Geographic Variation in the Petiole-Lamina Relationship of 325 Eastern Qinghai-Tibetan Woody Species: Analysis in Three Dimensions

Corner's Rules and Their Linkages With Twig Functions and Tree Productivity in Simple- and Compound-Leaved Tree Species

Corner's rules are well known in describing inter-specific scaling relationships for plant organ size-related traits, from species with thick terminal stems, large leaves, and sparsely branched twigs to species with opposite traits; however, the implications of organ size on physiological functions and growth performance of trees remain unclear. Moreover, whether Corner's rules spectra differ between tree species with simple and compound leaves is not known. Here, we measured key twig morphological traits, physiological characteristics, and radial growth rates of 27 simple- and 6 compound-leaved tree species in a common garden in Northeast China. The size scaling relationships between leaf lamina and supporting structures were mostly allometric (slope < 1) in simple-leaved species. In contrast, such relationships were predominantly isometric (slope = 1) in compound-leaved species. Consistently, twig hydraulic conductance and photosynthetic rate increased significantly faster as twig size increased across the compound-leaved species. Consequently, compound-leaved species equipped with twigs of fewer but larger leaves have the potential to achieve remarkably high growth rates. Our study revealed divergent investment-return strategies between the two functional groups, that is, 'diminishing returns' in simple-leaved species and 'stable returns' in compound-leaved species, and identified mechanistic associations among twig architecture, physiological characteristics and tree growth rate.

Effects of Drought Stress on Leaf Functional Traits and Biomass Characteristics of Atriplex canescens

Drought is a critical factor constraining plant growth in arid regions. However, the performance and adaptive mechanism of Atriplex canescens (A. canescens) under drought stress remain unclear. Hence, a three-year experiment with three drought gradients was performed in a common garden, and the leaf functional traits, biomass and biomass partitioning patterns of A. canescens were investigated. The results showed that drought stress had significant effects on A. canescens leaf functional traits. A. canescens maintained the content of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD), but the peroxidase (POD) and catalase (CAT) activity decreased, and the content of proline (Pro) and soluble sugar (SS) increased only under heavy drought stress. Under drought stress, the leaves became smaller but denser, the specific leaf area (SLA) decreased, but the dry matter content (LDMC) maintained stability. Total biomass decreased 60% to 1758 g under heavy drought stress and the seed and leaf biomass was only 10% and 20% of non-stress group, but there had no significant difference on root biomass. More biomass was allocated to root under drought stress. The root biomass allocation ratio was doubled from 9.62% to 19.81% under heavy drought, and the root/shoot ratio (R/S) increased from 0.11 to 0.25. The MDA was significantly and negatively correlated with biomass, while the SPAD was significantly and positively correlated with total and aboveground organs biomass. The POD, CAT, Pro and SS had significant correlations with root and seed allocation ratio. The leaf morphological traits related to leaf shape and weight had significant correlations with total and aboveground biomass and biomass allocation. Our study demonstrated that under drought stress, A. canescens made tradeoffs between growth potential and drought tolerance and evolved with a conservative strategy. These findings provide more information for an in-depth understanding of the adaption strategies of A. canescens to drought stress and provide potential guidance for planting and sustainable management of A. canescens in arid and semi-arid regions.

Patterns of Leaf and Fruit Morphological Variation in Marginal Populations of Acer tataricum L. subsp. tataricum

Marginal populations are usually smaller and more isolated and grow in less favourable conditions than those at the distribution centre. The variability of these populations is of high importance, as it can support the adaptations needed for the conditions that they grow in. In this research, the morphological variability of eight Tatar maple (Acer tataricum L. subsp. tataricum) populations was analysed. Tatar maple is an insect-pollinated and wind-dispersed shrub/tree, whose northwestern distribution edge is in southeastern Europe. Morphometric methods were used to analyse the variability of the populations using leaf and fruit morphology. The research revealed significant differences between and within populations. Furthermore, differences in the distribution of the total variability were noted, which suggest that different evolutionarily factors affect different plant traits. Correlation analysis confirmed a weak dependency between the vegetative and generative traits. In addition, no evidence was found for the presence of isolation by environment (IBE). However, the Mantel test for isolation by distance (IBD) was significant for the leaf morphometric traits and non-significant for the fruit morphometric traits. Being the marginal leading-edge populations, they are younger and were less likely to have had time for adaptation to local environments, which would have resulted in the development of IBE. Overall, edge populations of Tatar maple were characterised by great morphological variability, which helps these populations in their response to the intensive selective pressures they face in their environment.