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A direct comparison of the consequences of plant genotypic and species diversity on communities and ecosystem function

April 2011
Ecology 92(4):915-23

DOI:10.2307/41151215

Source
PubMed

Authors:

Scott H McArt

Cornell University

Amy L Parachnowitsch

University of New Brunswick

Jennifer S. Thaler

Cornell University

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Biodiversity loss is proceeding at an unprecedented rate, yet we lack a thorough understanding of the consequences of losing diversity at different scales. While species diversity is known to impact community and ecosystem processes, genotypic diversity is assumed to have relatively smaller effects. Nonetheless, a few recent studies suggest that genotypic diversity may have quantitatively similar ecological consequences compared to species diversity. Here we show that increasing either genotypic diversity of common evening primrose (Oenothera biennis) or species diversity of old-field plant species resulted in nearly equivalent increases (approximately 17%) in aboveground primary production. The predominant mechanism explaining this effect, niche complementarity, was similar for each type of diversity. Arthropod species richness also increased with both types of plant diversity, but the mechanisms leading to this effect differed: abundance-driven accumulation of arthropod species was important in plant genotypic polycultures, whereas resource specialization was important in plant species polycultures. Thus, similar increases in primary productivity differentially impacted higher trophic levels in response to each type of plant diversity. These results highlight important ecological similarities and differences between genotypic and species diversity and suggest that genotypic diversity may play a larger role in community and ecosystem processes than previously realized.

Plant diversity effects on productivity. (a) Genotypic and species polycultures had ∼17% more biomass than their respective monocultures (least-square means ± SE). Photographs of (b) genotypic polyculture and (c) species polyculture. (d) The overall diversity effect (means with 95% CI) can be partitioned into complementarity or selection effects (Loreau and Hector 2001) for genotype polycultures (gray bars) and species polycultures (white bars). Positive complementarity indicates that, on average, species are more productive in polyculture than would be predicted by their monoculture values. Positive selection indicates that highly productive species are dominating the polycultures, whereas negative selection indicates that smaller species are showing a disproportionately large increase in polyculture. Mean diversity effects ± 95% CI are shown. Our study was conducted on seeds of common evening primrose (Oenothera biennis) and 24 other old-field species collected around Ithaca, New York, USA.

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Relationship between plant diversity and arthropod species richness. (a) Overall arthropod richness (least-square means ± SE), with (top to bottom) predators represented in white, omnivores in light gray, herbivores in dark gray, and detritivores in black. (b) Rarefied arthropod richness decreased with plant genotypic diversity (least-square means ± SE). (c) After removing the dominant insect, Plagiognathus politus, from the data set (see Results), rarefied arthropod richness showed no change with plant genotypic diversity (least-square means ± SE). (d) Rarefied arthropod richness increased with plant species diversity (least-square means ± SE). At each level of plant relatedness, we used individual-based rarefaction (Ecosim 7.0; Gotelli and Entsminger 2006) to test the effect of cumulative arthropod abundance on cumulative richness. To test for differences in rarefied arthropod richness, we used ANOVA with post hoc independent contrasts. Abbreviations are: GM, genotypic monocultures; GP, genotypic polycultures; SM, species monocultures; SP, species polycultures.

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Ecology, 92(4), 2011, pp. 915–923

Ó2011 by the Ecological Society of America

A direct comparison of the consequences of plant genotypic and

species diversity on communities and ecosystem function

SUSAN C. COOK-PATTON,

SCOTT H. MCART,

2,3

AMY L. PARACHNOWITSCH,

JENNIFER S. THALER,

1,2

AND ANURAG A. AGRAWAL

1,2

Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853 USA

Department of Entomology, Cornell University, Ithaca, New York 14853 USA

Abstract. Biodiversity loss is proceeding at an unprecedented rate, yet we lack a thorough

understanding of the consequences of losing diversity at different scales. While species

diversity is known to impact community and ecosystem processes, genotypic diversity is

assumed to have relatively smaller effects. Nonetheless, a few recent studies suggest that

genotypic diversity may have quantitatively similar ecological consequences compared to

species diversity. Here we show that increasing either genotypic diversity of common evening

primrose (Oenothera biennis) or species diversity of old-ﬁeld plant species resulted in nearly

equivalent increases (;17%) in aboveground primary production. The predominant

mechanism explaining this effect, niche complementarity, was similar for each type of

diversity. Arthropod species richness also increased with both types of plant diversity, but the

mechanisms leading to this effect differed: abundance-driven accumulation of arthropod

species was important in plant genotypic polycultures, whereas resource specialization was

important in plant species polycultures. Thus, similar increases in primary productivity

differentially impacted higher trophic levels in response to each type of plant diversity. These

results highlight important ecological similarities and differences between genotypic and

species diversity and suggest that genotypic diversity may play a larger role in community and

ecosystem processes than previously realized.

Key words: arthropods; biodiversity; common evening primrose; community genetics; eastern North

America; ecosystem function; Oenothera biennis; old ﬁelds.

INTRODUCTION

Rapid human alterations of the environment are

leading to substantial reductions in biodiversity (Pimm

et al. 1995, Chapin et al. 2000). These changes may have

profound consequences, as diverse systems can be more

productive (Tilman et al. 1996, Cardinale et al. 2007 ),

stable (Reusch et al. 2005, Tilman et al. 2006), and

resistant to invasions (Levine 2000) than less diverse

systems. While most biodiversity research has focused

on species diversity, recent work has found that

genotypic diversity within species can also have pro-

nounced ecological consequences (Wimp et al. 2004,

Hughes et al. 2008, Parker et al. 2010). However, to

date, there has been no direct comparison of either the

relative importance of genotypic and species diversity or

the mechanisms by which genotypic and species diversity

alter community structure and ecosystem functioning.

Greater productivity in diverse mixtures may be due

to the increased probability of including a highly

productive species (i.e., the sampling effect), dominance

of highly productive species in polycultures (i.e., a

positive selection effect), or reduced competition in

polycultures due to niche partitioning or facilitation

among the interacting species (i.e., positive complemen-

tarity) (Loreau and Hector 2001, Hooper et al. 2005).

Niche partitioning, in particular, should be affected by

trait variation and relatedness among interacting organ-

isms (Petchey et al. 2004, Villeger et al. 2008, Cadotte et

al. 2009, Hillebrand and Matthiessen 2009). Plant

assemblages with greater trait variation are predicted

to exhibit less niche overlap, more efﬁciently utilize

resources, and achieve higher productivity than less

variable assemblages (Cadotte et al. 2009, Hillebrand

and Matthiessen 2009). Because trait variation within a

single species is expected to be lower than trait variation

among multiple species, one would predict that biomass

increases in response to plant genotypic diversity would

be less pronounced than that of species diversity.

Despite these expectations, a few recent studies have

suggested that plant genotypic diversity may have

similar impacts to species diversity on biomass, ﬁtness,

and other ecosystem functions (Schweitzer et al. 2005,

Crutsinger et al. 2006, Johnson et al. 2006). However,

these studies did not manipulate plant genotypic and

species diversity simultaneously.

