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1.
In Brazil, the semi-arid tropical zone comprises approximately 12% of its territory. In this region the Caatinga is the only exclusively Brazilian biome. Nonetheless, there is a lack of knowledge about its structure and functioning. This study aimed at assessing the effective depth of the root system of the preserved Caatinga biome, as well as its temporal and spatial variation. To this end, 72 soil profiles were evaluated, both in the dry and rainy seasons, including three soils (Acrisol, Luvisol and Regosol) and four profiles per trench, with three replications. The results showed that the effective depth of the Caatinga roots range from 0.60 m to 0.78 m in non-restrictive deep soils, three times smaller than values commonly used in hydrological models. Vegetation adapted to shallow soils, presenting effective root depth as low as 0.36 m. The effective depth of the roots showed spatial homogeneity, for each soil-vegetation association, regardless of the proximity of large trees. It was also observed that the root depth in the dry season is, on average, 10 cm shorter than that of the rainy season. This can indicate an adaptation strategy, generating soil secondary porosity to enhance infiltration in the root zone. 相似文献
2.
The soil dilution plate method was used to examine spatiotemporal changes in microfungal communities inhabiting the playa and interdune areas in the western Negev Desert, Israel. Soil samples were collected from the 0–50 cm depth at 10 cm intervals at both habitats during the wet and dry seasons of 2010. Forty-six species belonging to 31 genera were identified, 14 and 12 species were common to both habitats during the wet and dry seasons. The colony-forming units (CFUs) ranged from 75 to 4875 and from 500 to 6925 CFU g−1 dry soil at the playa and interdune, respectively. More diverse species and higher microfungal density were recorded during the wet season compared to the dry season at both habitats, and the microfungal communities inhabiting the playa were characterized by lower species diversity and CFU compared with the interdune regardless of soil depth and sampling season. With the increase in soil depth, decreasing trends were found in both species diversity and CFU throughout the study period, especially in the playa soils. Generally, Cladosporium cladosporioides, Alternaria alternata, Ulocladium atrum, and Fusarium spp. were widespread at the playa with high relative abundance, as were Penicillium and Aspergillus spp. at both habitats. 相似文献
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We argue for the use of nurse plants as an effective way to restore the Brazilian semiarid biome (the caatinga) – Brazil's most neglected ecosystem. This is a very topical issue in the light of the current publicity and controversy surrounding the alterations to the Brazilian Forest Code. We want to alert policy makers and land-owners to potential new ways to restore the Caatinga. 相似文献
5.
The largest population of the Argentinean Pampas deer Ozotoceros bezoarticus celer is found in the semiarid grasslands of the San Luis province. Despite relatively high deer numbers in the region, there has been concern that expansion of farming practices could displace the species. Since the 1990’s, cattle breeding has intensified especially as a result of the replacement of natural grassland with South African digit grass (Digitaria eriantha) and African lovegrass (Eragrostis curvula). In this study, we studied how deer in “El Centenario” ranch used available habitat types, especially to assess whether it preferentially used natural over exotic pastures. We employed 8 fixed line transects to record deer numbers and habitat use during the dry season, early rainy and late rainy seasons. We estimated a mean population size of 731 ± 121 individuals, a density of 1.95 ± 0.25 deer/km2. Our results also showed that deer did not appear to select natural pastures over exotic ones, though D. eriantha grasslands with cattle were used less during the late rainy season. Grazed pastures with D. eriantha without cattle were used significantly more during all time periods. Our results therefore suggest that Pampas deer are not shifted by exotic pastures but we caution that it is important to manage these habitats sustainably (e.g. cattle load adjusted to grassland nutritional supply, rotational crops with parcel rest period), to ensure the conservation of the species within agricultural areas. 相似文献
6.
用波谱分析法的研究结果表明,当地旱雨季土壤含水量差异较大:旱季土壤含水量<凋萎湿度,土壤水分严重亏缺。因受降水量的影响,土壤含水量呈周期为1a的波动变化。用谐波分析法还计算了各层次土壤含水量的谐波展开式,由此可预报土壤含水量变化趋势。 相似文献
7.
