半干旱地区不同地膜覆盖时期对土壤氮素有效性的影响

在年降水量415mm的半干旱地区黄绵土上,以春小麦为供试作物进行大田试验,研究地膜覆盖(包括不覆膜、播种后覆膜30d、覆膜60d和全程覆膜)对土壤水分、温度和氮素有效性的影响.结果表明,覆膜对2m土层贮水量基本没有影响,能显著提高0～20cm土层的含水量;覆膜对5cm处土壤温度的影响呈\"U”型变化,即在作物生长前期和后期影响显著,中期影响较小;覆膜能增加土壤呼吸和有机氮的矿化,因而显著影响土壤剖面中NO-3-N的累积表现为在收获时覆膜30d和60d处理剖面中NO-3-N的累积明显下降,而全程覆膜处理剖面中NO-3-N的累积显著增加,在覆膜的基础上施用氮肥,这种作用会更加突出.显然全程覆膜易造成有机质的大量矿化和NO-3-N的淋溶损失.     

The influence of glucose and other sources of carbon on nitrate reduction rates in two temperate forest soils

The effects of different sources of organic carbon on the potential NO ₃ ⁻ reduction rates in an acid mull and an anmoor (anmoor is a type of soil which is rich in organic matter, remains water saturated most of the time and where organic and mineral fractions are closely associated) were studied under anaerobic incubation. The disappearance of NO ₃ ⁻ was higher in the anmoor than in the mull in all cases. This contradicts our previous findings where the apparent denitrification was higher in the mull than in the anmoor in the presence of added glucose. This seems to indicate that drying of soil samples might have caused the formation of stable soil aggregates in the case of anmoor (containing 16% of organic matter). Thus a favourable condition was created for securing improved diffusion of nutrients in the anmoor. Glucose, a readily available source of carbon, led to a very high degree of NO ₃ ⁻ disappearance. Among other sources, the cellulose caused higher reduction of NO ₃ ⁻ than litter and lignin. The accumulation although small, of NH ₄ ⁺ which was presumably formed (at least partially) during dissimilatory reduction of NO ₃ ⁻ , and its biological immobilization were more apparent in the anmoor than in the mull.     

Nitrate accumulation in leaves of vegetation of a forested ecosystem receiving high amounts of atmospheric ammonium sulfate

Vegetation of an acid woodland, receiving an atmospheric ammonium input of about 3 kmol (40 kg N) per hectare per year, was analyzed on the content of organic nitrogen, ammonium and nitrate. A high nitrate content (50–320 μmol g⁻¹ dry weight) was found in bird-cherry, black-berry and bracken, whereas only low amounts (up to 2 μmol g⁻¹ dry weight) of nitrate were present in mountain-ash, hazel and the two dominant tree species oak and birch. The impact of this nitrate uptake and nitrate accumulation on soil pH and autotrophic nitrification is discussed.     

氮硅添加对青藏高原高寒草甸土壤氮矿化的影响

为了解全球气候变化背景下氮沉降对土壤氮矿化的影响及硅添加对土壤氮矿化的促进作用, 该试验设置不同浓度的氮肥单独添加(0、20、40、60 g·m ^-2, 分别为对照CK、N20、N40、N60)以及与硅肥配施(硅酸4 g·m ^-2, Si4), 测定不同处理下0-20、20-40、40-60 cm土层土壤硝态氮含量、铵态氮含量、净硝化速率、净氨化速率以及净矿化速率。结果显示: (1)单独添加氮肥, 各土层土壤硝态氮和铵态氮含量均随处理浓度的增加而增加, 0-20 cm土层N20、N40、N60处理下土壤硝态氮和铵态氮分别较CK增加63.48%、126.04%、247.03%和80.66%、152.52%、244.56%; 随着土层深度增加, 土壤硝态氮、铵态氮含量均有下降, 20-40、40-60 cm土层较0-20 cm土层硝态氮含量分别平均减少53.90%、76.05%, 铵态氮含量分别平均减少48.62%、68.23%。(2)土壤净硝化速率、净氨化速率及净矿化速率随着氮肥浓度增加均呈上升趋势。相同氮肥添加浓度下, 土壤净硝化速率、净氨化速率和净矿化速率随着土层深度增加逐渐下降(除CK外)。(3)与单独添加氮肥比较, 氮硅肥配施, 土壤氮含量有显著提高, 在0-20 cm土层硝态氮和铵态氮较CK分别增加98.78%、192.62%、330.16%和99.96%、195.82%、306.32%, 20-40、40-60 cm土层也有类似趋势。同时, 氮硅配施促进了土壤氮矿化行为, 在0-20 cm土层, N60Si4处理下的土壤净硝化速率、净氨化速率较单独施氮时分别增加35.88%、27.41%。以上结果表明, 与单独氮肥添加相比, 氮硅配施不但能提高土壤氮含量, 而且能促进土壤氮的矿化作用, 对大气氮沉降有一定的缓解作用。     

