Changes in log quality at different decay stages in an alpine forest

倒木是高寒森林生态系统重要的碳(C)库和养分库,其不同分解阶段的质量变化,是认识倒木分解过程中C和养分释放的重要基础。以一个分解序列的岷江冷杉(Abies faxoniana)倒木为研究对象,研究了心材、边材和树皮在5个分解阶段的C:N:P化学计量特征,以及木质素和纤维素含量动态。结果显示:I至III分解阶段,随着分解程度加深,树皮C含量升高,而心材和边材C含量降低,从IV分解阶段开始倒木各组分C含量均开始显著降低。除III分解阶段的心材外,倒木各组分N含量总体表现为随着分解程度加深而增加的趋势,除边材N含量在V分解阶段时显著升高外,其余组分均未达到显著性水平。心材和树皮P含量表现为先降后升的变化趋势,最小值分别出现在III和II分解阶段;边材P含量表现为随着分解程度加深而增加。在同一分解阶段,树皮相对于边材和心材均具有最低的C:N:P化学计量比,易分解比例Fm也表明树皮更易于分解。边材在I和II分解阶段的C:N:P化学计量比最高,心材在III到V分解阶段C:N:P化学计量比最高。心材C:P、树皮和边材的C:N和C:P临界值与N和P的初始值成反比。纤维素含量随着倒木分解而降低,不同分解阶段的纤维素含量表现为:心材>边材>树皮;但木质素含量随着分解程度加深而增加,表现为:树皮>边材>心材;倒木3个组分纤维素含量下降均快于木质素,此外,IV和V分解阶段的树皮木质素与纤维素比值显著增高,且一直处于较高水平。统计分析结果表明:倒木N含量显著影响不同分解阶段木质素和纤维素分解。由生态化学计量学理论推测:树皮分解前期易受N限制,整个分解阶段均易受P限制,心材和边材在整个分解阶段均易受N和P限制。     

Wood decomposition in an abandoned beech and oak coppiced woodland in SE England

The rate of litter decomposition is often expressed as a constant decay rate (k; g g⁻¹ yr⁻¹) or as the time required for a certain percentage (often 95% and estimated as 3/k) of it to decompose (termed turnover time). Estimates of k may be obtained by determining the weight loss of litter in the field and also by assuming a steady state and obtaining the ratio of litter input: standing crop. Both methods were used to estimate decay rate and turnover times for beech and oak branches and twigs decomposing on the forest floor and these were critically evaluated.
Considerable variation, ranging between 1.8–144.5 yr, was found between the 95% turnover time estimates of various size components of the two species, obtained from woodfall and standing crop data. Likewise variation in decay rate of 2–2.5 cm diameter beech branches, estimated from field experiments, was large both between and within groups of branches categorised according to initial state of decay and presence or absence of bark. The mean annual decay rate for the various categories ranged between k = 0.165-0.452 g g⁻¹yr⁻¹. Branches without bark generally decomposed more slowly than those with bark. Beech twig (<0.5 cm diameter) decomposition rates, from field experiments, ranged between k = 0.149-0.220 g g⁻¹yr⁻¹ and variation was relatively low compared with that of branches. No significant differences (P<0.05)were detected between twig decomposition rates obtained from experiments initiated at different seasons although there was a slight decline in decay rate in winter months. Twig and branch decomposition rates fell within the range found in the few other comparable studies.     

