Distribution and coupling characteristics of plant nitrogen and phosphorus along desertification gradients in alpine meadows, eastern Tibet Plateau

Analyses of plant nitrogen and phosphorus and their coupling relationships are important for determining the dynamics and functions of plant communities, as well as ecosystem processes. In this study, we analyzed the characteristics, patterns, and drivers of above- and belowground nitrogen and phosphorus contents and nitrogen: phosphorus ratios along desertification gradients in alpine grassland on the eastern Tibetan Plateau. Our results revealed that plant nitrogen content (mean value: 15.3 mg·g^–1) and the ratio of nitrogen to phosphorus (mean value: 5.2) in aboveground vegetation were lower than those in belowground parts (mean value: 28.2 mg·g^–1 and 12.5, respectively). With an increase in landscape degradation, nitrogen contents in the above- and belowground portions of plants initially increased and subsequently decreased, whereas there was no clear variation in the phosphorus contents of above- and belowground vegetation. Moreover, it was found that the above- and belowground portions of plants were generally limited by nitrogen, and the relationship between plant nitrogen and phosphorus showed virtually no correlation with desertification stress. Notably, soil water content was found to be a key factor affecting nitrogen and phosphorus contents in the above- and belowground parts of vegetation, with plants enhancing nitrogen and phosphorus contents to adapt to the soil water stress. Our findings will provide a theoretical reference for examining the survival strategies and mechanisms of plants in degraded alpine grassland ecosystems.