Development of a hydrothermal time seed germination model which uses the Weibull distribution to describe base water potential

Seed germination has been modelled extensively using hydrothermal time (HTT) models, that predict time to germination as a function of the extent to which seedbed temperature, T, and water potential, Ψ, exceed the base temperature, T_b, and base water potential, Ψ_b, of each seed percentile, g. Within a seed population the variation in time to germination arises from variation in Ψ_b(g) modelled by a normal distribution. We tested the assumption of normality in the distribution of Ψ_b(g) by germinating seed of two unrelated species with non-dormant seed (Buddleja davidii (Franch.) and Pinus radiata D. Don) across a range of constant Ψ at sub-optimal T. When incorporated into a HTT model the Weibull distribution more accurately described both the right skewed distribution of Ψ_b(g) and germination time course over sub-optimal T than the HTT based on the normal distribution, for both species. Given the flexibility of the Weibull distribution this model not only provides a useful method for predicting germination but also a means of determining the distribution of Ψ_b(g).     

Analysis of annual fluctuations of C. nodosa in the Venice lagoon: Modeling approach

A simple simulation model was developed to describe the growth trends of Cymodocea nodosa (Ucria) Ascherson based on data sets from the Venice lagoon. The model reproduces the seasonal fluctuations in the above and belowground biomass and in shoot density. The modeling results are in good agreement with data on net production, growth rates and chemical–physical parameters of water. It was assumed that light and temperature are the most important factors controlling C. nodosa development, and that the growth was not limited by nutrient availability. The aim was to simulate biomass production as a function of external forcing variables (light, water temperature) and internal control (plant density). A series of simulation experiments were performed with the basic model showing that among the most important phenomena affecting C. nodosa growth are: (1) inhibition of production and recruitment of new shoots by high temperature and (2) light attenuation due to seasonal fluctuation.     

Climate, canopy conductance and leaf area development controls on evapotranspiration in a boreal coniferous forest over a 10-year period: A united model assessment

The aim of this work was to test a process-based model (hydrological model combined with forest growth model) on the simulation of seasonal variability of evapotranspiration (ET) in an even-aged boreal Scots pine (Pinus sylvestris L.) stand over a 10 year period (1999-2008). The water flux components (including canopy transpiration (E_t) and evaporation from canopy (E_c) and ground surface (E_g) were estimated in order to output the long-term stand water budget considering the interaction between climate variations and stand development. For validation, half-hourly data on eddy water vapor fluxes were measured during the 10 growing seasons (May-September). The model predicted well the seasonal course of ET compared to the measured values, but slightly underestimated the water fluxes both in non-drought and drought (2000, 2003 and 2006) years. The prediction accuracy was, on average, higher in drought years. The simulated ET over the 10 years explained, on average, 58% of the daily variations and 84% of the monthly amount of ET. Water amount from E_t contributed most to the ET, with the fractions of E_t, E_c and E_g being, on average, 67, 11 and 23% over the 10-year period, respectively. Regardless of weather conditions, the daily ET was strongly dependent on air temperature (T_a) and vapor pressure deficit (D_a), but less dependent on soil moisture (W_s). On cloudy and rainy days, there was a non-linear relationship between the ET and solar radiation (R_o). During drought years, the model predicted lower daily canopy stomatal conductance (g_cs) compared with non-drought years, leading to a lower level of E_t. The modeled daily g_cs responded well to D_a and W_s. In the model simulation, the annual LAI increased by 35% between 1999 and 2008. The ratio of E_c: ET correlated strongly with LAI. Furthermore, LAI reduced the proportion of E_g as a result of the increased share of E_c and E_t and radiation interception. Although the increase of LAI affected positively E_t, the contribution of E_t in ET was not significantly correlated with LAI. To conclude, although the model predicted reasonably well the seasonal course of ET, the calculation time steps of different processes in the model should be homogenized in the future to increase the prediction accuracy.     

