Non-linear Growth Responses Research Articles

Particle-based model shows complex rearrangement of tissue mechanical properties are needed for roots to grow in hard soil.

When exposed to increased mechanical resistance from the soil, plant roots display non-linear growth responses that cannot be solely explained by mechanical principles. Here, we aim to investigate how changes in tissue mechanical properties are biologically regulated in response to soil strength. A particle-based model was developed to solve root-soil mechanical interactions at the cellular scale, and a detailed numerical study explored factors that affect root responses to soil resistance. Results showed how softening of root tissues at the tip may contribute to root responses to soil impedance, a mechanism likely linked to soil cavity expansion. The model also predicted the shortening and decreased anisotropy of the zone where growth occurs, which may improve the mechanical stability of the root against axial forces. The study demonstrates the potential of advanced modeling tools to help identify traits that confer plant resistance to abiotic stress.

Functional Adaptation of LPS-affected Dentoalveolar Fibrous Joints in Rats.

The functional interplay between cementum of the root and alveolar bone of the socket is tuned by a uniquely positioned 70-80µm wide fibrous and lubricious ligament in a dentoalveolar joint (DAJ). In this study, structural and biomechanical properties of the DAJ, periodontal ligament space (PDL-space also known as the joint space), alveolar bone of the socket, and cementum of the tooth root that govern the biomechanics of a lipopolysaccharide (LPS)-affected DAJ were mapped both in space and time. The hemi-maxillae from 20 rats (4 control at 6weeks of age, 4 control and 4 LPS-affected at 12weeks of age, 4 control and 4 LPS-affected at 16weeks of age) were investigated using a hybrid technique; micro-X-ray computed tomography (5µm resolution) in combination with biomechanical testing in situ. Temporal variations in bone and cementum volume fractions were evaluated. Trends in mineral apposition rates (MAR) in additional six Sprague Dawley rats (3 controls, 3 LPS-affected) were revealed by transforming spatial fluorochrome signals to functional growth rates (linearity factor - RW) of bone, dentin, and cementum using a fast Fourier transform on fluorochrome signals from 100-µm hemi-maxillae sections. An overall change in LPS-affected DAJ biomechanics (a 2.5-4.5X increase in tooth displacement and 2X tooth rotation at 6weeks, no increase in displacement and a 7X increase in rotation at 12weeks; 27% increase in bone effective strain at 6weeks and 11% at 12weeks relative to control) was associated with structural changes in the coronal regions of the DAJ (15% increase in PDL-space from 0 to 6weeks but only 5% from 6 to 12weeks compared to control). A significant increase (p < 0.05) in PDL-space between ligated and age-matched control was observed. The bone fraction of ligated at 12weeks was significantly lower than its age-matched control, and no significant differences (p>0.05) between groups were observed at 6weeks. Cementum in the apical regions grew faster but nonlinearly (11% and 20% increase in cementum fraction (CF) at 6 and 12weeks) compared to control. Alveolar bone revealed site-specific nonlinear growth with an overall increase in MAR (108.5µm/week to 126.7µm/week after LPS treatment) compared to dentin (28.3µm/week in control vs. 26.1µm/week in LPS-affected) and cementum (126.5µm/week in control vs. 119.9µm/week in LPS-affected). A significant increase in CF (p<0.05) in ligated specimens was observed at 6weeks of age. Anatomy-specific responses of cementum and bone to the mechano-chemo stimuli, and their collective temporal contribution to observed changes in PDL-space were perpetuated by altered tooth movement. Data highlight the "resilience" of DAJ function through the predominance of nonlinear growth response of cementum, changes in PDL-space, and bone architecture. Despite the significant differences in bone and cementum architectures, data provided insights into the reactionary effects of cementum as a built-in compensatory mechanism to reestablish functional competence of the DAJ. The spatial shifts in architectures of alveolar bone and cementum, and consequently ligament space, highlight adaptations farther away from the site of insult, which also is another novel insight from this study. These adaptations when correlated within the context of joint function (biomechanics) illustrate that they are indeed necessary to sustain DAJ function albeit being pathological.

