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1.
Impact of diet quality on demographic attributes in adult grasshoppers and the nitrogen limitation hypothesis 总被引:4,自引:0,他引:4
1. Various formulations of the nutrient stress hypothesis predict that insect herbivore populations will respond positively to increased nutrient quality of host plants, especially dietary nitrogen. Survival and reproduction by adult females of two grasshopper species [Acrididae;Melanoplus sanguinipes (Fabricius) and Phoetaliotes nebrascensis (Thomas)] were evaluated in response to defined diets that varied factorially in both total nitrogen (1–7%) and total soluble carbohydrate (4.3–26.7%). These grasshopper species coexist naturally but are typically shifted phenologically so that specific developmental stages normally encounter host plants of different nutritional quality under natural conditions. 2. Demographic responses by adult females of both species varied according to diet quality, but not in the same fashion. Diet quality affected survival significantly in P. nebrascensis but not in M. sanguinipes. Survival in P. nebrascensis was greatest on diets containing the lowest nitrogen concentrations; carbohydrate level had no effect. 3. Diet quality influenced reproduction significantly in both species. Egg production rate (eggs/day) in M. sanguinipes exhibited a negative linear response to increased carbohydrate, coupled with a significant quadratic response to nitrogen that reached a maximum at an intermediate level of about 4% total N. A significant quadratic response to total N for pod production rate (indicating the timing of reproduction) was also observed. Clutch size in M. sanguinipes exhibited a negative relationship with total carbohydrate in the diet, but no response to nitrogen. No interaction was observed between nitrogen and carbohydrate levels. For P. nebrascensis, response to diet quality was much weaker, with only a suggestive maximum at 4% total-N for both egg production rate (eggs/day) and clutch size (eggs/pod) and a suggestive linear response for pod production rate as carbohydrate level increased. Female body weight did not contribute to any reproductive response as a covariate variable. 4. Combined with a similar, previous analysis of demographic responses by the grass-feeding grasshopper, Ageneotettix deorum, these results challenge the ability to draw generalizations about host plant nutritional quality and grasshopper demographic responses. These three grasshopper species respond quite differently to defined diets that vary in total nitrogen and carbohydrate levels. Thus, although host plant quality can contribute significantly to grasshopper population responses, a uniform explanation is not likely. 相似文献
2.
Adrien C. Finzi 《Biogeochemistry》2009,92(3):217-229
It is commonly assumed that nitrogen (N) is the primary mineral resource limiting the productivity of temperate forests. Sustained
inputs of N via atmospheric deposition are altering the N status of temperate forests raising the possibility that nutrients
such as phosphorus (P) are increasingly limiting productivity. The objective of this study was to determine whether P availability
limits tree growth alone or in combination with N. This study was conducted in two forest types common throughout the New
England landscape of the northeastern United States; in sugar maple and white ash dominated stands growing on base rich parent
material characterized by rapid rates of N cycling and high N availability, and in red oak–beech–hemlock dominated stands
growing on base-poor parent material characterized by slow rates of N cycling and low N availability. Starting in 2004, N
and P were added to replicate plots in each forest type in factorial combination at a rate of 150 and 50 kg ha−1 year−1, respectively. Diameter growth rates of all trees >10 cm DBH were measured in 2005 and 2006 using dendrometer bands and converted
into units of basal area increment (BAI) and wood production. Following 2 years of fertilization, basal area increment in
the sugar maple–white ash forests remained strongly N limited. Fertilization with P did not significantly increase BAI alone,
although both N and P fertilization tended (P < 0.10) to increase diameter growth in white ash. Wood production in the N-fertilized plots increased by 100 g C m−2 year−1, roughly doubling production in the non-fertilized plots. In the red oak–beech–hemlock stands, there was no overall effect
of N or P fertilization on BAI or wood production because BAI in some species was stimulated by fertilization with N alone
(e.g., black cherry, red oak), while in other species BAI was unaffected (e.g., red maple, beech) or negatively affected by
fertilization with N or P (e.g., eastern hemlock). Given that BAI in several tree species responded to fertilization with
N alone and that only one species responded to P fertilization once N was added, this study suggests that decades of atmospheric
N deposition have not (yet) resulted in widespread P limitation or saturation of tree demand for N. 相似文献
3.
