Thinning drives C:N:P stoichiometry and nutrient resorption in Larix principis-rupprechtii plantations in North China

Carbon (C):nitrogen (N):phosphorous (P) stoichiometry and nutrient resorption play an important role in terrestrial biogeochemical cycling and functioning. However, little information is available about the changes in C:N:P stoichiometry and nutrient resorption following thinning in plantation forests. Here, to reveal how thinning affects the C:N:P stoichiometry and nutrient resorption and their relationships, green leaves, senesced leaves and soil samples were collected from a pure Larix principis-rupprechtii plantation in North China after 9 years of four different thinning treatments, i.e., control (CK, 0% thinning), low thinning (LT, 14% thinning), moderate thinning (MT, 28% thinning) and high thinning (HT, 42% thinning). The results showed that excluding the green leaf C contents, thinning significantly increased the C, N, and P contents in green leaves, senesced leaves, and soil (p < 0.05). Thinning significantly decreased the C:N and C:P ratios in green leaves, C:P and N:P ratios in senesced leaves, and C:N, C:P, and N:P ratios in soil (p < 0.05), while thinning did not significantly affect green leaf N:P and senesced leaf C:N ratios (p > 0.05). The N resorption efficiency (NRE) showed no significant differences among different thinning treatments (p > 0.05), while thinning significantly decreased the P resorption efficiency (PRE, p < 0.05). There were different degrees of correlations between nutrient contents, stoichiometry ratios and nutrient resorption, and most of which were affected by soil properties (bulk density, soil water contents, available nitrogen and phosphorus, pH, electrical conductivity, soil microbial biomass C and N, and the activities of soil beta-glucosidase, N-acetylglucosaminidase, and acid phosphatase). The N:P ratios of green leaves and senesced leaf litter and the nutrient resorption suggested that Larix principis-rupprechtii plantations in the study region were limited by N. Overall, the variations in nutrient contents, stoichiometry ratios, nutrient resorption, and soil properties demonstrate that thinning can significantly increase nutrient contents, promote nutrient cycling, and improve soil fertility. Among the four thinning treatments, in terms of nutrients, MT is recommended in Larix principis-rupprechtii plantations in North China. Furthermore, appropriate fertilization management strategies should be considered to improve N-limitation status.