Factors controlling postfire seedling establishment in southern California chaparral

Summary This paper discusses the interactions among prefire shrub abundance, soil moisture, and plant and animal species on postfire seedling establishment in mixed chparral in southern California. Postfire germination and survival of seedlings in a stand dominated by a facultative seeder (Adenostoma fasciculatum) and by an obligate seeder (Ceanothus greggii) were monitored for 2 years. Relative to prefire abundance, germination of C. greggii was higher than that of A. fasciculatum. Survival during the first year was also higher in C. greggii than in A. fasciculatum. During the second year, however, mortality of C. greggii was greater than that of A. fasciculatum, mostly due to a psyllid infection. Germination of A. fasciculatum was negatively related to prefire shrub abundance. C. greggii germination was not associated with prefire shrub abundance. Seedling mortality of both species was very strongly related to the depletion of soil moisture the first few months after germination. A. fasciculatum was more sensitive than C. greggii to the drying of the soil, especially in the upper levels. C. greggii seedlings had longer roots, greater root/shoot biomass ratios, higher water potentials, and a later peak in seasonal growth activity compared to A. fasciculatum. Herbs promoted greater survival of A. fasciculatum. Our results indicate that the obligate seeder species, C. greggii, is better adapted to establish seedling in chaparral by producing greater relative germination and greater seedling survival than the facultative seeder species A. fasciculatum. The greater adaptability of C. greggii to the physical environment is counteracted by interspecific interference by plant and animal interactions which tend to favor A. fasciculatum over C. greggii.     

The influence of dominant shrubs,fire, and time since fire on soil seed banks in mixed chaparral

The composition and density of soil seed banks beneath co-occurring Adenostoma fasciculatum and Ceanothus greggii shrubs from three chaparral stands last burned 9, 35 and 85 years before 1986 were investigated. The overall density of seeds in the soil, as estimated by germinations under greenhouse conditions, increased with time since fire (ca. 8000 to 25000/m²). However, this increase was due entirely to the accumulation of A. fasciculatum seed in the soil (ca. 2000 to 21000/m²). In contrast, the density of C. greggii seed was different in each of the three stands, but was not correlated with time since fire: maximum densities were recorded from the 35 year old stand (ca. 2000/m²).A total of 31 taxa germinated and 17 occurred in sufficient numbers to be analyzed statistically. Germinable seed densities of three herb species were not influenced by soil source (beneath A. fasciculatum or C. greggii), time since fire, or the direct effects of a controlled fire treatment. Germinable seed densities of a further nine species were significantly influenced by the elapsed time since stands last burned. The densities of four decreased and five increased. Four of the species that increased in seed density over the three stands were annuals, suggesting that the chaparral sub-canopy habitat is not as unfavorable for annuals as is often assumed. The fire treatment decreased germinable seed densities of four annual species by 40–70%, but increased the germinable seed densities of the shrubs A. fasciculatum and C. greggii, and the annual Phacelia brachyloba. Our results indicate that seeds of A. fasciculatum will increase in the soil bank for at least 85 years after fire in chaparral where it is dominant. In contrast, seed reserves of C. greggii appear to be influenced primarily by site-specific patterns of seed production and by the intensity of post-dispersal seed predation.     

A NEW NITROGEN-FIXING NON-LEGUME: CHAMAEBATIA FOLIOLOSA (ROSACEAE)

Specimens of Chamaebatia foliolosa Benth. with nodule structures on their roots fix atmospheric nitrogen. The nodules are similar to those of other non-legumes in gross morphology and structure, containing hyphal strands, some with club-shaped vesicles at their ends. A fixation rate of 130 nmoles N₂ per g fresh weight per hr is reported by using ¹⁵N₂ as a tracer. Equivalent rates of acetylene reduction were observed.     

