Seasonal change in the proportion of bacterial and phytoplankton production along a salinity gradient in a shallow estuary

We intended to evaluate the relative contribution of primary production versus allochthonous carbon in the production of bacterial biomass in a mesotrophic estuary. Different spatial and temporal ranges were observed in the values of bacterioplankton biomass (31–273 g C l^–1) and production (0.1–16.0 g C l^–1 h^–1, 1.5–36.8 mg C m^–2 h^–1) as well as in phytoplankton abundance (50–1700 g C l^–1) and primary production (0.1–512.9 g C l^–1 h^–1, 1.5–512.9 mg C m^–2 h^–1). Bacterial specific growth rate (0.10–1.68 d^–1) during the year did not fluctuate as much as phytoplankton specific growth rate (0.02–0.74 d^–1). Along the salinity gradient and towards the inner estuary, bacterio- and phytoplankton biomass and production increased steadily both in the warm and cold seasons. The maximum geographical increase observed in these variables was 12 times more for the bacterial community and 8 times more for the phytoplankton community. The warm to cold season ratios of the biological variables varied geographically and according to these variables. The increase at the warm season achieved its maximum in the biomass production, particularly in the marine zone and at high tide (20 and 112 times higher in bacterial and phytoplankton production, respectively). The seasonal variation in specific growth rate was most noticeable in phytoplankton, with seasonal ratios of 3–26. The bacterial community of the marine zone responded positively – generating seasonal ratios of 1–13 in bacterial specific growth rate – to the strong warm season increment in phytoplankton growth rate in this zone. In the brackish water zone where even during the warm season allochthonous carbon accounted for 41% (on average) of the bacterial carbon demand, the seasonal ratio of bacterial specific growth rate varied from about 1 to 2. During the warm season, an average of 21% of the primary production was potentially sufficient to support the whole bacterial production. During the cold months, however, the total primary production would be either required or even insufficient to support bacterial production. The estuary turned then into a mostly heterotrophic system. However, the calculated annual production of biomass by bacterio- and phytoplankton in the whole ecosystem showed that auto- and heterotrophic production was balanced in this estuary.     

Growth and production of the dominant pelagic fish, Acanthobrama terraesanctae, in subtropical Lake Kinneret, Israel

Acanthobrama terraesanctae (local name lavnun), an endemic planktivorous cyprinid, dominates total fish numbers (>80%) in Lake Kinneret, and may have a significant top-down impact on the lake ecosystem. The length of young-of-the-year fish calculated from the von Bertalanffy equation agreed with field observations of juvenile growth. An unusual bi-modal length-frequency distribution observed in May 1993 provided additional help in age identification. Males grew more slowly than females and reached a lower maximum length. Total mortality coefficients (exponents) of males and females >12 cm (minimal legal size of fish in the catch) were similar ( c. 1·52). An average cohort reaches maximum biomass during its second year. Maximum production is created at the end of the second year. The production: biomass ratio of the population was 1·16, and 36% of total lavnun standing stock was taken by fishing. From the late 1980s to early 1990s, when standing stock and population structure were stable, the average harvest of 1000 t was consistent with a total lavnun biomass of 2800 t, which constitutes 50–70% of the total fish stock measured acoustically in the lake. Such a biomass could be sustained by the known production of zooplankton. Absence of verified growth data for lavnun contributed to the collapse of the fishery in 1993, because it hampered timely revision of fishery policy in response to the drastic changes in the lavnun stock in 1992.     

Life-history strategies and production of Tinodes waeneri (L.) (Trichoptera) in Lake Esrom,Denmark

The life cycle and production of Tinodes waeneri (L.) was examined at five shallow littoral localities in Lake Esrom, Denmark, during 1979/80. Five larval instars were demonstrated. The differences in temporal composition of instars indicated three different life cycles. A bivoltine strategy was shown for the most exposed locality which also had the highest average abundance equal to 11 500 ind. m^–2. A univoltine population was found in the more sheltered NW part of the lake with an average density of 1 500 ind. m^–2. At the three remaining stations the life cycles were partly bivoltine with wintering populations of mixed cohorts and densities between 10 500 and 3 000 ind. m^–3. Two distinct flight periods with maxima in June and August were demonstrated for bi- and partly bivoltine populations. Differences in rates of growth and elimination added to the variability in life cycle. Growth rates peaked in August (5.0–7.4% d^–1) at an average temperature of 20°C. Estimates of production ranged from 1.9 to 17.5 g AFDW m^–2 a^–1 with an average of 8.0 g AFDW m^–2. The P/B ratios, which were within the expected range for uni- and bivoltine populations of trichopterans, were 5.73 for the bivoltine population and 3.31 for the univoltine population.Estimates of consumption revealed that the populations could be sustained by autochthonous epilithic production in the habitats. Variability in the quality and seasonal availability of food were judged to influence the type of life cycle.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.     

