. australis might result from the increased carboxylation capacity of the mesophyll, because of the central role of N in photosynthetic enzymes. Our findings suggest that the plants could absorb most of nitrogen in polluted water, while gravel displayed a high capacity for absorbing the suspended matters and phosphate salts. Therefore, biological and physiological pathways for pollutant removal should be integrated.

15N natural abundance during early and late succession in a middle-European dry acidic grassland

delta(15)N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N(2)-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and delta(15)N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed delta(15)N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific delta(15)N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant-mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N(2)-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N(2)-fixing legumes.

Trace elements in Phragmites australis growing in constructed wetlands for treatment of municipal wastewater

Biomass of Phragmites australis growing in four constructed wetlands with horizontal sub-surface flow (HF CWs) designed for treatment of municipal sewage in the Czech Republic have been analyzed for 19 trace elements. The biomass was harvested during the peak standing crop in early September and divided into stems, leaves, flowers, roots and rhizomes. Concentrations of monitored elements in both aboveground and belowground plant tissues were similar to those found in plants growing in natural stands. The highest concentrations were recorded for Al, Fe, Mn, Ba and Zn while the lowest concentrations were those of Hg, U and Cd. Concentrations decreased in the order of roots > rhizomes > leaves > stems. The root/leaf ratio averaged 70 and varied between 1.4 for molybdenum and 392 for cobalt. The belowground/aboveground concentration ratio ranged between 0.9 and 69.5 with an average value of 19. Due to average aboveground/belowground biomass ratio > 1, the belowground/aboveground standing stock ratios were lower with six elements (Ba, Zn, Se, Hg, Mo, and Mn) having this ratio < 1.

Retention and partitioning of polycyclic aromatic hydrocarbons in Sarcocornia fruticosa from two Portuguese salt marshes

Sixteen PAH compounds (containing three to six rings) were quantified in sediments from the Rosário and Mitrena salt marshes in the Tagus and Sado estuaries, respectively, colonized by Sarcocornia fruticosa, and in belowground and aboveground plant tissues. Sediments from Rosário presented higher PAH concentrations (0.83–8.71 µg g–1) than those from Mitrena (0.22–1.63 µg g–1). Levels in belowground plant tissues showed a pronounced contrast between the two marshes: 84–165 and 0.15–0.43 µg g–1, respectively. Belowground material in contaminated layers contained 9–55 times more PAHs than sediments, while ratios lower than one were obtained in lower contaminated layers. Five- and six-ring compounds predominated (60–75%) in sediments and belowground plant material from both sites. Aboveground plant tissues presented no differences in PAH concentrations (0.17–0.18 ng g–1) and composition in both marshes, only three- and four-ring compounds being detected. This narrow concentration range appears to indicate that atmospheric deposition is the predominant pathway of PAH accumulation in aerial plant tissues.

Effects of nutrient enrichment on Distichlis spicata and Salicornia bigelovii in a marsh salt pan

We investigated how nutrient addition affects the abundance, nutrient storage, and competition between Distichlis spicata and Salicornia bigelovii, two dominant species in salt pans of Northern Gulf of Mexico marshes. Namely, we compared fertilized and unfertilized plots in monospecific areas colonized respectively by D. spicata or S. bigelovii, and in a mixed area colonized by the two species. Nutrient addition generally increased the aboveground biomass and percent cover of the two species, and those increases were moderate to large in relation to the increases found for other marsh plant species. Nutrient addition also generally decreased the carbon:nitrogen and carbon:phosphorus ratios of aboveground and belowground tissues of the two species. Our results provide evidence that, under enhanced nutrient availability, D. spicata is a superior competitor over S. bigelovii in the mixed zone of the salt pan where the two species grow together. However, we did not detect large changes in biomass dominance by D. spicata following fertilization, possibly because the experiment only lasted 10 months. Our results suggest that nutrient addition, by increasing the structural complexity of the leaf canopy and the nutritional quality of plant tissues for first-order consumers, may enhance the value of salt pans as habitat for organisms

