| Plant ecological stoichiometry reflects the adaptive strategy of plant species to the environmental changes and provides a reference for predicting the prospects of plant growth and development. It can help to understand if and how plant growth is limited by nutrient elements and the soil nutrient. The study investigated the ecological chemometrics of carbon,nitrogen and phosphorus of typical plant communities and soil in different vegetation zones in the study area. Combined with meteorological data, terrain data and vegetation restoration years information, we then analyzed the spatial and temporal variations of ecological stoichiometry of carbon, nitrogen and phosphorus of typical plant community and soil. The results showed that:(1)The leaf total N and P concentrations(LN and LP, respectively), fine root total N concentration(RN), root total C concentration(RC), leaf C:N, C:P, and N:P ratios(LC/LN,LC/LP and LN/LP, respectively), and fine root C:N and N:P ratios(RC/RN and RN/RP,respectively) were significantly different at both the family and genus level(P < 0.05). In contrast, the leaf total C concentration(LC), fine root total P concentration(RP), and root C:P ratio(RC/RP) were not significantly different at either the family or genus level(P > 0.05).(2) The ecological stoichiometric characteristics of different plant genera had different responses to micro-topographical variations. The RC/RN ratio of plants in the Gramineae was significantly different at sites with either a south or north aspect. However, the concentrations of C, N, and P and the stoichiometric characteristics of leaf and fine root tissues of plants in the Gramineae, Leguminosae, and Asteraceae were not significantly different at sites with either a south or north aspect. The fine root N concentrations of in the Leguminosae were significantly different at different slope positions(P < 0.05). The LN, LC, root total N concentration, LC/LN, RC/RN of Asteraceae species differed significantly among different slope positions(P < 0.05). Plants in different families and genera adapted to the environment by reacting differently to the concentrations of C, N, and P and stoichiometric characteristics.Generally, plants in the Gramineae were mainly limited by N and P in the middle slope positions, while they were limited by N on the other slope positions. Leguminous plants weremainly limited by P in the upper and middle slope positions, whereas they were limited by N and P at Mao(mountaintop) and lower slope position. Asteraceae plants were mainly limited by N and P on the upper slopes, whereas they were limited by N on the other slope positions.The stoichiometric characteristics of plants belonging to different families and genera showed significant differences among different micro-topographical environments. This indicated that plants in different families and genera may be limited by different nutrient elements in different micro-topographical environments, and that these plants adapted to variations in the hilly and mountainous environment may have different adaptive strategies.(3) The total N concentration and N/P was significantly different(P<0.05) among vegetation restoration stages in 0-20 cm, 20-40 cm and 40-60 cm soil layers. The total N concentration and N/P decreased first and then increased with the vegetation restoration, and they reached the lowest value at the third stage(restored 16~22 years). Meanwhile, at any stages, the total N concentration, P concentration and N/P decreased with the increase of the soil layer depth. The total N concentration, P concentration and N/P in leaf and P concentration in fine root was significantly different(P<0.01) between different stages. The total N concentration, P concentration of leaf and P concentration of fine root decreased first and then increased with the vegetation restoration, and reached the lowest value at the third stage; while P concentration of fine root reached the lowest values in the fourth stage(restored25~40 years). The N/P of leaf was larger than that of fine root. The total N concentration, total P concentration and the N/P of leaf, fine root and soil had different correlativity. P was the limiting factor of plant growth and communities restoration in a forest-steppe zone in hilly and gully region of the Loess Plateau.(4) Leaf nitrogen content and phosphorus content, leaf carbon/nitrogen ratio, leaf nitrogen/phosphorus ratio had significant difference among different vegetation zones(P<0.05). The growth of plant was mainly limited by phosphorus in forest zone, the growth of plant was mainly limited by nitrogen in steppe zone and was limited by nitrogen and phosphorus in forest-steppe zone. Leaf C, N, P content and ecological stoichiometric ratio had different correlation with climate, topography, soil factors. The carbon content was mainly affected by slope position, followed by the slope; The leaf nitrogen content was mainly affected by slope, followed by average annual evaporation capacity; Leaf phosphorus content was mainly affected by average annual rainfall; Leaf carbon/nitrogen ratio was mainly affected by soil total phosphorus content, followed by average annual evaporation capacity;Different factors had different effects on leaf carbon/nitrogen ratio, with the effects of soil carbon content > average rainfall from July to September > slope. |
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