Denitrification by extremely halophilic bacteria

Abstract Extremely halophilic bacteria were isolated from widely separated sites by anaerobic enrichment in the presence of nitrate. The anaerobic growth of several of these isolates was accompanied by the production of nitrite, nitrous oxide, and dinitrogen. These results are a direct confirmation of the existence of extremely halophilic denitrifying bacteria, and suggest that such bacteria may be common inhabitants of hypersaline environments.     

BIOMASS AND DYNAMICS OF GROWTH OF ULVA SPECIES IN PALMONES RIVER ESTUARY1

During the last decade, the Palmones River estuary has undergone severe eutrophication followed by a green tide episode; two species of Ulva, rotundata Blid. and Ulva curvata (Kütz.) De Toni, were the main macroalgae responsible for this bloom. From November 1993 to December 1994, we followed the biomass, the growth dynamics, and tissue elemental composition (C:N:P)of Ulva species, as well as some physicochemical variables in the estuary. Maximum biomass (up to 375 g dry wt·m^?2 in some spots, corresponding to a thallus area index of nearly 17 m²Ulva·m^?2 sediment) were observed in June and December. However, the biomass varied among the sampling stations. Water nitrate, ammonia, and phosphate showed high concentrations throughout the year, with extremely high transient pulses, sustaining the high growth rates observed. Growth rates were estimated directly in the field. The rates were generally higher in Ulva discs maintained in net cages than those estimated by changes in biomass standing stock between two consecutive samplings. The difference between both estimates was used to quantify the importance of the processes causing loss of biomass, which were attributable to grazing, exported biomass, and thallus decomposition under anaerobic conditions resulting from extreme self-shading. Maximum chlorophyll content was found in winter, whereas the minimum was in spring. Atomic N:P ratios were generally higher in the algae than in the water. However, the absolute concentrations of tissue N and P were always higher than the critical levels for maximum growth, which suggests that growth was not limited by inorganic N or P availability. The results suggested that the increase in nutrient loading in the river may have triggered the massive development of green algae and that light limitation and temperature stress in summer seem to be the main factors controlling the abundance of Ulva in the estuary. In addition to light availability and thermal stress, the different loss processes may have a decisive role in the dynamics of Ulva biomass.     

Abundance and Production of Riparian Trees in the Lowland Floodplain of the Queets River, Washington

Riparian zones associated with alluvial rivers are spatially dynamic, forming distinct vegetative mosaics that exhibit sharp contrasts in structure and processes related to the underlying biophysical template. The productivity of riparian plants, especially trees, influences streamside community characteristics as well as the forms and fluxes of organic matter to adjacent streams – thereby strongly impacting patterns of channel morphology, water flow, sedimentation, and habitat in rivers. As part of a comprehensive investigation of riparian dynamics in coastal rain forest rivers of the Pacific Northwest (USA), we examined riparian tree abundance (density, basal area, and biomass) and rates of production (basal area growth [BAI] and bole wood biomass increase [P]) of seven common species – red alder (Alnus rubra), Sitka spruce (Picea sitchensis), bigleaf maple (Acer macrophyllum), western hemlock (Tsuga heterophylla), black cottonwood (Populus trichocarpa), vine maple (Acer circinatum) and willow (Salix spp.) – in the lowland floodplain of the Queets River (Olympic National Park), Washington. Measurements were made annually for three years (1999 – 2001) in 16 permanent plots on three biophysical templates that formed a toposequence – active floodplain, young terrace and mature terrace. Stem density was highest in the active floodplain (∼27,000 stems/ ha), decreasing in the young terrace (∼2,700 stems /ha) and the mature terrace (∼500 stems/ha). Basal area and total stem biomass were lowest in the active floodplain (∼16 m2/ha and ∼18 Mg dry weight/ha, respectively) and higher on the young terrace (∼32 m2/ha and ∼134 Mg dry weight/ha) and on the mature terrace (∼69 m2/ha and ∼540 Mg dry weight /ha). Total plot-scale BAI was not significantly different among the physical templates with mean values ranging from approximately 1.4 (low terrace) to approximately 2.8 m2/ha/y (active floodplain). In contrast, P was significantly higher on the mature terrace (10.3 Mg/ha) than the active floodplain (3.2 Mg/ha) but there was no significant difference between young terrace (6.5 Mg/ha) and mature terrace. For the entire Queets River floodplain (57 km² over 77 km of river length), the mature terrace contributed 81% of the total annual production (28,764 Mg) whereas the active floodplain and young terrace accounted only for 5 and 14%, respectively. Overall, we show that riparian trees grow quickly in this coastal Pacific Northwest system and that the older riparian forests on mature terraces are the main contributors to stem production at the plot and floodplain scales for at least 350 years after stand initiation. This suggests that, in combination with the rapid lateral migrations of many alluvial rivers, the older riparian forests on those terraces are important and sustained sources of organic matter (especially large woody debris, LWD) that, over decades to centuries, shape the character of coastal rivers in the Pacific Northwest.     

