In managed orchards, fertilization brings out not only high productivity expectations but also severe environmental pollution. Because economic profit takes priority over environmental cost, increasing amounts of fertilizer have been used in mature subtropical Torreya grandis orchards. However, given the magnitude of global nitrogen deposition, it’s worth considering whether heavy fertilizer treatment is necessary. To elucidate the balance between T. grandis nutrient demands and fertilizer supply, we determined the C, N, and P concentrations of foliar and soil ([C], [N], [P]) at 9 orchards undergoing long-term fertilizer treatments in two scenarios of N and N + P addition with different intensity. After documenting the dynamic variation of plant growth, nutrients characteristic, and the corresponding resorption efficiency, we found that excessive N addition interfered T. grandis’ sensibility to P availability in this N-enrichment area, leading to an increasing foliar [P] and resorption efficiency (PRE) and decoupling plant C:N:P ratios. As a result, enhanced fertilizer supply failed to improve carbon accumulation, plant growth, and yield effectively. These results demonstrate that extra fertilization in the N-saturated study area highly reduced the economic and ecological efficiency of fertilizers. Thus, our research suggests that N addition in the studied orchards should be rejected, and we recommend organic management as a more conducive method to achieve sustainable development.

Thermal dissipation of excess excitation energy is an important photoprotective mechanism that plants have evolved to cope with surplus illumination. However, light-energy-partitioning dynamics in an exotic sand-dune willow (Salix psammophila) commonly used in restoring and/or stabilizing sand lands in northwestern China is largely unknown. In this study, chlorophyll fluorescence (ChlF) of photosystem II (PSII) was continuously monitored in situ in Salix psammophila to investigate plant acclimation processes driven by excessive solar radiation and extreme air temperatures (T_a). As part of a heat-regulation mechanism, energy partitioning is shown to vary with prevailing environmental conditions. In this investigation, energy absorbed during periods of moderate photosynthetically active radiation (PAR < 1200 μmoL·m⁻²·s⁻¹) was largely allocated towards photochemistry (Φ_PSII) with nominal amounts to thermal dissipation through reversible thermal dissipation (Φ_NPQr). In extremely high solar radiation (PAR > 1500 μmoL·m⁻²·s⁻¹) or in a cold temperature (T_a < 0 °C), more energy was dissipated by way of non-regulated thermal energy (Φ_f,D) and sustained thermal dissipation (Φ_NPQs), leading to non-reversible photoinhibition or photodamage. This was mainly as a result of the low utilization and high absorption of light energy by PSII under cold conditions and physiologically-induced vulnerability. It was concluded that Salix psammophila had a clear tolerance to high temperatures and moderate solar radiation, but tended to be more vulnerable to high solar radiation and cold temperature. Based on species sensitivity to extreme environmental conditions, practical application and extension of Salix psammophila for land-restoration purposes should be approached cautiously, especially in high-latitude or high-altitude desert ecosystems commonly affected by events of high solar radiation and cold temperature.

Global change drivers, including drought and nitrogen (N) deposition, exert a wide-ranging influence on tree growth and fitness. However, our current understanding of their combined effects is still limited. Non-structural carbohydrate (NSC) storage is an important physiological trait for tree acclimation to drought. It acts as an important mobile carbon reserve to support tree function when carbon fixation or transport are reduced under drought. It is crucial to investigate how tree species with different NSC storage characteristics (e.g., storage level, partitioning) respond to drought events, and how N alters these patterns. We investigated the combined effects of drought (80% reduction in precipitation) and N addition (0, 30, and 120 kg/ha/year) on the growth and NSC storage of Pinus koraiensis and Fraxinus mandshurica (dominant species in the forests of Northeast China) saplings over two consecutive growing seasons. The results indicated that P. koraiensis exhibited high tolerance to drought, with growth unaffected by drought alone until the mid-growing season in the second year. However, N addition reversed its drought acclimation by impairing root development and exacerbating carbon shortage. In contrast, F. mandshurica was sensitive to drought, it had significantly reduced growth at harvest despite a large amount of NSC accumulation. The present study highlights the contrasting effects of N deposition on drought adaptation in coexisting conifer and temperate broadleaf species, the conifer showing a higher risk of carbon deficiency with increasing N deposition (i.e., a stronger reversal effect of N addition), whereas an earlier cessation of growth under drought defines a larger carbon safety margin for broadleaved species. These results have important implications for the development of adaptive forest management strategies such as to enhance the protection of conifers in the context of global change.

