Short-term Field Experiment Research Articles

Effect of lime or zeolite on N 2O and N 2 emissions from a pastoral soil treated with urine or nitrate-N fertilizer under field conditions

To understand the effect of soil amendments (i.e. lime or zeolite) on nitrous oxide (N 2O) and dinitrogen (N 2) emissions from pastoral soil, a field experiment was conducted using Topehaehae silt loam soil (Aeric Haplaquent) in a dairy catchment area at Toenepi, Hamilton, New Zealand during late September–November 2003. Field plots were treated with 2 N sources: cow urine or potassium nitrate (KNO 3) each applied at 200 kg N ha −1 rate with and without added lime or zeolite (clinoptilonite). The control (no N) plots also received lime or zeolite. Each treatment had 3 replicates. Nitrous oxide and N 2 emissions were measured periodically from field plots by taking intact soil cores, followed by incubating them in 1 L gas jars with or without acetylene (C 2H 2) under field conditions. Soil samples were also taken to determine soil pH and changes in soil ammonium (NH 4 +) and nitrate (NO 3 −) concentrations. Total N 2O emission was significantly higher from urine treated soils (7622 g N 2O-N ha −1) than from KNO 3 treated soil (3479 g N 2O-N ha −1) probably because of N 2O production by both nitrifier-denitrification and denitrification in the former. Zeolite significantly reduced total N 2O emissions by 11% from urine treated soils probably because of NH 4 + sorption by zeolite; while it had no such effect on N 2O emission in KNO 3 treated soils. Lime did not have any effect on N 2O emission in either urine or KNO 3 treated soils. Total N 2 emission was significantly higher from urine treated soil (1486 g N 2O-N ha −1) than from KNO 3 treated soil (795 g N 2O-N ha −1). Lime increased N 2 emissions by 11%, 6% and 101% in urine, KNO 3 treated soils and in the control, respectively; while zeolite had no such effect. N 2O:N 2 ratios were higher for urine treated soils followed by KNO 3 treated soils; while the lowest N 2O:N 2 ratios were observed in no N treatments. Lime lowered N 2O:N 2 ratios in urine treated soils and in the control treatment (no N), but had no such effect in KNO 3 treated soils. Changes in soil mineral N suggest low soil NH 4 + and reduced nitrification with zeolite in urine treated soil, while no such effect was observed in KNO 3 treated soils. Lime increased soil pH in all treatments. Lime applied with urine increased both soil NH 4 + and NO 3 − concentrations but no such trend was seen in KNO 3 treated soil. The results indicate that zeolite reduced N 2O emission while lime increased N 2 emissions and lowered N 2O:N 2 ratios during a short-term field experiment therefore long-term field studies are required to assess zeolite life cycle and its potentials as a mitigating tool for N 2O emissions from urine patches in grazed pasture system.

Factors controlling epilithon biomass in a temporary, karstic stream: the interaction between substratum and grazing

Factors affecting epilithon biomass were investigated at 3 sites along a temporary karst stream system on the Mediterranean island of Majorca. Two sites were on the mainstream axis (downstream site [T5], upstream site [T4]) and one site was in a spring-fed tributary (GB). The degree of abiotic control of periphyton biomass was examined at the 3 sites. Mean periphyton biomass during a surficial flow period (as chlorophyll a [chl a] and ash-free dry mass [AFDM]) was nearly 1 order of magnitude higher at T5 than at the other 2 sites. AFDM ranged from low values at GB to intermediate and very high levels at T4 and T5, respectively. Spatial variation in periphyton chl a was related to the coarser, and more stable, karstic substrata and higher discharge at T5 than at GB or T4. A significant proportion of the temporal variation in periphyton chl a at T4 and T5 was related to abiotic factors, but abiotic factors did not explain the temporal pattern at GB. A short-term field experiment was conducted at GB to determine the role of the dominant grazer, the glossosomatid caddisfly Agapetus quadratus, in regulating periphyton biomass. This experiment revealed that densities of A. quadratus may have controlled periphyton biomass at GB (where grazer densities were highest) because the relationship between A. quadratus density and chl a followed a negative exponential function. The grazer prevented an increase in chl a at intermediate and high densities (>4000 ind./m2), but no effect was found at lower grazer densities. Overall, the levels of calcareous deposition over substratum surfaces seemed to influence colonization by grazers, which, in turn, may have influenced periphyton accrual.

