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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.
Plant and Soil N Response of Southern Californian Semi-arid Shrublands After 1 Year of Experimental N Deposition 总被引:1,自引:0,他引:1
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.
Janette Wallis 《International journal of primatology》1995,16(3):435-451
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.
J. A. Rehg 《International journal of primatology》2006,27(5):1399-1428
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.
Andreas P. Mamolos Charilaos V. Vasilikos Demetrios S. Veresoglou 《Ecological Research》2011,26(3):583-593
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
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 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
11.
Monitoring plant physiological characteristics to evaluate mine site revegetation: A case study from the wet-dry tropics of northern Australia 总被引:1,自引:0,他引:1
Biologically driven markers or monitors were used to evaluate plant and ecosystem health of uranium-mining affected sites.
Plant water, nitrogen (N) and phosphorus (P) status were used to measure physiological characteristics of tree and shrub species
at sites perturbed by mining activities (waste rock dumps: WRD 1, WRD 2; mine wastewater irrigated woodland) and of species
at undisturbed woodland (tropical savanna). Plant water status was evaluated by measuring leaf relative water content (RWC)
and carbon isotope discrimination (δ13C). Leaf RWC varied significantly (P<0.0001) between wet and dry season in species at the woodland sites with higher RWC in
the wet season compared to the dry season. No seasonal differences were observed in RWC in species at the WRDs. Leaf δ13C was similar in species at woodland sites and WRD 2 (−28.8 to −28.1‰) but was significantly (P<0.05) lower in species at
WRD 1 (−27.6‰). This suggests that species at WRD 1 had a lower water availability and/or lower water use compared to species
at all other sites. WRD substrate had an up to 4-orders of magnitude greater availability of inorganic phosphate (Pi) compared
to woodland soil as determined using in situ ion exchange resin. Pi concentrations in xylem sap of species at WRDs were 2-
to 3-fold higher compared to species at woodland sites. Plant nitrate reductase (NR) activity was low in most species at woodland
and WRD 1. In contrast, Eucalyptus and Acacia species had high NR activities of up to 300–700 pkat g-1 fw at WRD 2 indicating that these species had greater nitrate use than species at all other sites. Nitrate availability in
the top five cm of the profile, as determined using in situ ion exchange resins, increased at all sites in the wet season,
but no significant differences were observed between sites using this method. However, traditional soil analysis revealed
that WRD substrate had a 2-times higher nitrate content (0 to 1000 mm depth) compared to woodland soil. Thus, it is likely
that plants at WRD2 accessed nitrate from deeper parts of the profile. Proline, an indicator of plant stress, was found in
appreciable quantities in leaves of herbaceous species but not in woody species. Soil and leaf δ15N were measured to investigate N-cycling and the contribution of diazotrophic N2 fixation to plant N nutrition. Soil δ15N values were highest and most variable at WRD 2 (6.2‰) compared to all other sites (irrigated woodland 3.1‰, undisturbed
woodland 2.5‰, WRD 1 0.9‰). This may indicate that N-turnover and nitrification was greatest at WRD 2 leading to greater 15N enrichment of soil N. At all sites, Acacia species were nodulated and putatively fixing N2. With the exception of WRD 2 where leaf δ15N of Acacia species averaged 0.9‰, Acacia species had 15N depleted values characteristic of species that receive N derived from N2 fixation (−0.8 to −0.6‰).
Eucalyptus species at the woodland also had 15N depleted values (average −0.4‰) but 15N enriched values (0.3 to 1.8‰) at the three mining affected sites. The results show that for the plants studied foliar δ15N could not be used as an unequivocal measure of plant N sources. The results suggest that biomonitoring of plant and ecosystem
health has potential in evaluating performance of mine site revegetation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Water quality, diatom species composition and biomass estimates were performed in the Gharasou River in western Iran. Five
sites along the River Gharasou were sampled every month from April to September 2005. Physical and chemical factors (pH, NO3–N, PO4–P, dissolved oxygen, total suspend solids, total dissolved solids, conductivity, turbidity, chemical oxygen demand and biological
oxygen demand) were measured along with biological properties of the periphyton including biomass, ash-free dry mass, chlorophyll-a concentration and the taxonomic composition diatom assemblages. Information from the diatom assemblage was used to calculate
the Trophic Diatom Index and biovolume. The TDI was significantly correlated with measures of human disturbance at the sites
(e.g. PO4–P, NO3–N and dissolved oxygen) as well as to biomass measures (chlorophyll a, ash-free dry mass and biovolume). The sensitivity of the TDI and its component metrics to environmental stressors supports
the use of this index for monitoring ecological conditions in streams in Iran and to aid diagnosis of the cause of their impairment.