Measuring Nitrogen and Phosphorus Uptake by Intact Roots of Mature Acer saccharum Marsh., Pinus resinosa Ait., and Picea abies (L.) Karst

A common method for measuring uptake by intact roots in situ is the depletion method, wherein intact fine roots are separated from soil and placed in nutrient solution. The difference between initial and final amounts of nutrient in solution is attributed to root uptake. Variations on this method include applying pretreatment solutions, training roots to grow into bags or trays, and varying concentrations of nutrient solution. We tested whether variations in methods affected measured net uptake rates of NH ₄ ⁺ , NO ₃ ⁻ , and PO ₄ ³⁻ . Intact roots of 60 year-old sugar maple (Acer saccharum Marsh.), red pine (Pinus resinosa Ait.), and Norway spruce (Picea abies (L.) Karst.) were given one of four treatments prior to measuring net uptake. “Trained” roots were grown in a sand-soil mixture. “Recovered” roots were excavated and allowed to recover in nutrient solution for two or four days (“two-day recovery” and “four-day recovery”, respectively). “No recovery” roots were excavated and used immediately in experiments. We exposed roots to three concentrations of nutrient solutions to observe the effects of initial nutrient solution concentration. Initial nutrient solution concentration was an important source of variation in measured uptake rates, and N uptake was stimulated by low antecedent concentrations. We found no significant differences in net uptake rates between pretreatments for any of the species studied, indicating that our pretreatments were not effective in improving measurement of uptake. Such pretreatments may not be necessary for measuring net uptake and may not hinder the comparison of rates measured using variations of the depletion method.     

A dynamic whole-plant model of integrated metabolism of nitrogen and carbon. 1. Comparative ecological implications of ammonium-nitrate interactions

The dynamics of ammonium (NH₄ ⁺) and nitrate (NO₃ ^-) concentrations in the soil solution is an important determinant of the species composition of natural vegetation. A mathematical model of uptake, assimilation and translocation of NH₄ ⁺ and NO₃ ^- is presented to assess the performance of species with respect to NO₃ ^-/NH₄ ⁺ feeding characterised by physiologically defined parameters. Nitrate efflux is explicitly considered. The capacities of NO₃ ^-, [U _NM], and NH₄ ⁺ influx, [U _AM], and NO₃ ^- reduction, [A _NM], appear sufficient to characterise whole-plant N metabolism including NO₃ ^- translocation. The parameter space made up by these parameters is represented by 276 parameter combinations (`species'). Simulated total net N uptake rate and C costs for uptake and assimilation per mole total net N taken up are used to decide on how a species profits or suffers from NO<sub>3</sub> <sup>-</sup>+NH<sub>4</sub> <sup>+</sup> mixtures relative to pure N forms with similar total N concentration for external concentrations up to 1.6 mM. Five response categories were identified and contrasted with categories defined by Bogner (1968) on the basis of experimental results on forest plants. The largest category comprises species that respond positively to NO<sub>3</sub> <sup>-</sup> and positively or indifferently to NH<sub>4</sub> <sup>+</sup>. These species have intermediate to high [U <sub>NM</sub>] and [A <sub>NM</sub>] and variable [U <sub>AM</sub>] and correspond to woodland edge species and forest plants on rich soil including typical `nitrophilic' species. This category fades into a group of species that respond positively to NO₃ ^- and negatively to NH₄ ⁺. These species have high [U _NM] and low [U _AM] and [A _NM]; several species from oak-hornbeam woodland (Carpinion) belong to this group. Many parameter combinations were found that responded positively to NH₄ ⁺ and indifferently to NO₃ ^-: low to medium [U _NM], medium to high [U _AM] and variable [A _NM]. This category includes all heathland species. No species were found which responded negatively to NO₃ ^-. The physiological background of differences between the categories is explained with respect to the equilibrium NO₃ ^- concentration in roots, influx, efflux, translocation and assimilation of NO₃ ^- and uptake and assimilation of NH₄ ⁺. The relationship between NO₃ ^- accumulation capacity and morphology is discussed. Some slow-growing species with high [U _NM] and low [A _NM] use NO₃ ^- mainly as an osmotic solute. Respiratory costs in roots of inherently slow-growing species are discussed with respect to patterns in NH₄ ⁺ and NO₃ ^- availabilities of their habitat. This revised version was published online in June 2006 with corrections to the Cover Date.     

