Carbon flow from plant to arbuscular mycorrhizal fungi is reduced under phosphorus fertilization

Plant and Soil - Iodine (I) deficiency is distinct from other micronutrient deficiencies in human populations in having a high endemic prevalence both in well-developed and in developing countries....     

Mycorrhizae, crop growth, and crop phosphorus nutrition in maize-soybean rotations given various tillage treatments

Previously, tillage has been found to reduce early-season phosphorus (P) uptake from soil in continuous maize cropping systems. This reduced P uptake has often been associated with delayed colonization of roots by arbuscular mycorrhizal (AM) fungi. Our aim was to determine if similar responses occur in maize-soybean rotations, which are more typical of current farming in Ontario, Canada. Similar responses were expected because both are AM crops, and the mechanism by which tillage reduces P uptake is thought to be a negative impact on the development of effective mycorrhizae. Simultaneous field experiments with either maize-soybean-maize or soybean-maize-soybean rotations were conducted in 1992–4. Treatments imposed were no-till (NT), ridge-tillage (RT), and conventional tillage using a moldboard plow (MP). In 1993, early-season dry mass of maize was similar among treatments, but colonization of maize roots by AM fungi and P uptake of maize were stimulated by NT and RT, compared with MP. In 1994, early growth was more rapid overall than in 1993, but it was reduced in the NT and RT treatments compared with MP for reasons not related to P. For soybean, AM colonization in NT and RT systems was higher than with MP, but P uptake was unchanged. As was found for maize in 1994, early-season shoot dry mass of soybean was higher in the MP treatment than with NT, but both in 1993 and 1994. We conclude that colonization of both maize and soybean by AM fungi is susceptible to slower development in tilled systems, and that for maize, stimulation of P uptake under reduced tillage can occur in rotations with soybean just as easily as it does with continuous maize. Taken with other studies, the data here suggest that responses to tillage of colonization of roots by AM fungi and of P uptake could apply to many cropping systems. The slow early-season shoot growth seen in some years in response to reduced tillage is discussed.     

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.     

Soil tillage reduces arthropod biodiversity and has lag effects within organic and conventional crop rotations

Crop rotation systems in organic and conventional farming systems differ in crop types, management and duration. However, changes in arthropod communities over the entire rotation system are poorly understood, as many studies have surveyed only single years or have not covered the entire rotation period. Here, we describe changes in arthropods in two contrasting systems at a split organic‐conventional farm: an 8‐year organically managed rotation with five crops and a 5‐year conventionally managed rotation with three crops. Arthropods were classified into three functional groups, representing epigeal predators, foliar predators/parasitoids and herbivores/pollinators. Epigeal predators were particularly reduced by soil tillage which occurred annually in the conventional rotation, but was intermittent in the organic. Arthropods were most abundant on the conventional rotation, but most taxonomically diverse on the organic. In the conventional system, all functional groups showed a cyclical change in their taxonomic composition that closely matched the crop rotation sequence, whereas in the organic rotation, the cycle was less clear. Whilst the current year's crop type was the major determinant of arthropod community composition, there was a significant “lag effect” for many taxa from the preceding year's crop. Our results suggest that both the amounts of soil tillage (e.g., in no‐till systems) and crop rotation order have major impacts on arthropods in agroecosystems. Rotations with excessive soil tillage are likely to reduce the abundance of some groups of beneficial arthropods, especially epigeal predators.     

No‐tillage and fertilization management on crop yields and nitrate leaching in North China Plain

