Ecological Stoichiometric Characteristics of C, N, and P in Pinus taiwanensis Hayata Needles, Leaf Litter, Soil, and Micro-Organisms at Different Forest Ages

The ecological stoichiometric characterization of plant and soil elements is essential for understanding the biogeochemical cycles of ecosystems. Based on three forest ages of Pinus taiwanensis Hayata (P. taiwanensis) plantations in the Gujingyuan National Nature Reserve (i.e., young (16 years), middle-aged (32 years), and mature forests (50 years)), we conducted a field experiment to analyzed C, N, and P stoichiometry and the relationships between needles, litter, soil, and micro-organisms in P. taiwanensis plantations. We intended to elucidate the nutritional characteristics and stability mechanisms of the artificial P. taiwanensis forest ecosystem. The results showed that the C contents of live needles, leaf litter, soil, and micro-organisms in P. taiwanensis plantation forests of the three forest ages were 504.17–547.05, 527.25–548.84, 23.40–35.85, and 0.33–0.54 g/kg, respectively; the respective N contents were 11.02–13.35, 10.71–11.76, 1.42–2.56, and 0.08–0.12 g/kg; and the respective P contents were 0.82–0.91, 0.60–0.74, 0.19–0.36, and 0.03–0.06 g/kg. Forest age significantly influenced both the C, N, and P contents in live needles, leaf litter, soil, and micro-organisms as well as stoichiometric characteristics (p < 0.05). Furthermore, although the litter N:P content was comparable to that of needles, the ratios of C:N and C:P in the litter were notably higher compared to those in needles. Soil C:P and N:P ratios were the highest in mature forests while microbial C:P and N:P ratios continuously decreased. Stoichiometric analyses of our findings suggest that forest stand age can influence divergent changes in element cycling among plants, soil, and micro-organisms. The presented results can aid in further understanding nutrient utilization strategies and regulatory mechanisms for P. taiwanensis plantation forest systems.