Depletion of macro-nutrients from rhizosphere soil solution by juvenile corn,cottonwood, and switchgrass plants

In situ sampling of rhizosphere solution chemistry is an important step in improving our understanding of soil solution nutrient dynamics. Improved understanding will enhance our ability to model nutrient dynamics and on a broader scale, to develop effective buffers to minimize nutrient movement to surface waters. However, only limited attention has been focused on the spatial heterogeneity and temporal dynamics of rhizosphere solution, and still less is known about how rhizosphere solution chemistry varies among plant species. Nutrients in rhizosphere soil solution and changes in root morphology of juvenile corn (Zea mays L. cv. Stine 2250), cottonwood (Populus deltoids L.), and switchgrass (Panicum virgatum L.) were monitored using mini-rhizotron technology. Plants were grown for 10 days in a fine-silty, mixed, superactive, mesic Cumulic Hapludoll (Kennebec series). Micro-samples (100–200 μL) of rhizosphere and bulk soil solution were collected at 24-h intervals at a tension of −100 kPa and analyzed for P, K, Ca, and Mg concentration using Capillary Electrophoresis techniques. Plants were harvested at the end of the 10-day period, and tissue digests analyzed for nutrient content by Inductively Coupled Plasma Spectroscopy. Corn plants produced roots that were 1.3 times longer than those of cottonwood, and 11.7 times longer than those of switchgrass. Similar trends were observed in number of root tips and root surface area. At the end of 10 days, rhizosphere solution P and K concentrations in the immediate vicinity of the roots (<1 mm) decreased by approximating 24 and 8% for corn, and 15 and 5% for cottonwood. A rhizosphere effect was not found for switchgrass. After correction for initial plant nutrient content, corn shoot P, K, and Mg were respectively 385, 132, and 163% higher than cottonwood and 66, 37, and 10% higher than switchgrass. Cottonwood shoot Ca concentration, however, was 68 to 133% higher than that of corn or switchgrass. There was no difference in root P concentration among the three species. Nutrient accumulation efficiency (μg nutrient mm⁻¹ root length) of cottonwood was 26 to 242% higher for P, 25 to 325% higher for Ca, and 41 to 253% higher for Mg than those of corn and switchgrass. However, K accumulation efficiency of corn was four to five times higher than that of the cottonwood and switchgrass. Nutrient utilization efficiency (mg of dry weight produced per mg nutrient uptake) of P, K, and Mg was higher in cottonwood than in corn and switchgrass. These differences are element-specific and depend on root production and morphology as well as plant nutrient status. From a practical perspective, the results of this study indicate that potentially significant differences in rhizosphere solution chemistry can develop quickly. Results also indicate that cottonwood would be an effective species to slow the loss of nutrients in buffer settings. An erratum to this article can be found at     

Difference in the predation impact enhanced by morphological divergence between introduced fish populations

The strength of predation impact on recipient environments may vary among introduced populations due to their local adaptations to different prey. We examined whether functional diversification associated with morphological differences may be observed among the introduced populations of invasive bluegill sunfish Lepomis macrochirus (Perciformes, Centrarchidae) in Japan. The two examined populations are morphologically different, although they were recently derived from a common American source and colonized in different lakes. We performed a laboratory experiment wherein these populations were fed the benthic (chironomid larva) and the pelagic prey (daphnid zooplankton). The results revealed that a population colonizing in a shallower lake and foraging on benthic invertebrates in the wild had a greater impact on the benthic prey, whereas the other population colonizing in a deeper lake and foraging on crustacean zooplankton have consumed the pelagic prey more efficiently. A series of regression analyses showed that morphological differences among individuals were responsible for these population differences. The evidence obtained suggests that morphological adaptations by introduced bluegill populations enhance the strength of predation impact on a prey resource consumed in a relevant environment, but reduce the impact on the other prey. Thus, although the introduced Japanese populations were recently derived from a common ancestor, the predation impacts on the native prey community vary due to morphological adaptations to different prey.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 601–610.     

