Hatching egg polyunsaturated fatty acids and the broiler chick

Transgenerational effects of certain nutrients such as essential fatty acids are gaining increased attention in the field of human medicine and animal sciences as a new tool to improve health and animal performance during perinatal life.Omega-3(n-3)and omega-6(n-6)fatty acids are denoted by the position of the first double bond from methyl end of the hydrocarbon chain.Alpha-linolenic acid(18:3 n-3)and linoleic acid(18:2 n-6)are essential n-3 and n-6 fatty acids and cannot be synthesized by the vertebrates including chickens.Alpha-linolenic acid and linoleic acid are the parent fatty acids of long chain(>20–22C)n-3 and n-6 polyunsaturated fatty acids(PUFA)such as eicosapentaenoic acid(20:5 n-3,EPA),docosapentaenoic acid(22:5 n-3/or 22:5 n-6,DPA),docosahexaenoic acid(22:6 n-3,DHA)and arachidonic acid(20:4 n-6).As components of cell membrane phospholipids,PUFA serves as precursors of eicosa-noids,act as ligands for membrane receptors and transcription factors that regulate gene expression and are pivotal for normal chick growth and development.Considering the role of egg lipids as the sole source of essential fatty acids to the hatchling,dietary deficiencies or inadequate in ovo supply may have repercussions in tissue PUFA incorpora-tion,lipid metabolism,chick growth and development during pre and early post-hatch period.This review focus on studies showing how maternal dietary n-3 or n-6 fatty acids can lead to remodeling of long chain n-3 and n-6 PUFA in the hatching egg and progeny chick tissue phospholipid molecular species and its impact on chick growth and PUFA metabolism during early life.

Carcass and Meat Characteristics of Hararghe Highland Bull after Draught Work Service

The objectives of the study were to examine the effects of draught work on carcass characteristics, meat yield potential, and distribution along primal cuts in Hararghe highland bulls fed on net energy requirement basis. Twelve bulls were sorted into three groups of four animals each and assigned to three treatment hours: control (0), 4, or 6, using a complete randomized design (CRD). The results of the study show that there are no significant differences (p > 0.05) in slaughter weight, hot carcass weight (HCW), chilling loss, total edible and non-edible offal, fat thickness (FT), deboned meat yield (kg), meat to bone ratio, muscle distribution, and proportion of kidney, pelvic, and heart fat (KPH%) among the treatment groups. However, the hot carcass-based dressing percentage was significantly lowered (p < 0.05) in bulls that work 4 or 6 hours a day. Meat yield was strongly correlated with HCW (r = 0.74) and FT (r = 0.73). Therefore, the number of hours the bull spent on draught work did not negatively impact meat yield or quality. Consequently, the research suggests that utilizing Hararghe highland bulls for draught service, four or six hours a day is viable for dual advantages: crop cultivation and marketable carcass.

Advances in fatty acids nutrition in dairy cows: from gut to cells and effects on performance

High producing dairy cows generally receive in the diet up to 5–6% of fat. This is a relatively low amount of fat in the diet compared to diets in monogastrics;however, dietary fat is important for dairy cows as demonstrated by the benefits of supplementing cows with various fatty acids(FA). Several FA are highly bioactive, especially by affecting the transcriptome;thus, they have nutrigenomic effects. In the present review, we provide an up-to-date understanding of the utilization of FA by dairy cows including the main processes affecting FA in the rumen,molecular aspects of the absorption of FA by the gut, synthesis, secretion, and utilization of chylomicrons;uptake and metabolism of FA by peripheral tissues, with a main emphasis on the liver, and main transcription factors regulated by FA. Most of the advances in FA utilization by rumen microorganisms and intestinal absorption of FA in dairy cows were made before the end of the last century with little information generated afterwards. However,large advances on the molecular aspects of intestinal absorption and cellular uptake of FA were made on monogastric species in the last 20 years. We provide a model of FA utilization in dairy cows by using information generated in monogastrics and enriching it with data produced in dairy cows. We also reviewed the latest studies on the effects of dietary FA on milk yield, milk fatty acid composition, reproduction, and health in dairy cows. The reviewed data revealed a complex picture with the FA being active in each step of the way, starting from influencing rumen microbiota, regulating intestinal absorption, and affecting cellular uptake and utilization by peripheral tissues, making prediction on in vivo nutrigenomic effects of FA challenging.

