关键词: 湘中丘陵区, 植被恢复, 碳氮磷化学计量比, 内稳态, 养分利用效率, 氮磷再吸收效率

Abstract:

Aims The aims of this study were to explore how vegetation restoration affects leaf, litter and soil C, N, P stoichiometry dynamics and nutrients cycling, and to characterize the homeostasis and nutrient use strategy of plants at different vegetation restoration stages in the mid-subtropical area of China.
Methods Four vegetation types representing the successional sequence in the secondary forests were selected using the “space for time substitution” approach in central hilly area of Hunan Province, China, which consists of Loropetalum chinense + Vaccinium bracteatum + Rhododendron simsii scrub-grass-land (LVR), Loropetalum chinense + Cunninghamia lanceolata + Quercus fabri shrubbery (LCQ), Pinus massoniana + Lithocarpus glaber + Loropetalum chinense coniferous-broad leaved mixed forest (PLL), and Lithocarpus glaber + Cleyera japonica + Cyclobalanopsis glauca evergreen broad-leaved forest (LCC). Permanent plots were established in each community. The organic carbon (C), total nitrogen (N) and total phosphorus (P) contents in leaf, undecomposed litter layer and 0-30 cm soil layer were quantified at each stage. The response and nutrient use strategy of plant to environmental changes were estimated by allometric growth, nutrient use efficiency and nutrient reabsorption efficiency.
Important findings 1) Along vegetation restoration, the leaf C:N, C:P ratios decreased significantly and the highest values were in LVR. Leaf C, N, P contents, soil C, N contents and soil C:N, C:P, N:P ratios increased significantly, in which leaf C, N contents and soil C, N contents, N:P in LCC were higher than those in LVR, LCQ and PLL, and leaf P content and soil C:N, C:P in PLL were higher than those in LVR, LCQ and LCC. Leaf N:P (>20) indicated that all restoration stages were P limited. C, N, P contents and their stoichiometry of litter fluctuated greatly. 2) The relationships between litter and leaf or soil nutrients and their stoichiometry were weak, and the significant correlations were found in the relationships between leaf and soil nutrients and their stoichiometry. Leaf C, N and P were positively correlated with soil C, N, C:N (except leaf C, N contents), C:P and N:P, while leaf C:N was negatively correlated with soil C, N, C:P and N:P, leaf C:P was negatively correlated with soil C content, C:N and C:P, and leaf N:P were negatively correlated with soil C:N. 3) During vegetation restoration, leaf N and P had significantly allometric growth relationship (p < 0.01) with the allometric index being 1.45. The use efficiency of N and P nutrients in leaf showed decreasing trends and reabsorption efficiency showed increasing trends, and the lowest N use efficiency was observed in LCC and the lowest P use efficiency was in PLL, but the highest N, P reabsorption efficiency were both in PLL. 4) The leaf N content had weak homeostasis, and leaf P content had strong homeostasis to maintain P balance in plant under P limited in soil. Vegetation restoration had significant effects on leaf, litter and soil C, N, P contents and their stoichiometry. The C, N, P contents and their stoichiometry had significant correlations between leaf and soil. Plants could adapt to the shortage of soil nutrient supply mainly by reducing nutrient use efficiency and improving nutrient reabsorption capacity. The N and P cycles of the leaf-litter-soil system gradually reached the “stoichiometric equilibrium” during vegetation restoration.

Key words: central hilly area of Hunan Province, vegetation restoration, carbon, nitrogen and phosphorus stoichiometry ratio, homeostasis, nutrient use efficiency, nitrogen and phosphorus reabsorption efficiency