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1.
In arid environments, soil fertility exhibits a high degree of spatial and temporal heterogeneity, which results from high climatic variability seasonally and heterogeneous plant distribution. However, because most desert areas have been altered by human activities, heterogeneous fertility would originate from grazing or logging activities. We evaluated spatial and temporal heterogeneity of soil fertility in cattle-excluded sites under and outside woody plant cover (Prosopis flexuosa and Larrea divaricata), and in sites disturbed by tree removal during wet and dry season in Ñacuñán Biosphere Reserve (Central Monte desert of Argentina). Soil organic matter, fulvic acids, bioavailable organic matter, and nitrate were lower outside plant canopy (8.9 mg g?1, 0.03 mg g?1, 8.2 mg g?1, and 4.17 mg kg?1, respectively). Total N, humic acids, and abundance of microbial functional groups did not show differences among sites. Most parameters differed between seasons, tending to be higher in the wet season. Overall soils of Ñacuñán Reserve are characterized by: a) more homogenous spatial pattern than expected from woody plant presence; b) very heterogeneous temporal pattern; and c) after two years, tree removal does not seem to induce infertile soil formation.  相似文献   

2.
This article reviews and analyzes the available information on range and livestock production in the Monte Desert. Cow–calf operations, goats for meat, and sheep for wool are the dominant production systems under continuous grazing. Rest-rotational grazing systems improved the efficiency of the current cow–calf production. Forage resources are primarily composed of perennial grasses and woody species. Rain-use efficiency for the total vegetation ranged from 3.9 to 4.8 kg DM ha?1 year?1 mm?1. Carrying capacity showed a broad range: 18.7, 4.5–64.5, and 21.6–89.3 ha AU?1 in the north, central, and south portions of the Monte, respectively. Mean crude protein (CP) content of grasses varied from 8.4 to 10.3 (wet season) and 7.1–3.7% DM (dry season) in the central west and Patagonia, respectively. Grasses predominated in the cattle diet, while the sheep diet was highly diverse because they ate most of the available plant species, and there was no unanimity as to the fact that goats are strictly browsers. Livestock diseases have lower prevalence indices than those recorded in other areas of the country. The high variability in carrying capacity values could be attributed to differences in rangeland condition and to the different methods used for its estimation. The CP levels in forage could meet cattle requirements provided that a proper-stocking rate were used. The most promising species for land rehabilitation are Opuntia, Atriplex spp., Eragrostis curvula and Cenchrus ciliaris. Priorities for future research should include topics such as assessment of the carrying capacity for most of the areas and nutrient content of the components of livestock diet, the livestock intake values, the economic feasibility of the use of complementary feeds and the development of seeding technology for valuable forage resources as Trichloris crinita, among others.  相似文献   

3.
Starting in 2005, we examined differences in vegetation for three consecutive years across an airport fence that separated heavily grazed areas from areas in which grazing had been excluded for 24 years in Mandalgobi, Mongolia. We performed repeated-measures analysis separately on two community types (dominated by Allium polyrrhizum and Achnatherum splendens, respectively) to compare the effects of fencing and year on the cover of different plant functional types. There was a significant fence × year interaction for grass cover in the Allium type (but not the Achnatherum type), due to greater cover of grasses inside the fence only when rainfall was sufficient during the growing season. The effect of grazing exclusion on perennial forb cover was confounded by a significant fence × year interaction in both types. In 2007, perennial forbs were found outside the fence, but had almost disappeared inside the fence, resulting in this interaction. Annual forbs only had much greater cover values inside the fence than outside in 2006, also resulting in a significant fence × year interaction in both community types. This study thus suggests that the high rainfall variability in arid and semi-arid rangelands may modify the effects of long-term exclosure on vegetation.  相似文献   

