Proportional Allocation Of Biomass Research Articles

Genotypic variation in response and dependency of Cajanus cajan (L.) Millsp., on arbuscular mycorrhizal fungi in a tropical Alfisol

Plant genotypes significantly differ in their growth characteristics and dependence on arbuscular mycorrhizal (AM) fungi for maximum growth and productivity at a given soil fertility level. Therefore, we examined the mycorrhizal dependency and response of seven pigeon pea (Cajanus cajan) genotypes (BRG–1, BRG–2, BRG–3, BRG–4, BRG–5, TRG–7 and Vamban–3) on native AM fungi. Plants of pigeon pea genotypes were grown in the presence and absence of native AM fungi for 45 days. At harvest, plant growth characteristics, root architecture, nodulation, AM fungal colonization, and plant nutrients were measured and nutrient uptake, nutrient use efficiencies and mycorrhizal dependency were calculated. The plant growth, root architecture, nodulation, and nutrient characteristics varied significantly among pigeon pea genotypes and were positively (except nutrient usage) influenced by AM fungi. The mycorrhizal dependency significantly varied among pigeon pea genotypes and ranged from 30.54% to 65.02%. The genotypes BRG–3 and BRG–4 were highly mycorrhizal dependent and accumulated maximum biomass under mycorrhizal conditions. Our results show that AM fungi in addition to improving plant growth and nutrient uptake can also modify the proportional allocation of biomass to shoot and root, root architecture, and nutrient use among pigeon pea genotypes.

The abundance of arbuscular mycorrhiza in soils is linked to the total length of roots colonized at ecosystem level.

Arbuscular mycorrhizal fungi (AMF) strongly affect ecosystem functioning. To understand and quantify the mechanisms of this control, knowledge about the relationship between the actual abundance and community composition of AMF in the soil and in plant roots is needed. We collected soil and root samples in a natural dune grassland to test whether, across a plant community, the abundance of AMF in host roots (measured as the total length of roots colonized) is related to soil AMF abundance (using the neutral lipid fatty acids (NLFA) 16:1ω5 as proxy). Next-generation sequencing was used to explore the role of community composition in abundance patterns. We found a strong positive relationship between the total length of roots colonized by AMF and the amount of NLFA 16:1ω5 in the soil. We provide the first field-based evidence of proportional biomass allocation between intra-and extraradical AMF mycelium, at ecosystem level. We suggest that this phenomenon is made possible by compensatory colonization strategies of individual fungal species. Finally, our findings open the possibility of using AMF total root colonization as a proxy for soil AMF abundances, aiding further exploration of the AMF impacts on ecosystems functioning.

Photosynthetic Acclimation, Biomass Allocation, and Water Use Efficiency of Garlic in Response to Carbon Dioxide Enrichment and Nitrogen Fertilization

Garlic (Allium sativum) is a commercially and culturally important crop worldwide. Despite the importance of garlic, there have been few studies investigating how garlic growth and development will be affected by the atmospheric enrichment of carbon dioxide (CO2). A split-plot experiment with CO2 concentrations as main plot and nitrogen (N) fertilization as subplot was carried out to examine the effects of elevated CO2 at (mean ± sd) 745 ± 63 µmol·mol−1 across three levels of N: high-N (16.0 mm), mid-N (4.0 mm), and low-N (1.0 mm). Three hypotheses were tested: 1) garlic plants will allocate proportionally more biomass to bulb when grown in elevated CO2 compared with the plants grown in ambient CO2; 2) plants will sustain improved photosynthesis without downregulation in elevated CO2, irrespective of N; and 3) elevated CO2 will improve plant water use efficiency (WUE) across N fertilization levels. We found that proportional biomass allocation to bulb was not significantly enhanced by CO2 enrichment in garlic. Overall biomass accumulation represented by leaf, stem, and bulb did not respond significantly to CO2 enrichment but responded strongly to N treatments (P < 0.001). Contrary to our hypothesis, photosynthetic downregulation was apparent for garlic plants grown in elevated CO2 with a decrease in Rubisco capacity (P < 0.01). Instantaneous leaf WUE improved in response to elevated CO2 (P < 0.001) and also with increasing N fertilization (P < 0.001). Finally, our results indicate that bulbing ratio is likely to remain unchanged with CO2 or N levels and may continue to serve as a useful nondesctructive metric to estimate harvest timing and bulb size.