重要理化因子对小球藻生长和油脂产量的影响

本文采用通气培养的方法研究了N、P、Fe3 、盐度、光照强度、温度对小球藻(Chlorella sp. XQ-200419)生长速率、生物量和油脂产量的影响。主要结果如下：N浓度对小球藻的生长和油脂产量均有显著的影响,在KNO3浓度0.05—0.3g/L范围内,小球藻生长速率随N浓度的增加而提高,并积累更多的生物量,而油脂含量随之递减,KNO3浓度为0.3g/L时,油脂产量最高。小球藻对P浓度变化的适应范围很大,K2HPO4浓度在10—160mg/L范围内,对小球藻的生长和油脂产量都没有显著影响。在小球藻培养后期补加不同浓度Fe3 对其生长速率没有显著影响,总脂含量随着Fe3 浓度升高呈现上升的趋势,均比对照有极显著提高,Fe3 浓度为0.75mmol/L时油脂产量最高。盐度对小球藻的生长有一定的抑制作用;油脂含量先随着盐度的增大而提高,当NaCl浓度达到0.6mol/L, 油脂含量又显著降低;油脂含量和油脂产量均在盐度为0.2mol/L时最高。光照强度对处于生长后期的小球藻的生长影响不大,但影响其油脂积累,小球藻的油脂含量和产量随光照强度的增大而显著提高,当光照强度增至280μmolm-2s-1时,油脂含量和油脂产量最高。温度对小球藻的生长速率、生物量、油脂含量和油脂产量都有显著的影响,在15-40℃范围内,随着培养温度的升高,生长速率、生物量、油脂含量和油脂产量都经历了一个先上升然后下降的过程,适合小球藻生长、积累油脂的温度范围是20-35℃,30-35℃时油脂产量最高,40℃时生物量、油脂含量和产量都最低。理化因子对生长和油脂含量的影响分为两种情况：1. 温度、光强、铁浓度和盐度的影响表现为在适宜生长的条件下提高油脂含量,这种模式可以称为“适宜模式”;2. 氮浓度的影响表现为在不利于生长的条件下提高油脂含量,这种模式可以称为“胁迫模式”。两种模式都可以提高油脂含量,但是,只有适宜模式才可以提高油脂产量。在筛选小球藻优良产油藻种时要注意,只有在适宜的培养条件下油脂含量高的藻种才具有高产油潜力。     

The application of growth kinetics to the control of Eichhornia crassipes (Mart) solms. Through nutrient removal by mechanical harvesting

The growth of Eichhornia crassipes (water hyacinth) under nitrate-nitrogen limiting conditions can be explained by the Monod rectangular model. The kinetic constants maximum specific growth rate, half saturation constant and yield coefficient were determined under nitrate-nitrogen limiting conditions in nutrient culture at an air temperature of 25°C. The practical application of these constants for the possible control of water hyacinth through nutrient limitation is illustrated.     