Measurement Uncertainty of Sulphur and Nitrogen Containing Inorganic Compounds By 1-Stage and 2-Stage Filter-pack Methods

The sampling and analysis properties of 1-stage and 2-stage filter-pack methods were studied in detail in monitoring of sulphur and nitrogen containing inorganic gases and particles (sulphur dioxide, sulphate, sum of nitric acid and nitrate and total ammonium). The limit of detection and the limit of quantitation for 24-h samples were estimated using the results of a short-term field experiment completed with available data from long-term monitoring and internal quality assurance. Furthermore, the combined expanded measurement uncertainty including sampling and analysis (Utot) was estimated for filter-pack methods in order to give a tool for distinguishing long-term trends in air quality from the measurement variability. Utot was found to be very near the analytical uncertainty when measuring higher air concentration levels, being ± 4.0% for sulphur concentrations > 1.0 μg m−3, ± 3.0% for sulphate concentrations > 0.5 μg m−3, ± 3.5% for the sum of nitrate and nitric acid concentrations > 0.3 μg m−3 and ± 4.5% for total ammonium concentrations > 0.8 μg m−3. At the lower air concentration range Utot increases significantly due to the field blank values. The precision of the 24-h filter-pack sample results expressed by means of modified median absolute difference (M.MAD) and coefficient of variance (CoV) gave 8.3% for sulphur dioxide and 5.4% for particulate sulphate. For the sum of gaseous nitric acid and particulate nitrate the CoV was 5.5% and for total ammonium 4.3%. In addition the suitability of the 24-h filter-pack methods in weekly sampling was proved.

Positive and negative effects of exotic Erodium cicutarium on an arid ecosystem

Many exotic species negatively affect native species and alter ecosystem function. Erodium cicutarium, an exotic annual plant, can attain high densities, but little is known about its effects on native plant communities. We first examined patterns of abundance of E. cicutarium and native annuals over a 16-year period at a long-term study site in southeastern Arizona. In years of high E. cicutarium abundance, the correlations between the abundance of E. cicutarium and native annuals in small-scale local communities were typically negative, suggesting a competitive interaction. To further examine the interaction between E cicutarium and native annuals, we conducted a short-term field experiment at the same location using plots that contained pairs of quadrats. One quadrat in each pair was subjected to E. cicutarium removal during the winter of 2003–2004 while the other served as a control. At the end of the growing season, E. cicutarium removal quadrats contained significantly higher abundance and richness of native annual plants. However, control plots contained significantly higher abundance of all annuals due to the presence of E. cicutarium. Thus, in the single growing season examined, while E. cicutarium appears to suppress the diversity and abundance of native species, its presence significantly increases community productivity.

Short-Term Impact of Clam Harvesting on Sediment Chemistry, Benthic Microbes and Meiofauna in the Goro Lagoon (Italy)

The effects of clam harvesting on sediment organic matter, bacteria, heterotrophic nanoflagellates, ciliates and meiofauna were investigated through a short-term experiment carried out in the Goro lagoon during summer 2000. Sediment samples were collected in two areas: an impacted and an undisturbed (both 25 m2), before and after (5, 24 and 48 h) clam harvesting. Immediately after sediment reworking, total organic matter content decreased for about 20%. Different organic compounds displayed different redeposition patterns resulting in the alteration of the biochemical composition of sediment organic matter. Bacterial abundance decreased significantly after clam harvesting, but microbial enzymatic activities and bacterial C production were relatively unaffected. Heterotrophic nanoflagellates displayed a positive response to sediment disturbance, whereas ciliate and meiofaunal abundance did not display any significant response. Results of this short-term field experiment suggest that clam harvesting determines a positive impact on nutritional availability of sediment organic matter, thus facilitating organic carbon transfer to higher trophic levels of the benthic microbial loop.

