放牧强度对高寒嵩草草甸土壤养分特性的影响

植物-土壤系统是草地生态和生产服务价值实现的基础,放牧是草地植物群落演替的重要因素。植物、土壤亚系统对放牧的敏感性是评价草地稳定性和提高草地恢复力的重要依据。以不同放牧强度下的高寒嵩草(Kobresia)草甸为研究对象,探讨土壤养分特征对放牧强度的响应及作用位点,结果表明:改变放牧强度可以明显改变植物群落数量特征,但没有明显改变土壤层次分类特征,说明土壤养分特征对一定范围内放牧强度具有自我稳定维持功能;但放牧干扰强度不同时,土壤剖面过渡层养分含量存在差异,说明长期放牧强度的差异会对土壤剖面养分性质产生影响,且这种影响起源于土壤剖面过渡层。在放牧高寒嵩草草甸植物-土壤系统中土壤剖面养分特征较植物群落数量特征更稳定;土壤剖面过渡层养分特征是土壤亚系统中对放牧的敏感因素;而放牧引起土壤剖面养分特征的改变主要表现在各过渡层上,并构成土壤发生层迁移的风险,因此推测,更为持久和更高强度的放牧干扰将最终改变土壤剖面特征及养分性质。     

桑沟湾春季叶绿素a浓度分布及其影响因素

依据2014年5月走航和定点连续调查资料,分析了桑沟湾叶绿素a的空间分布及昼日变化特征,结合理、化环境因素的相关性分析,探讨影响叶绿素a浓度的主要因素。(1)走航调查的结果显示,桑沟湾春季叶绿素a浓度较低,叶绿素a浓度范围为0.11—1.40μg/L,平均为(0.64±0.36)μg/L。叶绿素a浓度从湾内向湾外逐步降低,贝类区混养区海带区外海区;湾内表层叶绿素a浓度均高于底层,而湾外的非养殖区则相反(2)网箱区叶绿素a浓度最高,日平均为1.70μg/L,显著高于其它3个区;海草区最低,为0.57μg/L,与海带养殖区无显著性差异,显著低于贝类养殖区和网箱区。叶绿素a浓度的总体趋势为:网箱区贝类区海带区和海草区。而且,不同养殖区域,叶绿素a浓度昼夜变化规律各不相同,反映了养殖活动的影响。海草区白天表层高于底层,而夜间则相反;网箱区底层均高于表层;贝类区表层均高于底层;海带区表底层叶绿素a浓度呈现出升降交替的规律。(3)叶绿素a浓度与硅酸盐、水温显著正相关,与其他环境因子,如氨氮、亚硝酸盐、磷酸盐等无显著相关性。硅酸盐和温度可能为影响桑沟湾春季浮游植物生长的主要限制性因素。(4)桑沟湾春季浮游植物生长受多重因素的限制,湾内营养盐浓度与叶绿素a浓度并未呈现显著的规律性,营养盐的上行控制和贝类摄食的下行控制均能影响浮游植物的生长。     

Influence of nutrient restriction and melatonin supplementation of pregnant ewes on maternal and fetal pancreatic digestive enzymes and insulin-containing clusters

