Modelling the growth of plants with a uniform growth logistics.

BACKGROUND AND AIMS: The increment model has previously been used to describe the growth of plants in general. Here, we examine how the same logistics enables the development of different superstructures. METHODS: Data from the literature are analyzed with the increment model. Increments are growth-invariant molecular clusters, treated as heuristic particles. This approach formulates the law of mass action for multi-component systems, describing the general properties of superstructures which are optimized via relaxation processes. RESULTS: The daily growth patterns of hypocotyls can be reproduced implying predetermined growth invariant model parameters. In various species, the coordinated formation and death of fine roots are modeled successfully. Their biphasic annual growth follows distinct morphological programs but both use the same logistics. In tropical forests, distributions of the diameter in breast height of trees of different species adhere to the same pattern. Beyond structural fluctuations, competition and cooperation within and between the species may drive optimization. CONCLUSION: All superstructures of plants examined so far could be reproduced with our approach. With genetically encoded growth-invariant model parameters (interaction with the environment included) perfect morphological development runs embedded in the uniform logistics of the increment model.

On the structure-bounded growth processes in plant populations.

If growing cells in plants are considered to be composed of increments (ICs) an extended version of the law of mass action can be formulated. It evidences that growth of plants runs optimal if the reaction-entropy term (entropy times the absolute temperature) matches the contact energy of ICs. Since these energies are small, thermal molecular movements facilitate via relaxation the removal of structure disturbances. Stem diameter distributions exhibit extra fluctuations likely to be caused by permanent constraints. Since the signal-response system enables in principle perfect optimization only within finite-sized cell ensembles, plants comprising relatively large cell numbers form a network of size-limited subsystems. The maximal number of these constituents depends both on genetic and environmental factors. Accounting for logistical structure-dynamics interrelations, equations can be formulated to describe the bimodal growth curves of very different plants. The reproduction of the S-bended growth curves verifies that the relaxation modes with a broad structure-controlled distribution freeze successively until finally growth is fully blocked thus bringing about "continuous solidification".

Nutritional differences and leaf acclimation of climbing plants and the associated vegetation in different types of an Andean montane rainforest.

Climbing plants are known to play an important role in tropical forest systems, but key features for their distribution are only partly understood. Investigation was carried out to find if climbers differ from self-supporting vegetation in their adjustment of leaf parameters over a wide variety of light regimes in different forest types along an altitudinal gradient. Relative photon flux density (PFDrel) was assessed above 75 pairs of strictly linked climbers and supporting vegetation on seven plots between 2,020 and 2,700 m a.s.l. along a mountain range in South-Ecuador up to the Páramo vegetation. Leaf samples from both growth forms were analyzed for leaf area (LA), specific leaf mass (LMA), mass and area-based carbon and nitrogen concentration (C, Carea, N, and Narea) and concentrations of P, K, Ca, Mg, Mn and Al. Leaf size of climbers was independent of general light condition, whereas the leaf size of the self-supporting vegetation increased in shade. LMA increased as expected with altitude and irradiance for both growth forms, but climbers generally built smaller leaves with lower LMA. N, P, and K concentrations were higher in the leaves of climbers than in their supporters. Relationships of LMA and Narea to the light conditions were more pronounced within the climbers than within their supporters. Slope for the regression between climber's Narea and LMA was twice as steep as for the supporter leaves. Al accumulators were only found within the self-supporting vegetation. The investigated traits indicate improved adjustment towards light supply within climbers compared to self-supporting vegetation. Thus climbing plants seem to have a higher potential trade off in resource-use efficiency regarding irradiance and nutrients.

Photosynthetic capacity in relation to nitrogen in the canopy of a Quercus robur, Fraxinus angustifolia and Tilia cordata flood plain forest.

We measured gas exchange and various leaf parameters of ash (Fraxinus angustifolia Vahl.) and oak (Quercus robur L.) in the high canopy and of lime (Tilia cordata Mill.) in the lower canopy of a planted, 120-year-old floodplain forest in southern Moravia, Czech Republic. The high-canopy leaves of F. angustifolia and Q. robur had nitrogen concentrations on a leaf area basis (N(area)) that were twice those of low-canopy leaves of T. cordata. Upper-canopy leaves of F. angustifolia had a photosynthetic rate at light saturation (A(max)) of about 16 micromol CO2 m(-2) s(-1), whereas A(max) of the upper-canopy foliage of Q. robur achieved only about two thirds of this value. Contrary to previous investigations of photosynthetic performance in monospecific stands, leaves of the uppermost branches of T. cordata at 15-m height had the highest A(max) and transpiration rate among the species studied. Water-use efficiency (WUE) was low in T. cordata at 15-m canopy height, whereas WUE was significantly higher for Q. robur leaves at 27-m height than for the other species. Leaves of T. cordata at 15-m height showed the strongest relationship between A(max) and N(area) (R2 = 0.90) followed by F. angustifolia (R2 = 0.69). The strong correlation between photosynthesis and nitrogen concentration in T. cordata at 15 m, together with the steep regression slope for the A(max):N(area) relationship, indicated that nitrogen allocation to the photosynthetic apparatus resulted in high nitrogen-use efficiency of light-saturated photosynthesis (PNUE). Despite differences in PNUE among species, PNUE was fairly constant for leaves sampled from the same canopy position, suggesting that single-leaf parameters are matched to optimize PNUE for prevailing light conditions. High PNUE in T. cordata at 15 m partially compensated for the species' subordinate position in the canopy, and may be an important mechanism for its coexistence in highly structured vegetation.