共查询到20条相似文献,搜索用时 31 毫秒
1.
Michael S. Peek Andrew J. McElrone Irwin N. Forseth 《Journal of Arid Environments》2004,58(4):439-449
Over the course of a day, aridland plants experience a range of incident photosynthetic photon flux (PPF) spanning three orders of magnitude. Rapid photosynthetic responses to changes in PPF have large effects on individual plant carbon gain and water use patterns, hence are important to plant distribution and success. We investigated the response over time of photosynthesis (A), stomatal conductance (g), and inter-cellular CO2 concentration (Ci) to step changes in PPF in a long-lived aridland perennial that typically occurs in two contrasting microhabitats, shade under shrubs of other species and unshaded inter-shrub spaces. An initial rapid response in A and Ci for plants in both microhabitats occurred after abrupt changes in PPF. This was followed by slower changes in these parameters during the rest of the light or dark period. Stomatal conductance responded more gradually to step changes in PPF. The initial increase in A after a dark cycle was significantly greater for plants under shrubs than for plants in inter-shrub spaces, but other changes in A, g and Ci did not differ. We attribute the similar responses in plants from different microhabitats to natural variations in solar radiation and limited selection for differentiation due to population gene pools dominated by plants in the open. Our results support the hypothesis that variable light regimes select for photosynthetic gas exchange processes that closely track changes in incident PPF. Our data also support the hypothesis that gas exchange responses to variable light regimes in aridland plants minimize trade-offs between carbon gain and water loss. 相似文献
2.
大气CO2浓度升高和施氮对棉田土壤理化性质及微生物区系的影响 总被引:2,自引:0,他引:2
针对耕地非农转化过程中产生的一系列社会问题,采用参与性农户调查方法,对西部欠发达地区西宁市郊区5个样本村190户农户进行了随机入户调查。根据城市开发进程、到市区距离和种植类型等条件,将调查样本村分为近郊城区化农村、近郊农村和远郊农村,就农户对耕地非农转换的基本认知及耕地非农转换的经济、社会和环境价值感知进行分析。结果表明:耕地征用后农户能理性感知和判别耕地非农转换价值,并普遍认为失去耕地后生活费用增加、生活保障降低、收入来源和就业机会少;感知主要受耕地数量、区位条件、耕地开发阶段等因素的影响;处于不同区位条件的农户对耕地非农转换的价值感知存在差异性,城区化农户已逐渐适应城市生活,近郊农户的非农转换经济和社会感知压力最大,远郊农民也感知经济和生活保障压力,但更希望能通过打工增加收入。 相似文献
3.
The purpose of this study was to examine physiological correlates to the phenomenon of epidermal browning and saguaro decline in Saguaro National Monument. Gas exchange characteristics, surface temperatures, and the extent of epidermal browning in tissues of both healthy and declining saguaro cacti (Carnegiea gigantea) at different solar orientations were examined in eight long-term monitoring plots in the Rincon Mountain District of the Saguaro National Monument near Tucson, Arizona during both wet and dry seasons and years.Daily maximum surface temperatures were greatest on west-oriented tissues, as predicted by a simple model. However, south- and south-west-oriented tissues showed the highest browning indices, suggesting that browning may be more related to cumulative thermal loading than to extreme late afternoon temperature events. During the wet season, maximum nocturnal CO2uptake rates and total nocturnal CO2uptake were negatively correlated with browning index. Uptake rates during dry seasons and dry years was minimal, and not related to browning indices. However, healthy tissues of saguaros that also had tissues with high browning indices had wet-season maximum CO2uptake rates as high as saguaros without damaged tissues, suggesting that the browning is not systemic but rather is tissue- and angle-specific. Instantaneous measures of water-use efficiency did not vary significantly or predictably by angle, but rather were greatest during night-time and in tissues when CO2uptake was greatest. We suggest that browning symptoms on cacti are most likely due to natural abiotic stress, and are unrelated to systemic pollution stress or increased UV-B radiation. 相似文献
4.
