Experimental manipulation of water and nutrient input to a Norway spruce plantation at Klosterhede,Denmark

Water and nutrient supply to forest trees are major factors controlling tree growth and forest vitality. Therefore, changes in the supply of water and nutrients to the trees may be important contributing reasons to the forest damages observed in Europe. Such changes may be caused by several factors, e.g. air pollution, soil acidification and climate change. The present study investigates possible effects on tree growth, growth related parameters and nutrition related to changes in the water and nutrient supply. Water and nutrient supply to the forest soil was manipulated in three roof covered plots. The treatments consisted of 1) summer drought, 2) irrigation and 3) combined irrigation and fertilizer application (fertigation). The results from the roof covered treatment plots were compared to a control plot without roof. Increased supply of water during the spring and early summer increased the diameter growth, whereas application of nutrients in addition to irrigation had no additional effect on tree growth. Addition of nutrients increased the needle content of P, Mn, Ca and Mg. Extended summer drought for 2 months had no effect on the tree growth or other growth parameters, but drought reduced the root development in the upper soil layer. Furthermore, drought induced significant stress symptoms by increasing the cone shredding substantially.     

Soil feedback does not explain mowing effects on vegetation structure in a semi-natural grassland

Due to its ability to create aboveground conditions that favour plant diversity, mowing is often used to preserve the high conservation value of semi-natural species-rich grasslands. However, mowing can also affect belowground conditions. By decreasing plant carbon supply to soil, mowing can suppress the activity of soil decomposers, diminish plant nutrient availability and thus create a feedback on plant growth. In this study, we first documented the effects of three-year mowing on plant community structure in a species-rich grassland. We found that mowing decreased the total areal cover of woody plants and increased the total cover of leguminous forbs. At the species level, mowing further increased the cover of two non-leguminous forbs, Prunella vulgaris and Sagina procumbens. Mowing did not affect the species number, diversity or evenness of the plant community. To study whether any of these effects could be explained by mowing-induced changes in the soil, and particularly by reduced nutrient availability, we then collected soil from different treatment plots and monitored the growth of nine plant species in these soils in a greenhouse. Plant growth did not differ between soils collected from mowed and unmowed plots, suggesting that our mowing regimes did not impose such changes in soil decomposer activity and nutrient supply that would feedback on plant growth. Moreover, each of the nine species responded equally to the different nutrient availability in different parts of the grassland, which indicates that even if mowing had reduced plant nutrient supply, this would not have led to changes in plant community structure. It appears that those changes in aboveground vegetation that we recorded after three years of mowing were purely due to the aboveground effects, such as frequent cutting of woody plants and enhanced light availability for low-growing forbs.     

Interactions between plant nutrients,water and carbon dioxide as factors limiting crop yields

Biomass production of annual crops is often directly proportional to the amounts of radiation intercepted, water transpired and nutrients taken up. In many places the amount of rainfall during the period of rapid crop growth is less than the potential rate of evaporation, so that depletion of stored soil water is commonplace. The rate of mineralization of nitrogen (N) from organic matter and the processes of nutrient loss are closely related to the availability of soil water. Results from Kenya indicate the rapid changes in nitrate availability following rain.<br>Nutrient supply has a large effect on the quantity of radiation intercepted and hence, biomass production. There is considerable scope for encouraging canopy expansion to conserve water by reducing evaporation from the soil surface in environments where it is frequently rewetted, and where the unsaturated hydraulic conductivity of the soil is sufficient to supply water at the energy limited rate (e.g. northern Syria). In regions with high evaporative demand and coarse-textured soils (e.g. Niger), transpiration may be increased by management techniques that reduce drainage.<br>Increases in atmospheric [CO₂] are likely to have only a small impact on crop yields when allowance is made for the interacting effects of temperature, and water and nutrient supply. <br>     

Modelling zinc uptake by rice crop using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model which has been utilized extensively to describe and predict nutrient uptake by crop plants at different stages of crop growth was evaluated for its ability to predict the Zn uptake by rice seedlings. Uptake of the nutrient is, therefore, determined by the rate of nutrient supply to the root surface by mass flow and diffusion. Inter root competition and time dependent root density are accounted for by soil volume that delivers nutrients. The radii of these cylinders decline with increasing density. Since mass flow and diffusion each supply zinc to the root, the process can be described mathematically using the model of Barber-Cushman (1984). The 11 parameters of the model for the uptake by rice cultivars were measured by established experimental techniques. Zinc uptake at different growth stages predicted by the model was compared to measured zinc uptake by rice cultivars grown on sandy loam soil in a green house. Predicted zinc uptake was significantly correlated with observed uptake r ²=0.99^**. Sensitivity analysis was also used to investigate the impact of changes in soil nutrient supply, root morphological and root uptake kinetic parameters on simulated nutrient uptake. Overall results of sensitivity analysis indicate that the half distance between root axes, rate of root growth and water flux affect the uptake of zinc particularly at their higher values rather than at lower values and DaZn is the most sensitive parameter for zinc uptake at its lower values.     