Mechanisms of moisture stress in a mid-latitude temperate forest: Implications for feedforward and feedback controls from an irrigation experiment

While it is well established that stomata close during moisture stress, strong correlations among environmental (e.g., vapor pressure deficit, soil moisture, air temperature, radiation) and internal (e.g., leaf water potential, sap flow, root-shoot signaling) variables obscure the identification of causal mechanisms from field experiments. Models of stomatal control fitted to field data therefore suffer from ambiguous parameter identification, with multiple acceptable (i.e., nearly optimal) model structures emphasizing different moisture status indicators and different processes. In an effort to minimize these correlations and improve parameter and process identification, we conducted an irrigation experiment on red maples (Acer rubrum L.) at Harvard Forest (summers of 2005 and 2006). Control and irrigated trees experienced similar radiative and boundary layer forcings, but different soil moisture status, and thus presumably different diurnal cycles of internal leaf water potential. Measured soil moisture and atmospheric forcing were used to drive a transient tree hydraulic model that incorporated a Jarvis-type leaf conductance in a Penman–Monteith framework with a Cowan-type (resistance and capacitance) tree hydraulic representation. The leaf conductance model included dependence on both leaf matric potential, Ψ_L (so-called feedback control) and on vapor pressure deficit, D (so-called feedforward control). Model parameters were estimated by minimizing the error between predicted and measured sap flow. The whole-tree irrigation treatment had the effect of elevating measured transpiration during summer dry-downs, demonstrating the limiting effect that subsurface resistance may have on transpiration during these times of moisture stress. From the best fitted model, we infer that during dry downs, moisture stress manifests itself in an increase of soil resistance with a resulting decrease in Ψ_L, leading to both feedforward and feedback controls in the control trees, but only feedforward control for the irrigated set. Increases in the sum-of-squares error when individual model components were disabled allow us to reject the following three null hypotheses: (1) the f(D) stress is statistically insignificant (p = 0.01); (2) the f(Ψ_L) stress is statistically insignificant (p = 0.07); and (3) plant storage capacitance is independent of moisture status (p = 0.07).     

Comparison of absolute and relative growth patterns among five <Emphasis Type="Italic">Pinna nobilis</Emphasis> populations along the Tunisian coastline: an information theory approach

The variability in absolute and relative growth of Pinna nobilis along the Tunisian coastline was investigated. Five populations of P. nobilis were sampled, three from northern and two from eastern Tunisia. The specimens were aged and ten morphometric characters were measured on each individual. To test if differences existed in absolute and relative growth patterns among the different populations an information theory approach was followed. For absolute growth, von Bertalanffy, Gompertz, the logistic and the power models were fitted in combination with three assumptions regarding inter-population differences in absolute growth patterns: no differences, differences among all five populations or just between northern and eastern populations. The assumption of common absolute growth parameters among all five populations had the greatest support by the data, whereas the assumption of different growth patterns among all five populations had no support. Von Bertalanffy growth model and the power model were both equally supported by the data (while Gompertz had considerably less support and the logistic model had no support), and thus it may not be definitely concluded whether P. nobilis grows asymptotically or not. The P. nobilis populations of the Tunisian coastline had a slow growth and up to an age of ∼ 9 years their shells were smaller than from all other reported populations in the Mediterranean. For relative growth, apart from the classical allometric model Y = aX ^b , relating the size of a part of a body Y to another reference dimension X, more complicated models were used in combination with the three abovementioned assumptions regarding inter-population differences. Those models, of the form logY = f (logX), either assumed breakpoints in the relative growth trajectories or non-linearities. For most morphometric characters, the classical allometric model had no support by the data and more complicated models were necessary. In most cases, different relative growth either among all five populations or between the northern and eastern population groups was supported by the data. Further investigation is needed to relate the morphological differences observed among different populations of P. nobilis to environmental factors.     

RNA-DNA ratio: an index of larval fish growth in the sea

Data on water temperature, RNA-DNA ratio, and growth of eight species of temperate marine fish larvae reared in the laboratory were fit to the equation: $$G_{pi} = 0.93{\text{ }}\operatorname{T} + 4.75{\text{ RNA - DNA}} - 18.18$$ where G_pi is the protein growth rate in % d^-1 and T is the water temperature. Water temperature and larval RNA-DNA ratio explained 92% of the variability in growth rate of laboratory-reared larvae. The model is useful over the entire range of feeding levels (starvation to excess), temperatures (2° to 20°C) and fish species studied. Estimates of recent growth of larval cod, haddock, and sand lance caught at sea based on water temperature and RNA-DNA ratio ranged from negative to 26% d^-1. These data demonstrate the importance of food availability in larval fish mortality and suggest that short-term growth under favorable conditions may be considerably higher than expected from long-term indicators. RNA-DNA ratio analysis offers new possibilities for understanding larval growth and mortality, and their relation to environmental variability.     