Nodule growth and nitrogen fixation of <Emphasis Type="Italic">Calopogonium mucunoides</Emphasis> L. show low sensitivity to nitrate

It is well established that nitrate is a potent inhibitor of nodulation and nitrogen fixation in legumes. The objective of this study was to demonstrate the relative insensitivity of these processes to nitrate with Calopogonium mucunoides, a tropical South American perennial legume, native to the cerrado (savannah) region. It was found that nodule number was reduced by about half in the presence of high levels of nitrate (15 mM) but nodule growth (total nodule mass per plant) and nitrogen fixation (acetylene reduction activity and xylem sap ureide levels) were not affected. Other sources of N (ammonium and urea) were also without effect at these concentrations. At even higher concentrations (30 mM), nitrate did promote significant inhibition (ca. 50%) of acetylene reduction activity, but no significant reduction in xylem sap ureides was found. The extraordinary insensitivity of nodulation and N₂ fixation of C. mucunoides to nitrate suggests that this species should be useful in studies aimed at elucidating the mechanisms of nitrate inhibition of these processes.     

N2 fixation by Acacia species increases under elevated atmospheric CO2

In the present study the effect of elevated CO₂ on growth and nitrogen fixation of seven Australian Acacia species was investigated. Two species from semi‐arid environments in central Australia (Acacia aneura and A. tetragonophylla) and five species from temperate south‐eastern Australia (Acacia irrorata, A. mearnsii, A. dealbata, A. implexa and A. melanoxylon) were grown for up to 148 d in controlled greenhouse conditions at either ambient (350 µmol mol^?1) or elevated (700 µmol mol^?1) CO₂ concentrations. After establishment of nodules, the plants were completely dependent on symbiotic nitrogen fixation. Six out of seven species had greater relative growth rates and lower whole plant nitrogen concentrations under elevated versus normal CO₂. Enhanced growth resulted in an increase in the amount of nitrogen fixed symbiotically for five of the species. In general, this was the consequence of lower whole‐plant nitrogen concentrations, which equate to a larger plant and greater nodule mass for a given amount of nitrogen. Since the average amount of nitrogen fixed per unit nodule mass was unaltered by atmospheric CO₂, more nitrogen could be fixed for a given amount of plant nitrogen. For three of the species, elevated CO₂ increased the rate of nitrogen fixation per unit nodule mass and time, but this was completely offset by a reduction in nodule mass per unit plant mass.     

Biological Nitrogen Fixation is not a Major Contributor to the Nitrogen Demand of a Commercially Grown South African Sugarcane Cultivar

It has previously been reported that endophytic diazotrophic bacteria contribute significantly to the nitrogen budgets of some graminaceous species. In this study the contribution of biological nitrogen fixation to the N-budget of a South African sugarcane cultivar was evaluated using ¹⁵N natural abundance, acetylene reduction and ¹⁵N incorporation. Plants were also screened for the presence of endophytic diazotrophic bacteria using acetylene reduction and nifH-gene targeted PCR with the pure bacterial strains. ¹⁵N natural abundance studies on field-grown sugarcane indicated that the plants did not rely extensively on biological nitrogen fixation. Furthermore, no evidence was found for significant N₂-fixation or nitrogenase activity in field-grown or glasshouse-grown plants using ¹⁵N incorporation measurements and acetylene reduction assays. Seven endophytic bacterial strains were isolated from glasshouse-grown and field-grown plants and cultured on N-free medium. The diazotrophic character of these seven strains could not be confirmed using acetylene reduction and PCR screening for nifH. Thus, although biological nitrogen fixation may occur in South African sugarcane varieties, the contribution of this N-source in the tested cultivar was not significant.     

Non‐symbiotic nitrogen fixation during leaf litter decomposition in an old‐growth temperate rain forest of Chiloé Island,southern Chile: Effects of single versus mixed species litter

Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old‐growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy‐rich substrate that favours the occurrence of this energy demanding process. Following the niche ‘complementarity hypothesis’, we expected that decomposing leaf litter of a single tree species would support lower rates of non‐symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50–79) in an old‐growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova , Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h^?1 g^?1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h^?1 g^?1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h^?1 g^?1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h^?1g^?1). We interpret these results as follows: in N‐poor litter and high lignin content of leaves (e.g. N. nitida) free‐living N fixers would be at competitive advantage over non‐fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization.     

