Nutrient cycling by the subterranean termite Gnathamitermes tubiformans in a Chihuahuan desert ecosystem

Summary We estimated the density of subterranean termites Gnathamitermes tubiformans at 800,000 · ha^-1 for a standing crop biomass of 2 kg · ha^-1 Predation losses were estimated to be 5,73 kg · ha^-1 · yr^-1 representing the major release of nutrients from termites to surficial soil layers. Nutrient fluxes from termites to predators amounted to 410g N·ha^-1·yr^-1, 33 g S · ha^-1 · yr^-1 and 19 g P · ha^-1 · yr^-1. These fluxes account for 8% of the litter N, 1.5% of the litter P and 2.9% of the litter S. The termites fixed an estimated 66 g · ha^-1 · yr^-1 atmospheric N and returned an estimated 100 g · ha^-1 · yr^-1 in the surface gallery carton. Since losses of elements from subterannean termites were greater than standing crops, we estimated an annual turnover of N at 3.5 times per year, P of 2.5 times per year, and S of 2.5 per times per year.Since surface foraging, predation and alate flights are pulse regulated by rainfall, nutrient flows through subterranean termites are episodic and releases of nutrients accumulated in termite biomass preceeds or is coincident with productivity pulses of some shallow rooted plants. We propose that subterranean termites are important as regulators in desert nutrient cycles.     

Interference competition in desert subterranean termites

We examined interspecific aggression between two subterranean termite species, Heterotermes aureus (Snyder) (Rhinotermitidae) and Gnathamitermes perplexus (Banks) (Termitidae). In laboratory tests with worker termites, neither species was the inherently superior fighter, but rather the outcome of interspecific encounters depended on the number of conspecifics. We then investigated patterns of resource use by these species during a 13-month period in the Sonoran Desert. Baits consisted of toilet-paper rolls, which have been shown to be a mutually acceptable food source. Analyses of foraging activity demonstrated that the two species did not forage independently of each other. Not only were the two species negatively associated spatially, but extended periods of temporal segregation were observed. G. perplexus took significantly longer to return to sites that it had simultaneously occupied with H. aureus than to sites that G. perplexus had occupied alone. The pattern of co-occurrence of these two species is consistent with the hypothesis that interspecific interference competition affects their spatial and temporal distribution.     

Ecological organization of a Chihuahuan desert lizard community

Summary Niche relationships among 11 diurnal lizard species were studied for 3 years. The community appeared to be subdivided spatially into different subsets of only four to six species. Coexisting species of each subgroup were separated further by differential utilization of microhabitats. In late spring and early summer, when food shortage is likely, dietary overlaps between syntopic species were generally low but increased broadly after the rains, when food became plentiful. Because of the high similarity in prey-size utilization among large and medium species, effects of prey selection according to size were generally slight except for very different-sized species. Overlap in the three-dimensional resource space was high between Cnemidophorus scalaris and C. tigris, but close observation of the ecology of the two populations showed many small differences between them. We suggest that the very diversified ecological opportunism of C. scalaris allows it to coexist with C. tigris in a very heterogeneous ecosystem. Several hypotheses are discussed to explain the ecological determinism of resource partitioning within such a community.     

Decomposition of roots in a Chihuahuan Desert ecosystem

Summary Mass losses of tethered buried roots of two woody shrubs and two herbaceous annuals buried in plots irrigated at 25 mm·month^-1, 6 mm·week^-1 and no irrigation were measured. At the end of 1 year, 10–15% of the mass of the herbaceous annual roots remained and 60% of the mass of woody shrub roots remained. There were no differences in mass loss attributable to added water. Rates of mass losses of roots in the Chihuahuan Desert were equal to or higher than those reported from mesic ecosystems. Roots of woody shrubs had relatively constant C:N ratios through the experiment. There was significant N immobilization in Baileya multiradiata roots. Percent mass loss of grass roots, Erioneuron pulchellum, and herbaceous annual roots, B. multiradiata, in plots with termites was 62% and in plots without termites was 15%. These data suggest that subterranean termites are responsible for most of the mass loss and mineralization of carbon and nitrogen in dead grass and herbaceous roots in the northern Chihuahuan Desert.     

