Ecological Stoichiometric Characteristics of Plant-Litter-Soil Among Different Forest Stands in a Limestone Region of China

Abstract

The transformation of degraded stands represents an essential strategy for enhancing stand productivity and optimizing site adaptability. This study examined four typical monoculture forest stands transformed from underperforming Platycladus orientalis (PO) forests in the limestone area of Xuzhou, China: Acer pictum subsp. mono (AP), Pistacia chinensis (PC), Ligustrum lucidum (LL), and Firmiana simplex (FS). The contents of carbon (C), nitrogen (N), and phosphorus (P), along with the C:N:P stoichiometric ratios, were analyzed in plants (leaves and fine roots), litter, and soil. The relationships among these components and their main influencing factors were explored. The results indicated that FS leaves contained higher levels of N and P, whereas LL litter presented significantly elevated C:N and N:P ratios in comparison with those of the other forest stands (p < 0.05). With the exception of FS, leaves displayed lower P than fine roots, which presented pronounced P enrichment. The soil C, N, and P contents decreased with depth, with both the forest stand and depth significantly impacting the soil stoichiometry (p < 0.01). Redundancy analysis identified available potassium, total nitrogen, and microbial biomass carbon in the soil as key factors influencing the stoichiometric characteristics of the leaf-fine root-litter continuum. Collectively, the leaf N:P ratios (>16) and low soil P contents indicate that plantation growth was primarily constrained by P limitation. In response, AP, PC, and LL allocate more P to fine roots to adapt to the environment.

Keywords: ecological stoichiometry; limestone region; nutrient limitation; plant–litter–soil continuum.

Figure 1

Stoichiometric characteristics of leaves and fine roots across forest stands. Different uppercase letters indicate significant differences among forest stands for the same organ (p < 0.05); different lowercase letters denote significant differences between organs within the same forest stand (p < 0.05); Acer pictum subsp. mono (AP), Pistacia chinensis (PC), Ligustrum lucidum (LL), and Firmiana simplex (FS).

Figure 2

Stoichiometric characteristics of litter across forest stands. Different letters indicate significant differences between forest stands (p < 0.05).

Figure 3

Stoichiometric characteristics of soil across forest stands. Different uppercase letters indicate significant differences between forest stands within the same soil layer (p < 0.05), whereas different lowercase letters indicate significant differences within the same forest stand between different soil layers (p < 0.05).

Figure 4

(a) Leaf–fine root–litter stoichiometry relationship; (b) leaf, fine root, litter, and 0–5 cm soil stoichiometric relationships; (c) leaf, fine root, litter, and 5–10 cm stoichiometric relationships; (d) leaf, fine root, litter, and 10–20 cm stoichiometric relationships. LE, leaves; F, fine roots; L, litter; S, soil; C, carbon; N, nitrogen; P, phosphorus; symbol: *, p ≤ 0.05; **, p ≤ 0.01; ***, p ≤ 0.001. The closer a cell’s color gets to the red at the top of the scale, the stronger the positive correlation; the closer it gets to the blue at the bottom, the stronger the negative correlation.

Figure 5

(a) RDA of aboveground C, N, and P with respect to soil properties. (b) RDA of aboveground C:N:P ratios with respect to soil properties. Blue and red arrows represent the response variables and explanatory variables, respectively. LE, leaves; F, fine roots; L, litter; SW, soil water content; SOC, soil organic carbon; TN, total nitrogen; TP, total phosphorus; AP, available phosphorus; AK, available potassium; MBC, microbial biomass carbon; MBN, microbial biomass nitrogen; MBP, microbial biomass phosphorus.

Figure 6

Location of the study area and field images of four typical forest stands.