Net Main Production

Net primary production (NPP) is strictly divers as the divergence between the energy fixed by autotrophs and their respiration, and information technology is about unremarkably equated to increments in biomass per unit of country surface and fourth dimension.

From: Encyclopedia of Biodiversity , 2001

Volume five

C. Brannon Andersen , John Quinn , in Encyclopedia of the World'southward Biomes, 2020

Summary

HANPP is a model that estimates how much internet primary production humans appropriate, or co-opt ( Running, 2012), past country apply change, harvest, and burn down (Haberl et al., 2007). The model may have a relatively loftier uncertainty and not account for the environmental trade-offs of intensive agronomics which lowers HANPP. However, the global calibration results suggest that humans are appropriating approximately one-third of aboveground cyberspace primary product and one-quarter of total (in a higher place   +   below ground) NPP (Haberl et al., 2007, 2014; Krausmann et al., 2013), suggesting HANPP is a clear quantitative mensurate of global change. In add-on, and valuably for global synthesis, global HANPP patterns correlate well with anthropogenic biomes, suggesting that HANPP is a important and scalable measure of human impact on the terrestrial environs.

Read full affiliate

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780124095489124340

Imperiled Terrestrial Ecosystems: Nature in Retreat

Dominick A. DellaSala , in Reference Module in Globe Systems and Environmental Sciences, 2021

NPP is the cyberspace carbon assimilated by plants via photosynthesis. NPP determines the amount of free energy available for transfer through nutrient web dynamics. Deforestation, agriculture, and development consume an amount of NPP that otherwise would pass through trophic levels from base to superlative predator. In club to measure the impact of land use on NPP available for ecosystems, scientists have used a metric called human appropriation of net primary production (HANPP). Notably, HANPP has increased from 6.9  Gt C per yr in 1910–xiv.eight   Gt C per year in 2005, from 13% to 25% of the internet primary production of potential vegetation (Krausmann et al., 2013). For illustration purposes, a single Gt is roughly twice the mass of humanity, and then well-nigh fifteen   Gt of NPP consumed is equivalent to ~   xxx x the mass of humanity in plants eaten by us humans every single yr! Indeed, it is a race between us and the base of operations of a food chain already poised for collapse in many places (Millennium Ecosystem Assessment, 2005).

Read total chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B9780128211397000891

Biogeochemistry

F.Due south. ChapinIII, V.T. Eviner , in Treatise on Geochemistry (2nd Edition), 2014

10.6.2.1 What is NPP?

NPP is the net carbon gain by plants. It is the residue between the carbon gained by gross principal production (GPP – i.eastward., internet photosynthesis measured at the ecosystem scale) and carbon released past constitute mitochondrial respiration, both expressed per unit country area. Like GPP, NPP is generally measured at the ecosystem scale over relatively long fourth dimension intervals, such as a year (g biomass or g   C   m −2 year−   one). NPP includes the new biomass produced by plants, the soluble organic compounds that diffuse or are secreted into the surround (root or phytoplankton exudation), the carbon transfers to microbes that are symbiotically associated with roots (e.1000., mycorrhizae and nitrogen-fixing bacteria), and the volatile emissions that are lost from leaves to the atmosphere (Clark et al., 2001). Most field measurements of NPP document but the new constitute biomass produced and therefore probably underestimate the true NPP by at to the lowest degree 30% ( Table one ). New biomass production measures typically miss a few components of NPP: (i) root exudates, which are apace taken up and respired past microbes adjacent to roots and are generally measured in field studies as a portion of soil respiration, including the respiration of litter and surface organic layers; (two) volatile emissions are rarely measured but are generally a small fraction (<1 to 5%) of NPP and thus probably a small source of fault (Guenther et al., 1995); and (iii) biomass that dies or is removed by herbivores before it can be measured. For some purposes, these errors may not be too of import. A frequent objective of measuring terrestrial NPP, for example, is to judge the rate of biomass increase. Root exudates, transfers to symbionts, losses to herbivores, and volatile emissions are lost from plants and therefore do not directly contribute to biomass increase. Consequently, failure to measure these components of NPP does not bias estimates of biomass accumulation. Nevertheless, these losses of NPP from plants fuel other ecosystem processes such equally herbivory, decomposition, and nutrient turnover and are therefore important components of the overall carbon dynamics of ecosystems.