4.
The purpose of our study was to better understand seed germination ecology of the spring annual short-lived Olimarabidopsis pumila, which grows in the Gurbantonggut Desert, China. Seeds underwent after-ripening at 4, 20 ± 2 (room temperature) and 30 °C. After dormancy was broken, germination capacity was a function of temperature and presence of light. For the temperature range studied (4–30 °C), germination capacity was significantly higher between 15 and 25 °C than at temperatures above or below them. Alternating temperatures of 20/10, 25/10 and 25/15 °C were favorable for germination. Although GA3 did promote dark germination of seeds, GA3 did not replace light for germination. Seeds germinated to >75% if light exposure time was over 8 h and temperature and moisture conditions were favorable. Seeds were able to germinate at relatively low water potentials (83% at ?0.41 MPa), but decreasing water potentials produced detrimental effects on germination percentage and rate. Thus, dormancy characteristics and germination behavior of O. pumila seeds ensure that germination occurs in the desert only when soil moisture conditions are favorable for seedling establishment and survival.  相似文献   

5.
Pine plantations coexist with Stipa tenacissima grasslands in many semiarid western Mediterranean areas. We compared three microsites created by a 30-year-old Pinus halepensis plantation: below pine plantation line (BP), below canopy of pines (BC) and interline bare band (BA). They were evaluated in terms of soil properties, pine litter and suitability as recruitment niches for S. tenacissima. Next, in a manipulative experiment in growth chambers we tested the hypothesis that pine litter interferes with the seedling emergence of S. tenacissima. Three treatments in pots were compared: (a) soil from BA; (b) intact soil + litter from BP; and (c) soil + litter from BP, which was mixed in the laboratory (BPMX). In the field the main microsite differences were pine cover and litter cover and thickness. Seedling emergence was significantly greater in BA than in BP. Emergence and litter depth fits a linear regression model. In the growth chamber litter did not interfere with the emergence of S. tenacissima. However, seedlings grown without litter were 28% longer and their mass was 27% greater than in the litter treatments. The detected pine litter interference may be relevant for plant dynamics and might be considered in forestry management programs.  相似文献   

6.
Laboratory experiments were conduced to assess the synergic effect of chilling and light on photosystem II photochemistry of the halophyte, Sarcocornia fruticosa, grown at different salinity concentrations (0, 170, 340, 510 and 1030 mM). Chlorophyll fluorescence was measured after chilling (at 5 °C in darkness) and light-chilling (at 5 °C and 700 μmol m?2 s?1) treatments, and after 24 h of recovery (at 20 °C and 75 μmol m?2 s?1). At 5 °C and 700 μmol m?2 s?1, plants grown with 0 and 170 mM NaCl showed the lowest Fv/Fm values, whereas quantum efficiency of PSII (ΦPSII) was higher for plants grown at 170 and 340 mM NaCl, these results being consistent after two exposures to chilling treatments. Susceptibility to photoinhibition decreases when low temperature and high light are combined with high salinity. Therefore, populations of S. fruticosa that occur in arid environments with salinities c. 340 mM could show a higher tolerance to light-chilling.  相似文献   

7.
Due to the climate change, vegetation of tundra ecosystems is predicted to shift toward shrub and tree dominance, and this change may influence bryophytes. To estimate how changes in growing environment and the dominance of vascular plants influence bryophyte abundance, we compared the relationship of occurrence of bryophytes among other plant types in a five-year experiment of warming (T), fertilization (F) and T + F in two vegetation types, heath and meadow, in a subarctic–alpine ecosystem. We compared individual leaf area among shrub species to confirm that deciduous shrubs might cause severe shading effect. Effects of neighboring functional types on the performance of Hylocomium splendens was also analyzed.Results show that F and T + F treatments significantly influenced bryophyte abundance negatively. Under natural conditions, bryophytes in the heath site were negatively related to the abundance of shrubs and lichens and the relationship between lichens and bryophytes strengthened after the experimental period. After five years of experimental treatments in the meadow, a positive abundance relationship emerged between bryophytes and deciduous shrubs, evergreen shrubs and forbs. This relationship was not found in the heath site. Our study therefore shows that the abundance relationships between bryophytes and plants in two vegetation types within the same area can be different. Deciduous shrubs had larger leaf area than evergreen shrubs but did not show any shading effect on H. splendens.  相似文献   