Effects of decay classes and diameter classes on physico-chemical properties of Pinus koraiensis log in a typical mixed broadleaved-Korean pine forest

AimsLog is an important component for most of forest ecosystems. It plays crucial roles in maintaining soil fertility, sustaining biodiversity and cycling of carbon (C) and nutrient. However, physico-chemical properties of logs vary with decay classes and diameter classes. Our objective was to study effects of decay classes and diameter classes on physico-chemical properties of logs in a typical mixed broadleaved-Korean pine forest in northern China.MethodsIn this study, logs of Pinus koraiensis were chosen as it was the constructive species in the typical mixed broadleaved-Korean pine forest. Logs of P. koraiensis at each decay classes (I-V) were divided into four diameter classes, including diameter class i ≤ 10.0 cm, diameter class ii: 10.1-30.0 cm, diameter class iii: 30.1-50.0 cm, and diameter class iv > 50.0 cm. Then, we explored effects of different decay classes, diameter classes and their interactions on the physico-chemical properties of logs for both the heartwood and sapwood.Important findings The results showed that the physico-chemical properties of heartwood and sapwood generally exhibited similar variations. Their moisture content both increased with an increasing decay class, whereas wood density both decreased with an increased decay class and diameter class. The carbon concentrations of the sapwood showed a trend of gradual increasing during decomposition, and there was an accumulation in nitrogen (N) and phosphorus (P) concentrations of the heartwood and sapwood with an increased decay class, simultaneously. Only N and P concentrations of the heartwood increased and then decreased with an increasing diameter class. The cellulose content decreased with an increasing decay class. In contrast to the cellulose, the lignin content increased with an increased decay class. However, cellulose and lignin contents exhibited no distinct trend among diameter classes. The moisture content of logs had a significant positive correlation with C, N, P concentrations and lignin content (except P concentrations of the heartwood), but had a significant negative correlation with the cellulose content (p< 0.05). The wood density was negatively correlated with C, N, P concentrations and the lignin content, but it was positively correlated with the cellulose content (p< 0.05). Therefore, physico-chemical properties of logs had unique patterns along both decay classes and diameter classes, and the physical properties of logs (the moisture content and wood density) were important factor affecting the variations of their chemical contents.     

腐烂等级、径级对典型阔叶红松林红松倒木物理化学性质的影响

倒木是森林生态系统的重要组成部分, 在地力维护、生物多样性保持以及碳(C)和养分循环等方面具有重要意义, 但倒木物理化学性质随其腐烂等级和径级而变化。为了深入理解腐烂等级和径级对倒木物理化学性质的影响, 该研究以典型阔叶红松林的建群种——红松(Pinus koraiensis)的倒木为研究对象, 将其每个腐烂等级(I-V)下的倒木分为4个径级(径级i ≤ 10.0 cm、径级ii 10.1-30.0 cm、径级iii 30.1-50.0 cm、径级iv >50.0 cm), 研究了不同腐烂等级、径级及两者交互作用对倒木心材和边材物理化学性质的影响。结果表明: 心材和边材具有相似的变化规律。倒木心材和边材含水率随着腐烂等级增加而增加, 而木材密度随腐烂等级和径级的增加均呈下降趋势; 边材C含量以及心材和边材的氮(N)、磷(P)含量随腐烂等级增加呈上升趋势, 心材N、P含量随径级增加呈先增加后减少的趋势; 纤维素含量随腐烂等级增加呈下降趋势, 而木质素含量呈上升趋势, 纤维素和木质素含量随径级增加没有明显变化规律。倒木含水率与C、N、P、木质素含量(除心材P含量)显著正相关, 与纤维素含量显著负相关; 木材密度与C、N、P、木质素含量显著负相关, 与纤维素含量显著正相关。由此可见, 倒木物理化学性质受不同腐烂等级和径级的影响有各自的变化规律, 且倒木的物理性质(含水率和木材密度)是影响化学含量变化的重要因素。     