Spread of introduced Caulerpa species in macroalgal habitats

A short-term field experiment was designed to identify layers of Mediterranean macroalgal assemblage conducive to successful spread of two introduced Caulerpa species (Bryopsidales, Chlorophyta). By manipulation of species presence, three experimental assemblages were obtained: (1) encrusting algae, having removed the turf and erect species; (2) encrusting and turfing algae, having removed erect species; (3) encrusting, turfing and erect algae, that is, unmanipulated assemblages, which served as a control. Fragments of the two introduced species Caulerpa taxifolia (Vahl) C. Agardh and Caulerpa racemosa (Forsskål) J. Agardh were transplanted in each of the three assemblages. Width of the colony, blade density and percentage of the substratum covered by the two species were measured. The susceptibility of the indigenous community to the spread of Caulerpa species was related to type of assemblage. Blade density and amount of substratum covered by the two Caulerpa species were different between species and generally greater for C. taxifolia than for C. racemosa. Overall, the spread of these species was strongly dependent on the type but not directly on the complexity of the assemblage. Turf was more favourable than encrusting species alone, while the least advantageous habitat was where the macroalgal assemblage is composed of encrusting, turf and erect species. In other words, increased number of species in the assemblage reduces invasion of the Caulerpa species but the type of algae in the assemblage is likely to be more important than number of species. The presence of turf promotes the spread of Caulerpa species.

TERRITORIALITY IN A CANNIBALISTIC BURROWING WOLF SPIDER

Field experiments to test the hypothesis that a cannibalistic species is territorial are rare. We conducted two field experiments to test the hypothesis that adult females of the Mediterranean tarantula, Lycosa tarentula (L.) are territorial. In a relatively long-term experiment we placed a female intruder in an artificial burrow within the hypothesized territory of a resident. The intruders disappeared from their burrows at 7× the rate of spiders in a reference and two control treatments. Residency status, not relative size, determined whether the intruder or the resident remained, and evidence suggests that the winner frequently cannibalized the loser. We also conducted a short-term field experiment in which we induced encounters between females. The results were consistent with territorial defense because escalation was more likely if spiders were similar in size, and cannibalism, the outcome of one-third of the encounters, occurred only after escalation. Thus, adult females of the Mediterranean tarantula are territorial, and cannibalism may be a consequence of territorial defense.

Enhanced UV-B radiation, artificial wounding and leaf chemical defensive potential in Phlomis fruticosa L.

The combined effects of additional UV-B radiation and artificial wounding on leaf phenolics were studied in a short term field experiment with the drought semi-deciduous Mediterranean shrub Phlomis fruticosa L. The seedlings were grown under ambient or ambient plus supplemental UV-B radiation (biologically equivalent to a 15% ozone depletion over Patras, 38.3° N, 29.1° E) for 7 months before wounding. Unexpectedly, supplemental UV-B radiation decreased leaf phenolics. Subsequently, wounding was effected by removing leaf discs from some of the plants, while the rest remained intact and served as controls. Wounding significantly increased phenolics of the wounded leaves and the increase was more pronounced under supplemental UV-B radiation. In addition, wounding had a significant positive effect on the phenolics of the opposite, intact leaf, but only under additional UV-B radiation. We conclude that UV-B radiation, wounding and their combination may affect the chemical defensive potential of Phlomis fruticosa. In addition, increased levels of phenolics after herbivore attack under field conditions may afford extra protection against enhanced UV-B radiation levels.