Primiparous ewes (n=32) were assigned to dietary treatments in a 2×2 factorial arrangement to determine effects of nutrient restriction and melatonin supplementation on maternal and fetal pancreatic weight, digestive enzyme activity, concentration of insulin-containing clusters and plasma insulin concentrations. Treatments consisted of nutrient intake with 60% (RES) or 100% (ADQ) of requirements and melatonin supplementation at 0 (CON) or 5 mg/day (MEL). Treatments began on day 50 of gestation and continued until day 130. On day 130, blood was collected under general anesthesia from the uterine artery, uterine vein, umbilical artery and umbilical vein for plasma insulin analysis. Ewes were then euthanized and the pancreas removed from the ewe and fetus, trimmed of mesentery and fat, weighed and snap-frozen until enzyme analysis. In addition, samples of pancreatic tissue were fixed in 10% formalin solution for histological examination including quantitative characterization of size and distribution of insulin-containing cell clusters. Nutrient restriction decreased (P⩽0.001) maternal pancreatic mass (g) and α-amylase activity (U/g, kU/pancreas, U/kg BW). Ewes supplemented with melatonin had increased pancreatic mass (P=0.03) and α-amylase content (kU/pancreas and U/kg BW). Melatonin supplementation decreased (P=0.002) maternal pancreatic insulin-positive tissue area (relative to section of tissue), and size of the largest insulin-containing cell cluster (P=0.04). Nutrient restriction decreased pancreatic insulin-positive tissue area (P=0.03) and percent of large (32 001 to 512 000 µm²) and giant (⩾512 001 µm²) insulin-containing cell clusters (P=0.04) in the fetus. Insulin concentrations in plasma from the uterine vein, umbilical artery and umbilical vein were greater (P⩽0.01) in animals receiving 100% requirements. When comparing ewes to fetuses, ewes had a greater percentage of medium insulin-containing cell clusters (2001 to 32 000 µm²) while fetuses had more (P<0.001) pancreatic insulin-positive area (relative to section of tissue) and a greater percent of small, large and giant insulin-containing cell clusters (P⩽0.02). Larger insulin-containing clusters were observed in fetuses (P<0.001) compared with ewes. In summary, the maternal pancreas responded to nutrient restriction by decreasing pancreatic weight and activity of digestive enzymes while melatonin supplementation increased α-amylase content. Nutrient restriction decreased the number of pancreatic insulin-containing clusters in fetuses while melatonin supplementation did not influence insulin concentration. This indicated using melatonin as a therapeutic agent to mitigate reduced pancreatic function in the fetus due to maternal nutrient restriction may not be beneficial.     

The nutritional value of narrow-leafed lupine (Lupinus angustifolius) for fattening pigs

The aim of this study was to determine the nutrient digestibility of seeds of four varieties of narrow-leafed lupines (Lupinus angustifolius) and the possibility of soya bean meal (SBM) substitution by lupine seeds alone and in combination with rapeseed meal (RSM) in the diets of pigs. The seeds of the lupine varieties Kalif, Sonet, Zeus and Boruta were analysed. The apparent total tract digestibility (ATTD) was determined on 50 cross-bred pigs using the difference method with titanium dioxide as a marker. The substitution of SBM by lupine seeds alone (at 0 – 100%) was tested on 60 pigs (20–105 kg body weight (BW)) and by a combination of lupine seeds and RSM on 180 fattening pigs (35–80 kg BW). The chemical composition of lupine seeds differed considerably, especially in terms of crude protein and mineral content. All seeds contained less than 0.05% alkaloids and 9.3% oligosaccharides in dry matter. The ATTD of protein ranged from 70% to 74%, those of ether extract from 36% to 55% and those of gross energy from 77% to 84%. The entire replacement of SBM by lupine seeds (var. Sonet) did not have a negative effect on the performance of grower and fattener pigs. The substitution of SBM by a combination of lupines and RSM reduced the performance of growing and finishing pigs significantly.     

Nutrient utilisation,growth performance and blood metabolites in Murrah buffalo calves (Bubalus bubalis) divergently selected for residual feed intake

The aim of this study was to evaluate differences in efficiency of feed utilisation between buffalo calves with low and high residual feed intake (RFI) by comparing feed intake, nutrient digestibility, growth traits and blood metabolites. Eighteen male Murrah buffalo calves (aged 4–6 months; 70 ± 1.0 kg body weight) were fed ad libitum with a total mixed ration for 120 d. Based on linear regression models involving dry matter intake (DMI), average daily gain (ADG) and mid-test metabolic body size, calves were assigned into low and high RFI groups. The RFI varied from ?0.33 to +0.28 kg DM/d with an average RFI of ?0.14 and 0.14 kg DM/d in low and high RFI calves, respectively. Calves had a mean DMI of 1.9 and 2.4 kg/d and an ADG of 0.5 and 0.6 kg/d in low and high RFI groups, respectively. Low RFI calves ate 19.0% less DM each day and required significantly less metabolisable energy for maintenance compared with high RFI calves (12.5 vs. 16.7 MJ/d). Nutrient digestibility and nitrogen balance did not differ among low and high RFI calves. In more efficient animals (low RFI calves) higher (p < 0.05) plasma level of growth hormone, insulin-like growth factor-1 (IGF-1), triiodothyronine (T₃) and lower concentration of thyroxin hormone were detected. No significant differences in levels of insulin, hydroxyproline, plasma and urine creatinine, total protein and albumin between high and low RFI groups were found. Blood metabolites showed significant (p < 0.05) differences at initial and final stages of study in both groups. At final stage of study, RFI showed negative correlations with growth hormone, IGF-1, T₃, urine creatinine and albumin. Low RFI buffalo calves are more efficient in feed utilisation and the differences in blood metabolites are probably due to differences in feed intake and body metabolism.     

