Integrated effect of irrigation frequency and phosphorus level on lettuce: P uptake, root growth and yield

The objective of the present research was to assess the effects of fertigation frequency on plant phosphorus and water uptake. Special attention was given to root measurement in order to elucidate the mechanism that relates the fertigation frequency to P uptake and plant growth. Lettuce (Lactuca sativa L., cv. Iceberg) grown in pots filled with quartz sand was chosen as a test plant. The experiment comprised six treatments, with two concentrations of P in irrigation water (0.2 mM and 1.0 mM), and three daily fertigation frequencies (one, four and ten). It was found that high irrigation frequency induced a significant increase in plant-P concentration at low solution-P concentration, whereas at high P concentration the effect of irrigation frequency was insignificant. Increasing the irrigation frequency significantly enhanced the transpiration flux so that the transpiration flux of plants under low irrigation-P level at 10 daily irrigation events was similar to that of plants under high solution-P. The increases with irrigation frequency of P concentration in lettuce organs and of P influx to the roots, at the low P level, were attributed to the elimination of the depletion zone at the root-soil interface by the supply of fresh nutrient solution, and the enhancement of P uptake. The higher P uptake resulted from higher convective flux of dissolved P from the substrate solution to the root surface owing to the higher average moisture content associated with frequent irrigation. The only significant correlation revealed by multiple stepwise regressions relating nutrient concentrations in the plant to yield was that between plant-P concentration and the yield. On the basis of a quadratic regression, 97% of the dry weight variation could be explained by differences in P uptake, indicating that the main effect of fertigation frequency was related to an improvement in P mobilization and uptake. Thus, frequent irrigations may compensate for P shortage.     

Predicting invasiveness in exotic species: do subtropical native and invasive exotic aquatic plants differ in their growth responses to macronutrients?

We investigated whether plasticity in growth responses to nutrients could predict invasive potential in aquatic plants by measuring the effects of nutrients on growth of eight non-invasive native and six invasive exotic aquatic plant species. Nutrients were applied at two levels, approximating those found in urbanized and relatively undisturbed catchments, respectively. To identify systematic differences between invasive and non-invasive species, we compared the growth responses (total biomass, root:shoot allocation, and photosynthetic surface area) of native species with those of related invasive species after 13 weeks growth. The results were used to seek evidence of invasive potential among four recently naturalized species. There was evidence that invasive species tend to accumulate more biomass than native species ( P  = 0.0788). Root:shoot allocation did not differ between native and invasive plant species, nor was allocation affected by nutrient addition. However, the photosynthetic surface area of invasive species tended to increase with nutrients, whereas it did not among native species ( P  = 0.0658). Of the four recently naturalized species, Hydrocleys nymphoides showed the same nutrient-related plasticity in photosynthetic area displayed by known invasive species. Cyperus papyrus showed a strong reduction in photosynthetic area with increased nutrients. H. nymphoides and C. papyrus also accumulated more biomass than their native relatives. H. nymphoides possesses both of the traits we found to be associated with invasiveness, and should thus be regarded as likely to be invasive.     

Root/Shoot Allocation and Root Architecture in Seedlings: Variation among Forest Sites, Microhabitats, and Ecological Groups1

I analyzed patterns of variation in root mass allocation and root morphology among seedlings of woody species in relation to environmental factors in four Neotropical forests. Among forests, I explored the response of root traits to sites varying in water or nutrient availability. Within each forest, I explored the plastic response of species to different microhabitats: gaps and understory. Additionally, I explored evidence for life history correlation of root and shoot traits by comparing species differing in their successional group (light‐demanding [22 spp.] or shade tolerant [27 spp.]) and germination type (species with photosynthetic cotyledons or species with reserve cotyledons). At each forest site, young seedlings from 10 to 20 species were excavated. A total of 55 species was collected in understory conditions and 31 of them were also collected in gaps. From each seedling, six morphological ratios were determined. Allocation to roots was higher in forest sites with the lowest soil resources. Roots were finer and longer in the most infertile site, while roots were deeper in the site with the longest dry season. Seedling traits did not differ between germination types. Shade tolerant species allocated more to roots and developed thicker roots than light‐demanding species. Light‐demanding species showed stronger plastic responses to habitat than shade tolerant species, and species with photo‐synthetic cotyledons showed lower plasticity than species with reserve cotyledons. Overall, these results suggest that among Neotropical species, root allocation and root morphology of seedlings reflect plant adjustments to water or nutrient availability at geographic and microhabitat scales. In addition, life history specialization to light environments is suggested by differences among groups of species in their allocation to roots and in their root morphology.     