甘肃陇东旱塬不同树龄苹果园矿质氮的分布和积累特征

对甘肃陇东地区不同树龄苹果园土壤矿质氮的分布和积累特征进行了研究.结果表明：土壤铵态氮含量随着苹果树龄的增大呈上升趋势,2～3年生、5年生、10年生、15年生、20年生、22年生果园0～120 cm土层铵态氮含量分别为3.3、5.8、6.5、9.1、12.1和15.3 mg·kg^-1;不同树龄果园0～60 cm土层铵态氮含量大于60～120 cm土层.不同树龄果园硝态氮含量在0～40 cm土层相对较低,随土层深度增加,其含量迅速增加;随着种植年限增加,不同苹果园硝态氮累积量也呈显著增加趋势,22年生果园0～120 cm土层硝态氮累积量达到2602.5 kg·hm^-2.旱塬苹果园表现为土壤铵态氮呈浅层积累、而硝态氮呈深层积累的特征.     

Are differences in root growth of nitrogen catch crops important for their ability to reduce soil nitrate-N content,and how can this be measured?

An experiment was made to measure root growth of nitrogen catch crops, to investigate whether differences in root growth among plant species are related to their ability to deplete the soil nitrate-N pool. Large differences were observed in root growth parameters. Monocot species had rooting depth penetration rates in the range of 1.0 to 1.2 mm d^–1 °C^–1, whereas the non-legume dicot species had rates between 1.5 and 2.3 mm d^–1 °C^–1. Substantial differences were also found in the lag time from sowing until significant root growth was observed. The estimated temperature sum needed for the crops to reach a rooting depth of 1.0 m varied from 750 d °C for fodder radish to 1375 d °C for Italian ryegrass. The depth distribution of the root system varied strongly, and at a depth of 1.0 m the non-legume dicot species generally had root intensities (number of root intersections m^–1 line on the minirhizotrons) 12 times as high as the monocot species.The amount of nitrate left in the topsoil (0–0.5 m) was only weakly correlated to a few of the measured plant and root parameters, whereas nitrate left in the subsoil (0.5–1.0 m) was clearly correlated to several root parameters. Subsoil nitrate residues were well correlated to root intensity, but showed even stronger correlations to more simple estimates of rooting depth. In the deepest soil layer measured (1.0–1.5 m), the soil water nitrate concentration was reduced from 119 g L^–1 without a catch crop to 61 g L^–1 under Italian ryegrass and to only 1.5 g L^–1 under fodder radish.The results show that to identify the important differences in root growth among catch crops, root growth must be measured in deep soil layers. In this study, none of the measurements made aboveground or in the upper soil layers were well related to subsoil nitrate depletion.     

Nitrogen and base cation uptake in seedlings of Acer pseudoplatanus and Calamagrostis villosa exposed to an acidified environment

The effects of solution acidity and form of nitrogen on net nutrient uptake rates in Acer pseudoplatanus and Calamagrostis villosa seedlings were examined as part of a complex ecological study. Uptake rates were measured by the depletion method under controlled conditions (temperature 20 °C, irradiance 400 mol m^–2 s^–1 PAR) from a nutrient solution containing 1.5 mM nitrogen in the form of nitrate or ammonium or an equimolar mixture of both. The solution acidity was kept constant at pH 5.5 (control treatment), 4.5 or 3.5 (low pH treatments). Strongly acid pH decreased or stopped the uptake rates of NO₃ ^–, Mg²⁺ and Ca²⁺, but the uptake of NH₄ ⁺ was not changed in both species. Ammonium ions reduced the uptake rate of NO₃ ^– in Acer but increased the uptake rate in Calamagrostis. Ammonium as the sole source of nitrogen had a strong negative impact on the uptake rates of calcium and magnesium and this effect was independent of the media acidification usually connected with NH₄ ⁺ uptake and assimilation. However, the negative effect of ammonium ions on the base cation uptake was more pronounced at low pH values.     

