Nitrogen-poor Soils Research Articles

EFFECT ON GROWTH AND ROOT NODULATION OF CLOVERS, TRIFOLIUM SPP., BY GALLERIA MELLONELLA (L.) (LEPIDOPTERA: PYRALIDAE) INFECTED WITH STEINERNEMA CARPOCAPSAE (WEISER) (RHABDITA: STEINERNEMATIDAE) AND ITS SYMBIONT, XENORHABDUS NEMATOPHILUS POINAR AND THOMAS

AbstractRed and white clovers, Trifolium spp., were grown in nitrogen-poor soil containing cadavers of larval Galleria mellonella (L.) that were infected with Steinernema carpocapsae (Weiser) and its symbiont Xenorhabdus nematophilus Poinar and Thomas. Growth and root nodulation were not affected by the nematode treatment, leading us to conclude that they would not be impaired through the action of antimicrobial agents produced by Xenorhabdus spp. present in soils because of Xenorhabdus-infected insect cadavers.

Interactions Among Nitrogen, Carbon, Plant Shape, and Photosynthesis

As one travels northward and encounters lower sun angles and more nitrogen-poor soils, there is an increased dominance of plant communities by evergreens with conical canopies and a more favorable carbon balance in photosynthesis per unit nitrogen in leaves compared with deciduous species from the same environments. Despite the observed correlations between these biogeographic patterns and plant traits, there is no quantitative model that accounts for them. We derive such a model from coupled ordinary differential equations of carbon balance and nitrogen uptake, comparing qualitative equilibrium predictions of correlations among plant traits with experimental findings. The model suggests that many of the experimentally observed correlations among plant traits (e.g., photosynthesis and nitrogen content) are best viewed as constraints on plant growth rather than cause and effect. We use the model to account for some large-scale biogeographic trends in plants morphology and physiology. We also provide suggestions for experiments to test the model predictions.

Responses of Legumes to Herbivores and Nutrients During Succession on a Nitrogen‐Poor Soil

We measured legume abundance following 13— and 5—yr experiments testing for the effects of mammalian herbivores, nutrients, and climate on plant communities in an old field and a savanna in east central Minnesota. Total legume abundance was significantly greater in plots with herbivores excluded. Within herbivore exclosures, legumes were more abundant in plots to which P, K, S, Mg, Mn, Ca, Na, and trace minerals had been added. Legumes were significantly more abundant in the savanna than in the old field. Lathyrus venosus, a rapidly growing early—maturing species, was largely responsible for these results. Two other common legumes at our study site, Amorpha canescens and Lespedeza capitata, were not significantly affected by herbivore exclosures. However, within herbivore exclosures, addition of nutrients significantly reduced Lespedeza. Late summer total legume biomass within herbivore exclosures increased strongly following exclosure establishment in 1982, declined dramatically following a severe drought in 1988, and then increased again following the drought. This trend suggested that herbivore effects we measured in 1994 resulted from long—term accumulation of legumes following the establishment of exclosures. Our results suggest that herbivores and nutrients other than nitrogen can dramatically limit the abundance of some legume species that might otherwise dominate grassland plant communities on nitrogen—poor soils. Limitation of legumes by colonization and drought may also be important. Thus, herbivores and nutrients other than nitrogen may be critical in structuring grassland plant communities and influencing succession, even on nitrogen—poor soils.

A channel-like transporter for NH4+ on the symbiotic interface of N2-fixing plants

SYMBIOSIS with nitrogen-fixing bacteria (rhizobia) allows legumes to survive in nitrogen-poor soils. The nitrogen-fixing bacteroids are found inside root nodule cells within the symbiosome, an organelle bounded by the peribacteroid membrane1. Across this membrane the plant receives fixed nitrogen in exchange for reduced carbon2. It has been assumed that fixed nitrogen is released from the symbiosome as either NH3 or NH4+ , but until now the transport mechanism was unknown3–5. We report here the use of patch-clamp techniques to show, in membrane patches on isolated symbiosomes, smoothly activating currents that are passive and equivalent to the influx of cations to the plant cytoplasm. The currents are largest with NH4+ as the cation at physiological concentration and they are blocked by calcium ions on the bacteroid side of the membrane. The characteristics of the currents are more like those of a channel than of carrier-mediated transport. In vivo nitrogen would move passively as NH4+ to the cytoplasm upon energization of the membrane and calcium ions may be involved in regulation of the flux.