Carbon and nitrogen partitioning in the freshwater submerged macrophyte Vallisneria gigantea in response to ultraviolet-B irradiance

The aim of this study was to determine the effect of ultraviolet-B (UV-B) exposures (0.55 and 1.1 W m−2) on the distributional variations of plant carbon and nitrogen content in both below- and aboveground parts in Vallisneria gigantea Graebner in laboratory conditions for a 3-month period. Plant biomass, total organic nitrogen, total organic carbon, lignin, water soluble carbohydrates and chlorophyll a and b were analysed and compared using repeated measures of analysis of variance (ANOVA) between UV-B-exposed and nonexposed treatments. A significant reduction (F (2, 15) = 754.5, P < 0.001) was observed in leaf chlorophyll a concentrations at UV-B exposure levels. In the high UV-B irradiation group, a significant decrease (50.3%) was observed compared with the initial aboveground biomass. The total organic nitrogen content at both high and low UV-B exposure levels declined significantly by 25.6% and 24.3%, respectively, in aboveground samples, while significant increases of 39.6% and 40%, respectively, were observed in belowground tissues, compared with non-UV-B treatment groups. The partitioning of total organic carbon in the aboveground tissues was reflected by significant increase in lignin and water soluble carbohydrates in aboveground tissues under UV-B stress. However, total organic nitrogen demonstrated greater partitioning into the belowground tissues of V. gigantea. This study highlights the defense mechanisms of V. gigantea through changes in the percentage composition of carbon and nitrogen compounds with negative effects on nutrient regeneration, which can be accelerated in a system exposed to UV-B irradiation at or above biologically effective levels.

Below- and Aboveground Biomass of Spartina alterniflora: Response to Nutrient Addition in a Louisiana Salt Marsh

The responses of Spartina alterniflora above- and belowground biomass to various combinations of N, P, and Fe were documented in a 1-year field experiment in a Louisiana salt marsh. Five levels of N additions to 0.25 m2 plots resulted in 18% to 138% more live aboveground biomass compared to the control plots and higher stem densities, but had no effect on the amount of live belowground biomass (roots and rhizomes; R&R). There was no change in the aboveground biomass when P or Fe was added as part of a factorial experiment of +P, +N, and +Fe additions, but there was a 40% to 60% decrease in the live belowground biomass, which reduced the average R&R:S ratio by 50%. The addition of various combinations of nutrients had a significant affect on the belowground biomass indicating that the addition of P, not N, eased the need for root foraging activity. The end-of-the-growing-season N:P molar ratios in the live above- and belowground tissues of the control plot was 16.4 and 32.7, respectively. The relative size of the belowground standing stocks of N and P was higher than in the aboveground live tissues, but shifted downwards to about half that in fertilized plots. We conclude that the aboveground biomass was directly related to N availability, but not P, and that the accumulation of belowground biomass was not limited by N. We suggest that the reduction in belowground biomass with increased P availability, and the lower absolute and relative belowground standing stocks of P as plant tissue N:P ratios increased, is related to competition with soil microbes for P. One implication for wetland management and restoration is that eutrophication may be detrimental to long-term salt marsh maintenance and development, especially in organic-rich wetland soils.