When subterranean termites challenge the rules of fungal epizootics

Over the past 50 years, repeated attempts have been made to develop biological control technologies for use against economically important species of subterranean termites, focusing primarily on the use of the entomopathogenic fungus Metarhizium anisopliae. However, no successful field implementation of biological control has been reported. Most previous work has been conducted under the assumption that environmental conditions within termite nests would favor the growth and dispersion of entomopathogenic agents, resulting in an epizootic. Epizootics rely on the ability of the pathogenic microorganism to self-replicate and disperse among the host population. However, our study shows that due to multilevel disease resistance mechanisms, the incidence of an epizootic within a group of termites is unlikely. By exposing groups of 50 termites in planar arenas containing sand particles treated with a range of densities of an entomopathogenic fungus, we were able to quantify behavioral patterns as a function of the death ratios resulting from the fungal exposure. The inability of the fungal pathogen M. anisopliae to complete its life cycle within a Coptotermes formosanus (Isoptera: Rhinotermitidae) group was mainly the result of cannibalism and the burial behavior of the nest mates, even when termite mortality reached up to 75%. Because a subterranean termite colony, as a superorganism, can prevent epizootics of M. anisopliae, the traditional concepts of epizootiology may not apply to this social insect when exposed to fungal pathogens, or other pathogen for which termites have evolved behavioral and physiological means of disrupting their life cycle.     

Toxicity of seven termiticides on the formosan and eastern subterranean termites

Using both topical application and substrate (sand) treatments the toxicities of seven new generation soil termiticides were evaluated to determine the LD50 and LC50 against two economically important subterranean termite species, eastern subterranean termite, Reticulitermes flavipes (Kollar), and Formosan subterranean termite, Coptotermes formosanus Shiraki. The lethal dose toxicity (LD50) rankings for R. flavipes from highest to lowest were: fipronil > bifenthrin > chlorantraniliprole > cyantraniliprole > imidacloprid > chlorfenapyr > indoxacarb; the rankings for C. formosanus were fipronil > imidacloprid > chlorantraniliprole > cyanthraniliprole> bifenthrin > chlorfenapyr > indoxacarb. The respective lethal concentration toxicity (LC50) rankings were fipronil > bifenthrin > chlorfenapyr > indoxacarb > cyantraniliprole > chlorantraniliprole > imidacloprid for R. flavipes; and fipronil > chlorfenapyr > bifenthrin >imidacloprid > cyantraniliprole > chlorantraniliprole > indoxacarb for C. formosanus. The study provides an opportunity to directly compare toxicity, action speed, and bioavailability among this group of newer generation soil termiticides.     

Wood excavations of three species of subterranean termites

We compared the feeding excavations on wood blocks of three species of subterranean termites, Coptotermes formosanus Shiraki, Reticulitermes flavipes (Kollar), and R. virginicus (Banks). Feeding rate followed the order C. formosanus > R. flavipes > R. virginicus. Wood surface area (mm²) exposed per unit feeding was higher for C. formosanus and R. flavipes than for R. virginicus. This was caused by the tendency of C. formosanus and R. flavipes to make internally penetrating tunnels, thereby increasing surface area, whereas R. virginicus made trough- and bowl-like depressions on the outside of blocks, sometimes decreasing the size of blocks outwardly without a corresponding high increase in surface area typical with the tunnels of the other species. Consequently, wood surface area was sometimes reduced, rather than increased as a result of feeding by R. virginicus. Different patterns of wood excavation suggest that these termites have divergent roles in wood decay processes.

