Summary Fertilizer/soil N balance of cropped and fallow soil has been studied in a pot experiment carried out with grey forest soil (southern part of Moscow region) at increasing rates of15N labelled ammonium sulfate (0; 8; 16; 32 mg N/100 g of soil). The fertilizer15N balance has been shown to depend upon its application rate and the presence of growing plants. Fertilizer N uptake efficiency was maximum (72.5%) and gaseous losses-minimum (12.5%) at the application rate of 16 mg N/100 g of soil. Fertilizer N losses from the fallow soil were 130–220% versus those from the cropped soil. At the application of fertilizer N the plant uptake of soil N was 170–240% and the amount of soil N as N–NH4 exchangeable + N–NO3 in fallow was 350–440% as compared to the control treatment without nitrogen (PK).After cropping without or with N fertilizer application at the rates of 8 and 32 mg N/100 g of soil, a positive nitrogen balance has been found which is likely due to nonsymbiotic (associative) N-fixation. It has been shown that biologically fixed nitrogen contributes to plant nutrition. 相似文献
In a spaceflight experiment, autotropism by oat ( Avena sativa L.) coleoptiles following gravitropic responses was prominent in weightlessness: counter-reactions led to the straightening of the curved coleoptiles. This was not the case during clinorotation on earth. The autotropic reactions appeared to be related to the stimulus received during the stimulus period, i.e. the greater the response the greater the autotropic counter-reaction. Previous models of the gravitropic system which predicted that coleoptiles would not straighten in weightlessness are disproved. A modification to one of the models is proposed which includes the autotropic response observed in spaceflight. The nature of the counter-reactions in the absence of gravitropic stimulation is discussed. 相似文献
Juvenile Nucella lapillus of two different shell phenotypes, exposed shore and protected shore, were maintained in running seawater under each of three experimental conditions for 94 d: a) laboratory control, b) exposed to the effluent of crabs (Cancer pagurus) fed frozen fish (fish-crab), and c) exposed to the effluent of crabs fed live conspecific snails (snail-crab). Rates of barnacle consumption and rates of body weight change varied significantly between phenotypes and among experimental conditions. Individuals from the protected-shore consumed consistently fewer barnacles and grew consistently less than those from the exposed shore. Body weight increases in the fish-crab treatments were from 25 to 50% less than those in the controls and body weights in the snail-crab treatment either did not change or actually decreased. The perceived risk of predation thus appears to have a dramatic effect on the rates of feeding and growth of N. lapillus.At the end of the experiment, size-adjusted final shell weights for both phenotypes were consistently higher than controls (no crab) in both the fish-crab and snail-crab treatments. In addition, apertural tooth height, thickness of the lip, and retractability (i.e. the extent to which a snail could withdraw into its shell), with few exceptions all varied in an adaptive manner in response to the various risk treatments. Similar changes in the shell form of starved snails exposed to the same stimuli suggest very strongly that the morphological responses of both phenotypes were not just due to differences in rates of growth. These differences, at least in part, represented a direct cueing of the shell form of Nucella lapillus to differences in the perceived risk of predation. Somewhat surprisingly, the extent of phenotypic plasticity appeared to differ between the populations examined. Both field and laboratory evidence suggest that the exposed-shore population was much more labile morphologically than the protected-shore population.In many instances, particularly among starved snails, the development of antipredatory shell traits was greater in the fish-crab treatment than in the snail-crab treatment. Because the scent of crabs was present in both treatments, these results suggest a) that, at the frequency/concentration used in the experiments, the scent of damaged conspecifics may have been a supernormal stimulus and b) that the morphological response in these treatments might have been greater if the stimulus had been provided at a lower level. 相似文献
In order to study the effects of temperature enhancement on alpine calcareous grassland species, a warming experiment was carried out in the Berchtesgaden National Park (Southeast Germany, Northern Calcareous Alps) between 2002 and 2004. The study was conducted in stands of the Carex sempervirens and the Carex firma communities; the two most widespread grassland types in the alpine zone of the Northern Calcareous Alps. The temperature of the vegetation stand and the upper soil was passively enhanced using open top chambers (OTCs). The construction of the OTCs was appropriate since temperature was clearly increased while water conditions (humidity, soil water content) were not changed.