Peripartal rumen-protected methionine supplementation to higher energy diets elicits positive effects on blood neutrophil gene networks, performance and liver lipid content in dairy cows

Background： Main objectives were to determine to what extent Smartamine M（SM） supplementation to a prepartal higher-energy diet could alter neutrophil（PMN） and liver tissue immunometabolic biomarkers, and whether those responses were comparable to those in cows fed a prepartal lower-energy diet（CON）.Results： Twenty-eight multiparous Holstein cows were fed CON（NEL= 1.24 Mcal/kg DM） during d-50 to d-22 relative to calving. From d-21 to calving, cows were randomly assigned to a higher-energy diet（OVE, n = 9; NEL= 1.54 Mcal/kg DM）, OVE plus SM（OVE ＋ SM, n = 10; SM = 0.07 % of DM） or remained on CON（n = 9）. Al cows received the same basal lactation diet（NEL= 1.75 Mcal/kg DM）. Supplementation of SM（OVE ＋ SM） continued until 30 d postpartum. Liver biopsies were harvested at d-10, 7, and 21 relative to parturition. Blood PMN isolated at-10, 3, and 21 d relative to calving was used to evaluate gene expression. As expected, OVE increased liver lipid content postpartum; however,cows fed OVE ＋ SM or CON had lower concentrations than OVE. Compared with OVE, cows in CON and OVE ＋ SM had greater DMI postpartum and milk production. Furthermore, cows fed OVE ＋ SM had the greatest milk protein and fat percentage and lowest milk SCC despite having intermediate PMN phagocytic capacity. Adaptations in PMN gene expression in OVE ＋ SM cows associated with the lower SCC were gradual increases from-10 to 21 d in genes that facilitate migration into inflammatory sites（SELL, ITGAM）, enzymes essential for reducing reactive oxygen metabolites（SOD1, SOD2）, and a transcription factor（s） required for controlling PMN development（RXRA）. The greater expression of TLR4 on d 3, key for activation of innate immunity due to inflammation, in OVE compared with CON cows suggests a more pronounced inflammatory state. Feeding OVE ＋ SM dampened the upregulation of TLR4, despite the fact that these cows had similar expression of the pro-inflammatory genes NFKB1 and TNF as OVE. Cows in CON had lower overall expression of these inflammation-related genes and GSR, which generates reduced glutathione, an important cellular antioxidant.Conclusions： Although CON cows appeared to have a less stressful transition into lactation, SM supplementation was effective in alleviating negative effects of energy-overfeeding. As such, SM was beneficial in terms of production and appeared to boost the response of PMN in a way that improved overall cow health.

Nutrition and metabolism in poultry: role of lipids in early diet

Modern strains of broiler chickens are selected for fast growth and are marketed anywhere from 36 to 49 days after a21-day incubational period. For a viable healthy chick, all the necessary nutrients required for growth and development must be provided by the hen through the fertilized egg. The current feeding strategies for improved growth, health and productivity are targeted towards chicks after hatching. Considering the fact that developing chick embryo spends over 30 % of its total life span inside the hatching egg relying on nutrients deposited by the breeder hen, investigations on nutritional needs during pre-hatch period will improve embryonic health, hatchability and chick viability. In this context, investigations on hatching egg lipid quality is of utmost importance because, during incubation, egg fat is the major source of energy and sole source of essential omega-6（n-6） and omega-3（n-3） fatty acids to the chick embryo.Due to the unique roles of n-3 and n-6 fatty acids in growth, immune health, and development of central nervous system, this review will focus on the role of early exposure to essential fatty acids through maternal diet and hatching egg and its impact on progeny in meat-type broiler chickens.