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Résumé Les organismes pionniers qui modifient le bois et le rendent acceptable par les insectes qui le perforent sont généralement des champignons du bois pourri. Cependant, une fois que les termites ou autres insectes perforant le bois ont pénétré, leurs galeries favorisent les bactéries fixatrices d'azote, permettent l'invasion d'autres organismes décomposeurs, et de ce fait régularisent la décomposition du bois (Ausmus, 1977). L'exposition de la surface à l'intérieur des perforations jouant un rôle très important dans le processus de pourrissement, il est souhaitable de pouvoir quantifier la surface des galeries dues à l'alimentation des termites. Une courbe type permettant de prédire l'aire de la surface perforée a été construite en perçant 109 morceaux de bois de trous cylindriques de différents diamètres, en calculant l'aire de la surface des morceaux de bois, en appliquant et pesant une couche de vernis pour bois au polyuréthane, et en divisant la masse de polyuréthane par l'aire de la surface. Le modèle prédictif qui en découle est: Y=0,01443×-3,51825 (P=0,0001; r=0,68), y étant la masse de polyuréthane (en g) et x la surface (en mm²) du morceau de bois. En traitant de la même façon au polyuréthane les morceaux de bois perforés par les termites, nous pourrions déduire leur surface.Une expérience a été effectuée avec 3 espèces de rhinotermitides,- Coptotermes formosanus Shiraki, Reticulitermes flavipes (Kollar) et R. virginicus (Banks). Des groupes de chaque espèce se sont alimentés pendant 11 ou 12 jours sur des morceaux de bois non contaminés par des champignons. Nous avons déterminé la survie, la consommation, la modification de la surface du morceau de bois (par utilisation du modèle prédictif) et le changement de surface par terminte.La survie est la même, mais la consommation est dans l'ordre suivant: C. formosanus > R. flavipes > R. virginicus. L'aire de la surface exposée par unité d'alimentation était plus élevée pour C. formosanus et R. flavipes que pour R. virginicus (Tab. 1). Ceci est dû à la tendance de C. formosanus et R. flavipes de creuser des galeries vers l'intérieur, tandis que R. virginicus fait des cuvettes à la surface du bois. Les attaques superficielles de R. virginicus réduisent parfois le volume du morceau de bois sans accroître proportionnellement la surface comme le font les espèces creusant des galeries. Ainsi, avec R. virginicus la surface peut être réduite au lieu d'augmenter. Des différences entre colonies s'observent avec toutes les variables (Tab. 2).Nos résultats suggèrent que C. formosanus et R. flavipes contribuent plus que R. virginicus à exposer le bois aux autres organismes décomposeurs. Cependant, ces résultats peuvent être modifiés par un conditionnement préalable du bois par des champignons.

     

Infestation of African savanna ecosystems by subterranean termites

This review is an analysis of the dimensions of termite infestation in African savannas. The aim of this work is to draw the attention of ecologists, conservationists, policy makers and farmers to the current and future threats of subterranean termites to the functioning and sustainability of such ecosystem habitats. This study analyzes and describes termite problem (questionable changes in density and assemblage structure) in selected African savannah ecosystems, synthesizes information on the effects of various human induced habitat disturbance regimes on termites’ assemblage structure, predators, nests and feed resources to generate hypotheses relating termite infestation with anthropogenic activities; it describes and critiques existing termite management practices. The review is suggestive that the infestation and resultant undesirable effects of subterranean termites in African savannahs are largely a consequence of the inappropriate savannah management practices (overgrazing, indiscriminate tree cutting and overhunting) undertaken by humans in pursuit of various livelihood options. Based on the evidence presented herein, we hypothesized that (1) human induced habitat disturbance in savanna ecosystems alters the feeding group composition of termites’ assemblages, favoring grass harvesters and polyphagus termite feeders that forage on more abundant food items, paying little attention to rarer food items and (2) habitat disturbance through activities like heavy grazing and overhunting results in decline in the populations of both macro and microscopic termite predators, which eventually enhances the proliferation of termite populations, escalates the density of termite nests particularly epigeal mounds and intensifies consumption of herbaceous savannah vegetation. The review calls for dedicated efforts to develop ecological thresholds of savannah biotic and abiotic ecosystem components in which human induced disturbance regimes trigger the destructive behavior of termites. This would provide information that will act as a precautionary savannah habitat monitoring and decision support tool to prevent future infestation of savannah habitats with termites. Also, the review shows that majority of the termite control practices are ineffective, ecologically unsustainable and above all, do not address the root cause of termite infestation and thus merely provide temporary relief to the problem. As such, termite control methods that attempt to enhance proliferation of termite predators need to be studied, developed and emphasized. This review reveals that human induced habitat disturbance depletes termites’ predator populations, leading to proliferation of termite populations particularly grass harvesters that intensify their consumption on grass biomass and eventually contribute to denudation of herbaceous vegetation cover in savannah ecosystems.     

Vegetation patterns,microtopography, and soils on a Chihuahuan desert playa

Abstract. Spatial patterns of vegetation on an ephemeral lake bed (playa) in the northern Chihuahuan desert were closely correlated with elevation. Distributions of species along a 265 m transect from the center to the edge of the playa showed abrupt boundaries at 110 m and 220 m. These boundaries seem related to the maximum elevation covered with standing water following complete flooding, and to an edaphic boundary between heavy clay soils at the center of the playa and adjacent soils. The complete turnover in species composition across this transect, with an elevation change of only 85 cm, indicates that environmental gradients resulting from flooding and soil development are steep. Vegetative patterns within the lowest part of the playa were patchy, with patch diameters ranging from 2 to 5 m. These patches appear to be produced by differences in the duration and frequency of flooding between small knolls and depressions resulting from gilgai microtopography.     