Effect of bicarbonate on root growth and accumulation of organic acids in Zn-inefficient and Zn-efficient rice cultivars (Oryza sativa L.)

Bicarbonate has been regarded as a major factor for inducing Zn deficiency in lowland rice, but the mechanisms responsible for this effect are not yet fully understood. The objective of the present study was to test whether early effects of bicarbonate (HCO₃ ⁻)are inhibition of root growth due to the accumulation of organic acids induced by HCO₃ ⁻. Solution culture experiments were conducted using two rice cultivars differing in susceptibility to Zn deficiency, and four bicarbonate concentrations (0, 5, 10, 20 mM). Bicarbonate (5–20 mM) strongly inhibited root growth of the Zn-inefficient cultivar within 4 days of treatments. In contrast, root growth of the Zn-efficient cultivar was slightly stimulated with bicarbonate at 5–10 mM and not affected at 20 mM. The inhibitory effect of bicarbonate on root growth in the Zn-inefficient cultivar was mainly that of impairment of new root initiation rather than suppression of elongation of individual roots. Bicarbonate (5–20 mM) increased the concentrations of malate, succinate and citrate in the roots of both cultivars, but to a greater extent for the Zn-inefficient than for the Zn-efficient cultivars. The results suggest that the impairment of root growth was likely to be the initial action of bicarbonate in inducing Zn deficiency in lowland rice, and the inhibitory effect of bicarbonate on root growth of the Zn-inefficient cultivar might result from high accumulation and an insufficient compartmentation of organic acids in the root cells.     

Effect of organic fertilisers on the greening quality, shoot and root growth, and shoot nutrient and alkaloid contents of turf-type endophytic tall fescue, Festuca arundinacea

Increasing concern about the potential negative environmental impact of chemical fertilisers used in urban landscapes has provided impetus to develop organic fertilisers. However, little is known about the effect of organic fertilisers on turfgrass quality, growth and stress resistance. This study compared the effect of 11 organic fertilisers, applied at manufacturer's recommended rates, on greening quality, shoot and root growth, and shoot nutrient (an indication of nutrient uptake) and alkaloid content (an indication of insect resistance) in endophytic (infected with the fungus Neotyphodium coenophialum) tall fescue in the greenhouse. We measured turfgrass greening quality on a 1–9 scale weekly (9 being the highest), shoot and root growth monthly, and shoot contents of macro- and micronutrients and of various alkaloids at the end of 4 months. The results show that Corn Gluten and Cockadoodle Doo produce the highest turfgrass greening quality and shoot growth. Nature's Touch with enzymes enhanced root growth, and thus resulted in high root:shoot ratio, especially in third and fourth months after application. Compared with the most commonly used chemical fertiliser, Scott's Turf Builder, the organic fertilisers Cockadoodle Doo, Corn Gluten and Nature's Touch with enzymes generally resulted in better turf greening quality. Although Cockadoodle Doo, Vigoro and Scott's Turf Builder resulted in higher macronutrient contents in turfgrass shoots, there was no significant correlation between the nutrient contents in the fertilisers and in the shoots four months after application. Significant differences were found for all measured alkaloids in turfgrass shoots among the 13 treatments, and these differences varied with fertiliser. Overall, organic fertilisers produced higher turfgrass greening quality, root and shoot growth and insect resistance capacity (alkaloid content) compared with the chemical fertiliser, Scott's Turf Builder. On the basis of the high to excellent turfgrass greening quality ratings, root:shoot ratio, shoot nutrient and alkaloid contents in this study, we conclude that Cockadoodle Doo, Vigoro and Nature's Touch with enzymes are relatively superior organic fertilisers.     

