The inorganic nitrogen (N) that can be absorbed and utilized by plants is mainly ammonium N (NH₄⁺-N) and nitrate N (NO₃⁻-N), which may affect seedlings’ root morphology and growth through its heterogeneous distribution. Root morphology and seedling growth were investigated in a subtropical major conifer (Cunninghamia lanceolata) and a broadleaf tree species (Schima superba) under five different NH₄⁺-N to NO₃⁻-N ratios (10:0, 0:10, 7:3, 3:7, 5:5). Results: (1) While both species developed thinner roots under the treatment with a high NO₃⁻-N concentration, the roots of C. lanceolata were longer than those of S. superba. In contrast, the roots of both species were thicker under the treatment with a high NH₄⁺-N concentration, with those in S. superba being much longer than those in C. lanceolata. (2) The mixed NH₄⁺-N and NO₃⁻-N treatments were more conducive to the aboveground growth and biomass accumulation of both tree species and the underground growth of S. superba. N sources with high NO₃⁻-N concentrations were more suitable for underground growth in C. lanceolata seedlings and aboveground growth in S. superba seedlings. Under the N sources with high NH₄⁺-N concentrations, C. lanceolata tended to develop aboveground parts and S. superba tended to develop underground parts. (3) The roots of the two tree species adopted the expansion strategy of increasing the specific root length and reducing the root tissue density under the N sources with high NO₃⁻-N concentrations but the opposite with high NH₄⁺-N concentrations. The root-to-shoot ratio of C. lanceolata increased under high NO₃⁻-N concentrations, while that of S. superba increased under high NO₃⁻-N concentrations. These results indicate that the responses of root morphology to different N forms are species-specific. Furthermore, according to the soil’s N status, NH₄⁺-N can be appropriately applied to C. lanceolata and NO₃⁻-N to S. superba for cultivating seedlings.

To uncover the relationship between fine root traits and soil properties of trees under different fertilization treatments is important for understanding the nutrient acquisition strategies of woody oilseed plants under scientific fertilization management. An experiment of randomized complete block design was conducted in a Sapindus mukoross plantation using combinations of nitrogen (N), phosphorus (P) and potassium (K) fertilizers at different levels (Control: 0 kg·ha⁻² of N, P and K; level 1: 300 kg·ha⁻² of N, 250 kg·ha⁻² of P, and 200 kg·ha⁻² of K; level 2: 600 kg·ha⁻² of N, 500 kg·ha⁻² of P, and 400 kg·ha⁻² of K; and level 3: 900 kg·ha⁻² of N, 750 kg·ha⁻² of P, and 600 kg·ha⁻² of K). The response of fine root traits and soil properties of Sapindus mukoross to the application of different nitrogen (N), phosphorus (P) and potassium (K) combinations was investigated by measuring fine root traits and soil properties indices. The results showed that: (1) The soil surface is the main location of fine roots. In the 0–20 cm soil layer, the FRB, RLD, FSRL, and RAD of Sapindus mukoross were significantly increased under the fertilization treatment compared with the control. (2) In the 0–20 cm soil layer, the SOC, TN, TP, TK, AP, AK and AN of Sapindus mukoross soils were higher than those of the control group under different fertilization treatments, except for the pH. (3) Correlation analysis showed that FRB and RLD were significantly and positively correlated with SOC, AN and AP, while TP and AP were negatively correlated with FSRL and positively correlated with RAD. RDA showed that AP content in soil was the main factor which influenced the fine root traits of Sapindus mukoross. The results of the study revealed the response strategies of fine root traits and soil properties of Sapindus mukoross to N, P and K fertilizers, provided theoretical support for the scientific cultivation of woody oilseed species, and suggested scientific and rational fertilization and management strategies for Sapindus mukoross plantation forests, a species widely planted in the southern region of China.

Introduction: Paris polyphylla var. chinensis (Franch.) Hara (P. polyphylla) is a perennial medicinal plant with a reputation for therapeutic properties. It is imperative to study the photochemical processes of P. polyphylla in order to determine the optimal levels of shading and moisture management for its cultivation in artificial environments.Methods: In this study, six shading levels (no shading, 30%, 50%, 70%, 80% and 90% shading) and three soil water contents (20%, 40% and 60% of the soil water saturation capacity) were established to determine the appropriate shade intensity and soil moisture content for the growth of P. polyphylla.Results: The results showed that only the low shade groups (no shade and 30% shade) showed irreversible damage to the daily photosynthetic dynamics of the plant over the course of a day. It is important to note that excessive light can damage not only the quantum yield for electron transport (φDo) and PSII light quantum yield (Fv/Fm), but also various physiological mechanisms that can lead to overall plant damage and a decline in organic matter. A comparison of Fv/Fm during the midday period showed that the optimum shade intensity is between 50% and 70%. Low shading can significantly increase light use efficiency (LUE), but also reduces net photosynthetic rate (Pn) and transpiration (Tr), indicating the negative effect on P. polyphylla growth. Considering the balance between growth rate and damage incidence, 50% shade should be the optimal treatment for P. polyphylla, followed by 30% and 70% shade. It was also observed that treatment with low soil water content (20%) significantly reduced Pn and LUE, while increasing stomatal conductance (gs) and water use efficiency (WUE). This is associated with a decrease in the light response curve, indicating that low soil moisture inhibits the growth of P. polyphylla and increases the likelihood of irreversible light damage, so the optimum soil moisture content for P. polyphylla should be above 20%.Discussion: Considering the economic benefits and the growth and health of P. polyphylla in artificial cultivation, it is recommended that shade be controlled at around 50% while maintaining soil moisture between 40% and 60% of water content.