Species turnover on a protected subtropical barrier island: a long-term study

Abstract. The commercial development that threatens the biodiversity of coastal habitats is particularly severe along the sandy shores of subtropical Florida. The objective of our study was to test the applicability of the equilibrium theory of island biogeography to Cayo-Costa Island, the largest protected barrier island remaining in peninsular Florida. Our null hypothesis was that there would be no change in the number and composition of native vascular plant species on Cayo-Costa 15 years after the first inventory of the island's flora. Our reinventory documents a total of 230 native species in 1990–92 compared to 255 native species in 1975–77. Immigrants were represented by twenty-eight new species, while extinctions totalled fifty-three species. These results indicate a turnover rate of approximately 2.7 species yr^-1 with an extinction rate of 3.5 species yr^-1 and an immigration rate of 1.9 species yr^-1. The net loss of 1.6 species yr^-1 suggests a non-equilibrium condition that is not readily explained by changes in habitat diversity associated with the documented patterns of shoreline erosion and deposition. Cayo-Costa's net loss of twenty-five native species (including one tree species and four shrub species) was localized mainly in those habitats where there had been a significant increase in the relative abundance of the naturalized weedy exotic species Schinus terebinthifolius and Casuarina equisetifolia . We conclude that the spread of naturalized weedy species limits the applicability of the equilibrium theory of island biogeography to species-rich subtropical barrier islands, even in cases where the islands are protected from human disturbance.     

Densities and energetics of two streamliving larval populations of Sericostoma personatum (Trichoptera)

Two populations of Sericostoma personatum Spence were studied during one year in two first order woodland streams, varying in water flow and temperature regime. The life cycles look two and three years, respectively.
Numbers in drift varied with water flow, and daily elimination rates of about 1% due to catastrophic drift were found in one of the streams. Differences in elimination rates between the two populations are discussed in relation to predation, catastrophic drift, and quantity of food present during the year.
The production was about 0.9 g AFDW m^-2 yr^-1 in both streams, 20–22% of which was production of cases. P/B ratios were 2.4 and 3.8, and reflect differences in life cycle.
Total potential leaf consumption was estimated to about 50 g AFDW m^-2 yr^-1 in both streams, which makes up about 10% of yearly leaf input. The seasonal pattern of the consumption is discussed in relation to biomass, temperature and leaf input. There was little agreement between the patterns of leaf input and leaf consumption.     

人工长白落叶松树干边材、心材和树皮密度预测模型

基于黑龙江省林口林业局、东京城林业局和东北林业大学帽儿山实验林场的35株人工长白落叶松的解析样木数据,构建长白落叶松的边材、心材和树皮密度的Beta回归模型,采用赤池信息准则、决定系数、平均绝对偏差、均方根误差和似然比检验对模型的拟合优度进行比较评价,进而选取边材、心材和树皮密度的最优模型,最后采用刀切法对选择出的最优模型进行检验,评价模型预测能力。结果表明: 边材、心材和树皮密度的最优模型的自变量不完全相同,其中,边材密度与树木年龄、树高、相对高度和相对高度的平方关系较好,而心材密度最优模型的自变量为年生长量、相对高度和相对高度的平方,树皮密度最优模型的自变量为树木年龄、年生长量、相对高度和相对高度的平方。对最优模型分析可知,从树干基部到树梢,边材密度逐渐减小,心材密度先减小后增加,树皮密度先增加后减小。本研究所建立的Beta回归模型可以预估该研究区域的人工林内长白落叶松的边材、心材和树皮任意位置的木材密度,为树干平均密度和生物量的研究奠定基础。     

The Impact of Sheep Grazing on Net Nitrogen Mineralization Rate in Two Temperate Salt Marshes

Abstract: Nitrogen mineralization rate was studied in grazing trials with three different stocking rates (0, 3, 10 sheep ha^-1) in two man-made salt marshes, viz. a Puccinellia maritima -dominated low salt marsh and a high salt marsh dominated by Festuca rubra. Mineralization rates were derived from the amounts of mineral N which accumulated in situ during six-week incubation periods in tubes containing undisturbed soil cores from the upper 10 cm soil layer. The annual rates of net N mineralization were significantly higher in the better drained, high salt marsh (71 - 81 kg ha^-1 yr^-1) than in the low salt marsh (39 - 49 kg ha^-1 yr^-1). High amounts of belowground litter accumulated in the low salt marsh due to frequent water logging. Both N mineralization and nitrification rate were negatively correlated with soil water content. In the Puccinellia maritima salt marsh, grazing had neither an effect on N mineralization rates during any of the incubation periods nor on annual mineralization rates. In the Festuca rubra salt marsh, N mineralization rates increased earlier during spring at the intensively grazed site than at the moderately grazed and the ungrazed site. N mineralization and nitrification rates were significantly higher at the ungrazed site than at the intensively grazed site during the period of peak net N mineralization from the end of April until mid-June. Although sheep grazing affected the seasonal pattern of N mineralization in the high marsh, grazing did not affect the annual rate of net N mineralization.     

