Net primary production, net ecosystem production and nutrient availability Melillo J.M. Workshop agroecology Paris : CIHEAM Options Méditerranéennes : Série Etudes; n. 1984-I 1984

Net primary production, net ecosystem production and nutrient availability

Melillo J.M.

Workshop agroecology Paris : CIHEAM

Options Méditerranéennes : Série Etudes; n. 1984-I 1984

pages 95-110

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--- Melillo J.M. N et primary produ ction , n et ecosystem produ ction an d n u trien t availability.

Workshop agroecology. Paris : CIHEAM, 1984. p. 95-110 (Options Méditerranéennes : Série Etudes; n.

1984-I)

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N=

A V N . 1 .

J.

Biological Laboratory Woods Hole, 02543

doubtful that net of plants on a specific site can be

net of vegetation on that site to 1)

changes the amounts of available plant use; and 2) plants

have demands and use efficiencies than do plants

ecosystems. we can link the of in ecosystem to the availability of that system, and in link availability to demand ‘and thus the magnitude of NPP that a site can

Ecosystem maintenance involves two tasks: 1) keeping the system’s stocks

and 2) minimizing net losses of and the system. tasks invest-

ments in the system. A useful index of the magnitude of this investment in maintenance to

be net ecosystem Net ecosystem to the net change in

stocks in the system some defined of time. For is the sum of

and inputs (aswciated with minus the sum of plus

outputs (associated with and is negative, then the system is

The optimum of in systems is that a sufficient ^.

tion of the is invested to maintain equal tu or than should be or

*

96

Es poco la un específico

pueda a de la de la vegetación de dicho

su dos 1) el de el

disponibles su utilización la planta, y 2) las plantas cultivadas tienen, en

demandas y eficacia de utilización de los a S de plantas dominantes en los ecosiste- el nivel de de un a su disponibilidad de y, a su vez, disponibilidad de a la demanda del cultivo y, a la magnitud de del cultivo que dicho puede

La de los ecosistemas implica dos 1) los stocks y

del sistema, y 2) las y del sistema. Ambas

de en el sistema. La neta del ecosistema

u n indice útil de la magnitud de esta mantenimiento. La neta del

ecosistema se al cambio neto en los stocks de del un

definido. los la y los inputs de

(asociados con el abono), menos la suma de la más los outputs de nica (asocidos con la cosecha y la Si negativa, el sistema está

diendo El nivel óptimo de en los es aquél en que se una

suficiente de la la igual o que Los técnicos

o del sistema, no

The objective of this is to be discussed in goza

1) of

site be of

of the site’s vegetation?

2) What is of

a. site minimizing ecosys-

it of

of the site’s vege- tation?

the question we

use of vegeta-

tion. We also discuss how of

on these con- we conclude that it may be difficult

of of the site’s vege-

it may be possible to link the

of of the site’s

vegetation with in the system

system.’

we

net ecosystem is

tionship betwcen ecosystem metabolism and the maintenance of

ecosystems function such that most of the time of

tion is ^*

(net ecosystem

/

a

tion of is

so only a small amount of

(if any at all) is

/

ecosystem maintenance. This small investment in ecosystem

with an

of planting, weed in many

ecosystems to have negative net ecosystem

on both

we know that an ecosystem with a negative net ecosystem

in the system’s is usually a system in

which we

keep in o f .

one s,yStenï o f ‘an-

a ;

‘m.uS.t be a “pollution”

This’ us to the

conclusion

on- ^{. a} .site minimizing e.co:s.ystem

allow of

a sufficient of

R IAMZ-84/1

duction to maintain the site’s net ecosystem

OF OF

of any ecosystem is by

of

of

ecosystem to an will not

tion inputs to a site, it will

ecosystem to an ecosys-

is also a in the way

the plants use

use must be of o n a site can be

ed of of the

site’s

Changes Nutrient Availability Conversion

of the effects of element cycling and loss in

in em-

-standing among ecologists and soil scien- causes losses which could affect the long-

of

b in Stalfelt, 1960; 1935; Likens et al., 1978, Leaf, 1979).

on the effects

1974; Sollins er al., 1981). Element

’losses following have also been used of homeostasis of cycles

Likens, 1979; Swank and Waide, 19801, and they have been suggested as a useful of eco- system-level stability (O’Neill et al., 1977).