By comparing manipulated (temperature enhancement) with non-manipulated plots, the effects of warming on growth and reproduction of selected key species were studied. To test if vegetation response to temperature enhancement is at least partly due to increases in nutrient availability, soil solution concentrations of nitrate and ammonium were analysed.
We found that most of the studied plant species are sensitive to temperature enhancement. Growth and/or reproduction of 12 of the 14 studied species were significantly stimulated by warming. Only two species showed no response; none of the species experienced decreases in growth or reproduction. Dwarf shrubs and graminoids showed a stronger response than herbaceous perennials. A significant effect of warming on nutrient availability could not be detected. The observed response of vegetation is therefore mainly caused by direct and not by indirect temperature effects. 相似文献
The fate and availability of P derived from granular fertilisers in an alkaline Calcarosol soil were examined in a 65-year
field trial in a semi-arid environment (annual rainfall 325 mm). Sequential P fractionation was conducted in the soils collected
from the trial plots receiving 0–12 kg P ha−1crop−1, and the rhizosphere soil after growing wheat (Triticum aestivum L. cv. Yitpi) and chickpea (Cicer arietinum L. cv. Genesis 836) for one or two 60-day cycles in the glasshouse. Increasing long-term P application rate over 65 years
significantly increased all inorganic P (Pi) fractions except HCl–Pi. By contrast, P application did not affect or tended
to decrease organic P (Po) fractions. Increasing P application also increased Olsen-P and resin-P but decreased the P buffer
capacity and sorption maxima. Residual P, Pi and Po fractions accounted for an average of 32, 16 and 52% of total P, respectively.
All soil P fractions including residual P in the rhizosphere soil declined following 60-day growth of either wheat or chickpea.
The decreases were greater in soils with a history of high P application than low P. An exception was water-extractable Po,
which increased following plant growth. Changes in various P fractions in the rhizosphere followed the same pattern for both
plant species. Biomass production and P uptake of the plants grown in the glasshouse correlated positively with the residual
P and inorganic fractions (except HCl–Pi) but negatively with Po in the H2O-, NaOH- and H2SO4-fractions of the original soils. The results suggest that the long-term application of fertiliser P to the calcareous sandy
soil built up residual P and non-labile Pi fractions, but these P fractions are potentially available to crops. 相似文献
Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model‐data intercomparison project, where we tested the ability of 10 terrestrial biosphere models to reproduce the observed sensitivity of ecosystem productivity to rainfall changes at 10 sites across the globe, in nine of which, rainfall exclusion and/or irrigation experiments had been performed. The key results are as follows: (a) Inter‐model variation is generally large and model agreement varies with timescales. In severely water‐limited sites, models only agree on the interannual variability of evapotranspiration and to a smaller extent on gross primary productivity. In more mesic sites, model agreement for both water and carbon fluxes is typically higher on fine (daily–monthly) timescales and reduces on longer (seasonal–annual) scales. (b) Models on average overestimate the relationship between ecosystem productivity and mean rainfall amounts across sites (in space) and have a low capacity in reproducing the temporal (interannual) sensitivity of vegetation productivity to annual rainfall at a given site, even though observation uncertainty is comparable to inter‐model variability. (c) Most models reproduced the sign of the observed patterns in productivity changes in rainfall manipulation experiments but had a low capacity in reproducing the observed magnitude of productivity changes. Models better reproduced the observed productivity responses due to rainfall exclusion than addition. (d) All models attribute ecosystem productivity changes to the intensity of vegetation stress and peak leaf area, whereas the impact of the change in growing season length is negligible. The relative contribution of the peak leaf area and vegetation stress intensity was highly variable among models. 相似文献