The effects of soybean cultivar,rhizobium strain and nitrate on plant growth,nodule mass and acetylene reduction rate

Summary The effects of twelve strains ofBradyrhizobium japonicum and ten cultivars of soybean (Glycine max (L.) Merr.) on plant and nodule weights, and acetylene reduction rates (33 to 41 days) were measured in the presence and absence of 6mM nitrate. No interactions between strains and cultivars were observed. Strain by nitrate interactions were found for plant and nodule weights, and acetylene reduction rates per gram of nodule. Cultivar by nitrate interactions were found for nodule weights, acetylene reduction rates per plant and per gram of nodule. Blackhawk with all strains, and all cultivars with strains 110 and CB 1809, seemed to be able to grow as well in the absence of nitrate (utilizing nodule fixation) as in its presence. The problems of identifying strains and cultivars with especially good nitrogen fixing ability in the presence of nitrate are discussed.     

Comparative field water relations of four co-occurring chaparral shrub species

Summary The seasonal course of water relations was measured in the field in Adenostoma fasciculatum, Quercus dumosa, Ceanothus greggii, and Arctostaphylos glauca, four prominent members of the southern California chaparral vegetation. Ceanothus greggii and A. glauca developed similar seasonal patterns of minimum leaf water potentials, as estimated by xylem pressure measurements, which were much less negative than A. fasciculatum and Q. dumosa growing in close proximity on the same pole-facing slope site. Adenostoma fasciculatum on an adjacent equator-facing slope developed more negative water potentials than did A. fasciculatum on the pole-facing slope.Leaf conductance differed between species, and by leaf age class and slope exposure within a species. The greatest differences were measured between leaf age classes in A. fasciculatum on the pole-facing slope, with new leaves showing the greatest conductances early in the season. The same trend was measured in A. fasciculatum on the equator-facing slope, but the differences were less between leaf age classes and diminished earlier in the season than in A. fasciculatum on the pole-facing slope. The analysis of daily hysteresis in the leaf conductance-water potential relation suggests that early in the season when water is available, stomatal behavior is simultaneously governed by a complex of environmental factors, while late in the season stomatal behavior becomes increasingly dominated by tissue water status.     

Diurnal and seasonal patterns of nitrogen fixation in analnus hirsuta plantation of central Korea

We used an acetylene reduction assay to measure rates of nitrogen fixation on a 38-year-oldAlnus hirsuta plantation in central Korea. The diurnal pattern of acetylene reduction changed significantly during May, August, and October, typically varying by 3-fold throughout the course of the day. Maximum rates occurred at 3 p.m. in May and October, but at 6 p.m. in August. Increasing trends were evident during the early growing season, with sustained high rates from mid-May through late September; July had the highest rates, averaging 7.2 μmole g^-1 dry nodule h^-1. The average nodule biomass for this plantation was 220 kg ha ’. Rates of acetylene reduction were related to soil temperature, but not to soil moisture content. Combining these nodule biomass calculations with seasonal average acetylene reduction rates yielded an estimate of current annual nitrogen fixation of 60 kg N ha^-1 for the plantation. This rate of annual nitrogen addition was very large in relation to the yearly nitrogen requirements of coniferous and deciduous forests in central Korea.     

Interaction of nitrate uptake and nitrogen fixation in faba beans

An experiment was carried out to determine the relationship between nitrate uptake and nitrogen fixation of faba beans. Therefore inoculated and uninoculated faba beans were grown in nutrient solution with different nitrate concentrations. Nitrate uptake was measured every two days during the growing period. At the end of the experiment the nitrate uptake kinetics were determined with a short time depletion technique and nitrogen fixation was measured with the acetylene reduction method. A limitation of nitrate uptake due to nitrogen fixation was relatively small. Nitrate concentrations of approximately 1 mol m^–3 and 5 mol m^–3 decreased nitrogen fixation to values of 16% and 1% of the control plants which received no nitrate nitrogen. A reduction of nitrogen fixation was mainly due to a decrease of specific nitrogen fixation per unit nodule weight and to a lesser extent due to a reduction of nodule growth. Only the maximum nitrate influx (I_max) seemed to be influenced by nitrogen fixation. Michaelis-Menten constants (K_m) and minimum NO _inf3 ^– -concentrations (C_min) were not significantly influenced by nitrogen fixation.     