Savannas cover about 20% of the Earth's land area across a wide range of climatic conditions. As an important and distinct biome, savannas produce approximately 29% of global terrestrial net primary productivity. In these ecosystems the distribution of belowground resources remains poorly investigated and the relationship to the climatic conditions remains unclear. In the present study, vertical profiles of soil nutrients (chloride, nitrate, phosphate and sulfate) and nitrogen stable isotopes were analyzed at four sites along the Kalahari mega-transect, where a distinct rainfall gradient exists on a homogeneous soil substrate. The results show clear differences in nutrients and δ15N vertical distributions between wet and dry seasons. The results also show how the formation of “fertility islands” (i.e., the concentration of soil nutrients in the soils beneath tree canopies) is not necessarily coupled with belowground processes in that the distribution of soil nutrients at the surface does not match belowground patterns. The results also indicate that phosphorus may be a limiting nutrient in these savanna ecosystems with seasonal dynamics in its cycling. 相似文献
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Soil microarthropod communities in seed-harvester ant-nest (Messor spp.) soils and pits excavated by porcupines (Hystrix indica) were examined on a hill-slope catena in the Negev Desert to test the hypothesis that animal-produced soil disturbances increase abundance and diversity of soil biota. There were significantly fewer arthropods and lower taxonomic diversity of soil microarthropods at the top and mid-slope locations, with no consistent patterns of abundance between cool-wet and hot-dry seasons. Some prostigmatids, cryptostigmatids, and other arthropods in ant-nest, porcupine-pit, and undisturbed soils were more abundant in wet than dry seasons at some locations but more abundant in the hot-dry season at other locations and sample sites. Seven prostigmatid mite families that were relatively abundant in undisturbed soils were absent or of low abundance in ant-nest modified and porcupine-pit soils at mid- and low-slope catena locations. The data result in rejection of the hypothesis. However, the significant effects of topographic position on the catena on soil microarthropod communities emphasize the importance of examining broad spatial patterns and temporal variation before making generalizations about the effects of ecological engineers on arid ecosystem structure and function. 相似文献
9.
Due to high temporal variation of soil organic matter in arid regions, estimates of annual sequestered C might be overestimate. We assessed the soil stable organic matter (humic substances) in the transitional area between Dry Chaco and Monte eco-regions in western Argentina, as an approach to estimate realistic soil C sink. Soil samples were taken during wet and dry seasons in four sites along precipitation gradient. In each site three soil cover situations (under tree, under shrubs and on bare soils) were sampled (n = 5) and the quantity and type of residues (tree and shrub leaves, woody material, grasses and forbs) were recorded. Soil organic matter and humic substances (humic and fulvic acids) content were analyzed and non-humic substances were calculated by the differences between organic matter and humic substances. Soil humic substance proportion respect to SOM was low (20%) in all sites and it did not correspond with the precipitation gradient. Non-humic substances were lower in wet season indicating high C lability. The most important factors that affected soil humic substance content were the type and quantity of organic residues and soil cover type. Our results suggest that previous C sink estimations in Argentina dry forest probably are overestimated. 相似文献
10.
Soil texture greatly influences soil water movement, thus may affect the water balance and vegetation growth in the desert–Loess Plateau transition zone. This study is to determine if the water balance differs in homogeneous and layered soils with Caragana korshinkii stands in semiarid region. Soil water measurements up to 500-cm depth were taken in 2006 and 2007 on homogeneous sandy soil, homogeneous silt loam soil, and layered soil with sand overlying silt loam. HYDRUS-1D was used to simulate the soil water balance. The results indicated the annual water balance components were greatly affected by soil layering. The ratio of average actual evapotranspiration (ETa) to precipitation (P) during the two years in the layered soil was slightly lower than that in homogeneous soils. The ratios of annual actual transpiration (Tr) to evapotranspiration were 50.9%, 41.2% and 30.6% in layered soil, homogeneous sandy soil, and homogeneous silt loam soil, respectively. C. korshinkii grown in layered soil had deeper soil water recharge and higher Tr/ETa ratio, thus had more available water for transpiration than that in homogeneous soils. This study suggested the layered soil with sand overlying silt loam is more favorable to C. korshinkii growth in terms of water use than homogeneous soils in the desert–Loess Plateau transition zone. 相似文献
11.
The giant cactus Isolatocereus dumortieri is a dominant species of the semiarid scrub of central Mexico. Its reproductive period is during the dry season, and it produces essential resources (pollen, nectar and fruits) for a great variety of animal species. We related the production of reproductive structures with water variables in the soil–plant system. The main goal of the present study was to evaluate the consequences of a change in rainfall pattern on the phenology of I. dumortieri. We watered some plants in the dry season to simulate heavy rain events, and to test the hypothesis that water availability during the reproductive season has a negative effect on fruiting and a positive effect on vegetative growth. The seasonality of rain events caused variations in soil water potential and plant osmotic potential, and we found that both variables influenced fruit production. The regression models relating the number of fruits with soil water potential, rainfall and osmotic potential were significant for all three study periods. The highest production of reproductive structures occurred in the driest year (2009), during which there was an ENSO event. Watering did not have a significant effect on osmotic potential or growth in the cacti. However, the watering × time interaction had a negative effect on the number of immature fruits. That is, at the end of the experiment, the plants that received the most water showed a decrease in the number of fruits. Plant growth during the rainy period was significantly greater than during the dry period. The results support the hypothesis that a change in rainfall pattern during the dry season has an effect on fruit production. Vegetative growth, however, occurred only during the wet season. 相似文献
12.