Estimating Plecoglossus altivelis altivelis migration using a mass balance model expressed by hydrological distribution parameters in a major limpid river basin in Japan

We examined the influence of several hydrological and meteorological parameters on the migratory movements of ayu Plecoglossus altivelis altivelis in central Japan. When comprehensively evaluating rivers and ayu behaviour on a catchment scale, the subjects of analysis typically include human activities and hydrological and meteorological phenomena. However, limiting analyses to such factors may be too restrictive when human activities are being conducted. Accordingly, we incorporated a biological viewpoint into the evaluation method, analysing hydrological data (river discharge, river water temperature, sea water temperature) to determine watershed characteristics and examining the relationship between these characteristics and the habitat conditions of ayu. Then we constructed a numerical model for ayu migratory runs that incorporated ayu ecology and watershed characteristics. Analyses of ayu movements from a lower estuarine dam demonstrated that downstream displacements were associated with high water flows of more than 200 m³ s⁻¹ at the beginning of summer. We conclude that it is important to consider the effects of environmental parameters on the movements of different fish species to understand the causes of spatial variation in fish distribution in lowland rivers.     

Integrating effects of leaf nitrogen,age, rank,and growth temperature into the photosynthesis-stomatal conductance model LEAFC3-N parameterised for barley (Hordeum vulgare L.)

A crucial challenge for including biophysical photosynthesis–transpiration models into complex crop growth models is to integrate the plasticity of photosynthetic processes that is related to factors like nitrogen (N) content, age, and rank of leaves, or to the adaptation of plants to growth temperature (T_g). Here we present a new version of the combined photosynthesis-stomatal conductance model LEAFC3-N [Müller, J., Wernecke, P., Diepenbrock, W., 2005. LEAFC3-N: a nitrogen sensitive extension of the CO₂ and H₂O gas exchange model LEAFC3 parameterised and tested for winter wheat (Triticum aestivum L.). Ecological Modelling 183, 183–210.] that was revised, extended and completely re-parameterised for barley (Hordeum vulgare L.) with special regard for these factors to facilitate the use of the model in ecophysiological studies and in crop modelling. The analysis is based on novel comprehensive data on photosynthetic CO₂ and light response curves measured at two oxygen concentrations and different temperatures on leaves of barley (H. vulgare L.) differing in leaf N and chlorophyll content. Plants were grown in climatic chambers or in the field at different N and T_g.We thoroughly revised the existing and introduced new nitrogen relations for key model parameters that account for a linear increase with leaf N of V_max, J_max, T_p, and R_dmax (maximum rates of carboxylation, electron transport, triose phosphate export, and mitochondrial respiration), a saturation-type increase of φ (quantum yield of electron transport), and a non-linear decrease of θ and m (curvature of the light dependence of electron transport rate, scaling factor of the stomata model). The adaptation of photosynthetic characteristics to T_g was included into the model by linear relations that were observed between T_g and the activation energy ΔH_a of the temperature response characteristics of V_max, J_max, and T_p as well as of the nitrogen dependency of these characteristics. Based on an analysis of diurnal time courses of gas exchange rates it was found necessary including not only the relation between leaf water potential (Ψ) and stomatal conductance as used originally in LEAFC3, but additional effects on V_max and J_max. With the above-listed extensions, the model was capable to reproduce the observed plasticity and the recorded diurnal time courses of gas exchange rates fairly well. Thus, we conclude that the new model version can be used under a broad range of conditions, both for ecophysiological studies and as a submodel of crop growth models. The results presented here for barley will facilitate adapting photosynthesis models like LEAFC3-N to other C₃-species as well. The modelling of the effects of drought stress should be further elaborated in future based on more specific experiments.     