Summary Balance sheets were computed for total nitrogen and phosphorus in plough layer (0–15 cm) of a Typic Ustochrept soil under
continuous multiple cropping for seven years (1971–72 to 1977–78) with a fixed rotation of pearl millet (Pennisetum typhoideum L.) wheat (Triticum aestivum L.) (Vigna sinensis Savi.) The treatments considered of soil test-based rates of N, P and K, applied both singly and in combinations together with
farm yard manure, sulphur and zinc superimposed over optimum rates (100%) of NPK. Heavy, losses of N (762–899 kg ha−1) occurred in the plots which received high rates of Nviz. 150% of recommended NPK and 100% NPK plus FYM. Application of N alone accelerated N losses whereas addition of P, PK, PKS
to N minimised such losses. Enrichment of P (66 to 198 kg ha−1) occurred in all phosphate-treated plots. A marginal net decrease (29–54 kg ha−1) in P levels was observed in control and N alone treatments. 相似文献
4.
Biomass production was analysed in Festuca vivipara, grown for 3 months in pots with non-sterilized or sterilized soil after factorial addition of three levels of labile carbon
combined with high and low levels of N and P. The soil was a nutrient-poor subarctic heath soil. In the non-sterilized soil
plant biomass production increased strongly only in the treatment with high levels of both N and P, which suggests that both
nutrients limited plant growth. In the sterilized soil addition of a high level of N without P addition gave almost the same
growth response as in the combined NP treatment. This was because of a more than 30-fold increase of inorganic phosphorus
in the soil as P was released from the killed microbial biomass after sterilization. Sugar addition reduced plant growth in
all treatments. The reduction in plant growth was dose dependent within the range of 0–450 μg C g−1 soil added to the non-sterilized soil, but the response levelled off at 233 μg C g−1 soil in the soil that had been sterilized at the start of the experiment. The plant response, together with observed depletion
of soil inorganic N and P, indicated that the microbial biomass immobilized nutrients efficiently and reduced plant growth
when extra labile carbon was added. The inhibition of growth was lower, however, in the soil which had been sterilized, probably
because of a slow recovery of the microbial populations in it. Two of the nutrient-carbon solutions closely matched the N,
P and C concentrations in a solution containing leaf extracts of Cassiope tetragona and Betula tortuosa that had been used previously to test for possible allelopathic effects of compounds in the leaf extracts. These extracts
also reduced plant growth. The growth reduction was equally large or larger after nutrient-sugar addition than after addition
of leaf extracts in three out of the four possible combinations of species and sterilized or non-sterilized soil. In the fourth
case (Betula extract added to sterilized soil), the effect was larger when leaf extract was added than after addition of the nutrient-carbon
solution. This could be due to a low rate of microbial degradation of phytotoxic substances in this soil because of a slow
recovery of the microbial populations after sterilization. The generally stronger or equal effect of the nutrient-sugar addition
compared to the leaf extract addition leads to the conclusion that microbial nutrient immobilization and microbial competition
for nutrients increased as a function of labile carbon addition with the extract. Hence, it appears that enhanced microbial
activity and microbial nutrient immobilization rather than phytotoxic effects was the primary reasons for the reduced biomass
production in F. vivipara even after addition of the leaf extracts.
Received: 25 October 1996 / Accepted: 11 June 1997 相似文献
5.
K. Tanaka T. Watanabe H. Higuchi K. Miyamoto Y. Yusa T. Kiyonaga H. Kiyota Y. Suzuki T. Wada 《Population Ecology》1999,41(3):253-262
To examine density dependence in the survival, growth, and reproduction of Pomacea canaliculata, we conducted an experiment in which snail densities were manipulated in a paddy field. We released paint-marked snails of
15–20 mm shell height into 12 enclosures (pens) of 16 m2 at one of five densities – 8, 16, 32, 64, or 128 snails per pen. The survival rate of released snails was 95% and was independent
of snail density. The snail density had a significant effect on the growth and egg production of individual snails. This density
dependence may have been caused by reduced food availability. The females at high density deposited fewer and smaller egg
masses than those at low density, and consequently produced fewer eggs. The females at densities 8 and 16 deposited more than
3000 eggs per female, while the females at density 128 oviposited only 414 eggs. The total egg production per pen was, however,
higher at higher snail density. The survival rates of juvenile snails were 21%–37% and were independent of adult density.