Nonlinear Weather–Growth Relationships Suggest Disproportional Growth Changes of Norway Spruce in the Eastern Baltic Region

Norway spruce (Picea abies (L.) H. Karst.) is predicted to decrease its abundance in the Eastern Baltic region as a result of climatic changes, and this process is already explicit at the southern limit of species lowland distribution. Still, there are uncertainties about the growth potential of Norway spruce within the region due to the plasticity of local populations. In this regard, an assessment of regional weather–growth responses, assuming a nonlinearity of the ecological relationship, can aid in the clarification of uncertainties regarding growth. Nonlinear regional weather–growth relationships for Norway spruce were assessed based on tree-ring widths from 22 stands spreading from Southern Finland to Northern Germany using dendrochronological methods and a generalized additive mixed model. Temporal and spatial stationarity of local linear weather–growth relationships was evaluated. Considering the drought sensitivity of Norway spruce, meteorological variables related to the summer moisture regime were the main predictors of radial increment, though conditions in winter and spring had complementary effects. Generally, the linear weather–growth relationships were spatially and temporary nonstationary, with some exceptions in Poland and Northern Germany. Explicit local specifics in the linear weather–growth relationships, which are common in the marginal parts of species’ distribution, were observed in Estonia, Latvia, and Poland. The estimated regional weather–growth relationships were mostly nonlinear, implying disproportional responses to climatic changes, particularly to intensifying drought conditions across the studied climatic gradient. Still, the responses to winter temperature suggested that warming might contribute to growth. The estimated linear and nonlinear growth responses indicate strict limitation by drought conditions, implying reductions of increment due to climatic changes southward from Latvia, suggesting the necessity for proactive management. Nevertheless, in the northern part of the analyzed region, the projected climatic changes appear favorable for growth of Norway spruce in the near future.

PSII-17 Phosphorus Release Values in Growing Pigs Fed Increments of Optiphos Plus Phytase in Pelleted Diets

Abstract The efficacy of phytase (Pase) from OptiPhos Plus G (Huvepharma, Peachtree City, GA) was compared to inorganic phosphorus (iP) supplements to assess phosphorus equivalency. In 6 replicate 28-d trials, 288 crossbred F2 (Duroc X LR X LW) pigs (20.0 kg, 6 pigs/pen, 48 pens) were randomly assigned to 1 of 8 diets. Pig sex was balanced within pens. Basal corn-soybean meal diets, formulated to exceed nutrient requirements except for Ca and P, supplied 1.30% lysine from the same amounts of all ingredients. Sand was used to balance variable amounts of monocalcium phosphate and limestone. Diets supplied either 0.061, 0.156, or 0.241% iP from monocalcium phosphate or increments of 250, 500, 750, 1,000 and 1,500 FTU/kg from Pase. All diets were pelleted (160°F, 2.5 tons/hr). The modified pellet durability index averaged 92.8% and 88.7% for all diets in each of 2 mixes. Non-linear growth responses to increments of iP and Pase were detected (P &amp;lt; 0.05). Using nonlinear regression models, maximum gain was calculated at 0.23% iP and 1144 FTU/kg Pase (equivalent to 0.31% available P or 0.38% STTD P). Likewise, from non-linear responses (P &amp;lt; 0.05), maximum response in whole-body bone mineral content (WBBMC) from analysis of dual energy x-ray absorptiometry scans were calculated at 1227 FTU/kg Pase. The maximum Pase response for WBBMC was below expectations and raised concerns for potential Ca limitations in diets at higher Pase supplements. Only linear WBBMC responses (P &amp;lt; 0.001) to iP levels were detected. Responses across iP and Pase treatments for femur bone mineral content reflected the same conclusions as responses to WBBMC. As growth responses to iP and Pase diets were non-linear, simple conversions of phytase activity to phosphorus release was not straight-forward. However, non-linear equations can predict economic values of target levels as a function of ingredient costs.

An empirical, Bayesian approach to modelling crop yield: Maize in USA

We apply an empirical, data-driven approach for describing crop yield as a function of monthly temperature and precipitation by employing generative probabilistic models with parameters determined through Bayesian inference. Our approach is applied to state-scale maize yield and meteorological data for the US Corn Belt from 1981 to 2014 as an exemplar, but would be readily transferable to other crops, locations and spatial scales. Experimentation with a number of models shows that maize growth rates can be characterised by a two-dimensional Gaussian function of temperature and precipitation with monthly contributions accumulated over the growing period. This approach accounts for non-linear growth responses to the individual meteorological variables, and allows for interactions between them. Our models correctly identify that temperature and precipitation have the largest impact on yield in the six months prior to the harvest, in agreement with the typical growing season for US maize (April to September). Maximal growth rates occur for monthly mean temperature 18 °C–19 °C, corresponding to a daily maximum temperature of 24 °C–25 °C (in broad agreement with previous work) and monthly total precipitation 115 mm. Our approach also provides a self-consistent way of investigating climate change impacts on current US maize varieties in the absence of adaptation measures. Keeping precipitation and growing area fixed, a temperature increase of 2 °C, relative to 1981–2014, results in the mean yield decreasing by 8%, while the yield variance increases by a factor of around 3. We thus provide a flexible, data-driven framework for exploring the impacts of natural climate variability and climate change on globally significant crops based on their observed behaviour. In concert with other approaches, this can help inform the development of adaptation strategies that will ensure food security under a changing climate.