Concentration and transport of dissolved and suspended substances in the Orinoco River

The Orinoco River, which is hydrologically unregulated and has a minimally disturbed watershed, was sampled quantitatively over a four-year interval. In conjunction with the sampling, a method was developed for quantifying statistical uncertainty in the estimates of annual transport. The discharge-weighted mean concentration of total suspended solids in the Orinoco River is 80 mg/l, which corresponds to total annual transport of 90 × 10⁶ t/y, or, expressed per unit of watershed area, 960 kg/ha/y, of which 96% is inorganic. The mean for dissolved solids is 34 mg/l, of which 25 mg/l is inorganic. The total transport of inorganic material, with a small allowance for bedload, is 128 × 10⁶ t/y, which corresponds to an erosion rate of 4 cm/1000 y. Concentrations of dissolved and suspended constituents derived from rock weathering are very low because of dilution from high runoff (1190 mm/y), coverage of the southern part of the drainage by shield rock, and minimal watershed disturbance. Seasonal patterns in dissolved and suspended constituents are repeated with a high degree of consistency from one year to the next. For most variables, relationships between transport and discharge are described adequately by a power function. There are three categories of response to changing discharge: purging (exponent > 1: soluble organic fractions and all particulate fractions), dilution (exponent 0–1: major ionic solids and silicon), and conservation (exponent < 0: nitrate, interannual). Variability across seasons and across years is highest for the particulate constituents, but within this group variability is lower for the organic than for the inorganic components. Major ions that originate primarily from the atmosphere have a higher seasonal variability than major ions that originate primarily from weathering. Potassium and soluble silicon have the lowest variabilities. Variability is much lower across years than across seasons for most constituents. Because of high runoff per unit area, the Orinoco drainage has a high specific transport of organic carbon (72 kg/ha/y, 6.8 × 10⁶ t/y, 1.6% of global river transport), even though the concentrations of organic carbon in the river are not exceptionally high (mean, 4.4 mg/l dissolved, 1.4 mg/l particulate). Concentrations of ammonium (35 μg/l as N) and of nitrate (80 μg/l as N) are high given the undisturbed nature of the watershed and the high amount of runoff. The high transport rate for total nitrogen (5.7 kg/ha/y, 0.54 × 10⁶ t/y, l.5% of global river transport) can be sustained only by high rates of nitrogen fixation within the watershed. Concentrations of soluble phosphorus are within the range expected for undisturbed river systems (20 μg/l), but concentrations of particulate phosphorus are low because the amounts of particulate matter are small and the phosphorus per unit weight of suspended matter is low. Phosphorus transport (0.75 kg/ha/y) can be accounted for easily by weathering of the parent material, even within the Guayana Shield, where weathering rates are lowest. Biological modification of nutrient and carbon fractions during transit along the main stem are minimal.     