Table one. Major components of NPP and representative values of their relative magnitudes

Components of NPP a % of NPP
New institute biomass xl–70
Leaves and reproductive parts (fine litterfall) 10–30
Apical stalk growth 0–ten
Secondary stem growth 0–thirty
New roots 30–twoscore
Root secretions xx–40
Root exudates 10–xxx
Root transfers to mycorrhizae 15–30
Losses to herbivores and mortality 1–40
Volatile emissions 0–5
a
Seldom, if ever, take all of these components been measured in a single study.

Source: Chapin FS III, Matson PA, and Vitousek PM (2011) Principles of Terrestrial Ecosystem Ecology, 2nd edn. New York: Springer.

Some components of NPP, such every bit root production, are particularly difficult to measure out and have sometimes been assumed to be some constant ratio (due east.one thousand., 1:one) of aboveground production (Fahey et al., 1998). Fewer than 10% of the studies that report terrestrial NPP actually measure out belowground production (Clark et al., 2001). Estimates of aboveground NPP sometimes include only large plants (e.g., copse in forests) and exclude understory shrubs or mosses, which tin business relationship for a substantial proportion of NPP in some ecosystems. Most published summaries of NPP do not state explicitly which components of NPP have been included (or sometimes even whether the units are grams of carbon or grams of biomass). For these reasons, considerable circumspection must be used when comparing data on NPP or biomass among studies. In general, less is known about the true magnitude of terrestrial NPP than the extensive literature on the topic would suggest.

Read full affiliate

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780080959757008068

Biogeochemistry

F.Due south. Chapin III , V.T. Eviner , in Treatise on Geochemistry, 2007

8.06.2.1. What is NPP?

NPP is the net carbon gain by vegetation over a item time menses—typically a twelvemonth. It is the balance between the carbon gained by photosynthesis and the carbon released by establish respiration. NPP includes the new biomass produced by plants, the soluble organic compounds that lengthened or are secreted by roots into the soil (root exudation), the carbon transfers to microbes that are symbiotically associated with roots (due east.g., mycorrhizae and nitrogen-fixing bacteria), and the volatile emissions that are lost from leaves to the atmosphere (Clark et al., 2001).

"Measured" NPP is more than of an index of NPP than a true value. Near field measurements of NPP certificate merely the new found biomass produced and therefore probably underestimate the true NPP by at least 30% (Tabular array ane). At that place are many sources of mistake to this estimate. Some biomass above and beneath ground dies or is removed past herbivores before it tin can be measured, so fifty-fifty the new biomass measured in field studies is an underestimate of biomass production. Root exudates are speedily taken up and respired by microbes adjacent to roots and are generally measured in field studies every bit a portion of root respiration (i.e., a portion of carbon lost from plants), rather than a component of carbon proceeds. Volatile emissions are as well rarely measured, only are generally a pocket-size fraction (<5%) of NPP and thus are probably not a major source of error (Guenther et al., 1995; Lerdau, 1991). For some purposes, these errors may not be too important. A frequent objective of measuring NPP, for example, is to estimate the charge per unit of biomass aggregating. Root exudates, transfers to symbionts, losses to herbivores, and volatile emissions are lost from plants and therefore do not contribute directly to biomass aggregating. Consequently, failure to measure out these components of NPP does not bias estimates of biomass accumulation rates. Nonetheless, these losses of NPP from plants fuel other ecosystem processes such as nitrogen fixation, herbivory, decomposition, and food turnover, so they are important components of the overall carbon dynamics of ecosystems and strongly influence the rates of and interactions amidst chemical element cycles.

Table 1. Major components of NPP and typical relative magnitudes. a

Components of NPP % of NPP
New found biomass 40–70
  Leaves and reproductive parts (fine litterfall) 10–30
  Apical stem growth 0–10
  Secondary stem growth 0–30
  New roots 30–40
Root secretions xx–40
  Root exudates 10–thirty
  Root transfers to mycorrhizae 10–30
Losses to herbivores and mortality i–40
Volatile emissions 0–5
a
Seldom, if ever, have all of these components been measured in a unmarried study (Chapin et al., 2002).