The juvenile density was positively correlated with the total egg production per pen and hence was higher at higher adult
density. However, the density of juveniles larger than 5 mm in shell height, i.e., juveniles that can survive an overwintering
period, was not significantly different among density treatments. These results suggest that snail density after the overwintering
period is independent of the density in the previous year. Thus, density dependence in growth and reproduction might regulate
the population of P. canaliculata in paddies.
Received: October 23, 1998 / Accepted: July 16, 1999 相似文献
6.
Brandon K. Swan James M. Watts Kristen M. Reifel Stuart H. Hurlbert 《Hydrobiologia》2007,576(1):111-125
The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading.
However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration
rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes
succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods
of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution
of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved
oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03
mg P m−2 day−1) under saturated oxygen conditions, and highest (1.23–4.67 mg P m−2 day−1) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus
excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of
the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations
are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to
the overall production of the lake.
Guest Editor: John M. Melack
Saline Water and their Biota 相似文献
7.
Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased
by 9% to 22% at elevated CO2 (P < 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by
elevated CO2 (19.9 ± 1.3 and 21.1 ± 1.3 g N m−2 at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P
and tissue N:P ratios also were not altered by CO2 enrichment (12.5 ± 2 g N g−1 P in both treatments). In contrast to non-legumes (>98% of community aboveground biomass), legume C/N was not reduced at
elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N2 fixation (%Ndfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases
in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using
firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil.
Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to
elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities
were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction
between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P.
Received: 12 July 1997 / Accepted: 15 April 1998 相似文献
8.
Zoran Pavlović Ivanka Miletić Živan Jokić Slađana Šobajić 《Biological trace element research》2009,131(3):263-270
A 16-week experiment was conducted to compare effects of various levels of sodium selenite (SS) and Se-enriched yeast (SY),
on the whole-egg Se content and hen’s productivity. One hundred Shaver 579 hens, 27 weeks old, were placed on one of five
experimental treatments. Each treatment was replicated four times with five hens per cage. Treatments consisted of feeding
a low Se diet without supplementation (basal diet) or basal diet with one of two levels of supplemented Se (0.4 or 0.8 mg/kg)
supplied by SS or SY. All supplemented treatments had significantly higher whole-egg Se concentration from basal diet (P < 0.05). On the same supplemented level, hens fed on SY had higher egg Se content from hens feed on SS (P < 0.001). No effects of dietary treatments on egg weight, percentages of dirty and cracked egg, and feed intake and conversion
of feed were observed throughout the trial (P < 0.05). In the first 8 weeks, there was no significant difference (P < 0.05) in hen-day egg production among treatments. From the ninth week on to the end of the trial, supplementation of SY
to hen’s diet resulted in a higher egg production than SS (P < 0.01). 相似文献
9.
Interspecific and intraspecific variation in tree seedling survival: effects of allocation to roots versus carbohydrate reserves 总被引:13,自引:0,他引:13
We examined interspecific and intraspecific variation in tree seedling survival as a function of allocation to carbohydrate
reserves and structural root biomass. We predicted that allocation to carbohydrate reserves would vary as a function of the
phenology of shoot growth, because of a hypothesized tradeoff between aboveground growth and carbohydrate storage. Intraspecific
variation in levels of carbohydrate reserves was induced through experimental defoliation of naturally occurring, 2-year-old
seedlings of four northeastern tree species –Acer rubrum, A. saccharum, Quercus rubra, and Prunus serotina– with shoot growth strategies that ranged from highly determinate to indeterminate. Allocation to root structural biomass
varied among species and as a function of light, but did not respond to the defoliation treatments. Allocation to carbohydrate
reserves varied among species, and the two species with the most determinate shoot growth patterns had the highest total mass
of carbohydrate reserves, but not the highest concentrations. Both the total mass and concentrations of carbohydrate reserves
were significantly reduced by defoliation. Seedling survival during the year following the defoliation treatments did not
vary among species, but did vary dramatically in response to defoliation. In general, there was an approximately linear relationship
between carbohydrate reserves and subsequent survival, but no clear relationship between allocation to root structural biomass
and subsequent survival. Because of the disproportionate amounts of reserves stored in roots, we would have erroneously concluded
that allocation to roots was significantly and positively related to seedling survival if we had failed to distinguish between
reserves and structural biomass in roots.