Simulation study on the tunnel networks of subterranean termites and the foraging behavior

Most subterranean termites forage for food by creating tunnel galleries underground. These tunnel networks reflect a compromise between foraging efficiency and other environmental constraints, such as soil hardness and moisture content. Thus, understanding tunnel networks is important for understanding foraging behavior. Due to the difficulties in direct observation of tunneling patterns in the field, we used a theoretical approach for this analysis. We first constructed a lattice model to simulate the tunnel networks of Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar) on the basis of the experimental data provided by Su et al. (Su, N.-Y., Stith, B.M., Puche, H., Bardunias, P., 2004. Characterization of tunneling geometry of subterranean termites (Isoptera: Rhinotermitidae) by computer simulation. Sociobiology 44 (3), 471–483.). Using this model and two of its modified versions, we explored the relationship between the food encounter rate and food distributions and analyzed how this relationship is influenced by changes in the tunnel characteristic constituents, such as the branching tunnel length and frequency. Additionally, we investigated the effects of landscape heterogeneity on the foraging efficiency. In the discussion, we briefly introduced our novel individual-based model comprising individual termites and their surroundings, and we addressed the necessity of this model in the functioning of the network and the formation of the network in relation to foraging behavior.     

Simulation study of territory size distributions in subterranean termites

In this study, on the basis of empirical data, we have simulated the foraging tunnel patterns of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), using a two-dimensional model. We have defined a territory as a convex polygon containing a tunnel pattern and explored the effects of competition among termite territory colonies on the territory size distribution in the steady state that was attained after a sufficient simulation time. In the model, territorial competition was characterized by a blocking probability P_block that quantitatively describes the ease with which a tunnel stops its advancement when it meets another tunnel; higher P_block values imply easier termination. In the beginning of the simulation run, N=10, 20,…,100 territory seeds, representing the founding pair, were randomly distributed on a square area. When the territory density was less (N=20), the differences in the territory size distributions for different P_block values were small because the territories had sufficient space to grow without strong competitions. Further, when the territory density was higher (N>20), the territory sizes increased in accordance with the combinational effect of P_block and N. In order to understand these effects better, we introduced an interference coefficient γ. We mathematically derived γ as a function of P_block and N: γ(N,P_block)=a(N)P_block/(P_block+b(N)). a(N) and b(N) are functions of N/(N+c) and d/(N+c), respectively, and c and d are constants characterizing territorial competition. The γ function is applicable to characterize the territoriality of various species and increases with both the P_block values and N; higher γ values imply higher limitations of the network growth. We used the γ function, fitted the simulation results, and determined the c and d values. In addition, we have briefly discussed the predictability of the present model by comparing it with our previous lattice model that had been used to explain the territory size distributions of mangrove termites on the Atlantic coast of Panama.     

Durability of phenolic-resin-treated oil palm wood against subterranean termites a white-rot fungus

Oil palm wood (OPW) is seen as a strategic alternative wood material, especially in a country with huge oil-palm-planted areas such as Malaysia. The material is low in quality and various techniques have been used to improve its quality. This study was carried out to evaluate the resistance of low-molecular-weight phenol formaldehyde (Lmw-PF) resin treated OPW against subterranean termites and a white-rot fungus. Four sample groups including untreated OPW and treated OPW samples with three different compression levels (0%, 25%, and 50%) were prepared. Five specimens for each sample group were tested for resistance against subterranean termites (Coptotermes curvignathus) and the white-rot fungus Pycnoporous sanguineus, based on ASTM D 3345-74 and ASTM D 1413-99, respectively. Results showed that both treatment and compression level had significant effects on the percentage weight loss and mean decayed surface of the samples. Treated OPW with 50% compression yielded the best performance with the lowest weight loss on both termite and decay tests. Overall, Lmw-PF resin treated OPW with 25–50% compression can be used as an effective method to improve the durability of OPW.     