Some components of NPP, such every bit root production, are particularly difficult to measure and have sometimes been assumed to be some constant ratio (due east.g., 1:one) of aboveground production (Fahey et al., 1998). Fewer than 10% of the studies that study total ecosystem NPP really measure components of below-ground production (Clark et al., 2001). Estimates of aboveground NPP sometimes include just large plants (e.k., trees in forests) and exclude understory shrubs or mosses, which can account for a substantial proportion of NPP in some ecosystems. Virtually published summaries of NPP do not state explicitly which components of NPP accept been included (or sometimes fifty-fifty whether the units are grams of carbon or grams of biomass). For these reasons, considerable care must be used when comparing data on NPP or biomass amidst studies. These limitations suggest that the big number of NPP estimates that are available globally may non be a valid indication of our understanding of the procedure.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0080437516081305

Biomass: Impact on Carbon Bicycle and Greenhouse Gas Emissions

Carly Dark-green , Kenneth A. Byrne , in Encyclopedia of Energy, 2004

i.2 Net Primary Production

Net main production (NPP) is a measure of the almanac productivity of the plants in the biosphere. The 550  GtC of carbon in the global reservoir of plant biomass has a corresponding NPP of lx   GtC yr−1, which indicates that globally the average carbon residence fourth dimension on land is approximately 9 years with an boilerplate biomass production (NPP) of iv tCha−1 twelvemonth−one. However, average NPP, as reported past the Intergovernmental Panel on Climate Change (IPCC) (Tabular array I) and calculated residence time varies profoundly at ecosystem level and is dependent on plant species and management, ranging from one twelvemonth for croplands to approximately 15 years for forests.

Table I. Terrestrial Carbon Stock Estimates, NPP and Carbon Residence Fourth dimension Globally Aggregated past Biome

Biome Surface area (ten9 ha) Global carbon stocks (GtC) Carbon density (tC/ha) NPP (GtC/twelvemonth) Residence fourth dimension a
Tropical forests 1.75 340 194 21.9 15.v
Temperate forests 1.04 139 b 134 8.ane 17.2
Boreal forests i.37 57 42 ii.half dozen 22.1
Tropical savannas and grasslands 2.76 79 29 xiv.ix five.4
Temperate grasslands and Mediterranean shrublands one.78 23 13 seven.0 iii.3
Deserts and semi-deserts 2.77 x iv 3.5 3.2
Tundra 0.56 2 4 0.v 4.five
Croplands i.35 4 three 4.i i.0
Total fourteen.93 c

Source. Modified from Mooney et al., 2001.

a
Average carbon residence fourth dimension=(carbon density×area)/NPP.
b
Based on mature stand density.
c
1.55×10nine ha of ice are included.

Production forests are comparatively stable ecosystems, experiencing a longer growth cycle than food and energy crops. Food and energy crops are usually harvested at the end of a relatively short rapid growth phase, leading to a college average NPP per unit area. In contrast to stable forest ecosystems, the majority of the NPP associated with free energy and food crops ends up in products exported from the site. Soil carbon density is generally lower and may become depleted every bit a outcome.

Read full affiliate

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B012176480X004186

Advances in Boil-Flux Analyses, Remote Sensing, and Evidence of Climate change

Richard H. Waring , Steven W. Running , in Wood Ecosystems (Third Edition), 2007

D Cyberspace Principal Product (NPP)

Cyberspace primary product (NPP) is the balance after autotrophic respiration is subtracted from GPP. To predict variation in NPP across geographic units of increasing size requires progressive simplifications in models, every bit emphasized in Chapter 7 and the preceding discussion. Recently, a number of simplifying features have been incorporated into predictive models of wood growth that have been widely tested on natural forests and plantations (Landsberg et al., 2003). These simplifying features include expanding from daily to monthly fourth dimension steps (Coops et al., 2000), assuming that NPP represents an approximately constant proportion of gross photosynthesis (Fig. 3.9; Gifford, 2003; only come across Cannell and Thornley, 2000), and that the fraction of NPP allocated aboveground increases with soil fertility (Fig. iii.15) while that allocated to fine roots and mycorrhizae decreases proportionally (Hobbie, 2006).

Where model predictions deviate from direct measurement of NPP, the relative importance of climatic variation, soil fertility, and soil water storage can be assessed through sensitivity analyses (Rodriguez et al., 2002). Such analyses signal where boosted field measurements might improve model predictions. Stand historic period is a variable that likewise must be recognized because older forests generally grow more slowly than younger ones on similar sites (Ryan et al., 1997; Law et al., 2004), simply older forests may as well take admission to deeper soil resources through better developed root systems. Although young forests may showroom loftier NPP, the correlation with NEP is contingent, as emphasized earlier, on recovery following disturbance (Fig. 10.3).