Variation in aboveground and belowground biomass in progeny of selected stands of Pinus sylvestris

Forest biomass studies not only range from estimation of timber standing mass to assessing biogeochemical cycles, but may also reveal genetic variation in growth and biomass allocation. In this study, we investigated differences in biomass accumulation and allometric relationships between tree diameter and biomass of above and belowground components in two populations of Scots pine (Pinus sylvestris L.) (progeny of clonal seed orchards) differing in stem growth. At a common tree diameter, populations differed in accumulated belowground biomass, but not in total tree or aboveground components' biomass. Populations also differed in the root:shoot ratio and proportional allocation of biomass into stems. However, proportional allocation to stem mass decreased from smaller to larger trees, contrary to branch and foliage, which likely reflected a response to competition in the stand. The allometric equations predicted well the total tree, aboveground, and stem biomass independently of population, but separate equations were required for estimation of belowground biomass for the two populations. These results suggest that total stand and aboveground biomass in young Scots pine stands could be estimated without accounting for genetic component. Comparison of literature data with estimates obtained using our allometric equations indicate that equations were site-specific and should not be generalized to other sites, unless for rough approximation of aboveground biomass. More research is required for a more reliable assessment of genetic effect on allometric relationships for belowground biomass.

Expansion of Phragmites australis (Cav.) Trin. ex Steud. (Common Reed) into Typha spp. (Cattail) Wetlands in Northwestern Indiana, USA

Expansion of Phragmites australis (Cav.) Trin. ex Steud. (common reed) into stands of Typha spp. (cattail; Typha australis L. and T. x glauca) is common in the wetlands of northwestern Indiana (USA). To understand this phenomenon better, we investigated the production of shoot sprouts and proportional allocation of biomass as well as a potential role for the water table in the relative dominance of each species. The reduction in sprouts from rhizomes upon vegetative expansion of Phragmites appeared to be the most likely process causing the decline of Typha. The latter had a shoot density of 39/m2 in plots without Phragmites, but this dropped to 13 shoots m−2 in plots that had been invaded by Phramites. Such a decline was likely caused by reduced reserves; e.g., the belowground biomass of Typha decreased from 11.3 g m−2 without Phragmites to 8.1 g m−2 with Phragmites. The latter also reduced its belowground biomass but not its shoot density in the presence of Typha. The mean weight of Phragmites shoots was 2.9 g, and nearly all produced inflorescences. Meanwhile, Typha failed to develop spadices despite its shoots having a greater biomass (7 g). This suggests that Phragmites is more efficient than Typha in shoot growth. Springtime flooding appeared to promote the sprout of Typha shoots from shallow rhizomes (≈18 cm below the soil surface), whereas the shoot density of Phragmites showed no correlation with water level in that season. Deep-rooted Phragmites (≈39 cm) occurred on both high and low water-table sites, whereas the shallow-rooted Typha was limited to only the former. Phragmites will likely continue its expansion, by vegetative sprouts from rhizomes, into Typha wetlands.

Comparative population ecology of Senna occidentalis (L.) Link, a monsoon desert annual, in two different habitats

A demographic study of Senna occidentalis (L.) Link, a circumtropical weed, was conducted at two habitats: an old-field (a moister site) and a waste ground (a drier site). The survivorship curves of both the populations closely corresponded to Deevy type I (greater age-specific mortality at higher age). Moisture stress appeared to be the major cause of mortality. Seed rain occurred essentially during October with the highest seed-fall in the second and third weeks. Seed predation by bruchids was greater for the waste ground population compared to that of the old-field. The extent of seed predation differed significantly among individuals between the populations. Seed densities in soil at both the sites declined remarkably in late August due to rainfall and consequent germination while the seed bank was elevated in November due to production and dispersal. The proportional allocation of biomass to roots was small for both the populations. Reproductive allocation of biomass and phosphorus varied considerably between populations. Reproductive allocation of biomass and particularly phosphorus was much greater for the old-field compared to the waste ground population.