Differences in Earthworm Densities and Nitrogen Dynamics in Soils Under Exotic and Native Plant Species

Previous studies of the invasion of two exotic plants – Berberis thunbergii and Microstegium vimineum – in hardwood forests of New Jersey have shown a significant increase of pH in soils under the invasive plants as compared with soils from under native shrubs (Vaccinium spp). We present a further investigation of soil properties under the exotic plants in question. We measured the densities of earthworms in the soil under the two exotics and the native shrubs in three parks in New Jersey. In the same populations we also measured the extractable ammonium and nitrate in the top 5 cm of the soil, as well as the respiration of the soils and the potential rates of mineralization (aerobic lab incubation). In addition, we measured the nitrate reductase activity in leaves of the two exotic plants and several native shrubs and trees. Although there were differences between parks, we observed significantly higher earthworm densities in the soil under the exotic species. The worms were all European species. Soil pH, available nitrate and net potential nitrification were significantly higher in soils under the two exotic species. In contrast, total soil C and N and net ammonification were significantly higher under native vegetation. Nitrate reductase activities were much higher in the leaves of exotic plants than in the leaves of native shrubs and trees. Changes in soil properties, especially the change in nitrogen cycling, associated with the invasion of these two plant species may permit the invasion of other weedy or exotic species. Our results also suggest that even if the two exotic species were removed, the restoration of the native flora might be inhibited by the high nitrate concentrations in the soil.     

凋落物与单宁酸对森林土壤无机氮的影响

采用室内培养试验,研究了不同凋落物和单宁酸对森林土壤硝态氮和铵态氮的影响.结果表明：凋落物和单宁酸加入均降低了土壤硝态氮和铵态氮含量.杉木凋落物使红壤硝态氮和铵态氮含量分别降低6.1%～25.9%和19.7%～68.6%.杉木凋落物中黄红壤无机氮含量的降幅大于毛竹,对铵态氮的影响极显著.与对照相比,单宁酸处理能显著降低黄红壤中铵态氮含量,单宁酸浓度越高,其降幅越大,至高浓度(HG)时,其降幅达31.9%～57.8%.随着培养时间的延长,低浓度单宁酸处理(HL)中硝态氮含量降幅逐渐增大,第84天达到4.5%;在HG处理下,第7～28天的硝态氮含量增加了10.3%～18.5%,而第56和85天分别降低23.9%和42.3%.     

烤烟硝酸盐含量与土壤养分的关系

采用多元统计分析方法研究了湖南烤烟叶片硝酸盐、亚硝酸盐含量与土壤养分之间的关系,结果表明：（1）典型相关分析证实烟叶硝酸盐、亚硝酸盐含量与土壤主要含氮养分（土壤全氮、碱解氮、铵态氮）及有机质含量的关系密切,与土壤其他养分含量的相关性较小,反映出在一定范围内,随着土壤含氮养分及有机质含量的增加,烟叶（亚）硝酸盐含量呈现增加的趋势,且土壤含氮养分及有机质含量与烟叶硝酸盐含量关系的密切程度高于与亚硝酸盐含量的相关;（2）根据烟叶硝酸盐、亚硝酸盐含量及其相应的植烟土壤养分（有机质、全氮、碱解氮、铵态氮）含量的大小,通过聚类分析把同一等级的烟叶样品分为高、中、低3类,不同类别相比较,有机质含量越高的土壤,其土壤全氮、碱解氮、铵态氮含量以及相应的烟叶硝酸盐、亚硝酸盐含量也越高,说明土壤有机质的高低,直接影响了土壤氮素的供应状况,进而影响了烟叶硝态氮含量的积累;（3）根据聚类分析结果建立了不同等级烟叶硝酸盐、亚硝酸盐含量高低的判别函数,可作为烟叶硝态氮含量在不同土壤肥力条件下判别归类的参考依据。