高山森林林窗和生长基质对苔藓植物氮和磷含量的影响

苔藓在森林生态系统养分富集和循环方面有重要作用,苔藓植物在氮磷循环中的作用可能受到森林更新和生长基质的影响.为理解苔藓在森林生态系统养分循环中的作用,研究了高山森林不同位置(林窗中心、林窗边缘、林下)和不同生长基质(活立木、倒木、枯立木、大枯枝、根桩、地表)上的苔藓植物氮磷含量.结果表明:地表苔藓氮含量(3.12 mg·g^-1)显著低于其他生长基质上的苔藓,尽管枯立木附生苔藓氮含量高达17.41 mg·g^-1,但倒木、大枯枝、枯立木和活立木苔藓氮含量差异不显著;最高(1.09 mg·g^-1)和最低(0.61 mg·g^-1)的磷含量分别出现在森林地表和枯立木的苔藓,且森林地表的苔藓磷含量显著高于其他生长基质上的苔藓,但倒木、大枯枝、根桩和活立木上的苔藓磷含量差异不显著.林窗位置显著影响了倒木和大枯枝上的苔藓氮、磷含量,林窗内倒木和大枯枝上的苔藓氮、磷含量显著高于林窗边缘.粗木质残体的类型、腐烂等级对苔藓氮、磷含量的影响存在差异,两者交互作用的影响显著;第Ⅴ腐烂等级倒木上的苔藓氮含量显著高于其他腐烂等级;第Ⅲ腐烂等级大枯枝上的苔藓氮含量显著高于其他腐烂等级;第Ⅱ腐烂等级倒木上的苔藓磷含量显著高于其他腐烂等级;第Ⅳ腐烂等级枯立木上的苔藓磷含量显著高于其他腐烂等级.可见,森林林窗更新和粗木质残体腐解过程会影响苔藓植物的氮、磷含量,同时影响森林生态系统的养分循环过程.     

Fungal wood decomposer activities influence community structures of myxomycetes and bryophytes on coarse woody debris

Dead wood is an important habitat for forest organisms, and wood decay fungi are the principal agents determining the dead wood properties that influence the communities of organisms inhabiting dead wood. In this study, we investigated the effects of wood decomposer fungi on the communities of myxomycetes and bryophytes inhabiting decayed logs. On 196 pine logs, 72 species of fungi, 34 species and seven varieties of myxomycetes, and 16 species of bryophytes were identified. Although white rot was the dominant decay type in sapwood and heartwood, brown and soft rots were also prevalent, particularly in sapwood. Moreover, white rot and soft rot were positively and brown rot negatively correlated with wood pH. Ordination analyses clearly showed a succession of cryptogam species during log decomposition and showed significant correlations of communities with the pH, water content, and decay type of wood. These analyses indicate that fungal wood decomposer activities strongly influence the cryptogam communities on dead wood.     