Combined effect of microbial and chemical control agents on subterranean termites

Termite mortality was measured when fungi were combined with bacteria or a chemical termiticide to determine whether a synergistic effect occurred. The fungus Beauveria bassiana was combined with the non-repellant chemical termiticide imidacloprid. Of the three B. bassiana strains tested one, B. bassiana ATCC 90519, was sufficiently pathogenic on its own that the advantage of a supplementary chemical treatment was marginal. The mortality caused by another fungal strain, B. bassiana ATCC 26037, was improved in combination with imidacloprid at both of the tested chemical concentrations over the first 14 days. The remaining fungal strain, B. bassiana ATCC 90518, demonstrated an overall mortality rate in combination with imidacloprid of 82.5%, versus a rate of 65.0% for the fungus alone. The fungus Isaria fumosorosea (Ifr) was combined with the bacterium Bacillus thuringiensis (Bt). On day 5, Ifr, Bt, and the combined treatment at a 10⁶ spores or cells/ml dosage caused 8.8%, 22.5%, and 15.0% mortality, respectively. The Bt and combined mortality rates are not significantly different. Control mortality on day 5 was 5.0%. On day 13 the combined 10⁶ treatment mortality rate was 91.3%, which was significantly higher than all other treatments: control at 17.5%, Ifr at 36.3% and Bt at 35.0%. When Ifr and Bt were applied at a 10⁹ spores or cells/ml dosage, Ifr alone caused a mortality rate of 97.5% as early as day 5. The combination with Bt could not significantly increase the effectiveness of this dosage. These data demonstrate the potential for synergistic effects of fungal and chemical treatment methods, thereby broadening the use of microbial control agents and reducing the quantity of chemical agents necessary to effect control.     

The relative contributions of termites and microarthropods to fluff grass litter disappearance in the Chihuahuan Desert

Summary We tested the hypotheses that both subterranean termites and soil microarthropods are important in the disappearance of fluff grass (Erioneuron pulchellum) litter on the soil surface by an experiment designed to separate termite and microarthropod effects. Subterranean termites (Gnathamitermes tubiformans) removed more than 50% of the fluff grass litter in one year.Since there was no difference in mass loss of fluff grass with microarthropods present or excluded, they had no effect on decomposition of fluff grass litter. Microarthropod densities increased during the first 3 months then slowly decreased. The densities of microarthropods in fluff grass litter were too low to have a measurable effect on decomposition even if we assumed that the microarthropods consumed litter equivalent to their body weight each day.     

A strain of the fungus Metarhizium anisopliae for controlling subterranean termites

Alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki, collected after swarming in 2002 died within 48 h, and the cadavers were visibly infected with a fungus. Fungi were picked from the cadavers, transferred to media, and ultimately isolated to purity. The individual fungal cultures were then used to infect Formosan subterranean termite workers. A single fungal isolate, C4-B, taxonomically identified as Metarhizium anisopliae (Metschnikoff), was found to cause rapid mortality of Formosan subterranean termite alates. This is the first report of a biological control agent for termite alates. In initial experiments, C4-B was more lethal to both alates and workers compared with M. anisopliae strain ESC 1, previously marketed as the termite biocontrol agent BioBlast. Dose-response assays in which Formosan subterranean termite alates were exposed to a known concentration of C4-B spores revealed that 10(6) spores/microl killed 100% of the alates in 3 d, both 10(5) and 10(4) spores/microl in 6 d, 10(3) spores/microl in 9 d, and 10(0) spores/microl in 12 d. Assays with workers demonstrated that 10(6) and 10(5) spores/microl killed 100% of the workers in 6 d. In an experiment to test the transfer of inoculum from infected workers to uninfected nestmates, 62.8% of the workers died in 21 d when only 20% of the workers had been inoculated. Mortality of alates caused by C4-B was tested at two field sites by dispersing fungal spores on grassy lawns and collecting alates from the treated areas. Alates thus infected showed 100% mortality by day 5, whereas only 64.8% of untreated control alates from the same collection area were dead on that day.     