Two alternative hypotheses predict how general

patterns of arthropod community diversity will respond

to plant diversity (for hypotheses addressing responses

Manuscript received 20 May 2010; revised 27 September

2010; accepted 5 October 2010. Corresponding Editor: R. E.

Irwin.

Corresponding author. E-mail: shm33@cornell.edu

915

of speciﬁc trophic levels, see Root 1973, Barbosa et al.

2009.) The resource specialization hypothesis posits that

because many arthropods specialize on distinct host

plant species, increasing the number of plant species in a

patch will attract a more diverse fauna (Hutchinson

1959, Strong et al. 1984). Alternatively, the more

individuals hypothesis suggests that as available energy

(e.g., plant biomass) increases, there will be a greater

number of arthropod individuals present and thus a

higher probability of observing more arthropod species

(Srivastava and Lawton 1998). Because plant biomass is

expected to increase with plant diversity, arthropod

diversity is expected to also increase through abun-

dance-driven accumulation of species. When considered

in the context of plant trait variation, both of these

hypotheses predict that the response of arthropods to

plant species diversity will be greater than to plant

genotypic diversity. In contrast, two recent studies have

suggested that plant genotypic and species diversity may

similarly impact the structure of higher trophic level

communities (Crutsinger et al. 2006, Johnson et al.

2006).

In this study, we present the ﬁrst direct comparison of

the effects of plant genotypic and species diversity on

arthropod species diversity and plant productivity (an

ecosystem function) by simultaneously manipulating

these two levels of diversity within a single ﬁeld

experiment.

MATERIALS AND METHODS

Study species and plant propagation

We manipulated plant genotypic diversity with

Oenothera biennis L. (common evening primrose,

Onagraceae),a native herbaceous plant that is common

to old ﬁelds and disturbed areas in eastern North

America. Oenothera biennis reproduces via a permanent

translocation heterozygosity mating system, which

results in clonally related seeds (Cleland 1972) (i.e., all

seeds produced by an individual plant are genetically

identical to one another and the parent). Oenothera

biennis genotypes vary from an annual to perennial life-

history strategy that is known to plastically respond to

the environment (Johnson 2007).

We collected O. biennis seeds from individual plants in

24 distinct populations around Ithaca, New York, USA.

Each genotype used in this experiment was determined

to be unique using nine polymorphic microsatellite loci

speciﬁcally developed for O. biennis (Larson et al. 2008).

To reduce maternal effects, we ﬁrst grew the seeds in a

common garden in 2007, which was sprayed with

insecticide at regular intervals throughout the growing

season, and we used seeds collected from these plants (24

genotypes) for our experiment.

We focus on comparing the effects of plant genotypic

vs. species diversity exclusively (and not functional

group diversity) because genotypic variation within a

species presumably offers no functional group diversity.

Thus, for the species treatments we did not have

nitrogen-ﬁxers in the species pool, because the presence

of this functional group can overwhelm effects of

richness (Hooper et al. 2005, Cadotte et al. 2009). We

used 24 species that are common in old ﬁelds, co-occur

with O. biennis, germinate easily, and do not possess

particularly notable functional attributes: Carex sp. 1,

Carex sp. 2, Cichorium intybus,Daucus carota,Dianthus

armeria,Dipsacus sativus,Elymus repens,Epilobium

parviﬂorum,Galium mollugo,Leucanthemum vulgare,

Pastinaca sativa,Penstemon digitalis,Phleum pratense,

Plantago lanceolata,Rudbeckia hirta,Rumex crispus,

Saponaria ofﬁcinalis,Silene vulgaris,Solidago altissima,

Symphyotrichum simplex,Symphyotrichum lateriﬂorum,

Verbascum blattaria,Verbascum thapsus, and Verbena

hastata. Seeds were collected from multiple individuals

at three separate ﬁelds around Ithaca in 2007 and pooled

to generate genetically diverse seed sources for each

species. This species pool includes three annuals, six

biennials, and 15 perennials (Appendix B: Table B1).

We cold-stratiﬁed (48C, four days) all seeds in April

2007, sowed them into 96-well trays ﬁlled with soil (Pro-

mix ‘‘BX’’ with biofungicide; Premier Tech Horticulture,

Quakertown, Pennsylvania, USA), and thinned germi-

nated seedlings to a single individual per well. Plants

were watered ad libitum and fertilized weekly (21-5-20

NPK, 150 ppm) while in the greenhouse (14:10 hour

light : dark cycle, ﬁve weeks) and then ﬁeld-hardened in

an outdoor mesh cage (one week) prior to planting in the

ﬁeld.

Field establishment

In late May 2008, we established the experiment in an

abandoned agricultural ﬁeld where the soil was plowed,

but otherwise untreated. Using a substitutive design and

our pools of 24 O. biennis genotypes and 24 old-ﬁeld

species, we constructed four treatments: genotypic

monocultures (‘‘GM,’’ one O. biennis genotype), geno-

typic polycultures (‘‘GP,’’ eight O. biennis genotypes),

species monocultures (‘‘SM,’’ multiple genotypes of a

single species that did not include O. biennis), and

species polycultures (‘‘SP,’’ eight species that did not

include O. biennis). All plots contained eight equally

spaced individuals arrayed in a ring 0.5 m in diameter.

This density of plants is common in old-ﬁeld plant

communities and O. biennis populations (S. H. McArt

and S. C. Cook-Patton, personal observations). The

original design included 264 plots, but due to the loss of

individuals within plots, we restricted our analyses to the

230 plots that experienced no mortality (GM, n¼46;

GP, n¼69; SM, n¼66; and SP, n¼49). Every genotype

or species appeared ;20 times in polyculture and 2–3

times in monoculture (except for two O. biennis

genotypes that only had one monoculture each due to

mortality and Verbascum thapsus, which had no

monocultures due to mortality).

In addition to the ring of plants, we grew a single O.

biennis focal plant in the middle of every plot to test how

the diversity treatments impacted natural selection on O.

SUSAN C. COOK-PATTON ET AL.916 Ecology, Vol. 92, No. 4

biennis. We ensured that the focal plant was always a

different genotype than the O. biennis ring plants. Thus,

our treatments are balanced such that species ‘‘mono-

cultures’’ always contained two species (eight plants of

the same species in a ring and one O. biennis focal plant)

and genotype ‘‘monocultures’’ always contained two

genotypes (eight plants of the same O. biennis genotype

in a ring and one O. biennis focal plant of a different

genotype), while polycultures always contained nine

genotypes or nine species. The natural selection data will

be presented elsewhere, but here we include the focal

plant in analyses for completeness and accuracy (see

Plant analyses).

We separated plots by 1.5 m and clipped encroaching

weeds by hand every 2–3 weeks to ensure treatments

remained consistent throughout the summer. During the

experiment, 18 of the 24 species bolted and ﬂowered,

and all of the O. biennis genotypes bolted and ﬂowered.