Egg quality, fatty acid composition and immunoglobulin Y content in eggs from laying hens fed full fat camelina or flax seed

Background： The current study was conducted to evaluate egg quality and egg yolk fatty acids and immunoglobulin（Ig Y） content from laying hens fed full fat camelina or flax seed.Methods： A total of 75, 48-week-old Lohman brown hens were randomly allocated to 3 treatments, with 5replicates containing 5 laying hens each replicate. The hens were fed corn-soybean basal diet（Control）, or Control diet with 10 % of full fat camelina（Camelina） or flax seed（Flax） for a period of 16 wk. Hen production performance egg quality, egg yolk lipids, fatty acids and Ig Y were determined every 28 d during the experimental period.Results： Egg production was higher in hens fed Camelina and Flax than in Control hens（P 〈 0.05）. Egg weight and albumen weight was lowest in eggs from hens fed Camelina（P 〈 0.05）. Shell weight relative to egg weight（shell weight %）, and shell thickness was lowest in eggs from hens fed Flax（P 〈 0.05）. No difference was noted in Haugh unit, yolk：albumen ratio, and yolk weight. Significant increase in α-linolenic（18：3 n-3）, docosapentaenoic（22：5 n-3）and docoshexaenoic（22：6 n-3） acids were observed in egg yolk from hens fed Camelina and Flax. Total n-3 fatty acids constituted 1.19 % in Control eggs compared to 3.12 and 3.09 % in Camelina and Flax eggs, respectively（P 〈 0.05）. Eggs from hens fed Camelina and Flax had the higher Ig Y concentration than those hens fed Control diet when expressed on a mg/g of yolk basis（P 〈 0.05）. Although the egg weight was significantly lower in Camelina-fed hens, the total egg content of Ig Y was highest in eggs from hens fed Camelina（P 〈 0.05）.Conclusions： The egg n-3 fatty acid and Ig Y enhancing effect of dietary camelina seed warrants further attention into the potential of using camelina as a functional feed ingredient in poultry feeding.

Matrix Metalloproteinases and Tissue Inhibitors of Matrix Metalloproteinases as Plasma Indicators of Bovine Cystic Ovarian Disease

Cystic ovarian disease (COD) is one of the main causes of infertility in dairy cattle and has a high economic impact on farmers. COD is caused by an endocrine imbalance within the hypothalamic-pituitary-ovarian axis preventing the mature Graafian follicle from ovulating. The cause at the molecular level is not well understood. However, the matrix metalloproteinases (MMP) and plasminogen activator/plasmin families of extracellular (ECM) matrix-degrading proteinases are involved in Graafian follicle breakdown and oocyte release in the ovulation process. Our research investigated the possibility of using plasma concentrations of MMP-2 and -9 and their natural tissue inhibitors (TIMP) -1 and -2 as prognostic indicators of COD. Plasma samples from cystic and non-cystic dairy cows were analyzed using ELISA. Although plasma concentrations of MMP-2 and -9 were greater and TIMP-2 was lower in non-cystic compared to cystic cows, no significant differences were observed in MMP-2 and -9 and TIMP-1 and -2 due to cyst status. However, the TIMP-1:MMP-9 and TIMP-2:MMP-2 molar ratios were greater, (P = 0.099) and (P = 0.038), respectively, in cystic compared to non-cystic cows, suggesting a proteolytic insufficiency in cows with COD that may be a contributing factor to the anovulatory pathology. These data may provide the groundwork for future research and development of tools for dairy farmers to selectively choose replacement heifers less likely to develop COD.

The interplay between non-esterified fatty acids and bovine peroxisome proliferator-activated receptors: results of an in vitro hybrid approach

