Physio-ecological adaptability and service function in karst rocky desertification control of Premna puberula

Increased soil erosion as a consequence of karst rocky desertification (KRD) reduces soil quality and plant diversity. Premna puberula Pamp. is a perennial understory shrub that can adapt to the harsh environment of KRD and has potential value for KRD environmental restoration. We measure morphological and photosynthetic characteristics, nutrient accumulation, and soil physical and chemical properties of two-year-old P. puberula planted in KRD habitat and non-rocky desertification areas, and investigate how it adapts to this habitat. In KRD areas, P. puberula reduces aboveground water loss by decreasing leaf area, stomatal conductance, and transpiration rate, while increasing leaf thickness, root length and number, and increases belowground biomass to absorb more water and nutrients. In KRD areas, drought leads to decreased leaf water content, stomatal conductance, intercellular CO₂ concentration, and chlorophyll content, and decreased photosynthetic rate. Soluble sugar and protein contents increase in KRD areas in response to water stress, but pectin and flavonoid contents decrease. Correlation analysis reveals that leaf area and thickness are important functional traits that affect leaf water content and photosynthesis. Totals of leaf carbon, nitrogen, and phosphorus, along with C: N, C: P, and N: P ratios, are coupled with leaf photosynthetic characteristics and root development. Redundancy analysis reveals that available K and P, and total P, K, and N in soil mainly influence the differences in plant functional traits, explaining 95.8%, 95.5%, 91.1%, 85.8%, and 74% of variation, respectively. We hypothesize that P. puberula reduces aboveground productivity to maintain its water balance, and acquires more water and nutrients by increasing belowground biomass. It indicates that this species adapts to arid KRD environments.