Differences between Bradyrhizobium strains NC92 and TAL1000 in their nodulation and nitrogen fixation with peanut in iron deficient soil

The effects of Bradyrhizobium (strains NC92 and TAL1000) and Fe supply on nodulation and nitrogen fixation of two peanut (Arachis hypogaea L.) cultivars (cv. Tainan 9 (Fe inefficient) and cv. 71-234 (Fe efficient)) grown under Fe deficient conditions (imposed by adding 40% CaCO₃ to a ferruginous soil) were examined in a glasshouse experiment. When inoculated with TAL1000 without Fe, both cultivars had low shoot N concentration, very low nodule numbers and weight and no measurable acetylene reduction activity per plant. Inoculation with NC92 without Fe increased all these parameters substantially; addition of Fe with NC92 had no further effect on N concentration but doubled nodule number, weight and acetylene reduction activity per plant. Addition of Fe with TAL1000 increased all parameters to the same level as Fe+NC92, indicating that the poorer nodulation and N₂ fixation of TAL1000 in the absence of Fe, resulted from a poorer ability in getting its Fe supply from the alkaline soil. The nodules from all treatments with measurable activity had the same specific acetylene reduction activity suggesting that Fe deficiency limited nodule development.The results support previous suggestions that Bradyrhizobium strains differ greatly in their ability to obtain Fe from soils and that selection of Fe efficient strains could complement plant breeding in the selection of legume crops for Fe deficient soils.     

Environmental and genetic control of crassulacean acid metabolism in two crassulacean species and an F1 hybrid with differing biomass δ13C values

Abstract The growth, biomass δ¹³C values, and ability to accumulate titratable acidity at night were compared in eight environmental treatments for Cremnophila linguifolia, Sedum greggii, and their F₁ hybrid. In the phytotron, differences in treatment daylength, day/night temperature and water availability were all found to have effects on total plant dry weight, nocturnal accumulation of titratable acidity and biomass δ¹³C value of at least some of the genotypes. However, there were differences between the genotypes both in the magnitude and direction of response of the phenotypic properties to the treatment variables. The phytotron δ¹³C values ranged from -12.9 to -19.2‰ for C. linguifolia, from -22.2 to -33.4‰ for S. greggii, and from -19.2 to -24.9‰ for the hybrid. After with-holding water for 76 h both C. linguifolia and the hybrid had midday Ψ_leaf values of -0.23 MPa; however, S. greggii had a value of -1.05 MPa. In contrast to past observations of other species, the daily watered plants of C. linguifolia had less negative δ¹³C values than did the plants watered only weekly.     

Nitrogen cycling in an Antarctic ecosystem 2. Estimation of the amount of nitrogen fixation in a moss community on East Ongul Island

Nitrogen fixation by cyanobacteria in a moss community on East Ongul Island (69°00'S 39°35'E), Antarctica was investigated using the acetylene reduction method. The mean acetylene reduction rate at 10°C and 200 μE·m⁻²·s⁻¹ photosynthetically active radiation was 7.12 nmol C₂H₄ per square centimeter of moss community per hour. The effects of temperature, radiation, desiccation and rehydration on the acetylene reduction rates were examined. A simple predictive model was constructed in order to estimate the amount of nitrogen fixed in the field. Using this model, the daily amount of nitrogen fixation was calculated from microclimatic data (temperature and radiation) measured in the experimental field at Syowa Station on East Ongul Island between 1983 and 1984. The cumulative amount of nitrogen fixation in the growing season during this period was estimated to be 329 mg N per square meter of moss community. It is suggested that nitrogen fixation by cyanobacteria in the moss community is important as a nitrogen source for the community growth on East Ongul Island.     

Control of Nutrient Solution pH with an Ion Exchange System: Effect on Soybean Nodulation

Growth and nodulation response of soybean (Glycine max (L.) Merr.) to various single nitrogen sources in solution culture is confounded by unequal shifts in solution pH. A recirculating ion exchange system was designed in which a cation exchange resin (Amberlite IRC 50) was used to control the pH of solutions in which soybeans were grown. Nutrient solution pH levels were established at range extremes of 9.0 to 3.7 with 100% Ca²⁺ or H⁺ forms of resin, respectively. Intermediate pH levels were established by varying the ratio of Ca²⁺ to H⁺ forms of resin. The system is capable of maintaining pH within 0.5 to 0.9 units of the initial pH over a two-week growth period of soybeans with either nitrate- or urea-N sources. In the absence of the resin column, pH of the urea nutrient solution rapidly declined to less than pH 4 which resulted in depressed plant nodule development. The optimum pH range for nodule mass and N₂ fixation (measured by acetylene reduction) was between 5.2 and 7.0 with urea nutrition. Both nitrate- and ammonium-N sources were inhibitory to acetylene reduction in comparison with urea which allowed extensive nodule development and activity.     