For O. biennis genotypes and plant species that bolted,

nearly every individual plant bolted and bolting did not

vary by diversity treatments (O. biennis genotypes,

Pearson v

¼0.06, P¼0.80; plant species, Pearson v

¼0.39, P¼0.53). Thus, diversity did not affect life-

history expression of the plants.

Plant analyses

During the second and third weeks of October, we

harvested the aboveground biomass of every plant,

which was then dried (658C) and weighed to the nearest

0.1 g. We analyzed plant productivity via a two-way

analysis of variance with main effects of diversity level

(monocultures or polycultures) and level of plant

relatedness (genotypic or species), plus their interaction

(JMP, version 7; SAS Institute, Cary, North Carolina,

USA). An alternative approach is to view this experi-

ment as four distinct treatments and conduct analyses

via a one-way ANOVA, which we have also done to

verify that all two-way ANOVA results were similar to

one-way ANOVA results. To account for spatial

heterogeneity in the ﬁeld, we divided the experiment

into six blocks, where each block contained equal

proportions of the four treatments, and included block

as a random effect in all analyses. We analyzed both the

full plot data (the sum of eight ring plants plus the focal

plant) as well as the ring data alone (sum of the eight

ring plants) for all of our analyses. Excluding the focal

plant from our analyses (i.e., analyzing only the ring

plants) did not alter the direction or signiﬁcance of any

of our results. We present the full plot data because it

includes all the interactions that occurred in the plot.

Loreau and Hector (2001) devised a method to

partition diversity effects into complementarity and

selection effects. We modiﬁed this technique slightly to

account for the absence of true monocultures (due to the

focal plant in the middle of the ring; see Table 1).

Whether a genotype occurred in the center or the ring

had a substantial effect. For example, a single,

representative genotype produced, on average, 110 g

biomass in the ring vs. 69 g as a focal plant. Thus, to

determine the expected biomass of a ring plant in

polyculture, we used the average value of an individual

genotype or species from the monoculture ring. To

determine the expected biomass of a focal plant, we took

the average value of the two or three times that this

genotype occurred in the middle of a genotypic

monoculture (if calculating expected values for a

genotypic polyculture) or a species monoculture (if

calculating expected values for a species polyculture).

Complementarity is calculated as N

DRY 

Miand

selection as Ncov(DRY,M). If we exclude the focal

plant, the modiﬁcation produces mathematically equiv-

alent results to the original method and our results do

not qualitatively change (see Appendix B). Note that

one species, Verbascum thapsus, did not survive in

monoculture, so the three monocultures and 10 species

polycultures with this species were excluded from the

complementarity and selection analyses.

To examine how competition intensity changed from

monoculture to polyculture we calculated the corrected

index of relative competition intensity (CRCI) (Oksanen

et al. 2006). This index reduces bias inherent to other

indices by extending the range of arguments in which the

function behaves linearly. To minimize errors due to the

aberrant behavior of individuals, we ﬁrst calculated

mean values of individual genotype or species perfor-

mance in each treatment. We then calculated competi-

tion intensity as CRCI ¼arc sin((X

X

)/(max X

))

(Oksanen et al. 2006) where X

is the mean performance

of a particular genotype or species in monoculture and

is the mean value in polyculture. Note that CRCI is

unitless, and values further from 0 indicate greater

differences in competition intensity between treatments.

Arthropod analyses

In mid-July and again in mid-August, we censused

arthropods by visually surveying every plant in the

experiment (N¼2070 plants). We identiﬁed familiar

arthropods in the ﬁeld or collected specimens of

unknown arthropods for later identiﬁcation. To identify

arthropods, we consulted relevant literature and the

expertise of E. R. Hoebeke. Arthropods were identiﬁed

to the lowest taxonomic level possible, generally species

or genus and occasionally family. We also assigned

arthropods to a feeding guild (herbivore, predator,

omnivore, or detritivore) based on relevant literature

and the expertise of E. R. Hoebeke. We lumped together

parasitoid species that were less than 3 mm in length (n¼

10) because of logistical difﬁculties associated with their

ﬁeld identiﬁcation. We did not attempt to count or

identify arthropods that were less than 1 mm in length

(e.g., thrips, collembola).

Similar to the plant analyses, we used a two-way

ANOVA with block as a random effect to test for the

effects of plant diversity on cumulative arthropod

abundance and richness. Repeated-measures analyses

yielded qualitatively identical results to the cumulative

April 2011 917PLANT GENOTYPIC VS. SPECIES DIVERSITY

data set, so we chose the latter to facilitate more

sophisticated follow-up analyses. We used a log þ1

transformation on the abundance data to improve

normality.

To test for the effect of plant biomass on arthropod

abundance we divided arthropod abundance by the

biomass of each plant and log-transformed the resulting

data to improve normality. Division assumes a linear

relationship between these two variables and indeed a

linear function provided the best ﬁt for the data (R2

lin ¼

0.40, R2

log ¼0.34). Next, because of the well-known

nonlinear relationship between arthropod abundance

and richness, we used individual-based rarefaction

(Ecosim 7.0; Gotelli and Entsminger 2006) to test the

effect of cumulative arthropod abundance on cumula-

tive richness. We conducted rarefaction at each level of

plant relatedness independently in order to compare

arthropod communities drawn from the same distribu-

tion (Gotelli and Graves 1996). To test for differences in

rareﬁed arthropod richness we used ANOVA with post

hoc independent contrasts.

We visualized the similarity among arthropod assem-

blages on genotypes and species with nonmetric

multidimensional scaling (NMDS, Vegan 1.15-1, R

version 2.8.1; R Foundation for Statistical Computing,

Vienna, Austria). The semimetric Bray-Curtis dissimi-

larity coefﬁcient was used to compare arthropod

assemblages on monocultures of O. biennis genotypes

and plant species using a presence/absence data set. We

then conducted 500 simulations on a random data set

with identical parameters (McCune and Grace 2002) to

verify that random stress (mean ¼0.28) was signiﬁcantly

higher than model stress (mean ¼0.23).

RESULTS

We found an overall positive effect of diversity on

plot-level plant productivity (diversity, F

1, 221.4

¼15.62,

P¼0.0001). Genotypic and species polycultures showed

nearly equivalent increases in productivity (diversity 3

relatedness level, F

1, 221.4

¼1.84, P¼0.18): total biomass

was 16.8%and 16.9%greater in genotypic and species

polycultures than in monocultures, respectively (Fig.

1a). Analysis via one-way ANOVA produced similar

results (F

3, 221.3

¼122.6, P,0.0001): post hoc

independent contrasts on plant biomass indicated that

genotypic polycultures were more productive than

genotypic monocultures (F

1, 221.4

¼14.0, P¼0.0002)

and that species polycultures were marginally more

productive than species monocultures (F

1, 221.1

¼3.4, P¼

0.065). While selection effects were weak to negative

(Fig. 1d), we found that complementarity among

individuals contributed to the increases in plant pro-

ductivity and did not differ between each level of

relatedness (F

6, 102

¼1.06, P¼0.39; Fig. 1d). Another

metric more commonly employed in the plant compe-

tition literature, the corrected index of relative compe-

tition intensity (CRCI) (Oksanen et al. 2006), showed

similar results: there were similar decreases in competi-

tion intensity with increasing plant diversity (0.79 for

genotypic diversity and 0.56 for species diversity, F

1,45

¼0.07, P¼0.79). Thus, our comparable changes in

complementarity and competition intensity may explain

the remarkably similar increases in plot-level productiv-

ity that we observed in both genotypic and species

polycultures of plants.