A field experiment was performed from 2003 to 2008 to evaluate the effects of tillage system and nitrogen management regimes on crop yields and nitrate leaching from the fluvo-aquic soil with a winter wheat (Triticum aestivum L.)–maize (Zea mays L.) double-cropping system. The tillage systems consisted of conventional tillage (CT) and no-tillage (NT). Three nitrogen management regimes were included: 270 kg N ha⁻¹ of urea for wheat and 225 kg N ha⁻¹ of urea for maize (U), 180 kg N ha⁻¹ of urea and 90 kg N ha⁻¹ of straw for wheat and 180 kg N of urea and 45 kg N ha⁻¹ of straw for maize (S), 180 kg N ha⁻¹ of urea and 90 kg N ha⁻¹ of manure for wheat and 180 kg N ha⁻¹ of urea and 45 kg N ha⁻¹ of manure for maize (M). An array of tension-free pan lysimeters (50 cm × 75 cm) were installed (1.2 m deep) to measure water flow and -N movement. No significant effect of the N management regime on yields of winter wheat and maize grain was found in the 5-year rotation. Tillage systems had significant influences on -N leaching from the second year and thereafter interacted with N management regimes on -N loads during all maize seasons. The average yield-scaled -N leaching losses were in order of CTS < NTS< CTU < NTU −1 for winter wheat system and from 0.99 (CTS) to 6.27 (NTM) kg N Mg⁻¹ for summer maize system for 5 rotation years. The results showed that CTS decreased the yield-scaled -N leaching losses while sustaining crop grain yields. Considering the lower costs, NTS could be a potential alternative to decrease yield-scaled -N leaching losses and improve soil fertility while maintaining crop yield for the winter wheat–maize double-cropping systems in the North China Plain.     

Effects of field experimental warming on wheat root distribution under conventional tillage and no‐tillage systems

Despite the obvious importance of roots to agro‐ecosystem functioning, few studies have attempted to examine the effects of warming on root biomass and distribution, especially under different tillage systems. In this study, we performed a field warming experiment using infrared heaters on winter wheat, in long‐term conventional tillage and no‐tillage plots, to determine the responses of root biomass and distribution to warming. Soil monoliths were collected from three soil depths (0–10, 10–20, and 20–30 cm). Results showed that root biomass was noticeably increased under both till and no‐till tillage systems (12.1% and 12.9% in 2011, and 9.9% and 14.5% in 2013, in the two tillage systems, respectively) in the 0–30 cm depth, associated with a similar increase in shoot biomass. However, warming‐induced root biomass increases occurred in the deeper soil layers (i.e., 10–20 and 20–30 cm) in till, while the increase in no‐till was focused in the surface layer (0–10 cm). Differences in the warming‐induced increases in root biomass between till and no‐till were positively correlated with the differences in soil total nitrogen (R² = .863, p < .001) and soil bulk density (R² = .853, p < .001). Knowledge of the distribution of wheat root in response to warming should help manage nutrient application and cycling of soil C‐N pools under anticipated climate change conditions.     

Nitrous oxide emissions following application of residues and fertiliser under zero and conventional tillage

Emissions of N₂O were measured following combined applications of inorganic N fertiliser and crop residues to a silt loam soil in S.E. England, UK. Effects of cultivation technique and residue application on N₂O emissions were examined over 2 years. N₂O emissions were increased in the presence of residues and were further increased where NH₄NO₃ fertiliser (200 kg N ha^–1) was applied. Large fluxes of N₂O were measured from the zero till treatments after residue and fertiliser application, with 2.5 kg N₂O-N ha^–1 measured over the first 23 days after application of fertiliser in combination with rye (Secale cereale) residues under zero tillage. CO₂ emissions were larger in the zero till than in the conventional till treatments. A significant tillage/residue interaction was found. Highest emissions were measured from the conventionally tilled bean (Vicia faba) (1.0 kg N₂O-N ha^–1 emitted over 65 days) and zero tilled rye (3.5 kg N₂O-N ha^–1 over 65 days) treatments. This was attributed to rapid release of N following incorporation of bean residues in the conventionally tilled treatments, and availability of readily degradable C from the rye in the presence of anaerobic conditions under the mulch in the zero tilled treatments. Measurement of ¹⁵N-N₂O emission following application of ¹⁵N-labelled fertiliser to microplots indicated that surface mulching of residues in zero till treatments resulted in a greater proportion of fertiliser N being lost as N₂O than with incorporation of residues. Combined applications of ¹⁵N fertiliser and bean residues resulted in higher or lower emissions, depending on cultivation technique, when compared with the sum of N₂O from single applications. Such interactions have important implications for mitigation of N₂O from agricultural soils.     

