Understanding the concept of biomass is crucial in ecological studies as it provides a quantitative measure of the living or recently living biological material in a particular habitat or ecosystem. Biomass is a key indicator of ecosystem productivity and health. It reflects the ability of the ecosystem to support life, both in terms of quantity (how much biomass is present) and quality (what types of organisms make up the biomass). Measuring biomass helps in assessing the energy flow through different trophic levels, as biomass at each level represents the potential energy available to the next level. It also aids in understanding carbon cycling, as biomass is a major component of the global carbon pool. Changes in biomass can indicate alterations in ecosystem dynamics, such as shifts in species composition, impacts of invasive species, or responses to environmental changes like climate change or pollution. Biomass estimates are also crucial for managing natural resources, for instance, in forestry, fisheries, and wildlife management, where they help in making informed decisions about sustainable practices and conservation efforts.

Changes in atmospheric carbon dioxide levels can significantly influence primary production in ecosystems. Carbon dioxide is a key reactant in the process of photosynthesis, where it is converted into glucose and oxygen by plants. An increase in atmospheric CO₂ can enhance photosynthesis, a phenomenon known as the CO₂ fertilization effect. This effect is particularly pronounced in C₃ plants, which make up the majority of terrestrial plant species. Higher CO₂ levels can lead to increased rates of photosynthesis, resulting in higher Gross Primary Production (GPP) and potentially higher Net Primary Production (NPP) if other factors like nutrients and water are not limiting. However, this effect may be moderated or nullified by other environmental factors such as temperature, water availability, and nutrient limitations. Additionally, prolonged exposure to high CO₂ levels can lead to acclimation, where plants adjust to the new conditions and the initial boost in photosynthesis diminishes. On the other hand, decreasing CO₂ levels could reduce photosynthetic rates and thus lower primary production. It's also important to note that changes in CO₂ levels can affect different types of plants (C₃, C₄, and CAM) in varying ways, and their responses are influenced by a complex interplay of environmental factors.

Using calorimetry to estimate the chemical energy store in biomass, while useful, has several limitations. First, the method requires the destruction of the sample, which means it cannot be used for long-term or repeated measures in the same area of an ecosystem. This limits its application in monitoring changes over time. Second, calorimetry measures only the energy that can be released through combustion, which may not fully represent the energy available for biological processes in the ecosystem. Some compounds in the biomass, like lignin, may not combust completely, leading to an underestimation of the total energy content. Third, the method does not account for variations in energy content among different types of biomass. Different plant species and different parts of the same plant can have varying energy densities, which calorimetry does not differentiate. Additionally, environmental factors like moisture content and mineral composition can affect the combustion process, introducing variability in the results. Finally, calorimetry requires specialized equipment and controlled conditions, which might not be feasible in all field settings. Despite these limitations, calorimetry remains a valuable tool for estimating the energy content of biomass, especially when combined with other methods for a more comprehensive understanding.

Human activities can significantly impact the Net Primary Production (NPP) of ecosystems. One of the primary ways is through land use changes, such as deforestation, urbanization, and agricultural practices. Deforestation, for instance, reduces the number of trees and plants available for photosynthesis, directly decreasing the GPP and consequently the NPP. Urbanization replaces natural landscapes with buildings and roads, which similarly reduces the area available for photosynthesis. In agriculture, practices like monoculture planting, use of fertilizers, and irrigation can alter NPP. While these practices can increase NPP in some cases by enhancing growth conditions for crops, they can also lead to soil degradation and biodiversity loss, potentially reducing NPP in the long term. Additionally, pollution, such as the release of nitrogen oxides and sulfur dioxide, can affect plant health and photosynthetic efficiency, thereby influencing NPP. Climate change, driven by human activities, is also altering temperature and precipitation patterns, which can impact the photosynthetic rates and growth periods of plants, thus affecting NPP. Overall, human interventions can both positively and negatively affect NPP, depending on the nature of the activity and its impact on the ecosystem's health and functioning.

The efficiency of photosynthesis plays a critical role in energy transfer within an ecosystem. Photosynthesis efficiency refers to how well plants can convert light energy into chemical energy (as glucose). This efficiency is influenced by factors like light intensity, carbon dioxide concentration, water availability, and temperature. A higher photosynthetic efficiency means that plants can capture more solar energy and convert it into chemical energy, thereby increasing the Gross Primary Production (GPP). Since Net Primary Production (NPP) is derived from GPP (NPP = GPP - Respiration), more efficient photosynthesis leads to a higher NPP. This increased NPP results in more energy being available for the rest of the ecosystem, including herbivores, carnivores, and decomposers. Therefore, ecosystems with plants that have high photosynthetic efficiency typically support more biomass and have higher levels of productivity. Conversely, factors that reduce photosynthetic efficiency, such as insufficient light or water stress, can significantly decrease the energy available for other organisms, impacting the overall energy flow and productivity of the ecosystem.