Hesperaloe funifera 《Journal of Arid Environments》1996,33(4):399-407
Hesperaloe funifera(Agavaceae) is being investigated as a new specialty-fiber crop for arid lands. The objective of this study was to examine the effects of reduced solar radiation on photosynthesis and growth in this CAM species.Peak CO2uptake integrated through 24 h was found to be highest during the fall. Although shading greatly reduced CO2uptake in fall and winter, the decrease was not statistically significant for the spring and summer. Total biomass was significantly different for the three light treatments, with average fresh weights of 5243 g, 4488 g, and 3671 g for the full-sun, 53%-sun, and 20%-sun treatments, respectively. The greatest differences were found in the crown growth, which would affect future production of both leaves and flower stalks.Photosynthesis and growth results suggest that the cultivation ofHesperaloe funiferawill be favored in well-lit environments characteristic of arid or semi-arid climates. 相似文献
5.
Domestication of wild plants needs efforts focused particularly on the development of the theoretical basis of plant responses to environmental conditions. The objective of this study was to assess the effect of radiation on seedling growth and physiology of Prosopis alba, P. chilensis, P. flexuosa and P. glandulosa. Seedlings were grown in a greenhouse and randomly assigned to three light environments: full-sun, 52% sun, and 38% sun. No significant differences were found in the rate of leaf appearance and plant height 60 days after the light treatments began. Instantaneous CO2uptake was not affected by the light environment during leaf development and did not differ among species. Variations in radiation availability resulted in significant differences in biomass accumulation, shoot/root ratio, protein and total non-structural carbohydrates contents. The practice of shading seedlings reduces the chances of survival ofProsopis due to an increase of the shoot/root ratio and a reduction of total biomass, stored carbohydrates, and the C:N balance. 相似文献
6.
采用动态密闭气室法测定分析了科尔沁沙地典型玉米(Zea mays)农田垄上和垄间土壤呼吸速率的差异及自养和异养呼吸特征,并估算了生态系统碳平衡。结果表明:(1)垄上和垄间土壤呼吸速率存在极显著差异(p0.001),且存在线性关系(p0.05);季节水平上垄上土壤呼吸可解释垄间土壤呼吸98.4%的变异。(2)季节水平上土壤总呼吸(RS)、异养呼吸(RH)和自养呼吸(RA)的温度敏感性指数Q10大小顺序为:RA(4.35)RS(3.10)RH(2.08)。(3)RS和RH之间存在显著差异,RA与RS和RH之间不存在显著差异;RA占RS比例的季节变化范围为28.1%~71.1%,生长季RH和RA占RS的比例均值分别为44.4%和55.6%。(4)科尔沁沙地典型农田生态系统在生长季为碳汇,可净固存大气CO2-C的量为659.1g·m-2。 相似文献
7.
The effects of elevated atmospheric carbon dioxide [CO2] on microbial communities in arid rhizosphere soils beneath Larrea tridentata were examined. Roots of Larrea were harvested from plots fumigated with elevated or ambient levels of [CO2] using Free-Air CO2 Enrichment (FACE) technology. Twelve bacterial and fungal rRNA gene libraries were constructed, sequenced and categorized into operational taxonomical units (OTUs). There was a significant decrease in OTUs within the Firmicutes (bacteria) in elevated [CO2], and increase in Basiomycota (fungi) in rhizosphere soils of plots exposed to ambient [CO2]. Phylogenetic analyses indicated that OTUs belonged to a wide range of bacterial and fungal taxa. To further study changes in bacterial communities, Quantitative Polymerase Chain Reaction (QPCR) was used to quantify populations of bacteria in rhizosphere soil. The concentration of total bacteria 16S rDNA was similar in conditions of enriched and ambient [CO2]. However, QPCR of Gram-positive microorganisms showed a 43% decrease in the population in elevated [CO2]. The decrease in representation of Gram positives and the similar values for total bacterial DNA suggest that the representation of other bacterial taxa was promoted by elevated [CO2]. These results indicate that elevated [CO2] changes structure and representation of microorganisms associated with roots of desert plants. 相似文献
8.
