以株龄1 a的桑树（Morus alba Linn.）实生苗为材料，采用盆栽实验，研究不同生物炭施加量（20~50 g·kg^-1）对盐碱土（盐度0.4%）中桑树幼苗生长、叶片光合特性和抗氧化特性及土壤性质的影响，并对桑树幼苗生长、生理指标与土壤性质间的相关性进行分析。结果表明：施加40 g·kg^-1生物炭的盐碱土中桑树幼苗株高、单株干质量、总根长、总根面积、总根体积及根平均直径较未施加生物炭处理（对照）显著（P＜0.05）增加，增幅分别为29.82%、24.88%、78.32%、139.69%、231.07%和32.50%，叶片脯氨酸含量、可溶性糖含量、丙二醛含量及过氧化物酶活性较对照显著降低，降幅分别为45.48%、25.04%、29.21%和54.87%，表明施加适量生物炭可以缓解盐碱胁迫对桑树幼苗的氧化胁迫。施加30 g·kg^-1生物炭的盐碱土中桑树幼苗叶片叶绿素a含量、类胡萝卜素含量、总叶绿素含量、净光合速率、气孔导度、PSⅡ实际光合效率及相对电子传递速率较对照显著提高，增幅分别为38.52%、43.48%、37.21%、56.14%、100.00%、2.90%和33.14%，缓解了盐碱胁迫对光合系统的损伤。施加40 g·kg-1生物炭的盐碱土的pH值较对照显著降低，降幅为4.04%，阳离子交换量、有机质含量、铵态氮含量、硝态氮含量、速效磷含量、脲酶活性及碱性磷酸酶活性较对照显著升高，增幅分别为4.86%、84.90%、50.98%、58.04%、17.26%、46.67%和23.23%。相关性分析结果显示：总体上看，桑树幼苗生长指标与土壤有机质含量、硝态氮含量、速效磷含量、脲酶活性、蔗糖酶活性呈显著或极显著（P＜0.01）正相关，光合色素含量、净光合速率和气孔导度与土壤铵态氮含量呈显著或极显著正相关，叶片渗透调节物质含量和丙二醛含量与土壤有机质含量呈极显著负相关，叶片抗氧化酶活性与土壤速效磷含量呈显著或极显著负相关，表明生物炭通过改善盐碱土肥力与微环境，协同促进桑树幼苗根系形态结构优化、光合效率提升及抗逆响应调控。综上所述，施加30~40 g·kg^-1生物炭可作为滨海盐碱地区桑树种植的适宜栽培措施，并有助于盐碱土改良。

Taking one-year-old Morus alba Linn. seedlings as materials, the effects of different biochar application amounts （20-50 g·kg^-1） on seedling growth of M. alba, photosynthetic characteristics and antioxidant properties of leaves, and soil properties in saline-alkali soil （salinity of 0.4%） were investigated by using a pot experiment, and the correlations between growth and physiological indexes of M. alba seedlings and soil properties were analyzed. The results show that the plant height, dry mass per plant, total root length, total root area, total root volume, and average root diameter of M. alba seedlings in the saline-alkali soil with 40 g·kg^-1 biochar are significantly （P<0.05） increased by 29.82%, 24.88%, 78.32%, 139.69%, 231.07%, and 32.50% respectively compared with no biochar application treatment （the control）, while proline content, soluble sugar content, malondialdehyde content, and peroxidase activity of leaves are significantly decreased by 45.48%, 25.04%, 29.21%, and 54.87% respectively, indicating that applying an appropriate amount of biochar can alleviate oxidative stress in M. alba seedlings caused by saline-alkali stress. The chlorophyll a content, carotenoid content, total chlorophyll content, net photosynthetic rate, stomatal conductance, actual photosynthetic efficiency of PSⅡ, and relative electron transfer rate in leaves of M. alba seedlings in the saline-alkali soil with 30 g·kg^-1 biochar are significantly increased by 38.52%, 43.48%, 37.21%, 56.14%, 100.00%, 2.90%, and 33.14% respectively compared with the control, mitigating the damage to photosynthetic systems caused by saline-alkali stress. The pH value of saline-alkali soil with 40 g·kg^-1 biochar is significantly decreased by 4.04% compared with the control, while cation exchange capacity, organic matter content, ammonium nitrogen content, nitrate nitrogen content, available phosphorus content, urease activity, and alkaline phosphatase activity are significantly increased by 4.86%, 84.90%, 50.98%, 58.04%, 17.26%, 46.67%, and 23.23% respectively compared with the control. The correlation analysis result shows that in general, growth indexes of M. alba seedlings show significant or extremely significant （P<0.01） positive correlations with organic matter content, nitrate nitrogen content, available phosphorus content, urease activity, and sucrase activity of soil, photosynthetic pigment content, net photosynthetic rate, and stomatal conductance show significant or extremely significant positive correlations with soil ammonium nitrogen content, leaf osmotic adjustment substance content and malondialdehyde content show extremely significant negative correlations with soil organic matter content, while leaf antioxidant enzyme activities show significant or extremely significant negative correlations with soil available phosphorus content, indicating that biochar synergistically promotes the optimization of root morphological structure, photosynthetic efficiency improvement, and stress resistance response regulation in M. alba seedlings by improving saline-alkali soil fertility and microenvironment. In conclusion, applying 30-40 g·kg^-1 biochar can serve as a suitable cultivation measure for M. alba planting in coastal saline-alkali areas, and contribute to the improvement of salinealkali soil.