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The scaling relationship between leaf dry mass and leaf surface area has important implications for understanding the ability of plants to harvest sunlight and grow. Whether and how the scaling relationships vary across environmental gradients are poorly understood. We analyzed the scaling relationships between leaf mass and leaf area of 121 vascular plant species along an altitudinal gradient in a subtropical monsoon forest. The slopes increased significantly with altitude, it varied from less than 1 at low altitude to more than 1 at high altitude. This means that plants growing at high altitude allocate proportionately more biomass to support tissues in larger leaves and less in smaller leaves, whereas the reverse is true at low altitude. This pattern can be explained by different leaf strategies in response to environmental pressure and constrains.

Debate continues in theoretical ecology over whether and why the scaling exponent of biomass-density (M-N) relationship varies along environmental gradients. By developing a novel geometric model with assumptions of allometric growth at the individual level and open canopy at the stand level, we propose that plant height-crown radius and canopy coverage-density relationships determine the above-ground M-N relationship in stressful environments. Results from field investigation along an aridity gradient (from eastern to western China) confirmed our model prediction and showed that the above-ground M-N scaling exponent increased with drought stress. Therefore, the 'universal' scaling exponents (-3/2 or -4/3) of the M-N relationship predicted by previous models may not hold for above-ground parts in stressful environments.

The ability of abscisic acid (ABA) to modulate positive interactions between Arabidopsis thaliana individuals under salinity stress was investigated using abi1-1 (insensitive to ABA), era1-2 (hypersensitive to ABA) mutant and wild type plants. The results showed that sensitivity to ABA affects relative interaction intensity (RII) between Arabidopsis thaliana individuals. The neighbor removal experiments also confirmed the role of phenotypic responses in linking plant-plant interactions and sensitivity to ABA. For abi1-1 mutants, the absolute value differences between neighbor removal and control of stem length, root length, leaf area, leaf thickness, flower density, above biomass/belowground biomass (A/U), photosynthetic rate, stomatal conductance, leaf water content and water-use efficiency were smaller than those of the wild type, while for era1-2 mutants, these absolute value differences were larger than those of the wild type. Thus, it is suggested that positive interactions between Arabidopsis thaliana individuals are at least partly modulated by different sensitivity to ABA through different physiological and phenotypic plasticity. [ABSTRACT FROM AUTHOR]