Complexity confers stability: Climate variability, vegetation response and sand transport on longitudinal sand dunes in Australia’s deserts

Abstract The relationship between antecedent precipitation, vegetation cover and sand movement on sand dunes in the Simpson and Strzelecki Deserts was investigated by repeated (up to four) surveys of dune crest plots (≈25 × 25 m) over a drought cycle (2002–2012) in both winter (low wind) and spring (high wind). Vegetation varied dramatically between surveys on vegetated and active dune crests. Indices of sand movement had significant correlations with vegetation cover: the depth of loose sand has a strong inverse relationship with crust (cyanobacterial and/or physical) while the area covered by ripples has a strong inverse relationship with the areal cover of vascular plants. However, the relationship between antecedent rainfall and vegetation cover was found to be complex. We tentatively identify two thresholds; (1) >10 mm of rainfall in the preceding 90 days leads to rapid and near total cover of crust and/or small plants 400 mm of rainfall in the preceding three years leads to higher cover of persistent and longer-lived plants >50 cm tall. These thresholds were used to predict days of low vegetation cover on dune crests. The combination of seasonality of predicted bare-crest days, potential sand drift and resultant sand drift direction explains observed patterns of sand drift on these dunes. The complex vegetation and highly variable rainfall regime confer meta-stability on the dunes through the range of responses to different intervals of antecedent rainfall and non-linear growth responses. This suggests that the geomorphic response of dunes to climate variation is complex and non-linear.

Variation in monsoon precipitation drives spatial and temporal patterns of Larrea tridentata growth in the Sonoran Desert

Summary 1. Broad-scale patterns of above-ground net primary production (ANPP) are closely coupled to climate features, particularly the distribution and magnitude of rainfall. In arid and semi-arid regions, however, the precipitation regime, together with local geomorphology and plant life history traits, combine to regulate soil water availability and patterns of growth, complicating simple correlations with climatic variables. 2. To better understand the drivers of plant growth in desert ecosystems, we characterized the rates and spatial heterogeneity of stem elongation by the dominant perennial shrub, creosote bush (Larrea tridentata) in the northern Sonoran Desert of Arizona (USA). Estimates of stem growth were made over a 5-year period (2006–2010) from 60 plots at 15 sites spanning c. 120 km across the Central Arizona–Phoenix (CAP) Long-term Ecological Research (LTER) area. 3. We observed both the highest and lowest rates of stem growth during summer, and these patterns were related to the amount of monsoon rainfall and local rates of water infiltration. The relationship between growth and precipitation in the summer was nonlinear, with rates increasing more than eightfold at plots receiving more than 100 mm of seasonal rainfall. Conversely, growth during the winter/spring was intermediate in magnitude, similar among years and poorly correlated with seasonal precipitation. 4. The spatial heterogeneity of stem growth also differed markedly between seasons and was greater both within and among sites during summer compared to winter/spring growing periods. At broad scales, spatial heterogeneity of shrub growth was correlated with seasonal changes in the spatial variability of rainfall across the study area. At small spatial scales, greater heterogeneity during the summer appears linked to local soil properties that influence infiltration and water availability following monsoon storms. 5. Overall, the strong, nonlinear growth response by L. tridentata to monsoon rainfall suggests that the recurrence interval of wet summer seasons is an important driver of ANPP for this long-lived shrub. More generally, our results illustrate how regional climate variability and local soil properties can interact to influence the rates and heterogeneity of desert plant growth at multiple scales.

Does Soil Organic Layer Thickness Affect Climate–Growth Relationships in the Black Spruce Boreal Ecosystem?

The observed long-term decrease in the regional fire activity of Eastern Canada results in excessive accumulation of organic layer on the forest floor of coniferous forests, which may affect climate–growth relationships in canopy trees. To test this hypothesis, we related tree-ring chronologies of black spruce (Picea mariana (Mill.) B.S.P.) to soil organic layer (SOL) depth at the stand scale in the lowland forests of Quebec’s Clay Belt. Late-winter and early-spring temperatures and temperature at the end of the previous year’s growing season were the major monthly level environmental controls of spruce growth. The effect of SOL on climate–growth relationships was moderate and reversed the association between tree growth and summer aridity from a negative to a positive relationship: trees growing on thin organic layers were thus negatively affected by drought, whereas it was the opposite for sites with deep (>20–30 cm) organic layers. This indicates the development of wetter conditions on sites with thicker SOL. Deep SOL were also associated with an increased frequency of negative growth anomalies (pointer years) in tree-ring chronologies. Our results emphasize the presence of nonlinear growth responses to SOL accumulation, suggesting 20–30 cm as a provisional threshold with respect to the effects of SOL on the climate–growth relationship. Given the current climatic conditions characterized by generally low-fire activity and a trend toward accumulation of SOL, the importance of SOL effects in the black spruce ecosystem is expected to increase in the future.

