Growth,biomass allocation and plant nitrogen concentration in Chilean temperate rainforest tree seedlings: effects of nutrient availability

Seedlings of nine southern Chilean trees were grown at three nutrient supply rates, to examine the roles of growth rate, biomass distribution and nutrient use traits in determining species natural distributions on resource gradients. Relative growth rate (RGR) showed no overall relationship with species site requirements, although RGR of fertile-site species tended to be more responsive to nutrient supply. In the low-nutrient treatment, infertility-tolerant Fitzroya cupressoides showed a higher RGR rank than a fertility-demanding species (Laurelia philippiana) which outgrew it substantially at the highest supply rate. This reversal of RGR ranks was associated with divergent nutrient use responses: at high nutrient supply both spp. had similar plant nitrogen concentrations (PNC), whereas at the low supply rate Fitzroya’s production of biomass per unit of assimilated N was twice that of Laurelia’s. However, this pattern does not appear to serve as a general explanation of the respective distributions of the study species, as RGR ranks of most species were unaltered by nutrient supply. At low nutrient availability, no clear differences in shoot:root ratio (SRR) were apparent between poor-site and fertile-site species. However, at high nutrient availability, SRR was markedly higher in the latter, resulting from differences in biomass allocation to stems (not leaves). Leaf area ratios (LAR) were higher in fertile-site species than in those tolerant of low fertility, because of differences in specific leaf area rather than leaf weight ratio. Very high LAR at high nutrient supply was characteristic of most shade-tolerant angiosperms, but not of shade-tolerant conifers. Although PNC showed no overall differences between poor- and fertile-site species, sensitivity of PNC to external supply rate was greatest in two infertility-tolerant conifers. In contrast, the angiosperm Weinmannia trichosperma, although tolerant of low fertility, responded to increased nutrient supply with greatly increased RGR and little change in PNC. Results show little trait convergence between conifers and angiosperms in adaptation both to shade and to infertile soils; i.e. fitness of different taxa in a given environment may hinge on different trait combinations. Received: 12 September 1995 /Accepted: 14 June 1996     

Changes in plant biomass in fens in the vechtplassen area,as related to nutrient enrichment

Species-rich floating fen ecosystems in former turf ponds in the western part of The Netherlands are subject to nitrogen enrichment because of high atmospheric N deposition (50 kg ha^–1,Y^–1,). and supply of polluted river water in dry summer periods. Further, some fens have become more influenced by rain water because downward seepage to the groundwater has increased due to hydrological alterations. This paper describes changes in plant biomass production by comparing seasonal maximum biomass values for 15 fen sites determined with standard procedures in 1981 and 1988. Fen sites in different polders showed different species composition, which is related to differences in hydrology and history of fen management among the polders. The mid-succession fens (type 1) which are characteristically N-limited have shown a biomass increase in spite of the annual mowing regime, which shows that these fens are becoming enriched with nitrogen. There are indications that the role of phosphorus as a limiting factor increases in these fens, and that a shift of N-limited towards P-limited phanerogam growth occurs. This may bring these fens eventually in the late-succession stage, as presently found in Het Hol (type 2). The fens in this stage are P-limited and have a different species composition. It was concluded that the mesotrophic fens in the Vechtplassen area, characterized by a species-rich vegetation, can only persist in their eutrophicated environment if they are located in a groundwater discharge area and if they are annually harvested in the summer. If all fens in the area, will eventually become P-limited it is expected that the species composition will change to a more uniform late-succession vegetation type.     

