Different microhabitats affect soil macroinvertebrate assemblages in a Mediterranean arid ecosystem

Spatio-temporal variability is a key factor in conservation, management and restoration of ecosystems. Spatial heterogeneity is caused in many cases by organisms that are able to modify their environments. This is especially relevant in arid systems, where organisms such as shrubs and ants create patches of high nutrient availability (fertile islands) surrounded by a low-nutrient matrix. Although variations in structure and physiology among shrubs provoke differences in their effects as fertile islands, whether different microhabitats vary in their influence on animal communities is poorly known. The principal aim of our study is to analyse the effects of different shrub species and Messor harvester ant-nest mounds on the structure of soil macroarthropod assemblages in a strongly seasonal desert location of SE Spain. Shrub microhabitats and ant-nest mounds maintained higher species density, abundance and biomass of soil macroinvertebrates than the surrounding soil matrix. The different microhabitats differed in taxonomic and trophic composition, abundance, and biomass of soil macroinvertebrates, at both litter and belowground levels. Also, variations of invertebrate abundance among microhabitats changed throughout sampling periods. Thus the spatio-temporal heterogeneity of the study site affected the distribution and dynamics of the macroinvertebrate community. The above results indicate that the spatio-temporal mosaic created by microhabitat and seasonal variations on macroinvertebrate assemblages is a relevant issue to be considered in conservation, sustainable management and environmental restoration in heterogeneous arid systems to preserve their biodiversity and ecosystem functioning.     

Isotopic discrimination during long-term decomposition in an arid land ecosystem

Discrimination in carbon and nitrogen isotopes of decomposing plant litter in the northern Chihuahuan Desert was determined for a 5-year period. Factors influencing isotopic change were assessed from inter-species comparisons of litter chemistry, mass loss patterns, and isotope values of associated soil. Average δ¹⁵N_litter values of buried roots increased 1.2 and 2.6‰ for Big Blue Stem (Schizachyrium gerardi, grass) and Varital (Drypetes glauca, hardwood) during the study, respectively. Small but inconsistent variations were observed for Slash Pine (Pinus elliotii, conifer) roots. Average δ¹⁵N values of wooden dowels from Ramin (Gonystlylus bancanus, hardwood) increased ca. 2.0‰ during years 1–4, and then decreased slightly during year 5. Changes in δ¹⁵N_litter were independent of N content, and may reflect microbial fractionation or preferential retention of ¹⁵N enriched substrates. Surprisingly, there was no clear relationship between litter N dynamics and C/N ratios. There were no discernable changes in δ¹³C_litter values for Gonystlylus bancanus and Pinus elliotii. Average δ¹³C_litter values for Schizachyrium gerardi decreased ∼2.0‰ during years 0–2 and then increased slightly. In contrast, average δ¹³C_litter values for Drypetes glauca increased ∼0.5‰ from years 0–1 then remained relatively constant until decreasing slightly in year 5. δ¹³C_litter discrimination may have been masked by interfering δ¹³C fractionations or feedbacks between decomposers and litter chemistry. Our data indicate that isotopic discrimination is characteristic of early litter decay stages. These results may highlight aspects of isotope discrimination and nutrient cycling unique to arid land environments. Additional studies will be needed to confirm this.     

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.     

Farmers' perception of vegetation changes in semi‐arid Niger

Vegetation changes due to climate and human impact in Sahelian countries are rarely documented at species composition level. The decrease or disappearance of certain plant species reduces vegetation cover and enhances the exposure of soil surfaces to wind and water erosion leading to increased land degradation. Men and women in Niger were asked to note plant species and relate their numerical development to pre‐defined observation criteria comparing the present and past. Plant species in decline or that had disappeared were reported more often than species that had increased or were newly introduced. The increasing species that were mentioned were often in use for different purposes and seem to be robust enough and well adapted to the semi‐arid environment. But the interviewed farmers also stated the loss of many valuable species that they used for construction and hand tools, consumption, medicine or fodder. Those declining species are of socio‐economic importance for individual households and the rural ecology. Men mentioned 18 species that had disappeared. Differences in the perception of men and women could be found. Women seemed to have a better perception for species which had increased or were newly introduced, whereas men perceived more a decrease or disappearance of species. Copyright © 2000 John Wiley & Sons, Ltd.     