Figure 10.3. Net Ecosystem Production (NEP) increases linearly with Net Principal Product (NPP) except when forests are disturbed (black diamond). In the latter case, soil respiration is much enhanced. (After Pregitzer and Euskirchen, 2004.)

Read full chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/article/pii/B9780123706058500177

Ecosystem Function Measurement, Terrestrial Communities

Sandra Díaz , in Encyclopedia of Biodiversity, 2001

Two.B. Biomass Production

Net primary product (NPP) is strictly divers as the deviation between the free energy fixed by autotrophs and their respiration, and it is nearly commonly equated to increments in biomass per unit of measurement of land surface and fourth dimension. Because the increment in biomass over a given fourth dimension depends on the rate at which new biomass is produced and likewise on the initial amount of carbon-assimilating photosynthetic tissue, stands with a large standing biomass often show higher NPP than stands with lower biomass. Therefore, another useful concept is that of relative productivity rate, or the time needed by a vegetation stand up to produce its standing biomass. For example, the estimated relative productivity charge per unit for a dry tropical wood can exist many years, whereas in an annual grassland it is less than one year.

The fate of alloyed carbon—that is, whether it is allocated to increase the pools of aboveground or belowground biomass, root exudates, litter, soil organic matter, grazers, symbionts, or parasites—varies strongly between ecosystems, depending on prevailing climatic atmospheric condition, disturbance regimes, and allotment patterns of dominant plant functional types (Fig. four).

Effigy iv. Carbon pools in major ecosystem types. Soil stocks include biomass, soil organic mass, and litter. Pie diagrams signal percentage of soil carbon in belowground biomass (gray) and in soil organic mass (white) [modified from Anderson (1991) Physiological Plant Pathology, and Larcher, Fig. 2.81 (1995) © Springer-Verlag, with permission.].

At the regional scale, net primary production can be largely accounted for by climatic factors. For example, precipitation, potential evapotranspiration, and radiation are plenty to business relationship for the aboveground net primary product (ANPP) of North American forests, deserts, and grasslands. In regions of the United States with up to 1400   mm of annual rainfall, almanac precipitation is enough to account for 90% of the variability in ANPP of grasslands (Fig. 5a). At higher atmospheric precipitation, ANPP depends more on other factors, and equations based on almanac rainfall lose office of their predictive power. At the site level, variability in product seems to exist accounted for past almanac precipitation and soil water-property capacity (whc; Fig. 5b). Soil whc can take a positive or negative effect depending on the atmospheric precipitation value. In dry regions, major losses of soil water occur via blank soil evaporation. Nonetheless, where sandy soils occur, bare soil evaporation is lower than in loamy soils because water penetrates deeper into the soil. For the aforementioned reason, surface runoff is also lower in sandy soils than in loamy soils. In more humid regions, substantial water losses occur via deep percolation, which is reduced in soils with high whc. This is known equally the inverse texture hypothesis, proposed by I. Noy-Meir in 1973.

Effigy v. Regional- and site-level controls over aboveground cyberspace master production (ANPP) of U.South. grasslands, (a) Annual precipitation (APPT) is the master factor at the regional level, with ANPP = 0.6 (APPT − 56) (r 2 = 0.ninety), where 0.half-dozen represents the average h2o use efficiency of the customs, and 56   mm/twelvemonth is the "ineffective precipitation" (precipitation volume which is non enough to consequence in production). Improver of temperature and potential evapotranspiration did not improve the model, (b) Annual precipitation and soil water-holding capacity (whc) are the main factors at the site level, with ANPP = 32 + 0.45 APPT − 352 whc + 0.95 whc APPT; r 2 = 0.67) (reproduced with permission from Sala et al., 1988).

At finer scales of analysis (e.g., paddocks and vegetation patches), more variables are needed to account for ANPP. Species composition and land-utilize regime become important factors, although drivers at a coarser scale are still in performance and constrain responses (e.g., irrespective of management or species composition, annual precipitation will ready an upper purlieus to ANPP). For example, in Argentine montane and pampean natural grasslands, ANPP decreased between 50% and more 300% when subjected to moderate to heavy grazing. Species composition is crucial at this level; for case, ANPP tends to be higher in legume-dominated pastures than in grass-dominated ones because legume growth is much less limited by soil nitrogen availability due to their chapters for symbiotic nitrogen fixing.