Effects of ramet clipping and nutrient availability on growth and biomass allocation of yellow nutsedge

A glasshouse experiment was conducted to examine how the interactions of nutrient availability and partial ramet clipping affect growth, reproduction and biomass allocation of Cyperus esculentus, an invasive sedge. The plants sprouting from tubers were grown at low and high nutrient levels, and were subject either to no clipping, one, two or three clippings, with each clipping cutting half of the existing ramets at soil level. Our results show that nutrient availability and clipping frequency tended to independently affect most of growth, reproduction and biomass allocation parameters of Cyperus esculentus examined in the present study. Increased supply of nutrients led to an increase in plant productivity and its associated traits. All of the traits, except for the number of ramets, displayed a decreasing pattern with increasing clipping frequency, indicating that Cyperus esculentus had undercompensatory responses to ramet clipping. It is likely that the patterns of plants response to clipping are species specific, and depend on morphological characters of species. Its susceptibility to ramet clipping can offer opportunities for controlling this invasive species through mechanical methods such as mowing. Clipping had little effects on biomass allocation; however, root weight fraction increased with increasing clipping frequency. While nutrient availability and clipping frequency had no influence on leaf carbon concentration at harvest, both of them increased leaf nitrogen concentration, and hence reduced leaf C/N ratio.     

The influence of stand development on nutrient demand,growth and allocation

As an even-aged stand develops growth is concentrated first on leaves and fine roots, as a result nutrient accumulation is very rapid. During this early stage there is a distinct species effect whereas later nutrient uptake becomes a function of growth rate irrespective of species. Once canopy is closed up to two thirds of the nutrients required for growth can be obtained by retranslocation from older or dying tissues, an efficient conservation mechanism that leads to a reduction in the demands that are further reduced by the cycle through the litter layer. In consequence nutritional problems are most likely in the early years while the green crown is being constructed. Later in the rotation problems are unlikely unless nutrient cycles are disturbed, for example by thinning or as a result of excessive accumulation of humus. The eventual clear felling is a major disruption to nutrient cycles. Accelerated litter decomposition can lead to leaching losses, although this can be short lived, and burning if practised can have a major impact on poor sites. Nutrient loss in material removed from the felling site, whether or not harvested, is not high but is much increased if crowns are removed, particularly for the heavily crowned species. The importance of such loss clearly varies with site but may be significant for more than just loss of nitrogen, with loss of calcium, phosphorus or even organic matter per se all being possibly causes of worry.     

Short-term interactive effects of ultraviolet radiation,carbon dioxide and nutrient enrichment on phytoplankton in a shallow coastal lagoon

The main goal of this study was to evaluate short-term interactions between increased CO₂, UVR and inorganic macronutrients (N, P and Si) on summer phytoplankton assemblages in the Ria Formosa coastal lagoon (SW Iberia), subjected to intense anthropogenic pressures and highly vulnerable to climate change. A multifactorial experiment using 20 different nutrient-enriched microcosms exposed to different spectral and CO₂ conditions was designed. Before and after a 24-h in situ incubation, phytoplankton abundance and composition were analysed. Impacts and interactive effects of high CO₂, UVR and nutrients varied among different functional groups. Increased UVR had negative effects on diatoms and cyanobacteria and positive effects on cryptophytes, whereas increased CO₂ inhibited cyanobacteria but increased cryptophyte growth. A positive synergistic interaction between CO₂ and UVR was observed for diatoms; high CO₂ counteracted the negative effects of UVR under ambient nutrient concentrations. Nutrient enrichments suppressed the negative effects of high CO₂ and UVR on cyanobacteria and diatoms, respectively. Beneficial effects of CO₂ were observed for diatoms and cryptophytes under combined additions of nitrate and ammonium, suggesting that growth may be limited by DIC availability when the primary limitation by nitrogen is alleviated. Beneficial effects of high CO₂ and UVR in diatoms were also induced or intensified by ammonium additions.     