Differential survival of chaparral seedlings during the first summer drought after wildfire

Summary Big Pod Ceanothus (Ceanothus megacarpus) is an obligate seeder after fire; Laurel Sumac (Rhus laurina) is primarily a resprouter after fire. Both species commonly occur together in mixed stands and are dominant members of the coastal chaparral of southern California. We compared the mean survival of post-fire seedlings of each species during the first summer drought after fire and found C. megacarpus to have a mean survival of 54% while R. laurina had a mean survival of only 0.1%. Rooting dephs were similar between species but predawn water potentials and leaf temperatures were higher for R. laurina seedlings. Leaf temperatures for R. laurina reached a mean value of 46.8° C on hot, summer days, about 5° C higher than seedlings of C. megacarpus. By the end of the first growing season, 92% of all C. megacarpus seedlings had suffered herbivory compared to only 17% of all R. laurina seedlings. Herbivory did not appear to be the immediate cause of seedling mortality. Transect data indicated that full recovery of prefire species composition and density at our study site was likely but the mode of recovery was different for the species examined. R. laurina recovered primarily by sprouting, C. megacarpus totally by seedling establishment and a third species, Adenostoma fasciculatum (chamise), by a combination of sprouting and seedling establishment. We attribute the higher mortality of R. laurina seedlings to the greater sensitivity of its tissue to water stress. It may be that differential survival of shrub seedlings and differential modes of reestablishment after fire play an important role in maintaining species diversity in the chaparral communities of coastal, southern California.     

Decadal-scale Dynamics of Water, Carbon and Nitrogen in a California Chaparral Ecosystem: DAYCENT Modeling Results

The Mediterranean climate, with its characteristic of dry summers and wet winters, influences the hydrologic and microbial processes that control carbon (C) and nitrogen (N) biogeochemical processes in chaparral ecosystems. These biogeochemical processes in turn determine N cycling under chronic N deposition. In order to examine connections between climate and N dynamics, we quantified decadal-scale water, C and N states and fluxes at annual, monthly and daily time steps for a California chaparral ecosystem in the Sierra Nevada using the DAYCENT model. The daily output simulations of net mineralization, stream flow and stream nitrate (NO₃⁻) export were developed for DAYCENT in order to simulate the N dynamics most appropriate for the abrupt rewetting events characteristic of Mediterranean chaparral ecosystems. Overall, the magnitude of annual modeled net N mineralization, soil and plant biomass C and N, nitrate export and gaseous N emission agreed with those of observations. Gaseous N emission was a major N loss pathway in chaparral ecosystems, in which nitric oxide (NO) is the dominant species. The modeled C and N fluxes of net primary production (NPP), N uptake and N mineralization, NO₃⁻ export and gaseous N emission showed both high inter-annual and intra-annual variability. Our simulations also showed dramatic fire effects on NPP, N uptake, N mineralization and gaseous N emission for three years of postfire. The decease in simulated soil organic C and N storages was not dramatic, but lasted a longer time. For the seasonal pattern, the predicted C and N fluxes were greatest during December to March, and lowest in the summer. The model predictions suggested that an increase in the N deposition rate would increase N losses through gaseous N emission and stream N export in the chaparral ecosystems of the Sierra Nevada due to changes in N saturation status. The model predictions could not capture stream NO₃⁻ export during most rewetting events suggesting that a dry-rewetting mechanism representing the increase in N mineralization following soil wetting needs to be incorporated into biogeochemical models of semi-arid ecosystems.     