Evolutionary increase in sexual and clonal reproductive capacity during biological invasion in an aquatic plant Butomus umbellatus (Butomaceae)

To test the hypothesis that increased allocation to reproduction is selected during biological invasion, we compared germination, survival, growth, and reproduction of native vs. introduced populations of the invasive aquatic plant Butomus umbellatus in a common greenhouse environment. Although seedling emergence and establishment did not differ consistently, survival thereafter was twice as high for eight introduced North American than eight native European populations. As predicted, introduced plants were more likely to produce sexual inflorescences and clonal asexual vegetative bulbils, and they invested much more biomass in both reproductive modes. Higher reproductive investment was due to higher proportional allocation of biomass rather than larger plant size. These results are consistent with selection for increased reproduction during range expansion. However, population genetic surveys indicate that recruitment from seed rarely occurs in introduced populations. Hence increased sexual allocation is not an adaptive response to invasion. Although increased clonal reproduction may be advantageous in expanding populations, genetic evidence from introduced populations of B. umbellatus suggests that increased clonal allocation may have arisen via stochastic processes during long-distance transport or a selective filter right at introduction, rather than incremental natural selection during range expansion.

Effects of nutrient enhancement on the fecundity of a coral reef macroalga

On coral reefs, there is concern that increased nutrient supply (e.g. due to eutrophication) causes increased algal growth and hence increased algal abundance, in turn causing colonisation and invasions of coral populations, resulting in reef degradation, or a coral–algal phase shift. For example, species of Sargassum, a highly seasonal, large, brown seaweed, are suggested to be colonising corals on inshore coral reefs of the Great Barrier Reef, as a result of anthropogenic increases in terrestrial runoff of sediments and nutrients. However, implicit in this argument is the assumption that nutrient-related increases in growth will lead to increased fecundity (and/or propagule success), since without such changes, increased abundance can only occur by vegetative means. Whilst plausible, there is no experimental evidence for this assumption in coral reef algae. We here present an initial study in which experimental increases in nutrient supply apparently did not lead to increased fecundity of Sargassum siliquosum; rather, density and biomass of receptacles were reduced in nutrient-enhanced algae. There was little effect of nutrient treatments on the proportional allocation of biomass to reproductive and vegetative structures: nutrient enhancement led to similar decreases in biomass of reproductive and vegetative tissue. Tissue nutrient levels indicated effective enhancement of nitrogen supply, although phosphorus levels were not different across nutrient treatments. The reduced fecundity with increased nutrients may reflect either a genuine inhibition by higher nutrient levels, as found in previous studies, or accelerated maturation, causing increased tissue losses due to more advanced seasonal senescence. Either way, this exploratory experiment provides initial evidence that nutrient effects on tropical coral reef macroalgae may be complex, and does not support the assumption that increased nutrient supply will result in a numeric increase in populations of Sargassum spp. Our results should not be taken as an unequivocal demonstration that nutrients inhibit fecundity overall, but illustrate the need to distinguish between effects on different life-history processes (e.g. growth and reproduction). For increased growth of pre-existing individuals to contribute to algal invasions and phase shifts, that growth must result in either increased fecundity, or increased propagule success.