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature – herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local‐scale herbivory, and its interaction with nutrient enrichment and climate, within global‐scale models to better predict land–atmosphere interactions under future climate change.     

Water Supply Changes N and P Conservation in a Perennial Grass Leymus chinensis

Changes in precipitation can influence soil water and nutrient availability, and thus affect plant nutrient conservation strategies. Better understanding of how nutrient conservation changes with variations in water availability is crucial for predicting the potential influence of global climate change on plant nutrient-use strategy. Here, green-leaf nitrogen (N) and phosphorus (P) concentrations, N- and P-resorption proficiency (the terminal N and P concentration in senescent leaves, NRP and PRP, respectively), and N- and P-resorption efficiency (the proportional N and P withdrawn from senescent leaves prior to abscission, NRE and PRE, respectively) of Leymus chinensis (Trin.) Tzvel., a typical perennial grass species in northern China, were examined along a water supply gradient to explore how plant nutrient conservation responds to water change. Increasing water supply at low levels (< 9000 mL/year) increased NRP, PRP and PRE, but decreased green-leaf N concentration. It did not significantly affect green-leaf P concentration or NRE. By contrast, all N and P conservation indicators were not significantly influenced at high water supply levels (> 9000 mL/year). These results indicated that changes in water availability at low levels could affect leaf-level nutrient characteristics, especially for the species in semiarid ecosystems. Therefore, global changes in precipitation may pose effects on plant nutrient economy, and thus on nutrient cycling in the plant-soil systems.     

Stoichiometric homeostasis in response to variable water and nutrient supply in a Robinia pseudoacacia plant–soil system

刺槐植物-土壤系统生态化学计量内稳性对水分和养分变异的响应特征 所有生物体都需要一定比例的元素来维持正常的生理代谢过程,它们的可塑性取决于它们利用外部资源的效率。阐明不同资源供应水平下植物、土壤和土壤微生物生物量生态化学计量特征之间的相互作用非常重要。本研究以一年生刺槐(Robinia pseudoacacia)幼苗为研究对象,测定不同水平水分、氮素和磷素处理下刺槐叶片、细根、土壤和微生物生物量C、N、P含量及其化学计量学指标。结果表明,刺槐叶片、细根、土壤和微生物生物量C、N、P含量及其化学计量特征会对其生存环境水分和养分条件的变化表现出一定程度的可塑性;方差分解分析结果表明,细根计量比解释了微生物生物量计量比方差的很大一部分;结构方程模型进一步揭示了细根计量比和叶片计量比是影响土壤微生物生物量C:N和C:P 的两个直接因素,而细根计量比具有较大的直接作用。此外,内稳性特征分析表明土壤微生物生物量C 和C:P对土壤养分变化较为敏感,其他指标均具有内稳性。这些结果明确了土壤微生物生物量化学计量的重要性,提高我们对不同生境水分和养分供应水平下植物-土壤系统养分循环机理的认识。     

Global change and root function

Global change includes land-use change, elevated CO₂ concentrations, increased temperature and increased rainfall variability. All four aspects by themselves and in combination will influence the role of roots in linking below- and above-ground ecosystem function via organic and inorganic resource flows. Root-mediated ecosystem functions which may be modified by global change include below-ground resource (water, nutrients) capture, creation and exploitation of spatial heterogeneity, buffering of temporal variations in above-ground factors, supply and storage of C and nutrients to the below-ground ecosystem, mobilization of nutrients and C from stored soil reserves, and gas exchange between soil and atmosphere including the emission from soil of greenhouse gases. The theory of a functional equilibrium between root and shoot allocation is used to explore predicted responses to elevated CO₂ in relation to water or nutrient supply as limiting root function. The theory predicts no change in root:shoot allocation where water uptake is the limiting root function, but substantial shifts where nutrient uptake is (or becomes) the limiting function. Root turnover will not likely be influenced by elevated CO₂, but by changes in regularity of water supply. A number of possible mechanisms for root-mediated N mineralization is discussed in the light of climate change factors. Rhizovory (root consumption) may increase under global change as the balance between plant chemical defense and adapted root consuming organisms may be modified during biome shifts in response to climate change. Root-mediated gas exchange allows oxygen to penetrate into soils and methane (CH₄) to escape from wetland soils of tundra ecosystems as well as tropical rice production systems. The effect on net greenhouse gas emissions of biome shifts (fens replacing bogs) as well as of agricultural land management will depend partly on aerenchyma in roots.     