Background: In dairy cows circulating non-esterified fatty acids(NEFA) increase early post-partum while liver and other tissues undergo adaptation to greater lipid metabolism, mainly regulated by peroxisome proliferator-activated receptors(PPAR). PPAR are activated by fatty acids(FA), but it remains to be demonstrated that circulating NEFA or dietary FA activate bovine PPAR. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows.Methods: The dose-response activation of PPAR by NEFA or dietary FA was assessed using HP300 e digital dispenser and luciferase reporter in several bovine cell types. Cells were treated with blood plasma isolated from Jersey cows before and after parturition, NEFA isolated from the blood plasma, FA released from lipoproteins using milk lipoprotein lipase(LPL), and palmitic acid(C16:0). Effect on each PPAR isotype was assessed using specific synthetic inhibitors.Results: NEFA isolated from blood serum activate PPAR linearly up to ~ 4-fold at 400 μmol/L in MAC-T cells but had cytotoxic effect. Addition of albumin to the culture media decreases cytotoxic effects of NEFA but also PPAR activation by ~ 2-fold. Treating cells with serum from peripartum cows reveals that much of the PPAR activation can be explained by the amount of NEFA in the serum(R~2 = 0.91) and that the response to serum NEFA follows a quadratic tendency, with peak activation around 1.4 mmol/L. Analysis of PPAR activation by serum in MAC-T, BFH-12 and BPAEC cells revealed that most of the activation is explained by the activity of PPARδ and PPARγ, but not PPARα. Palmitic acid activated PPAR when added in culture media or blood serum but the activation was limited to PPARδ and PPARα and the response was nil in serum from post-partum cows. The addition of LPL to the serum increased > 1.5-fold PPAR activation.Conclusion: Our results support dose-dependent activation of PPAR by circulating NEFA in bovine, specifically δand γ isotypes. Data also support the possibility of increasing PPAR activation by dietary FA;however, this nutrigenomics approach maybe only effective in pre-partum but not post-partum cows.

Evaluation of rainwater harvesting and shrub establishment methods for sustainable watershed management in northern Afghanistan

Watershed rangelands in Northern Afghanistan provide various ecosystem services that support the local people's livelihoods,but they are now highly degraded essentially due to the continuous high grazing pressure and recurrent droughts.Effects of shrub establishment method enhanced by water harvesting techniques to rehabilitate degraded rangelands have not been well addressed.The main goal of this study was to evaluate the impact of direct seeding and transplanting of seedlings in combination with semi-circular bunds on growth,yield,and survival rate of four shrub species(Atriplex halimus,Atriplex nummularia,Atriplex lentiformis,andMaireana brevifolia)under semi-arid conditions of Sayyad village,Khulm watershed.Survival rate(%),plant height,width,and plant length(cm)and plant cover(%)were measured for each plant over five occasions.A non-destructive reference unit was used to estimate biomass production.The results showed that growth attributes and biomass production of shrubs were consistently greater in the transplanting compared to direct seeding.On average,the plant length,width,height,volume,cover,and biomass production of transplanted shrubs were greater than direct-seeded shrubs by 24.3%,8.6%,8.7%,121.5%,13.8% and 34.1%,respectively.Biomass production of transplanted seedlings was the highest for A.nummularia(1313.5 g DM/plant)and A.halimus(800 g DM/plant).There was a strong correlation between plant biomass production and plant volume(R^(2)_(Plant volume)=0.88)for the shrub A.nummularia,indicating that plant volume is a key variable for assessing biomass production for this species.Additionally,the survival rate of M.brevifolia was 100% in both planting methods,suggesting that based on better survival this halophytic plant has great potential when restoring degraded rangelands.Collectively,on the basis of better growth rates,yield,and survival,transplanting A.nummularia andA.halimus may enhance shrub establishment and contribute to the rehabilitation of sloping semi-arid degraded areas of Northern Afghanistan.

Comparative Growth Performance, Carcass Characteristics and Meat Quality of Local Horro and Exotic Cockerels of Tropical Origin Fed Growers Diet