To determine the effects of plant biodiversity on

higher trophic-level communities, we nondestructively

surveyed arthropods, which naturally recruited to each

plant, twice during peak growing season. In total, we

made 76 753 observations of ;252 arthropod species.

We found that arthropod richness increased with both

types of plant diversity, but changed more dramatically

in plant species polycultures (diversity 3relatedness

level, F

1, 221.5

¼10.96, P¼0.001; Fig. 2a). Predators

showed the most pronounced response to plant diver-

sity, increasing in abundance 80%in species polycultures

and 30%in genotypic polycultures (diversity, F

1, 221

18.62, P,0.0001; diversity 3relatedness level, F

1, 221.6

4.42, P¼0.037; see Appendix A), while increasing in

richness 54%and 17%, respectively (diversity, F

1, 221.3

17.92, P,0.0001; diversity 3relatedness level, F

1, 221.8

3.87, P¼0.051; Fig. 2a). Herbivores increased in

TABLE 1. Loreau and Hector’s methods (2001) were modiﬁed to accommodate the inclusion of a focal plant in our common-garden

design.

Abbreviation Deﬁnition

average yield of an individual from species or genotype iin the low-diversity treatment; for species this is

the average of all individuals in a ring; for genotypes this was either the average of all individuals in a

ring or of all individuals in the center of a genotypic or species monoculture

observed yield of species ior genotype iin the polyculture

¼R

total observed yield of the polyculture

expected relative yield of species ior genotype iin a polyculture (which is 1 because the yield is expected

to be identical to that in the monoculture)

¼Y

observed relative yield of species ior genotype iin the polyculture

¼RY

¼M

expected yield of an individual from species or genotype iin the polyculture

¼R

total expected yield of the polyculture

DY¼Y

Y

deviation from total expected yield in the polyculture

DRY

¼RY

–RY

deviation from expected relative yield of species ior genotype iin the polyculture

Nnumber of species or genotypes in the polyculture

Note: Our changes are indicated in boldface, while the remainder of the text is replicated from the original paper.

SUSAN C. COOK-PATTON ET AL.918 Ecology, Vol. 92, No. 4

abundance 44%and 30%in plant species and genotypic

polycultures (diversity, F

1, 221

¼8.54, P¼0.004; diversity

3relatedness level, F

1, 221.2

¼0.007, P¼0.93; Appendix

A), while increasing in richness 30%and 10%, respec-

tively (diversity, F

1, 221.4

¼28.76, P,0.0001; diversity 3

relatedness level, F

1, 220.9

¼6.80, P¼0.010; Fig. 2a).

Omnivores and detritivores showed similar patterns of

increases in abundance and richness at both levels of

relatedness (Fig. 2a, Appendix A), although responses

were not as pronounced. A one-way ANOVA approach

to these analyses produced qualitatively identical results

(not shown).

FIG. 1. Plant diversity effects on productivity. (a) Genotypic and species polycultures had ;17%more biomass than their

respective monocultures (least-square means 6SE). Photographs of (b) genotypic polyculture and (c) species polyculture. (d) The

overall diversity effect (means with 95%CI) can be partitioned into complementarity or selection effects (Loreau and Hector 2001)

for genotype polycultures (gray bars) and species polycultures (white bars). Positive complementarity indicates that, on average,

species are more productive in polyculture than would be predicted by their monoculture values. Positive selection indicates that

highly productive species are dominating the polycultures, whereas negative selection indicates that smaller species are showing a

disproportionately large increase in polyculture. Mean diversity effects 695%CI are shown. Our study was conducted on seeds of

common evening primrose (Oenothera biennis) and 24 other old-ﬁeld species collected around Ithaca, New York, USA.

April 2011 919PLANT GENOTYPIC VS. SPECIES DIVERSITY

To further understand how plant diversity at each

level of relatedness affected arthropod community

structure, we ﬁrst evaluated the inﬂuence of plant

productivity on the number of arthropod individuals.

After dividing arthropod abundance by plant biomass,

the previously signiﬁcant effect of plant diversity on

arthropod abundance disappeared (F

1, 221.6

¼0.19, P¼

0.66). Thus, arthropod abundance at both levels of

relatedness was largely controlled by plant productivity

and not by plant diversity per se.

We next used rarefaction to determine whether

increases in arthropod species richness would be best

explained by arthropod abundance (more individuals

hypothesis) or by arthropod specialization on distinct

host plants (resource specialization hypothesis). Con-

trary to expectations, rareﬁed richness decreased with

plant genotypic diversity (post hoc contrast, F

1, 212

9.04, P¼0.003; Fig. 2b). This decrease in genotypic

polycultures derives from a nonadditive increase in the

abundance of a single dominant species, Plagiognathus

politus (Miridae), resulting in a lower richness than

expected for that insect abundance. Removing P. politus

from the data set resulted in no difference in rareﬁed

richness between treatments (Fig. 2c). Both of these

results are consistent with greater arthropod abundances

causing higher arthropod species richness in genotypic

polycultures, supporting the more individuals hypothe-

sis. Conversely, rareﬁed richness increased with plant

species diversity (post hoc contrast, F

1, 212

¼6.27, P¼

0.01; Fig. 2d), indicating that the diversity of host-

speciﬁc resources was important for the increase in

arthropod richness. This result, in addition to the fact

that the arthropod communities found on each plant

species were far more divergent than the arthropod

communities on each plant genotype (nonparametric

MANOVA, F

1,46

¼6.78, P,0.0001, Fig. 3), highlights

the importance of resource specialization for the

arthropod community response to plant species diversi-

ty.

DISCUSSION

We found that increasing either plant genotypic or

species diversity led to quantitatively similar increases in

primary production and that the plausible mechanisms

responsible for these effects, niche complementarity or

decreased intensity of competition, were also similar for

each type of diversity. A recent meta-analysis of the

effects of biodiversity on primary productivity found

that the most diverse species assemblages had on

average 1.7 times more biomass than monocultures

FIG. 2. Relationship between plant diversity and arthropod species richness. (a) Overall arthropod richness (least-square means

6SE), with (top to bottom) predators represented in white, omnivores in light gray, herbivores in dark gray, and detritivores in

black. (b) Rareﬁed arthropod richness decreased with plant genotypic diversity (least-square means 6SE). (c) After removing the

dominant insect, Plagiognathus politus, from the data set (see Results), rareﬁed arthropod richness showed no change with plant

genotypic diversity (least-square means 6SE). (d) Rareﬁed arthropod richness increased with plant species diversity (least-square

means 6SE). At each level of plant relatedness, we used individual-based rarefaction (Ecosim 7.0; Gotelli and Entsminger 2006) to

test the effect of cumulative arthropod abundance on cumulative richness. To test for differences in rareﬁed arthropod richness, we

used ANOVA with post hoc independent contrasts. Abbreviations are: GM, genotypic monocultures; GP, genotypic polycultures;

SM, species monocultures; SP, species polycultures.