8.
Corsac fox (Vulpes corsac) and red fox (Vulpes vulpes) diets often consist of small quantities of vegetation, including fruit and seeds that may represent important sources of energy and nutrition. However, details of the species consumed are few, but may provide insight into the role of foxes as seed dispersers. We analyzed scats of corsac (n = 408) and red foxes (n = 533) collected in an arid region of Mongolia from June 2006 to June 2007. We found 13 seed species in corsac scats, the most common being Allium polyrhizum, Asparagus gobicus, and Tribulus terrestris, and 12 species in red fox scats, the most common being Amygdalus pedunculata, Corispermum mongolicum, and T. terrestris. The proportion of scats with seeds varied significantly by season for both foxes. Seeds occurred most frequently during the breeding period, which corresponded with winter, and least frequently during the dispersal period in autumn for both species. We detected no differences in the proportion of scats with seeds between species seasonally. Our results suggest that fruit represents an important component of diet, especially during winter when availability of other prey items is low, and that both foxes may facilitate seed dispersal of some plant species.  相似文献   

9.
A quantitative ethnobotanical study was conducted in the semi-arid Bolivian Andes community of Apillapampa to evaluate the impact of site accessibility on the diversity and perceived usefulness of (sub-)woody plants. Vegetation was sampled in thirty-six transects of 50 × 2 m2, whereas data on plant uses were obtained from 13 local Quechua participants. Accessibility of sample sites correlated negatively with plant diversity, but positively with perceived usefulness. Hence, in spite of being less diverse, vegetation of more accessible sites was perceived as more useful to people than vegetation of more remote and also more diverse sites. This result contributes to the validity of the widely accepted notion that “more accessible plant resources are more useful to people”, not only at the level of individual plant species, but also for entire vegetation communities. In this respect, our finding that people attribute an equal usefulness to the vegetation of two local ecological zones (i.e. prepuna and puna) most likely reflects their similar accessibility from the village centre, which is located on the edge between both zones.  相似文献   

10.
Biological soil crusts cover large areas of the Gurbantunggut Desert in northwestern China where they make a significant contribution to soil stability and fertility. The aim of this study was to quantify the potential nitrogen-fixing activity (NA) of different types of biological soil crusts in the Gurbantunggut Desert. The results suggest that NA (nmol C2H4 m?2 h?1) for each type of crusts was highly variable. Seasonal variation was also important, with all three types of crusts responding in a similar way to changes in environmental conditions. From March to May, NA was relatively low for all crust types. During this season, NA was 2.26 × 103 for cyanobacterial crust followed by lichen crust (6.54 × 102) and moss crust (6.38 × 102). From June to October, all crust types reached their highest level of NA, especially lichen crust and moss crust (p < 0.01). The NA of cyanobacterial crust (9.81 × 103) was higher than that of lichen crust (9.06 × 103) and moss crust (2.03 × 103). From November to February, when temperatures were consistently low (<0 °C), NA was at its lowest level, especially in cyanobacterial crust (4.18 × 102) and moss crust (5.43 × 102) (p < 0.01). Our results indicate that species composition is critical when estimating N inputs in desert ecosystems. In addition, all three types of crusts generally responded in a similar way to environmental conditions. The presence of N fixation activity in all crusts may contribute to the maintenance of fertility in sparsely vegetated areas and provide surrounding vascular plant with fixed nitrogen.  相似文献   

11.
To obtain the basic information required before using Populus alba L. to phytoremediate degraded saline environments, we investigated the effects of saline irrigation on the growth, survival, Na partitioning, and Na dynamics of 1-year-old rooted cuttings. The plants were grown in a greenhouse in lysimeters containing sandy soil and were watered with field water (control) or solutions containing either 2000 or 5000 mg L?1 of a mixture of NaCl and CaCl2 (low- and high-salt treatments, respectively). All plants in the control and the low-salt treatment survived after 1 year of treatment, but the high-salt treatment significantly decreased growth and caused 20% mortality. Strong Na partitioning was observed in the roots in all three treatments, suggesting that this is an important salt tolerance mechanism in P. alba. Total Na uptake was similar in the low-salt and high-salt treatments, and was about 3 times the value in the control. However, the compartmentalization of Na in fallen leaves, dead leaves and dead branches in the high-salt treatment was about twice the level in the low-salt treatment. The plants accumulate Na under moderate levels of salinity, suggesting that P. alba is a good candidate for phytoremediating salinized soil.  相似文献   