Growth performance, carcass characteristics and meat quality of male chickens were evaluated using eight-week-old 360 cockerels from three exotic (Koekoek, Kuroiler and Sasso-R) and one Ethiopian indigenous (Horro) genotypes. Cockerels in each breed (90) were randomly allocated into three replications of 30 birds each and housed in deep litter pens for the experiment that lasted for 8 to 16 weeks. The experiment was arranged in a Completely Randomized Design. Seven birds per breed were slaughtered at the end to determine carcass yield, chemical composition and quality attributes of meat. The Kuroiler breed has higher body weight, body weight change (1621.8 g), average daily gain (28.9 g/day), daily feed consumption (127.4 g/day) and better feed conversion ratio (4.40) than other breeds. The Kuroiler breed has heavier slaughter weight (2716.3 g), dressed carcass weight (2201.0 g), eviscerated carcass weight (1905.1 g), breast weight (537.7 g), thigh weight (303.1 g) and drumstick weight (274.8 g) than other breeds. Total edible offal was higher for Kuroiler (324.2 g) and Sasso-R (306.1 g), intermediate in Koekoek (204.4 g) and low in Horro (152.4 g) breed. The relative proportion of breast and drumstick (% slaughter weight) were lower in Koekoek and Sasso-R (17.3 and 8.9) breeds, respectively. Abdominal fat weight (13.7 g and 1.02%) was lowest in Horro. Sasso-R showed higher percent edible offal weight (13.4%) than Horro breed (11.4%). The DM content in breast and thigh meat was higher for Horro breed than the rest. The CP content in the breast and thigh meat was lower for the Kuroiler and Koekoek breeds, respectively. Higher EE in the thigh meat was recorded for Sasso-R (8.9%), whereas, EE content in the breast meat was similar (3.4% - 3.7%) among the breeds. Flavor, tenderness, juiciness and general acceptability of breast and thigh meat were not affected by breed. The highest net return was observed in the Kuroiler breed. Based on the results obtained, it is suggested that the Kuroiler breed can be used for cockerel meat production in Ethiopia where intensive broiler production is not well developed.

Measurement of Metabolic and Inflammatory Serum Markers and Immune Marker Gene Expression during Superovulation in Beef Cattle

Health status of donor cows during superovulation is important to ensure optimal embryo quality at time of collection. Because nutritional and metabolic status impact embryo quality some form of nutritional supplementation is often provided before and during superovulation. OmniGen-AF® (OG) feeding has been shown to assist in the maintenance of animal health through regulation of metabolic status and balance and supporting aspects of immune function. We observed feeding donor cows OG decreased percent degenerate embryos recovered following superovulation increased serum progesterone concentration and improved in vitro embryo development. Evaluation of OG feeding on markers of metabolic function and inflammatory and immune function in beef cattle embryo donors are reported here. Similarly, cow metabolic and inflammatory response with repeated superovulation protocols is not known. Biomarkers to monitor and evaluate cow health during superovulation may provide management options to improve embryo recovery and quality. Twenty-four Angus cross-bred cattle were randomly assigned to four treatment groups, fed 0 or 56 g/hd/day for 49 days and superovulated with 200 or 400 mg Folltropin V (FSH). Blood was collected weekly for analyses. The protocol was repeated on all cows 90 - 120 d later with cows reassigned to their original groups. No differences (P > 0.10) were observed due to OG feeding or FSH dose on metabolic and inflammatory markers. Replicate exerted a significant effect where serum concentration of albumin, IL1β, IL6, PGE2 and leptin were lower (P < 0.05) in Replicate 1 compared to 2. There was also a similar pattern of change in several of the metabolic and inflammatory markers during the superovulation protocol where concentrations were higher at the time of estrus and ovulation. Taken together, physiologic changes during the estrous cycle and the number of superovulation protocols can modulate metabolic markers and inflammatory response.

Prepartum dietary energy intake alters adipose tissue transcriptome profiles during the periparturient period in Holstein dairy cows

