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41.
Short-term patterns in water and nitrogen acquisition by two desert shrubs following a simulated summer rain 总被引:9,自引:0,他引:9
BassiriRad H. Tremmel D.C. Virginia R.A. Reynolds J.F. de Soyza A.G. Brunell M.H. 《Plant Ecology》1999,145(1):27-36
A field experiment was conducted at the Jornada Long-Term Ecological Research (LTER) site in the Chihuahuan Desert of New Mexico to compare the rapidity with which the shrubs Larrea tridentata and Prosopis glandulosa utilized water, CO2 and nitrogen (N) following a simulated summer rainfall event. Selected plants growing in a roughly 50-m2 area were assigned to treatment and control groups. Treatment plants received the equivalent of 3 cm of rain, while no supplemental water was added to the control plants. Xylem water potential (x) and net assimilation rate (Anet) were evaluated one day before and one and three days after watering. To monitor short-term N uptake, soils around each plant were labeled with eight equally distant patches of enriched 15N before watering. Each tracer patch contained 20 ml of 20 mM 15 NH4
15NO3 (99 atom%) solution applied to the soil at 20 cm from the center of the plant at soil depths of 10 and 20 cm. Nitrogen uptake, measured as leaf 15N, was evaluated at smaller time intervals and for a longer period than those used for x and Anet. Both Anet and x exhibited a significant recovery in watered vs. control Larrea plants within 3 days after the imposition of treatment, but no such recovery was observed in Prosopis in that period. Larrea also exhibited a greater capacity for N uptake following the rain. Leaf 15N was five-fold greater in watered compared to unwatered Larrea plants within 2 days after watering, while foliar 15N was not significantly different between the watered and unwatered Prosopis plants during the same period. Lack of a significant change in root 15 NO–
3 uptake kinetics of Larrea, even three days after watering, indicated that the response of Larrea to a wetting pulse may have been due to a greater capacity to produce new roots. The differential ability of these potential competitors in rapidly acquiring pulses of improved soil resources following individual summer rainfall events may have significant implications for the dynamic nature of resource use in desert ecosystems. 相似文献
42.
Nutrient mobilization and processing in Sonoran desert riparian soils following artificial re-wetting 总被引:3,自引:0,他引:3
Research in river-floodplain systems has emphasized the importance of nutrient delivery by floodwaters, but the mechanisms by which floods make nutrients available are rarely evaluated. Using a laboratory re-wetting experiment, we evaluated the alternative hypotheses that increased nutrient concentrations in riparian groundwater during flash floods are due to (H1) elevated nutrient concentrations in surface floodwaters entering the riparian zone or (H2) re-mobilization of nutrients from riparian soils. We sampled soils from the riparian zone of a 400m reach of Sycamore Creek, AZ. Two sub-samples from each soil were re-wetted with a solution that mimicked the chemistry of floodwaters, with one sub-sample simultaneously treated with a biocide. We also measured structural characteristics of soils (texture, organic matter, moisture, and extractable nutrients) to investigate relationships between these characteristics and response to re-wetting. Riparian soils exhibited considerable variation in physical and chemical structure. Soil organic matter, moisture, and texture co-varied among samples. Re-wetting increased concentrations of nitrate and ammonium, and decreased SRP, relative to initial concentrations. Live soils were significantly lower in NO3-and SRP than biocide-treated samples. Extractable DIN pools were the best predictors of mobilization, and soil organic matter was strongly correlated with nitrate losses, probably via its relationship with microbial uptake. Nutrient mobilization and processing also varied considerably with depth, lateral position, and among plots. We estimate that 70–80% of N in riparian groundwater during flash floods is re-mobilized from riparian soils, but are unable to reject the hypothesis that flood inputs may be important sources of nutrients to riparian soils over longer time scales. 相似文献
43.
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45.
The effects of microhabitat differentiation on small-scale plant community structure in the Chiuhuahuan Desert were studied using multivariate analysis. The results showed that microhabitats (i.e., kangaroo rat mounds, ant mounds, shrubs, half-shrubs, and open areas) played a critical role in structuring small-scale plant community structure and maintaining species diversity. Annual plants were much more sensitvive to the presence of differentiated microhabitats than perennials and winter annuals exhibited stronger microhabitat perferences than summer annuals. Species diversity was highest on ant mounds while open areas supported the lowest diversity during both winter and summer. Biomass was highest in the shrub habitats followed by kangaroo rat mounds, ant mounds, half-shrubs, and open areas. Much of the diversity of these plants could be explained by the individualistic responses of species to the biotic effect of other plants or to disturbance by animals, or individualistic responses of species to differences in microenvironments. 相似文献
46.