Y. Olvera-Carrillo I. Méndez M.E. Sánchez-Coronado J. Márquez-Guzmán V.L. Barradas P. Huante A. Orozco-Segovia 《Journal of Arid Environments》2009,73(4-5):414-420
We studied in Opuntia tomentosa the effect of plant shade (orientation and distance), and the place where the seeds remained before germination. Seeds were collected in 1998 and a) sown immediately on soil (non-buried seeds), b) stored in the laboratory and sown on soil during the 1999 rainy season (control) or c) buried after collection (under the shade of a tree, a rock and in an open space), exhumed 7 months later and sown in 1999 (exhumed seeds). Seeds were sown under or outside the shade of several trees; or on the northern, eastern and western sides of a 14-m-tall tree. In 1999, germination was high in all samples, but the control seeds had delayed germination. After two rainy seasons, non-buried seeds had the lowest germination rate. Germination was not affected by the distance from the tree. Outside of the plant's shade, germination was low. Germination was affected more by the environmental heterogeneity than by the individual plant shade. Germination probabilities were the highest at 16–19 °C; field germination was zero at 20.6 °C. Seed polymorphism and microenvironmental heterogeneity spread germination across two rainy seasons creating a permanent seed bank. 相似文献
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河流在碳的运输过程中扮演着重要角色。为探究河流筑坝拦截后龙滩水库溶解无机碳(DIC)的来源和变化特征,于2016年7月和2017年1月采集水样,然后分析了河水DIC及其碳稳定同位素(δ13C)值。研究结果表明:(1)δ13CDIC值具有显著的时空差异,表明两个季节影响DIC的主要因素和DIC的来源并不相同。雨季,DIC及其δ13C主要分布在2.04~4.12 mmol·L^-1和-5.52‰^-2.87‰的范围内;旱季,水体DIC为3.33~4.61 mmol·L^-1,而δ13CDIC显著低于雨季为-15.90‰^-9.12‰。雨季,稀释效应显著降低了DIC浓度,由于水体热分层使得DIC在水柱剖面上差异显著,而旱季由于混合作用的影响,在剖面上差异较低。(2)在雨季,河流δ13CDIC较旱季明显偏正,碳酸盐岩的强烈风化输入大量HCO3-是DIC的主要来源。在旱季,DIC和δ13CDIC成反比关系,δ13CDIC在旱季变得更低,其大部分的DIC来自于土壤CO2输入和原位有机呼吸作用。旱季水体热分层消失,混合作用使得底部具有较低δ13C值的含碳水体上涌,并与表水层混合导致其δ13CDIC值低于雨季。这种季节性模式与自然河流不同,而是与湖泊的季节变化特征更为类似,说明河流拦截蓄水后逐渐湖沼化,并显著影响了DIC的循环。 相似文献
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We evaluated growth, abandonment, decay and emergence of new nests of the Neotropical termite Constrictotermes cyphergaster (Termitidae) and its association with the supporting vegetation in an area of caatinga (arid thorn scrub in the state of Paraíba, northeastern Brazil). In an area of 1 ha, a total of 272 nests were observed monthly, from March 2005 to March 2007. Of these, 245 nests were small, 9 were of medium size, and 18 were large nests. During the rainy season (from June to February), nests grew 94.2 L, whereas during the dry season (March–May), their total growth was 23 L. The number of abandoned nests was positively correlated with rainfall. Decomposition of nests was greater during the rainy season. The pattern of nest distribution was associated with the distribution of the primary supporting plants. Rainfall appears to be one of the most important factors in the dynamics of growth of nests of C. cyphergaster in the caatinga. 相似文献
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Biological soil crusts exhibit a dynamic response to seasonal rain and release from grazing with implications for soil stability 总被引：2，自引：0，他引：2
A. Jimenez Aguilar E. Huber-Sannwald J. Belnap D.R. Smart J.T. Arredondo Moreno 《Journal of Arid Environments》2009,73(12):1158-1169
In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments. 相似文献
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美国新墨西哥州中部的Sevilleta荒漠-草原生态交错区是监测全球气候变化和人类活动对生物影响的重要区域之一。本文以Sevilleta荒漠-草原生态交错区为例,利用气象资料和物候观测数据,通过回归和相关分析,研究在当前全球气候变暖的条件下,温度变化对交错群落的影响。研究结果表明,最近10年（19891998）该区域的温度变化具有反向不对称性:夏秋季节最高气温升高很明显,冬春季节最低气温降低较明显,而年平均最高气温升高较明显,平均最低气温和平均气温变化不明显。本区荒漠/草原过渡群落的两种优势物种Bouteloua eripoda和Bouteloua gracili对温度的变化表现出不同的动态响应。第二优势种Bouteloua gracilis的盖度随着冬春最低气温的降低呈现明显的下降趋势。第一优势种Boutel-oua eripoda的盖度与冬春最低气温之间没有明显的相关性。温度的变化对群落的结构目前还没有产生明显的影响。 相似文献