D.E. Fresnillo Fedorenko O.A. Fernández C.A. Busso O.E. Elia 《Journal of Arid Environments》1996,33(4):409-416
The phenology ofMedicago minimavar.minimaandErodium cicutariumwas studied at two different field sites in the Calden District (approx. 10 million ha), a temperate semi-arid phytogeographical region in central Argentina. One site had been protected from wild and domestic herbivores for the 6 previous years. The other adjacent site had been exposed to continuous grazing by cattle for several decades. A phenological key was made for each species in 1988, and this key was improved during the 1989 growing season when phenological observations were made every 1–3 weeks.The growth cycle ofM. minimaandE. cicutariumwas similar at the two studied sites. Initiation of the cycle occurred in autumn and appeared to be associated with soil water availability. Phenological patterns were very dynamic at the reproductive stage in both species. This stage started earlier and was faster inE. cicutariumthan inM. minima. The end of the growing season occurred during late spring, concomitant with high maximum air temperatures. Our results suggest that these species hasten their development when air temperature increases and soil water availability decreases. This could be an important strategy in these species which allows them to persist as seeds, and produce a new generation under favourable environmental conditions. 相似文献
9.
Bo Elberling Rasmus Fensholt L. Larsen A-I. S. Petersen Inge Sandholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):47-56
Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO2 to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO2 effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO2 production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO2 effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO2 m?2 s?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO2 production was simulated to be in the range of 31–38 mol C m?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter. 相似文献
10.
H. Gonzlez Rodríguez I. Cantú Silva M. V. Gmez Meza R. G. Ramírez Lozano 《Journal of Arid Environments》2004,58(4):214
As an approach to understand how diurnal and seasonal plant water potentials (Ψ) are related to soil water-content and evaporative demand components, the responses of six thornscrub shrubs species (Havardia pallens, Acacia rigidula, Eysenhardtia texana, Diospyros texana, Randia rhagocarpa, and Bernardia myricaefolia) of the north-eastern region of Mexico to drought stress were investigated during the course of 1 year. All study species showed the typical diurnal pattern of variation in Ψ. That is, Ψ decreased gradually from predawn (Ψpd) maximal values to reach minima at midday (Ψmd) and began to recover in the late afternoon. On a diurnal basis and with adequate soil water-content (>0.20 kg kg−1), diurnal Ψ values differed among shrub species and were negatively and significantly (p<0.001) correlated with air temperature (r=−0.741 to −0.883) and vapor pressure deficit (r=−0.750 to −0.817); in contrast, a positive and significant (p<0.001) relationship was found to exist with relative humidity (r=0.758–0.842). On a seasonal basis, during the wettest period (soil water-content>0.20 kg kg−1), higher Ψpd (−0.10 MPa) and Ψmd (−1.16 MPa) values were observed in R. rhagocarpa, whereas lower figures (−0.26 and −2.73 MPa, respectively) were detected in A. rigidula. On the other hand, during the driest period (soil water-content<0.15 kg kg−1), Ψpd and Ψmd values were below −7.3 MPa; i.e. when shrubs species faced severe water deficit. Soil water-content at different soil layers, monthly mean relative humidity and monthly precipitation were significantly correlated with both Ψpd (r=0.538–0.953; p<0.01) and Ψmd (r=0.431–0.906; p<0.05). Average soil water-content in the 0–50 cm soil depth profile explained between 70% and 87% of the variation in Ψpd. Results have shown that when gravimetric soil water-content values were above 0.15 kg kg−1, Ψpd values were high and constant; below this threshold value, Ψ declined gradually. Among all shrub species, A. rigidula appeared to be the most drought tolerant of the six species since during dry periods it tends to sustain significantly higher Ψpd in relation to B. myricaefolia. The remaining species showed an intermediate pattern. It is concluded that the ability of shrub species to cope with drought stress depends on the pattern of water uptake and the extent to control water loss through the transpirational flux. 相似文献
11.
CO2 and temperature records at Mauna Loa, Hawaii, and other observation stations show that the correlation between CO2 and temperature is not significant. These stations are located away from big cities, and in various latitudes and hemispheres. But the correlation is significant in global mean data. Over the last five decades, CO2 has grown at an accelerating rate with no corresponding rise in temperature in the stations. This discrepancy indicates that CO2 probably is not the driving force of temperature change globally but only locally (mainly in big cities). We suggest that the Earth''s atmospheric concentration of CO2 is too low to drive global temperature change. Our empirical perception of the global warming record is due to the urban heat island effect:temperature rises in areas with rising population density and rising industrial activity. This effect mainly occurs in the areas with high population and intense human activities, and is not representative of global warming. Regions far from cities, such as the Mauna Loa highland, show no evident warming trend. The global monthly mean temperature calculated by record data, widely used by academic researchers, shows R2=0.765, a high degree of correlation with CO2. However, the R2 shows much less significance (mean R2=0.024) if calculated by each record for 188 selected stations over the world. This test suggests that the inflated high correlation between CO2 and temperature (mean R2=0.765-0.024=0.741) used in reports from the Intergovernmental Panel on Climate Change (IPCC) was very likely produced during data correction and processing. This untrue global monthly mean temperature has created a picture:human emission drives global warming. 相似文献
12.