A mathematical analysis of the divergence problem in dendroclimatology

Tree rings provide a primary data source for reconstructing past climates, particularly over the past 1,000 years. However, divergence has been observed in twentieth century reconstructions. Divergence occurs when trees show a positive response to warming in the calibration period but a lesser or even negative response in recent decades. The mathematical implications of divergence for reconstructing climate are explored in this study. Divergence results either because of some unique environmental factor in recent decades, because trees reach an asymptotic maximum growth rate at some temperature, or because higher temperatures reduce tree growth. If trees show a nonlinear growth response, the result is to potentially truncate any historical temperatures higher than those in the calibration period, as well as to reduce the mean and range of reconstructed values compared to actual. This produces the divergence effect. This creates a cold bias in the reconstructed record and makes it impossible to make any statements about how warm recent decades are compared to historical periods. Some suggestions are made to overcome these problems.

Spectral measures and mixed models as valuable tools for investigating controls on land surface phenology in high arctic Greenland

BackgroundChanges in land surface phenology are of major importance to the understanding of the impact of recent and future climate changes in the Arctic. This paper presents an extensive study from Zackenberg Ecological Research Operations (ZERO) where snow melt, climate and growing season characteristics of six major high arctic vegetation types has been monitored during 1999 to 2005. We investigate the growth dynamics for dry, mesic and wet types using hand held measurements of far red normalised difference vegetation index (NDVI-FR) and generalized additive mixed models (GAMM).ResultsSnow melt and temperature are of major importance for the timing of the maximum growth as well as for the seasonal growth. More than 85% of the variance in timing of the maximum growth is explained by the models and similar for the seasonal growth of mesic and wet vegetation types. We find several non-linear growth responses to the environmental variables.ConclusionWe conclude that the uses of GAMMs are valuable for investigating growth dynamics in the Arctic. Contrary to several other studies in the Arctic we found a significant decreasing trend of the seasonally integrated NDVI-FR (SINDVI) in some vegetation types. This indicates that although greening might occur wide-spread in the Arctic there are variations on the local scale that might influence the regional trends on the longer term.

Modeling Tree-Ring Growth Responses to Climatic Variables Using Artificial Neural Networks

Abstract Modeling the nonlinear and complex relationships between climate and tree-ring growth is of significance in dendroclimatic studies, but difficult to implement using traditional linear regression approaches. To overcome this difficulty, the technique of Artificial Neural Network (ANN) was employed in this study to develop the growth response models using the climate/growth database for Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) on southern Vancouver Island, Canada. The results show that the ANN models are able to extract nonlinear growth response patterns from the observed climate/tree-ring datasets, and to generate more accurate predictions than multiple linear regression approaches. The ANN-extracted climate-growth relationships can be displayed by scenario analysis; for example, when all other input variables are held fixed at their means, the limiting effect of April-July precipitation on tree growth decreases with increased precipitation. The main difficulty of applying ANN technique in dendroclimatology is the problem of overlearning (i.e., the ANN learns too many specific climate-growth patterns and loses the ability to generalize between similar climate-growth patterns). This problem can be alleviated by carefully designing the ANN, such as reducing the number of input variables, choosing a variety of training/testing sets, designing partially connected architectures with a small number of neurons in the hidden layer, and using early stopping during training process. The reliability of the derived ANN models is assessed by validation on independent testing datasets. The main advantages of the ANN technique over traditional dendroclimatic approaches are its ability to capture nonlinear climate-growth response, and its nonreliance on preassumed functional relationships for describing the observed datasets. The ANN method introduced in this article is sufficiently general to be applicable to many forest ecological modeling applications. For. Sci. 46(2):229-239.

Genetic variation in nutrient response functions

Genetic differences in the non-linear growth response function of Pinus sylvestris seedlings to five nutrient levels are analyzed to estimate the causes of variation. Analyses of genotypic differences as quadratic response functions, as stability coefficients, and as separable functions indicate that the estimation of genetic effects can vary widely depending on the analytical model assumed. The existence of different reaction norms is demonstrated.