Geo-ecological soil features and the vegetation pattern in an arid dune area in the Northern Negev,Israel

Soils are suggested to be an important factor influencing the vegetation pattern. In order to prove this hypothesis in an arid and sandy Negev ecosystem of longitudinal dunes and interdune corridors near Nizzana, Israel, the distribution of soil units and plant communities were compared on a very small-distance level. The Nizzana site has a size of nearly 100 ha. 250 soil pits with 3–5 horizons were mapped and sampled within the soil geographical monitoring. Soil water capacity and cation exchange capacity were estimated from the field data. In addition 176 plots of 100 m² were established around the soil pits with emphasis on plants, coveting the environmental gradient across the dune ridges. Plant mapping plots were arranged into groups with the same dominating perennial species and a key for the vegetation mapping was developed. In the investigated desert site topography, soil surface crust, soil texture and salt content partly can explain the distribution of plant communities. A soil classification proposal is based on these parameters and is a useful tool to indicate correlations between soil units and the vegetation pattern. Nevertheless, dependent on topography and surface and/or subsurface water flow as well as the occurrence of “fertile islands” the moisture and nutrient regimes influence the vegetation pattern with respect to plant growth to a greater extent than the soils themselves.     

A comparison of methods for estimating fractional vegetation cover in arid regions

We compared a set of methods for estimating the fractional vegetation cover (f_c) of sparse desert vegetation over an arid region of southern Xinjiang, China. Six kinds of remote sensing inversion models (an NDVI regression, a spectral mixture analysis (SMA), a pixel dichotomy model, a three-band maximal gradient difference (TGDVI) model and two modified TGDVI models) were used to derive f_c from remote sensing data, and the results were compared with f_c values measured in the field to select an appropriate model to derive the fractional cover of sparse desert vegetation in arid regions. The NDVI regression based on field f_c and the NDVI for the sampled pixels in September 2006 showed the highest precision, while the results of 2007 showed that the NDVI regression method is inappropriate for depicting vegetation characteristics in other growing season because the empirical model highly depend on the specified in situ measurement. The SMA approaches yielded higher precision than the other models, indicating that it is applicable for analysing the coverage of sparse desert vegetation. The pixel dichotomy model can yield a high precision based on finely detailed vegetation maps. However, it requires the measurement of many parameters. The TGDVI model is simple and easy to implement, and the values that it predicted for the coverage of high-density vegetation and barren areas were close to those measured in the field, but the f_c values of sparsely vegetated areas were underestimated. The predictions of the modified TGDVI models were close to the values measured in the field, indicating that these modified models can reliably and effectively extract information on the fractional cover of sparse vegetation in an arid region. We analyzed the models’ sensitivity with respect to rainfall because the short-wavelength infrared bands used in the two TGDVI models proposed in this study are sensitive to moisture. The results showed that the modified TGDVI models’ accuracy was not affected by increasing soil moisture content caused by rain. However, the NDVI regression, SMA and TGDVI were sensitive to the change of soil moisture content. Moreover, the two modified TGDVI models yielded negative values for water sources, such as reservoirs and rivers, implying that they are effective for characterising water bodies. However, the modified TGDVI models cannot predict f_c in snow- and glacier-covered regions, producing abnormally high rather than zero values. Additionally, the predictions before and after snowfall on the top of a mountain show a linear increasing relationship, suggesting that the short-wavelength infrared band may be useful to predict snow depth.     

Impact of sulphur and nitrogen deposition on plant species assemblages in natural vegetation

In the present study twelve years of changes in natural plant communities and their relation to S and N deposition are analysed. The Acid-tolerance index (ATI) and Nitrogen-demand index (NDI) based on Ellenberg's indicator values, and the Shannon-Wiener index were employed for characterizing the species assemblages of communities. The deposition at the sites was dramatically higher in the south than in the north of the country. NDI, but not ATI, was significantly correlated to N deposition. Species diversity at each site was quite stable over time. In PCA ordination species diversity, ATI and NDI were almost independent from each other, and were represented by three different principal components. There only NDI was strongly correlated to S and N deposition, while ATI was almost independent of them. Regression analysis suggested that species richness and diversity were weakly correlated to N deposition.     