Handling editor: L. Naselli-Flores 相似文献
13.
Land-Use Change and Biogeochemical Controls of Methane Fluxes in Soils of Eastern Amazonia 总被引:3,自引:0,他引:3
Tropical soils account for 10%–20% of the 15–35 Tg of atmospheric methane (CH4) consumed annually by soils, although tropical deforestation could be changing the soil sink. The objectives of this study
were (a) to quantify differences in soil CH4 fluxes among primary forest, secondary forest, active pasture, and degraded pasture in eastern Amazonia; and (b) to investigate
controlling mechanisms of CH4 fluxes, including N availability, gas-phase transport, and soil respiration. At one ranch, Fazenda Vitória, annual uptake
estimates (kg CH4ha−1 y−1) based on monthly measurements were: primary forest, 2.1; secondary forest, 1.0; active pasture, 1.3; degraded pasture, 3.1.
The lower annual uptake in the active pasture compared with the primary forest was due to CH4 production during the wet season in the pasture soils, which is consistent with findings from other studies. In contrast,
the degraded pasture was never a CH4 source. Expressing uptake as a negative flux and emission as a positive flux, CH4 fluxes were positively correlated with CO2 fluxes, indicating that root and microbial respiration in the productive pastures, and to a lesser extent in the primary
forest, contributed to the formation of anaerobic microsites where CH4 was produced, whereas this productivity was absent in the degraded pasture. In all land uses, uptake rates of atmospheric
CH4 were greater in the dry season than in the wet season, indicating the importance of soil water content and gas transport
on CH4 fluxes. These clay soils had low annual uptake rates relative to reported rates on sandy soils, which also is consistent
with gas transport within the soil being a limiting factor. Nitrogen availability indices did not correlate with CH4 fluxes, indicating that inhibition of CH4 oxidation was not an important mechanism explaining differences among land uses. At another ranch, Fazenda Agua Parada, no
significant effect of pasture age was observed along a chronosequence of pasture ages. We conclude that land-use change can
either increase or decrease the soil sink of CH4, depending on the duration of wet and dry seasons, the effects of seasonal precipitation on gas-phase transport, and the
phenology and relative productivity of the vegetation in each land use. 相似文献
14.
Specific leaf area and leaf nitrogen concentration in annual and perennial grass species growing in Mediterranean old-fields 总被引:1,自引:0,他引:1
We evaluated the hypothesis that photosynthetic traits differ between leaves produced at the beginning (May) and the end
(November–December) of the rainy season in the canopy of a seasonally dry forest in Panama. Leaves produced at the end of
the wet season were predicted to have higher photosynthetic capacities and higher water-use efficiencies than leaves produced
during the early rainy season. Such seasonal phenotypic differentiation may be adaptive, since leaves produced immediately
preceding the dry season are likely to experience greater light availability during their lifetime due to reduced cloud cover
during the dry season. We used a construction crane for access to the upper canopy and sampled 1- to 2-month-old leaves marked
in monthly censuses for six common tree species with various ecological habits and leaf phenologies. Photosynthetic capacity
was quantified as light- and CO2-saturated oxygen evolution rates with a leaf-disk oxygen electrode in the laboratory (O2max) and as light-saturated CO2 assimilation rates of intact leaves under ambient CO2 (Amax). In four species, pre-dry season leaves had significantly higher leaf mass per unit area. In these four species, O2max and Amax per unit area and maximum stomatal conductances were significantly greater in pre-dry season leaves than in early wet season
leaves. In two species, Amax for a given stomatal conductance was greater in pre-dry season leaves than in early wet season leaves, suggesting a higher
photosynthetic water-use efficiency in the former. Photosynthetic capacity per unit mass was not significantly different between
seasons of leaf production in any species. In both early wet season and pre-dry season leaves, mean photosynthetic capacity
per unit mass was positively correlated with nitrogen content per unit mass both within and among species. Seasonal phenotypic
differentiation observed in canopy tree species is achieved through changes in leaf mass per unit area and increased maximum
stomatal conductance rather than by changes in nitrogen allocation patterns.
Received: 7 March 1996 / Accepted: 1 August 1996 相似文献
15.