Biomass production from local to global scales tin also exist estimated past remote sensing. The normalized deviation vegetation index, derived from the reflectance in the red and infrared bands measured by the metereological satellites NOAA/AVHRR (National Oceanic and Atmospheric Administration/Advanced Very High Resolution Radiometer), shows strong correlation with vegetation processes such as photosynthesis and primary productivity and has been widely used to appraise primary production (Fig. 6).

Figure 6. Utilize of normalized divergence vegetation index (NDVI) in the interpretation of annual and seasonal patterns of principal production, (a) Human relationship between the internet principal production and NDVI of unlike vegetation types: ane, tundra; two, tundra–taiga ecotone; three, boreal coniferous chugalug; 4, humid temperate coniferous woods; five, transition from coniferous to deciduous broad-leaved forests; half-dozen, deciduous forests; 7, oak-pino mixed forests; 8, pino forests; 9, grassland; 10, agricultural state; 11, bushland; 12, desert (reproduced with permission from Physiological Plant Pathology, Larcher, Fig. 2.77, 1995, © Springer-Verlag). (b) Seasonal changes in NDVI for a native grassland, a wheat field, and double-cropping wheat–soybean in the Argentine Pampas (reproduced with permission from Sala and Paruelo, 1997).

Read full chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/article/pii/B0122268652000894

Ecosystem Structure and Role

Timothy D. Schowalter , in Insect Environmental (Second Edition), 2006

B Secondary Productivity

Net principal production provides the energy for all heterotrophic activeness. Consumers capture the energy stored within the organic molecules of their food sources. Therefore, each trophic level acquires the energy represented by the biomass consumed from the lower trophic level. The charge per unit of conversion of NPP into heterotroph tissues is secondary productivity. As with primary productivity, we tin can distinguish the total charge per unit of energy consumption past secondary producers from the free energy incorporated into consumer tissues (net secondary productivity) after expenditure of free energy through respiration. Secondary productivity is limited by the amount of net primary production because only the net free energy stored in plants is available for consumers, secondary producers cannot swallow more than thing than is available, and free energy is lost during each transfer between trophic levels.

Non all nutrient energy removed by consumers is ingested. Consumer feeding often is wasteful. Scraps of nutrient are dropped, or damaged institute parts are abscissed (Faeth et al. 1981, Risley and Crossley 1993), making this material available to decomposers. Of the energy contained in ingested material, some is not assimilable and is egested, becoming available to reducers. A portion of alloyed energy must be used to support metabolic piece of work (due east.g., for maintenance, food acquisition, and various other activities) and is lost through respiration (come across Chapter 4). The remainder is bachelor for growth and reproduction (secondary product).

Secondary product tin can vary widely amongst heterotrophs and ecosystems. Herbivores by and large have lower efficiencies of nutrient conversion (ingestion/GPP <10%) than practise predators (<15%) considering the chemical composition of animal food is more digestible than is found food (Whittaker 1970). Heterotherms take higher efficiencies than exercise homeotherms because of the greater respiratory losses associated with maintaining constant body temperature (Golley 1968; see likewise Chapter iv). Therefore, ecosystems dominated by invertebrates or heterothermic vertebrates (e.g., most freshwater aquatic ecosystems dominated by insects and fish) will have higher rates of secondary production, relative to internet primary product, than volition ecosystems with greater representation of homeothermic vertebrates.

Eventually, all plant and animal matter enters the detrital pool every bit organisms die. The free energy in detritus then becomes available to reducers (detritivores and decomposers). Detritivores fragment detritus and inoculate homogenized detritus with microbial decomposers during gut passage. Detrital material consists primarily of lignin and cellulose, merely detritivores often amend their efficiency of energy assimilation past association with gut microorganisms or by reingestion of feces (coprophagy) following microbial decay of cellulose and lignin (eastward.1000., Breznak and Brune 1994).

