Different studies revealed an increased biomass production in grasslands due to elevated CO₂ (eCO₂). Thus, the question arises whether forage quality of grassland biomass is also influenced.

In the present study, we assessed the long-term effects of eCO₂ in context of the accompanied site conditions soil moisture, air temperature and precipitation on different forage quality and energy parameters of grassland biomass in an extensively managed temperate grassland. The study took place at the Free-Air Carbon dioxide Enrichment site near Giessen [GiFACE], which was set up in 1998. Our main objective was to assess the differences in the quality and energy content of grassland forage, exposed to elevated CO₂ [+ 20%; eCO₂] and ambient CO₂ (aCO₂) concentrations. Crude protein, C/N-ratio, crude fat, total non-structural carbohydrates, ash, crude fibre, metabolisable energy [ME] and net energy for lactation [NEL] were determined to assess the forage quality and energy content of grassland biomass separated in grasses and forbs, which was harvested twice per year (end of May, beginning of September), over the period of 2006–2015.

Forbs showed a significant decrease for most tested parameters under eCO₂ at both harvests, except for crude fibre, which showed a significant increase at the second harvest of the year under eCO₂. Grasses showed a significant negative CO₂ effect for ash content at the first harvest of the year. In addition to eCO₂, site and climatic conditions, e.g. soil moisture, affected the investigated parameters.

Based on the last 10 observation years (2006–2015) within the 18 year long experiment, eCO₂ is likely to cause a decline in forage quality, especially of forbs caused by reduced crude protein and fat contents and increased crude fibre content, in extensively managed grassland ecosystems. However, site and climatic conditions should also be considered showing the importance of long-term observations that contain the full range of climatic conditions. Periods of heat, drought and precipitation, which are expected to increase in the future, lead to a decrease of the CO₂ fertilization effect on grassland biomass and also to a negative impact on forage quality.

不同的研究表明，由于CO ₂（eCO ₂）升高，草原生物量生产增加。因此，产生了一个问题，即草原生物量的草料质量是否也受到影响。

在本研究中，我们评估ECO的长期影响₂在伴有现场条件的土壤水分，气温和降水在一个广泛的管理温带草原草地生物量的不同的饲料质量和能量参数的上下文。这项研究是在1998年成立的吉森[GiFACE]附近的自由空气二氧化碳浓缩场进行的。我们的主要目的是评估暴露于CO ₂ [ ₂ ]的草原饲草的质量和能量含量的差异[ + 20％; eCO ₂ ]和环境CO ₂（aCO ₂）浓度。测定粗蛋白，C / N比，粗脂肪，总非结构性碳水化合物，灰分，粗纤维，代谢能[ME]和泌乳净能[NEL]，以评估分离出的草地生物质的饲草质量和能量含量在草和草丛中收获，在2006-2015年期间每年收获两次（5月底，9月初）。

在这两个收获期，除了在eCO ₂下一年中第二次收获的粗纤维显着增加外，在eCO ₂下大多数测试参数的前叉均显着下降。在一年的第一收获期，草对灰分显示出显着的负面CO ₂效应。除了eCO _2之外，地点和气候条件（例如土壤湿度）也影响调查的参数。

根据为期18年的实验中的最近10个观察年（2006-2015年），eCO ₂可能会导致粗饲料质量下降，尤其是粗蛋白和脂肪含量降低以及粗纤维含量增加所导致的饲草质量下降受管理的草地生态系统。但是，还应考虑现场和气候条件，以显示长期观测的重要性，这些观测值应包含所有气候条件。预计将来会增加的高温，干旱和降水时段，将导致CO ₂施肥对草地生物量的影响降低，并对草料质量产生负面影响。