CONSTITUTIVE AND INDUCED DEFENSES TO HERBIVORY IN ABOVE- AND BELOWGROUND PLANT TISSUES

A recent surge in attention devoted to the ecology of soil biota has prompted interest in quantifying similarities and differences between interactions occurring in above- and belowground communities. Furthermore, linkages that interconnect the dynamics of these two spatially distinct ecosystems are increasingly documented. We use a similar approach in the context of understanding plant defenses to herbivory, including how they are allocated between leaves and roots (constitutive defenses), and potential cross-system linkages (induced defenses). To explore these issues we utilized three different empirical approaches. First, we manipulated foliar and root herbivory on tobacco (Nicotiana tabacum) and measured changes in the secondary chemistry of above- and belowground tissues. Second, we reviewed published studies that compared levels of secondary chemistry between leaves and roots to determine how plants distribute putative defense chemicals across the above- and belowground systems. Last, we used meta-analysis to quantify the impact of induced responses across plant tissue types. In the tobacco system, leaf-chewing insects strongly induced higher levels of secondary metabolites in leaves but had no impact on root chemistry. Nematode root herbivores, however, elicited changes in both leaves and roots. Virtually all secondary chemicals measured were elevated in nematode-induced galls, whereas the impact of root herbivory on foliar chemistry was highly variable and depended on where chemicals were produced within the plant. Importantly, nematodes interfered with aboveground metabolites that have biosynthetic sites located in roots (e.g., nicotine) but had the opposite effect (i.e., nematodes elevated foliar expression) on chemicals produced in shoots (e.g., phenolics and terpenoids). Results from our literature review suggest that, overall, constitutive defense levels are extremely similar when comparing leaves with roots, although certain chemical classes (e.g., alkaloids, glucosinolates) are differentially allocated between above- and belowground parts. Based on a meta-analysis of induced defense studies we conclude that: (1) foliar induction generates strong responses in leaves, but much weaker responses in roots, and (2) root induction elicits responses of equal magnitude in both leaves and roots. We discuss the importance of this asymmetry and the paradox of cross-system induction in relation to optimal defense theory and interactions between above- and belowground herbivory.

Prediction of atmospheric δ13CO2 using fossil plant tissues

Reconstruction of the carbon isotope composition of atmospheric CO2 is critical to the understanding of long‐term global carbon cycling. We have suggested that the δ13C value of land plant carbon (δ13Cp) preserved in the geologic record should reflect the δ13CO2 at the time during which the plants grew (δ13Ca), based on a meta‐analysis of modern plant data. Here we present the results of laboratory experiments designed to quantify the relationship between plant tissue δ13C and δ13CO2 values under varying environmental conditions, including differential pCO2 ranging from 1 to 3 times today's levels. As predicted, plants grown under elevated pCO2 showed increased average biomass compared to controls grown at the same temperature. Across a very large range in δ13Ca (≈24‰) and pCO2 (≈740 ppmv) we observed a consistent correlation between δ13Ca and δ13Cp (p &lt; 0.001). We show an average isotopic depletion of −25.4‰ for aboveground tissue and −23.2‰ for belowground tissue of Raphanussativus L. relative to the composition of the atmosphere under which it formed. For aboveground and belowground tissue, grown at both ∼23°C and ∼29°C, correlation was strong and significant (r2 ≥ 0.98 and p &lt; 0.001); variation in pCO2 level had little or no effect on this relationship. These results validate our initial conclusion that in the absence of environmental stress, plant δ13C primarily reflects atmospheric δ13CO2 linearly across pCO2 levels; the demonstrated excellent correlation in δ13Ca and δ13Cp suggests a high level of predictive power across varying environmental conditions.

Effects of filamentous algal mats on sulfide invasion in eelgrass ( Zostera marina)

The effect of filamentous algae invasion into Zostera marina meadows on water quality, sediment sulfur pools and sulfide invasion into plant tissues was studied experimentally. Sulfide invasion was assessed through analysis of sulfur isotopic composition ( δ 34S) and total sulfur (TS) concentrations in plant tissues. The algal mats (5 and 10 cm thickness) depleted oxygen in the mats and increased the pools of sulfides in the sediments. Plants exposed to algal mats had δ 34S signals closer to the δ 34S of sediment sulfide, whereas plants with no mats present had δ 34S signals closer to the δ 34S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to algal mats. The δ 34S varied between the plant tissues with the leaves having more positive δ 34S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS concentrations were higher in plants exposed to algal mats suggesting that sulfur derived from sediment sulfide accumulated in the plants. F sulfide showed that up to 50% of the sulfides in the plants were derived from sedimentary sulfides. The combined effect of water column anoxia in the lower parts of the meadow and high sulfide invasion into the plants lead to significantly reduced growth rates after 3 weeks and the below-ground tissues showed signs of degradation suggesting that algal mats invasion in to Zostera marina meadows can result in seagrass decline.