Studies of cycling and loss following in ecosystems have empha- sized

1) is the element most often limiting to plant and substantial losses follow-

2) losses of

_-

IAMZ-84/1

(especially do losses of

et al., 1970; Vitousek et al., 1979).

3) loss

in ecosystems

solution losses of cations, since the supply of

1960; Likens et al., 1969; Johnson and Cole, 1980).

4)

1978)

et al., of

5) to

be a health 1977).

a limiting we will focus in this

section of eco-

systems to ecosystems will

on of

between cycling

of flux-

es soils, we

is to the time

since of vege-

tation on the of

on a

a is given 1.

we plot net as a function

tion is of

gen pool) that exceeds

of system via leaching gaseous flux.

at the site is

is a function of changes in soil

changes in the’

of

to enzyme attack, and

inactive enzymes may

active againj.

The easily metabolized components of the soil to

of site

loss

.

i

l Figure l . The general pattern nitrogen turnover (in the absence fertilization) in a site converted l f r o m -forest to cropland plotted as a function time. net nitrogen minèraliza-

l tion, ,the fiaction of inorganic nitrogen produced ( f o m the soil organic nitrogen pool) that

l exceeds the microbial demand f o r nitrogen.

- ~.

~. ^~ -~

- .~

-

~- ^I

CONVERSION O F FOREST TO CROPLAND

M FROM STOCK

easily metabolized soil is

a in below

what it was in ecosystem that occu- to

Thus we have a of constantly changing at the site following con-

change in will

be in the of

the site since have high

demands. have been a

of most since domes-

tication.

and High Nitrogen Availability:

in History

of developed

wild on sites

by soil high

New and have been

by N5w

species of Solanum,

Lycopersicum, Cucurbita, Dioscorea, Ama-

and all

in west-

and Venezuela) in

vegeta-

tive of

followed by of Amaranthus and

emphasized an d Cucurbita.

man was

spe- found wild in hill and moun-

tain in and ^*

These sites of

soil

and man’s

activities.

As we soil

of to

availability with fits with a weedy species to soils in

seed sowing both involve soil avail- ability. is logical that weedy

be selected in both

instances (Loomis 1975).

Comparison of of

Crop and

The high of

to be linked to that

enable these plants to this section we

of plentiful and

ces often in supply. Again we will focus

Chapin (1980) physiological

of plants in envi-

(e. g. with those in low to ecosystems). The of

his in 2.

of effectively

exploited by

capacity of these plants i's

high is sensitive to and depends upon a high

(a) plants in

and (b) these species have

high The plants' also have

a high

This

to leaf in some cases

so that, if is

not maintained at photosynthetic and decline.

declines with leaf age

tion capacity declines with age, so that maintenance of both depends upon .

of both lea-

ves of tissue ^'

loss in senesced tissues because of inefficiency of .

C / N lignin so that

is essential to maintain high and

'

of of sites.

At the low

most successfully

exploited by low

be adequately maintained by low

capacities photosynthesis and ^.

tion. A

vide little advantage in dif-.

fusion of bulk soil to the

is

acquistion by

biomass, and

in slow The

long-lived of in by

low

capacity. The low

to flushes

- - - . ~.

Figure 2. Comparison of physiological characteristics o plants high tumient environments (such- as crop plants) those in to interme iate nutrient environments (plants dominating most natural ecosystems) f r o m Chapin (1980).

HIGH NUTRIENT ENVIRONMENT LOW NUTRIENT ENVIRONMENT

-

nutrient Large

rnelobolically octive

obsocplion Slow nulrient

Lar-n"lr,cnl 1 4 1 1

R I A M t 8 4 / 1

100 -

, . t ^: ,.

* c

. r + ' . .. c: <. . '

, of

and in

this way of exceptionally low

: availability in soil.

, these' species low because of (a)

slow low

senesence and ^~

-Jeaefiín,g. Th'e by these plants

has. a C

/

, lignin by

plants adapted to of plants

of low

pose low

condition-: Finally,' within

sites have

use efficiencies th.an on

sites.

Between Natural and Agricultural ï's ,opinion that .it will be difficult to

of of the site's vegeta- of a ecosystem to an

'

is above the

e in ..the ecosystem

labile of the site is

it is below the availability in system

to

use

efficiencies of of

most plants found in ecosystems.

plants have demands and

of tissue

plants &ve use efficiencies;

use efficiency is defined as the of the weighted mean

._ ^~

- ^--

. - -.