Water requirements for germination and early seedling establishment in four African savanna woody plant species 总被引:1,自引:0,他引:1
The aim of this study was to determine the water requirements for germination and early seedling establishment of four African savanna tree species, namelyAcacia karroo, A. nilotica, A. tortilisandMundulea sericea. The acacias are characteristic of nutrient-rich, andM. sericeaof nutrient-poor savannas. Imbibition times of scarified seeds ofA. karroo(4 h),M. sericea(6 h) andA. tortilis(8 h) were rapid relative toA. nilotica(28 h) and were inversely correlated with seed size. Imbibed water is lost in about 2 h after drying at 25°C for all species exceptA. nilotica(only 70% moisture loss). Seeds ofA. karrooandM. sericeakept at 40°C dried to below their original moisture contents within 2 h. Seeds ofA. niloticaandA. tortilisdried at 40°C lost viability relative to (undried) control seeds, while there was no significant loss of viability forA. karrooandM. sericea. For fully imbibed seeds to germinate in sandy savanna soils, all four species required at least the equivalent of 3 mm rainfall every 2 days under mild greenhouse conditions. However, most ungerminated seeds were still viable despite drying-out from a fully imbibed state. Maintenance of soil at 50% field capacity (FC), or watering to FC every 9th day is the maintenance requirements for 2-week-old seedlings ofA. niloticaandM. sericeato continue growth for a further 5 weeks under greenhouse conditions, althoughA. niloticamostly survived 25% FC with one seedling surviving 12·5% FC. Root penetration was rapid in sandy soils, withA. niloticaandM. sericeaattaining a depth of 40 cm within 15 days. Frequent, but not necessarily high, rainfall appears to be essential for germination and seedling survival over the first 7 weeks. 相似文献
13.
The alleviative effects of exogenous salicylic acid(SA) on plants against drought stress were assessed in Gardenia jasminoides seedlings treated with different concentrations of SA.Drought stress was simulated to a moderate level by 15% polyethylene glycol(PEG) 6000 treatment.Seedlings exposed to 15% PEG for 14 days exhibited a decrease in aboveground and underground dry mass,seedling height,root length,relative water content,photosynthetic pigment content,net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and water use efficiency.In PEG-stressed plants,the levels of proline,malondialdehyde(MDA),hydrogen peroxide(H_2O_2),and electrolyte leakage rose significantly,whereas antioxidative activity,including superoxide,peroxidase,and catalase activities,declined in leaves.However,the presence of SA provided an effective method of mitigating PEG-caused physiological stresses on G.jasminoides seedlings,which depended on SA levels.PEG-treated plants exposed to SA at 0.5–1.0 mmol/L significantly eased PEG-induced growth inhibition.Application of SA,especially at concentrations of 0.5–1.0 mmol/L,considerably improved photosynthetic pigments,photosynthesis,antioxidative activity,relative water content,and proline accumulation,and decreased MDA content,H_2O_2 content,and electrolyte leakage.By contrast,the positive effects were not evident,or even more severe,in PEG+SA4 treatment.Based on these physiological and biochemical data,a suitable concentration of SA,potential growth regulators,could be applied to enhance the drought tolerance of G.jasminoides. 相似文献
14.
Effects of pruning on biomass growth in Prosopis juliflora were examined under dryland conditions in the Sudan. Growth parameters were followed for a total period of 32 months and water content, and gas exchange measurements were carried out. Heavily pruned trees yielded more than six times larger usable wood volume and produced 60% more leaf biomass than the control. The water status in pruned trees was improved which also had a more efficient CO2 assimilation rate, associated with higher stomatal conductance. The results and their implications for the management of sparsely spaced P. juliflora are discussed in relation to agroforestry. 相似文献
15.