Background: The bacterial communities of the root surface and rhizosphere play a crucial role in the decomposition and transformation of soil nitrogen (N) and are also affected by soil N levels and distribution, especially the composition and diversity, which are sensitive to changes in the environment with high spatial and temporal heterogeneity of ammonium N (NH₄⁺-N) and nitrate N (NO₃^--N).Methods: One-year-old seedlings of Cunninghamia lanceolata and Schima superba were subjected to N stress (0.5 mmol L^-1) and normal N supply (2 mmol L^-1), and five different N form ratios (NH₄⁺-N to NO₃^--N ratio of 10:0, 0:10, 8:2, 2:8, and 5:5) were created. We analyze the changes in composition and diversity of bacteria in the root surface and rhizosphere of two tree species by high-throughput sequencing.Results: Differences in the composition of the major bacteria in the root surface and rhizosphere of C.lanceolata and S. superba under N stress and N form ratios were not significant. The dominant bacterial phyla shared by two tree species included Proteobacteria and Bacteroidota. Compared to normal N supply, the patterns of diversity in the root surface and rhizosphere of two tree species under N stress were distinct for each at five N form ratios. Under N stress, the bacterial diversity in the root surface was highest at NH₄⁺-N to NO₃^--N ratio of 10:0 of C. lanceolata, whereas in the root surface, it was highest at the NH₄⁺-N to NO₃^--N ratio of 0:10 of S. superba. The NH₄⁺-N to NO₃^--N ratio of 5:5 reduced the bacterial diversity in the rhizosphere of two tree species, and the stability of the bacterial community in the rhizosphere was decreased in C. lanceolata. In addition, the bacterial diversity in the root surface was higher than in the rhizosphere under the N stress of two tree species.Conclusion: The bacterial compositions were relatively conserved, but abundance and diversity changed in the root surface and rhizosphere of C. lanceolata and S. superba under N stress and different N form ratios. The heterogeneity of ammonium and nitrate N addition should be considered for N-stressed environments to improve bacterial diversity in the rhizosphere of two tree species.

Context: Root plasticity is an important physiological mechanism for trees to adapt to nitrogen (N) deficiency and the unequal distribution of ammonium nitrogen (NH ₄ ⁺ -N) and nitrate nitrogen (NO ₃ ⁻ -N) for promoting growth. However, the response of root plasticity in Cunninghamia lanceolata and Schima superba remains unclear. Methods: A pot experiment with C . lanceolata and S. superba compared N deficiency (0.5 mmol L ^- ¹) and normal N (2.0 mmol L ^- ¹) under five NH ₄ ⁺ -N to NO ₃ ^- -N ratios (10:0, 8:2, 5:5, 2:8, 0:10). Root morphological and physiological traits and seedling growth were investigated. Results: Under N deficiency, C . lanceolata showed significantly higher total root surface (TRS) and total root volume (TRV) at higher NO ₃ ⁻ -N concentrations, although the roots were shorter and thicker than normal N. It also showed an increased root tissue density (RTD) while specific root length (SRL) and specific root surface area (SRS) decreased. In contrast, roots of S. superba elongated at higher NH ₄ ⁺ -N concentrations, with an increase in TRS, TRV, SRL, and SRS, while RTD decreased. Different N supply treatments significantly affected N-metabolism enzyme activities in the roots of both species. The root biomass of C . lanceolata and S. superba increased compared with normal N supply level, and the relatively high NH ₄ ⁺ -N concentrations favored aboveground growth in both species. Principal component and correlation analysis revealed that there were differences in the response of C . lanceolata and S. superba to different N supply treatments. Conclusion: Appropriately increasing the application of NH ₄ ⁺ -N under N-deficient conditions promotes the growth of C . lanceolata and S. superba .

This study investigates how exogenous volatile organic compounds (VOCs) influence the root responses of Cunninghamia lanceolata under nutrient limitations. Specifically, we assessed the differential effects of syringic acid and 1-butene on root morphology, phosphorus acquisition, and stress resilience. Clonal Chinese fir seedlings were utilized to test the effects of treatment with these two exogenous VOCs under both phosphorus supply (1.0 mM KH2PO4) and no phosphorus supply (0 mM KH2PO4) treatments in a controlled pot experiment. Compared to syringic acid, 1-butene significantly enhanced root morphological traits, including root length, specific surface area, and root volume. These morphological changes enhanced the root’s ability to acquire phosphorus. Moreover, the addition of 1-butene increased the underground phosphorus use efficiency (PUE) by 25.6% compared to the addition of syringic acid. Furthermore, the addition of 1-butene stimulated higher activity of antioxidant enzymes such as superoxide dismutase (SOD) and peroxidase (POD). Proteomic analysis revealed that 1-butene induced significant changes in root protein expression, particularly in proteins associated with stress responses, phenylpropanoid biosynthesis, and phosphate transport. Compared to syringic acid, 1-butene promoted the differential expression of phosphate transporter proteins, indicating its beneficial effects on the root systems of Chinese firs under low-phosphorus stress. These findings underscore the potential of 1-butene in promoting root efficiency and phosphorus acquisition in forest species, providing insights for enhancing plant adaptation to nutrient limitations.