Modeling seasonal course of carbon fluxes and evapotranspiration in response to low temperature and moisture in a boreal Scots pine ecosystem

Environmental conditions act above and below ground, and regulate carbon fluxes and evapotranspiration. The productivity of boreal forest ecosystems is strongly governed by low temperature and moisture conditions, but the understanding of various feedbacks between vegetation and environmental conditions is still unclear. In order to quantify the seasonal responses of vegetation to environmental factors, the seasonality of carbon and heat fluxes and the corresponding responses for temperature and moisture in air and soil were simulated by merging a process-based model (CoupModel) with detailed measurements representing various components of a forest ecosystem in Hyytiälä, southern Finland. The uncertainties in parameters, model assumptions, and measurements were identified by generalized likelihood uncertainty estimation (GLUE). Seasonal and diurnal courses of sensible and latent heat fluxes and net ecosystem exchange (NEE) of CO₂ were successfully simulated for two contrasting years. Moreover, systematic increases in efficiency of photosynthesis, water uptake, and decomposition occurred from spring to summer, demonstrating the strong coupling between processes. Evapotranspiration and NEE flux both showed a strong response to soil temperature conditions via different direct and indirect ecosystem mechanisms. The rate of photosynthesis was strongly correlated with the corresponding water uptake response and the light use efficiency. With the present data and model assumptions, it was not possible to precisely distinguish the various regulating ecosystem mechanisms. Our approach proved robust for modeling the seasonal course of carbon fluxes and evapotranspiration by combining different independent measurements. It will be highly interesting to continue using long-term series data and to make additional tests of optional stomatal conductance models in order to improve our understanding of the boreal forest ecosystem in response to climate variability and environmental conditions.     

Demographic variation within spatially structured reef fish populations: when are larger-bodied subpopulations more important?

Environmental heterogeneity frequently induces spatial variability in somatic growth, which can cause inter-population differences in reproductive output among organisms for which fecundity is dependent upon body size. Mean asymptotic body size, L_∞, varies among populations of several reef fish species. Deterministic models suggest L_∞ has little effect on population growth, so subpopulations with larger L_∞ may not have disproportionate effects in sustaining an open system. We used a stochastic simulation model to examine the potential role of a larger L_∞ subpopulation in aspects of population dynamics beyond population growth under a range of assumptions about the prevailing recruitment relationships. We compared dynamics of a demographically homogeneous system with a system that included one subpopulation with 20% larger L_∞. Despite the magnitude of the increase in L_∞, mean population size and average time at large population sizes differed little between the homogenous system and that with the larger L_∞ subpopulation. However, including the larger L_∞ subpopulation did result in less time spent at very small population sizes, which could reduce extinction risks. Effects of the larger L_∞ subpopulation were most pronounced when a deterministic recruitment cycle was imposed in combination with high stochastic variability in recruitment. This was due to regular series of poor recruitment years shifting the population structure toward older cohorts where differences in body size (and reproductive output) between the larger L_∞ subpopulation and the other subpopulations were greatest. Differences were also greater when recruitment variability was regionally correlated. When recruitment variability was locally independent, the probability of system-wide declines was reduced because declines of individual populations at one time were replenished by unaffected neighbors in subsequent years. Our study suggests that variation in L_∞ within a network of interconnected subpopulations may not be an important determinant of population behavior under certain conditions, but might be important in coping with periods of persistent, system-wide recruitment failure.     

Introducing effects of temperature and CO2 elevation on tree growth into a statistical growth and yield model

Impacts of elevated temperature and CO₂ on tree growth were introduced into a statistical growth and yield model for Finnish conditions based on corresponding predictions obtained from a physiological growth model. This one-way link between models was made by means of species-specific transfer functions describing the increase in stem volume growth of trees as a function of elevated temperature and CO₂, stand density and the tree's competition status in a stand of Scots pine (Pinus sylvestris), silver birch (Betula pendula) and Norway spruce (Picea abies). This method allows the inner dynamics of the statistical model to be followed when the impacts of temperature and CO₂ elevation on tree growth are introduced into the calculation of volume growth and further allocated between diameter and height growth. In this way compatibility with previous predictions of tree growth by means of statistical models and related model systems under current climatic conditions could be retained.The performance of the statistical model with species-specific transfer functions was evaluated by comparing its predictions with corresponding predictions given by a physiological model under conditions of elevated temperature and CO₂. These calculations revealed that the growth response of individual trees to elevated temperature and CO₂ can be introduced into the statistical model from a physiological growth model with an outcome that results in fairly satisfactory growth responses at the stand level as well.     

