Changes in nitrogen and phosphorus limitation during secondary succession in a karst region in southwest China

Abstract

Nitrogen (N) and/or phosphorus (P) limitation to primary productivity and other biological processes can change in a variety of ways as ecosystems develop. How N limitation and P limitation change from the early to the late stages of a secondary succession following farmland abandonment remains unclear in karst ecosystems in southwest China. We used community foliar N:P ratio, soil alkaline phosphatase activity (APA) and other indicators of nutrient status (soil organic carbon [SOC], total soil N [TN], and total soil P [TP], Alkali-hydrolyzable N [AN], and available soil phosphorus [AP] concentrations) to examine changes in N and P status during secondary vegetation succession. Four types of plant communities (grasslands, shrublands, secondary forest, and primary forest) represented the early, middle, late, and very late successional stages, respectively. Community foliar N:P ratio, APA, and APA per unit SOC increased as succession proceeded from the grassland to the secondary and primary forest communities. Moreover, community foliar N:P ratios in the grassland were positively correlated with soil TN, while community foliar N:P ratios in the secondary forest and primary forest were negatively correlated with soil TP, but were not correlated with soil TN. Community foliar N:P ratios in the shrubland were not correlated with either soil TN or TP. Our results suggest that the grassland in the karst region of southwest China is N limited, that the secondary and primary forests are P limited, and that the shrubland is constrained by N and P together or by other nutrients.