12.
Monitoring cattle inflows and outflows over time is a good indicator of herd productivity. In this study, ninety households were monitored for a year to determine the effect of season, rangeland type and herd size on births, purchases, sales, deaths, off-take, cattle production potential (CPP) and cattle production efficiency (CPE) in the sweet and sour rangelands of South Africa. Most births were recorded in large herds in the sour rangelands during the hot-wet season (P < 0.05). Farmers with large herd sizes purchased significantly more cattle compared to those with small herd sizes. Cattle sales were significantly high in the large herds in the cool-dry season. Mortality was significantly high in the hot-wet season in the sour rangeland and was mainly caused by gall-sickness (24%) and redwater (20%). The highest mortalities were observed in cows (45%). Households owning small herds in the sweet rangeland had the lowest CPP in the cool-dry season (P < 0.05). The CPE was significantly high in the households owning large herds in the sweet rangeland. It was concluded that, although the CPP was low in the sweet rangeland, households in these areas had higher CPE compared to those in the sour rangelands.  相似文献   

13.
Although Jatropha curcas, an important tropical biofuel crop, is reputed for its drought resistance, its ability to perform under dry conditions has hardly been investigated. In a greenhouse experiment we investigated the plant–water relationships of Jatropha seedlings from different accessions under different levels of drought stress. There was little difference in plant–water relations between accessions. Drought significantly reduced leaf area, biomass and relative growth rate, but had no effect on specific leaf area, daily range in leaf water potential, leaf water content, transpiration efficiency or aboveground biomass water productivity, corrected for atmospheric conditions. Stem wood density was equally low (0.26 g cm?3) for all treatments. Stem water content was lowest for dry treatment seedlings. Based on these results, Jatropha could be characterized as a stem-succulent tree. In contrast to other stem-succulent deciduous trees, leaves were not shed immediately after the seedlings were confronted with drought. Instead, at the onset of drought, leaves with a higher adaxial stomatal density were formed, after which leaves were only gradually shed. The role of the succulent stem in the water economy of Jatropha was confined to balancing the small water losses of the leaves during drought.  相似文献   

14.
Agave angustifolia is taken from wild populations in the desert of Sonora, Mexico, to make the alcoholic drink known as “bacanora”. An increase in the demand for this beverage has led to overexploitation of these agaves. We used AFLP to measure the genetic variability within and between natural populations of the species. The fixation index (FST) and population genetic distances (GD) were determined for three populations of A. angustifolia. At the clonal level, the expected heterozygosis (HE), the proportion of polymorphic loci (P), and the genetic similarity indices (GSIs) were lower in one population. Total GSI for adults and offshoots was 0.924. There were no differences in the GSI within or between the populations and dendrogram showed three groups that partially reflect the geographical distribution of the populations. Some degree of genetic variation between mother plants and their vegetatively produced rhizomes was observed. At the species level, total expected heterozygosity was high (HT = 0.314) with a P value of 78%, and intermediate gene flow (Nm = 1.18), giving rise to a moderate fixation index (FST = 0.175). Nm, FST and GD values observed, indicate that urgent measures must be implemented to preserve the genetic diversity.  相似文献   

15.
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   

16.
Aboveground biomass in Tibetan grasslands   总被引：2，自引：0，他引：2  
This study investigated spatial patterns and environmental controls of aboveground biomass (AGB) in alpine grasslands on the Tibetan Plateau by integrating AGB data collected from 135 sites during 2001–2004 and concurrent enhanced vegetation index derived from MODIS data sets. The AGB was estimated at 68.8 g m?2, with a larger value (90.8 g m?2) in alpine meadow than in alpine steppe (50.1 g m?2). It increased with growing season precipitation (GSP), but did not show a significant overall trend with growing season temperature (GST) although it was negatively correlated with GST at dry environments (<200 mm of GSP). Soil texture also influenced AGB, but the effect was coupled with precipitation; increased silt content caused a decrease of AGB at small GSP, and generated a meaningful increase under humid conditions. The correlation between AGB and sand content indicated an opposite trend with that between AGB and silt content. An analysis of general linear model depicted that precipitation, temperature, and soil texture together explained 54.2% of total variance in AGB. Our results suggest that moisture availability is a critical control of plant production, but temperature and soil texture also affect vegetation growth in high-altitude regions.  相似文献   