Effects of ammonia and lactate on hybridoma growth, metabolism, and antibody production

The influence of ammonia and lactate on cell growth, metabolic, and antibody production rates was investigated for murine hybridoma cell line 163.4G5.3 during batch culture. The specific growth rate was reduced by one-half in the presence of an initial ammonia concentration of 4 mM. Increasing ammonia levels accelerated glucose and glutamine consumption, decreased ammonia yield from glutamine, and increased alanine yield from glutamine. Although the amount of antibody produced decreased with increasing ammonia concentration, the specific antibody productivity remained relatively constant around a value of 0.22 pg/cell-h. The specific growth rate was reduced by one-half at an initial lactate concentration of 55 mM. Although specific glucose and glutamine uptake rates were increased at high lacatate concentration, they showed a decrease after making corrections for medium osmolarity. The yield coefficient of lactate from glucose decreased at high lactate concentrations. A similar decrease was observed for the ammonia yield coefficient from glutamine. At elevated lactate concentrations, specific antibody productivities increased, possibly due to the increase in medium osmolarity. The specific oxygen uptake rate was insensitive to ammonia and lactate concentrations. Addition of ammonia and lactate increased the calculated metabolic energy production of the cells. At high ammonia and lactate, the contribution of glycolysis to total energy production increased. Decreasing external pH and increasing ammonia concentrations caused cytoplasmic acidification. Effect of lactate on intracellular pH was insignificant, whereas increasing osmolarity caused cytoplasmic alkalinization.     

Biomass turnover in populations of viviparous sphaeriid clams: Comparisons of growth,fecundity, mortality and biomass production

This paper reports studies carried out on natural populations of two species of viviparous clams, Sphaerium striatinum and S. simile, at three localities in two mesotrophic lakes in upstate New York. Sphaeriids are dominant members of the benthic fauna at the second trophic level in these localities, and more generally are cosmopolitan and ubiquitous animals.A growth survey involved monthly collections of regular samples, and these were used in measurements of growth, fecundity, mortality, and biomass production. S. striatinum proved to have an 18 to 24 month lifespan and S. simile one of about 26 months. Differences in reproduction included a maximum brood size of 12 in S. striatinum and of only 6 in S. simile, spat recruitment extending over 8 months in S. striatinum and over 9 months in S. simile, and a mean spat size at birth of 3.6 mm in S. striatinum and 6.4 mm in S. simile. The gross fecundity is thus markedly lower than that in the majority of molluscs. Mortality is to some extent compensating, adult survivorship being greater in S. simile, but mortality rates are remarkably steady and relatively low in both species. Field assessments of density showed that S. striatinum was dominant in one locality, and S. simile in another locality in the same lake, but that S. striatinum occurred at greater densities than any other sphaeriid species.Cage experiments confirmed the steady mortality rates and low fecundity values for these sphaeriids. Individual growth rates in cages are considerably higher than the mean values from population samples, since growth rates there are not obscured by recruitment of spat.A more complete analysis of growth in both species involved a series of over 400 determinations of total nitrogen (by micro-Dumas). These were utilized in computations of productivity. Embryonic production makes up only a small fraction (< 10 per cent) of the biomass turnover in these viviparous sphaeriids. The overall annual productivity (in terms of total nitrogen) is o.8 grams nitrogen per square meter per year for S. striatinum and only 0.28 grams nitrogen per square meter per year for S. simile. In a discussion of these figures they are shown to correspond to about 33 per cent of the second trophic level productivity for S. striatinum and about to per cent for S. simile. Since sphaeriids are long-lived, these percentages reflect a real dominance. In further discussion of the coexistence of these two species, it is pointed out that mortality is higher for the less common species in each locality.This research was supported by an N.S.F. pre-doctoral traineeship to the author and an N.I.H. Grant GM 11693 to Dr. W. D. Russell-Hunter, and represents a portion of a dissertation submitted as partial satisfaction for the Ph.D. at Syracuse University.     