SUSAN C. COOK-PATTON ET AL.920 Ecology, Vol. 92, No. 4

(Cardinale et al. 2007). However, effect sizes ranged

dramatically, and nearly 21%of studies showed negative

to no effect of increasing diversity (Cardinale et al.

2007). The limited genotypic diversity literature also

reports a wide range of increases in productivity across a

diverse set of species: ;0%in Poa pratensis (Vellend et

al. 2010), ;14%in Cakile edentula (Dudley and File

2007), ;17%(Kotowska et al. 2010) and ;69%

(Crawford and Whitney 2010) in Arabidopsis thaliana,

;36%in Solidago altissima (Crutsinger et al. 2006),

;39%in Lupinus angustifolius (Milla et al. 2009), and

;58%in Zostera marina (Reusch et al. 2005) (mean ¼

33%). Thus, the 17%increases in productivity that we

observed at both levels of plant diversity were lower

than average, but not atypical for genotypic or species

diversity experiments. This variation among experi-

ments, in addition to the comparison of vastly different

experimental designs, highlights the importance of

comparing the effects of genotypic and species diversity

within a single ﬁeld experiment, under similar condi-

tions, and for the same duration of time.

Several factors may have contributed to the similar

increases in plant productivity we observed with each

type of diversity in this study. First, because the effect of

species diversity on plant productivity generally increas-

es with time (Cardinale et al. 2007), the similar effects of

genotypic and species diversity that we observed may be

a short-term phenomenon. Because plants comprising

genotypic monocultures acquire resources very similarly,

genotypic monocultures may become resource-limited

more quickly than genotypic and/or species polycultures

(where plants may differ in their patterns of resource

utilization and thus may utilize a larger pool of

resources). Resource limitation is believed to be a key

mechanism of increased plant productivity in response

to diversity (Hooper et al. 2005), and temporal

variability in post-disturbance resource limitation along

a continuum of plant genotypic to species diversity may

be critical in predicting the effect size of increases in

productivity. For example, a recent study investigating

the effects of Solidago altissima genotypic diversity

found that the standardized effect size of genotypic

diversity on plant productivity over one growing season

was similar to the effect size of species diversity from a

multiyear experiment (Crutsinger et al. 2006). Under-

standing how trait variation and plant diversity interact

temporally to affect ecosystem functioning represents an

important gap in the literature, and we suggest that

further studies are needed in this area of research.

A second factor that may have impacted our plant

productivity results are the speciﬁc species selected for

this experiment. Genotypic diversity–productivity rela-

tionships have only been investigated in a handful of

species (Reusch et al. 2005, Crutsinger et al. 2006,

Dudley and File 2007, Milla et al. 2009, Bischoff et al.

2010, Crawford and Whitney 2010, Kotowska et al.

2010). Some of these species are particularly abundant in

their communities (i.e., dominant species), for example,

goldenrods (Solidago altissima [Crutsinger et al. 2006])

in old-ﬁeld communities and eelgrass (Zostera marina

[Reusch et al. 2005]) in coastal estuaries. Due to the

myriad biotic and abiotic conditions experienced by

dominant species, they may accumulate relatively large

amounts of intraspeciﬁc trait variation, thus increasing

the likelihood that the species will show a genotypic

diversity–productivity effect. While O. biennis is not

particularly dominant in old-ﬁeld communities, it did

respond positively to the growing conditions at our ﬁeld

site, producing the greatest amount of aboveground

biomass of all species in our study (Fig. 1, Appendix C ).

It is possible that larger plants are more likely to

manifest a diversity effect since they may more fully ﬁll

the available niche space, thus accentuating the impor-

tance of niche partitioning. An ideal future experiment,

though logistically large, might simultaneously manip-

ulate genotypic diversity in multiple different species

with species diversity from a broad range of functional

groups or phylogenetic distances.

A third possible mechanism for the similar increases

in plant productivity we observed in this study may be

that higher trophic levels are dampening the response of

species polycultures and/or amplifying the response of

genotypic polycultures. For example, in a separate

experiment with O. biennis, levels of arthropod herbiv-

ory were 26%higher in genotypic monocultures

FIG. 3. Nonmetric multidimensional scaling (NMDS)

ordination of arthropod communities on each common evening

primrose (Oenothera biennis) genotype (black circles) and each

old-ﬁeld species (gray circles) obtained using two dimensions

and 100 permutations. Each point represents the summed

community of three monoculture plots of either an individual

genotype or an individual species. Analysis of Bray-Curtis

dissimilarity coefﬁcients indicates that arthropod community

assemblages are more dissimilar among species than among

genotypes (nonparametric MANOVA, R

¼0.13, F

1,46

¼6.78, P

,0.0001). Five hundred simulations on a random data set with

identical parameters were used to verify that random stress

(mean ¼0.28) was signiﬁcantly higher than model stress (mean

¼0.23).

April 2011 921PLANT GENOTYPIC VS. SPECIES DIVERSITY

compared to polycultures (S. H. McArt, unpublished

data). If greater differences in herbivory occur between

genotypic diversity treatments compared to those that

occur between species diversity treatments, interactions

with higher trophic levels may amplify the biomass

increases observed with genotypic diversity. The contri-

bution of herbivory to overyielding in plant diversity

experiments has received some recent attention (e.g.,

Haddad et al. 2009, Parker et al. 2010), but has yet to be

compared among different types of plant diversity.

Lastly, nonlinear declines in competition intensity

with increasing genetic distance may explain the similar

increases in plant productivity we observed in the

genotypic and species diversity treatments. In other

words, small changes in genetic distance among plants in

genotypic monocultures vs. genotypic polycultures may

reduce competition to the same degree as much larger

changes in genetic distance among plants in species

monocultures vs. species polycultures. Our data cannot

distinguish among these multiple possibilities, yet each

hypothesis is testable.

The second part of our study links arthropod

community responses to each type of plant diversity.

As expected, arthropod species richness responded less

to plant genotypic diversity than species diversity (Fig.

2a). Interestingly, divergent mechanisms led to the

increases in arthropod richness with each type of plant

diversity (Figs. 2b–d, 3). Our data support the hypoth-

esis that resource specialization inﬂuenced the arthropod

response to plant species diversity while abundance-

driven accumulation of species (more individuals hy-

pothesis) inﬂuenced the arthropod response to plant

genotypic diversity. These patterns ﬁt the notion that

insects are more likely to specialize on host plant species

than host plant genotypes. However, resource speciali-

zation may be an important driver of arthropod

responses to plant species hybrids and their backcrossed

progeny (Dungey et al. 2000, Wimp et al. 2004, Evans et

al. 2008), suggesting that comparing the similarity of

arthropod communities (e.g., Fig. 3) across wider and

more quantitative ranges of plant relatedness could

greatly inform how plant genetics inﬂuences patterns of

specialization and ultimately shapes arthropod commu-

nity structure.