Root starch storage and allocation patterns in seeder and resprouter seedlings of two Cape Erica (Ericaceae) species

Post-fire sprouting of dormant buds in resprouter plants is facilitated by stored carbohydrate reserves, with starch being the critical reserve. Starch is mainly stored in xylem parenchyma ray tissue of woody underground organs, such as burls, lignotubers, and roots. We carried out a comparative analysis of the pattern of starch storage and the proportion of parenchymatic ray tissue in the upper root or cotyledonary region of seedlings from seeder and resprouter forms within two Cape Erica (Ericaceae) species: E. coccinea L. and E. calycina L., which were raised in the greenhouse under controlled irrigation. We also explored the root-to-shoot allocation patterns of seeder and resprouter seedlings in these two species. Resprouter seedlings of both species showed higher relative amounts of upper-root starch and upper-root storage tissue as well as a higher root-to-shoot allocation than their seeder counterparts. Pronounced swelling of the upper root region suggests ontogenetic development of a lignotuber in the resprouter forms of the two Erica species. The distinct allocation of starch in roots seems to be genetically determined and would account for the apparent differences in the root-to-shoot allocation patterns between both regeneration forms from the early seedling stage.     

岷江干旱河谷25种植物一年生植株根系功能性状及相互关系

相同条件下相同生长期的植物根系生长与适应策略及其差异性还不清楚。因此,采集岷江干旱河谷地区25种乡土植物(木本15/草本10种)的种子于2009年3月播种在同一干旱环境中,9月测定了1年生植株的最大根深(RDmax)、根幅(RW)与根生物量(RB),计算了总根长(TRL)、比根长(SRL)及细/粗根生物量比(RBf/c),分析了它们之间的关系,进行了根系功能组划分。结果表明:1)25种植物1年生植株RDmax与RW变异较小,总变异率为14.9%和20.7%;TRL和SRL变异相对较大,分别为28.5%和34.7%,草本植物SRL明显大于木本植物;RB和RBf/c种间变异较大,总变异率分别为50.1%和70.5%;2)25种植物的RDmax、RW、RB和TRL间呈显著正相关关系,表明根系较深的物种RW较大,TRL和RB也较高;SRL与RDmax呈极显著负相关关系,与RBf/c呈极显著正相关关系,表明根系垂直分布较浅的物种细根发达,SRL较大;3)主成分分析显示,25种植物可分为3个功能组:第1组具有较大RDmax、RW和RB,资源利用持续时间较长;第2组具有较大TRL、SRL和RBf/c,资源利用效率较高;第3组根系功能性状没有一致的突出特点,可能通过降低自身生理机能适应生存条件。综合分析表明,岷江干旱河谷区25种植物1年生植株根系的功能性状变异明显,可塑性大,历经长期自然选择压力而形成了不同的环境适应策略,但生长型并不必然表达出1年生植株根系功能性状的差异性。     

The effects of CO2, temperature and their interaction on the growth and yield of carrot (Daucus carota L.)

Stands of carrot (Daucus carota L.) were grown in the field within polyethylene-covered tunnels at a range of soil temperatures (from a mean of 7·5°C to 10·9°C) at either 348 (SE = 4·7) or 551 (SE = 7·7) μmol mol⁻¹ CO₂. The effect of increased atmospheric CO₂ concentration on root yield was greater than that on total biomass. At the last harvest (137d from sowing), total biomass was 16% (95% CI = 6%, 27%) greater at 551 than at 348 μmol mol⁻¹ CO₂, and 37% (95% CI = 30%, 44%) greater as a result of a 1°C rise in soil temperature. Enrichment with CO₂ or a 1°C rise in soil temperature increased root yield by 31% (95% CI = 19%, 45%) and 34% (95% CI = 27%, 42%), respectively, at this harvest. No effect on total biomass or root yield of an interaction between temperature and atmospheric CO₂ concentration at 137 DAS was detected. When compared at a given leaf number (seven leaves), CO₂ enrichment increased total biomass by 25% and root yields by 80%, but no effect of differences in temperature on plant weights was found. Thus, increases in total biomass and root yield observed in the warmer crops were a result of the effects of temperature on the timing of crop growth and development. Partitioning to the storage roots during early root expansion was greater at 551 than at 348 μmol mol⁻¹ CO₂. The root to total weight ratio was unaffected by differences in temperature at 551 μmol mol⁻¹CO₂, but was reduced by cooler temperatures at 348 μmol mol⁻¹ CO₂. At a given thermal time from sowing, CO₂ enrichment increased the leaf area per plant, particularly during early root growth, primarily as a result of an increase in the rate of leaf area expansion, and not an increase in leaf number.     

