Carbon, nitrogen and phosphorus stoichiometry in Pinus tabulaeformis forest ecosystems in warm temperate Shanxi Province, north China

Although carbon (C), nitrogen (N), and phosphorous (P) stoichiometric ratios are considered good indicators of nutrient excess/limitation and thus of ecosystem health, few reports have discussed the trends and the reciprocal effects of C:N:P stoichiometry in plant-litter-soil systems. The present study analyzed C:N:P ratios in four age groups of Chinese pine, Pinus tabulaefonnis Cam, forests in Shanxi Province, China: plantation young forests (AY, < 20 year-old); plantation middle-aged forests (AM, 21-30 year-old); natural young forests (NY, < 30 year-old); and natural middle-aged forests (NM, 31-50 year-old). The average C:N:P ratios calculated for tree, shrub, and herbaceous leaves, litter, and soil (0-100 cm) were generally higher in NY followed by NM, AM, and AY. C:N and C:P ratios were higher in litter than in leaves and soils, and reached higher values in the litter and leaves of young forests than in middle-aged forests; however, C:N and C:P ratios were higher in soils of middle-aged forests than in young forests. N:P ratios were higher in leaves than in litter and soils regardless of stand age; the consistent N:P < 14 values found in all forests indicated N limitations. With plant leaves, C:P ratios were highest in trees, followed by herbs and shrubs, indicating a higher efficiency in tree leaf formation. C:N ratios decreased with increasing soil depth, whereas there was no trend for C:P and N:P ratios. C:N:P stoichiometry of forest foliage did not exhibit a consistent variation according to stand age. Research on the relationships between N:P, and P, N nutrient limits and the characteristics of vegetation nutrient adaptation need to be continued.