Received: 14 December 1999 / Accepted: 2 June 1999 相似文献
10.
The present study was carried out to determine the effects of different sources of selenium (Se; sodium selenite [Na2SeO3] or selenomethionine [Se-Met]) supplementation on egg production, egg quality, levels of malondialdehyde (MDA), and Se in
serum and egg yolk in heat-stressed Japanese quail (Coturnix coturnix japonica). The birds (n = 360; 55 days old) were randomly assigned to 12 treatment groups consisting of six replicates of five birds each in a 2 × 2 × 3
factorial arrangement of treatments (temperatures, selenium sources, selenium levels). Birds were kept in wire cages in a
temperature-controlled room at either 22 (thermoneutral) or 34°C (heat stress) for 8 h/day (09:00–17:00; till the end of study)
and fed a basal (control) diet or the basal diet supplemented with either 0.15 or 0.30 mg of Na2SeO3 or selenomethionine/kg of diet. Heat exposure decreased live weight, feed intake, feed efficiency, egg production, and egg
quality when basal diet was fed (P < 0.0001). A linear increase in feed intake (P = 0.001) and body weight (P = 0.001), egg production (P = 0.001), and improvement in feed efficiency (P = 0.001) and egg quality (P = 0.001) were found in Se-supplemented quail reared under heat stress conditions. Serum, egg white, and egg yolk Se (P ≤ 0.001) concentrations increased linearly, whereas serum, liver, and egg yolk MDA concentrations decreased linearly (P = 0.001) as dietary Na2SeO3 or Se-Met supplementation increased. An interaction between dietary Se sources, temperature, and levels of supplementation
(P ≤ 0.05) for these parameters was detected. Supplementation with Se improved egg production, egg quality, and antioxidant
status of birds, and the effects of Se-Met were relatively greater than Na2SeO3 in heat-stressed quail. Results of the present study suggest that supplementation with Se-Met can be considered to be more
protective than Na2SeO3 by reducing the negative effects of oxidative stress induced by heat stress in quail. 相似文献
11.
To investigate the effects of different carbohydrate (CHO) levels in the diet of Wuchang bream Megalobrama amblycephala, the fish were randomly divided into six treatment groups. Five groups were fed 19, 25, 31, 38 and 47% CHO, respectively, for 8 weeks, and a control group was fed a diet with no CHO. Growth performance and feed utilization were significantly (P < 0.05) affected by the dietary carbohydrate level. Maximum weight gain and specific growth rate occurred at the 31% dietary carbohydrate level. Compared to the control, the 31% CHO group had a significantly increased serum total protein content, respiratory burst activity of leucocytes, serum complement 3 (C3) levels, serum lysozyme activity, serum alkaline phosphatase (AKP) activity and hepatic total antioxidative capacity (T‐AOC), as well as a decrease in serum glutamic‐oxaloacetic transaminase (GOT) activity. Compared to the control, the 47% CHO group had significantly increased serum GOT activity, and a tendency toward an increase in serum cortisol content and a decrease in serum lysozyme activity, hepatic superoxide dismutase (SOD) activity and T‐AOC. The relative level of hepatic heat shock protein 70 (HSP70) mRNA in fish fed the 38% CHO diet was significantly higher than those of fish fed the 19, 25 and 31% CHO diets, respectively (P < 0.05). After challenge with Aeromonas hydrophila, fish fed the 47% CHO had the significantly lowest post‐challenge survival, and fish fed the 31% CHO had the significantly highest post‐challenge survival (P < 0.05). The results of this study suggest that ingestion of excessive dietary CHO can impact the non‐specific immune responses, decrease the hepatic antioxidant abilities, and thus affect the health status of M. amblycephala. 相似文献
12.