Effects of the administration of cadmium and zinc on the concentration of zinc in the thymus of rats

The zinc content of thymus glands of male Wistar rats has been determined during five weeks of treatment with ZnCl₂ and CdCl₂, and compared with a group of control rats. THymus gland extracts were chromatographed on columns of Sephadex G-75 and the zinc content of the one hundred fractions obtained were determined by atomic absorption spectrophotometry. The rats treated with ZnCl₂ showed an increase in the thymus concentration of zinc bound to high and low molecular weight proteins. The rats treated with CdCl₂ showed an increase in zinc concentration, as opposed to the control group, during the first three weeks of treatment, and thereafter show a toxic effect of cadmium on the gland, with ulterior regression of the latter, and a decrease in the concentration of zinc.     

Soil solution dynamics and plant uptake of cadmium and zinc by durum wheat following phosphate fertilization

A growth chamber study was conducted to evaluate the effect of application of phosphate fertilizer on soil solution dynamics of cadmium (Cd) and Cd accumulation in durum wheat (Triticum turgidum L. var. durum). Treatments consisted of three phosphate fertilizer sources containing 3.4, 75.2, and 232 mg Cd kg^?1 applied at three rates (20, 40 and 80 mg P kg^?1) plus a no fertilization control. An unplanted treatment at 40 mg P kg^?1 was included to separate the effects on soil solution Cd dynamics of the crop from that of the fertilizer. Soil solution samples were obtained using soil moisture samplers every 10 days after germination. The experimental results indicated that plant biomass significantly increased with P application rates and decreased with increased Cd concentration in the phosphate fertilizers. Total cadmium concentration in soil solution was not consistently affected by phosphate fertilization rate and fertilizer sources, and therefore Cd concentration in the fertilizer. Application of phosphate fertilizer, however, increased the concentration and accumulation of Cd and shoot Cd/Zn ratio, and decreased shoot Zn concentration in durum wheat. Phosphate sources had a marginally significant effect (P?=?0.05) on shoot Cd concentration and did not affect Cd accumulation in durum wheat. Concentration of Cd in soil solution was unrelated to Cd concentration in durum wheat. These results suggest that the immediate increase in Cd concentration and Cd accumulation in durum wheat with phosphate application is due more to competition between Zn and Cd for absorption into plants, enhanced root to shoot translocation and enhanced root development, than to a direct addition effect from Cd contained in phosphate fertilizer. In the short term, application of phosphate fertilizers can increase Cd concentration in the crops, regardless of the Cd concentration of the fertilizer. An optimal P fertilization, possibly in combination with Zn application, may offer an important strategy for decreasing Cd concentration and accumulation in crops.     

长期施肥和不同生态条件下我国作物产量可持续性特征

采用产量可持续性指数（SYI）法,研究了我国不同生态条件下20个长期试验点8个肥料处理的水稻、玉米和小麦产量的可持续性.结果表明：作物SYI值因施肥、作物种类和水热因子不同而呈显著差异.长期不施肥（CK）条件下,水稻、玉米和小麦的SYI值较低,分别为0.55、0.44和0.43;施肥尤其是NPK化肥配施有机肥可显著提高作物产量的可持续性,水稻、玉米和小麦的SYI值分别为0.66、0.58和0.57;单施N肥或NK肥的玉米和小麦的SYI值在0.36～0.47.SYI值大于0.55表明可持续性较好,小于0.45表明可持续性差.经纬度和气象因子对作物SYI也有不同程度的影响,3种作物不施肥时,水稻SYI变异较小,与各因子间没有显著相关性,玉米SYI变异最大且与各因子间存在显著的相关关系,小麦介于两者之间.因此,NPK配施有机肥有利于作物高产稳产,是维持系统可持续性的最优施肥模式.     