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780120887729500376

Inland Waters

William H. Schlesinger , Emily S. Bernhardt , in Biogeochemistry (Fourth Edition), 2020

Autochthonus inputs—Primary productivity in rivers

Net chief production in streams and rivers is typically estimated using i of two approaches, respirometer chambers or in situ changes in dissolved oxygen concentrations ( Bott, 2006). Respirometer chambers are analogous to the light/nighttime canteen methods described for lakes, and involve isolating stream sediments and water in closed containers and measuring changes in the dissolved oxygen concentration in the overlying water over time. Although chamber estimates are useful for comparative studies and experimental manipulations, NPP estimates derived from chambers are especially hard to extrapolate to river ecosystems. First, enclosing stream sediments in a airtight vessel reduces or eliminates menstruation, nutrient supply, and the gas commutation weather condition of natural streams (Bott, 2006). Second, considering river sediments are typically very heterogeneous, scaling to the whole ecosystem requires all-encompassing sampling of all benthic habitat types (Hondzo et al., 2013). Finally, chambers typically do non include subsurface sediments, so they tend to considerably underestimate rates of ecosystem respiration by ignoring oxygen consumption in the hyporheic zone r (Fellows et al., 2001).

In contrast, open-channel techniques involve measuring daily fluctuations of stream h2o oxygen, or less commonly CO2 concentrations, and linking these changes to the processes of product, respiration and exchange with groundwater or the temper (Odum, 1956) (Fig. eight.11). For any time step:

(8.13) ΔO 2 = GPP – R ± E ,

where East is atmospheric exchange as estimated using a gas tracer (Wanninkhof et al., 1990; Hall and Ulseth, 2020). These data are analyzed as described for lakes. The chief divergence is that, in rivers, turbulence is a more of import driver of gas diffusion than is air current, so gas tracer-derived estimates of diffusion must exist made at the same flows for which oxygen changes are measured. In general, chamber methods point that chief product often exceeds respiration in well lit streams (Minshall et al., 1983; Bott et al., 1985), whereas open-channel methods are more likely to notice net heterotrophy (Finlay, 2011; Hoellein et al., 2013; Hall and Tank, 2003; Bernot et al., 2010). A compilation of whole ecosystem measures of chief productivity and ecosystem respiration from flowing waters finds that the bulk of both pocket-size streams and big rivers are net heterotophic (Table viii.5, Battin et al., 2009) and that smaller streams tend to take higher rates of ecosystem respiration than big rivers.

Table 8.5. A Compilation of Literature Estimates of GPP, R, and NEP for Streams, Rivers, and Estuaries from Whole-Ecosystem Metabolism Estimates.

Ecosystem GPP (g   C m−   ii  d−   1) R (g   C m−   2  d−   1) NEP (g   C grand−   ii  d−   1) Global R (Pg   C   year−   1) Global net heterotrophy (Pg   C   yr−   1)
Streams (due north = 62) 0.73   ±   0.14 (0.02–5.62) 1.93   ±   0.19 (0.29–8.16) −   1.20   ±   0.fifteen (−   v.86–2.51) 0.xix 0.12
River (n = 37) 0.91   ±   0.10 (0.06–2.28) 1.53   ±   0.15 (0.xx–3.54) −   0.66   ±   0.11 (−   2.06–1.lx) 0.sixteen 0.07
Estuaries (n = 31) 3.14   ±   0.41 (0.72–10.4) 3.51   ±   0.32 (0.83–7.58) −   0.39   ±   0.21 (−   2.98–two.86) 1.20 0.xiii

Note: Given is the mean standard error and the minimum and maximum in brackets.

Adapted from Battin et al. (2009).

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780128146088000086

Ecosystem Role Measurement, Terrestrial Communities

Sandra Díaz , in Encyclopedia of Biodiversity (2d Edition), 2013

Biomass Production

Net primary production (NPP) is strictly defined as the departure betwixt the energy fixed by autotrophs and their respiration, and it is most commonly equated to increments in biomass per unit of land surface and fourth dimension. Because the increment in biomass over a given fourth dimension depends on the rate at which new biomass is produced and as well on the initial amount of carbon-assimilating photosynthetic tissue, stands with a large standing biomass ofttimes bear witness higher NPP than stands with lower biomass. Therefore, another useful concept is that of relative productivity charge per unit, or the time needed by a vegetation stand up to produce its standing biomass. For example, the estimated relative productivity charge per unit for a dry tropical forest can be many years, whereas in an annual grassland it is less than 1 year.