The potential of the satellite derived green chlorophyll index for estimating midday light use efficiency in maize, coniferous forest and grassland

Light use efficiency (LUE) is an important variable in carbon cycle and climate change research. We present an investigation of remotely estimating midday LUE using the green chlorophyll index (CI_green) derived from the cloud-free Moderate Resolution Imaging Spectroradiometer (MODIS) images in maize, coniferous forest and grassland. Similar temporal patterns are observed in both canopy chlorophyll content and midday LUE which indicates that the chlorophyll content in the maize canopy servers as a proxy of midday LUE (R² = 0.736, p < 0.001). Therefore, the CI_green, tested as a good indicator of canopy chlorophyll content (R² = 0.840, p < 0.001), has been demonstrated to be a reliable candidate in providing reasonable estimates of midday LUE with determination coefficient R² equals to 0.820 and a root mean square error (RMSE) of 0.002 mol CO₂ per mol incident photosynthetic photon flux density (PPFD). Further validation of the prediction model derived from the maize site demonstrates that the CI_green has potential to be applied in the coniferous forest and grassland ecosystems with RMSE of 0.005 and 0.004 mol CO₂ mol⁻¹ PPFD, respectively. A comparison analysis between different vegetation types is included and these results could be helpful in the development of future LUE and terrestrial models.     

Stomatal innovation and the rise of seed plants

Stomatal valves on the leaves of vascular plants not only prevent desiccation but also dynamically regulate water loss to maintain efficient daytime water use. This latter process involves sophisticated active control of stomatal aperture that may be absent from early-branching plant clades. To test this hypothesis, we compare the stomatal response to light intensity in 13 species of ferns and lycophytes with a diverse sample of seed plants to determine whether the capacity to optimise water use is an ancestral or derived feature of stomatal physiology. We found that in seed plants, the ratio of photosynthesis to water use remained high and constant at different light intensities, but fern and lycophyte stomata were incapable of sustaining homeostatic water use efficiency. We conclude that efficient water use in early seed plants provided them with a competitive advantage that contributed to the decline of fern and lycophyte dominated-ecosystems in the late Paleozoic.     

铜绿假单胞菌对镉胁迫苗期水稻根系活力及叶片生理特性的影响

为揭示耐镉铜绿假单胞菌缓解镉胁迫水稻的生理效应,以无镉处理为对照,通过添加菌液、空载体、菌剂及20μmol·L^-1 Cd进行水培试验,分析了菌株对苗期水稻根系活力及叶片生理特性的影响.结果表明:镉胁迫显著抑制了水稻的根系活力,降低了叶片光合效率、抗氧化酶活性及可溶性蛋白、类黄酮与总酚含量,提高了叶片丙二醛(MDA)和超氧阴离子(O2-)含量.与镉处理相比,添加菌液、菌剂处理的水稻根系活力分别提高了36.1%~42.5%、49.4%~53.0%;叶片净光合速率提高了118.5%~147.1%、137.6%~156.9%;可溶性蛋白含量提高了37.0%~49.3%、37.7%~72.6%.菌剂处理的水稻叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性分别比Cd处理提高了36.9%~42.6%、82.7%~92.6%、43.3%~52.2%,菌液处理的SOD、POD、CAT则分别比Cd处理提高了25.8%~36.6%、40.9%~55.9%、24.0%~29.2%,菌剂对水稻叶片抗氧化酶的促进效应显著高于菌液;菌剂、菌液处理的水稻叶片MDA含量分别比Cd处理降低了44.8%~54.7%、29.4%~41.9%;O2-含量减少了9.9%~10.2%、3.0%~7.1%;菌剂处理后类黄酮、总酚含量分别比Cd处理提高了125.4%~135.7%、100.8%~119.4%;菌液处理后则分别提高了139.4%~146.7%、115.0%~134.7%.可见,铜绿假单胞菌及其菌剂通过提高苗期水稻根系活力、光合作用促进了苗期水稻的生长.铜绿假单胞菌通过增强水稻抗氧化酶活性、提高类黄酮和总酚等抗氧化物质含量,表现出显著的缓解镉胁迫效应.     