Güçlü BK Kara K Beyaz L Uyanik F Eren M Atasever A 《Biological trace element research》2008,125(2):160-169
This study was performed to determine the effects of copper proteinate on performance, blood chemistry, lipid peroxidation
status, and organs as well as copper deposition in the liver and eggs of laying hens. Seventy-two 30-week-old Bovans laying
hens were distributed into four groups with three replicates. Animals were fed basal diet containing at least 17% crude protein
and 2,800 kcal/kg metabolizable energy supplemented with either 0, 150, 300, or 450 mg/kg copper as copper proteinate. Supplementation
of 150 and 300 mg/kg copper increased egg production, whereas 450 mg/kg copper decreased (p < 0.001). Liver copper levels were elevated in 300 and 450 mg/kg copper-supplemented groups (p < 0.001). Egg copper contents increased in all treatment groups (p < 0.01). An increase in glucose (p < 0.001) and decreases in albumin (p < 0.01) and total cholesterol (p < 0.05) levels were determined with 300 and 450 mg/kg copper. Supplementation of 450 mg/kg copper increased alkaline phosphatase
and gamma glutamyl transpeptidase activities (p < 0.05), malondialdehyde, and high-density lipoprotein levels (p < 0.01) but decreased alanine aminotransferase and lactate dehydrogenase activities (p < 0.01). No gross and microscopic changes were observed in the liver and kidneys. These results indicated that 150 and 300 mg/kg
copper increased egg production without having marked adverse effects, but 450 mg/kg copper altered some blood chemistry variables
and reduced egg production in laying hens. 相似文献
13.
Lenka Vojtíšková Edita Munzarová Olga Votrubová Hana Čížková Helena Lipavská 《Hydrobiologia》2006,563(1):73-85
Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using
water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6
mM) and/or forms of N (NH4+ versus NO 3–) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH4+–N nutrition described in our previous study [Vojtíšková et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure
NH4+–N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH4+–N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates
(TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and
negatively affected by high N availability (P = 0.001), as well as by NH4+–N nutrition (P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch
in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to
33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high
content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue
differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%,
Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH4+ received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was
not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH4+ nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in
favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could
explain the reduced growth of Acorus plants under high N and sole NH4+–N nutrition described previously. 相似文献
14.
Sommer U 《Oecologia》2009,159(1):207-215
The feeding selectivity and the growth and reproductive success of the copepod Acartia tonsa have been studied in mesocosms fertilized at different Si:N ratios (0–1.75:1) and, therefore, at different compositions of
the phytoplankton communities. Phytoplankton composition showed a strong response to nutrient ratios, with diatoms comprising
>90% at Si:N ratios >1:1 of total biomass as opposed to <20% at the lowest ratio. A. tonsa strongly preferred feeding on motile prey (flagellates and ciliates) to feeding on diatoms. Nevertheless, diatoms comprised
a substantial part of the diet at the highest Si:N ratios. A. tonsa egg production and the final (after 4 weeks) abundance of adults and copepodites showed no response to Si:N ratios while
nauplii production slightly increased with Si:N ratios. It is concluded that the frequently reported deleterious effect of
diatoms on copepod reproduction is rather unusual when copepods are confronted with a naturally diverse phytoplankton assemblage
instead of clonal cultures in the laboratory. 相似文献
15.
Previous studies have tested the “vernal dam” hypothesis of spring ephemeral herbs in hardwood forests. The desert annual
is a component of the desert ecosystem that takes advantage of water resources and temperature conditions during the rainy
season to rapidly complete its life cycle within several months. To understand the role desert annual/ephemeral plants play
in nutrient flow, we studied vegetation cover, nitrogen content and litter production of annual plants and litter decomposition
rate in plant communities dominated by four shrubs (Haloxlon ammodendron, Hedysarum scoparium, Calligonum mongolicum, and Nitraria tangutorum) and two dominant annuals (Agriophyllum squarrosum and Halogeton arachnoideus Moq) in Minqin, northwestern China. Results indicate that over half of the total vegetation cover was provided by annuals.
