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.

The main dominant tree species of karst forest at the microtopography and the microhabitat scale were taken as the research object in this study, and the stoichiometric characteristics of different components and their influencing factors were analyzed in order to reveal the survival strategy of karst forest plants in harsh habitats and their mechanism of adaptation to complex terrain. The results showed that the nutrient distribution among different components of the plant was closely related to its organizational structure and functional attributes. The microtopography had a significant effect on plant nutrient accumulation. However, the effect of the microhabitat on plant stoichiometric characteristics was relatively small. Different ecological factors had various regulatory effects on the stoichiometric characteristics of plant components, among which the specific leaf area (SLA) was the most critical biological factor affecting the stoichiometric characteristics of new leaves. Leaf dry matter content (LDMC) had the greatest effect on mature leaves, litter, and branches, and the trunks were mainly affected by plant species. There are synergistic tradeoffs between different plant components, and the interaction between each element mainly shows antagonistic and synergistic effects. Plants adapt to the changes in the karst microtopography and microhabitat by adjusting resource allocation and structural and functional traits. In the upslope, shady slope, and semi-shady slope regions and slopes above 25°, the plants adopted a conservative strategy. In depressions, on sunny slopes, and on flat land, as well as on slopes below 25°, the resource acquisition strategy was adopted. This is the result of the interaction of biological and abiotic factors, which reflects the resource acquisition and nutrient allocation strategies of plants in different habitats, and it is also an mechanism of adaptation to a complex and changeable environment.

Twenty-four plants were studied in Guizhou province, China. Based on various microhabitats (soil surface, stone gully, and stone surface) and microtopographies (slope aspect, slope position, and slope degree), the photosynthetic characteristics of the plants were measured, including the net photosynthetic rate (P_n), carboxylation efficiency (CE), stomatal conductance (G_s), water use efficiency (WUE), transpiration rate (T_r), intercellular CO₂ concentration (C_i), and light use efficiency (LUE). The results demonstrated remarkable variations in the WUE of four types of plants in three microhabitats, showing that stone gully > soil surface > stone surface; there were no remarkable variations in the P_n, T_r, C_i, G_s, CE, and LUE in the three microhabitats. The P_n, T_r, G_s, and LUE of deciduous trees exhibited remarkably higher values compared to the other species studied in the three microhabitats. The evergreen trees’ WUE was much higher than that of the other plants when they were growing on stone surfaces or in a stone gully. There were remarkable variations in the plants’ photosynthetic characteristics dependent on the microtopography. In terms of slope steepness, the P_n, CE, and LUE were the highest in plants on slopes ≤ 5°. Meanwhile, in terms of slope position, the P_n, T_r, CE, and LUE were highest for plants growing in depressions. Concerning slope aspect, the P_n, G_s, CE, and LUE reached the largest values in plants growing on flat land. Principal component analysis (PCA) indicated that the P_n, LUE, and WUE were the key photosynthetic parameters reflecting the adaptation of plants to karst environments. Correlation analysis revealed that the P_n and LUE displayed a striking positive correlation with the T_r, C_i, G_s, CE, and WUE. The T_r displayed a striking positive correlation with the C_i, G_s, CE, and LUE, while a striking negative correlation was observed with WUE. This study indicated that evergreen trees exhibit conservative strategies, while deciduous trees use strategies associated with high growth rates. This study provides insights important for the restoration and reconstruction of vegetation in karst regions.

To explore environmental differentiation in the stoichiometric characteristics of carbon (C), nitrogen (N), phosphorus (P), potassium (K), and their ratios among tree species organs in different lithological karst regions of Guizhou, six common species were selected from the limestone karst area of Liping and the dolomite karst area of Shibing. The analysis focused on the differences in the contents of C, N, P, and K, as well as the ratios of C/N, C/P, C/K, and N/P, and the correlations among these elements in branches, leaves, and roots, with the aim of investigating the allocation distribution patterns of nutrient elements among organs in tree species under different lithological karst conditions. The results showed the following: In both dolomite and limestone karst regions, the tree species exhibited a distinct characteristic: their leaves exhibited high C levels, but relatively low N and P levels. Tree species in both karst regions showed high C/N, C/P, and C/K ratios, indicative of rapid C assimilation rates and efficient utilization of N, P, and K. Plant growth in the dolomite region was N-limited, while plant growth in the limestone region was P-limited. However, plant growth in neither region was K-limited. The nutrient characteristics and adaptation strategies of plants in dolomite and limestone karst regions were the result of multiple factors, such as lithology, plant organs, and interactions among elements. In conclusion, considering the differences in lithology during vegetation restoration and management in karst regions, targeted application of nitrogen or phosphorus fertilizers is expected to promote plant growth and further enhance the carbon sequestration capacity of both karst plants and soils.

In order to reveal the adaptation strategies of karst forest plants to “high-calcium (Ca)–low-phosphorus (P) heterogeneous” habitats, the dominant shrubs and herbs in the Maolan karst area were taken as the research objects. The carbon (C), nitrogen (N), P, potassium (K), Ca, and magnesium (Mg) contents of plant components and their stoichiometric ratios in different microhabitats were systematically measured, and the environmental driving factors were analyzed by redundancy analysis (RDA) and variance partitioning analysis (VPA). The results showed that there were no significant differences in the plant nutrient contents and stoichiometric ratios in different microhabitats, but there were significant differences with respect to the components. The contents of N, P, K, and Mg in shrub leaves were significantly higher than those in branches and roots, while the contents of C/N, C/P, and C/K in branches and roots were significantly higher than those in leaves. The K content of herb leaves was significantly higher than that of roots. This reflects the functional differentiation of plant components and the different trade-off strategies for resource acquisition and storage. The stoichiometric characteristics of shrub leaves are dominated by species characteristics, while herb leaves are controlled by leaf tissue density (LTD), and soil-exchangeable Ca has a significant regulatory effect on the roots of both plant forms. Shrubs directly obtain bedrock slow-release nutrients through deep roots penetrating rock crevices and combine high C/N and C/P to improve nutrient utilization efficiency, forming a “mechanical resistance priority–metabolic cost optimization” adaptation strategy. Herbs respond to environmental fluctuations through functional trait plasticity and achieve rapid growth with high specific leaf area (SLA) and low LTD.