Nobel Park S. Zhang Hehui Sharifi Rasoul Castañeda Miguel Greenhouse Barry 《Photosynthesis research》1998,56(1):67-73
Encelia farinosa is one of the most abundant and highly studied species of the Sonoran Desert, yet characteristics of its leaf development and long-term photosynthetic capacity are relatively unknown. The net CO2 uptake rate and the Rubisco activity per unit leaf area for E. farinosa in a glasshouse increased in parallel for about 18 days after leaf emergence (leaf area was then 5 cm2), after which both were constant, suggesting that Rubisco levels controlled net CO2 uptake. Instantaneous net CO2 uptake rates at noon for well-watered E. farinosa in the glasshouse at different temperatures and light levels correctly predicted differences in daily net CO2 uptake at four seasonally diverse times for transplanted plants under irrigated conditions in the field but overpredicted the daily means by 13%. After this correction, seasonally adjusted net CO2 uptake per unit leaf area multiplied by the estimated monthly leaf area predicted that 42% of the net carbon gain was incorporated into plant dry weight over a 17-month period. The ecological success of E. farinosa apparently reflects an inherently high daily net CO2 uptake and retention of a substantial fraction of its leaf carbon gain. 相似文献
47.
About 20-year-old desert plants of C4 species, Haloxylon ammodendron, growing at the southern edge of the Badain Jaran Desert in China, were selected to study the photosynthetic characteristics
and changes in chlorophyll fluorescence when plants were subject to a normal arid environment (AE), moist atmospheric conditions
during post-rain (PR), and the artificial supplement of soil water (SW). Results showed that under high radiation, in the
AE, the species down-regulated its net assimilation rate (A) and maximum photochemical efficiency of PS II (Fv/Fm), indicating photoinhibition. However, under the PR and SW environments,
A was up-regulated, with a unimodal diurnal course of A and a small diurnal change in Fv/Fm, suggesting no photoinhibition. When the air humidity or SW content was increased, the
light compensation points were reduced; light saturation points were enhanced; while light saturated rate of CO2 assimilation (A
max) and apparent quantum yield of CO2 assimilation (ΦC) increased. ΦC was higher while the A
max was reduced under PR relative to the SW treatment. It was concluded that under high-radiation conditions drought stress causes
photoinhibition of H. ammodendron. Increasing air humidity or soil moisture content can reduce photoinhibition and increase the efficiency of solar energy
use. 相似文献
48.
Patrick L Cable J Potts D Ignace D Barron-Gafford G Griffith A Alpert H Van Gestel N Robertson T Huxman TE Zak J Loik ME Tissue D 《Oecologia》2007,151(4):704-718
Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is
anticipated to affect biosphere/atmosphere exchanges of both CO2 and H2O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level
fluxes of CO2 and H2O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004).
In addition, the responses of leaf, soil, and ecosystem fluxes of CO2 and H2O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event.
We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs
and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses
in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally
watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime
soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO2 m−2 s−1 ground area day−1. As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO2 during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and
shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment
differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater
amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem. 相似文献
49.
Joseph R. Coelho Charles W. Holliday Jon M. Hastings Elizabeth Maty Meghan Swigart Angela Mendell 《Journal of thermal biology》2007
(1) Male western cicada killers (Sphecius grandis) had elevated, apparently regulated, thorax temperatures during territorial patrolling. (2) Abdomen temperature increased steeply with increasing ambient temperature, approaching thorax temperature when ambient temperature exceeded 35 °C. (3) Both indirect evidence and heating experiments demonstrated the apparent ability to shunt heat from thorax to abdomen. (4) Dead, dry wasps reached lethal temperatures when placed in full sunlight on the bare ground, and substantially lower temperatures on plants. (5) The percentage of males perching was extremely low, occurring primarily during early morning hours. Most perching occurred on plants, and very little on the ground. (6) In contrast to what has been reported for eastern cicada killers (Sphecius speciosus), S. grandis males did not appear to use sophisticated behaviors to regulate body temperature during territorial defense, relying primarily on physiological mechanisms. (7) This strategy may be more appropriate for S. grandis in the hotter, drier environment of the lowland Chihuahuan desert. 相似文献
50.
Ngoc-Phuc Hua Fumihisa Kobayashi Yasunobu Iwasaka Guang-Yu Shi Takeshi Naganuma 《Aerobiologia》2007,23(4):291-298
Several halotolerant bacteria were isolated from dust allowed to settle passively on saline medium in Higashi-Hiroshima, Japan
during Asia dust events in 2005–2006. The primary identification, based on the sequence similarity of the 16S rRNA gene, revealed
that these isolates were strains of Bacillus subtilis, B. licheniformis, Staphylococcus epidermidis, Gracillibacillus sp., and Halomonas venusta. A parallel investigation carried out on desert sand collected directly from sand dunes in Dunhuang, Gobi Desert, China resulted
in the revivification of seven bacterial strains that were highly identical to the B. subtilis and B. licheniformis strains obtained in Higashi-Hiroshima (99.7 and 100% of 16S rDNA sequence similarity, respectively). A subsequent genetic
analysis on the group of B. licheniformis isolates based on the universally house-keeping genes, gyrB and parE, revealed high sequence similarities in both genes among the strains of both locations (99.0–99.4%), which clustered them
in a monophyletic line. Phenotype characterized by numerical taxonomy for 150 physiological tests confirmed the close relatedness
between strains (similarity coefficient S
SM = 96.0%). The remarkable agreement between phenotype and genotype of the bacterial isolates allows us to conclude that there
may have been an aerosolized dispersion of a Gobi Desert B. licheniformis by dust storms to Japan. This study provides evidence of microbial transport by yellow dust events in North-East Asia. 相似文献