Zhigang Yi

Soil acidification severely threatens soil health, tea quality and yield in tea plantations, making it essential to use appropriate soil amendments to address this issue. Biochar can enhance the agricultural soil environment, but its effects on microbial communities, soil fertility, tea quality and yield remain incompletely understood. In this field study, three treatments were applied in a strongly acidic tea plantation: CK (traditional fertilization), BC1 (CK with 4.5 t ha⁻¹ biochar) and BC2 (CK with 9 t ha⁻¹ biochar). Soil chemical properties, microbial communities, tea quality and yield were measured, and their correlations were analyzed. Compared with CK, BC2 significantly increased soil pH from 4.25 to 4.58 and elevated soil total carbon, total nitrogen and ammonium nitrogen by 99.18%, 21.29% and 166.67%, respectively. The BC2 treatment also enhanced soil microbial diversity and increased the relative abundance of potentially beneficial bacterial genera, which were positively correlated with improved tea quality and yield. In particular, BC2 increased free amino acids, water extracts (WE) and tea yield by 10.64%, 13.01% and 13.65%, respectively. Applying biochar at 9 t ha⁻¹ combined with traditional fertilization appears to be a promising management practice under the conditions of this study to improve soil conditions, tea quality and yield in strongly acidic plantations.

The application of biochar and magnesium (Mg) fertilizer can alleviate acidification, improve soil fertility, and enhance tea quality. However, the effects of different biochar application rates on soil properties, tea photosynthesis, and quality remain unclear. To elucidate their effects, a 90-day pot experiment was conducted with nine treatments: conventional fertilization (CK), improved conventional fertilization (CF), Mg fertilizer (MF), low/medium/high biochar (LBCF, MBCF, HBCF), and their combination with Mg (LBMF, MBMF, HBMF) in a controlled growth chamber, and soil properties, tea plant photosynthesis, and tea quality were measured. The results showed that higher application rates of biochar with Mg significantly alleviated soil acidification, increasing pH by 0.20–0.24 units. HBMF significantly enhanced key soil nutrients: total carbon (+198.11%), total nitrogen (+116.43%), and ammonium nitrogen (+73.89%). Ex-Mg increased with Mg addition and was further promoted by biochar, and photosynthetic rates increased by 71.69–101.41% in biochar and Mg application. These improvements increased free amino acids, caffeine, and soluble sugars in tea leaves by 39.56%, 46.88%, and 30.79% respectively under HBMF. Additionally, the relative contents of alcohols and esters increased by 93.29% and 62.20%, with marked rises in linalool and methyl salicylate. The increased tea quality is linked to higher activities of β-glucosidase and lipoxygenase observed in HBMF. In conclusion, the combined application of high biochar (2% of soil weight) and Mg fertilizer (15% of fertilizer weight) effectively improved soil quality, enhanced photosynthesis, and ultimately elevated both the taste and aroma quality of tea.

Soil water availability and nitrogen (N) deposition critically influence biogenic volatile organic compound (BVOC) emissions, thereby affecting atmospheric chemistry. However, their differential short- and long-term effects remain unclear. Here, Ormosia pinnata and Pinus massoniana seedlings were exposed to three water regimes (moderate drought, MD; normal irrigation, NI; near-saturated irrigation, NSI) and two nitrogen (N0; 0 kg N ha⁻¹ yr⁻¹; N80; 80 kg N ha⁻¹ yr⁻¹) treatments for 20 months. Branch-level BVOC emissions and leaf physiological and biochemical traits were examined after 8 months (short term) and 16 months (long term). In the short term, P. massoniana predominantly emitted α-pinene, β-pinene, and γ-terpinene, whereas O. pinnata emitted isoprene (ISO). After prolonged exposure, ISO became the dominant in both species. Short-term MD and NSI conditions stimulated ISO emissions in O. pinnata, with N80 addition further amplifying this effect. In contrast, long-term treatments tended to suppress ISO emissions in O. pinnata, particularly under N80. Short-term water treatments had no significant effect on monoterpene (MT) emissions in P. massoniana. Under long-term water treatments, N80 suppressed ISO emissions; nevertheless, ISO emission rates (ISOrate) progressively increased with increasing soil water availability. Although leaf intercellular CO₂ concentration (Ci), stomatal conductance (g_s), and photosynthesis-related enzymes exhibited partial correlations with BVOC emissions, an overall decoupling between leaf traits and emission patterns was evident. Our findings demonstrate the significant changes in both BVOC composition and emission magnitudes under the joint effects of water availability and nitrogen deposition, providing important implications for improving regional air quality modeling and BVOC emission predictions.

Biochar is commonly used to improve acidic soil and reduce nitrogen loss. However, the impact of biochar on soil nitrogen retention, especially at varying pH levels, is not fully understood. Soil samples were obtained from an acidic red soil citrus orchard. The soil pH was adjusted using CaO, with five levels (4.0, 5.1, 5.8, 6.6, and 7.2), and two biochar doses (0% and 1%) were applied. The study used ¹⁵N-Tracer and Ntrace to investigate biochar’s influence on soil nitrogen retention at different pH levels. The results showed that soil amendment with biochar improved gross mineralization rates (TM) and gross NH₄⁺ immobilization rates (TI), except at pH 4.0 for TI. Biochar enhanced heterotrophic nitrification (O_Nrec) within pH 4.0–7.4, with a threshold for autotrophic nitrification (O_NH4) at pH 6.4. The findings revealed biochar’s positive effect on soil nitrogen retention within pH 4.5–6.4. Biochar had a greater impact on TI than TM and inhibited O_NH4, potentially enhancing nitrogen retention in this pH range. These results highlight the significance of considering biochar incorporation for improving nitrogen use efficiency and reducing NO₃⁻-N loss in subtropical pomelo orchards.

Nitrogen (N) deposition is increasingly aggravating and has significant impact on the processes of forest soil carbon (C) cycling. However, how N deposition affects forest soil C cycling processes in the scenario of future drought-frequent climate is still unclear. Therefore, we conducted a 2.5-year experiment at two levels of N addition treatments (control and N addition) and three levels of moisture (well-watered: ca. 80% of field capacity, moderate drought: ca. 60% of field capacity, severe drought: ca. 40% of field capacity) to investigate the impact of N addition, drought, and their interaction on soil respiration (Rs) and soil organic carbon (SOC) content. The results showed that N addition significantly increased Rs and SOC content, and severe drought decreased Rs and SOC content. In a well-watered condition, N addition significantly increased annual mean Rs, but in moderate drought and severe drought condition, N addition did not obviously affect Rs. In the control group, severe drought significantly decreased annual mean Rs by 61.5%, and decreased SOC content in 0–10 cm and in 10–20 cm by 3.0% and 1.6%, respectively. However, in the N addition group, moderate drought and severe drought significantly decreased annual mean Rs by 27.6% and 70.5%, respectively. Meanwhile, compared to the well-watered condition, severe drought significantly decreased SOC content in 0–10 cm and in 10–20 cm by 12.4% and 11.9% in the N addition group, respectively. Severe drought also decreased aboveground and belowground biomass, fine root biomass, MBC, and specific respiration in N addition group. The Rs and SOC content were positively correlated with aboveground biomass, belowground biomass, and fine root biomass. These results suggest that under future global change scenarios, severe drought might offset the promotive effects of N deposition on soil respiration and C sequestration in the young subtropical forest. Moreover, the N deposition may enhance the suppressive effect of drought on soil respiration and C sequestration in the future.