黄土高原白羊草、沙棘和辽东栎细根比根长特性

以黄土高原地区典型草本（白羊草）、灌木（沙棘）和乔木（辽东栎）为对象,研究了3种植物细根比根长在不同土层的分布状况以及与其它细根参数和土壤物理因子之间的相关性。结果表明,3种植物细根比根长的变化范围为6～55ram／rag。在0,80cm土层,白羊草、沙棘和辽东栎细根比根长变化范围分别为18—55mm／mg,14—4JDmm／mg,6—33mm／mg。3种植物0--80cm土层平均细根比根长从大到小依次为白羊草〉沙棘〉辽东栎。3种植物0-10cm土层细根比根长依次为沙棘〉辽东栎〉白羊草,10-80cm依次为白羊草〉辽东栎〉沙棘,表明3种植物细根比根长不仅在这两土层中的分布不具一致性,而且与0-80cm土层平均比根长也不具有一致性,进一步说明3种植物沿土壤剖面的生物量分配策略不同。相关分析表明,3种植物细根比根长与其它细根参数之间的相互关系各不相同,制约程度存在差异。与土壤物理因子的相关分析表明,3种植物细根比根长均随土壤含水量的增加而减少。土壤各级水稳性团聚体和土壤颗粒对3种植物细根比根长并无一致的影响。     

Effects of nitrogen and phosphorus deficiencies on levels of carbohydrates, respiratory enzymes and metabolites in seedlings of tobacco and their response to exogenous sucrose

A simple method of growing plants in agar was exploited to investigate the effect of long-term nitrogen (N) and phosphorus (P) deficiencies on respiratory metabolism and growth in shoots and roots of Nicotiana tabacum seedlings, and their interaction with exogenously supplied sucrose. Levels of hexose phosphates and 3-phosphoglyceric acid (3-PGA) were low in P-deficient shoots and roots and high in N-deficient shoots and roots. The ratio of hexose phosphates to 3-PGA and levels of fructose-2,6-bisphosphate were high in P-deficient plants and low in N-deficient plants. These data reflect differences in the way metabolism was perturbed, yet both deficiencies were associated with increased root growth relative to shoot growth, starch accumulation in the shoots, and soluble carbohydrate accumulation, especially hexoses, in the roots. Enzymes for sucrose degradation (sucrose synthase, acid and alkaline invertase) and glycolysis (phosphofructokinase, pyrophosphate-dependent phospho-fructokinase and pyruvate kinase) remained unaltered or declined in the shoots and roots. The accumulation of hexoses in roots of N- and P-deficient plants may result from maintenance of high invertase activities relative to sucrose synthase and glycolytic enzymes in the roots. The possibility that hexose accumulation may drive preferential root growth osmotically in N and P deficiencies is discussed. The addition of sucrose to roots to further investigate the interaction of carbohydrates with growth and allocation in low N and low P produced clear effects even though endogenous levels of soluble carbohydrate were already high in the nutrient-deficient plants. In complete nutrition, growth was stimulated, protein content particularly of the roots was increased and there was a preferential increase in activity of sucrose synthase in roots. At low P, enzyme activities in roots were increased, including sucrose synthase, and protein content increased, particularly in the roots, but there was no increase in growth. In N-deficient plants, exogenous sucrose led to decreased protein, Rubisco and chlorophyll content in shoots, in contrast to the other conditions, and a higher protein content and a general increase of catabolic enzyme activities and growth in the roots.     

