Increased atmospheric carbon dioxide (CO₂) is a consequence of recent anthropogenic environmental changes, and few studies have evaluated its effects on tropical grasses used in Brazilian pastures, the main feed source for major part of ruminant livestock. This study evaluated forage production, chemical composition, in vitro total gas production and organic matter degradability of Brachiaria brizantha under contrasting CO₂ atmospheric conditions in a free air carbon dioxide enrichment (FACE) facility. The forage plants were sown in each of the 12 octagonal rings of the FACE facility: six under ambient atmospheric CO₂ concentration of approximately 390 μmol/mol, hereafter referred to as control (CON) plots, and other six rings enriched with pure CO₂ flux to achieve a target CO₂ concentration of 550 μmol/mol, hereafter called elevated CO₂ (eCO₂) plots. Soil samples were collected to determine carbon and nitrogen concentrations. After seventy days of sowing, a standardization cutting was performed and then at regular intervals of 21 days the forage was harvested (ten harvest dates) and forwarded to laboratorial analyses. Forage above‐ground biomass production (dry matter (DM): 6,143 vs. 6,554 kg/ha), as well as morphological characteristics (leaves: 71% vs. 68%; stem: 28% vs. 31%), chemical composition (crude protein: 162.9 vs. 161.8; neutral detergent fibre: 663.8 vs. 664.3; acid detergent fibre: 369.5 vs. 381; lignin: 60.1 vs. 64.1 g/kg DM; total C: 45.9 vs. 45.9; total N: 2.8 vs. 2.8; total S: 0.2% vs. 0.2%), organic matter in vitro degradability (573.5 vs. 585.3 g/kg), methane (5.7 vs. 4.3 ml/g DM) and total gas (128.3 vs. 94.5 ml/g DM) production did not differ significantly between CON and eCO₂ treatments (p > .05). The results indicated that at least under short‐term enrichment, B. brizantha was not affected by eCO₂.

中文翻译：

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在短时间内，CO2施肥不会影响C4热带草的生物量生产和营养价值

大气中二氧化碳（CO ₂）的增加是最近人为环境变化的结果，很少有研究评估其对巴西草场中反刍动物主要饲料的主要来源热带草的影响。这项研究评估了在大气二氧化碳富集（FACE）设施中，在对比CO ₂大气条件下，Brachiaria brizantha的草料生产，化学成分，体外总气体生产和有机物降解性。在FACE设施的12个八角形环中的每一个中播种了饲草植物：其中6个在环境大气CO _2下大约390μmol/ mol的浓度（以下称为对照（CON）图），以及其他六个带有纯CO ₂通量的环，以达到550μmol / mol的目标CO ₂浓度，以下称为升高的CO ₂（eCO ₂）地块。收集土壤样品以确定碳和氮的浓度。播种七十天后，进行标准化切割，然后以21天的定期间隔收获草料（十个收获日期），并转发至实验室分析。地上饲料生物量产量（干物质（DM）：6,143 vs. 6,554 kg / ha），以及形态特征（叶：71％vs. 68％;茎：28％vs. 31％），化学成分（粗蛋白：162.9 vs. 161.8；中性洗涤剂纤维：663.8 vs. 664.3；酸性洗涤剂纤维：369.5 vs. 381；木质素：60.1 vs. 64.1 g / kg DM；总C：45.9 vs. 45.9；总N：2.8 vs 2.8；总S：0.2％对0.2％），体外有机物降解性（573.5对585.3 g / kg），甲烷（5.7对4.3 ml / g DM）和总气体（128.3对94）。_2种治疗方法（p>  .05）。结果表明，至少在短期富集下，B。brizantha不受eCO _2的影响。