Seasonal variations in carbon, nitrogen and phosphorus concentrations and C: N: P stoichiometry in different organs of a Larix principis- rupprechtii Mayr. plantation in the Qinling Mountains, China

Understanding how concentrations of elements and their stoichiometry change with plant growth and age is critical for predicting plant community responses to environmental change. We used long-term field experiments to explore how the leaf, stem and root carbon (C), nitrogen (N) and phosphorous (P) concentrations and their stoichiometry changed with growth and stand age in a L. principis-rupprechtii Mayr. plantation from 2012-2015 in the Qinling Mountains, China. Our results showed that the C, N and P concentrations and stoichiometric ratios in different tissues of larch stands were affected by stand age, organ type and sampling month and displayed multiple correlations with increased stand age in different growing seasons. Generally, leaf C and N concentrations were greatest in the fast-growing season, but leaf P concentrations were greatest in the early growing season. However, no clear seasonal tendencies in the stem and root C, N and P concentrations were observed with growth. In contrast to N and P, few differences were found in organ-specific C concentrations. Leaf N: P was greatest in the fast-growing season, while C: N and C: P were greatest in the late-growing season. No clear variations were observed in stem and root C: N, C: P and N: P throughout the entire growing season, but leaf N: P was less than 14, suggesting that the growth of larch stands was limited by N in our study region. Compared to global plant element concentrations and stoichiometry, the leaves of larch stands had higher C, P, C: N and C: P but lower N and N: P, and the roots had greater P and C: N but lower N, C: P and N: P. Our study provides baseline information for describing the changes in nutritional elements with plant growth, which will facilitates plantation forest management and restoration, and makes a valuable contribution to the global data pool on leaf nutrition and stoichiometry.