干旱内陆河流域生态系统服务空间权衡与协同作用分析

为了测度生态系统服务的空间权衡/协同关系,该文以干旱内陆河流域典型地区嘉峪关-酒泉地区为研究区,对其2000年和2010年食物供给、碳储存、水源涵养和土壤保持4种生态系统服务物质量进行定量测算.利用相关分析法和空间热点制图等方法,分析了生态系统服务时空变化,从县域尺度和区域尺度上分析了生态系统服务之间的权衡协同关系,识别了某种服务的物质量或价值量极高的热点区.结果表明:研究区单位面积食物供给的高值区分布在中东部的肃州区及嘉峪关市,碳储存表现为东部及南部较高的分布格局;土壤保持在2000年和2010年变化不大,呈现出从西到东逐渐增大的分布趋势;单位面积水源涵养值由2000年的0.40mm/(m2·a)提高到2010年的0.99mm/(m2·a).县域尺度上,各种生态系统服务之间大多为协同关系,其中食物-碳和水源-碳之间的协同程度较高;区域尺度上,食物供给和土壤保持、水源涵养和土壤保持生态系统服务间存在此消彼长的权衡关系.4种生态系统服务的值均未超过各自平均值的0类服务区和只有1种生态系统服务的值超过其所对应平均值的1类服务区分别占总面积的58.50%和25.20%.该研究结果可为制定差别化的区域发展与生态保护双赢政策提供科学参考.     

Simulated rain addition modifies diurnal patterns and temperature sensitivities of autotrophic and heterotrophic soil respiration in an arid desert ecosystem

The timing and magnitude of rainfall events in arid and semiarid regions are expected to change dramatically in future decades, which will likely greatly affect regional carbon cycles. To understand how increases in rainfall affect the diurnal patterns and temperature sensitivities (Q₁₀) of soil respiration (R_S) and its key components (i.e. heterotrophic respiration (R_H) and autotrophic respiration (R_A)), we conducted a manipulative field experiment in a desert ecosystem of Northwest China. We simulated five different scenarios of future rain regimes (0%, 25%, 50%, 75% and 100% increase over local annual mean precipitation) each month from May to September in 2009. We measured R_S and R_H every three hours on 6 and 16 days after the rain addition, and estimated R_A by calculating the difference between R_S and R_H. We found that rain addition significantly increased the daily mean R_S and its components on the two measurement days during the growing season. However, the diurnal pattern was different between the two respiration components. Rain addition significantly increased the daily Q₁₀ value of R_H but suppressed that of R_A on Day 6. Rain addition had no influence on daily Q₁₀ value of both respiration components on Day 16 when soil moisture was lower. In addition, we observed significantly higher daily Q₁₀ of R_H than R_A under all five rain addition treatments, indicating that microbial respiration is more temperature sensitive than root respiration in a short-time scale in this desert ecosystem. Thus, partitioning soil respiration into its two components, and analyzing the differential responses of R_H and R_A to future climate changes should be considered for more accurate predictions of soil respiration and regional carbon cycle in these arid and semiarid regions.     

干旱区人工生态系统的持续发展与耗散结构理论

运用耗散结构理论并结合持续发展理论对干旱区生态系统进行了剖析,提出建立和开发人工绿洲生态系统、实施持续发展战略是干旱区生态系统由荒漠向耗散结构生态经济系统发展的必由之路。     

Mercury concentrations in an aquatic ecosystem during twenty years following abatement the pollution source

Phenyl Hg was widely used as a slimicide in Finnish pulp industry until the end of 1967. The use of Hg caused a significant increase of Hg levels in fish in several areas. High concentrations were measured in Lake Kirkkojärvi in Hämeenkyrö, SW Finland. Vast amounts of Hg are still present in the lake sediments. Since 1968 uncontaminated fibres have partly covered the contaminated layers. Since 1971 Hg has been monitored in fish, sediments and aquatic plants in the water course downstream from the pulp and paper factory. The Hg concentration of a 1-kg pike (Esox lucius) has decreased from 1.5 µg g^?1 in the years 1971–74 to 0.8 µg g^?1 in 1990.     