Effects of Elevated Temperature on Growth and Gas Exchange in Dominant Plant Species from Maowusu Sandland,China

We compared the effect of elevated temperature on morphological development, biomass accumulation and allocation, and gas exchange of three dominant plants (Caragana intermedia Kuanget H.C. Fu, Hedysarum mongolicum Turcz., and Artemisia ordosica Krasch.) growing in Chinese Maowusu sandland. Plants were grown in two temperature chambers (25/20, 28/23 °C, day/night) during 60 d. Tree height, number of leaves, and leaf area were increased in C. intermedia and H. mongolicum seedlings, while in A. ordosica temperature only affected tree height. Elevated temperature increased biomass and reduced the root : shoot ratio in C. intermedia and H. mongolicum seedlings, but not in A. ordosica seedlings. The net photosynthetic rate (P _N) and transpiration rate (E) were increased at days 40 and 60 in C. intermedia and H. mongolicum seedlings, while in A. ordosica seedlings no significant effects on E were observed, and P _N was increased only at day 60. Water use efficiency (WUE) was reduced at days 40 and 60 in H. mongolicum seedlings, and at day 60 in C. intermedia seedlings. No temperature effect on WUE was observed in A. ordosica seedlings. These different responses indicate that climate change could alter plant communities in Maowusu sandland.     

青藏高原三种优势植物生物量分配的变化规律

该研究利用4个由高到低不同海拔的同质园实验,以青藏高原高寒草地优势植物垂穗披碱草(Elymus nutans)、矮嵩草(Kobresia humilis)和珠芽蓼(Polygonum viviparum)为对象,分析了植物个体根、茎、叶生物量分配及根冠比的变化规律及影响因素。结果表明:(1)植物个体根、茎、叶质量比和根冠比具有显著的种间差异;与垂穗披碱草和珠芽蓼相比,矮嵩草具有显著较高的根质量比而叶、茎质量比较低,所以其根冠比较高。(2)在向低海拔移栽的过程中,珠芽蓼叶质量比保持不变,茎质量比显著降低而根质量比显著升高,根冠比表现出显著上升的趋势;垂穗披碱草则相反,即叶、茎质量比显著升高而根质量比显著降低,根冠比表现出显著下降的趋势;矮嵩草根、茎、叶质量比和根冠比则无显著变化。(3)随着海拔降低,年均气温明显升高而年均降雨量明显降低,且在植物个体种源地和土壤基质保持一致的条件下,向低海拔移栽过程中温度是导致珠芽蓼根、茎、叶生物量分配及根冠比变化的重要因素,而水分是垂穗披碱草根、茎、叶生物量分配及根冠比变化的重要驱动因素;矮嵩草根、茎、叶生物量分配及根冠比受其遗传因素影响较大。因此,在将来暖干化的背景下,青藏高原高寒草地植物生物量的分配将会发生改变,导致它们对资源(光照、水分和土壤养分)获取和利用的变化而改变它们的种间关系,从而影响群落的物种多样性与组成,最终可能导致生态系统功能的变化。     

Enhancing phosphorus and zinc acquisition efficiency in rice: a critical review of root traits and their potential utility in rice breeding

Background

Rice is the world''s most important cereal crop and phosphorus (P) and zinc (Zn) deficiency are major constraints to its production. Where fertilizer is applied to overcome these nutritional constraints it comes at substantial cost to farmers and the efficiency of fertilizer use is low. Breeding crops that are efficient at acquiring P and Zn from native soil reserves or fertilizer sources has been advocated as a cost-effective solution, but would benefit from knowledge of genes and mechanisms that confer enhanced uptake of these nutrients by roots.

Scope

This review discusses root traits that have been linked to P and Zn uptake in rice, including traits that increase mobilization of P/Zn from soils, increase the volume of soil explored by roots or root surface area to recapture solubilized nutrients, enhance the rate of P/Zn uptake across the root membrane, and whole-plant traits that affect root growth and nutrient capture. In particular, this review focuses on the potential for these traits to be exploited through breeding programmes to produce nutrient-efficient crop cultivars.