A modified drop-net method for sampling mobile epifauna on marine shallow sandy bottoms

The seasonal variations in numbers and biomass of the mobile epifauna of a shallow, sandy bay in Gullmar Fjord (Sweden) was investigated during 1976–1977 using the drop-net technique. Juvenile plaice, Pleuronectes platessa L., sand goby, Pomatoschistus minutus (Pallas), and brown shrimp Crangon crangon L. are the dominant epifaunal species. A net enclosing an area of 100 m² was used, and the organisms captured were collected with a small trawl. Three stations with a water depth≤ 1 m were regularly sampled with a total number of 73 drops. Maximum abundance was for plaice in June (6 ind m^-2), for the shrimp in July-August (61 ind m^-2), and for sand goby in September (2 ind m^-2). Standing stocks (dry wt) were 0.2, 1.5 and 0.2 g m^-2 respectively. Production estimates were based on seasonal changes in size frequency and information on specific growth rates. The production rate was for plaice (0-group) 0.3 g m^-2 yr^-1, for the shrimp 1.5, and for sand goby 0.2 g m^-2 yr^-1. Reliable estimates of the absolute abundance can be derived from the mean catch per unit area only when the efficiency of the fishing gear is known. After 6 hauls with the trawl in the drop-net enclosure more than 85% of the shrimps were caught and after the fifteenth haul less than 1% were still left. The fishing efficiency of a push-net in relation to the drop-net was for the shrimp 50%, for plaice 35% and for sand goby 17%.     

Water balance of conifer logs in early stages of decomposition

Seasonal and long-term changes in the water balance of conifer logs during the first 8 years of decomposition were studied in an old-growth Pseudotsuga/Tsuga forest in the Oregon Cascade Mountains. Measurements were made of the moisture content of outer bark, inner bark, sapwood, and heartwood and of the flow of water into and out of logs of four species (Abies amabilis, Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla). After the logs had decomposed from 1 to 2 years, 38–47% of the canopy throughfall landing upon them ran off the surface, 29–34% leached from the bottom, and 21–30% was absorbed and evaporated. After 8 years of decomposition, water entering and then leaching from logs increased 1.3 times while runoff decreased a similar amount. The proportion of water stored by and evaporated from logs in this study indicates that in old growth forests they may intercept 2–5% of the canopy throughfall to the forest floor and that, even in early stages of decomposition, they may affect the hydrological cycle of Pacific Northwest old-growth forests.This is paper 2945 of the Forest Research Laboratory, Oregon State University, Corvallis     

Radial and vertical variation of wood nutrients in Bornean tropical forest trees

Nitrogen, phosphorus, potassium, calcium, and magnesium concentrations in woody tissue are poorly documented, but are necessary for understanding whole-tree nutrient use and storage. Here, we report how wood macronutrient concentrations vary radially and along the length of a tree for 10 tropical tree species in Sabah, Malaysia. Bark nutrient concentrations were consistently high: 2.9–13.7 times greater than heartwood depending on the nutrient. In contrast, within the wood both the radial (sapwood vs. heartwood) and vertical (trunk bottom vs. trunk middle) variation was modest. Higher concentrations in sapwood relative to heartwood provide empirical support for wood nutrient resorption during sapwood senescence. Dipterocarp species showed resorption rates of 25.3 ± 7.1% (nitrogen), 62.7 ± 11.9% (phosphorus), and 56.2 ± 12.5% (potassium), respectively, while non-dipterocarp species showed no evidence of nutrient resorption in wood. This suggests that while dipterocarps have lower wood nutrient concentrations, this family is able to compensate for this by using wood nutrient resorption as an efficient nutrient conservation mechanism. In contrast to other nutrients, calcium and magnesium tended to accumulate in heartwood. Wood density (WD) showed little vertical variation along the trunk. Across the species (WD range of 0.33 to 0.94 mg/cm³), WD was negatively correlated with wood P and K concentration and positively correlated with wood Ca concentration. As our study showed exceptionally high nutrient concentrations in the bark, debarking and leaving the bark of the harvested trees on site during logging operations could substantially contribute to maintaining nutrients within forest ecosystems.     