The fate of assimilated carbon – that is, whether information technology is allocated to increase the pools of aboveground or belowground biomass, root exudates, litter, soil organic matter, grazers, symbionts, or parasites – varies strongly between ecosystems, depending on prevailing climatic weather, disturbance regimes, and allocation patterns of ascendant institute functional groups (Effigy iii). It should exist noted that NPP is not the same as Net Ecosystem Productivity or NEP. As stressed by Chapin et al. (2005), NEP is the net biomass accumulation by a whole ecosystem and depends non just on NPP, but too on carbon losses due to the respiration of animals and microbes, leaching, erosion, exportation by animals, and in some cases volatilization due to fires.

Figure 3. Carbon pools in major ecosystem types. Soil stocks include biomass, soil organic mass, and litter. Pie diagrams indicate percentage of soil carbon in belowground biomass (greyness) and in soil organic mass (white).

 Modified from Anderson JM (1991) The effects of climate change on decomposition processes in grassland and coniferous forests. Ecological Applications three: 326–347, and Larcher W (1995) Physiological Plant Pathology. Berlin: Springer.

At the regional scale, NPP can be largely accounted for past climatic factors, rainfall, and temperature. For instance, atmospheric precipitation, potential evapotranspiration, and radiation are plenty to account for the net aboveground main production (NAPP) of North American forests, deserts, and grasslands. In regions of the US with up to 1400   mm of annual rainfall, annual atmospheric precipitation is enough to business relationship for ninety% of the variability in NAPP of grasslands (Effigy 4(a)). At college atmospheric precipitation, NAPP depends more on other factors, and equations based on annual rainfall lose part of their predictive power. At the site level, variability in production seems to be accounted for by annual precipitation and soil h2o-holding capacity (whc; Effigy 4(b)). Soil whc can have a positive or negative consequence depending on the atmospheric precipitation value. In dry out regions, major losses of soil water occur via bare soil evaporation. Nevertheless, where sandy soils occur, bare soil evaporation is lower than in loamy soils because water penetrates deeper into the soil. For the same reason, surface runoff is also lower in sandy soils than in loamy soils. In more humid regions, substantial water losses occur via deep percolation, which is reduced in soils with high whc. This is known every bit the inverse texture hypothesis, proposed by Noy-Meir in 1973.

Figure 4. Regional- and site-level controls over internet aboveground primary production (NAPP) of Usa grasslands, (a) Almanac precipitation (APPT) is the main cistron at the regional level, with NAPP=0.6 (APPT−56) (r 2=0.xc), where 0.half-dozen represents the boilerplate water use efficiency of the community, and 56   mm   year−1 is the 'ineffective precipitation' (precipitation volume which is non enough to event in product). Improver of temperature and potential evapotranspiration did not improve the model, (b) Annual precipitation and soil water-belongings capacity (whc) are the main factors at the site level, with NAPP=32+0.45 APPT−352 whc+0.95 whc APPT; r ii=0.67).

 Reproduced from Sala OE, Parton WJ, Joyce LA, and Lawenroth WK (1988) Principal product of the central grassland region of the United states. Ecology 69: 40–45.

At effectively scales of analysis (e.m., paddocks and vegetation patches), more variables are needed to account for NAPP. Species limerick and land-use government become of import factors, although drivers at a coarser scale are however in operation and constrain responses (e.g., irrespective of management or species composition, almanac precipitation will ready an upper boundary to NAPP). For instance, the NAPP of Argentine natural grasslands has been shown to decrease between 50% and more than 300% nether moderate to heavy grazing, depending on regional climatic weather. Species composition is crucial at this level; for example, NAPP tends to be higher in legume-dominated pastures than in grass-dominated ones considering legume growth is much less limited by soil nitrogen availability due to their capacity for symbiotic nitrogen fixing.

Biomass production from local to global scales can also exist estimated past indices obtained from remote sensing. The normalized difference vegetation index (NDVI) is tightly related to the fraction of the photosynthetically active radiation absorbed by the vegetation. This spectral alphabetize is derived from the reflectance in the red and infrared bands measured past unlike sensors (e.m., MODIS, AVHRR, and LandSat TM). Combined with data about incident radiation and an energy conversion gene, NDVI can be used to calculate productivity. The source of images to be used will depend on the spatial and temporal scales and resolution required for a particular study.

Read total affiliate

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780123847195000423