Effects of rock lithology and soil nutrients on nitrogen and phosphorus mobility in trees in non-karst and karst forests of southwest China

The primary productivity of terrestrial plants is widely limited by nitrogen (N) and phosphorus (P), and the mobility of N and P in plants is the key to predicting plant growth and development. Non-karst and karst forests soil have different nutrient supply capacities due to the difference in soil parent material, but the effect mechanism of the two soil nutrient conditions on the N and P mobility process of trees remains unclear. In this study, forests dominated by three typical tree species, Eucalyptus maideni, Pinus yunnanensis, and Quercus franchetii were selected as the research objects in non-karst and karst areas of southwest China to investigate the effects of soil nutrient conditions on plants' N and P foraging, transportation and resorption. The results showed that the rock lithology had significant effects on the soil nutrients, plants' N and P foraging, transportation, and resorption. The soil total N and P concentrations, soil organic carbon concentration, and pH were higher in karst forests than those in the non-karst forests, but the green leaves N and P concentrations exhibited opposite characteristics. The root foraging potential for N and P in non-karst forests was significantly higher than that in karst forests. The N resorption efficiency of trees in karst forests was higher than that in non-karst forests, but the P resorption efficiency was lower than that in non-karst forests. The trade-offs of foraging, transportation and resorption of trees were adjusted according to changes in nutrient conditions, but the trade-offs of the three processes were not continuous in non-karst and karst forests. Compared with non-karst forests, the decreased degree of root nutrient foraging potential in karst forests was greater than the transportation factor and resorption efficiency. The slow-growing Quercus franchetii among the three typical forests showed better adaptability to foraging, transportation, and resorption of N and P in karst areas. The results revealed the response of different forests' N and P mobility patterns of trees to different nutrient conditions in non-karst and karst areas, which was helpful to improve the prediction and mechanistic understanding of nutrient cycling in local forest ecosystems.