The possibility of predicting solute uptake and plant growth response from independently measured soil and plant characteristics

Summary A model of the way the rate of growth of a plant may be affected by the level of supply of a nutrient is presented. Growth rate is linked to the nutrient level of the photosynthetic tissues, which is assumed to control changes in the net assimilation rate, the leaf area per unit shoot weight, the shoot: root ratio, the root surface area, and the distribution of nutrient between root and shoot. The uptake of nutrient depends on the concentration of nutrient at the root surface, the root surface area and its absorbing power. All these relationships may be determined in stirred solution culture. A method of applying this information to soil grown plants is suggested.Soil Science Laboratory, Department of Agricultural Science, University of Oxford     

A global study of relationships between leaf traits, climate and soil measures of nutrient fertility

Aim This first global quantification of the relationship between leaf traits and soil nutrient fertility reflects the trade‐off between growth and nutrient conservation. The power of soils versus climate in predicting leaf trait values is assessed in bivariate and multivariate analyses and is compared with the distribution of growth forms (as a discrete classification of vegetation) across gradients of soil fertility and climate. Location All continents except for Antarctica. Methods Data on specific leaf area (SLA), leaf N concentration (LNC), leaf P concentration (LPC) and leaf N:P were collected for 474 species distributed across 99 sites (809 records), together with abiotic information from each study site. Individual and combined effects of soils and climate on leaf traits were quantified using maximum likelihood methods. Differences in occurrence of growth form across soil fertility and climate were determined by one‐way ANOVA. Results There was a consistent increase in SLA, LNC and LPC with increasing soil fertility. SLA was related to proxies of N supply, LNC to both soil total N and P and LPC was only related to proxies of P supply. Soil nutrient measures explained more variance in leaf traits among sites than climate in bivariate analysis. Multivariate analysis showed that climate interacted with soil nutrients for SLA and area‐based LNC. Mass‐based LNC and LPC were determined mostly by soil fertility, but soil P was highly correlated to precipitation. Relationships of leaf traits to soil nutrients were stronger than those of growth form versus soil nutrients. In contrast, climate determined distribution of growth form more strongly than it did leaf traits. Main conclusions We provide the first global quantification of the trade‐off between traits associated with growth and resource conservation ‘strategies’ in relation to soil fertility. Precipitation but not temperature affected this trade‐off. Continuous leaf traits might be better predictors of plant responses to nutrient supply than growth form, but growth forms reflect important aspects of plant species distribution with climate.     

Modeling magnesium,phosphorus and potassium uptake by loblolly pine seedlings using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model, which has been utilized extensively to describe and predict nutrient uptake by crop plants, was evaluated for its ability to predict K, Mg, and P uptake by loblolly pine (Pinus taeda L.) seedlings. Sensitivity analyses were also used to investigate the impact of changes in soil nutrient supply, root morphological, and root uptake kinetics parameters on simulated nutrient uptake. Established experimental techniques were utilized to define the 11 parameters needed to model uptake by 1-0 seedlings of K, Mg, and P from a modified A horizon soil (Lilly series). Model predictions of K and P uptake over a 180-d growth period were underestimated by 6 and 11%, respectively. Estimates of Mg uptake were underestimated by 62%. While the level of agreement between predicted and observed K and P values was quite acceptable, analysis of parameter values and results of sensitivity analyses both indicated that the model underestimation of Mg uptake was the result of applying an I_max value developed under relatively low Mg concentration to a situation in which the functional I_max would be much higher due to the dominance of passive versus active uptake. Overall results of sensitivity analyses indicate that under the circumstances investigated, I_max, was the primary variable controlling plant uptake of K, Mg, and P. The dominance of this term over others was due to the relatively high C_li values for all three nutrients. Reducing (-50%) or increasing (+ 100%) other soil supply, root morphological, and remaining root uptake kinetics values did not substantially alter model estimates of nutrient uptake.     

