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1.
The effect of seasonal water availability on soil nutrients and soil N transformations was investigated by irrigating two large plots of mature tropical forest on Barro Colorado Island (BCI), Panama, during the dry season for five consecutive years. Methods included (i) nutrient accumulation by ion-exchange resins placed on the surface of the mineral soil for contiguous 21-day periods, (ii) monthly mineral soil (0–10 cm) extractions and incubations for inorganic N and P concentrations, and (iii) leaching loss of nutrients from leaf litter samples. Rates of nutrient accumulation by the resins showed a great deal of variation between sampling dates and among years in control plots; albeit, seasonal patterns were slight, except for the highest Ca values near the end of the wet season and inorganic P (Pi) and SO4 values that peaked during the dry season. Irrigation had remarkably little effect on nutrient accumulation rates by resins, except for an increase in Mg and Na values, but did affect the timing in the temporal variation in K, Na, Ni and Pi values. In contrast, inorganic N (Ni) and Pi pools and N transformation rates in the mineral soil hardly varied among sampling dates and did not show any response to irrigation. We hypothesize that the timing of leaf litterfall and nutrient leaching from forest floor litter can set up temporal patterns in the levels of soil nutrient at the surface of the mineral soil, but the temporal patterns essentially disappear with depth in the mineral soil.  相似文献   

2.
Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg N ha−1 (added N) added as NH4NO3 during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher accumulation of extractable inorganic N (NH4−N + NO3−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm) mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ 15N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type chaparral and CSS shrublands of southern California.  相似文献   

3.
The spatial and temporal distributions of dissolved inorganic nutrients were investigated between May 1996 and April 1997 in Mida Creek, a mangrove area along the north coast region of Kenya. The nutrient levels of pore water from boreholes/wells within the surrounding area of the creek were also investigated for comparison. In addition, phytoplankton distribution in Mida Creek was assessed in three stations within the creek in order to determine the structure and succession stages of the phytoplankton community and to provide an indication of the status of primary productivity of the creek. Measurements carried out within the creek revealed that the mean concentration ranges for NH4+ –N, (NO 2 + NO3)−N, PO43− −P and SiO32− −Si were: 0.002–5.45; 0.12–5.63; 0.10–0.58 and 1.31–81.36 μM, respectively. For the case of boreholes/wells found in the surrounding area, their respective nutrient levels were found to lie in the ranges 0.4–907.0; 16.7–4897.0; 1.09–22.39 and 83.9–596.0 μM. A total of 295 species of phytoplankton belonging to 78 genera were identified with great temporal variability in abundance in all the stations sampled. The most dominant algal members in the Creek included Chaetoceros spp., Chroococcus limneticus and Oscillatoria spp. The diversity values recorded were indicative of mesotrophic conditions. The highest nutrient concentration levels within the creek were measured during the wet season as compared to dry season and this trend closely corresponded with that of the phytoplankton productivity. However, no significant variation ( p > 0.05) was found in all cases with respect to the tidal cycles. On the contrary, diurnal nutrient concentrations especially in areas with high flooding duration (>12 h) were found to be highest during the dry season as opposed to wet season for all nutrients except for SiO32−. The relatively high nutrient laden groundwater outflow into the creek water, coupled with surface runoff events during wet season, are the two main factors responsible for the elevated nutrients in the creek waters in the absence of river inflow into the creek.  相似文献   