Temporal and spatial partitioning of water resources among eight woody species in a Hawaiian dry forest 总被引:14,自引:0,他引:14
Lowland dry forests are unique in Hawaii for their high diversity of tree species compared with wet forests. We characterized
spatial and temporal partitioning of soil water resources among seven indigenous and one invasive dry forest species to determine
whether the degree of partitioning was consistent with the relatively high species richness in these forests. Patterns of
water utilization were inferred from stable hydrogen isotope ratios (δD) of soil and xylem water, zones of soil water depletion,
plant water status, leaf phenology, and spatial patterns of species distribution. Soil water δD values ranged from –20‰ near
the surface to –48‰ at 130 cm depth. Metrosideros polymorpha, an evergreen species, and Reynoldsia sandwicensis, a drought-deciduous species, had xylem sap δD values of about –52‰, and appeared to obtain their water largely from deeper
soil layers. The remaining six species had xylem δD values ranging from –33 to –42‰, and apparently obtained water from shallower
soil layers. Xylem water δD values were negatively correlated with minimum annual leaf water potential and positively correlated
with leaf solute content, an integrated measure of leaf water deficit. Seasonal patterns of leaf production ranged from dry
season deciduous at one extreme to evergreen with near constant leaf expansion rates at the other. Species tapping water more
actively from deeper soil layers tended to exhibit larger seasonality of leaf production than species relying on shallower
soil water sources. Individuals of Myoporum sandwicense were more spatially isolated than would be expected by chance. Even though this species apparently extracted water primarily
from shallow soil layers, as indicated by its xylem δD values, its nearly constant growth rates across all seasons may have
been the result of a larger volume of soil water available per individual. The two dominant species, Diospyros sandwicensis and Nestegis sandwicensis, exhibited low leaf water potentials during the dry season and apparently drew water mostly from the upper portion of the
soil profile, which may have allowed them to exploit light precipitation events more effectively than the more deeply rooted
species. Character displacement in spatial and temporal patterns of soil water uptake was consistent with the relatively high
diversity of woody species in Hawaiian dry forests.
Received: 20 May 1999 / Accepted: 2 March 2000 相似文献
16.
Summary Inoculation of water fernAzolla pinnata R. Brown (Bangkok isolate) at the rate of 500kg fresh weight ha−1 in rice fields at weekly intervals after planting in addition to 30 kg N ha−1 as urea showed a decrease in its growth and N2-fixation with delay in application. Use of Azolla up to 3 weeks after planting (WAP) during wet and 4 WAP during dry season
produced significantly more grain yield than 30 kg N ha−1, whereas its application upto one WAP produced more grain yield than 60 kg N ha−1. Grain yield with Azolla applied at the time of planting was similar to that of 60 kg N treatment during the wet season.
Higher grain yields in zero and one WAP Azolla treatments resulted due to increase in both number of panicles m−2 and number of grains/panicle while the subsequent Azolla inoculations increased grain yield mainly by producing more number
of grains/panicle.
Dry matter and total N yields at maturity of rice crop were more with Azolla application upto 3 WAP during wet and 2 WAP during
dry season while the reduction in sterility (%) was observed upto one WAP over 30 kg N ha−1 during both seasons. Number of tillers m−2 and dry matter production at maximum tillering and flowering were more than 30 kg N ha−1 with the use of Azolla upto one WAP. Increased grain N yield was observed with the use of Azolla upto 4 WAP during two seasons
whereas straw N yield increased upto one WAP during wet and 2 WAP during dry season. 相似文献
17.
Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) 总被引:2,自引:0,他引:2
Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season
and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height
into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7–10 μmol mol−1 below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or
to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events,
resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50␣μmol mol−1. Temporal and spatial variations in [CO2]canopy were reflected in changes of δ13Ccanopy and δ18Ocanopy values. Tight relationships were observed between δ13C and δ18O of canopy CO2 during both seasons (r
2 > 0.86). The most depleted δ13Ccanopy and δ18Ocanopy values were measured immediately above the forest floor (δ13C = −16.4‰; δ18O = 39.1‰ SMOW). Gradients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ13C, and between 1.0‰ and 3.5‰ for δ18O. The δ13Cleaf and calculated c
i/c
a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a
constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ13Cleaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c
i/c
a. Plotting 1/[CO2] vs. the corresponding δ13C ratios resulted in very tight, linear relationships (r
2 = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent
mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ13C of respired sources were close to the measured δ13C of soil respired CO2 and to the δ13C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δe, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season.