The role of plant resources in forest succession: changes in radiation, water and nutrient fluxes, and plant productivity over a 300-yr-long chronosequence in NW-Germany

In the past insufficient attention has been paid to quantitative measurements of resource fluxes in ecosystems that undergo successional change. In this study, simultaneous changes in seven plant resources (photosynthetically active radiation (PAR), water, nitrogen, phosphorus, calcium, magnesium and potassium) are quantified by a chronosequence approach for a 300-yr-long secondary succession on poor soil from Calluna vulgaris heathland to Fagus sylvatica-Quercus petraea late-successional forest (heathland-to-forest succession).Above-ground net primary production increases sevenfold, and total above-ground phytomass about fortyfold during heathland-to-forest succession. Plant organs that capture resources increase much more slowly (leaf area index: threefold; fine root biomass: 1.3-fold). The increase in productivity is based both on higher absorptivity and conversion efficiency of PAR by the canopies of the successional plants.Accumulation of organic material on the forest floor significantly improves soil water availability. Evapotranspiration losses increase early in succession as the growing vegetation increases in both height and leaf area but tend to decrease again in the late-successional community. Drainage losses are at their minimum at the conifer-dominated pioneer forest stage.Accumulation of available nutrients in the soil is a key process in heathland-to-forest succession that significantly improves plant nutrient availability but leads to only minor changes in carbon/nutrient ratios and humus quality. Litter decomposition rates increase and result in a more rapid nutrient turnover in late successional stages. External nutrient inputs (from the atmosphere and soil weathering) significantly contribute to plant nutrient supply early in succession, whereas the internal cycling of nutrients through litter fall and nutrient mineralisation by far exceeds external inputs at the late stages.Vitousek & Reiners' (1975) ecosystem nutrient loss hypothesis is supported by the heathland-to-forest succession data. Odum's (1969) hypotheses on how nutrient cycles change during the course of succession is, in one part, rejected, in part supported. Tilman's (1988) hypothesis on nutrient limitation early, and light limitation late in primary succession is rejected.     

Interactive effects of soil temperature, atmospheric carbon dioxide and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth

Nutrient requirements for plant growth are expected to rise in response to the predicted changes in CO(2) and temperature. In this context, little attention has been paid to the effects of soil temperature, which limits plant growth at early stages in temperate regions. A factorial growth-room experiment was conducted with winter wheat, varying soil temperature (10 degrees C and 15 degrees C), atmospheric CO(2) concentration (360 and 700 ppm), and N supply (low and high). The hypothesis was that soil temperature would modify root development, biomass allocation and nutrient uptake during vegetative growth and that its effects would interact with atmospheric CO(2) and N availability. Soil temperature effects were confirmed for most of the variables measured and 3-factor interactions were observed for root development, plant biomass components, N-use efficiency, and shoot P content. Importantly, the soil temperature effects were manifest in the absence of any change in air temperature. Changes in root development, nutrient uptake and nutrient-use efficiencies were interpreted as counterbalancing mechanisms for meeting nutrient requirements for plant growth in each situation. Most variables responded to an increase in resource availability in the order: N supply >soil temperature >CO(2).     

模拟降雨变化对古尔班通古特沙漠土壤养分及酶活性的影响

土壤酶参与土壤系统的养分循环过程,是联系植物和土壤养分的关键纽带。土壤酶活性对降水格局变化响应敏感,这种响应对于缺水且养分贫瘠的荒漠生态系统显得尤为重要。然而,早春积雪完全融化后首次降雨时间及降雨量如何影响土壤养分及土壤酶活性还鲜见相关报道。以新疆古尔班通古特沙漠为研究区,在早春积雪完全融化后,设置3个首次降雨时间(积雪完全融化后第10天、20天和30天)和3个降雨梯度(5 mm、10 mm和15 mm),于植物生长旺季采集土壤样品,研究土壤养分含量和土壤酶活性的响应特征。结果表明：积雪完全融化后不同首次降雨时间下5mm降雨处理以及积雪完全融化后第30天下各降雨量处理对土壤养分和酶活性影响不显著。积雪完全融化后第10天,随降雨量增加,土壤全碳呈显著先下降后增加趋势,全钾呈显著增加趋势,而土壤微生物量碳呈显著降低趋势;积雪完全融化后第20天,随降雨量增加,速效氮、土壤蔗糖酶活性、土壤微生物量碳氮呈先下降后增加趋势,土壤全碳和多酚氧化酶活性显著下降,土壤全钾和碱性磷酸酶活性显著增加。模拟10 mm降雨,随首次降雨时间推迟,土壤全氮、速效氮、速效磷、土壤蔗糖酶活性和土壤微生物量碳呈增加趋势;...     

