Plant traits refer to a series of core plant properties that are closely related to plant colonization, survival, growth, and death. They can significantly affect ecosystem functions and reflect the responses of vegetation to environmental changes (Wright et al., 2004, 2007). Compared with most studies that are based on plant classifications and quantifications, plant traits have become a reliable focus when aiming to solve important ecological problems in populations at community and ecosystem scales (He et al., 2018). In recent years, research on the distribution patterns of plant traits has mainly focused on global and regional scales. At a global scale, many researchers have studied leaf morphology, structure, and physiological traits, nitrogen and phosphorus content in leaves, seed weight, tall tree, and trunk characteristics, and furthermore the famous global plant leaf economic spectrum and tree trunk economic spectrums have been developed (Wright et al., 2004, 2017; Reich et al., 2004, 2014). At a regional scale, investigations have reported the traits and functions of forest ecosystems along a 3700 km gradient in the south-north sample zone of eastern China, and developed a set of methods to scientifically deduce the traits of organ level measurements at the community scale (Tan et al., 2017).
Trade-offs are a common balance among plants traits, and is a combination of traits formed after natural selection. In other words, species are arranged in adaptive or competitive positions along a certain ecological strategy axis (Wright et al., 2004). These trade-offs not only include those between the aboveground and underground traits of plants (Yao et al., 2010; Yang et al., 2019), but also the trade-offs between traits, such as the leaf and branch and trunk traits, leaf traits, reproductive traits and quantity, and reproductive traits and seedling leaves (He et al., 2018; Messier et al.,2017). The trade-offs between plant traits not only help to understand the differences of plant ecological strategies in different environments, but also explore the internal mechanisms of niche differentiation and species coexistence (Chave et al., 2009).
Plant traits determine the growth, reproduction, and survival of plants and play an important role in the distribution patterns of species along environmental gradients. The relationships between plant traits and the environment, are not only conducive to the study of ecosystem functions and the coexistence mechanisms of community species, but also for predicting the effects of global climate change on plant distributions (Wang et al., 2012). Many studies have shown that the life strategies of plants formed by different morphological and physiological traits among species, are reflected in their rapid resource acquisitions and high resource conservation, in different ecosystems and biological communities (Terashima et al., 2011). The distribution of plant traits at different scales, is the result of multi-factor filtrations from a large to small scale. Many studies have confirmed that climate factors, such as temperature, light, and precipitation, play a decisive role in the distribution of plant traits on a global or regional scale (Zhang et al., 2015, 2019). At a medium scale, land use and disturbance play a major role in plant traits (Ocheltree et al., 2012). However, at a small or local scale, the distribution of plant traits is determined by geomorphic and soil factors (Li et al., 2014). Compared with climatic and geographical factors, studies on the tradeoffs between habitats and plant traits, have been more concerned with degraded than non-degraded ecosystems.
The Karst region in the southwest of China is approximately 540 000 km2, its primary forest is an evergreen broad-leaved forest and there is a seasonal rain forest. However, due to human disturbances, most of the evergreen and deciduous broad-leaved mixed forest and seasonal rainforest in the region of the limestone and dolomite have been degraded into secondary forests and shrubs (Nie et al., 2012). In recent years, with the implementation of major ecological projects such as the Grain for Green Program (GGP) by the government of the People’s Republic of China, there has been a reduction in stony desertification and an increase in the restoration of vegetation (Zou et al., 2019). However, the loss of soil nutrients and soil water in the karst region is an ongoing problem because of crop cultivation by local famers (Du et al., 2015). At the same time, the rate of shrub changing successions to forest is becoming low, due to the serious seasonal droughts and the supply constraints of the soil nutrients (Tan et al., 2017). In addition, in the shrub communities in some regions, there is a serious leakage of soil nutrients and water, that is degrading them to grass communities or even bare rock desertification. This makes it difficult to realize the goal of sustainable vegetation recover in karst areas (Du et al., 2015; Zhang et al., 2017). Therefore, a better understanding of the shrub traits in the karst microhabitat is fundamentally important for rapid vegetation restoration of the degraded karst ecosystems in southwest China.
Although some previous studies have examined the relationship between vegetation and karst environmental factors (Du et al., 2015; Zou et al., 2020), there has been little research regarding the variations and tradeoffs of the shrubs. In this research, we examined a suite of leaf traits in shrub plants based on field work in Huanjiang County, Guangxi Province. The aims of this research were to quantify the variations and trade-offs among the traits, and the leaf trait–karst habitat relationships, using multivariate analyses.