LEAF STOICHIOMETRIC TRAIT AND SPECIFIC LEAF AREA OF DOMINANT SPECIES IN THE SECONDARY SUCCESSION OF THE LOESS PLATEAU

Ecological stoichiometry is the study of the balance of multiple chemical elements in ecological interactions. Terrestrial plants exhibit inter- and intra-specific differences in leaf C:N:P stoichiometry that has been used to study plant competition and succession, nutrient use efficiency N and P nutrient limitation. However, little is known about leaf C:N ratio, N:P ratio in the Loess Plateau, particularly the pattern of leaf C:N:P stoichiometry during the secondary succession. Thus, leaf stoichiometric traits and specific leaf area (SLA) of dominant species at different secondary successional stages in the Loess Plateau were measured. The study was conducted at the Lianjiabian forest region of the Loess Plateau (35.03 degrees-36.37 degrees N and 108.10 degrees-109.08 degrees E), Gansu, China. Leaf C:N:P stoichiometry and specific leaf area of 18 dominant species (herb) community stage (Stipa bungeana Trin, Bothriochloa ischaemun (Linn.) Keng, Carex lanceolata Boott, Artemisia sacrorurn Ledeb, Pulsatilla chinensis (Bunge) Regel, Potentilla chinensis Ser), shrub community stage (Sophora viciifolia Hance, Hippophae rhamnoides (Linn.), Ostryopsis davidiana Decne, Rubus palmatus Thunb, Rosa xanthina Lindl, Acer ginnala Maxim, Spiraea pubescens Turcz, Ziziphus jujuba var. spinosa), early forest community stage (Populus davidiana Dode, Betula platyphylla Suk, Platycladus orientalis (Linn.) Franco), climax forest community stage (Quercus liaotungensis Koidz)) at four secondary successional stages were determined in the Loess Plateau in early June of 2006. The herb and shrub community stage had higher SLA than that in the early forest community stage and climax forest community stage. The Leaf C, N, C:N ratio and N:P ratio at different secondary successional stages were significantly different (P <0.05), but the leaf P didn't differ. The N:P ratio of herb community stage were significant difference from those of the others stages (shrub community stage, early forest community stage and climax forest community stage), but there were not significant difference among the shrub community stage, early forest community stage and climax forest community stage. N:P ratio shifts of the species were consistent along the successional sere, although the N:P ratio of the different species at a successional stage varied considerably. On community level, the lowest N:P ratio (9.8) was found in herb community stage in the secondary succession, the N:P ratio increased to 12.9 in shrub community stage, declined to 12.4 in early forest community stage, and increased in climax forest community stage (e.g. 12.6 in the Quercus liaotungensis Koidz community). The results suggest that the vegetation productivity of the Loess Plateau was N-limited at each secondary successional stage.