Effect of vegetation restoration on ant nest‐building activities following mobile dune stabilization in the Horqin Sandy land,Northern China

Measurements of the density and characteristics (size and height) of ant mounds were carried out on mobile, semi‐mobile, semi‐fixed and fixed dunes in the Horqin Sandy Land, Northern China. The relationships between the distribution of ant mounds and the plant community (abundance and cover) were investigated, for areas within and across the dune stages. Changes in spatial pattern of ant mounds were also analysed following mobile dune stabilization. The results showed no ant mounds on mobile dunes; the mound density was significantly higher on fixed dunes than on semi‐fixed or semi‐mobile dunes. The mound density depended on plant density and cover across all dune stages, but not within any dune stage. The mound diameter increased but the mound height decreased from semi‐mobile dunes to fixed dunes. However, the mound diameter and height were not related to plant cover and density within any stabilization stage or across all dune stages. The spatial pattern of ant mounds tended to change from more clumped (semi‐mobile and semi‐fixed dunes) to less clumped and approached a random pattern (fixed dunes) along the dune stabilization gradient, which was related to the changing vegetation pattern during succession. Although the quantification of the number of ant species present was not attempted on each dune, the observed differences in ant colour and size suggest at least eight species were present. Fixed dunes were more attractive for different kinds of ant species, but the mound distribution exhibited a more random pattern with more continuous vegetation. Thus, different environmental conditions, especially in terms of the plant communities present at different dune stages, affected the activities and behaviour of the ants (including the distribution of mounds), but did not affect mound size and height. Copyright © 2009 John Wiley & Sons, Ltd.     

Multiple‐scale soil moisture distribution and its implications for ecosystem restoration in an arid river valley,China

The spatial distribution of soil moisture and its multiple‐scale correlations to other environmental factors were examined along the Upper Minjiang River valley, China, a landscape subject to severe land degradation of soil and water erosion but also under investigation for potential ecosystem restoration. Results showed that: (1) Soil moisture was highest in the headwaters, and lowest in the arid valley, while moderate values characterized outside the arid valley. The polynomial model of soil moisture distribution on slopes was concave in the lightly disturbed headwaters, convex in the highly damaged arid valley, while convex on south facing slopes and concave on north facing slopes in highly damaged areas in better environmental condition. (2) Soil moisture was correlated with environmental factors at different scales, where elevation and air humidity were only correlated at the sample plot scale, light intensity and wind speed were found to be significant at both slope and site scales and slope and sample plot scales; while slope angle was correlated at all the three scales. From this we conclude that it is possible to improve soil moisture conditions in the arid valley by lowering slope angle and adding low‐cost irrigation systems. (3) The practical threshold of soil moisture for growing meadows, shrubs, and forests were 11ċ800 per cent, 3ċ925 per cent, and 16ċ078 per cent respectively; the arid valley displayed soil‐moisture conditions unfavourable to forest growth. The planned reforestation project is not ecologically reasonable. Reducing human disturbance and revegetating with natural shrubs and meadows may produce more effective results. Copyright © 2004 John Wiley & Sons, Ltd.     

Vegetation cover and rain timing co-regulate the responses of soil CO2 efflux to rain increase in an arid desert ecosystem

Climate models often predict that more extreme precipitation events will occur in arid and semiarid regions, where C cycling is particularly sensitive to the amount and seasonal distribution of precipitation. Although the effects of precipitation change on soil carbon processes in desert have been studied intensively, how vegetation cover and rain timing co-regulate the responses of soil CO₂ efflux to precipitation change is still not well understood. In this study, a field manipulative experiment was conducted with five simulated rain addition treatments (natural rains plus 0%, 25%, 50%, 75%, 100% of local annual mean precipitation) in a desert ecosystem in Northwest China. The rain addition treatments were applied with 16 field rain enrichment systems on the 10th day of each month from May to September, 2009. Soil water content, soil temperature and soil CO₂ efflux rates were measured in both bare and vegetated soils before and after the rain addition during a 3-week period for each rain treatment. The response magnitude and duration of soil CO₂ efflux to rain addition depended not only on the rain amount but also on the type of vegetation covers and the timing of rain addition treatments. Soil water content responded quickly to the rain addition regardless of rain amount and timing, but soil CO₂ efflux increased to rain addition only in May–July but not in late growing season (September). In addition, soil CO₂ efflux from the bare and vegetated soils showed similar increase to rain additions in May–July, but they demonstrated distinct responses to rain addition in September. The differences in the responses of soil CO₂ efflux to rain addition between the bare and vegetated soils could be explained by the root activities stimulated by added rain water, while the difference in soil CO₂ efflux response to rain addition among treatment times could be attributed to soil water condition prior to rain addition and/or soil temperature drop following rain addition. Thus, both vegetation cover and rain timing can co-regulate responses of soil CO₂ efflux to future precipitation change in arid desert ecosystems, which should be considered when predicting future carbon balance of desert ecosystems in arid and semiarid regions.     