Field and laboratory studies were conducted during the period May 1993–April 1994 on the cocoons and hatchlings ofAporrectodea calignosa(Savigny 1826), a common earthworm found in Benghazi, Libya. Cocoon production started in August 1993 and continued until April 1994. A positive correlation between soil moisture (r=0.74;p< 0.05) and cocoon production, and a negative one between soil temperature (r=−0.85;p< 0.05) on cocoon production were found. Mean incubation time was 47 days. Some cocoons contained a single worm (single hatchling) whereas the majority of them (68%) contained two, the first hatchling and second hatchling. The rate of change of body mass (F=2.18;p>0.05) and the average body mass (F=1.25;p>0.05) of the single, first and second hatchlings were similar. 相似文献
16.
Metabolic activity of Biological Soil Crusts (BSCs) is principally dependent on moisture availability, but also on temperature and light conditions. Less understood is how BSCs respond to elevated atmospheric CO2. This paper reports laboratory experimental results of elevated atmospheric CO2 on carbon fluxes for cyanobacterial BSCs. The study uses newly designed dynamic gas exchange chambers in which the internal atmosphere was controlled. CO2 flux was monitored during controlled experiments in two phases under simulated rainfall events (2 & 5 mm plus control with no wetting) each lasting 3 days with a dry period in between. Phase 1 subjected crusts to 392 ppm CO2 (representing ambient level) in dry air; in phase 2, the CO2 concentration was 801 ppm. Both phases exhibited significant efflux (respiration) of CO2 immediately after wetting, followed by substantial influx (sequestration) of CO2. Samples subject to 2 mm wetting sequestered an order of magnitude more C under elevated CO2 than at ambient CO2; for samples subject to 5 mm wetting, this increase was threefold. The findings highlight the role of BSCs in future carbon budgets by enabling greater sequestration into dryland soils even under enhanced atmospheric CO2 concentrations, following both light and heavy rainfall events. 相似文献
17.
We designed, constructed, calibrated and field-tested a lightweight (30 kg), 4.2 m diameter, 16.4 m3 polyethylene-covered dome static chamber ecosystem gas exchange cuvette that can quantify ecosystem CO2 and water vapour fluxes as low as 0.1 μmol CO2 m−2 s−1 and 0.1 mmol H2O m−2 s−1 with little impact on environmental conditions. Fluxes measured in May 2001 in an intact Great Basin sagebrush ecosystem at midday were significantly higher than in an adjacent post-wildfire successional ecosystem, with observed ranges from –0.71 to 1.49 μmol CO2 m−2 s−1 for CO2 and from –0.09 to 0.53 mmol H2O m−2 s−1 for water vapour. 相似文献
18.
Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in response to nitrogen supply and water stress 总被引:1,自引:0,他引:1
A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUEP) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg−1 soil) regimes. Water stress decreased C, N and P accumulation, NUEP, N and P uptake efficiency (NUtEN and NUtEP) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUEP, NUtEN and NUtEP in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUEP, although NUtEN and NUtEP increased with Nh in the same water treatment. Even so, NUEN decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUEP. 相似文献
19.
蒸腾速率(Tr)是植物生理生态学研究中表征蒸腾耗水的常用指标,研究植物的蒸腾耗水有助于了解当地生态系统稳定性和水资源的可持续利用,但在遥感应用尤其在干旱区遥感应用中很少被使用。本文以古尔班通古特沙漠南缘的主要建群种多枝柽柳(Tamarix ramosissima)作为研究对象,应用高光谱指数法对其Tr日变化过程进行研究,寻找和确定最佳的Tr光谱指数。选择的6个光谱指数判定系数R2介于0.06~0.73,其中简单比值(SR)光谱指数有最高的判定系数(R2=0.73)、较低的均方根误差(RMSE=0.24)和较为简单的形式,光谱范围处于近红外波段(1 645~1 655nm)/(1 775~1 785nm)。SR作为Tr最佳光谱指数,对植被水分关系变化敏感,能够较好地记录和监测Tr日变化过程,有益于揭示光谱指数物理和生理机制。 相似文献
20.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants. 相似文献