The Plastic Growth Responses of Three Agamospecies of Dandelion to Two Levels of Nutrient

The ability of a genotype to produce different phenotypes inresponse to variable environments is a crucial aspect of lifehistory strategies as it determines the shape of the fitnessset for the population. Apomictic dandelions generate littlegenetic variation between parent and offspring and plasticityis the main strategy in the face of environmental variability.The plastic response of three coexisiting dandelions has beenmeasured over two nutrient regimes. Cyclical growth patternsare species specific and in some cases independent of nutrientlevels. Differences between the agamospecies are greater athigh nutrient levels and the agamospecies appear to produceonly one phenotype at low nutrient levels. Taraxacum, plasticity, phenotypes, nutrient level     

Contribution of subsurface peat to CO2 and CH4 fluxes in a neotropical peatland

Tropical peatlands play an important role in the global carbon cycling but little is known about factors regulating carbon dioxide (CO₂) and methane (CH₄) fluxes from these ecosystems. Here, we test the hypotheses that (i) CO₂ and CH₄ are produced mainly from surface peat and (ii) that the contribution of subsurface peat to net C emissions is governed by substrate availability. To achieve this, in situ and ex situ CO₂ and CH₄ fluxes were determined throughout the peat profiles under three vegetation types along a nutrient gradient in a tropical ombrotrophic peatland in Panama. The peat was also characterized with respect to its organic composition using ¹³C solid state cross‐polarization magic‐angle spinning nuclear magnetic resonance spectroscopy. Deep peat contributed substantially to CO₂ effluxes both with respect to actual in situ and potential ex situ fluxes. CH₄ was produced throughout the peat profile with distinct subsurface peaks, but net emission was limited by oxidation in the surface layers. CO₂ and CH₄ production were strongly substrate‐limited and a large proportion of the variance in their production (30% and 63%, respectively) was related to the quantity of carbohydrates in the peat. Furthermore, CO₂ and CH₄ production differed between vegetation types, suggesting that the quality of plant‐derived carbon inputs is an important driver of trace gas production throughout the peat profile. We conclude that the production of both CO₂ and CH₄ from subsurface peat is a substantial component of the net efflux of these gases, but that gas production through the peat profile is regulated in part by the degree of decomposition of the peat.     

The first record of gynodioecy in a species of Gnidia (Thymelaeaceae) from South Africa

Sexual polymorphism was studied in the shrub Gnidia wikstroemiana (Thunb.) Meisn. from the semiarid Nama Karoo Biome, South Africa. The populations comprised plants bearing either female flowers, or hermaphrodite flowers with variable female function. In two populations, female plants accounted for 36–37% of the flowering plants. Female flowers were smaller and their stamens were reduced to staminodes, but their styles were significantly longer than those of hermaphrodite flowers. Energy investment in flowers and fruits for females and hermaphrodites was measured using bomb calorimetry. Females produce a greater number of less costly flowers than hermaphrodites, and invest less energy per unit in production of flowers and inflorescences. In contrast, females invest more energy per unit in production of fruits and infructescences than hermaphrodites. Females overall invest 7.3% more energy in reproduction than hermaphrodites. Female flowers were obligate out-crossers (xenogamous), with 35% of nonmanipulated, open-pollinated flowers setting fruit, comparable with fruit set among selfed hermaphrodite flowers. The breeding strategy of G. wikstroemiana most closely resembles gynodioecy. This is the first report of sexual dimorphism in Gnidia L. and sub-Saharan Thymelaeaceae.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 219–233.     

On the Metabolism of Tortula ruralis Following Desiccation and Freezing: Respiration and Carbohydrate Oxidation

Recovery from desiccation by Tortula ruralis (Hedw.) Gaertn., Meyer and Scherb was accompanied by an immediate, rapid increase in respiration (measured as oxygen uptake) at 25.5°C or 3.5°C. The respiratory burst was greater on rehydration of moss which had been rapidly desiccated over silica gel than that which had been more slowly desiccated in atmospheres of high relative humidity. No respiration was observed in dry moss. Dried moss which had been placed in liquid nitrogen resumed respiration on rewarming and rehydration but moss which had been frozen in the hydrated state respired to a lesser extent and showed signs of freeze damage. In the initial stages of slow drying a slight increase in respiration was noted, followed by a gradual decrease as drought became more severe. In contrast to observations made on many higher plants under drought stress, this moss did not exhibit any changes in its starch and sugar content during or following desiccation, nor were there any changes in free proline levels. Using (1-¹⁴C)-glucose and (6-¹⁴C)-glucose, the relative activities of the Embden–Meyerhof–Parnas and pentose phosphate pathways in hydrated and rehydrated moss were determined, as were the activities of specific enzymes involved in these pathways. An increased activity of the Embden–Meyerhof–Parnas pathway of glucose oxidation on rehydration of Tortula was observed. The possible significance of this latter observation is outlined.     

Differential Na2SO4 tolerance in tobacco plants regenerated from Na2SO4-grown callus

Abstract The regenerated shoots from sodium sulphate (Na₂SO₄) grown callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) were evaluated for Na₂SO₄ tolerance based on shoot proliferation and rooting in vitro, and seed germination in vivo in response to Na₂SO₄. An increase in Na₂SO₄ concentration resulted in significantly decreasing shoot fresh weight, number of shoots, shoot length and leaf size, and increasing per cent shoot dry weight of both control and Na₂SO₄-grown cultures. In rooting, shoots of Na₂SO₄-grown cultures exhibited the highest per cent rooting (85%) in the presence of 1% w/v Na₂SO₄. However, per cent rooting, root number per rooted cutting and root fresh weight decreased significantly with increasing Na₂SO₄ concentration when shoots were transferred to the medium in the absence of Na₂SO₄ for 4-monthly passages. Following acclimatization of the rooted shoots of Na₂SO₄-grown cultures, phenotypic variation was observed during growth and development. There were 13.2% sterile plants. Fertile plants were sorted into normal (N), tolerant (T), and sensitive (S) categories and the respective percentages of plants were 31.6, 44.7 and 10.5, based on per cent germination, germination velocity index and seedling survival to Na₂SO₄. The response of N, T and S types to Na₂SO₄ in subsequent shoot proliferation was similar to that of seed germination.