The response of plant and insect assemblages to the loss of Calluna vulgaris from upland vegetation

Across large areas of upland Britain Molinia caerulea and Nardus stricta are replacing Calluna vulgaris as the dominant plant species of the vegetation assemblage. Associated changes in the composition of the whole plant assemblage and a phytophagous insect group, the Hemiptera, were investigated. Vegetation and hemipteran assemblages were sampled at six moorland sites in northern England and Scotland. Sampling at each site was carried out in Calluna vulgaris-dominated areas and grass-dominated areas that had previously been dominated by C. vulgaris. Vegetation assemblages of heath and grass sites differed significantly even when species by which sites were selected for sampling (C. vulgaris, M. caerulea and N. stricta) were removed from the analysis with the highest species richness in dry grassland sites. Hemipteran assemblages differed significantly between heath and grass sites with greater species richness also being in grass sites. Plant species composition was the most important explanatory variable of hemipteran assemblages with temperature, latitude, soil loss on ignition and vegetation height also explaining a significant proportion of the variation. Overall a range of vegetation composition and structural variables explained 40.8% of variation in the Hemiptera species data with ranges of soil and biogeographic variables explaining an additional 8.7%.This research demonstrates that the replacement of one dominant plant species by another is associated with a change in other aspects of moorland biodiversity. In particular the loss of C. vulgaris actually leads to an increase in the species richness of Hemiptera and plants although the number of specialist species declines.     

Soil organic carbon balance and nutrients (NPK) availability under treated wastewater irrigation for bioenergy sorghum production in an arid ecosystem

This column study evaluated the effects of irrigation with two water qualities (WW and FW) to produce bioenergy sorghum on SOC balance, nutrients availability and salt constituents in two soils (TX and NM) amended with gypsum & elemental sulfur (S) and un-amended. Study results indicated that SOC concentration was higher in freshwater irrigated columns (7.41 g kg^?1) than wastewater irrigated soils (7.32 g kg^?1) across growth year-soil type-amendments-depth. Soils amended with gypsum and sulfur registered significantly higher value of 7.52 and 7.41 g kg^?1 compared to 7.30 and 7.23 g kg^?1 in non-amended soils under fresh and wastewater irrigation, respectively. Lower SOC in WW irrigated columns could be due to the combined effects of increased salinity and priming effects. Although SOC content initially increased in gypsum and S amended soils to about 10g kg^?1, at the end of the study SOC in all treatments decreased to levels significantly below the pre-study. WW irrigation added 2.00, 1.10 and 4.40 times the N, P and K added by fertilizers and was able to meet 65%, 87%, and 210% of bioenergy sorghum uptake of respective nutrients. Sulfates and chlorides of sodium and calcium were dominant salts, which significantly affected SOC and nutrients.

Abbreviations: FW: freshwater; WW: treated wastewater; G + S: gypsum and elemental sulfur; NA: no amendment, TX: Texas soil and NM: New Mexico soil     

Mechanisms of pH change in wood ant (Formica polyctena) nests

We conducted a study to determine why the pH of wood ant nest materials is typically higher than that of the surrounding forest soil. An experiment with litter bags demonstrated that the pH of litter increased significantly (after only 7 months) in ant nests. Because the food that foraging ants bring into the nest contains easily decomposed carbohydrates and basic cations (largely in the form of honeydew and prey) that can cause increases in pH, we then estimated the amount of this influ of basic cations and easily decomposed carbohydrates. Based on these estimates, we conducted a second experiment to determine whether addition of field-determined quantities of an easily decomposed carbohydrate (glucose) or a basic cation (Ca²⁺) would increase the pH of the litter in artificial ant nests in the forest. Both glucose and Ca²⁺ additions significantly increased the pH of the litter but the increase was greater with Ca²⁺. The rate of pH increase in the artificial nests was similar to the rate of increase in natural nests. According to our study, ants collect substantial amounts of mineral-enriched materials in this ecosystem, which collectively increase the pH of nest material.     