Overall, our results emphasize that diversity is

inherently hierarchical and that within-species diversity

may play a more important role in competitive

interactions and community structure than previously

realized. It is currently unclear whether the same factors

causing declines in species diversity similarly impact

genotypic diversity or whether these two levels of

biodiversity are causally connected (Vellend 2005,

Lankau 2009). Nonetheless, variation within species is

inevitably lost before species themselves go extinct

(Vitousek et al. 1997). Considering our results in

relation to the long-standing focus on plant species

diversity and ecosystem functioning (Chapin et al. 2000,

Reich et al. 2001, Hooper et al. 2005, Tilman et al.

2006), we suggest that more emphasis be placed on

conserving variation within species, elucidating the

ecological consequences of genotypic diversity, and

discerning how diversity among traits, relatedness, and

trophic levels interact.

ACKNOWLEDGMENTS

S. C. Cook-Patton and S. H. McArt contributed equally to

this work. We thank J. Simonis for assistance with R code for

the ordination plot and analyses and E. R. Hoebeke for

assistance with insect identiﬁcations. We thank M. Hunter, N.

Gotelli, L. Oksanen, and R. Bingham for advice; M. Stastny, A.

Hastings, A. Erwin, S. Campbell, S. Rasmann, B. Blossey, M.

Geber, M. Weber, M. Johnson, M. Vellend, and several

anonymous reviewers for manuscript critique; and M. Kersch-

Becker, G. Petchenka, M. Stastny, C. Becker, S. Campbell, A.

Erwin, P. Llambias, and numerous Cornell undergraduates for

ﬁeld assistance. The NSF (DEB- 0950231 to A. A. Agrawal and

IGERT small grant in Biogeochemistry and Environmental

Biocomplexity to S. H. McArt, S. C. Cook-Patton, and A. L.

Parachnowitsch) and USDA-NRI (2006-35302-17431 to J. S.

Thaler) supported this work.

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APPENDIX A

Responses of arthropod abundance and richness at individual trophic levels to plant genotypic and species diversity (Ecological

Archives E092-077-A1).

APPENDIX B

Summary of life-history and performance characteristics for each plant species (Ecological Archives E092-077-A2).

APPENDIX C

Complementarity and selection effects for genotype and species polycultures excluding the focal plant from analyses (Ecological

Archives E092-077-A3).

April 2011 923PLANT GENOTYPIC VS. SPECIES DIVERSITY

Ecological Archives E092-077-A1

Susan C. Cook-Patton, Scott H. McArt, Amy L. Parachnowitsch,

Jennifer S. Thaler, and Anurag A. Agrawal 2011. A direct

comparison of the consequences of plant genotypic and species

diversity on communities and ecosystem function. Ecology 92:915–

923.

Appendix A (TABLE A1). Responses of arthropod abundance and richness to

plant genotypic and species diversity. Results summarize two-way ANOVA and

post-hoc independent contrasts. Significant results (P < 0.05) are indicated in

bold.

Effect Response Whole model Plant species Plant genotypes

Diversity

F P F P F P

Abundance 12.45 0.001 0.52 0.473 18.46 < 0.001

Predators 18.62 < 0.001 19.67 < 0.001 2.24 0.136

Omnivores 8.40 0.004 0.02 0.898 18.12 < 0.001

Herbivores 8.54 0.004 3.87 0.050 4.96 0.027

Detritivores 9.07 0.003 5.90 0.016 3.35 0.069

Richness 44.86 < 0.001 47.50 < 0.001 6.57 0.011

Predators 17.92 < 0.001 18.62 < 0.001 2.88 0.091

Omnivores 11.75 0.001 11.03 0.001 2.31 0.130

Herbivores 28.76 < 0.001 29.67 < 0.001 3.88 0.050

Detritivores 6.38 0.012 6.17 0.014 1.17 0.280

Level of

Relatedness

Whole model Monoculture Polyculture

Abundance 85.77 < 0.001 22.44 < 0.001 70.44 < 0.001

Predators 0.42 0.516 3.73 0.055 1.07 0.302

Omnivores 86.89 < 0.001 19.14 < 0.001 78.26 < 0.001

Herbivores 36.04 < 0.001 16.77 < 0.001 19.35 < 0.001

Detritivores 5.73 0.018 3.96 0.048 1.94 0.165

Richness 2.45 0.119 10.72 0.001 1.20 0.274

Predators 0.26 0.608 2.81 0.095 0.95 0.332

Ecological Archives E092-077-A1

[Back to E092-077]

Omnivores 11.92 0.001 11.09 0.001 2.37 0.125

Herbivores 1.18 0.278 0.97 0.326 6.51 0.011

Detritivores 12.22 0.001 9.97 0.002 3.15 0.077

Diversity

Level of

Relatedness

Whole model

Abundance 6.30 0.013

Predators 4.42 0.037

Omnivores 9.53 0.002

Herbivores 0.01 0.930

Detritivores 0.19 0.659

Richness 10.96 0.001

Predators 3.87 0.051

Omnivores 1.68 0.197

Herbivores 6.80 0.010

Detritivores 1.01 0.315

Ecological Archives E092-077-A1

Ecological Archives E092-077-A2

Susan C. Cook-Patton, Scott H. McArt, Amy L. Parachnowitsch,

Jennifer S. Thaler, and Anurag A. Agrawal 2011. A direct

comparison of the consequences of plant genotypic and species

diversity on communities and ecosystem function. Ecology 92:915–

923.

Appendix B (TABLE B1). Information for species employed in this experiment.

Life history information is denoted as A = annuals, B = biennials, and P =

perennials, and derives from the USDA Plants Database (http://plants.usda.gov).

Biomass data is the average mass across the experiment per species (mean

biomass per individual ± 1 s.e.m.).

* 24 distinct genotypes of Oenothera biennis were employed in the genotypic

diversity manipulation. Seeds for other species were genetically mixed for the

species diversity manipulations.