Increased precipitation modulates the influence of nitrogen and litter inputs on the nutrient resorption proficiency rather than efficiency of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Resorption of nutrients from senescing organs is an important conservation mechanism that is usually influenced by the supply of soil nutrients and plant growth requirements. Therefore, it is likely that increases in nitrogen (N), precipitation, and litter could lead to changes in nutrient resorption because of changes in nutrients in the soil and accelerated plant growth in response to the alleviation of water limitations in arid and semiarid environments. In the current study, we investigated the effects of water, N, and litter addition on the nutrient resorption efficiency and proficiency of N and phosphorus (P) in leaves and stems of Leymus chinensis in Inner Mongolia, China. Our results showed that N addition significantly decreased the N resorption efficiency in leaves under water addition, and increased P resorption efficiency under ambient precipitation conditions. There was no apparent influence of either litter or water addition on N and P resorption efficiencies. However, N and litter addition significantly altered N and P resorption proficiencies, and these effects were modulated by water availability. Furthermore, changes in resorption proficiencies were mainly associated with alterations in the nutritional status of green organs in response to water, N and litter addition, except for leaf P. Our findings highlight the importance of increased precipitation in modulating the nutrient resorption proficiency of plants under potentially increased nutrient availability in semiarid grasslands. Therefore, global changes in precipitation and N, and corresponding litter changes could result in complex effects on plant nutrient economies and, in turn, could influence the return of nutrients to the soil.     

Causes of increased nutrient concentrations in post-fire regrowth in an East African savanna

The aim of the present study was to investigate the causes of increased macronutrient concentrations in above-ground post-fire regrowth in an East African savanna (Northern Tanzania). Experiments were set up to discriminate between the following possible causes: (1) increased soil nutrient supply after fire, (2) relocation of nutrients from the roots to the new shoots, (3) rejuvenation and related changes in plant tissue composition and (4) changes in nutrient uptake in relation to above-ground carbon gains. N, P, K, Ca and Mg concentrations in post-burn graminoid vegetation were compared with clipped and with unburned, control vegetation during the post-burn growth season. One month after burning and clipping, nutrient concentrations in live grass shoots in the burned and clipped treatments were significantly higher than in the control. This effect, however, declined in the course of the season and, except for Ca, disappeared three months after onset of the treatments. There were no significant differences in live grass shoot nutrient concentrations between burned and clipped treatments which suggests that the increased nutrient concentration in post-fire regrowth is not due to increased soil nutrient supply via ash deposition. The relatively low input of nutrients through ash deposition, compared to the amount of nutrients released through mineralisation during the first month after burning and to the total nutrient pools, supports this suggestion. There was no difference between burned and unburned vegetation in total root biomass and root nutrient concentrations. Relocation of nutrients from the roots to the new shoots did not, therefore, appear to be a cause of higher post-fire shoot nutrient concentrations. The present study shows that in this relatively nutrient-rich savanna, the increased nutrient concentration in above-ground post-fire regrowth is primarily due to increased leaf:stem ratios, rejuvenation of plant material and the distribution of a similar amount of nutrients over less above-ground biomass. This revised version was published online in June 2006 with corrections to the Cover Date.     

Species ecological strategy and soil phosphorus supply interactively affect plant biomass and phosphorus concentration

Excess soil phosphorus often constrains ecological restoration of degraded semi-natural grasslands in Western-Europe. Slow-growing species, often target of restoration (measures), are at a disadvantage because they are outcompeted by fast-growing species. Gaining insight into the responses of plant species and communities to soil phosphorus availability will help understanding restoration trajectories of grassland ecosystems. We set up two pot experiments using twenty grassland species with contrasting growth forms (i.e. grasses versus forbs) and nutrient use strategies (i.e. acquisitive versus conservative nutrient use). We quantified the nutrient use strategy of a species based on the stress-tolerance value of the CSR framework (StrateFy et al. 2017). We grew these species (1) as monocultures and (2) in mixtures along a soil phosphorus gradient and measured the aboveground biomass and plant phosphorus concentrations. Plant phosphorus concentration generally increased with soil phosphorus supply and biomass increased with soil phosphorus supply only in conservative communities. Forbs had higher plant phosphorus concentrations compared to grasses both in monocultures and mixtures. The species’ nutrient use strategy had contrasting effects on plant tissue phosphorus concentrations, depending on soil phosphorus supply (interaction effect) and vegetation biomass (dilution effect). Our findings contribute to the knowledge required for successful ecological restoration of species-rich grasslands. Our results suggest that under specific conditions (i.e. nitrogen limitation, no dispersal limitation, no light limitation), slow-growing species can survive and even thrive under excess soil phosphorus availability. In the field, competition by fast-growing species may be reduced by increased mowing or grazing management.     