The effect of moisture potential on growth and survival of root nodule bacteria in peat culture and on seed

Peat from three sources was dried, milled and packed separately in polyethylene bags and sterilized by irradiation. The carrier was impregnated with broth cultures of either Rhizobium leguminosarum bv. trifolii strain WU95, Bradyrhizobium japonicum strain CB1809 or B. lupini strain WU425 and sterile water to provide five moisture potentials in the range > - 1 × 10⁴ - 1 × 10⁶ Pa. The packets were stored at 26°C under conditions which restricted moisture loss. Numbers of root nodule bacteria were counted at intervals up to 12 weeks. No single moisture potential was optimum for all strains in all carriers because of a significant ( P < 0.05) interaction between moisture potential × strain × carrier × time. Where direct comparisons could be made, all strains survived best at - 1 × 10⁴ and/or −3.2 × 10⁴ Pa. Seeds of Trifolium subterraneum and polypropylene beads (used to avoid seed coat toxicity), were inoculated with WU95 prepared in two sources of peat and at each of the above moisture potentials and stored at 15°C. Seed coat toxicity significantly effected the log death rate ( k ) of WU95 on subterraneum clover seed for the period 0–0.25 d ( k 1.796) compared with k - 0.399 for polypropylene beads. In the first 24 h moisture did not affect survival but by 28 d rhizobia grown in Badenoch peat survived best at −3.2 × 10⁴ Pa. In Millicent peat, survival was equally as good at −3.2 × 10⁴ and −1 × 10⁴ Pa.     

Acetylene reduction in conifer logs during early stages of decomposition

Acetylene reduction was examined periodically for as long as 68 months in the outer and inner bark, sapwood, and heartwood of decaying logs of western hemlock [Tsuga heterophylla (Raf.) Sarg.] western redcedar (Thuja plicata D. Don), Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], and Pacific silver fir (Abies amabilis Dougl. ex Forbes) in the western Oregon Cascade Mountains. Tissues from freshly cut logs from sound trees were unable to reduce acetylene. However, after 18 months of decomposition, acetylene reduction was found in all log tissues except heartwood. Over the 68-month study period, no significant relationship between reduction rate and tissue moisture was found. Acetylene reduction rates differed significantly among tissues, log species, and time of exposure to decomposers. Although acetylene reduction generally showed a steady increase with time, tissues of some species showed a more complex, nonlinear pattern of change. Although the amount of nitrogen fixed is low compared to the total present in decaying logs, it might be an important source of readily available nitrogen for the microbiota responsible for decomposition.Paper 2587, Forest Research Laboratory, Oregon State University, Corvallis.Paper 2587, Forest Research Laboratory, Oregon State University, Corvallis.     

Wood decomposition in an abandoned beech and oak coppiced woodland in SE England

Stand structure and rates and patterns of wood litterfall, between 23 June 1977 and 27 June 1979, are described for two sites In a coppiced beech Fagus sylvatica L. and oak Quercus petraea (Mattuschka) Liebl. woodland in south-east England.
Total wood fall (excluding trunks) was estimated at 1264 kg ha⁻¹ and 593 kg ha⁻¹ for the two years of sampling at one site and 776 kg ha⁻¹ during the second year on the other site. The majority of leaf fall occurred in autumn; the maximum twig (wood < 1 cm diameter) and branch (wood ≥ 1 cm diameter) fall, occurred in winter at times generally corresponding with high wind speeds. Many oak twigs, however, abscissed in early November irrespective of wind speed.
Branch characteristics at fall (size, state of decay and bark cover) were documented. The most significant feature observed was that a large amount of decay frequently occurred in branches whilst still in the canopy.     

Biological nitrogen fixation in coniferous forest watershed areas in Central Sweden

An investigation on biological nitrogen fixation in the forest floor was carried out in five watershed areas in Central Sweden during the summers 1978 and 1979. Five different types of bottom layers with underlying soil horizons were investigated for nitrogen fixation. An inventory on the occurrence of potential nitrogen fixing lichens and alder trees was also carried out.
Low fixation rates were determined in mesic-soil mosses, F/H,layers and mineral soil. Though two orders of magnitude higher than in mesic-soil mosses, the nitrogen fixation in the investigated Sphagnum mosses must be considered as low, probably due to absence of blue-green algal associations. The contribution to total nitrogen fixation by lichens is low, but Alnus incana may play an important role. The estimated biological nitrogen fixation calculated as a weighted mean over the five watersheds is in the order of 0.5 kg N ha^-1 yr^-1.     