Annuals also took up a large amount of nitrogen (0.46–3.78 g N m−2) along the oasis–desert ecotone. Litter production and nutrient content were higher in areas dominated by annual plants than
in areas dominated by shrubs. Furthermore, the litter decomposition rate of the annuals was higher than that of the shrubs,
except for the shrub H. ammodendron, although almost all of the litter’s carbon (C) and nitrogen (N) remained after 6 months of decomposition. Without the annuals,
more nutrients and rainwater might be lost through leaching or dust transfer caused by the wind erosion. In addition, green
twigs of the annuals are the food for some animals, we found some green twigs and litter from annuals left in front of gerbil
and rabbit burrows, sometimes even blocking these burrows. Thus, desert summer annuals, like nutrient reservoirs and providers,
take up nutrients during the rainy season, providing some animals and microbes with food, and finally release these nutrients
after death.
Bao-Ming Chen and Gen-Xuan Wang contributed equally to this work. 相似文献
16.
Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), commonly called gram pod borer, is a serious pest of pulse crops in India and damages
chickpea (Cicer arietinum L). On average a 30% crop loss is reported. One of the potential natural enemies reported for its biological control is Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae), an idiobiont parasitic wasp that attacks second instar larvae of the pod borer. Male-biased
sex ratios hinder efforts to mass release parasitic Hymenoptera for biological control by making the production of females
costly. Parental age at time of mating is known to affect the progeny sex ratio in some Braconidae. In this view, we examined
the reproduction and survival of the parasitoid C. chlorideae in the laboratory [22 ± 4°C, 70 ± 10% R.H. and 10:14 h light:dark photoperiod]. All the nine (i.e. 3 × 3) combinations of
possible mating were made for males and females, being each of different age groups (0–12, 48–60 and 96–108 h old). Second
instar larvae of the pod borer were reared on chickpea and exposed to mated females of different mating age group combinations.
Results revealed that (a) newly emerged females (0–12 h old) mated to aged males yielded more progeny contrasted to the older
females inseminated by newly emerged males (0–12 h old). This implies that increased maternal age at mating caused greater
reduction in the progeny yield than that of paternal age; (b) the progeny sex ratio was lowest (0.344 ± 0.057) (mean ± SD)
when parents mated just after emergence (0–12 h old). It became more and more male biased as parents were deprived of mate
and was highest (0.666 ± 0.701) for 96–108 h old parents. The analysis of variance of the data shows that mate deprived males
caused greater contribution in the production of sons, resulting a male-biased progeny sex ratio. Our conclusion indicate
that newly emerged parasitoids (0–12 h old) are most fecund and should be used in rearing practices in order to enhance the
progeny yield, particularly with respect to daughters.
Handling Editor: Torsten Meiners 相似文献
17.
Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches 总被引:1,自引:0,他引:1
Production was estimated for Aporrectodea spp. and Lumbricus spp. populations in corn agroecosystems with a 5-year history of manure or inorganic fertilizer applications during 1994–1995
and 1995–1996. Earthworm biomass and production were greater in manure than inorganic fertilizer plots, although biomass and
production declined by about 50% between 1994–1995 and 1995–1996 due to unfavorable climatic conditions. Production was highest
during the spring and autumn when soil temperatures were between 4 and 22°C. Production was higher in Lumbricus spp. than Aporrectodea spp. populations due to greater Lumbricus spp. biomass. Aporrectodea spp. production was 3.47–16.14 g ash-free dry weight (AFDW) m–2 year–1, while Lumbricus spp. production was 6.09–18.11 g AFDW m–2 year–1, depending on the fertilizer treatment and the method used to estimate production. However, production estimates from the
instantaneous growth rate method were within 27% of the values calculated using the size-frequency method. Nitrogen flux through
earthworms was used to estimate efficiency quotients. Net production efficiency (P/A) ranged from 0.64 to 0.76, assimilation efficiency (A/C) ranged from 0.1 to 0.3, and gross production efficiency (P/C) ranged from 0.06 to 0.22. Annual N flux through earthworm populations was higher in manure than inorganic fertilizer plots,
and ranged from 2.95 to 5.47 g N m–2 year–1 in 1994–1995 and 1.76 to 2.92 g N m–2 year–1 in 1995–1996. The N flux through earthworms represented an amount equivalent to 16–30% of crop N uptake during 1994–1995
and 11–18% of crop N uptake during 1995–1996. We concluded that the effects of earthworms on N cycling in corn agroecosystems
were substantial, and that N flux through earthworms was influenced significantly by fertilizer amendments.