Aboveground biomass allocation,leaf growth,and photosynthesis patterns in tundra plant forms in arctic Alaska

Summary Tundra plant growth forms can generally be characterized as consisting predominantly of low-growing perennial grasses and sedges, perennial herbaceous forbs, dwarf deciduous shrubs, and dwarf evergreen shrubs. Gross aboveground carbon allocation, leaf growth, and photosynthesis pattern studies were initiated to develop a quantitative understanding of the functional importance of these particular tundra growth forms. Photosynthetic capacities of 13 species were determined under standardized exposure conditions using a¹⁴CO₂ field system and ranged between 5 and 47 mg CO₂·g dry wt^-1·h^-1. These results, in conjunction with detailed leaf growth determinations, support the generalization that species with an evergreen growth form have lower photosynthetic capacities than species with a perennial graminoid, forb, or deciduous shrub growth form. However, these low photosynthetic capacities in evergreen shrubs are associated with relatively extended leaf longevities. Conversely, deciduous shrub forms exhibited high photosynthetic capacities, but were offset by relatively short leaf longevity periods. The perennial grasses, sedges, and forbs showed patterns intermediate to these. As a result, it appears that among tundra species of different growth form, photosynthetic capacity is inversely related to leaf longevity.     

The influence of below ground herbivory and plant competition on growth and biomass allocation of purple loosestrife

Experiments investigating plant-herbivore interactions have primarily focused on above-ground herbivory, with occasional studies evaluating the effect of below-ground herbivores on plant performance. This study investigated the growth of the wetland perennial Lythrum salicaria (purple loosestrife) under three levels of root herbivory by the weevil Hylobiustransversovittatus and three levels of plant competition by the grass Phleumpratense in a common garden. Plant growth, flowering phenology, and biomass allocation patterns of purple loosestrife were recorded for two growing seasons. During the first year, root herbivory reduced plant height; plant competition delayed flowering; and the interaction of root herbivory and plant competition resulted in reductions in plant height, shoot weight and total dry biomass. Plant competition or larval feeding did not affect the biomass allocation pattern in the first year. These results indicate the importance of interactions of plant competition and herbivory in reducing plant performance – at least during the establishment period of purple loosestrife. In the second growing season, root herbivory reduced plant height, biomass of all plant parts, delayed and shortened the flowering period, and changed the biomass allocation patterns. Plant competition delayed flowering and reduced the dry weight of fine roots. The interaction of root herbivory and plant competition delayed flowering. Root herbivory was more important than plant competition in reducing the performance of established purple loosestrife plants. This was due, in part, to intense intraspecific competition among the grass individuals effectively preventing shoot elongation of P. pratense and resulting in a carpet like growth. Received: 3 April 1997 / Accepted: 27 July 1997     

Nitrogen, phosphorus and light effects on growth and allocation of biomass and nutrients in wild rice

Separating plastic from ontogenetic and growth-limiting responses of plants to changes in resource availability can be challenging because there are a total of eight combinations of these three types of responses. These can, however, be uniquely distinguished on plots of root:shoot ratios against total biomass through time. We used this approach to separate ontogenetic, plastic, and growth-limiting responses of wild rice (Zizania palustris L.) to changes in nitrogen, phosphorus, and light availabilities. Relative growth rate was limited primarily by nitrogen but responded to increased light and phosphorus after nitrogen limitations were alleviated. Nitrogen addition increased relative growth rate because it simultaneously increased unit leaf rate, specific leaf area, and leaf weight ratio. Increased light did not change relative growth rate because decreased specific leaf area and leaf weight ratio compensated the increased unit leaf rate. Phosphorus did not change either relative growth rate or its underlying components. Plants responded ontogenetically to increased nitrogen and light availabilities by accelerating their developmental rate, and plastically by decreasing or increasing their root:shoot ratios, respectively. Plants did not respond either ontogenetically or plastically to increased phosphorus availability. Ontogenetic changes in growth can be separated from plastic and growth-limiting responses by plotting root:shoot ratio against total biomass in the context of the eight possible responses identified above, and also by examining how the underlying components of relative growth rate respond.     