4.
Seasonal influence on reproduction in chimpanzees of gombe national park   总被引:3,自引:0,他引:3  
Although wild chimpanzees are not seasonal breeders, there are seasonal effects on several aspects of chimpanzee reproduction. I examined the seasonal incidence of anogenital swelling in cyclic, pregnant, and acyclic female chimpanzees in Gombe National Park, May 1975–April 1992, and surveyed important reproductive events to determine whether there is a seasonal effect. I analyzed data by season (wet vs. dry) and seasonal quarter;early dry season = May–July;late dry = August–October;early wet = November–January;late wet = February–April. When data for the 17 years are combined, the percentage of females in each reproductive state remains consistent throughout the year. In a given month, 30–35% of subjects were in the cyclic category, 11–15% were pregnant, and 54–61% were acyclic. Cyclic females showed full swelling more often during the late dry season. Pregnant females exhibited anogenital swelling more often during the late dry and early wet seasons. Acyclic females also exhibited a seasonal effect with more anogenital swelling during the late dry season. There is no seasonal difference in frequency of live births (dry, 20;wet, 23). However, the timing of conception showed a seasonal effect (dry, 32;wet, 16). Consistent with earlier reports, the onset of postpartum cycles is highly seasonal;30 occurred during dry season, 9 during wet season. The occurrence of first full swellings for young females is also concentrated in the late dry season. It appears that the dry season is a time of great change for Gombe chimpanzee reproductive physiology. Previous studies indicated that seasonal changes in food availability play a role in increasing group size during the dry season and social contact between females can enhance cyclicity. Accordingly, I suggest that seasonal changes in diet may play a role, either directly (food content) or indirectly (social contact), to alter reproductive physiology.  相似文献   

5.
Miconia albicans, a common evergreen cerrado species, was studied under field conditions. Leaf gas exchange and pre-dawn leaf water potential (Ψpd) were determined during wet and dry seasons. The potential photosynthetic capacity (P Npmax) and the apparent carboxylation efficiency (ε) dropped in the dry season to 28.0 and 0.7 %, respectively, of the maximum values in the wet season. The relative mesophyll (Lm) and stomatal (Ls) limitations of photosynthesis increased, respectively, from 24 and 44 % in the wet season to 79 and 57 % at the peak of the dry season when mean Ψpd reached −5.2 MPa. After first rains, the P Npmax, ε, and Lm recovered reaching the wet season values, but Ls was maintained high (63 %). The shallow root system growing on stonemason limited by lateral concrete wall to a depth of 0.33 m explained why extreme Ψpd was brought about. Thus M. albicans is able to overcome quickly the strains imposed by severe water stress.  相似文献   

6.
In drylands of southeastern Utah, USA, the invasive exotic grass Bromus tectorum L. occurs in distinct spatial patterns suggesting soil control of ecosystem susceptibility to invasion. To improve our understanding of these patterns, we examined performance of B. tectorum in relation to additions of water, KCl, MgO, and CaO at seventeen 1600 m2 sites distributed across a calcareous soil gradient in Canyonlands National Park. Water additions resulted in a 57% increase in B. tectorum establishment. Fall establishment was significantly correlated with silt and clay content in wet plots but not in dry plots, suggesting that texture effects on B. tectorum establishment patterns may be greater in wet years than in dry years. Applications of MgO resulted in a 49% decrease in B. tectorum establishment, although MgO had no effect on whole-plot biomass at the end of the growing season. B. tectorum–soil relations were strongest during winter (December–March) when relative growth rates were negatively related to soil acid-neutralizing potential, sand and CaCO3 content, and a measure of bioavailable Mg; and positively related to silt and clay content, total N, measures of bioavailable Mn, P, and K, and a measure of magnetite indicating distributional patterns of eolian dust. As soils were persistently moist during this period, we attribute strong B. tectorum–soil patterns in winter to effects of low temperature on diffusion, microbial activity, and/or production of root exudates important for nutrient mobilization and uptake. In spring, there was a reversal in B. tectorum–soil relations such that loamy soils with higher B. tectorum densities were unfavorable for growth relative to sandy soils with higher warm-season water potentials. We conclude that resource limitations for B. tectorum in this study area shift seasonally, from water limitation of fall establishment, to nutrient limitation of winter growth, and back to water limitation of spring growth. Because study sites generally were arrayed along a hillslope gradient with downslope trends in soil vtexture and nutrient content, close B. tectorum–soil relations documented in this study indicate that a geomorphic framework is useful for understanding and predicting B. tectorum invasion patterns in dryland ecosystems of this region.Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. Section Editor: T. KalaposThe U.S. Government’s right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged  相似文献   