Species Family Plant

type Life

history Average

biomass

Oenothera biennis* Onagraceae Forb AB 124.8 ± 2.8

Carex sp.1 Cyperaceae Graminoid 5.2 ± 0.8

Carex sp.2 Cyperaceae Graminoid 3.6 ± 0.5

Cichorium intybus Asteraceae Forb BP 37.9 ± 6.3

Daucus carota Apiaceae Forb AB 82.0 ± 8.6

Dianthus armeria Car

oph

llaceae Forb AB 9.5 ± 3.0

Dipsacus sativus Dipsacaceae Forb AB 25.0 ± 2.4

Elymus repens Poaceae C3 grass P 7.0 ± 0.7

Epilobium parviflorum Onagraceae Forb P 27.5 ± 12.2

Galium mollugo Rubiaceae Forb P 25.0 ± 1.9

Leucanthemum vulgare Asteraceae Forb P 37.9 ± 3.7

Pastinaca sativa Apiaceae Forb BP 22.8 ± 2.1

Penstemon digitalis Scrophulariaceae Forb P 8.0 ± 1.7

Phleum pratense Poaceae C3 grass P 11.1 ± 0.9

Ecological Archives E092-077-A2

[Back to E092-077]

Plantago lanceolata Plantaginaceae Forb ABP 46.1 ± 3.2

Rudbeckia hirta Asteraceae Forb ABP 57.5 ± 5.1

Rumex crispus Polygonaceae Forb P 21.7 ± 2.8

Saponaria officinalis Car

oph

llaceae Forb P 13.5 ± 1.6

Silene vulgaris Car

oph

llaceae Forb P 11.4 ± 1.5

Solidago altissima Asteraceae Forb P 47.9 ± 4.9

Symphyotrichum

simplex Asteraceae Forb P 63.0 ± 7.0

Symphyotrichum

lateriflorum Asteraceae Forb P 7.1 ± 2.0

Verbascum blattaria Scrophulariaceae Forb B 11.8 ± 2.5

Verbascum thapsus Scrophulariaceae Forb B 3.8 ± 1.6

Verbena hastata Verbenaceae Forb BP 50.1 ± 3.4

Ecological Archives E092-077-A2

Ecological Archives E092-077-A3

Susan C. Cook-Patton, Scott H. McArt, Amy L. Parachnowitsch,

Jennifer S. Thaler, and Anurag A. Agrawal 2011. A direct

comparison of the consequences of plant genotypic and species

diversity on communities and ecosystem function. Ecology 92:915–

923.

Appendix C (FIG. C1). Complementarity and selection effects for genotype

olycultures (dark columns) and species polycultures (light columns) excluding the

focal plant from analyses (means ± 95% confidence intervals).

[Back to E092-077]

Ecological Archives E092-077-A3

Plant genetic diversity affects multiple trophic levels and trophic interactions

Article

Full-text available

Dec 2022

Intraspecific genetic diversity is an important component of biodiversity. A substantial body of evidence has demonstrated positive effects of plant genetic diversity on plant performance. However, it has remained unclear whether plant genetic diversity generally increases plant performance by reducing the pressure of plant antagonists across trophic levels for different plant life forms, ecosystems and climatic zones. Here, we analyse 4702 effect sizes reported in 413 studies that consider effects of plant genetic diversity on trophic groups and their interactions. We found that that increasing plant genetic diversity decreased the performance of plant antagonists including invertebrate herbivores, weeds, plant-feeding nematodes and plant diseases, while increasing the performance of plants and natural enemies of herbivores. Structural equation modelling indicated that plant genetic diversity increased plant performance partly by reducing plant antagonist pressure. These results reveal that plant genetic diversity often influences multiple trophic levels in ways that enhance natural pest control in managed ecosystems and consumer control of plants in natural ecosystems for sustainable plant production. Plant genetic diversity has been shown to provide multiple ecosystem services (e.g. biological control 1) in terrestrial 1-5 and marine 6 ecosystems. In natural ecosystems, plant genetic diversity is a key component of species and ecosystem health and can be manipulated by modifying the population genetic richness of plants within or around managed lands 1,2,7 or aquatic habitats 8. In particular, increasing plant genetic diversity can increase plant productivity 9,10 and crop yield 1 , suppress plant antagonists such as insect herbivores 11 , weeds (i.e. harmful plants in human-controlled settings such as farm fields) 12 , plant diseases 2,13 or plant-feeding nematodes 14 , and promote natural enemies of pests 15,16. One of the most important reasons that plant genetic diversity can affect trophic groups is due to intraspecific variation of plant chemistry within a species 17. Single genotypes in monocultures may be associated with reduced crop yields 18 , increased pressure from herbivores 19 and plant diseases (i.e., pathogenic bacteria, fungi, and viruses) 20 , and support fewer natural enemies of invertebrate herbivores 21 compared to more genetically diverse cropping systems. Together, these findings indicate a possible influence of plant genetic diversity that extends across multiple interacting trophic levels. However, a global synthesis on the effects of plant genetic diversity across trophic levels covering different plant life forms, ecosystems or climatic zones is still lacking, leaving it unclear whether results are consistent or context dependent. Trophic interactions among plants, plant antagonists (e.g., invertebrate herbivores and plant pathogens) and natural enemies of her-bivores (e.g., predators and parasitoids) are universal in nature 22,23 and

Plant genetic diversity affects multiple trophic levels and trophic interactions

Article

Full-text available

Nov 2022

Plant genetic diversity affects interactions among multiple trophic levels

Preprint

Full-text available

May 2022

Intraspecific diversity (genetic diversity) is an important component of biodiversity. A substantial body of evidence has demonstrated positive direct or indirect effects of plant genetic diversity on plant performance. However, it has remained unclear whether plant genetic diversity increases plant performance by reducing the pressure of plant-damaging organisms across trophic levels in different plant life forms, ecosystems and climatic zones. Here, we analyse 4702 effect sizes reported in 413 studies that consider effects of plant genetic diversity on trophic groups and their interactions. We found that increasing plant genetic diversity decreases the performance of plant-damaging organisms including invertebrate herbivores, weeds, plant-feeding nematodes and plant diseases, while increasing the performance of plants and natural enemies of herbivores. We also provide evidence that plant genetic diversity increases plant performance by reducing plant-damaging organism pressure. These results reveal that plant genetic diversity often influences multiple trophic levels in ways that enhance natural pest control in managed ecosystems and consumer control of plants in natural ecosystems for sustainable plant production.

Positive relationships between species diversity and genetic diversity on a local scale at Mt. Wu Yi, China

Article

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Aug 2023
BIODIVERS CONSERV

Variations of biodiversity levels are not always independent in the ecological processes driving community assembly. Recently, SGDC (Species–genetic diversity correlation) has been used to infer community assembly rules. However, SGDC was not congruent, varying with different ecological process and scales. For figuring out the relationship between species diversity (SD) and genetic diversity (GD) on a local scale, the study tested relationship between α- and β- diversity within SD and GD, based on forest dynamics plot at Mt. Wuyi, China. The results shows that weak positive correlation between species richness and genetic diversity, due to mismatch effects of topography and resource competition on SD and GD. However, a significantly positive β-SGDC was found between species dissimilarity and genetic divergence. Meanwhile, results of multiple regression on matrices (MRM) show that geography distance has a slight effect on community assembly suggesting that influence of disperse on the community assembly. The variation partitioning further clarified that the neutral process had an important impact on the community construction at Mt. Wuyi. In conclusion, both α- and β- SGDC informed that we could infer from one biodiversity level to another, and link SD and GD through ecological process. From the view of conservation planning, overemphasis on the complementarity of one level of diversity can be detrimental to another. We need to pay more attention to natural ecological processes to protect both biodiversity levels in parallel.