Reproduction, molting, and growth of two Mexican uniparental forms of the tadpole shrimp Triops (Branchiopoda: Notostraca) under a recirculating culture system

Two forms (here called short and long) of the tadpole shrimp Triops from the Baja California peninsula (Mexico) exhibit interesting features for aquacultural purposes; rapid growth, early maturation (six days) and uniparental reproduction via cysts (i.e. drought-resistant dormant eggs). The use of Triops for aquaculture depends on the standard production of viable cysts. Basic information on the reproductive potential of Triops is scarce. Using a recirculating system, we studied, through two culture tests, the cyst production, frequency of molting, and growth rate of the two Mexican forms. For each form, individual data were obtained from five specimens in Test 1 over 15 days, and from 10 specimens in Test 2 over 20 days. Hatching response of cysts produced in Test 1 was also studied. The short-form showed a high fecundity depositing groups of cysts from the ovisacs several times a day. The mean cyst production per day was 156–306 (Test 1 & 2), and the mean total cyst production was 2028 (range 728–3193) (Test 1), and 5821 (range 4136–7554) (Test 2). The maximum number of cysts deposited by one short-form individual in a day was 1231 (Test 2). The reproductive performance of the long-form was poor. The mean cyst production per day was only 4.2–7.9 (Test 1 & 2). The short-form molted every 2.5–2.8 days and the long-form molted every 2.8–3.7 days. The mean growth rate calculated from the standard length (mm d^–1) of the short-form was 0.43–0.84 (Test 1 & 2), and in the long-form the values were 0.84–1.25 (Test 1 & 2). The poor cyst production of the long-form may be explained by inadequate food resources that did not fulfill the nutritional requirements for reproduction. Given its prolific uniparental reproduction (vs. biparental reproduction), the short-form Triops appears as a good potential candidate for aquaculture.     

Effect of insulin on a serum-free hybridoma culture

Insulin is often included in serum-free media for animal cell cultivation. However, the necessity of insulin for a specific cell line is rather uncertain. In this article we report the effects of insulin on the cultivation of a hybridoma cell line in a serum-free medium. It was found that insulin affected neither the cell growth nor the antibody production. The specific growth rate and specific antibody production rate were very similar in the cultures with or without insulin. However, the presence of insulin affected the nutrient consumption rate and cell metabolism. Including insulin in the medium resulted in a higher specific glucose consumption rate, a shorter exponential growth stage, and a lower final antibody concentration. The elimination of insulin from the medium allowed antibody to accumulate to a concentration substantially higher than that in the insulin-containing cultuvre. (c) 1995 John Wiley & Sons, Inc.     

Dynamics of energy utilization in male and female turkeys during growth

Determining energy utilization in growing animals enables to adjust the nutritional constraints to nutrient requirements while maximizing the ratio between lean retention and fat retention to improve feed efficiency. In turkey production, the important sexual dimorphism and differences between strains may contribute to differences in basal energy metabolism and the partitioning of energy retention between protein and lipid. The objective of this study was to determine the dynamics of energy utilization in males and females of a heavy strain of turkeys fed ad libitum from 1 to 23 weeks of age. Heat production (HP) was determined by indirect calorimetry and retained energy (RE) was calculated as the difference between metabolizable energy (ME) intake and HP. The RE as protein was determined by a nitrogen balance, while the remaining RE was assumed to be lipid. A modeling procedure allowed partitioning HP between fasting HP (FHP), activity-related HP and thermic effect of feeding. A multiple regression analysis was used to estimate the maintenance energy expenditure (ME(m)) and the energy efficiencies of protein and lipid retention (k(p) and k(f), respectively). Results were expressed either per day or per kg BW(0.75) per day. In comparison with females, males consumed more feed (440 v. 368 g/day), grew faster (163 v. 147 g/day) and retained more protein (38 v. 28 g/day) during the experimental period. Expressed per kg BW(0.75) per day, ME intake decreased linearly with increasing age and was not affected by gender. Similarly, RE as protein decreased with increasing age and tended to be greater in males than in females, whereas RE as lipid increased with increasing age and was lower in males than in females. In addition, HP decreased with increasing age and was greater in males than in females, because of greater activity-related HP and FHP (47% and 9% greater in males compared with females). The FHP averaged 417 kJ/(kg BW)(0.75) per day during the first 3 weeks of age and decreased to 317 and 277 kJ/(kg BW)(0.75) per day in males and females, respectively, from 20 weeks of age onwards. Similar to FHP, ME(m) was lower in females than in males ((586 to 12 × BW) and (586 to 5 × BW) kJ/(kg BW)(0.75) per day, respectively) and the k(p) and k(f) were estimated at 0.63 and 0.87, respectively. This study shows that the partitioning of RE and HP differs between genders in growing turkeys, which likely results in differences in nutrient requirements.     