While we do not believe it will be possible to

of of the sites vege-

tation, it may be possible to- link of of the site's vegeta-

tion with in the system and

in availability in the system

to demand of

the sections that follow we suggest that the of ecosystem can be used to

of We can

then use of the way

of will

in time.

of be combined with

mation on the yield of a of

available The decision can then be made site can supply the

yield. is

level can be yield.

and Net Nitro- gen

T o

is of

in soils that exceeds the be taken up by

system via leaching gaseous flux.

situ studies of of soil in closed polyethylene bags

is used,

soil in (polyethy-

lene bags boxes) a specified

one month) at the depth in the soil which content of

and at the end of gives an

estimate of

The technique has been applied in

and is also now being used in

a good of

the technique in Wes-

(1981) close

N by

and as

ed above and = 0.98,

n = 23,

<

in situ ^\

index of in soil.

be- tween

of in

3 shows a set of elght stands in Wisconsin.

R _{IAMZ-84/ I}

Figure 3. Aboveground as a .function f o r eight forest stmrds Wisconsin. From et al. (1984).

I

h

ZI

R P Ó

I 1

20 40 100

N MINERALIZATION yr-’)

Changes in Net Nitrogen Conversion

As we noted (see l), of

in the soil is time since the is being used.

When is we would

expect in may be

initially by a Q l o a specified we would expect the of

decline an exponential

decay

may have to be specified to climate and soil type. Nonetheless it will

Net nitrogen mheralization and yield

many

functions that between

yield

specific

4.

just such a

ledge of the N of the site and

with yield

/

yield of

be As is shown in

2,

needed at a site to achieve a specific yield can also be calculated.

Srrmmary

of

ecosystems with of ecosys-

tems is in 6. we sug-

gest of

can be used to system

Next we use of

the way of a will change fol-

to in

t,, to t,,).

(ti) the of in

site (t;)), can be combined

mation on the yield of a of

As

to site can supply

gen to achieve the yield.

is no, a application can be (1982, this volume) useful in

N demands of sites

Ecosystem maintenance involves two tasks: keep-

102

Figure 4. Yield of cabbage grown in of N fertilizer

applied at two levels of and f r o m

- . - ~ (1974).

r

AND POTASSIUM

4 0 ⁿ

l

o0

5 0

NO ADDITIONAL AND POTASSIUM

PHOSPHORUS

200 400 600 N ( kg ha-'

1

Figure of site converted from forest to cropland as a function of time. Dashed line describes h' required f o r desired crop yield. Distance between solid and dashed lines represents amount of fertilizer that must be applied to achieve desired crop yield.

CONVERSION FOREST TO CROPLAND

N MIN REQUIRED FOR CROP YIELD DESIRED

- - - t

N FERTILIZER REQUIREMENT

1

t

N FROM S O I L N STOCK

R

Figure 6. Summary of proposed approach a natural ecosystem an agricuitural ecosystem See text f o r further explanation.

ing the system’s

minimizing net losses

of these in the system.

A useful of the magnitude of this

investment in be its net

ecosystem

and to Net

Net ecosystem to the

ecosystem. Ecologists have developed a

definition of that can be stated as follows:

=

-

is is

of of

defined in equation l

inputs and outputs of

“fixed” as those associated with

may be of

culate” with

vest be we

when we

ecosystems. The following definition is posed:

Equation 2 is

is

-~ ^~ . - - _{- . -}

- -

ecosys- tems in Table 1. all of these systems

is positive; that is, all of

not all ecosystems

ecosystem in natu-

be even less than suggests that net ecosystem

of is to the

7).

is less than is negative. time, the living vegeta-

its site

exceeds is

in

have been in Table 1.

ecosystems have a

Between and Nutrient Cycling

Ecosystems with a positive

ecosystems which exhibit a net accumulation of with a negative which exhibit a net loss of

A complex set of in

net losses of sites immedia-

tely following 1983); a

time when is negative. Shading of the soil

.-

m E

g

~~

E

i2

m

C o C m X P ' . " " -

5 2 2 S N N

. ' ? ' ? 4 o \ c .

R

-

IAMZ-84/

Figure 7. as a function time a mid-successional. forest that cut and regrows to an old age forest.

HARVEST

> O

S

TIME +

soil

1973; 1977). Addi-

of soil usually least 2-3 even in sites that to

1972; Gholz, 1980; et al., 1981). With flux

the soil is so losses of leaching

can be

A consequence of these changes in tim-

is an in of

in sites 1971; Stone, 1973;

Stone et al., 1979; Likens, 1975).