17.
We researched the soil seed bank dynamics of Thymus funkii subsp. funkii, a gypsovag shrub endemic to the southeastern Iberian Peninsula, to determine possible reasons for low recruitment in isolated populations growing on crusted gypsum soils. Recruitment-restriction hypotheses involving main factors in the seed bank dynamics were analysed, and a diagrammatic dynamics model drafted from a population perspective. Viable seed production averaged 362 per plant. Seed shadows resulting from primary dispersal were concentrated under the mother plant. There were two thyme-seed predators: coleopteran larvae (pre-dispersal phase) and Messor bouvieri ants (pre- and post-dispersal phases), which predated 16.4% and 3.8% of population yield, respectively. However, ants may simultaneously contribute to the spatial secondary dispersal, since they lost a small fraction of seeds they harvested. Seeds showed innate physiological dormancy to high summer temperatures, although this disappeared rapidly. The response of germination to other temperature × light conditions was wide and rapid. No permanent seed bank was detected in the soil. Seeds buried in the upper soil layer (2 cm) germinated highly and fast. In contrast, a significant fraction of seeds buried deeply (8 cm) remained viable for over one year. Germination in the field accounted for only 1.0% of the seed output, and seed death due to pathogen attack and aging was also low (3.0%). Seedling emergence was confined to autumn and showed a high correlation with total plant cover, irrespective of plant species. Seedling survival was very low. The small spatial correspondence between primary dispersal and seedling emergence patterns may reflect the importance of secondary dispersal in T. funkii seed bank dynamics. Hypotheses and consequences of such horizontal seed movements for conservation management are discussed.  相似文献   

18.
Allometric equations and community biomass stocks are presented for Guiera senegalensis J.F. Gmel (Gs) and Piliostigma reticulatum (DC.) Hochst (Pr) – two native shrub species in the Sahel. These shrubs are of interest because they dominate semi-arid sub-Sahalien Africa but have been largely overlooked as a key biomass component and regulator of ecosystem composition and function in this landscape. In Year 1, best predictors of aboveground biomass were height and number of stems (Gs) and crown diameter (Pr); and for belowground biomass were height and basal diameter (Gs) and basal diameter (Pr). In Year 2, height and crown diameter were the best predictors of aboveground biomass (R2 = 0.90 for Gs and 0.87 for Pr), whereas basal diameter and number of stems (Gs) and basal diameter (Pr) were best predictors of belowground biomass. Peak-season biomass estimates ranged from 0.44 to 4.58 ton ha?1 (mean = 2.38 ton ha?1) in the Gs sites and from 0.33 to 7.38 ton ha?1 (mean = 3.71 ton ha?1) in the Pr communities. Both species exhibited unusually large root:shoot ratios (4.5:1 for Gs and 10.2:1 for Pr). Although models differ between years, allometric relationships provide reasonable biomass estimates for Gs and Pr.  相似文献   

19.
Sexual reproduction and vegetative propagation require the establishment of morphologically diverse reproductive structures (seedlings and stem segments). This study assesses both types of Cylindropuntia leptocaulis recruitment in two microenvironments protected from herbivory (in open space and under the canopy of Larrea tridentata) and with two soil types (collected below L. tridentata canopy and from open space).An observational study revealed that sexual establishment was very limited (only 8 juveniles/ha were found), while clonal establishment was more frequent (59 juveniles/ha); both types of propagule were found only under shrub canopy.Field experiments showed that, as in other Cylindropuntia species but contrasting with findings for Opuntia species, seeds germinated and seedlings survived under nurse plants as well as in open space, but they grew faster in the former environment. Faster growth under canopy shade provides better chances of successful recruitment to later life-cycle stages. Stem segments never established in open space, requiring the shade of nurse plants. This may be due to physiological constraints imposed by their small volume. In synthesis, the results indicate that clonal propagation is the most important recruitment mechanism in C. leptocaulis populations, and that it takes places under shrub canopy.  相似文献   

20.
《Polar Science》2009,3(4):235-245
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