Received: 3 March 1996 / Accepted: 19 October 1996 相似文献
18.
Phosphorus cycling in rainfed lowland rice ecosystems is poorly understood. Soil drying and grazing of rice straw during the
long dry season, the growth of volunteer pastures during the early wet season, and intermittent loss of soil-water saturation
while the rice crop is growing are important distinguishing characteristics of the rainfed lowlands in relation to P cycling.
We studied P cycling in an acid sandy rainfed lowland soil that covers about 30% of the rice growing area of Cambodia. Soils
with similar properties in comparable rainfed sub- ecosystems occur in Laos and northeast Thailand. We developed a general
schema of P pools and fluxes in the crop and soil for rice-based cropping systems in the rainfed lowlands of Cambodia. The
schema was derived from a number of field experiments carried out over five consecutive cropping seasons to quantify the residual
value of P fertiliser, P mass balances, soil P fractions, the effect on subsequent rice crops of crop residues and volunteer
pastures incorporated into the soils, and the dynamics of P turnover in the soil. With a single rice crop yielding 2.5–3 t
ha−1, application of 8–10 kg P ha−1 maintained yields and a small positive P balance in the soil. However, the soil P balance was sensitive to the proportion
of rice straw returned to the soil. Volunteer pastures growing during the early wet season accumulated significant amounts
of P, and increased their P uptake when soils were previously fertilised with P. These pastures recycled 3–10 kg P ha−1 for the succeeding rice crops. While inorganic soil P pools extractable with ion exchange resins and 0.1 M NaOH appeared
to be the main source of P absorbed by rice, microbial and organically-bound P pools responded dynamically to variation in
soil water regimes of the main wet, dry and early wet seasons. The schema needs to be developed further to incorporate site-specific
conditions and management factors that directly or indirectly affect P cycling, especially loss of soil-water saturation during
the rice cropping cycle. The paper discusses the application of results for acid sandy soils to other significant rice soils
in the rainfed lowlands of southeast Asia. 相似文献
19.
In evergreen broad-leaved forests (EBLFs) in Tiantong National Forest Park, Eastern China, we studied the soil chemistry and plant leaf nutrient concentration along a chronosequence of secondary forest succession. Soil total N, P and leaf N, P concentration of the most abundant plant species increased with forest succession. We further examined leaf lifespan, leaf nutrient characteristics and root–shoot attributes of Pinus massoniana Lamb, the early-successional species, Schima superba Gardn. et Champ, the mid-successional species, and Castanopsis fargesii Franch, the late-successional species. These species showed both intraspecific and interspecific variability along succession. Leaf N concentration of the three dominant species increased while N resorption tended to decrease with succession; leaf P and P resorption didn’t show a consistent trend along forest succession. Compared with the other two species, C. fargesii had the shortest leaf lifespan, largest decay rate and the highest taproot diameter to shoot base diameter ratio while P. massoniana had the highest root–shoot biomass ratio and taproot length to shoot height ratio. Overall, P. massoniana used ‘conservative consumption’ nutrient use strategy in the infertile soil conditions while C. fargesii took up nutrients in the way of ‘resource spending’ when nutrient supply increased. The attributes of S. superba were intermediate between the other two species, which may contribute to its coexistence with other species in a wide range of soil conditions. 相似文献
20.
The purpose of this work is to increase ecological understanding of Avicennia germinans L. and Laguncularia racemosa (L.) Gaertn. F. growing in hypersaline habitats with a seasonal climate. The area has a dry season (DS) with low temperature and vapour pressure deficit (vpd), and a wet season (WS) with high temperature and slightly higher vpd. Seasonal patterns in interstitial soil water salinity suggested a lack of tidal flushing in this area to remove salt along the soil profile. The soil solution sodium/potassium (Na+/K+) ratio differed slightly along the soil profile during the DS, but during the WS it was significantly higher at the soil surface. Diurnal changes in xylem osmolality between predawn (higher) and midday (lower) were observed in both species. However, A. germinans had higher xylem osmolality compared to L. racemosa. Xylem Na+/K+ suggested higher selectivity of K+ over Na+ in both species and seasons. The water relations parameters derived from pressure–volume P–V curves were relatively stable between seasons for each species. The range of water potentials (Ψ), measured in the field, was within estimated values for turgor maintenance from P–V curves. Thus the leaves of both species were osmotically adapted to maintain continued water uptake in this hypersaline mangrove environment. 相似文献