More than 5,000 measurements from 1,943 plant species were used to explore the scaling relationships among the foliar surface area and the dry, water, and nitrogen/phosphorus mass of mature individual leaves. Although they differed statistically, the exponents for the relationships among these variables were numerically similar among six species groups (ferns, graminoids, forbs, shrubs, trees, and vines) and within 19 individual species. In general, at least one among the many scaling exponents was <1.0, such that increases in one or more features influencing foliar function (e.g., surface area or living leaf mass) failed to keep pace with increases in mature leaf size. Thus, a general set of scaling relationships exists that negatively affects increases in leaf size. We argue that this set reflects a fundamental property of all plants and helps to explain why annual growth fails to keep pace with increases in total body mass across species.foliar traits ͉ plant allometry ͉ scaling relations S ize variations in foliar functional traits have received intense recent attention, because leaves are the principal photosynthetic organs of the majority of plant species, because the manner in which foliar traits change within or across species as a function of differences in leaf size can profoundly affect plant growth, reproduction, and ecosystem function, and because standing leaf mass is a critical component in empirical and theoretical plant allometry models (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Surprisingly, however, our knowledge about some very basic size-dependent (scaling) relationships is very incomplete, particularly in terms of how intra-and interspecific differences in mature leaf dry mass (M D ) correlate with foliar water mass (M W ), surface area (SA), and the nitrogen or phosphorus mass per leaf lamina (N L and P L , respectively), either within individual species or across taxonomically different species groups sharing the same life forms (and thus presumably similar foliar architectures and other functional traits).The importance of quantifying size-dependent variations among functional traits is evident from the general scaling relationship X ϭ ␤ M D ␣ , where X represents one among many functional traits influencing the physiological or mechanical functions of leaves (e.g., SA or M W ) and where ␤ and ␣ are, respectively, the elevation and slope of the log-transformed X vs. M D regression curve. Noting that the change in X with respect to differences in mature leaf M D (i.e., ѨX/ѨM D ) equals ␣ ␤ M D ␣Ϫ1 , the magnitude of X will be independent of intra-or interspecific differences in M D when ␣ ϭ 1.0; it will increase disproportionately with increasing M D when ␣ Ͼ 1.0; and it will fail to keep pace with intra-or interspecific increases in M D when ␣ Ͻ 1. Among these three possibilities, the first and second do not a priori result in negative consequences as mature leaf mass increases intra-or interspecifically. The first is size-independent and results in a ''break even'' relationship, w...

We adopted previous N : P stoichiometric models for zooplankton relative growth to predict the relative growth rates of the leaves l L of vascular plants assuming that annual leaf growth in dry mass is dictated by how leaf nitrogen N L is allocated to leaf proteins and how leaf phosphorus P L is allocated to rRNA. This model is simplified provided that N L scales as some power function of P L across the leaves of different species. This approach successfully predicted the l L of 131 species of vascular plants based on the observation that, across these species, N L scaled, on average, as the 3/4 power of P L , i.e. N L µ P 3=4 L . When juxtaposed with prior allometric theory and observations, our findings suggest that a transformation in N : P stoichiometry occurs when the plant body undergoes a transition from primary to secondary growth.

The transition from an aquatic ancestral condition to a terrestrial environment exposed the first land plants to the desiccating effects of air and potentially large fluctuations in temperature and light intensity. To be successful, this transition necessitated metabolic, physiological, and morphological modifications, among which one of the most important was the capacity to synthesize hydrophobic extracellular biopolymers such as those found in the cuticular membrane, suberin, lignin, and sporopollenin, which collectively reduce the loss of water, provide barriers to pathogens, protect against harmful levels of UV radiation, and rigidify targeted cell walls. Here, we review phylogenetic and molecular data from extant members of the green plant clade (Chlorobionta) and show that the capacity to synthesize the monomeric precursors of all four biopolymers is ancestral and extends in some cases to unicellular plants (e.g. Chlamydomonas). We also review evidence from extant algae, bryophytes, and early-divergent tracheophytes and show that gene duplication, subsequent neo-functionalization, and the co-option of fundamental and ancestral metabolic pathways contributed to the early evolutionary success of the land plants.

We report the biomechanics and anatomy of fruit wall peels (before and after cellulase/pectinase treatment) from two Lycopersicon esculentum cultivars (i.e., Inbred 10 and Sweet 100 cherry tomatoes). Samples were tested before and after enzyme treatment in uniaxial tension to determine their rate of creep, plastic and instantaneous elastic strains, breaking stress (strength), and work of fracture. The fruit peels of both cultivars exhibited pronounced viscoelastic and strain-hardening behavior, but differed significantly in their rheological behavior and magnitudes of material properties, e.g., Inbred 10 peels crept less rapidly and accumulated more plastic strains (but less rapidly), were stiffer and stronger, and had a larger work of fracture than Sweet 100 peels. The cuticular membrane (CM) also differed; e.g., Sweet 100 CM strain-softened at forces that caused Inbred 10 to strain-harden. The mechanical behavior of peels and their CM correlated with anatomical differences. The Inbred 10 CM develops in subepidermal cell layers, whereas the Sweet 100 CM is poorly developed below the epidermis. Based on these and other observations, we posit that strain-hardening involves the realignment of CM fibrillar elements and that this phenomenon is less pronounced for Sweet 100 because fewer cell walls contribute to its CM compared to Inbred 10.

Research indicates that increases in total leaf area (A(T)) may fail to keep pace with increases in total leaf mass (M(L)) across plants differing in size (e.g., as measured by stem diameter, D). This "diminishing returns" hypothesis predicts that the scaling exponent for A(T) vs. M(L) will be less than one and that the exponent for specific leaf mass (i.e., A(T) / M(L)) vs. D will be negative. These predictions were examined using data from 46 plants ranging between 0.125 cm ≤ D ≤ 0.485 m across 25 woody dicot species. Standardized major axis slopes were used to quantify scaling exponents and random effects models were used to quantify species and size effects on the numerical values of exponents. The exponents for A(T) vs. M(L) and A(T) / M(L) vs. D differed among species and different species groupings. In general, the exponent for A(T) vs. M(L) was less than one and the exponent for A(T) / M(L) vs. D was negative, as predicted. However, random effects models indicated that species effects overshadowed size effects, although size effects were statistically significant. The diminishing returns hypothesis therefore receives statistical support, i.e., although the numerical values of exponents are "species-dependent," they are less than unity, as predicted by theory.