Conclusions

Few root traits have so far been used successfully in plant breeding for enhanced P and Zn uptake in rice or any other crop. Insufficient genotypic variation for traits or the failure to enhance nutrient uptake under realistic field conditions are likely reasons for the limited success. More emphasis is needed on field studies in mapping populations or association panels to identify those traits and underlying genes that are able to enhance nutrient acquisition beyond the level already present in most cultivars.     

Responses of Pinus clausa, Pinus serotina and Pinus taeda seedlings to anaerobic solution culture. I. Changes in growth and root morphology

Seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.] and two edaphic seed sources of loblolly pine ( P. taeda L., dry- and wet-site seed sources) were grown in non-circulating, continuously flowing solution culture under aerobic (250 μ M O₂) and anaerobic (≤ 23 μ M O₂) conditions. Survival was 100% for all seedlings at 11 weeks. Although shoot height, biomass and leaf emergence of loblolly and pond pine seedlings were not significantly affected by 15 or 30 days of anaerobic growth conditions, root biomass was significantly reduced. Sand pine suffered the largest reduction in biomass, showing extensive root dieback and shoot chlorosis with retarded leaf development. These anaerobically induced symptoms of flooding injury were less severe in dry-site loblolly pine, and absent in wet-site loblolly and pond pine seedlings. Adventitious or new, secondary roots, and stem or taproot lenticels were particularly abundant under the 30-day anaerobic treatment in wet-site loblolly and pond pine seedlings, present to a lesser degree in dry-site loblolly pine, and nearly absent in sand pine seedlings. These results indicate that much of the immediate damage from flooding is due to the anoxic condition of the root rather than to the build-up of phytotoxins or soil nutrient imbalances. On the basis of overall seedling vigor, root plasticity and growth, we suggest the following flooding-tolerance/intolerance species (seed source) gradient: pond pine ≥ wet-site loblolly pine > dry-site loblolly pine > sand pine.     

Patterns in root traits of woody species hosting arbuscular and ectomycorrhizas: implications for the evolution of belowground strategies

Root traits vary enormously among plant species but we have little understanding of how this variation affects their functioning. Of central interest is how root traits are related to plant resource acquisition strategies from soil. We examined root traits of 33 woody species from northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined root trait distribution with respect to plant phylogeny, quantifying the phylogenetic signal (K statistic) in fine root morphology and architecture, and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal associations had different root traits. We found a pattern of species forming roots with thinner diameters as species diversified across time. Given moderate phylogenetic signals (K = 0.44–0.68), we used PICs to examine traits variation among taxa forming AM or EM, revealing that hosts of AM were associated with lower branching intensity (r_PIC = −0.77) and thicker root diameter (r_PIC = −0.41). Because EM evolved relatively more recently and intermittently across plant phylogenies, significant differences in root traits and colonization between plants forming AM and EM imply linkages between the evolution of these biotic interactions and root traits and suggest a history of selection pressures, with trade-offs for supporting different types of associations. Finally, across plant hosts of both EM and AM, species with thinner root diameters and longer specific root length (SRL) had less colonization (r_PIC = 0.85, −0.87), suggesting constraints on colonization linked to the evolution of root morphology.     

Root:shoot ratios of old and modern,tall and semi-dwarf wheats in a mediterranean environment