The effects of simulated acid rain (SAR) on the photosynthetic performance of subtropical coniferous species have not been thoroughly investigated. In this study, we treated two coniferous species, Pinus massoniana (PM) and Cunninghamia lanceolata (CL), with four gradients of SAR and then analyzed their photosynthetic activities through measurements of gas exchange, prompt fluorescence (PF), delayed fluorescence (DF), and modulated reflection at 820 nm (MR₈₂₀). Gas exchange analysis indicated that the decrease in the net photosynthetic rate (Pn) in PM and CL was unrelated to stomatal factors. For the PF transients, SAR induced positive K-band and L-band, a significant reduction in photosynthetic performance index (PI_ABS), the quantum yield of electron transfer per unit cross-section (ET_O/CS_m), and maximal photochemical efficiency of photosystem II (F_v/F_m). Analysis of the MR₈₂₀ kinetics showed that the re-reduction kinetics of PSI reaction center (P700⁺) and plastocyanin (PC⁺) became slower and occurred at later times under SAR treatment. For the DF signals, a decrease in the amplitude of the DF induction curve reduced the maximum value of DF (I₁). These results suggested that SAR obstructed photosystem II (PSII) donor-side and acceptor-side electron transfer capacity, impaired the connectivity between PSII and PSI, and destroyed the oxygen-evolving complex (OEC). However, PM was better able to withstand SAR stress than CL, likely because of the activation of a protective mechanism.

Revealing the interactions between stand structure factors and ecosystem functions is crucial for enhancing forest soil and water conservation, as well as carbon storage. However, the optimal stand structure configuration for achieving superior ecological functions remains unclear, particularly in complex subtropical evergreen broad-leaved forests. Using Schima superba Gardn. et Champ. forests in Dongbai Mountain as a case study, this study investigated the effects of seven stand structure factors—stand density, canopy density, uniform angle index, and mixing degree—on three key ecosystem functions, water-holding function, soil improvement function, and carbon sequestration. Redundancy analysis (RDA) and structural equation modeling (SEM) were employed to quantify these relationships. The results identified stand density as the most influential factor, directly or indirectly affecting ecosystem functions by regulating other structural attributes. Optimal structural configurations were determined, including stand densities of 1228, 1532, and 1675 plants·hm⁻² for maximizing water-holding function, soil improvement function, and carbon sequestration, respectively. Recommendations emphasize adjusting stand density, canopy density, uniform angle index, and mixing degree according to site-specific conditions. Practical strategies, such as replanting, intercropping, and introducing functionally complementary species, should aim to enrich vertical structure, maintain species randomness, and avoid dominance by a single species or excessive density. These findings offer actionable insights for improving the ecological functions of subtropical forests and have broader implications for sustainable forestry management, advancing regional carbon neutrality, and addressing global ecological challenges.

Numerous studies on biodiversity–ecosystem functioning (BEF) have shown that mixed plantations can improve the ecological benefits of forest ecosystems. However, few studies have employed a multi-dimensional approach to study the integrated ecological benefits of mixed plantations. This study aims to evaluate the stand characteristics and ecological benefits of different forest types by examining various ecological indicators, including trees, shrubs, herbs, and soil properties. Focusing on typical mixed broadleaf–conifer plantations (MBCPs), mixed coniferous plantations (MCPs), and pure Cunninghamia lanceolata (Lamb.) Hook plantations (PCLs) at the Guiyang Plantation Farm, Suichang, we analyzed growth performance, spatial structure, understory vegetation diversity, and soil physicochemical properties across these forest types. For each forest type, one 100 × 100 m plot was established. Within each plot, five 20 × 20 m subplots were selected for investigation. Our results show that the aboveground biomass of MCPs is higher than that of MBCPs and PCLs, with increases of 46.58% and 177.29%, respectively. Furthermore, both mixed plantations offer better stand structure compared to pure plantations. In mixed plantations, the MBCPs exhibited a high degree of niche overlap, indicating that interspecific competition outweighed complementarity, whereas the MCPs demonstrated a more favorable stand structure. MCPs also exhibit significantly greater understory vegetation diversity compared to MBCPs and PCLs, with increases of 4.19%–13.04% and 10.34%–36.99%, respectively. Additionally, mixed plantations enhance soil moisture retention and fertility. With the onset of global warming and the increasing prevalence of extreme weather events, the establishment of artificial mixed plantations is an essential strategy to address climate change and enhance the ecological benefits of plantations.