镉与磷、锌、铁、钙等元素的交互作用及其生态学效应

镉是动物和植物的非必需元素 ,也是毒性最大的重金属之一。环境镉污染对植物、动物和人体均产生毒害作用。镉与许多生命必需营养元素存在着交互影响关系 ,相互影响着对方的功能发挥。镉污染胁迫可影响动植物和人体对营养元素的吸收 ,相反补充营养元素可减轻镉的毒害。但是 ,由于每个元素的性质和功能不一样 ,因此不同元素与镉的交互作用存在着差异性。镉与营养元素的交互作用研究可为生物镉污染防治提供科学依据。     

耕作措施和施肥方式对麦田杂草密度和生物量的影响

为明确我国华北地区麦玉轮作系统小麦免耕的推广和施肥方式的改变对麦季杂草生长的影响,在免耕实施5年后,调查了麦田杂草密度、单株质量和生物量。结果表明:华北地区小麦生长早期,免耕有降低麦田杂草总密度和优势种播娘蒿密度趋势,但差异并不显著;相对于传统耕作,免耕秸秆覆盖和不覆盖处理总杂草生物量显著降低,其中播娘蒿生物量分别降低了57%和73%;免耕也使播娘蒿单株质量降低了27%～53%;免耕秸秆覆盖和不覆盖处理播娘蒿的株高分别比传统耕作降低了25%和19%;但一般情况耕作方式并没有显著影响离子草和麦家公生长;相对于分次施肥,集中施肥杂草生物量降低了21%～68%,播娘蒿生物量降低了58%～65%,麦家公降低91%;免耕在一定程度上抑制了某些杂草的生长,但追肥促进了杂草的快速生长。     

Effect of long-term tillage and mineral phosphorus fertilization on arbuscular mycorrhizal fungi in a humid continental zone of Eastern Canada

Aims

Evidence shows that tillage modifies soil properties, especially phosphorus (P) dynamics. Our objective was to disentangle long-term effects of P-fertilization and tillage on arbuscular mycorrhizal fungal (AMF) proliferation and community structure.

Methods

Changes in the community structure of AMF and in the density of their hyphae and spores induced by moldboard plow (MP) or no till (NT), and fertilization with 0, 17.5, or 35 kg?P?ha^?1 were sought in the 0–15 cm and 15–30 cm soil layers after soybean harvest, at a long-term (17 years) experimental site in a humid continental zone of eastern Canada. The relationships among AMF, soil and plant attributes were examined.

Results

The 0–15 cm and 15–30 cm soil layers had different properties under NT, but were similar under MP, after 17 years, and MP increased soil available P levels. Phosphorus fertilization increased P levels in soil and in soybean. Treatment effects on AMF spore and hyphal density at 0–15 cm were greater than that at 15–30 cm, whereas effects on AMF community structure did not change with soil depths. At 0–15 cm, P-fertilization increased AMF spore density and reduced AMF hyphal density, and MP reduced AMF spore density. A total of eight AMF phylotypes were detected. Phosphorus fertilization reduced AMF phylotype richness and Shannon diversity index. Soil P availability increased under MP and hence the influence of P-fertilization treatments on the frequency of AMF phylotype detection varied with tillage system; it declined with P-fertilization under MP, but increased under NT.

Conclusions

Phosphorus fertilization shifts resource partitioning in AMF propagules rather than in their hyphae, and degrades the genetic diversity of AMF in soil; tillage increases soil P availability and hence aggravates the impact of P-fertilization.     

Biomass and nutrient dynamics of Chinese fir seedlings under conventional and exponential fertilization regimes

Containerized Chinese fir (Cunninghamia lanceolata (Lamb) Hook) were reared from seed at four fertilizer levels (0, 15, 45, 75 mg N seedling-1 season-1) and two topdressing schedules (conventional or exponential) for a 22-week greenhouse rotation to assess growth, nutrition and nutrient loading capacity of seedlings. Extra P supplemented high fertilization (or nutrient loading) treatments to test for induced deficiency of this element. The schedule and rate of fertilization significantly affected growth and nutrient dynamics of the seedlings. Steady-state nutrition and superior growth performance were achieved by seedlings fertilized exponentially at the operational dose (15 mg N), yielding 23, 72 and 52% more in respective biomass, N uptake and P uptake than seedlings fertilized conventionally at the equivalent dose. The improved growth and fertilizer efficiency were attributed to close synchronization of exponential nutrient supply with exponential growth and nutrient demand of plants. High dose exponential fertilization (45 and 75 mg N) induced steady state-nutrition late in the season, increasing seedling N and P uptake by 72–83% and 50–96% compared to low dose exponential fertilization, demonstrating effective nutrient loading of plants without changing biomass. The extra P stimulated P uptake without altering growth or N uptake, thus P was probably not limiting during the greenhouse culture despite high N additions.     