The relative importance of light and nutrient limitation of phytoplankton growth: a simple index of coastal ecosystem sensitivity to nutrient enrichment

Anthropogenic nutrient enrichment of the coastal zone is now a well-established fact. However, there is still uncertainty about the mechanisms through which nutrient enrichment can disrupt biological communities and ecosystem processes in the coastal zone. For example, while some estuaries exhibit classic symptoms of acute eutrophication, including enhanced production of algal biomass, other nutrient-rich estuaries maintain low algal biomass and primary production. This implies that large differences exist among coastal ecosystems in the rates and patterns of nutrient assimilation and cycling. Part of this variability comes from differences among ecosystems in the other resource that can limit algal growth and production – the light energy required for photosynthesis. Complete understanding of the eutrophication process requires consideration of the interacting effects of light and nutrients, including the role of light availability as a regulator of the expression of eutrophication. A simple index of the relative strength of light and nutrient limitation of algal growth can be derived from models that describe growth rate as a function of these resources. This index can then be used as one diagnostic to classify the sensitivity of coastal ecosystems to the harmful effects of eutrophication. Here I illustrate the application of this diagnostic with light and nutrient measurements made in three California estuaries and two Dutch estuaries.     

Root, mycorrhiza and earthworm interactions: their effects on soil structuring processes, plant and soil nutrient concentration and plant biomass

Earthworms, arbuscular mycorrhiza fungi (AMF) and roots are important components of the belowground part of terrestrial ecosystem. However, their interacting effects on soil properties and plant growth are still poorly understood. A compartmental experimental design was used in a climate chamber in order to investigate, without phosphorus (P) addition, the single and combined effects of earthworms (Allolobophora chlorotica), AMF (Glomus intraradices) and roots (Allium porrum) on soil structure, nutrient concentration and plant growth. In our experimental conditions, plant roots improved soil structure stability (at the level of macroaggregates) whereas earthworms decreased it. AMF had no effect on soil structure stability but increased P transfer from the soil to the plant and significantly increased plant biomass. Earthworms had no direct influence on P uptake or plant biomass, and the N/P ratio measured in the shoots indicated that P was limiting. Interactions between AMF and earthworms were also observed on total C and N content in the soil and on total root biomass. Their effects varied temporally and between the different soil compartments (bulk soil, rhizosphere and drilosphere). After comparison with other similar studies, we suggest that effects of earthworms and AMF on plant production may depend on the limiting factors in the soil, mainly N or P. Our experiment highlights the importance of measuring physical and chemical soil parameters when studying soil organism interactions and their influence on plant performance.     

The effects of nutrient enrichment on a freshwater meiofaunal assemblage

1. The effects of eutrophication on phytoplankton, zooplankton and fish in lakes are well known. By contrast, little is known about the response of the zoobenthos to nutrient enrichment, while smaller organisms, such as the meiofauna, have for the most part been neglected. 2. In a long‐term (16 months) microcosm experiment, we assessed the effects of five levels of nutrients [total phosphorus (TP), 7–250 μg L^?1; nitrate, 2–8 mg L^?1] on a freshwater meiofaunal assemblage and on nematode diversity in particular. 3. Within the first 8 months, meiofaunal succession was only weakly affected, whereas, during the last 4 months, nutrient addition influenced most of the main taxa, with a concomitant change in the assemblage structure. 4. The density of the numerically dominant nematodes decreased upon nutrient enrichment, whereas ostracods became more numerous. Other taxa, including copepods, reached a maximum at intermediate nutrient levels or, in case of oligochaetes, were almost unaffected by nutrient enrichment. However, the changes in the density of the main taxa were usually insufficient to alter their biomass. Consequently, meiofaunal biomass was remarkably unresponsive to nutrient addition, while meiofaunal density displayed a unimodal relationship, with a peak at a TP concentration of 30 μg L^?1. In addition, nematode species richness decreased significantly with increasing nutrient concentrations. 5. We hypothesise that the response of meiofaunal taxa to nutrients is attributable to the development of primary producers, which shifted with enrichment from low densities of edible diatoms and unicellular green algae to large standing stocks of inedible forms, such as Lemna minor and Cladophora spp.     