Influence of inoculum age on hybridoma culture kinetics

To determine the influence of the inoculum age on the kinetics of hybridoma growth and metabolism, spinner flasks have been inoculated with cells previously propagated in T flasks for 43, 52, 62 and 71 hr respectively. Increasing the age of the inoculum is found to result in a longer lag phase, in a lower maximum specific growth rate and in a reduced maximal cell density. During the growth phase specific rates of glucose and glutamine uptake and of ammonia and lactate production are similar. However, with the older inoculum, much higher metabolic activities are observed during the lag phase. The production of antibodies is delayed with increasing inoculum age, but the final antibody concentrations are similar, which indicates a higher specific antibody production rate when inoculating with older cells.     

Effects of the sea louse Lepeophtheirus salmonis on temporal changes in cortisol,sex steroids,growth and reproductive investment in Arctic charr Salvelinus alpinus

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean ±s.e . 0·15 ± 0·01 sea lice Lepeophtheirus salmonis g^?1 fish mass) (HI), medium (0·07 ± 0·00 sea lice g^?1 fish mass) (MI) or no [control (C)] sea‐lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml^?1; male c. 80 ng ml^?1). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex‐steroid concentrations were influenced negatively by sea‐lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea‐lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea‐lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.     

Growth and production of O+ bream (Abramis brama), O+ roach (Rutilus rutilus) and O+ carp (Cyprinus carpio) in 10 drainable 0.1 Ha ponds

In ten 0.1 ha drainable ponds O⁺ cyprinids were stocked to assess their impact on the aquatic community. Bream and roach were stocked in early June, 1986, and carp in early July, 1986. The ponds were drained mid November, 1986. The relationship between the fish community and its food resource was estimated in terms of production and consumption with use of the data on growth and mortality of the fish. The average gross production of the fish species in the ten ponds (48.4 kg during the experiment) was dominated by the carp (58.5%). A minimum estimate of the food consumption of the O⁺ cyprinids is 760 kJ.m^–2. The average production of bream and roach was much lower than that of carp due to a higher mortality and a more specialized feeding pattern. The gross productions of carp, bream and roach in the ten ponds were not significantly related, although stomach analysis showed diet overlap between the carp and the bream.     

沙棘对中国亚湿润干旱区的杨树人工林生长与生产力的影响(英文)

通过将沙棘(Hippophae rhamnoides L．)与3种杨树品种(小黑杨(Populus cv.“Xiaohei”),昭林6号杨(P．cv．“Zhaolin06”)和欧美杨64号(P．euramericane cv．“N3016”))的人工林分别按株混和行混两种方式进行混交实验,研究了固氮植物沙棘对亚湿润干旱区的杨树人工林生长和生产力的影响。研究结果表明：无论哪一种杨树品种或混交方式,沙棘与杨树混交后能显著地增加杨树人工林的生长量,林分平均胸径增加6％～38％,林分平均高增加8％～23％。在株混方式中,杨树地上部生物量大于杨树纯林的地上部生物量。但是在行混方式中,呈现相反的规律,这是由于行混方式中单位面积的杨树株数少。无论哪一种杨树品种或混交方式,杨树与沙棘混交林的地上部净生产力大于杨树纯林的地上部生产力。在株混和行混两种方式中,沙棘占总地上部净生产力的比例分别为20％和41％,但草本植物所占的比重很小。     

人工林生产力年龄效应及衰退机理研究进展

研究人工林生长规律具有重要的经济和生态意义。同龄林林分郁闭后,地上部净初级生产量随着林龄增加而降低的现象近几十年引起了林业工作者的兴趣和注意并成为研究热点。多数研究试图通过光合生理、林分营养、生物量分配和林分结构等随林龄的变化规律来解释林分生产力衰退机理。研究认为,林分郁闭后水分传输阻力的增加减少了树木的光合能力;林地养分的减少使得根系生物量分配增加,导致林分叶面积减少,树木光合能力下降;对资源的竞争使得树木优势度发生变化,资源利用率降低。光合能力、林分叶面积和资源利用率的降低以及根系生物量分配的增加是林分生产力衰退的关键,而林分呼吸和林木衰老的作用不大。今后深入研究树体水分运输及其补偿机制、逆境下根系的生长过程及适应机制,并跟踪研究林分生长规律,更有助于揭示人工林生产力衰退的实质。