Research progress of trade-off relationships of plant functional traits.
Trade-offs among different plant functional traits reflect the different strategies of plants in resource acquisition and allocation and have been a hot topic in ecological research in recent years. Starting from research scales, leaf traits, organs, and plant groups, this review briefly introduces how the study of trait relationships has gradually expanded and deepened based on the leaf economic spectrum (LES) in recent decades. (1) Relevant studies have been focused on the species living in extremely harsh environments. LES is relatively stable along environmental gradients studied. Both intra- and inter-specific leaf trait relationships are similar. (2) Leaf decomposition rate and flammability are significantly related to the morphological traits and nutrient contents. The relationship between leaf economic traits and hydraulic traits depends on environmental water availability. (3) Leaf mass per area is coupled with wood density and seed size. However, the morphological traits of leaf are not related to relevant traits of root and flower, indicating that these organs may have evolved independently. (4) LES can well explain the growth/survival strategies of some special vascular plants: invasive plants have relatively high resource use efficiencies and fast relative growth rates, locating on the "low investment-quick returns" end in LES. In contrast, the leaves of the carnivorous plants are capable of catching prey, but have relatively low photosynthetic and growth rates, distributing on the other end of LES. Besides, LES pertains to not only the oldest seed plant cycads but also ferns and poikilohydric plants (bryophytes and lichens). This review summarizes the research progress of this topic and presents some suggestions, hoping to provide some new insights for future studies.