Stoichiometric Characteristics of Leaf, Litter and Soil during Vegetation Succession in Maolan National Nature Reserve, Guizhou, China

Abstract

Carbon (C), nitrogen (N), phosphorus (P) and potassium (K) are the main nutrient elements widely found in soil, litter and leaves, and their stoichiometric ratios are important indicators of ecosystem functions. However, there is little research on the effects that nutrient cycle and vegetation succession have on leaf, litter and soil nutrients and stoichiometric ratios, especially in the fragile karst areas. To reveal the nutrient cycling characteristics and ecosystem stability mechanism during vegetation succession, leaf, litter and soil samples were collected from the herbaceous community (HC), shrub community (SC), secondary forest community (SF) and primary forest community (PF) in a typical karst area at growth and senescence phases. The results showed that the nutrient contents and stoichiometric ratios of leaf, litter and soil in the main layers of each community were significantly different at the growth and senescence phase. The utilization efficiency of N in the leaves of the main layers of each succession community first decreased and then increased at different growth stages, and the utilization efficiency of P increased but the reabsorption rates of N and P showed a continuous decreasing trend. In addition, there was a significant allometric relationship between N and P contents in plant leaves during the growth phase. More importantly, the internal stability of N content in plant leaves was higher than the P content, suggesting that vegetation succession significantly affected leaf, litter and soil nutrient contents and their stoichiometric ratios in our study region. The strength of the relationship between them reflects the inheritance and co–variation of nutrient content to a certain extent, and the differences in the strategies that different species in the community use to adapt to the fragile karst environment. This study concludes that plants in the karst region mainly improve their P utilization efficiency to adapt to low phosphorus stress in soil and ensure the normal physiological and biochemical responses in the process of vegetation succession.

Responses of carbon, nitrogen, and phosphorus contents and stoichiometry in soil and fine roots to natural vegetation restoration in a tropical mountainous area, Southern China

“…Therefore, vegetation restoration could increase SOC and TN through multiple mechanisms such as litter and root turnover and biological N fixation in the study area. The findings from numerous studies are consistent with our results ( Xu et al., 2018 ; Su et al., 2019 ; Wu et al., 2022 ). It has been suggested that the vegetation biomass increment leads to an increase in P uptake by plants and therefore a decrease in soil P content ( Chen et al., 2000 ).…”

“…The soil C:P ratio is an indicator of soil P effectiveness and a measure of soil P immobilization by soil microorganisms ( Tian et al., 2010 ), and soil N:P ratio is a predictor of N saturation and can be used to evaluate nutrient limitation thresholds ( Peñuelas et al., 2012 ). In the present study, soil C:P and N:P ratios increased significantly with vegetation restoration ( Table 2 , Figures 2E, F ), which is similar to the findings reported in many previous studies ( Xu et al., 2018 ; Lu et al., 2022 ; Wu et al., 2022 ). SOC and TN content increased with vegetation restoration, but TP content did not change significantly ( Figures 2A–C ), leading to the increase in soil C:P and N:P ratios, confirming that the potential of soil microorganisms to release P from mineralized organic matter gradually decreases or remains stable over the different restoration stages.…”

“…As a basic skeletal element of plants, C maintains good homeostasis in plants ( Braakhekke and Hooftman, 1999 ). Similar to previous studies ( Su et al., 2019 ; Su and Shangguan, 2021 ; Wu et al., 2022 ), our study also suggested that fine root C content was not affected by vegetation restoration. The increase in vegetation biomass during restoration caused plants to require more P- and N-rich substances (e.g., enzymes and transported proteins) to take part in metabolic activities, which increased the nutrient uptake by fine roots ( Su et al., 2019 ).…”

“…Our study showed that vegetation restoration significantly increased SOC and TN content, whereas TP content was not significantly affected ( Table 2 ; Figures 2A–C ). Natural restoration from grassland to forest results in a larger increase in vegetation productivity, litter production, and root biomass, and thus, a significant increase in both C and N returned to the soil ( Xu et al., 2018 ; Wang and Zheng, 2021 ; Wu et al., 2022 ). Furthermore, the restoration of N-fixing tree species (e.g., the Fabaceae tree species Archidendron eberhardtii and Ormosia pachycarpa , see Table 1 ) also promotes the accumulation of N in the forest soil.…”

“…During the peak growing season (August) in summer 2021, four vegetation restoration stages, namely, grassland, shrubland, secondary forest, and primary forest, were selected on a hillside on Shiwan Mountain ( Figure 1 ) based on the spatio-temporal substitution method ( Lu et al., 2022 ; Wu et al., 2022 ). Five plots, each of 20 m × 20 m, were established for each stage.…”