干旱荒漠区土地利用变化对地表温度的影响

该文以Landsat TM 遥感影像为主要数据源,获取了宁夏中卫市沙坡头区1992年和2007年的土地利用信息;利用单窗算法反演了对应时期该区域的地表温度（LST）;据此分析了土地利用变化与地表温度变化之间的关系。结果显示：1）不同利用方式的土地的LST有显著差异,流动沙地的LST最高,其次是固沙用地、草原化荒漠等;2）过去15 a间,研究区内最为明显的土地利用变化方向是“草原化荒漠转变为农田”和“流动沙地转变为固沙用地”;3）“草原化荒漠转变为可灌溉农田”会导致LST明显下降,“草原化荒漠转变为压砂田”     

新疆干旱区湿地景观格局遥感动态监测与时空变异

为了解和掌握全球变化环境下中国干旱区湿地的分布现状、变化过程和时空格局特征,该文通过多源遥感技术手段,采用面向对象分类方法和目视解译相结合,完成了干旱区湿地信息的多期监测,实现了新疆地区2000、2005和2010年的湿地分布制图,并利用动态度模型和地统计方法计算了近10 a时空变化情况,分析了湿地变化的时空特征。研究结果表明:1)近10 a来全疆干旱区湿地约增加了10.1%,2010年新疆湿地总面积达到22 438 km2,较2000年约增加了2 065 km2;2)在类型构成上,2010年河流湿地、湖泊湿地、沼泽湿地和人工湿地所占比例分别为42.73%、29.43%、17.98%、8.92%和0.94%;3)在空间分布上,南北疆呈现不均衡,南疆湿地约占总体的76%,北疆湿地仅占24%;主要分布在塔里木流域,以河流湿地为主,空间分布差异显著;4)新疆湿地面积总体上呈增多的趋势,不同类型的湿地面积变化幅度差异较大。沼泽湿地和人工湿地的动态度分别为:2.58%、2.43%,河流湿地与湖泊湿地的动态度为:0.59%、0.43%;净增量最大的是沼泽湿地和河流湿地,分别增加了827.92和531.86 km2,占湿地净增量的65.85%。在变化原因上,全球变暖、新疆区域气温升高和降水增多是湿地近年来增加的主要原因;人类活动的干扰,加剧了湿地变化的复杂性和空间差异性。研究结果可为区域生态环境变化研究以及湿地资源的保护规划提供数据支持和结论参考。     

Photoacceleration of plant litter decomposition in an arid environment

In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular enzyme activities (EEA) were measured over 639 days. The composition of the fungal communities associated with the decomposing litters was compared by analyses of fungal ITS nrDNA sequences. Litter exposed to ambient sunlight had greater mass loss rates than shaded litter, independent of the water treatment: Populus increased by 100%, Pinus by 86% and Juniperus by 46%. The increases were proportional to exposed litter surface area per g dry mass. EEA potentials, particularly oxidative activities, were low in comparison to those measured in mesic ecosystems. For Populus litter, the principal driver of photoacceleration appeared to be photodegradation of cellulose; for Pinus, it was photodegradation of polyphenols; for Juniperus accelerated mass loss was associated with photodegradation of both polysaccharides and polyphenols. Fungal community composition varied by litter type, but the dominant colonizers were yeasts and dark-septate hyphal taxa; a finding consistent with the low enzymatic oxidation potential. This study shows that photochemical oxidation can supplement enzymatic oxidation and increase decomposition rates. As a result, organic matter decomposition in arid ecosystems is not restricted to periods of high moisture availability as is plant production. This decoupling may partly account for the low soil organic matter content of these ecosystems.