Small scale variation in decay rate within logs one year after felling: Effect of fungal community structure and moisture content

Abstract Fungal species composition, moisture content, percentage weight loss, and instantaneous decay rate (expressed by rate of CO₂ evolution) was assessed for a total of 186 8 cm³ cubes from 10 beech logs which had been decomposing on the forest floor for 14 months. There was considerable within and between branch variation in decay rate and water content. Water content at the time of sampling was not directly correlated with percentage weight loss or instantaneous decay rate, nor was it correlated with position in the log. However, wood occupied by Ascomycotina (other than Nectria ) tended to be drier than that occupied by Basidiomycotina. In particular wood occupied by Xylaria hypoxylon was drier than that occupied by all other species, although wood in which X. hypoxylon was replacing other fungi was wetter than when X. hypoxylon was alone. Variation in percentage weight loss could not be explained in terms of water content and fungal species composition at the time of sampling, but variation in instantaneous decay rate could. Thus, decay rate by Ascomycotina was significantly less ( P < 0.05) than by Basidiomycotina, and rate of CO₂ evolution from wood occupied by X. hypoxylon alone was significantly slower than from wood in which X. hypoxylon was replacing H. fragiforme or Nectria . The latter was partially correlated with water content but whether this is a cause and effect relationship is uncertain.     

Ecology and exploitation pattern of a landlocked population of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece)

Age, growth, mortality and exploitation pattern of sand smelt, Atherina boyeri (Risso 1810), in Trichonis Lake (western Greece) were studied from samples taken from catches of local fishermen. Individuals ranged between 44 and 109.53 mm in total length (TL). Age determinations based on scale readings show that the population has a 4-year life cycle. Sand smelt grows allometrically (b=3.18) and relatively rapidly, achieving 52.3% of the growth during the first year; thereafter the annual growth rate drops quickly. The von Bertalanffy growth parameters for all individuals are: L_∞=112.40 mm, k= 0.42 years⁻¹και t_o=−0.40 years. The total mortality rate was Z=1.65 years⁻¹ and the natural mortality rate M=1.07 years⁻¹. The exploitation rate indicates that the population is rather underexploited (E=0.35).     

Growth and growth substrate levels in spinach under non-steady state conditions of nitrogen nutrition and light

Spinach plants ( Spinacia oleracea L. cv. Subito) were grown in a complete nutrient solution under ample light intensity (14 h day⁻¹ at 660 μmol m⁻² s⁻¹) before being transferred either to a minus-N solution (experiment 1), or to limiting light conditions (6 h day⁻¹ at 220 μmol m⁻² s⁻¹; experiment 2). Shoot growth in experiment 1 decreased significantly from 0.24 day⁻¹ to 0.07 day⁻¹ after the fourth day of transfer. Root relative growth rate increased after 1 day from 0.25 to 0.31 day⁻¹, but decreased on the fifth day after transfer to 0.11 day⁻¹. Shoot growth in experiment 2 decreased significantly from 0.25 to 0.17 day⁻¹ after the fourth day of transfer, while root growth decreased to half of its original level (0.25 day⁻¹) already on the second day. Growth substrate levels in the plants (free sugars, free amino acids) and starch levels depended on the plant age, the moment in the diurnal cycle, and the imposed treatment. Fluctuations in shoot growth or root growth resulting from the light or N limitation could not be explained by a correspondent increase or decrease in the levels of growth substrates. The hypotheses underlying the functional equilibrium theory, assuming shoot and root growth to be controlled by N- and C-containing substrates respectively, and several other growth and partitioning models are therefore questioned. A neglect of the osmotic role of the free sugars in these models might be the explanation for this.