Background:The aim of the study was to investigate the effect of energy overfeeding during the dry period on adipose tissue transcriptome profiles during the periparturient period in dairy cows.Methods:Fourteen primiparous Holstein cows from a larger cohort receiving a higher-energy diet(1.62 Mcal of net energy for lactation/kg of dry matter;15%crude protein)for ad libitum intake to supply 150%(OVR)or 100%(CTR)of energy requirements from dry off until parturition were used.After calving,all cows received the same lactation diet.Subcutaneous adipose tissue(SAT)biopsies were collected at−14,1,and 14d fromparturition(d)and used for transcriptome profiling using a bovine oligonucleotide microarray.Data mining of differentially expressed genes(DEG)between treatments and due to sampling time was performed using the Dynamic Impact Approach(DIA)and Ingenuity Pathway Analysis(IPA).Results:There was a strong effect of over-feeding energy on DEG with 2434(False discovery rate-corrected P<0.05)between OVR and CTR at−14 d,and only 340 and 538 at 1 and 14 d.The most-impacted and activated pathways in the Kyoto Encyclopedia of Genes and Genomes(KEGG)database that were highlighted by DIA analysis at−14 d in OVR vs.CTR included 9 associated with carbohydrate metabolism,with‘Pyruvate metabolism’,‘Glycolysis/gluconeogenesis’,and‘Pentose phosphate pathway’among the most-activated.Not surprisingly,OVR led to marked activation of lipid metabolism(e.g.‘Fatty acid biosynthesis’and‘Glycerolipid metabolism’).Unexpected metabolic pathways that were activated at−14 d in OVR included several related to metabolism of amino acids(e.g.branched chain)and of cofactors and vitamins(thiamin).Among endocrine and immune system pathways,at−14 d OVR led to marked activation of‘PPAR signalling’and‘Antigen processing and presentation’.Among key pathways affected over time in OVR,a number were related to translation(e.g.mTOR signaling),endocrine/immune signaling(CXCR4 and IGF1),and lipid metabolism(oxidative phosphorylation)with greater activation in OVR vs.CTR specifically at−14 d.Although statistical differences for several pathways in OVR vs.CTR nearly disappeared at 1 and 14 vs.−14 d,despite the well-known catabolic state of adipose depots after calving,the bioinformatics analyses suggested important roles for a number of signaling mechanisms at−14 vs.14 than 1 vs.-14 d.This was particularly evident in cows fed to meet predicted energy requirements during the dry period(CTR).Conclusions:Data underscored a strong activation by overfeeding energy of anabolic processes in the SAT exclusively prepartum.The study confirmed that higher-energy diets prepartum drive a transcriptional cascade of events orchestrated in part by the activation of PPARγthat regulate preadipocyte differentiation and lipid storage in SAT.Novel aspects of SAT biology to energy overfeeding or change in physiologic state also were uncovered,including the role of amino acid metabolism,mTOR signaling,and the immune system.

Effects of Feeding OmniGen-AF^®during Superovulation on <i>in Vitro</i>Development of Embryos Recovered from Donor Beef Cows

Embryo quality is crucial when selecting embryos for transfer. Variation in quality may be attributed to poor oocytes, semen, stress, inflammation, and potential immune system dysregulation. OmniGen-AF® (OG) feeding supports immune system function and animal health. Our laboratory recently reported lower percent degenerate embryos recovered and increased plasma progesterone in beef cattle donors fed OG during superovulation. In vitro development of embryos recovered from donor cows fed OG prior to collection is presented here. Embryos were recovered from 24 beef cows assigned to four treatment groups: 0 g OG/hd/d and 200 mg Folltropin®-V (FSH) (0/200);0 g OG/hd/d and 400 mg FSH (0/400), 56 g OG/hd/d, 200 mg FSH (56/200) and 56 g OG/hd/d and 400 mg FSH (56/400). Good to excellent quality early blastocysts were cultured for 8 d. and development through hatching, embryonic volume and plasminogen activator (PA) production were quantified. The complete protocol was repeated 90 - 120 d later as Replicate 2. Optimal development was observed by embryos recovered from 0/200 cows where percent blastocysts hatching was greater (P < 0.05) compared to 56/200 and 0/400 cows and embryonic volume was greatest (P < 0.05) in Replicate 1. However, percent blastocysts hatching from 0/200 cows was similar (P > 0.10) to 56/400 cows and embryos recovered from 56/400 cows in Replicate 1 produced more (P < 0.05) PA compared to all other groups. For cows superovulated with the standard 400-mg FSH dose, feeding OG supported in vitro embryo development similar to that observed for 0/200 cows.