Fitting a parabola to growth data of fishes and some applications to fisheries

Denoting a fish length or weight at age t by X _t , a reference age by t _m , and the corresponding fish length or weight by X _m , the relation between age and length or weight may be described by a parabola as follows: $$\left| {X_t } \right. - X_m \left| = \right.a + b(\left| {t - t_m } \right.\left| ) \right. + c(\left| t \right. - t_m \left| ) \right.^2$$ or $$X_t = A + b(\left| {t - t_m } \right.\left| ) \right. + c(\left| t \right. - t_m \left| ) \right.^2$$ where a, b and c are constants. Each of the above Eqs. describes one curve at ages older than t _m and another one at younger ages, which is made possible by means of the transformation of t to (|t-t _m |). In 2 cases out of 10, the parabola takes the form of a cubic equation. Evidence is given that, as the growth data become fewer, the better fit of the parabola or cubic equation will probably be less in comparison to the von Bertalanffy equation (1938, 1949) as developed by Beverton and Holt (1957) and the power-growth equation (Rafail, 1971), and vice versa. This growth equation is used to derive models for estimating the optimum age and yield for fish populations.     

Growth and life span of the small octopus Octopus tehuelchus in San Matías Gulf (Patagonia): three decades of study

Phenotypic plasticity in response to environmental variability is one of the main characteristics of cephalopods. This study compares growth and life span of Octopus tehuelchus in different coastal environments of San Matías Gulf (Patagonia) at three different periods. The progression of maturity jointly with modal progression analysis and the detection of hatchlings in the natural environment were used to differentiate cohorts and assign ages. Growth was described using the oscillatory von Bertalanffy growth model. Within San Antonio Bay, O. tehuelchus seems to have the most favourable conditions for an extended spawning season and the development of two sub-annual cohorts. O. tehuelchus growth is strongly seasonal with slow growth rates during winter. There were differences in the growth pattern between sites and particularly between sub-annual cohorts in San Antonio Bay. The growth pattern in each site seems to be similar along the last 26 years. The results of our study make evident the variability and plasticity of O. tehuelchus in response to the environment.     

Egg and early larval stages of Baltic cod, Gadus morhua, are robust to high levels of ocean acidification

The accumulation of carbon dioxide in the atmosphere will lower the pH in ocean waters, a process termed ocean acidification (OA). Despite its potentially detrimental effects on calcifying organisms, experimental studies on the possible impacts on fish remain scarce. While adults will most likely remain relatively unaffected by changes in seawater pH, early life-history stages are potentially more sensitive, due to the lack of gills with specialized ion-regulatory mechanisms. We tested the effects of OA on growth and development of embryos and larvae of eastern Baltic cod, the commercially most important fish stock in the Baltic Sea. Cod were reared from newly fertilized eggs to early non-feeding larvae in 5 different experiments looking at a range of response variables to OA, as well as the combined effect of CO₂ and temperature. No effect on hatching, survival, development, and otolith size was found at any stage in the development of Baltic cod. Field data show that in the Bornholm Basin, the main spawning site of eastern Baltic cod, in situ levels of pCO₂ are already at levels of 1,100 μatm with a pH of 7.2, mainly due to high eutrophication supporting microbial activity and permanent stratification with little water exchange. Our data show that the eggs and early larval stages of Baltic cod seem to be robust to even high levels of OA (3,200 μatm), indicating an adaptational response to CO₂.     

A new method for high-resolution bivalve growth rate studies in hydrothermal environments

The age and shell growth rate of deep-sea hydrothermal bivalves were investigated for the first time using in situ chemical staining combined with high-resolution micro-increment analysis. A staining chamber developed for this purpose was applied to a patch of Bathymodiolus thermophilus mussels at 2,500 m depth at the 9°47′N vent field on the East Pacific Rise (EPR) in May 2010. This approach minimizes disturbance of the mussels in their habitat. Bathymodiolus thermophilus grows according to a circalunidian rhythm, with one increment formed each day, and displays tide-related growth rate variability. Based on the von Bertalanffy growth rate model, the largest shell collected (SL = 20.5 cm) would be 10.0 year old, with a growth rate of 4.2–1.1 cm year^?1 as the shell ages. This fast growth rate is consistent with the instability of the environment in this section of the EPR and observed recolonization rates and could reflect a specific adaptation of this species.     