东北黑土成土母质培肥过程中土壤肥力变化特征

利用已设置14年的黑土成土母质(表层以下2.0～3.0 m深)培肥定位试验,研究不同农艺措施培肥后土壤肥力指标的变化特征,结合小麦盆栽耗竭试验评估土壤供肥能力,综合评价不同农艺措施对黑土母质培肥的效应。与初始母质相比,黑土母质培肥14年后,土壤总有机碳、全氮、团聚结构稳定性和其他养分含量均不同程度提高,土壤肥力水平的高低直接影响盆栽试验中土壤对小麦的供肥能力。主成分分析发现,母质经过14年的培肥,碳投入量较大的农田秸秆还田处理和苜蓿培肥处理与表层(0～20 cm)黑土更接近,其次是农田有机肥和自然草地培肥处理,农田单施化肥和不施肥处理培肥效果最差。14年连续的外源碳输入通过改善土壤团聚结构和进入土壤的碳分解转化,影响土壤的物理和生物化学性质,促进母质土壤肥力发育。农田秸秆还田、施用有机肥和种植苜蓿对黑土母质肥力提升效果最好,是保证黑土肥力和土壤培肥的有效措施,研究结果可为东北黑土区退化土壤培肥提供理论依据和指导。     

N, K and P deficiency in chronosequential cut summer-dry grasslands on gley podzol after the cessation of fertilizer application

With the intensification of agricultural practices, formerly species rich marginal grassland communities of high botanical value in the Netherlands have been fertilized or manured since the first part of the twentieth century. This type of land use resulted in a dramatic decrease of the original plant species-richness. In the early 1970's yearly nutrient input to many of these grasslands was ceased as a nature management practice, while hay-cropping was continued. This type of grassland management is carried out to decrease overall nutrient supplying ability of the soil to plant cover in order to restore their original high botanical richness. The effect of this management on the type and the extent of nutrient deficiency was studied by comparing the short-term shoot responsiveness of undisturbed turfs to added nutrients and the nutrient status of fieldgrown dominants of four hay-field communities which were not fertilized for 3, 7, 20 or 25 years.Contrary to expectation, hay-cropping without input of additional nutrients did not impose an increase of species-richness of grassland on gley podzol. During early vegetation change strong inadequacy of N supply and moderate inadequacy of K supply by the soil regulate (shoot) growth. P-deficiency was not established. Prolonged discontinuation of fertilizer application caused concomitant inadequate supplies of N, K and P. In the last field (25 years unfertilized), nutrient deficiencies could not be detected by shoot growth responses to added nutrients but only by a low nutrient status. It appeared that during this type of vegetation change N-deficiency is the most pronounced and that K-deficiency developes much more rapidly than P-deficiency. The strong decline in total aerial pool sizes of N, K and P also emphasizes these simultaneously occurring shifts.We conclude that cut grassland composition on gley podzol soil is regulated by co-deficiencies of at least the soil phytoavailable macronutrients nitrogen, potassium and phosphorus. The absence of change in plant species number is likely not regulated by the nutrient supplying ability of the soil. Seed dispersal from elsewhere seems to be the most important factor.     

The nutritional control of root development

Root development is remarkably sensitive to variations in the supply and distribution of inorganic nutrients in the soil. Here we review examples of the ways in which nutrients such as N, P, K and Fe can affect developmental processes such as root branching, root hair production, root diameter, root growth angle, nodulation and proteoid root formation. The nutrient supply can affect root development either directly, as a result of changes in the external concentration of the nutrient, or indirectly through changes in the internal nutrient status of the plant. The direct pathway results in developmental responses that are localized to the part of the root exposed to the nutrient supply; the indirect pathway produces systemic responses and seems to depend on long-distance signals arising in the shoot. We propose the term `trophomorphogenesis' to describe the changes in plant morphology that arise from variations in the availability or distribution of nutrients in the environment. We discuss what is currently known about the mechanisms of external and internal nutrient sensing, the possible nature of the long-distance signals and the role of hormones in the trophomorphogenic response.