Soil carbon dynamics of conventional tillage and no-till agroecosystems at Georgia Piedmont — HSB-C models

This model was designed to simulate the dynamics of soil organic matter (SOM) and biomass change of detritus soil food webs after the application of crop residue in agroecosystems. Background data and literature parameters were used to initialize the model and a short-term field experiment was conducted to calibrate the model. Our model is a synthesis and integration of many others’ previous studies because many others’ ideas on food web or SOM modeling were incorporated into our model. In our model, soil microorganisms were considered to be the major decomposers of organic matter with soil animals playing an important role in decomposing organic matter by controlling the population of soil microorganisms through trophic interactions. Though we did not model the soil food web into species or functional groups, we attempted to represent the hierarchical structure and trophic interactions of soil food webs as complete as possible. The whole soil food web was conceptualized as a ‘super organism’ to process organic matter in the model diagram. State variables of our model were categorized into soil organic matter pools, inorganic carbon pool, and soil organism pools. Flows were modeled based on first order kinetics. A tillage effect was introduced in our model by assuming that soil microorganisms, microarthropods and earthworms decrease temporarily immediately after the tillage operation. We also introduced a ‘minimum population’ protection mechanism for each group of soil organisms by assuming that predation ceases when energy obtained can not offset the energy expended in prey-searching and feeding. We found that the simulation outputs fitted the measured data very well, the simulation outputs were in the range of field measurements in most cases. However, there was a significant discrepancy in respiration between simulation output and field measurement in both conventional tillage (CT) and no-till (NT), particularly in NT agroecosystems. We hypothesized that plant roots should be responsible for this discrepancy. The sensitivity analysis of our model showed that the population of soil microorganisms was controlled by resources rather than predators. However, the populations of soil protozoa, nematodes and microarthropods were controlled by both resources and predators.

The Response of Several Citrus Genotypes to High-salinity Irrigation Water

The effect of irrigation with saline water on several citrus genotypes was evaluated in a short-term field experiment. Salinity levels ranged from 2.0 to 6.4 dS·m–1. Comparatively salt-tolerant Citrus species and Citrus × Poncirus hybrids were tested for their possible use as rootstocks for commercial citrus cultivars irrigated with brackish water. All the tested genotypes survived the highest salinities. At all salinity levels, the best chloride excluder was Cleopatra mandarin (Citrus reshni Hort. ex Tan.), and the worst was sour orange (C. aurantium L.). Gou Tou Cheng (C. aurantium hybrid?) and Rangpur (C. limonia Osb.) × Troyer citrange (C. sinensis L. × Poncirus trifoliata L.) RT803 were found to be promising genotypes for further evaluation as rootstocks tolerant to high salinities. Rangpur was unsuitable because of foot rot.

Predator-prey interactions in a benthic stream community: a field test of flow-mediated refuges.

Ecological theory suggests that the impact of predation can be strongly modified by the existence of regions of the environment in which prey are less accessible to predators, which underscores the need for empirical studies examining the factors influencing the availability and importance of such prey refuges. Our study tested whether benthic microhabitats with high flows provide suspension-feeding larval black flies (Simulium␣vittatum) with a spatial refuge in which the negative impact of predatory flatworms (Dugesia dorotocephala) is reduced. We conducted a short-term field experiment in Chester Creek (southeastern Pennsylvania, United States) to examine how the number of black fly larvae inhabiting tile substrates responded to manipulated variations in flatworm abundance and current speed. The abundance of flatworms declined with increasing current speed, thereby creating the potential for sites with high flows to provide larvae with a refuge from these predators. Multiple regression analysis revealed that the final abundance of larvae exhibited a significant negative relationship to flatworm abundance and a significant positive relationship to current speed. After adjusting for variations in elapsed time and initial larval abundance, flow and predators explained 38% of the variation in the rate of change in larval abundance. The positive correlation between larval abundance and flow had two components: a positive, direct effect of flow on larvae, which arises because these food-limited consumers prefer to reside within sites with faster flows where they can feed at higher rates; and a negative effect of flow on predators, and of predators on larvae, which combine to yield a positive indirect effect of flow on larvae. This indirect effect demonstrates the existence of flow-mediated refuges (i.e., microhabitats in which the impact of predation is reduced due to high flows), although the effect accounts for a small proportion of total variation in larval abundance. A consideration of biomechanical relationships suggests that microhabitats with high flows are likely to create prey refuges in a wide range of freshwater and marine benthic environments. In particular, predators will often experience greater dislodgement forces than prey because of their larger size and because they project farther above the bed where current speeds are faster. Moreover, the ability to resist a given dislodgement force may be greater for many prey, especially those that are sessile or semi- sessile.