Evaluating weather effects on interannual variation in net ecosystem productivity of a coastal temperate forest landscape: A model intercomparison

Forest productivity is strongly affected by seasonal weather patterns and by natural or anthropogenic disturbances. However weather effects on forest productivity are not currently represented in inventory-based models such as CBM-CFS3 used in national forest C accounting programs. To evaluate different approaches to modelling these effects, a model intercomparison was conducted among CBM-CFS3 and four process models (ecosys, CN-CLASS, Can-IBIS and 3PG) over a 2500 ha landscape in the Oyster River (OR) area of British Columbia, Canada. The process models used local weather data to simulate net primary productivity (NPP), net ecosystem productivity (NEP) and net biome productivity (NBP) from 1920 to 2005. Other inputs used by the process and inventory models were generated from soil, land cover and disturbance records. During a period of intense disturbance from 1928 to 1943, simulated NBP diverged considerably among the models. This divergence was attributed to differences among models in the sizes of detrital and humus C stocks in different soil layers to which a uniform set of soil C transformation coefficients was applied during disturbances. After the disturbance period, divergence in modelled NBP among models was much smaller, and attributed mainly to differences in simulated NPP caused by different approaches to modelling weather effects on productivity. In spite of these differences, age-detrended variation in annual NPP and NEP of closed canopy forest stands was negatively correlated with mean daily maximum air temperature during July-September (T_amax) in all process models (R² = 0.4-0.6), indicating that these correlations were robust. The negative correlation between T_amax and NEP was attributed to different processes in different models, which were tested by comparing CO₂ fluxes from these models with those measured by eddy covariance (EC) under contrasting air temperatures (T_a). The general agreement in sensitivity of annual NPP to T_amax among the process models led to the development of a generalized algorithm for weather effects on NPP of coastal temperate coniferous forests for use in inventory-based models such as CBM-CFS3: NPP′ = NPP − 57.1 (T_amax − 18.6), where NPP and NPP′ are the current and temperature-adjusted annual NPP estimates from the inventory-based model, 18.6 is the long-term mean daily maximum air temperature during July-September, and T_amax is the mean value for the current year. Our analysis indicated that the sensitivity of NPP to T_amax was nonlinear, so that this algorithm should not be extrapolated beyond the conditions of this study. However the process-based methodology to estimate weather effects on NPP and NEP developed in this study is widely applicable to other forest types and may be adopted for other inventory based forest carbon cycle models.     

Effects of changing climate on water and nitrogen availability with implications on the productivity of Norway spruce stands in Southern Finland

An integrated process-based model was used to study how the changing climate affects the availability of water and nitrogen, and consequently the dynamics of productivity of Norway spruce (Picea abies) on sites with different initial soil water conditions in southern Finland over a 100-year period. The sensitivity of the total stem volume growth in relation to short-term availability of water and nitrogen was also analyzed. We found that a high proportion (about 88–92%) of the total precipitation was lost in total evapotranspiration (incl. canopy evaporation (E_c), transpiration (E_t) and ground surface evaporation (E_g)), under both current and changing climate. Furthermore, under the changing climate the cumulative amount of E_c and E_g were significantly higher, while E_t was largely lower than under the current climate. Additionally, the elevated temperature and increased expansion of needle area index (L) enhanced E_c. Under the changing climate, the increasing soil water deficit (W_d) reduced the canopy stomatal conductance (g_cs), the E_t, humus yield (H, available nitrogen source) and nitrogen uptake (N_up) of the trees. During the latter phases of the simulation period, the canopy net photosynthesis (P_nc) was lower due to the reduced N_up and soil water availability. This also reduced the total stem volume production (V_s) on the site with the lower initial soil moisture content. The growth was slightly more sensitive to the change in precipitation than to the change in nitrogen content of the needles, when the elevated temperature was assumed. According to our findings, drought stress episodes may become more frequent under the changing climate. Thus, adaptive management strategies should be developed to sustain the productivity of Norway spruce in these conditions, and thus, to mitigate the adverse impacts of climate change.