Agronomic evaluation of a tiller inhibition gene (tin) in wheat. II. Growth and partitioning of assimilate

Wheats with reduced tillering have been proposed for areas regularly subject to a terminal drought. A wheat plant with a genetic disposition to produce fewer stems is now possible through the introgression of a gene that inhibits tillering (tin). This study was conducted to determine the effect of the tin gene on the dynamics of tillering, light interception, and dry-matter production and partitioning in several different cultivars of wheat. Commercial cultivars and their near-isogenic pairs differing in the presence of the tin gene were grown in well-watered tubes and also in the field in south-eastern Australia where terminal drought is common. Tiller number, light interception, leaf area index (LAI), biomass, and the partitioning of biomass were recorded at various intervals throughout the growing season. Water-soluble carbohydrate (WSC) levels in the stems of field-grown plants were also determined in some environments at anthesis and maturity. In tubes and in field environments, lines with the tin gene produced tillers at the same rate as their free tillering counterparts but ceased tillering sooner. Under conditions where the free tillering lines produced over 1000 shoots/m2, lines containing the tin gene produced 600 shoots/m2. However, by maturity, fertile spike numbers were 350 and 450/m2 for lines with and without the tin gene, respectively. Despite the large difference in tillering, there were only small differences in LAI, light interception throughout the season, and biomass. There were small differences in the proportional allocation of biomass, and the tin lines partitioned more of their biomass towards spikes at anthesis and stored more WSC in stems. Dry weight distribution varied with genetic background, but in general the tin gene increased leaf area ratio and root to shoot ratio but decreased specific leaf area. It is concluded that the tin gene may be advantageous under terminal drought. This would come from the reduced light interception prior to anthesis and thereby potential for greater transpiration during grain filling as well as a greater capacity for stem carbohydrate storage and remobilisation. These factors are consistent with a greater harvest index and kernel weight associated with lines containing the tin gene.

Using a system mixed-effects modeling method to estimate tree compartment biomass for intensively managed loblolly pines?an allometric approach

Allometric relationships between total and individual tree compartment (stem, root, branch, and foliage) biomass were investigated for intensively managed loblolly pine (Pinus taeda L.) plantations in the Lower Coastal Plain and Piedmont of Georgia. It was found that the percent of stem biomass increases with age while the inverse relationship was found for foliage and branches. Cultural treatments also impacted the proportional allocation among various tree compartments. Specifically, this investigation showed that compared with unfertilized trees, annually fertilized trees in the Lower Coastal Plain had a larger proportional biomass allocation to the stem relative to root, branch, and foliage compartments. A system of related compartment biomass models was developed that reproduces observed relationships in the raw data. This system of models uses total tree biomass to obtain estimates of biomass for other tree compartments. The flexibility of the system of biomass prediction models allows users to estimate biomass for the various compartments as a function of another known compartment biomass.

Using a system mixed-effects modeling method to estimate tree compartment biomass for intensively managed loblolly pines—an allometric approach

Allometric relationships between total and individual tree compartment (stem, root, branch, and foliage) biomass were investigated for intensively managed loblolly pine ( Pinus taeda L.) plantations in the Lower Coastal Plain and Piedmont of Georgia. It was found that the percent of stem biomass increases with age while the inverse relationship was found for foliage and branches. Cultural treatments also impacted the proportional allocation among various tree compartments. Specifically, this investigation showed that compared with unfertilized trees, annually fertilized trees in the Lower Coastal Plain had a larger proportional biomass allocation to the stem relative to root, branch, and foliage compartments. A system of related compartment biomass models was developed that reproduces observed relationships in the raw data. This system of models uses total tree biomass to obtain estimates of biomass for other tree compartments. The flexibility of the system of biomass prediction models allows users to estimate biomass for the various compartments as a function of another known compartment biomass.

Propagation of trembling aspen and hybrid poplar for agroforestry: potential benefits of elevated CO 2 in the greenhouse

We examined the usefulness of elevated CO 2 in the greenhouse to aid in early selection of genotypes and in the propagation of Populus tremuloides Michaux aspen and hybrid poplars for agroforestry, afforestation, or reclamation. Growth in elevated 800 ppm vs ambient 375 ppm CO 2 for 95 days resulted in greater height 14%, stem caliper 16%, overall biomass, and proportional allocation of biomass to roots as well as elevated net assimilation and water-use-efficiency. Aspen clones selected for superior growth based on phenotypic selection broke bud significantly earlier than unselected clones under both CO 2 levels; superior clones were also taller with greater stem caliper under both CO 2 treatments but not significant. Under ambient CO 2 male aspen were taller than females while under elevated CO 2 female aspen were taller than males and also had greater caliper but not significant. Hybrid poplar grown under elevated vs ambient CO 2 broke bud significantly earlier and had significantly greater net assimilation and water-use efficiency; they were also taller with greater caliper but not significant. Differences in performance among the eight hybrid clones were enhanced by growth under elevated CO2. Under ambient CO2, P38P38 was the clone that broke bud earliest, was tallest with greater caliper and had a lower shoot:root biomass ratio. Sargentii, on the other hand, was the shortest with the smallest caliper. The implications of these results need to be considered in the context of using aspen and hybrid poplar for largescale agroforestry, afforestation and reclamation across Canada.