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Several Prosopis species have been introduced into South Africa in the last century and many of them have become invasive. This study investigates the water relations, effects of clearing, and the seasonal dynamics of groundwater use by invasive Prosopis trees. The trees were growing on deep sandy soils in the floodplain of an episodic river in the arid Northern Cape Province of South Africa. Data were collected on tree water uptake, evapotranspiration and water table depth over different seasons. Effects of tree clearing on groundwater were quantified by comparing data from a Prosopis invaded and an adjacent cleared area. Transpiration rates were less than 1.0 mm/d throughout the year and the trees showed structural and physiological adaptations to the combined low rainfall and low water holding capacity of the soils by developing very narrow sapwood areas and by closing their stomata. The trees abstracted groundwater as evidenced by the decline in borehole water levels in the Prosopis stand before the rainy season. Groundwater savings of up to 70 m3/month could be achieved in spring for each hectare of Prosopis cleared. The study suggests that clearing of invasive Prosopis would conserve groundwater in the arid parts of South Africa. 相似文献
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哀牢山北段地区气候特征及变化趋势 总被引：2，自引：0，他引：2
以哀牢山北段地区不同位置的景东（西侧盆地）、徐家坝（山顶）和楚雄（东侧盆地）为研究对象,利用三地1980～2005年同期气候观测资料,通过统计分析,探讨了哀牢山东、西侧盆地及山顶气温和降雨特征及长期变化趋势。结果表明：哀牢山北段地区最热月均出现在6月;最冷月,西侧盆地和山顶为1月,东侧盆地最冷月为12月;降雨的季节差异十分显著,雨季降雨量占全年的85％以上,以7月降雨量最多。从气候的长期变化趋势来看,年、季和月平均气温均呈现显著的升高趋势,气温的显著升高主要发生在干季,增温率为干季〉年〉雨季。最冷月均温增温率最大,最热月均温没有显著增加,气温年较差呈减小趋势。研究表明,哀牢山北段地区山顶及两侧盆地均呈现显著的变暖趋势,与植物生存直接相关的∑t≥0℃有效积温和∑t≥10℃活动积温也显著增加。气温的变化具有显著的空间差异,增温速率为东侧盆地〉山顶〉西侧盆地。山地迎风坡面（西坡）气温垂直递减率显著减小,背风坡面（东坡）气温垂直递减率整体呈增大趋势。降雨整体呈增加趋势,不同季节间降雨的变化差异显著,年降雨量的增加主要由于雨季降雨的增加,干季降雨呈微弱上升或下降趋势,降雨的增加率为东侧盆地〉山顶〉西侧盆地。哀牢山北段地区干季的干热气候特征进一步加剧,这种变化趋势在山地的背风坡面（东坡）表现得更加剧烈。 相似文献
20.
Spatial and temporal variability of soil properties under Caragana microphylla shrubs in the northwestern Shanxi Loess Plateau, China 总被引：1，自引：0，他引：1
Shrub-induced spatial and temporal heterogeneity of soil properties is common in arid and semiarid ecosystems, and it facilitates the development of plant species diversity. We selected 5-, 10-, 20-, 30-, and 40-year-old Caragana microphylla shrubs in the Shanxi Loess Plateau to evaluate the spatial and temporal heterogeneity of soil properties under and outside the shrub canopy. In addition, the presence of adventitious plant species was investigated to assess the development of herbaceous species diversity. Soil samples were collected from two depths (0-5 cm and 5-10 cm). The establishment and development of shrubs promoted temporal variation, improved soil texture, enhanced soil organic matter (SOM), total nitrogen (TN), and cation exchange capacity (CEC), and decreased pH, bulk density (BD), and soil water content (SWC). The results further confirmed that SOM, TN, and CEC were significantly higher at the center than at the outside of the shrub canopies (P < 0.05) and were higher at the 0-5 cm depth than at the 5-10 cm depth. Moreover, the differences in SOM, TN, and CEC from the center to the outside of shrub canopies were greater under 30- and 40-year-old shrubs than under 10- and 5-year-old shrubs. Furthermore, the spatiotemporal heterogeneity of the soil properties facilitated the development of herbaceous species diversity. 相似文献