Resource capture, biomass allocation and growth in herbaceous plants

Plant species differ widely in their rate of biomass production, even when grown under optimal conditions. A key question concerns the extent to which these growth rates correlate with the uptake of carbon and nitrogen and with the biomass allocation between leaves and roots. Recent data show that the answer to this question differs for mono- and dicotyledons, and that more than biomass allocation, it is the ratio between the activities of leaves and roots that correlates with the growth rate of a plant.     

The effects of CO2 and nutrient enrichment on photosynthesis and growth of Poa annua in two consecutive generations

We studied short- and long-term growth responses of Poa annua L. (Gramineae) at ambient and elevated (ambient +200???mol?mol^?1) atmospheric CO₂. In experiment 1 we compared plant growth during the early, vegetative and final, reproductive growth phases. Plant growth in elevated CO₂ was significantly enhanced during the early phase, but this was reversed in the reproductive phase. Seed mass and percentage germination were significantly reduced in elevated CO₂. Experiment 2 tested for the impact of transgenerational and nutrient effects on the response of Poa annua to elevated CO₂. Plants were grown at ambient and elevated CO₂ for one or two consecutive generations at three soil nutrient levels. Leaf photosynthesis was significantly higher at elevated CO₂, but was also affected by both soil nutrient status and plant generation. Plants grown at elevated CO₂ and under conditions of low nutrient availability showed photosynthetic acclimation after 12?weeks of growth but not after 6?weeks. First-generation growth remained unaffected by elevated CO₂, while second-generation plants produced significantly more tillers and flowers when grown in elevated CO₂ compared to ambient conditions. This effect was strongest at low nutrient availability. Average above- and belowground biomass after 12?weeks of growth was enhanced in elevated CO₂ during both generations, but more so during plant generation 2. This study demonstrates the importance of temporal/maternal effects in plant responses to elevated CO₂.     

Relative growth rate,biomass partitioning and nutrient allocation in seedlings of two threatened trees grown under different light conditions

The present study investigates the variation in the relative growth, biomass and nutrient allocation in two threatened tree species viz. Magnolia punduana Hook.f. & Th. and Elaeocarpus prunifolius Wall. ex Müll. Berol. grown under three different levels of irradiance. The irradiance ranged between 1 and 12 mol m^?2 d^?1. Results showed that the highest relative growth rate (RGR) was achieved under the intermediate light treatment for both the species (mean: 0.005 mg mg^?1 d^?1). The growth response coefficient (GRC) model revealed that net assimilation rate (NAR) was the factor driving the RGR in both species. A significant positive correlation was found between NAR and RGR (R² = 0.33, p = 0.000) whereas specific leaf area (SLA) and leaf mass fraction (LMF) was negatively correlated to RGR. Overall, multiple regression of the studied species based on the independent variables viz. NAR, SLA, and LMF showed a significant relation with RGR (F(3,50,53 = 13.001, p = 0.000, R² = 0.43). The biomass distribution in the studied species is in agreement with the “balanced-growth hypothesis” where high irradiance increased allocation to below ground biomass fraction and decreased irradiance increased allocation to the above ground fraction. The highest nitrogen concentration in leaves was observed under the intermediate light treatment. Overall seedlings growth under intermediate light had a higher mean RGR indicating the species' preference for partial light conditions. Long-term experiments under varied light conditions as in the present study would provide useful insight into plant growth strategies in varied environmental conditions.     