On the Vegetative Biomass Partitioning of Seed Plant Leaves, Stems, and Roots

A central goal of comparative life-history theory is to derive the general rules governing growth, metabolic allocation, and biomass partitioning. Here, we use allometric theory to predict the relationships among annual leaf, stem, and root growth rates (GL, GS, and GR, respectively) across a broad spectrum of seed plant species. Our model predicts isometric scaling relationships among all three organ growth rates: GL is proportional to GS is proportional to GR. It also provides a conceptual basis for understanding the differences in the absolute amounts of biomass allocated to construct the three organ types. Analyses of a large compendium of biomass production rates across diverse seed plant species provide strong statistical support for the predictions of the theory and indicate that reproductive investments may scale isometrically with respect to vegetative organ growth rates. The general rules governing biomass allocation as indexed by the scaling exponents for organ growth rates are remarkably indifferent to plant size and taxonomic affiliation. However, the allometric "constants" for these relationships differ numerically as a function of phenotypic features and local environmental conditions. Nonetheless, at the level of both inter- and intraspecific comparisons, the same proportional biomass allocation pattern holds across extant seed plant species.

On the Vegetative Biomass Partitioning of Seed Plant Leaves, Stems, and Roots

A central goal of comparative life‐history theory is to derive the general rules governing growth, metabolic allocation, and biomass partitioning. Here, we use allometric theory to predict the relationships among annual leaf, stem, and root growth rates (GL, GS, and GR, respectively) across a broad spectrum of seed plant species. Our model predicts isometric scaling relationships among all three organ growth rates: $$G_{\mathrm{L}\,}\propto G_{\mathrm{S}\,}\propto G_{\mathrm{R}\,}$$. It also provides a conceptual basis for understanding the differences in the absolute amounts of biomass allocated to construct the three organ types. Analyses of a large compendium of biomass production rates across diverse seed plant species provide strong statistical support for the predictions of the theory and indicate that reproductive investments may scale isometrically with respect to vegetative organ growth rates. The general rules governing biomass allocation as indexed by the scaling exponents for organ growth rates are remarkably indifferent to plant size and taxonomic affiliation. However, the allometric “constants” for these relationships differ numerically as a function of phenotypic features and local environmental conditions. Nonetheless, at the level of both inter‐ and intraspecific comparisons, the same proportional biomass allocation pattern holds across extant seed plant species.

Genotypic effects of fertilization on seedling sweetgum biomass allocation, N uptake, and N use efficiency.

Screening and selecting tree genotypes that are responsive to N additions and that have high nutrient use efficiencies can provide better genetic material for short-rotation plantation establishment. A pot experiment was conducted to test the hypotheses that (1) sweetgum (Liquidambar styraciflua L.) families have different patterns in biomass production and allocation, N uptake, and N use efficiency (NUE), because of their differences in growth strategies, and (2) sweetgum families that are more responsive to N additions will also have greater nutrient use efficiencies. Seedlings from two half-sib families (F10022 and F10023) that were known to have contrasting responses to fertility and other stress treatments were used for an experiment with two levels of N (0 vs. 100 kg N/ha equivalent) and two levels of P (0 vs. 50 kg P/ha equivalent) in a split-plot design. Sweetgum seedlings responded to N and P treatments rapidly, with increases in both size and biomass production, and those responses were greater with F10023 than with F10022. Growth response to N application was particularly strong. N and P application increased the proportional allocation of biomass to leaves. Under increased N supply, P application increased foliar N concentration and content, as well as total N uptake by the seedlings. However, NUE was decreased by N addition and was higher in F10023 than in F10022 when P was not limiting. A better understanding of genotype by fertility interactions is important in selecting genotypes for specific site conditions and for optimizing nutrient use in forestry production.