Distribution of biomass and nitrogen among plant parts and soil nitrogen in a young Alnus incana stand

Grey alder, Alnus incana (L.) Moench, was inoculated with the local source of Frankia and planted in nitrogen-poor soil in northern (63.8°N, 20.3°E) Sweden. Each alder root system was enclosed in a cylinder that served as an open-ended cuvette for nitrogenase activity measurements. The alders grew well, especially during the 2nd year of the study. The final leaf area in each season was more closely related to total alder biomass than final height of alders. The alders lost 17% of their total dry mass as leaf litter each year. This corresponded to 33 g dry mass and 0.67 g N per alder during the 2nd year. During the 2 years the soil N increment was 0.52 g N per alder. Leaf litter N and the increase in soil N corresponded to 27 and 17%, respectively, of the N2 fixed in the 2 years. Already at a young age, N2-fixing A. incana can apparently contribute to an improved fertility of N deficient soils. Key words: aboveground biomass, Alnus incana, belowground biomass, leaf litter, nitrogen content, soil N increment.

N2 fixation in a young Alnus incana stand, based on seasonal and diurnal variation in whole plant nitrogenase activity

N2 fixation by grey alder, Alnus incana (L.) Moench, was studied in the field during two growing seasons in northern Sweden. Alders were planted in a nitrogen-poor soil. Each alder had its root system enclosed in an open-ended cylinder that was closed with a gas-tight lid around the stem base to serve as cuvette during nitrogenase activity (acetylene reducing activity) measurements. To follow the seasonal variation, nitrogenase activity was measured at noon on 15 occasions for each alder in 1987 and on 15 occasions in 1988. Diurnal variation in nitrogenase activity was studied at six occasions, but no obvious pattern in the diurnal variation was found. Nitrogenase activity began shortly after leaf emergence at the very end of May, increased in June, stayed high although with some variation through July and August, declined during September, and was zero in early October. Cumulative nitrogenase activity over the season was converted to cumulative N2 fixation after determination of molar ratio nitrogenase activity to N2 fixation. This conversion was facilitated as the Frankia chosen as symbiont was lacking hydrogenase activity. Control experiments showed that the introduced symbiont was the only infective Frankia in the soil. N2 fixation was estimated to be 0.23 and 2.83 g N/(alder∙year) in the 1st and 2nd year, respectively. Despite its young age, A. incana was apparently capable of high N2 fixation rates at the high latitude studied. Key words: Alnus incana, hydrogenase, intact plants, N2 fixation, seasonal variation, spreading of Frankia.

Plant Traits and Resource Reduction For Five Grasses Growing on a Nitrogen Gradient

