生物炭对盐碱胁迫下黑麦草和紫花苜蓿光合及抗氧化特征的影响

为探究黑麦草和紫花苜蓿在盐碱胁迫初期的响应机制，揭示生物炭对盐碱胁迫初期黑麦草和紫花苜蓿两种典型牧草光合及抗氧化系统的短期影响，采用盆栽试验方法，设置4种处理：盐碱胁迫处理（C0, 150 mmol/L等摩尔NaCl、Na2CO3、NaHCO3混合盐碱溶液）、盐碱胁迫+1%生物炭（C1）、盐碱胁迫+3%生物炭（C2）、盐碱胁迫+5%生物炭（C3），并设置无盐碱胁迫的空白对照（CK），分析盐碱胁迫初期不同生物炭添加量对植物生长指标、光合特性、丙二醛含量及抗氧活酶活性的影响。结果表明：1）14 d盐碱处理显著影响黑麦草和紫花苜蓿的生长状况，降低生物量累积、净光合速率、气孔导度、蒸腾速率、胞间CO2浓度，提高丙二醛（Malondialdehyde）含量，及超氧化物歧化酶（Superoxide dismutase）、过氧化物酶（Peroxidase）和过氧化氢酶（Catalase）活性，但对叶绿素含量和根长无显著影响（P>0.05）。2）盐碱胁迫初期，生物炭可有效提高黑麦草和紫花苜蓿的抗胁迫能力，显著降低丙二醛含量，缓解盐碱胁迫对黑麦草和紫花苜蓿生长和光合反应的抑制作用，其中3%生物炭处理的生物量、株高、根长较盐碱胁迫分别增加了48.50%～82.34%、31.19%～44.16%、17.15%～48.09%，气孔导度、蒸腾速率增加了118.69%～358.99%、98.66%～526.53%，紫花苜蓿的叶绿素含量和净光合速率分别增加了7.97%和519.09%。3）盐碱胁迫下，随施炭量增加，黑麦草和紫花苜蓿的生长指标、光合特性、细胞膜透性及抗氧化酶活性基本呈现出低添加量促进、高添加量抑制的趋势。综上所述，适量生物炭可有效缓解盐碱胁迫对黑麦草和紫花苜蓿生长的抑制作用，其中3%的生物炭施用量效果最好。

Effects of biochar on the photosynthetic and antioxidant characteristics of ryegrass and alfalfa under saline-alkali stress

Plants generally behave in different response mechanisms under stress. This study aims to reveal the effects of biochar on photosynthesis and antioxidant system of ryegrass and alfalfa at the early stage of salt-alkali stress. Four treatments were conducted in the pot experiment: saline-alkali stress treatment (C0, 150 mmol/L equal mol NaCl, Na2CO3, NaHCO3 mixed saline solution), saline-alkali stress +1% biochar (C1), saline-alkali stress +3% biochar (C2), saline-alkali stress +5% biochar (C3), and set blank control (CK) without additives. Conventional cultivation was also carried out before the experiment, and then a stress test was conducted 40 d later. The stress treatment lasted for a total of 14 d, where 100 mL mixed saline solution was added to C0, C1, C2, and C3 treatments at one time, and 100 mL deionized water was added to CK treatment. Subsequently, the response of ryegrass and alfalfa was determined on the 14th day of the experiment, including growth indices, photosynthetic characteristics, malondialdehyde content, and antioxidant enzyme activities under various levels of biochar addition. The results showed as follows: 1) 14 d salt-alkali treatment dominated the growth of ryegrass and alfalfa. Specifically, there was a significant decrease in biomass accumulation, net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. But there was no significant effect on the chlorophyll content and root length. Furthermore, the content of malondialdehyde increased significantly, indicating the antioxidant system responded positively. Similarly, the activities of superoxide dismutase, peroxidase, and catalase increased to alleviate the saline-alkali stress on plants. 2) The addition of biochar effectively improved the stress resistance of perennial ryegrass and alfalfa, thereby inducing a positive response in the antioxidant system. As such, the salinity-alkalinity stress was effectively relieved, particularly from the osmotic stress. The malondialdehyde content decreased obviously, whereas the alfalfa superoxide dismutase increased significantly, indicating that the perennial ryegrass antioxidant system was given a priority with the decomposition of hydrogen peroxide enzyme. The biomass, plant height, and root length of ryegrass and alfalfa increased by 48.50%-82.34%, 31.19%--44.16%, and 17.15%-48.09%, respectively, under 3% biochar treatment, compared with that under the salt-alkali stress. Additionally, the stomatal conductance and transpiration rate increased by 118.69%-358.99%, and 98.66%-526.53%, and the chlorophyll content and net photosynthetic rate increased by 7.97% and 519.09%, respectively. 3) The antioxidant enzyme activities and malondialdehyde content of ryegrass and alfalfa remained stable or decreased with the increase of biochar amount under the short-term salt-alkali stress. A trend was also found that the promoting at a low supplemental level and inhibiting at a high supplemental level for the growth indexes and photosynthetic characteristics. Consequently, there was a significant effect of salinity-alkalinity stress on the growth of perennial ryegrass and alfalfa, where a positive response was found at the beginning of stress. Correspondingly, an optimal addition of biochar can be expected to improve the stress resistance of perennial ryegrass and alfalfa, while the positive reaction of the oxidation system can effectively relieve the short-term salinity-alkalinity stress. The best effect was also achieved in the 3% biochar application. The findings can provide a sound reference for the scientific application of biochar to promote crop growth and yield.