Primary production - Wikipedia
Key message A negative productivity-diversity relationship was determined for biomass-dominant species at the community level. This study. Download scientific diagram | The relationship between biomass productivity and TN removal. from publication: Effect of N/P Ratio on the Biomass Productivity. Aim We aim to determine the empirical relationship between above‐ground forest productivity and biomass. There are theoretical reasons to.
Spatial pattern of estimated aboveground net primary productivity across the Hubbard Brook valley for Error estimates are given in the text. The most notable decoupling between biomass and productivity is for fir-birch-spruce dominated stands at the upper elevations, where the production: The temporal pattern of NPP following large-scale disturbance follows the usual pattern of increase to a peak value after a few decades, followed by decline at greater ages. Such an age-related decline in NPP appears to be virtually universal in all forests Ryan et al.
These temporal and spatial patterns beg the basic question: In general, forest NPP is limited by a variety of environmental conditions e.
In the cold temperate climate of the Northeast the short growing season during which temperatures are suitable for plant growth i.
For example, the time interval between leaf out and senescence for the broadleaf deciduous trees varies by about 30 d across years at HBEF ca.
One key effect of rising atmospheric CO2 concentration on forest physiology is to allow greater stomatal control over water loss. Water-use efficiency WUE is defined as the ratio of plant photosynthesis per unit water loss by transpiration. Recent measurements indicate that the WUE of northeastern U.
Although precipitation is moderately high at HBEF and evenly distributed through the year, soil moisture deficits and drought stress occur occasionally. The dominant tree species are drought avoiders that close their stomata at relatively high soil water potential, thereby reducing potential damage but restricting photosynthetic C gain Federer Notably, regional climate warming, which in the absence of CO2-induced increases in WUE would promote higher water loss by the trees, has been accompanied by increasing annual precipitation see Climate Change chapter The role of soil fertility in limiting NPP of northern hardwood forests has received considerable study over the years.
Based on a recent meta-analysis of forest fertilization studies, Vadeboncoeur concluded that NPP of most young northern hardwood forests e. Evidence for nutrient limitation of NPP in mature forests was mixed. Recent results from an ongoing N x P nutrient amendment experiment in and around HBEF suggest that P limitation may be widespread in mature northern hardwood forests.
The effects of natural variation in soil nutrient availability on biomass accumulation and NPP of the Hubbard Brook forest have been modified by inputs of pollutants derived from human activity: Although direct evidence that N deposition has altered NPP of the mature forest is scant, reduction of NPP owing to depletion of soil base cations by acid deposition has been shown conclusively in the Ca remediation experiment on W1 at HBEF Battles et al.
As noted earlier, the unexpected plateau in forest biomass on W6 is explained in part by this effect. Specifically, soil Ca depletion has limited biomass accumulation primarily by causing decline of the dominant species, sugar maple, which is particularly sensitive to low soil Ca availability Long et al. In addition to reduced net photosynthesis owing to LAI loss, higher costs of wound repair and plant defense accompany the impaired Ca nutrition of sugar maple in the reference forest Huggett et al.
As detailed by Tominaga et al. An interesting case study of the development of forest biomass and NPP following large-scale disturbance in northern hardwoods is provided by the deforestation study on W2.
There was a problem providing the content you requested
Surprisingly, despite an initial lag in biomass accumulation and net primary productivity, the forest on W2 followed a trajectory similar to though on the low end of comparable sites that had been harvested by conventional methods Figure 5.
The slowest growth and biomass accumulation were observed in the upper elevation zone of the watershed where soils are thinner and less fertile Johnson et al. These observations illustrate that northern hardwoods forests on moderately fertile soils exhibit strong resilience of productivity. The mechanisms contributing to this high resilience deserve further study but may include biologically-enhanced weathering of primary minerals Blum et al.Ecological pyramids
Forest Biomass and NPP: Questions for Further Study. What are the mechanisms contributing to soil nutrient limitation of forest productivity?
How does BNPP associated with rhizosphere carbon flux vary across the forest landscape, and what environmental and biotic factors influence this flux pathway? Conversely, will the depletion of soil calcium resulting from whole-tree harvest limit forest NPP on WS5? How will forest NPP and biomass accumulation respond to continued changes in climate and atmospheric carbon dioxide concerntration?
Table of Contents References Bailey, A. Hydro-meteorological database for Hubbard Brook Experimental Forest: Restoring soil calcium reverses forest decline. Environmental Science and Technology Letters 1 1: Mycorrhizal weathering of apatite as an important calcium source in base-poor forest ecosystems.
Vascular plants are also represented in the ocean by groups such as the seagrasses. Unlike terrestrial ecosystems, the majority of primary production in the ocean is performed by free-living microscopic organisms called phytoplankton. Larger autotrophs, such as the seagrasses and macroalgae seaweeds are generally confined to the littoral zone and adjacent shallow waters, where they can attach to the underlying substrate but still be within the photic zone. There are exceptions, such as Sargassumbut the vast majority of free-floating production takes place within microscopic organisms.