Five grass species (Agrostis scabra, Agropyron repens, Poa pratensis, Schizachyrium scoparium and Andropogon gerardi) were grown in monoculture for 3 yr on an experimental nitrogen gradient. The species differed significantly in the levels to which they reduced soil solution (0.01 mol/L KCI extractable) nitrate and ammonium concentrations and light penetration to the soil surface. Soil nitrate concentration was an inverse function of root mass, which explained 73% of the observed variance in nitrate. Other species differences explained an additional 9.2%, and total soil N an additional 5% of this variance. Extractable soil ammonium also depended on these variables, but total soil N explained the most variance. Light penetration to the soil surface in these monocultures was a negative exponential function of aboveground biomass (R2 — 0.79). Schizachyrium and Andropogon, the species that reduce soil solution N to the lowest levels on infertile soils, had lower vegetative growth rates, higher root allocation, lower reproductive allocation, and lower tissue N than the other species. Many of these traits are associated with plants on infertile habitats, suggesting a direct link between ecophysiology, resource reduction, and distributional patterns. Because all species survived on even our most nitrogen—poor soil (subsurface sand), differential nutrient reduction, not tolerance, may be the main mechanism favoring these traits in infertile habitats. On infertile soils, the three earlier successional species (Agrostis, Agropyron, and Poa) allocated more to reproduction (rhizome or seed) than the later successional species, but did not reduce soil solution nitrate and ammonium to as low levels. This suggests that our early successional species may be superior colonists but inferior nitrogen competitors compared to the prairie bunchgrasses. Our results can be used to make explicit predictions as to the outcome of nitrogen competition among all possible combinations of these five species.

Growth of Old Field Herbs on a Nitrogen Gradient

Eight species of herbs that reach peak abundance at different times during the first 50 years of secondary succession on a nitrogen impoverished sand plain were grown at both low and high density for one and two field seasons along an experimental nitrogen gradient. The data demonstrate that intraspecific competition is strong even on extremely nitrogen poor soils. The dependence of relative growth rates (RGR), biomass per plant, yield per pot, root:shoot ratios and seed:shoot ratios on soil total nitrogen were determined. These nitrogen-dependent characteristics were compared with the known successional status of the species. Species most abundant on early successional, nitrogen poor soils tend to have higher RGRmaX, lower root:shoot ratio, higher yield per pot and higher seed:shoot ratio than late successional species of more nitrogen rich soils. This suggests that early successional species may be inferior nitrogen competitors but have faster growth rates and better colonization abilities than later successional species. This supports the hypothesis that the successional dynamics of these herbs are the transient dynamics of colonization and competitive displacement, but tends to refute the equilibrial version of the resource ratio hypothesis of succession (i.e. succession caused by changing nitrogen to light ratios). Key-words: Successional herbs, nitrogen-limited growth, root:shoot, seed:shoot, succession on a sand plain, relative growth rates, transient dynamics, successional trade-offs

Invasion of clear-cuttings by the actinorhizal plant Comptoniaperegrina

Three years after harvesting a mixed conifer–hardwood forest in Ontario, the density of sweet fern (Comptoniaperegrina (L.) Coult.) was far greater on a whole-tree harvest site (logging slash removed) than on an adjacent conventional harvest site (logging slash present). These differences were related to the degree of site disturbance, particularly forest floor removal. Nodule fixation rates also appeared to reflect the degree of disturbance, being highest in plants growing along a logging road where the sandy, nitrogen-poor mineral soil was exposed, and exceptionally low on the conventional harvest site (0.67 μmol C2H4 g dry weight−1 h−1). Overall, acetylene reduction activity showed a significant negative correlation (r = −0.77, p < 0.001) with total N.

Nitrogen‐Limited Growth in Plants from Different Successional Stages

The effect of nitrogen availability on the plant growth was studied using nine plant species, some of which are commonly found in recently abandoned old fields while others are more characteristic of native prairie. Each species was grown by itself in nine different soil mixtures in which total soil nitrogen (as N) per unit soil mass ranged from 20 to 850 mg/kg, spanning the range of total soil nitrogen observed in a chronosequence of old fields at Cedar Creek Natural History Area, Minnesota. For each species there was a significant (P < 0.5), positive correlation between the biomass attained after 12 wk of growth and the total soil nitrogen. These data allowed the species to be ranked, from those that attained the greatest biomass as seedling at low nitrogen levels to those that attained the least, as follows: Ambrosia artemisiifolia, Achillea millefolium, Chenopodium album, Agropyron repens, Agrostis scabra, Poa pratensis, Sorghastrum nutans, Schizachyrium scoparium, and Liatris aspera. There was a highly significant tendency for early successional species to grow more rapidly at low nitrogen levels and to acquire more nitrogen per plant from nitrogen—poor soils than late successional species. However, late successional species did not grow more rapidly at high nitrogen levels than early successional species. These results are consistent with the hypothesis that early successional species are dominant following old field abandonment at Cedar Creek because of their ability to compete for soil nitrogen.