锌肥对不同基因型大麦吸收积累镉的影响

对土壤添加不同Zn、Cd条件下两种基因型(Sahara和Clipper)大麦对Zn、Cd的吸收积累研究表明,在本实验条件下土壤添加Zn、Cd对植物地上部生物量没有显著影响,但土壤添加Zn抑制植物根系生长,在土壤不缺Zn情况下添加Zn<20mg·kg^-1时并没有对大麦体内Cd浓度产生显著影响;当土壤Zn添加量达到40mg·kg^-1时,植物体内Cd浓度明显降低,植物吸收Cd的总量随着土壤添加Zn的增加而显著下降,这主要是由于根系生物量的下降所致,两个基因型大麦品种Zn效率存在显著差异,但这一差异对植物吸收Cd的总量没有影响,Zn高效品种Sahara根部Cd浓度显著低于Clipper。     

Characterization of cadmium concentration and translocation among ramie cultivars as affected by zinc and iron deficiency

Zn and Fe are essential nutritional elements in plants and play important roles in various physiological processes of plants. Zn and Fe are chemically similar to cadmium (Cd); therefore, Zn and Fe may mediate Cd-induced physiological or metabolic changes in plants. In order to evaluate the interaction between Cd, Zn and Fe, we conducted a hydroponics experiment to determine the plant biomass, photosynthetic characteristics, and Cd accumulation of ten ramie cultivars under Zn/Fe-sufficient or Zn/Fe-deficient conditions in the presence of 32 µM CdCl₂. Ramie varied among cultivars in morpho-physiological response to Cd stress as well as Cd accumulation, translocation and distribution. Zn and Fe deficiency increased the concentration and amount of Cd in plant organs, but decreased TF_{stem to leaf} and TF_{root to stem}. Cultivars with more Cd in roots and shoots showed smaller increase in Cd accumulation under Zn and Fe-deficiency stress. Xiangzhu 7 and Duobeiti 1 showed a higher capacity of Cd accumulation in their shoots. Zn and Fe deficiency decreased Pn, but increased Ci, Gs, and E in most cultivars. The difference in Cd translocation among ramie cultivars was mainly ascribed to the difference in plant transpiration.     

长期磷肥处理农田黑土细菌群落特征

研究了公主岭国家黑土长期定位站不同施肥处理（对照、磷、氮 磷、氮 磷 钾、有机肥-磷、有机肥-氮-磷、有机肥-氮-磷-钾等）土壤基本理化性质及细菌群落特征.结果表明：有机肥处理土壤有机质（OM）、总氮（TN）、有效磷（AP）、碱解氮（AN）、速效钾（AK）等养分含量显著增加,而单施化肥各处理OM、AN含量无明显变化.与未施肥对照处理相比,有机肥-氮-磷配施与有机肥-氮-磷-钾配施处理总细菌磷脂脂肪酸分别增加34%和62%,G⁺菌磷脂脂肪酸分别增加58%和74%,G^-菌磷脂脂肪酸分别增加64%和69%.各化肥处理细菌脂肪酸含量均有所下降,以磷处理最低.除G⁺菌磷脂脂肪酸外（有机肥-磷配施显著大于氮-磷-钾肥配施）,氮-磷肥配施、氮-磷-钾肥配施与有机肥-磷肥配施三者间细菌脂肪酸含量无显著差异.相关分析表明,各细菌磷脂脂肪酸与OM、AP、AN、AK、NO₃^--N含量呈极显著相关.     

Cellular uptake of cadmium and zinc

CHO mutants, resistant to over 100-fold of a normally toxic level of extracellular cadmium have been used to examine the mutually antagonistic effect of Cd and Zn on their uptake. Cadmium uptake in these mutants is only 7–10% that of the parental cells. Zinc uptake in these mutants is equal to or greater than that in the wild-type cells. Results of kinetic studies on uptake indicated that the two metals interact by competitive inhibition. TheK _m andK _i values for Cd and/or Zn were different in some of the mutants and indicate multiple carriers may be involved in the transport of these metals. The reduction in Cd uptake and concomitant increase in Zn uptake contribute to the increased Cd resistance in these mutants.