Differences in relative photosynthesis between plankton species under different irradiance The factors limiting primary production in the ocean are also very different from those on land. The availability of water, obviously, is not an issue though its salinity can be. Similarly, temperature, while affecting metabolic rates see Q10ranges less widely in the ocean than on land because the heat capacity of seawater buffers temperature changes, and the formation of sea ice insulates it at lower temperatures.
However, the availability of light, the source of energy for photosynthesis, and mineral nutrientsthe building blocks for new growth, play crucial roles in regulating primary production in the ocean. This is a relatively thin layer 10— m near the ocean's surface where there is sufficient light for photosynthesis to occur.
Light is attenuated down the water column by its absorption or scattering by the water itself, and by dissolved or particulate material within it including phytoplankton. Net photosynthesis in the water column is determined by the interaction between the photic zone and the mixed layer. Turbulent mixing by wind energy at the ocean's surface homogenises the water column vertically until the turbulence dissipates creating the aforementioned mixed layer.
The deeper the mixed layer, the lower the average amount of light intercepted by phytoplankton within it. The mixed layer can vary from being shallower than the photic zone, to being much deeper than the photic zone.
When it is much deeper than the photic zone, this results in phytoplankton spending too much time in the dark for net growth to occur. The maximum depth of the mixed layer in which net growth can occur is called the critical depth. As long as there are adequate nutrients available, net primary production occurs whenever the mixed layer is shallower than the critical depth.
Both the magnitude of wind mixing and the availability of light at the ocean's surface are affected across a range of space- and time-scales. The most characteristic of these is the seasonal cycle caused by the consequences of the Earth's axial tiltalthough wind magnitudes additionally have strong spatial components. Consequently, primary production in temperate regions such as the North Atlantic is highly seasonal, varying with both incident light at the water's surface reduced in winter and the degree of mixing increased in winter.
In tropical regions, such as the gyres in the middle of the major basinslight may only vary slightly across the year, and mixing may only occur episodically, such as during large storms or hurricanes. Annual mean sea surface nitrate for the World Ocean. Data from the World Ocean Atlas Mixing also plays an important role in the limitation of primary production by nutrients. Inorganic nutrients, such as nitratephosphate and silicic acid are necessary for phytoplankton to synthesise their cells and cellular machinery.
Because of gravitational sinking of particulate material such as planktondead or fecal materialnutrients are constantly lost from the photic zone, and are only replenished by mixing or upwelling of deeper water.
This is exacerbated where summertime solar heating and reduced winds increases vertical stratification and leads to a strong thermoclinesince this makes it more difficult for wind mixing to entrain deeper water. Consequently, between mixing events, primary production and the resulting processes that leads to sinking particulate material constantly acts to consume nutrients in the mixed layer, and in many regions this leads to nutrient exhaustion and decreased mixed layer production in the summer even in the presence of abundant light.
The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests.
However, as long as the photic zone is deep enough, primary production may continue below the mixed layer where light-limited growth rates mean that nutrients are often more abundant. Iron[ edit ] Another factor relatively recently discovered to play a significant role in oceanic primary production is the micronutrient iron.
A major source of iron to the oceans is dust from the Earth's desertspicked up and delivered by the wind as aeolian dust. In regions of the ocean that are distant from deserts or that are not reached by dust-carrying winds for example, the Southern and North Pacific oceansthe lack of iron can severely limit the amount of primary production that can occur.
These areas are sometimes known as HNLC High-Nutrient, Low-Chlorophyll regions, because the scarcity of iron both limits phytoplankton growth and leaves a surplus of other nutrients. Some scientists have suggested introducing iron to these areas as a means of increasing primary productivity and sequestering carbon dioxide from the atmosphere.
Gross production is almost always harder to measure than net, because of respiration, which is a continuous and ongoing process that consumes some of the products of primary production i.
Also, terrestrial ecosystems are generally more difficult because a substantial proportion of total productivity is shunted to below-ground organs and tissues, where it is logistically difficult to measure. Shallow water aquatic systems can also face this problem. Scale also greatly affects measurement techniques. The rate of carbon assimilation in plant tissues, organs, whole plants, or plankton samples can be quantified by biochemically based techniquesbut these techniques are decidedly inappropriate for large scale terrestrial field situations.
There, net primary production is almost always the desired variable, and estimation techniques involve various methods of estimating dry-weight biomass changes over time.
Biomass estimates are often converted to an energy measure, such as kilocalories, by an empirically determined conversion factor. Terrestrial[ edit ] In terrestrial ecosystems, researchers generally measure net primary production NPP. Although its definition is straightforward, field measurements used to estimate productivity vary according to investigator and biome. Field estimates rarely account for below ground productivity, herbivory, turnover, litterfallvolatile organic compoundsroot exudates, and allocation to symbiotic microorganisms.
There are a number of comprehensive reviews of the field methods used to estimate NPP. The major unaccounted pool is belowground productivity, especially production and turnover of roots.
Belowground components of NPP are difficult to measure. Gross primary production can be estimated from measurements of net ecosystem exchange NEE of carbon dioxide made by the eddy covariance technique. During night, this technique measures all components of ecosystem respiration. This respiration is scaled to day-time values and further subtracted from NEE. In systems with persistent standing litter, live biomass is commonly reported.