Plant growth and fate of nitrogen in mixed cropping, intercropping and crop rotation. II. Nitrogen content of wheat in association with pea or broad bean.

Wheat were grown alone or in association with pea (Pisum sativum L.) or broad bean (Vicia faba L.) under several treatment conditions of nitrogen application, temperature and clipping in nitrogen-poor soil. The results are summarized as follows. 1. Without nitrogen fertilizer and with nitrogen 1 kg/10 a, top dry weight and nitrogen content of wheat in association with pea were the same as those grown alone on the 60th and the 70th day after sowing, but were remarkably larger on the 85th day when tops of the pea died and almost all the root nodules sloughed off (Figs. 1, 2, 3 and 4). With nitrogen 8 kg/10 a, however, they were less than those grown alone 60, 70 and 85 days after sowing. 2. Wheat grown in association with broad bean yielded smaller top dry weight and nitrogen than those grown alone till the 83rd day after planting at 10°, 15°, 20°and 25°C (Figs. 5 and 6). In the early stage of anthesis of broad bean 4 months after planting, the wheat at 15°, 20° and 25°C yielded more dry weight and nitrogen, being largest at 20°C where broad bean growth was most marked on the 53rd and 83rd day (Figs. 8 and 9). Four months after planting, acetylene reduction activity declined markedly and some of the root nodules sloughed off (Fig. 9). At 10°C, top dry weight and nitrogen content of wheat did not increase by association with broad bean. 3. Clipping the tops of broad bean plants in soil culture increased top dry weight and nitrogen content of associated wheat at 15°, 20° and 25°C. These increase were observed 30 days after clipping at 20° and 25°C and after 66 days at 15OC (Figs. 5 and 6). Broad bean grown in gravel culture containing no nitrogen fertilizer increased inorganic nitrogen in the culture solution after clipping their tops. The amount of nitrogen increased markedly at 20°C than at 10°C (Table 2). It is found from these results that the increase of nitrogen content of wheat by association with these two legumes is observed 3 to 4 months after sowing or planting and also that this increase is promoted by the favorable conditions for nodulation and nitrogen fixation, such as nitrogen-poor soil and appropriate temperature.

Plant growth and fate of nitrogen in mixed cropping, intercropping and crop rotation. IV Residual effect of some legumes on nitrogen content of succeeding crops.

Some legumes were examined on residual effect on nitrogen content of succeeding gramineous crops in pot culture using nitrogen-poor soil. The tested legumes were pea (Pisum sativum L.), broad bean (Vicia faba L.), alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.). After these legumes, corn and wheat were cultured successively. The results are summarized as follows. 1. Nitrogen content of tops was highest in broad bean and in red clover, medium in alfalfa and lowest in pea. Nitrogen contents of underground parts of alfalfa and red clover were higher than those of broad bean and pea (Table 1). 2. Nitrogen content of tops of the succeeding first crop, corn, was not proportional to the nitrogen contents of underground part of the preceding legumes. The corn following red clover produced the highest nitrogen yield, that following alfalfa or broad bean medium and that following pea the lowest (Fig. 1). 3. Nitrogen contents of tops of the succeeding second crop, corn, and of the third crop, wheat, were lower than that of the first corn. The nitrogen contents of these crops varied with the species of the preceding legumes. The nitrogen content after alfalfa was the highest, whereas that after red clover or pea was the lowest (Figs. 2 and 3). It is found from these results that legumes increase nitrogen contents of succeeding corn and wheat and that this increase varies with the species of the legumes. It is suggested that this variation is due not only to nitrogen content of legume residues after harvest but also to decay rate of the residues.