The response of planktonic and microbenthic algal assemblages to nutrient enrichment in shallow coastal waters,southwest Sweden

Field and laboratory nutrient (nitrogen and phosphorus) enrichment experiments were performed using natural phytoplankton and microphytobenthic assemblages from the brackish water Öresund, S.W. Sweden. The response of algae from a low-nutrient area (Falsterbo Canal) was compared to that of algae from a polluted, nutrient-rich area (Lomma Bay).The biomass (measured as chlorophyll a) of both phytoplankton and microphytobenthos from the Falsterbo Canal increased after the addition of nitrogen. Phytoplankton growth was stimulated by the addition of phosphorus to the nitrogen-rich water of the polluted Lomma Bay. Sediment chlorophyll a showed no significant increase after the addition of nutrients in the Lomma Bay. In containers without sediment, phytoplankton uptake was calculated to account for ≈ 90% of the disappearance of inorganic fixed nitrogen from the water. In the sediment containers the microphytobenthos was estimated to account for ≈20% of the nitrogen uptake. The rest was presumably lost mainly through denitrification.When containers with microphytobenthos from Lomma Bay were kept in the dark, phosphorus was released at a rate of up to ≈ 180 μM · m^?2 · day^?1. We suggest that by producing oxygen microbenthic algae keep the sediment surface oxygenated thereby decreasing phosphorus transport from the sediment to the overlying water.     

The interaction between wetland nutrient content and plant quality controls aquatic plant decomposition

We conducted an in situ decomposition experiment to better understand how habitat nutrient content controls aquatic plant decomposition and, more precisely, to determine the relative importance of the wetland conditions in decomposition, and the intrinsic degradability of plant tissues. We collected the green leaves of three aquatic plant species with contrasting plant strategies from three wetlands of differing nutrient contents, and allowed them to decompose in seven wetlands along a nutrient gradient. The plant mass loss was higher for competitive and ruderal species collected in nutrient richer wetlands as well as when they were led to decompose in nutrient richer wetlands. Plant water content correlated with mass loss for the competitive and ruderal species, which may explain the increase in mass loss with increasing nutrient content in the collection wetlands. Litter decomposition rate may be enhanced by wetland eutrophication, because of both the modification of wetland decomposition conditions and by changes in plant tissue quality.     

Mangrove growth in New Zealand estuaries: the role of nutrient enrichment at sites with contrasting rates of sedimentation

Mangrove forest coverage is increasing in the estuaries of the North Island of New Zealand, causing changes in estuarine ecosystem structure and function. Sedimentation and associated nutrient enrichment have been proposed to be factors leading to increases in mangrove cover, but the relative importance of each of these factors is unknown. We conducted a fertilization study in estuaries with different sedimentation histories in order to determine the role of nutrient enrichment in stimulating mangrove growth and forest development. We expected that if mangroves were nutrient-limited, nutrient enrichment would lead to increases in mangrove growth and forest structure and that nutrient enrichment of trees in our site with low sedimentation would give rise to trees and sediments that converged in terms of functional characteristics on control sites in our high sedimentation site. The effects of fertilizing with nitrogen (N) varied among sites and across the intertidal zone, with enhancements in growth, photosynthetic carbon gain, N resorption prior to leaf senescence and the leaf area index of canopies being significantly greater at the high sedimentation sites than at the low sedimentation sites, and in landward dwarf trees compared to seaward fringing trees. Sediment respiration (CO₂ efflux) was higher at the high sedimentation site than at the low one sedimentation site, but it was not significantly affected by fertilization, suggesting that the high sedimentation site supported greater bacterial mineralization of sediment carbon. Nutrient enrichment of the coastal zone has a role in facilitating the expansion of mangroves in estuaries of the North Island of New Zealand, but this effect is secondary to that of sedimentation, which increases habitat area and stimulates growth. In estuaries with high sediment loads, enrichment with N will cause greater mangrove growth and further changes in ecosystem function.     

Ideal nutrient productivities and nutrient proportions in plant growth

Abstract I propose that one single formulation can be applied to relate growth and content of several nutrients, including the most important macronutrients, of most plant species. The plant growth rate is proportional to the nutrient content minus a given minimal concentration of the nutrient in minimum. The proportionality factor, the nutrient productivity, and the minimum concentration are species specific properties. The nutrient productivity formulation is shown to apply for very different plant species and for different nutrients.