Sulfur cycling in a forested Sphagnum bog in northern Minnesota

The mass balance and internal cycle of sulfur within a small forested,Sphagnum bog in northern Minnesota are presented here based on a 4-year record of hydrologic inputs and outputs (precipitation, throughfall, streamflow, upland runoff) and a 3-year measurement of plant growth and sulfur uptake. Concentrations and accumulation rates of inorganic and organic sulfur species were measured in porewater. The bog is a large sink for sulfur, retaining 37% of the total sulfur input. Because of the relatively large export of organic S (21% of inputs), retention efficiency for total-S (organic S + SO ₄ ⁼ ; 37%) is less than that for SO ₄ ⁼ (58%). There is a dynamic cycle of oxidation and reduction within the bog. Annual oxidation and recycling of S is equal to total inputs in the center of the bog. Plants receive 47% of their uptake requirement from atmospheric deposition, 5% from retranslocation from foliage, and the remainder from sulfur remineralized from peat. Mineralization is most intense in the aerobic zone above the water table. Inorganic sulfur species comprise <5% of the total sulfur burden within the peat.     

施肥对水稻产量和稻田土壤理化性质的影响

稻田土壤中养分的平衡主要取决于养分的输入与输出,其又主要受肥料的输入与植物所带走的养分所制约。不同的肥料品种、不同的施肥时期都影响养分在土壤中的吸收、转化与淋失,从而影响养分的输入与输出。稻田土壤生态系统中养分循环的研究已有很多报道。主要是不同耕作制度、不同施肥水平下,各输入输出因子的研究以及对土壤肥     

Responses to internal nitrogen and phosphorus concentrations of two Taraxacum microspecies of contrasting mineral ecology: critical N and P concentrations of whole plants

Of the two Taraxacum microspecies used. Taraxacum sellandii Dahlst. usually occurs in grasslands with a high nutrient level; Taraxacum nordstedtii Dahlst. is generally restricted to undisturbed and mineral-poor habitats. Growth response curves for internal N and P were established, based on relative yield of (whole) plant tissue water and (whole plant) internal mineral concentration on a tissue water basis. Critical nutrient concentrations of N and P were determined from the response curves derived. For both macroelements, T. nordstedtii showed lower critical nutrient concentrations. The difference in critical N concentrations coincided with differences in internal NO₃^-₃ concentrations between the microspecies. Finally, we discuss the use of tissue water as a (whole) plant growth parameter and internal mineral concentration on tissue water basis as a parameter describing the mineral status.     

A comparative study on nutrient cycling in wet heathland ecosystems

Summary The term relative nutrient requirement is introduced in order to measure and to compare the nutrient losses from different perennial plant populations and the amount of nutrient that they need to absorb to compensate these losses. The relative nutrient requirement (L) is defined as the amount of the growth-limiting nutrient that must be taken up to maintain or replace each unit of biomass during a given time interval (e.g., mgN g^-1 biomass year^-1). It is derived that in a plant community with two competing perennial plant populations, species¹ will become dominant if the relative competition coefficient k ₁₂ (sensu De Wit 1960) exceeds the ratio between the relative nutrient requirements of the two species (L ₁/L ₂), whereas species 2 will become dominant, if k ₁₂ is below this critical ratio. The above-ground litter production was measured inwet heathland communities dominated by Erica tetralix or by Molinia caeruleain order to estimate N and P losses from theaboveground biomass and to calculate the relative N and P requirements of these species. Molinia lost during one year 63% and 34%, respectively, of the amount of N and P present in the above-ground biomass at the end of the growing season. These losses were in Erica 27% and 31%, respectively. The relative N requirements of the two species show the same difference: 7.5 and 2.6 mg N g^-1 yr^-1, respectively, in Molinia and in Erica. Also the relative P requirement of Molinia is higher as well as that of Erica (0.18 versus 0.08 mg P g^-1 yr^-1). The relative competition coefficient of Molinia with respect to Erica (k _me ) is equal to unity under unfertilized conditions but increases with increasing nutrient supply. Under nutrient-poor conditions k _me is below the critical ratio of the relative nutrient requirements of the two species (L _m /L _e =2.9 or 2.3), so that Erica will be the dominant species. After an increase in nutrient availability k _me increases and exceeds this critical limit which results in Molinia replacing Erica. During the last 20 years this replacement of Erica-dominant communities by monocultures of Molinia has been observed in almost all wet heathlands in The Netherlands along with a strong increase in nitrogen availability.