Nitrogen vs. phosphorus limitation across an ecotonal gradient in a mangrove forest

Mangrove forests are characterized by distinctive tree-height gradientsthat reflect complex spatial, within-stand differences in environmentalfactors,including nutrient dynamics, salinity, and tidal inundation, across narrowgradients. To determine patterns of nutrient limitation and the effects ofnutrient availability on plant growth and within-stand nutrient dynamics, weused a factorial experiment with three nutrient treatment levels (control, N,P)and three zones along a tree-height gradient (fringe, transition, dwarf) onoffshore islands in Belize. Transects were laid out perpendicular to theshoreline across a mangrove forest from a fringe stand along the seaward edge,through a stand of intermediate height, into a dwarf stand in the interior ofthe island. At three sites, three trees were fertilized per zone for 2yr. Although there was spatial variability in response, growth byR. mangle was generally nitrogen (N) -limited in thefringe zone;phosphorus (P) -limited in the dwarf zone; and, N- and/or P-limited in thetransition zone. Phosphorus-resorption efficiency decreased in all three zones,and N-resorption efficiency increased in the dwarf zone in response to Penrichment. The addition of N had no effect on either P or N resorptionefficiencies. Belowground decomposition was increased by P enrichment in allzones, whereas N enrichment had no effect. This study demonstrated thatessential nutrients are not uniformly distributed within mangrove ecosystems;that soil fertility can switch from conditions of N to P limitation acrossnarrow ecotonal gradients; and, that not all ecological processes respondsimilarly to, or are limited by, the same nutrient.     

Combined analysis of group recorded feed intake and individually recorded body weight and litter size in mink

In the mink industry, feed costs are the largest variable expense and breeding for feed efficient animals is warranted. Implementation of selection for feed efficiency must consider the relationships between feed efficiency and the current selection traits BW and litter size. Often, feed intake (FI) is recorded on a cage with a male and a female and there is sexual dimorphism that needs to be accounted for. Study aims were to (1) model group recorded FI accounting for sexual dimorphism, (2) derive genetic residual feed intake (RFI) as a measure of feed efficiency, (3) examine the relationship between feed efficiency and BW in males (BWM) and females (BWF) and litter size at day 21 after whelping (LS21) in Danish brown mink and (4) investigate direct and correlated response to selection on each trait of interest. Feed intake records from 9574 cages, BW records on 16 782 males and 16 875 females and LS21 records on 6446 yearling females were used for analysis. Genetic parameters for FI, BWM, BWF and LS21 were obtained using a multivariate animal model, yielding sex-specific additive genetic variances for FI and BW to account for sexual dimorphism. The analysis was performed in a Bayesian setting using Gibbs sampling, and genetic RFI was obtained from the conditional distribution of FI given BW using genetic regression coefficients. Responses to single trait selection were defined as the posterior distribution of genetic superiority of the top 10% of animals after conditioning on the genetic trends. The heritabilities ranged from 0.13 for RFI in females and LS21 to 0.59 for BWF. Genetic correlations between BW in both sexes and LS21 and FI in both sexes were unfavorable, and single trait selection on BW in either sex showed increased FI in both sexes and reduced litter size. Due to the definition of RFI and high genetic correlation between BWM and BWF, selection on RFI did not significantly alter BW. In addition, selection on RFI in either sex did not affect LS21. Genetic correlation between sexes for FI and BW was high but significantly lower than unity. The high correlations across sex allowed for selection on standardized averages of animals’ breeding values (BVs) for RFI, FI and BW, which yielded selection responses approximately equal to the responses obtained using the sex-specific BVs. The results illustrate the possibility of selecting against RFI in mink with no negative effects on BW and litter size.     

土壤大气湿度组合对玉米生长和WUE效应研究

采用人工气候生长箱盆栽试验,模拟土壤和大气湿度不同组合处理,发现土壤干旱和大气干旱显著抑制玉米生长。大气湿度提高,在一定程度能改善作物的水分状况,降低蒸腾,解除土壤干旱危害,产生生长和生理补偿效应,明显提高水分利用效率。