Ecological aspects of nitrogen fixation by Purshia tridentata

Summary This study examines several aspects of nitrogen fixation by Purshia tridentata (Pursh) D.C., a rosaceous shrub widespread in the Central Oregon pumice region, especially as an understory species in Pinus ponderosa and Pinus contorta forests. Acetylene reduction was used to assay nodule activity in both field and greenhouse plants. The maximum rates were observed at 20°C, although summer soil temperatures were frequently around 15°C, at which a much lower rate was observed. Acetylene reduction by excised nodules was linear for 5 h and then slowly declined, finally ceasing after 19 h. Nodule activity declined in water stressed plants, essentially ceasing in plants with xylem pressure potentials below –25 bars.Field studies at five sites revealed that nodule activity began in mid-May or early June when soil temperature at 20 cm increased to above 10°C. Activity began later and remained lower until July 20 in plants located under Pinus contorta, probably because of the cooler temperatures at this site. Nodule activity at all sites was maximum in June and July. In late July, nodule activity declined sharply, corresponding with moisture stress readings in the –25 bar range. Acetylene reduction rates declined sharply during the night; this decline was even more severe late in the season.Only 46 per cent of Purshia plants were nodulated. Several possible explanations for this low nodulation are discussed, but the primary reasons appear to be low soil temperature and unfavorable moisture conditions. Previous speculations that Purshia may contribute significant amounts of nitrogen to the ecosystems in which it occurs are disputed using estimates based on seasonal acetylene reduction rates and a determination of nodule biomass at one site. The estimated nitrogen accretion rate was only 0.057 kg N/ha.yr. re]19760310     

Occurrence and activity of hydrogenase in symbiotic Frankia from field-collected Alnus incana

Occurrence and activity of the hydrogen uptake enzyme were studied in root nodule homogenates made from plants of Alnus incana (L.) Moench collected from field sites in the northern part of Sweden. Nitrogenase (EC 1.7.99.2) activity (estimated by acetylene reduction) and hydrogen evolution were studied in excised nodules. All Frankia sources showed acetylene reduction activity, and possessed a hydrogen uptake system. Hydrogen uptake in nodule homogenates from the Frankia sources measured at 23.8 μM H₂ ranged from 0.04 to 5.0 μmol H₂ (g fresh weight nodule)⁻¹ h⁻¹. The H₂ uptake capacity of nodule homogenates from one of the Frankia sources was almost 8 times higher than the hydrogen evolution from nitrogenase, both expressed on a nodule fresh weight basis. Frankia sources from field sites 6 and 11 showed K_m for H₂ of 13.0 and 23.6 μM H₂, respectively. This indicates similarities in the hydrogen uptake enzymes in the two Frankia sources. It is concluded that hydrogen uptake is a common characteristic in Frankia.     

Influence of lime on nitrogen fixation by tropical and temperate legumes

Summary A nitrogen deficient Oxisol which had been fertilized with P, K, Zn and Mo received CaCO₃ at rates which increased continuously from zero to 22 tons/ha. Liming produced a range of pH in the saturation paste from 4.7 to 7.1; a range of calcium in the saturation extract from 0.3 to 3 meq/l; and a significant decline in available manganese. Responses of 9 tropical and 7 temperate legumes were compared across the pH variable.For Stylosanthes spp. nodule numbers and weight and plant yield declined above pH 5.5. Arachis hypogaea and Vigna sinensis, whose yield increased by only 30%, showed no clear improvement in nodulation or nodule effectiveness (acetylene reduction rate per unit nodule weight).Increased nodule effectiveness could account for most of the growth increase in Dolichos axillaris and Glycine max var. Kahala. Both the number and effectiveness of nodules increased for Desmodium intortum, Glycine wightii, Medicago sativa, and Trifolium subterraneum. Nodule size and effectiveness increased for G. max var. Kanrich. Only in one species, Coronilla varia, could increase in nodule numbers alone account for the increased growth associated with liming, although increased numbers of nodules probably accounted for much of the response by Lotus corniculatus, and by Desmodium canum and D. intortum up to pH 5.3.Increased nodulation and plant N contents were consistent with the conclusion that for most species improved N₂-fixation was the cause of growth improvement associated with liming. However, percent N was high in leaves of Vigna and Phaseolus vulgaris at all lime levels. In Phaseolus, variation in nodulation and growth were unrelated. The growth improvement was associated with decline in leaf N, suggesting that something other than N nutrition was limiting.Journal Series No. 1957 of the Hawaii Agricultural Experiment Station.Department of Soils and Plant Nutrition, University of California, Davis.Department of Agronomy and Soil Science, University of Hawaii, Honolulu, Hawaii.