Die Standortamplitude der Großen Brennessel (Urtica dioica L.)—eine Auswertung vegetationskundlicher Aufnahmen auf der Grundlage der Ellenbergschen Zeigerwerte )

SUMMARY The ecological amplitude of stinging nettle ( Urtica dioica L.) was characterized on the basis of average indicator values sensu Ellenberg (1974). Based on 1132 phytosociological descriptions the following results were obtained:— Urtica dioica had a narrow amplitude for soil acidity (R-value), centered close to neutral— Nitrogen-rich sites were clearly preferred, but the habitat amplitude was greater for nitrogen supply than for soil acidity. Nitrogen-poor soils were not colonized.— Moist sites were preferred. Drier and wetter sites were colonized only after anthropogenic disturbance.— The nettles occured on both sunny and shaded sites, but their main distribution was on nitrogen-rich soils with partial shade.

BIOLOGICAL AND AGRONOMIC ASPECTS OF LEGUME INOCULATION IN ISRAEL

Inoculants prepared for farm use consist of cultures of rhizobial strains selected for their invasiveness and effectivity in greenhouse and field trials. The acetylene reduction assay, hemoglobin content of nodules and plant nitrogen content were used for evaluation of nitrogen fixation intensity. An autoclaved local enriched peat constituted a very suitable substrate for all fast-growing rhizobia, but was often toxic to slow-growing ones. This was overcome by culturing the slow-growing rhizobia together with fast-growing (non-infective), slime-producing bacteria. Chemically treated and fragile seeds, e.g. common bean or peanut, were inoculated by applying the bacterial suspension directly into the planting furrows. For soils not bearing local specific rhizobia, relatively small amounts of inoculant (100–500 g/ha) were sufficient for adequate nodulation. However, to overcome competition of native rhizobial population, it was often necessary to use greatly increased amounts of inoculant. The effect of irrigation regimes commonly used in Israel on success of inoculation, rate of nodulation, and plant vegetative and reproductive development was investigated. In nitrogen-poor soils, symbiotic nitrogen fixation could not only substitute for mineral nitrogen, but even provide higher yields than nitrogen fertilization. A high content of available soil nitrogen may lead to serious difficulties in legume inoculation practice. Ways of overcoming these difficulties were examined. In certain soils fertilization with adequate amounts of phosphorus was found to be a prerequisite for proper nodulation and symbiotic nitrogen fixation. In calcareous and alkaline soils, application of iron chelate was necessary for N 2 fixation to occur.

Response of Mustard to Nitrogen and Irrigation Under High Water Table Conditions in Hirakud Ayacut Area

Growth and development of toria mustard (Cv. Appressed mutant) grown in a nitrogen poor loamy sand high land soil in Hirakud ayacut area responded linearly upto 75 kg N/ha. Under high water table conditions fluctuating within 69-120 cm below sur. face during November to January, the response to irrigation at 25, 50 and 75% deple- tion of available moisture was not significant. Consumptive use and water requirements: were 216 and 241 mm. respectively.

Mycorrhizal Nodules and Growth of Podocarpus in Nitrogen-poor Soil

MOST genera with nodulated roots are legumes, and the nodules form after infection by nitrogen-fixing bacteria. Thirteen other genera of dicotyledons may also develop root nodules, which form only after infection, and in which nitrogen fixation has been proved or inferred, but in these the endophytes seem to be actinomycetes1,2. Among the gymnosperms, however, in Araucariaceae and Podocarpaceae, nodules develop without any stimulus from microorganisms3 although in nature they usually contain a coarse phycomycetous mycelium. This infection has been synthesized using Endogone spores4 and, like typical Endogone mycorrhizas, infected nodules sustain the growth of seedlings in phosphorus-deficient soils5. There is also a long standing belief that they fix nitrogen, supported recently by some experiments with 15 N (ref. 1). I have tested this hypothesis by attempting to grow seedlings of Podocarpus totara in a nitrogen-deficient soil.