Growth and physiology of Picea abies populations from elevational transects: common garden evidence for altitudinal ecotypes and cold adaptation

1. There are conflicting reports concerning the adaptive features of tree populations originating from cold, high‐altitude environments. We hypothesize that such trees will possess adaptive features that will be demonstrated in a common environment, such as elevated rates of net CO2 exchange, elevated needle nitrogen concentration and high proportional biomass allocation to roots. To test this hypothesis we measured tree and seed properties of 54 populations of Norway spruce [Picea abies (L.) Karst.] located along eight altitudinal transects (from c.600 to 1500m) in southern Poland. We also measured growth, biomass partitioning, net photosynthetic capacity (Amax), needle dark respiration (RS) and carbohydrate, nitrogen (N) and chlorophyll concentration of seedlings originating from these populations grown for 2 to 7 years in a common garden at 150m elevation. Measured in situ along the elevational transects, there were linear declines in seed mass, average d.b.h. and height growth increment of seed trees with increased altitude or lower mean annual temperature. 2. In the common garden, the Norway spruce populations from colder, high‐altitude habitats had higher N concentration in needles than those from low altitudes. Both Amax and needle RS increased with altitude of seed origin and were significantly related to needle N concentration. High‐altitude populations also had higher concentrations of chlorophyll and carotene than those from low elevations. Despite higher photosynthetic rates in high‐altitude populations, seedling height and dry mass in the common garden declined with altitude of seed origin. Proportional dry mass partitioning to roots nearly doubled with increasing altitude of origin, while the length of the shoot‐growth period was reduced. The high respiration rates, high allocation to roots and reduced shoot‐growth period are probably responsible for the low growth rate potential of high‐altitude populations, more than offsetting their higher photosynthetic rates. 3. The results of this study showed that Norway spruce populations from cold mountain environments are characterized by several potentially adaptive features. Because these were similar to conifer population responses along a latitudinal gradient of origin, they are probably driven by climate. These climate‐driven differences were common to all transects: for a given altitude or mean annual temperature, plant traits were independent of mountain range of origin. However, populations originating from cold high‐elevation sites often differed per unit change in altitude or mean annual temperature more than did low elevation populations. The scaling of nitrogen, CO2 exchange and biomass and allocation patterns may be useful in modelling Norway spruce response on montane forest ecosystems under changing environments.

Population density and module demography in Trapa natans (Trapaceae), an annual, clonal aquatic macrophyte

The effects of population density on module demography were studied in Trapa natans L., an annual aquatic macrophyte capable of extensive clonal propagation. At low density, the floating plants produced ten times as many ramets (clonal offshoots) as those at high density. Module mortality occurred at three levels: leaf, ramet (shoot), and genet (genetic individual). There was 100‐fold variation in the size of nuts containing germinable seeds. In early summer there was a highly significant linear relationship between dry mass of nuts and the total mass of ramets that each had produced. In early summer most (73–83%) of the variation in total plant biomass was attributable to variation in initial nut size. However the significance of initial nut size was diminished later in the season. The great success of the exotic weed T. natans at colonizing and monopolizing an aquatic habitat is a function of its highly productive clonal growth response to low‐density conditions, combined with greater proportional allocation of biomass to reproductive structures, resulting in greatly increased nut production at low initial density. The species appears able to develop and maintain a population at extremely high density: plant buoyancy and the production of large, well‐protected nuts allow rapid early growth from the sediment each year and early pre‐emption of the water surface.