Reference gene selection for quantitative PCR studies in bovine neutrophils

Reference genes are essential for studying mRNA expression with quantitative PCR (qPCR). We investigated 11 candidate whole-blood neutrophil reference genes (ACTB, B2M, G6PD, GAPDH, GYPC, HPRT, PGK1, RPL19, SDHA, TFRC, and YWHAZ) for beef calves, both males and females, with or without selenium supplementation. Initial screening was based on gene expression level (<28 Cq cycles), variability (SD < 1.5 Cq cycles), excluded GYPC and TFRC from further analysis. Expression stability of the remaining genes was evaluated using four software programs: geNorm, NormFinder, BestKeeper, and the comparative delta Cq method. The neutrophil reference genes, YWHAZ, PGK1, and RPL19, consistently ranked among the top four most stable genes under these experimental conditions. The commonly used reference genes, ACTB and HPRT, were not reliable, underscoring the need to validate neutrophil reference genes under different experimental conditions. Multiple reference genes rather than a single gene may provide more robust and reliable results. The best pair of reference genes in whole-blood neutrophils from beef calves overall was PGK1|YWHAZ.

控制西美圆柏数量对美国俄勒冈州中部生态系统氮储量的影响

在美国俄勒冈州,控制西美圆柏(Juniperus occidentalis)的数量是一种公认的牧场管理措施,该做法有助于恢复蒿草草原(sagebrush steppe)生境,该生境对野生动物和家畜都十分重要。然而,尽管控制木本植物数量会对当地的流域管理和区域性氮库造成重要影响,但砍伐西美圆柏对生态系统中氮元素的影响问题尚未得到很好的解决。本文定量研究了两个相邻流域生态系统中的氮储量,其中一个流域经过处理(流域内的大部分圆柏已被清除掉),而另一个流域未处理(圆柏未被清除)。在圆柏被移除13年后,我们测定了两个流域里圆柏树林、灌木丛、草丛和枯枝落叶层的地上氮储量,以及两个流域中两个土层(0–25和25–50 cm)内的地下氮储量(根系和土壤氮储量)。研究结果表明,未处理流域的地上氮储量是处理流域的6.9倍,因为未处理流域的地上生物量要大得多。然而,由于砍伐圆柏导致林下植被的根系生物量增加,所以处理流域的根系氮储量是未处理流域的3.1倍。0–25和25–50 cm土层氮储量没有受到圆柏砍伐的影响。总体而言,生态系统总氮储量在处理流域(9536 kg N ha−1)和未处理流域(9456 kg N ha−1)之间并没有显著差异。在两个流域里,生态系统中最大的氮积累量(至少95%的生态系统总氮量)均存在于地下(0–25 cm深的土壤以及根系)。这项研究证明,清除圆柏并不会显著影响生态系统的储氮能力。

植物的养分吸收和气体交换为干旱适应和物种共存带来的启示

尽管气候变化很可能会导致干旱生态系统的降水量变化幅度增大,但沙漠灌木群落对降水变化的响应模式尚不清楚。因为适应干旱的植物具有多种生存机制以利于其物种的共存,所以认识沙漠灌木群落对降水变化的响应具有重要的意义。我们在美国大盆地地区(美国加利福尼亚州欧文斯谷)开展了一项同质园实验,对8种干旱适应性植物(其中包括了禾本科植物、灌木和杂类草植物)在3种不同夏季降水量(分别为每月1.3、2.6和3.9 cm)的响应进行了测定。检测了上述植物在矿物养分吸收(碳、氮、磷、钾、钙、镁、锰、铜、硼、锌、铁和钠)和气体交换参数(光合速率和气孔导度)方面的变化。研究结果显示,两种禾本科植物[鼠尾粟草(Sporobolus airoides)和匍匐野麦赖草(Leymus triticoides)]与一种耐盐灌木物种[密叶滨藜(Atriplex confertifolia)]在水分供给增加时,光合速率和/或气孔导度增加。在这8个物种中,有5个物种表现出了水分供给与营养物质吸收之间的显著相关性。光合速率更高的三齿蒿(Artemisia tridentata)含有更多的钾、铜和硼,而光合速率更高的北极灯心草(Juncus arcticus)具有更高的镁和铁含量以及更低的钠含量。北极灯心草以及3种适盐性物种[密叶滨藜、盐草(Distichlis spicata)和鼠尾粟草]在气孔导度和营养素浓度方面表现出了相关性。这些结果表明,干旱适应性物种之间对水分增多情形的生理响应机制的差异以及相关的营养吸收策略可能有助于它们在夏季雨水增多时的相互共存。