Received: 20 September 1999 / Accepted: 24 March 2000 相似文献
18.
The individual and combined effects of two arbuscular mycorrhizal fungi (AMF), Meloidogyne arenaria, and phosphorus (P) fertilization, (0, 25, 75, and 125 μg/g soil) on peanut plant growth and pod yield were determined in
greenhouse studies. Best growth and yield usually occurred at 75 or 125 μg P regardless of inoculation treatment. Peanut growth
and yield were generally stimulated by AMF development, and growth alone was suppressed by M. arenaria at 0 and 25 μg P. In challenge inoculations, VAM increased peanut plant tolerance to the nematode and offset the growth reductions
caused by M. arenaria at the two lower P levels. However, VAM and added P increased galling and M. arenaria egg production/g root, thereby increasing peanut susceptibility to nematode attack. M. arenaria had only a minimal effect on root colonization by AMF and sporulation by the fungi.
Accepted: 9 June 1995 相似文献
19.
We quantified the amount, spatial distribution, and importance of salmon (Oncorhynchus spp.)-derived nitrogen (N) by brown bears (Ursus arctos) on the Kenai Peninsula, Alaska. We tested and confirmed the hypothesis that the stable isotope signature (δ15N) of N in foliage of white spruce (Picea glauca) was inversely proportional to the distance from salmon-spawning streams (r=–0.99 and P<0.05 in two separate watersheds). Locations of radio-collared brown bears, relative to their distance from a stream, were
highly correlated with δ15N depletion of foliage across the same gradient (r=–0.98 and –0.96 and P<0.05 in the same two separate watersheds). Mean rates of redistribution of salmon-derived N by adult female brown bears were
37.2±2.9 kg/year per bear (range 23.1–56.3), of which 96% (35.7±2.7 kg/year per bear) was excreted in urine, 3% (1.1±0.1 kg/year
per bear) was excreted in feces, and <1% (0.3± 0.1 kg/year per bear) was retained in the body. On an area basis, salmon-N
redistribution rates were as high as 5.1±0.7 mg/m2 per year per bear within 500 m of the stream but dropped off greatly with increasing distance. We estimated that 15.5–17.8%
of the total N in spruce foliage within 500 m of the stream was derived from salmon. Of that, bears had distributed 83–84%.
Thus, brown bears can be an important vector of salmon-derived N into riparian ecosystems, but their effects are highly variable
spatially and a function of bear density.
Received: 11 February 1999 / Accepted: 7 July 1999 相似文献
20.
Conrad Cloutier 《Journal of Insect Behavior》1997,10(4):581-598
Competitive interactions in arthropod predators are well-known, but positive interactions have received less attention. The
two-spotted stinkbugPerillus bioculatus often feeds gregariously on leaf beetle larvae and caterpillar prey. Consequences of prey sharing amongP. bioculatus conspecifics of dissimilar size (instar) was studied using Colorado potato beetle (CPB) prey. Rearing second-instar (N2)
nymphs ofP. bioculatus with an N5 conspecific facilitated early feeding on L4 CPB larvae (a difficult prey to handle by N2 nymphs but not by N5’s),
thus increasing survival and accelerating development. One in every 20 cases ofP. bioculatus foraging in the field was accounted for by pairs or small groups of mostly feeding individuals. CPB egg masses and L4’s represented
a disproportionate number of cases of aggregated feeding byP. bioculatus, compared to feeding singly. Small CPB larvae decreased in the diet of aggregated stinkbugs compared to L4 larvae and egg
masses, suggesting that sharing these prey may be favorable or unavoidable. In a field test measuring residence/survival of
N2’s limited to L4 prey, the N2’s rate of residence/survival increased significantly when large nymphs acting as food providers
were also present. The function of communal feeding inP. bioculatus is discussed, as well as the potential for greater impact on prey density that may be expected from tolerance to opportunistic
feeding by conspecifics in slightly gregarious predators. 相似文献