Boron retention in limed forest mor

Boron (B) retention was studied in the mor humus of podzolic soil from boreal Norway spruce (Picea abies (L.) Karst.) forests. In a long-term liming experiment, ground limestone had been applied 30 years earlier and again 12 years before sampling. Additionally a short-term field experiment was done to separate the effect of increased pH from calcium (Ca) addition. In the short-term experiment the treatments were control and two doses of CaCO 3, CaSO 4 and sodium + potassium (Na + K) carbonate mixture. These treatments were applied in the year before sampling. The B retention data conformed to a Freundlich model better than to a Langmuir model. Considerable B adsorption occurred, probably mostly due to the large organic matter content of mor. Liming significantly increased the quantity of adsorbed B in both experiments. Incubation with added B for 8 weeks considerably increased B retention and reduced the difference between limed and unlimed soil. CaSO 4 had no effect on B retention characteristics, whereas Na + K treatment caused changes similar to those of lime. Therefore Ca probably has little influence on B adsorption in this pH range (3.0–5.9).

Abiotic factors regulating nitrification in a Swedish arable soil

The effects of temperature, water potential and ammonium concentrations were studied in field and laboratory experiments on arable soil. The two field experiments used different sampling intervals, one at daily (short-term) and the other at monthly (long-term) intervals. In the short-term field experiment, the numbers and activities of nitrifiers were assessed before and after natural rain or irrigation. The nitrifiers were apparently outcompeted by heterotrophs during the first days after wetting the soil. Potential nitrification was affected only slightly by changes in water potential, whereas the numbers of ammonium and nitrite oxidizers appeared more sensitive to these changes. The numbers of ammonium and nitrite oxidizers correlated strongly during the daily samplings. The potential nitrite-oxidation rates correlated with water potentials whereas the potential ammonium oxidation rates did not. Extractable ammonium decreased in proportion to increasing nitrate concentrations in both the rain-fed and the irrigated plots. In the long-term field experiments, the numbers of ammonium oxidizers correlated with water potentials but not with in situ temperature or with ammonium concentrations. The potential ammonium-oxidation rates correlated with water potentials and with ammonium-oxidizer numbers. The potential nitrite-oxidation rates correlated strongly with the potential ammonium-oxidation rates. The field experiments implied that nitrite oxidizers obtained substrate from ammonium oxidizers but also from nitrate reduction. In laboratory experiments nitrate accumulated at a Q 10 of about 2 and the V max for nitrification was observed at a water potential of −0.11 MPa (65% of water-holding capacity). The K m for ammonium oxidation at pH 8.2 was 1.72 mg l−1 soil water.

Effect of nutrient enrichment on growth of the eelgrass Zostera marina in the Chesapeake Bay, Virginia, USA

The addition of two commerical fertilizers, one 5% NH4NO3, 10% P2O5, 10% K2O, and the other 10% NH4NO3, 10% P2O5, 10% K2O, ahd a dramatic effect on the growth of Zostera marina in the Chesapeake Bay. There was a significant increase in the length, biomass and total number of turions of fertilized plots compared with controls during a 2 to 3 month period. Data from this short-term field experiment suggest that Z. marina beds in the Chesapeake Bay are nutrient-limited, that the grwoth form of Z. marina may be related to the sediment nutrient supply, and that Z. marina may competitively exclude Ruppia maritima by light-shading.