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Summary: Tolerance of abiotic stress in woody plants is known to be constrained by biological trade‐offs between different forms of stress, especially shade and drought. However, there is still considerable uncertainty on the relationship between tolerances and the limits on tolerance combinations.Using the most extensive database available on shade, drought, waterlogging and cold tolerance for 799 northern hemisphere woody species, we determined the number of dimensions needed to summarise their tolerance combinations, and the best trade‐off model among those currently available, for description of the interdependence between tolerances.Two principal component analysis (PCA) dimensions summarised stress tolerance combinations. They defined a triangular stress tolerance space (STS). The first STS dimension reflected segregation between drought‐tolerant and waterlogging‐tolerant species. The second reflected shade tolerance, which is independent of the other tolerances. Cold tolerance scaled weakly with both dimensions. Tolerance combinations across the species in the database were limited by boundary‐line trade‐offs.The STS reconciles all major theories about trade‐offs between abiotic stress tolerances, providing a unified trade‐off model and a set of coordinates that can be used to examine how other aspects of plant biology, such as plant functional traits, change within the limits of abiotic stress tolerance. [ABSTRACT FROM AUTHOR]

Summary: Two experiments were conducted in which the influence of size of clones and the persistence of stolon connections on subsequent development were examined in Glechoma hederacea. In the first experiment, clones were grown from either one unrooted ramet or from either one, two or three connected, rooted ramets, for 8 weeks, in either nutrient‐rich or nutrient‐poor sand. The survival, number of ramets and dry weight of the clones produced were dependent on the number of established ramets at the start of the experiment. Clones in nutrient‐rich sand developed a greater number of ramets, stolon branches, total length of stolon, mean leaf area per ramet and total leaf area per clone than clones of corresponding initial size in nutrient‐poor sand. In the second experiment, the stolon connections between ramets of G. hederacea clones growing in boxes were either left intact or severed soon after each ramet had rooted. After 10 weeks of growth, the total dry weight of the intact clones and the mean dry weight of their ramets were significantly greater than the corresponding values for severed clones. The spatial distribution of ramets showed marked differences between the treatments. Severed clones produced a greater number of rooted ramets within the boxes and a smaller number of unrooted ramets beyond the box edges than intact clones. Density of ramets more than doubled when stolons were severed. Maintenance of stolon connections in G. hederacea is advantageous because it improves the probability of daughter ramet survival, promotes rapid lateral expansion of the clone and reduces inter‐ramet competition through the production of fewer, larger ramets. [ABSTRACT FROM AUTHOR]

The influence of number of seeds per clump upon germination of Plantago coronopus L. was investigated at different salinity levels on filter paper, sand and soil. These substrates provide both artificial and semi-natural microenvironments for seed germination. On all substrates, germination was positively dependent on clump density and seeds in clumps had a higher tolerance of salinity as reflected in higher germination percentages. Final percentage germination for a given clump size and salinity level depended upon substrate, being far higher on filter paper and sand than on soil, whilst the time required to reach final germination also increased in that order. The possible ecological significance of density-dependent seed germination is discussed. [ABSTRACT FROM AUTHOR]