杉木人工林生态系统水文学过程的养分特性

根据5a定位观测的数据,对湖南会同24～28a生的杉木人工林生态系统各水文学过程中的养分特性进行了研究。结果表明：林冠降水是杉木人工林生态系统养分输入的重要来源,其中Ca的养分含量最高,P的含量最低。林内穿透水各养分元素的含量明显高于林冠降水中养分的含量。除Ca外,树干茎流中其它养分元素的含量为林冠降水的6倍以上。可见,林内穿透水和树干茎流是杉木林生态系统内养分循环的重要组成部分,有利于提高系统的养分利用率。地表径流中除硝态氮外,各元素的含量与穿透水的含量接近,其中P、Na和K三种元素的含量较低,但未超过林冠降水中养分元素含量。地下径流中N和K的含量较低,而Ca的含量与林冠降水相比没有差异。因而地表径流和地下径流不可避免的造成生态系统的养分损失,但24～28a生杉木林生态系统的调控能力较强,地表径流和地下径流量较小,生态系统的养分损失也相对较小,养分为净积累。不同季节之间水文学过程中养分元素含量存在一定程度的差异。降水形态、雷电和地形等要素影响养分元素含量。硝态氮在冰雹中未检出,而在雨水中的含量是雪水的2倍。铵态氮、K和Mg等元素在雨水中的含量最高。P和Ca以雪水的含量最高,与雨水和冰雹相比不存在数量级差异。雷电明显增加降水中养分的含量,特别是林冠上层的低空放电使降水中N的含量增加3～5倍。由于山谷和山麓的立地条件较好,其穿透水中养分含量比山坡的高,山谷与山麓的大致相等。在采集水样进行养分分析时,应考虑降水时间、降水形态和地形等因子的影响。     

Attraction of subterranean termites (Isoptera) to carbon dioxide

Subterranean termites, Reticulitermes spp., were attracted to carbon dioxide (CO2) in laboratory and field tests. In behavioral bioassays, Reticulitermes flavipes (Kollar), Reticulitermes tibialis Banks, and Reticulitermes virginicus Banks were attracted to CO2 concentrations between 5 and 50 mmol/mol. In further bioassays, R. tibialis and R. virginicus were attracted to the headspace from polyisocyanurate construction foam that contained 10-12 mmol/mol CO2. In soil bioassays in the laboratory, more termites foraged in chambers containing CO2-generating formulations than in unbaited control chambers. In field tests, stations containing CO2-generating baits attracted R. tibialis away from wooden fence posts at rangeland sites in Colorado. For all of the CO2 formulations tested, termites foraged in significantly more bait stations at treatment fenceposts than in bait stations at the control fenceposts. By the end of the 8-wk study, the number of bait stations located by termites at treatment fenceposts ranged from 40 to 90%. At control fenceposts, termites foraged in only a single station and the one positive station was not located by termites until week 5 of the study. At treatment fenceposts, termites foraged equally in active stations (containing a CO2-generating bait) and passive stations (with no CO2-generating bait), indicating that bait stations may benefit passively from a proximal CO2 source in the soil. CO2 used as an attractant in current baiting systems could improve their effectiveness by allowing earlier exposure of termites to an insecticide.     

Synopsis of Canotia (Celastraceae) including a new species from the Chihuahuan desert

Canotia, a genus of holacanthoid shrubs of southwestern United States and northern Mexico, is redescribed, and reasons are advanced for retaining it in the family Celastraceae. Two species are recognized, includingC. wendtii sp. nov. from Chihuahua.     

Environmental controls on nitric oxide emission from northern Chihuahuan desert soils

A survey of nitric oxide (NO) emission from Chihuahuan desert soils found mean NO fluxes <0.1 ng NO-N cm^–2h^–1 during the dry season. These fluxes were at thelower end of the range reported for temperate grassland and woodlandecosystems. NO fluxes from wet or watered soils were higher(0.1–35 ng NO-N cm^–2 h^–1).Watering of black grama grassland soils produced an initial pulse of 12ng cm^–2 h^–1 (12-h after 1-cm watering)with high fluxes sustained over 4 days with repeated watering. Initialpulses from shrubland soils were lower (maximum 5 ngcm^–2 h^–1), and fluxes declined withrepeated watering. Repeated watering of creosotebush soils depleted thesoil NH ₄ ⁺ pool, and NO emissions weredirectly related to soil NH ₄ ⁺ concentrationsat the end of the experiment. In watered andNH ₄ ⁺ -fertilized creosotebush soils, NO fluxeswere positively related to potential net nitrification rates.NH ₄ ⁺ -fertilization boosted the initial NOpulse 15 times in the shrubland and 5 times in black grama grasslandrelative to watered controls. These experimental results point towardgreater substrate limitation in shrublands. In this desert basin, NOemission averaged 0.12 kg N ha^–1 y^–1in untreated soil and 0.76 kg N ha^–1y^–1 in watered soil. We multiplied these averages bythe distribution of grassland and shrubland vegetation within a58,600-ha area of the Jornada del Muerto basin to estimate regionallosses of 0.15–0.38 kg NO-N ha^–1y^–1 for this area of the Chihuahuan desert.