A field study tested the hypothesis that modern wheat varieties invest a lesser proportion of the total dry matter (root plus shoot) in the root system compared to old varieties. The study was carried out on a duplex soil (sand over clay) at Merredin, Western Australia in a Mediterranean type environment. We also compared the root:shoot dry matter ratios of near-isogenic lines for Rht dwarfing genes.Root:shoot ratios decreased with crop growth stage and were closely related to the developmental pattern of a variety. All varieties appeared to accumulate more dry matter into shoots after the terminal spikelet stage. For the modern variety Kulin this occurred as early as 55 days after sowing (DAS), but did not occur until 90 DAS in the old variety Purple Straw. For all varieties, root dry matter reached its maximum at anthesis, while shoot dry matter continued to increase till maturity. At anthesis there were no significant differences in shoot dry matter between varieties, but from Purple Straw to Kulin root dry matter and thus root:shoot ratio decreased.The tall and dwarf isogenic lines had similar developmental and root:shoot dry matter accumulation patterns.At anthesis, the old variety Purple Straw had significantly higher root dry matter and root length density in the top 40-cm of the profile than modern variety Kulin. There were no varietal differences in rooting depth, water extraction or water use. At maturity about 30% of the total dry matter was invested in the roots among wheat varieties. Grain yield, harvest index (HI) and water use efficiency of grain (WUE_gr) increased from old to modern varieties.The reduced investment of dry matter in the root system and thus the lower root:shoot ratio from early in the growing season may partly explain the increased HI and WUE_gr of modern compared to old varieties.     

黑河中游荒漠草地地上和地下生物量的分配格局

草地生态系统中地上和地下生物量的分配方式对于研究生态系统碳储量和碳循环有着重要的意义。为了解黑河中游荒漠草地的地上和地下生物量分配格局, 从群落和个体两个水平对黑河中游的地上和地下生物量进行了调查。结果表明: 群落水平上地上生物量介于3.2-559.2 g·m^-2之间, 地下生物量介于3.3-188.2 g·m^-2之间, 个体水平上地上生物量介于6.1-489.0 g·株^-1之间, 地下生物量介于2.4-244.2 g·株^-1之间, 群落水平上的根冠比(R/S)为0.10-2.49, 个体水平上为0.07-1.55, 地下生物量均小于地上生物量, 群落水平上R/S值大于个体水平。群落和个体水平地上和地下生物量的拟合斜率分别为1.1001和0.9913, 与1没有显著差异, 说明地上与地下生物量呈等速生长关系。群落和个体水平土壤表层0-20 cm和0-30 cm的根系生物量分别占全部根系生物量的89.81%、96.95%和81.42%、93.62%, 表明地下生物量主要集中在0-20 cm和0-30 cm土壤表层。     

Concentrations of nitrogen and phosphorus in streams draining the mixed land-use Dee Catchment, north-east Scotland

1.  There is still some uncertainty about large-scale influences on nutrient budgets in rivers. In particular, reduced forms of nitrogen (N) in organic forms might represent a significant fraction of the soluble N present in headwater streams, but this is not well quantified. Nitrate increases in relative importance downstream within agriculturally dominated areas. Here we appraise variations in N dynamics for a representative temperate but upland river, the Dee.
2.  In the Dee catchment, the source of organic N appears to vary seasonally. During summer under low flow conditions it originates primarily from in-stream biological production, while during the winter–spring period leaching from the plant–soil system would be the major contributor.
3.  On any individual sampling day, a wide range of N : P ratios can occur in the catchment area. Generally the narrowest N : P ratios occur during the summer and early autumn, particularly for upland catchments dominated by semi-natural vegetation. It is possible that some of the tributaries and upper region of the main river may be limited by N during the summer. The interpretation of the N : P ratios depends greatly upon the potential biological availability of the organic N, which remains unknown.
4.  Together, these data further illustrate that simple ideas about the relative limiting effects of N and P in temperate freshwaters may be misleading.     

Size and morphology of root systems of perennial grasses from contrasting habitats as affected by nitrogen supply

This paper discusses interspecific differences and phenotypic responses to nitrogen supply in various root parameters of five perennial grasses from contrasting habitats. The following root parameters were studied: root:shoot ratio, specific root length, specific root area, mean root diameter, frequency of fine roots, and the length and density of root hairs. Significant between-species variation was found in all of these features. Species from fertile sites had higher root:shoot ratios at high nitrogen supply than species from infertile habitats. All species growing at low nitrogen supply showed a significant increase in root:shoot ratio. Specific root length, specific root area, mean root diameter and frequency of fine roots were not affected significantly by nitrogen supply. Species from infertile sites responded to low nitrogen supply by a significant increase in root hair length and root hair density.