Population Density and Module Demography in Trapa natans (Trapaceae), an Annual, Clonal Aquatic Macrophyte

The effects of population density on module demography were studied in Trapa natans L., an annual aquatic macrophyte capable of extensive clonal propagation. At low density, the floating plants produced ten times as many ramets (clonal offshoots) as those at high density. Module mortality occurred at three levels: leaf, ramet (shoot), and genet (genetic individual). There was 100-fold variation in the size of nuts containing germinable seeds. In early summer there was a highly significant linear relationship between dry mass of nuts and the total mass of ramets that each had produced. In early summer most (73–83%) of the variation in total plant biomass was attributable to variation in initial nut size. However the significance of initial nut size was diminished later in the season. The great success of the exotic weed T. natans at colonizing and monopolizing an aquatic habitat is a function of its highly productive clonal growth response to low-density conditions, combined with greater proportional allocation of biomass to reproductive structures, resulting in greatly increased nut production at low initial density. The species appears able to develop and maintain a population at extremely high density: plant buoyancy and the production of large, well-protected nuts allow rapid early growth from the sediment each year and early pre-emption of the water surface.

Consequences of Patchy Distribution of Light for the Growth of the Clonal Herb Glechoma Hederacea

The hypothesis that the clonal plant Glechoma hederacea can forage for light in environments with spatially patchy light supply was tested experimentally using artificial habitats in the glasshouse. There were five light treatments. Two treatments were homogeneous, with uniformly low or high light. Three treatments were patchy, each consisting of one high light patch and one low light patch. In the patchy treatments the position of the light patches differed with respect to the position at which the clone commenced growth. Several morphological responses were predicted if foraging for light through morphological plasticity took place : (I) there should be a greater concentration of ramets and biomass, a greater frequency of branching, greater leaf area, a lower proportional allocation of biomass to stolons and a higher proportional allocation of biomass to leaves in high light than in low light patches ; (2) there should be increased petiole lengths and a higher proportional allocation of biomass to stolons and petioles in low light patches than in high light patches ; (3) different primary stolons should assume different morphologies when exposed, simultaneously, to different light regimes. Structures directly involved in light acquisition in G. hederacea showed the greatest responses to changes in light conditions. In the patchy light treatments the frequency of branching, the leaf area of primary ramets and the proportional allocation to leaf biomass were significantly greater in high light patches and petiole length and proportional allocation to petiole biomass were significantly greater in low light patches. The greater leaf area, coupled with greater branching, allowed clones to harvest light energy more efficiently in high light conditions and the increase in petiole length allowed clones to escape from poor light conditions. However, these foraging responses were shown only when clones grew from low light to high light patches or when different primary stolons were exposed simultaneously to either high or low light. Foraging responses were suppressed when clones grew from high light to low light patches. These results imply that responses to patchy light conditions are not clone-wide, but localised within individual stolons, and that individual stolons can adjust morphology rapidly only when high resource patches are encountered after low resource patches. The converse - adjustment to a low resource patch following a period in a high resource patch - does not occur or occurs slowly, due to physiological integration within stolons and the predominantly acropetal nature of resource translocation.

Effects of an organic sediment on performance of young Phragmites australis clones at different water depth treatments

Performance of young Phragmites australis plants was examined after 7 weeks on an artificial nutrient-enriched inorganic substrate and on the same substrate to which an organic sediment from a eutrophic lake was added, at three different water depth treatments. Growth decreased, and proportional allocation of biomass to roots increased, with the addition of sediment. These differences were significant in shallow and deep water, but not at a medium depth. Concentrations of phosphorus and nitrogen in plant biomass decreased, and concentration of iron increased, with addition of sediment. The effects of sediment addition may have resulted from a decreased availability of nutrients in the substrate or from an impaired root functioning. Nutrient exhaustion in the substrate, due to a fast plant growth, can explain the relatively strong effects in shallow water. Deep water, on the other hand, probably restricted oxygen transport to the roots, resulting in an impaired root functioning in the low-redox sediment environment. The results show that, especially in relatively deep water, growth of undisturbed plants of P. australis may be inhibited by eutrophication of sediments, probably because of an impaired root functioning in sediments containing reduced toxic compounds (e.g. ferrous iron).