The

1976; 1979); and without

will The combination of

(which consumes oxygen) and soils (which slow oxygen diffusion) may

of within the

soil.

losses of et .al., 1983) and

and unpublished data).

hilly sites, consequence of tion is an in soil

in of soil

is ( l ) the soil

is and less cohesive, and (2) the decay of

cohesiveness of soil and and

R y

of et

al., 1981), and (3)

of infil-

of

on the and can thus

flows in sites

able

et al., 1974). The tionship between flow

often has an so the capacity

than 'in peak

land use, will be main-

'et al., 1974;

1975) unless no-till

1.980).- .

Net in Agricultural

We know of only one detailed study of net

ecosystem in ecosystems.

The was done by L. on

-

(TsbJ$-

field had a negative of 11 1.g C m-?. The positive in the potato field was achieved by of 263g C m-?. 'Without

this field would have.

exhibited a negative of 160g C m-?.

Negative net ecosystem is common in

106

Table 2. Comparative metabolic parameters of agricultural ecosystems. All values are grams of carbon m-’ yr”. Data of (personaÌ*communication). calculated acoording to equatiotl 2.

Comparative

metabolic parameters

,

Net

input

output Net ecosystem

Potato field

1286 43 1 a49 263 500

509 103

is no net accumula-

tion of in the vegetation on the site and because cultivation of soil causes a net

tion of the site’s soil

of soil loss is and is

to the time since of the site

to of

of systems to

the type of on the

of of in

Young use of an expo-

loss ecosystems to soils of the

suggested a of decay

10 in the

ance to less than 1 of

cultivation”. This soil loss is in

a simplified of the of

change following of a

which in 8. T h e

of is most negative immediately following as the labile component of the soil

field

1006 342 664 O 3 10 465 -111

bon stock is activity

of and soil a

of cultivation and the depletion of a

of the labile of the

may become the mechanism ^. of the

stocks. The implications of negative

cycling in systems the

systems: that is a

negative in losses.

To minimize the net loss of

ecosystem it to be

to have a high of

so that a sufficient of it can be invested i n

the investment of some

of in

to be

such an investment can have negative conse-

quences in -

the of left on site is

will be immo:

bilized activity

stages of decay

K

y

IAMZ-841

Figure 8. ecosystem production plotted as a f m c t i o n time a mid-successional forest that converted f o cropland.

NEP > O

\

N E P = O

N E P < O

_i

CONVERSION OF FOREST TO CROPLAND

- . - - -

meet the immobilization demand can avail- of involved in

and 1984).

Finally, it must be

is a designed to

gen, in of

lost must

. be Ì-eplaced. by adding

in by

of

the land by is accompanied by

and leads to a positive

Biomass us the Organization in un An ecosystem is a basic functional unit of

non-living

by a of

to (1963), biomass is the keeper organization in such a system. The

;y-

amount of biomass is viewed as being tional to the influence that an

within its bounda- an ecosystem with a amount of biomass,

and function of the system in

con- ditions thdn on inputs to the system. Such a situation, then, is one in which homeostasis is less biomass heavily influenced by inputs.

-it follows that an ecosystem’s sensitivity to inputs will if the amount of biomass of the

significantly and then maintained at a

low level. The homeostasis of a system that has of change will be much

to its

ecosystems tend to be of the “input sensitive” type. to such a system have to be quantitatively to system

with those demands, the inputs will pass the system.

systems, with

stocks (living and non-living biomass), have

mechanisms immobilization in

decaying plant litter (which is related to both mamagehl as whole ecosystems. Of course we the quantity and quality of the arganic matter should be concerned about crop yield. But we stocks) that allow the system to be less “input should also be concerned about. ecosystem

sensitive”. These mechanisms reduce the need of a site’s organic ^. for the synchrony of (nutrient) supply to the matter and nutrient stocks will assure long-term system and demand of the plant component of productivity. Agriculturalists should be “ca.reta-

the system. kers” “builders” and not “miners”.

summary, we urge that agricultural plots be

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A. S. 1971. in a podzol on

J. W. 1980. Soil and biochemical changes associated with tillage. Soil Science Society of

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J. 1980. oxide

L. 1980. of vegetation in element cycles on

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~. .~ - .

110

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