7.
Polyspecific associations (PSA) occur when 2 or more species maintain proximity or coordinate activities. PSA may provide ecological benefits similar to those of monospecific groups, i.e., protection against predation and improved foraging efficiency, but may also impart costs, such as feeding competition. I studied 3 New World Callitrichidae—Callimico goeldii, Saguinus fuscicollis, and S. labiatus—in northwestern Brazil over 18 mo between April 1999 and August 2003, during which single primary study groups of C. goeldii, S. labiatus, and S. fuscicollis consistently associated with one another. I compared patterns of PSA participation to variation in plant diets during wet and dry seasons. All 3 species associated an average 61% of observation time, but with significant seasonal variation in PSA. During the dry season, April–September, PSA occurred significantly less frequently than during the wet season, October–March (37% vs. 88%). The variation in PSA corresponded with seasonal shifts in plant food diets, resulting in less dietary overlap among all 3 species during the dry season, particularly between Callimico goeldii and Saguinus labiatus. Dietary richness, diversity, and evenness were also lower in the dry compared to the wet season for each species. The results suggest a link between PSA participation and diet among the taxa; foraging-related costs or feeding competition may constrain PSA during the dry season.  相似文献   

8.
The frillneck lizard, Chlamydosaurus kingii, is a conspicuous component of the fauna of the wetdry tropics of northern Australia during the wet season, but it is rarely seen in the dry season. Previous studies have demonstrated that during the dry season the field metabolic rate (FMR) is only about one-quarter of the wet-season rate, and one factor involved in this seasonal drop is a change in the behavioural thermoregulation of the species such that lower body temperatures (T bs) are selected during dry-season days. Here we examine other factors that could be responsible for the seasonal change in FMR: standard metabolic rates (SMR) and activity. Samples from stomach flushing revealed that the lizards in the dry season continued to feed, but the volume of food was half as much as in the wet season. SMR in the laboratory was 30% less in the dry season. During the dry season, the energy expended by the lizards is 60.4 kJ kg-1 day-1 less than during the wet season. Combining laboratory and field data, we determined the relative contribution of the factors involved in this energy savings: 10% can be attributed to lower nighttime T b, 12% is attributable to lower daytime T b, 12% is attributable to decreased metabolism, and the remaining 66% is attributable to other activities (including e.g. locomotion, reproductive costs, digestion). Calculations indicate that if FMR did not drop in the dry season the lizards would not survive on the observed food intake during this season. Seasonal analysis of blood plasma and urine indicated an accumulation of some electrolytes during the dry season suggesting modest levels of water stress.  相似文献   

9.
Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance (g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season.  相似文献   

10.
The temporal patterns of growth and nutrient accumulation into shoots of coexisting species were studied at two neighbouring areas contrasting with respect to long-term water availability, in an upland herbaceous grassland. Plant growth limiting nutrients were nitrogen (N) in the wet area, and N and phosphorus (P) in the dry area. A series of seven harvests allowed assessment of temporal patterns of peaks for dry matter, N, P and potassium (K) accumulation into shoots and their respective rates of accumulation. Additionally, “pairwise species’ proportion similarities” and “pairwise species’ overlaps” were estimated from shoot biomass data. The peaks of N and P accumulation preceded those of K and dry matter accumulation. Similar trends were evident for the respective rates of accumulation. Compared to the dry area, in the wet area there was a prolonged growing period that increased the inter-species temporal variability in the rates of nutrient accumulation. Abundance of species was correlated (negatively) to species N and P concentrations only in the dry area. It is argued that the significant negative correlation between abundance and either N or P concentrations in the dry area was indicative of intensified inter-species competition resulting from declined temporal complementarity.  相似文献   

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