Organic farming of maize crop enhances species evenness and diversity of hexapod predators

Article

Jul 2023

Arthropod species diversity enhances ecosystem productivity and sustainability by increasing pollination and biological control services. Although, it is declining rapidly due to conventional agricultural intensification, organic agriculture with reduced reliance on agronomic inputs can regenerate ecosystems’ resilience and restore them. Here, we report whether hexapod communities differ on both types of farming systems in small-scale field plot experiments, wherein Maize variety AG-589 was grown organically and conventionally in the 2020 and 2021 seasons. Livestock manure was applied in organic fields, whereas nitrogen and phosphorous were used as synthetic fertilizers in conventional fields. Hexapods were sampled three weeks after sowing once a week from the middle rows of subplots from both organically and conventionally grown maize. Twelve species of herbivores and four species of predators were recorded. Hexapod abundance overall and that of herbivores only was higher in conventionally cultivated maize, while predator abundance was higher in organic maize. Herbivores species diversity and evenness were significantly higher in conventional maize. Predator species diversity and evenness were significantly higher in organic maize fields. We noted predator abundance, diversity, and evenness as strong predictors to lower herbivore populations. These findings suggest that organic farming conserves natural enemies’ biodiversity and regulates herbivores with increased provision of suitable habitats and prey resources for natural enemies, leading to enhanced relative abundance in their specialized niches. Thus, organic agriculture can potentially mediate better ecosystem services.

An Overview of the Impact of Tillage and Cropping Systems on Soil Health in Agricultural Practices

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May 2023

There is currently a demand to grow more crops in less area as a result of urbanization's reduction of agricultural land. As a result, soil fertility is gradually declining. To maintain soil fertility, various management methods are used in modern times. The conventional tillage method is a traditional tillage method that damages soil structure, but zero tillage can improve soil quality. By maintaining soil structure with no-tillage, biological processes are frequently improved, and microbial biodiversity is increased. This review helps to understand the role of tillage as well as cropping systems in increasing crop production by maintaining soil fertility. For agricultural production and environmental protection to be sustained for future generations, soil quality must be maintained and improved in continuous cropping systems. The nodulation, nitrogen fixation and microbial community are all impacted by different cropping systems and tillage methods. They also alter soil properties including structure, aeration and water utilization. The impact of tillage and cropping system practices such as zero and conventional tillage systems, crop rotation, intercropping, cover cropping, cultivator combinations, and prairie strip techniques on soil fertility is carefully summarized in this review. The result highlights that conservational tillage is much better than conventional tillage for soil quality and different aspects of different tillage and their interaction. On the other hand, intercropping, crop rotation, cover cropping, etc. increase the crop yield more than monocropping. Different types of cropping systems are highlighted, along with their advantages and disadvantages. Using zero tillage can increase crop production as well as maintain soil fertility which is highlighted in this review. In terms of cropping systems and tillage management, our main goal is to improve crop yield while minimizing harm to the soil's health.

Diversity--functioning relationships across hierarchies of biological organization

Preprint

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May 2023

Numerous biodiversity–ecosystem functioning (BEF) experiments have shown that plant community productivity typically increases with species diversity. In these studies, diversity is generally quantified using metrics of taxonomic, phylogenetic, or functional differences among community members. Research has also shown that the relationships between species diversity and functioning depends on the spatial scale considered, primarily because larger areas may contain different ecosystem types and span gradients in environmental conditions, which result in a turnover of the species set present locally. A fact that has received little attention, however, is that ecological systems are hierarchically structured, from genes to individuals to communities to entire landscapes, and that additional biological variation occurs at levels of organization above and below those typically considered in BEF research. Here, we present cases of diversity effects at different hierarchical levels of organization and compare these to the species-diversity effects traditionally studied. We argue that when this evidence is combined across levels, a general framework emerges that allows the transfer of insights and concepts between traditionally disparate disciplines. Such a framework presents an important step towards a better understanding of the functional importance of diversity in complex, real-world systems.

The impact of environmental and climatic variables on genetic diversity and plant functional traits of the endangered tuberous orchid (Orchis mascula L.)

Article

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Nov 2022

Understanding how environmental factors shape patterns of genetic and phenotypic variations in a species is necessary for conservation and plant breeding. However, these factors have not yet been completely understood in tuberous orchid species used to make ‘Salep’, an important ingredient in traditional medicine and beverages in middle eastern countries and India. In many areas, increasing demand has pushed species to the brink of extinction. In this study, 198 genotypes from 18 populations of the endangered species Orchis mascula L. spanning a large-scale climatic gradient in northern Iran were used to investigate patterns of genetic diversity and plant functional traits. Populations were sampled from three land cover types (woodland, shrubland, and pastureland/grassland). Plant height, stem length, number of flowers, bulb fresh and dry weight, glucomannan, and starch concentrations showed high variation among populations and were significantly related to land cover type. In general, genetic diversity was high, particularly in those from eastern Hyrcanian; additionally, populations showed a high level of genetic differentiation (G'st = 0.35) with low gene flow (Nm = 0.46). The majority of genetic differentiation occurred within populations (49%) and land cover types (20%). The population structural analysis using the AFLP marker data in K = 4 showed a high geographical affinity for 198 O. mascula genotypes, with some genotypes having mixed ancestry. Temperature and precipitation were found to shape genetic and phenotypic variation profoundly. Significant isolation by the environment was observed, confirming the strong effect of environmental variables on phenotypic and genetic variation. Marker-trait association studies based on MLM1 and MLM2 models revealed significant associations of P-TGG + M-CTT-33 and E-AGG + M-CGT-22 markers with plant height and glucomannan content. Overall, a combination of large-scale climatic variables and land cover types significantly shaped genetic diversity and functional trait variation in O. mascula populations.

Monitoring genetic diversity with new indicators applied to an alpine freshwater top predator

Article

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Sep 2022
MOL ECOL

Genetic diversity is the basis for population adaptation and long-term survival, yet rarely considered in biodiversity monitoring. One key issue is the need for useful and straightforward indicators of genetic diversity. We monitored genetic diversity over 40 years (1970-2010) in metapopulations of brown trout (Salmo trutta) inhabiting 27 small mountain lakes representing 10 lake systems in central Sweden using >1200 fish per time point. We tested six newly proposed indicators; three were designed for broad, international use in the UN Convention on Biological Diversity (CBD and are currently applied in several countries. The other three were recently elaborated for national use by a Swedish science-management effort and applied for the first time here. The Swedish indicators use molecular genetic data to monitor genetic diversity within and between populations (indicators ΔH and ΔFST , respectively) and assess the effective population size (Ne -indicator). We identified 29 genetically distinct populations, all retained over time. Twelve of the 27 lakes harbored more than one population indicating that brown trout biodiversity hidden as cryptic, sympatric populations are more common than recognized. The Ne indicator showed values below the threshold (Ne ≤500) in 20 populations with five showing Ne <100. Statistically significant genetic diversity reductions occurred in several populations. Metapopulation structure appears to buffer against diversity loss; applying the indicators to metapopulations suggest mostly acceptable rates of change in all but one system. The CBD indicators agreed with the Swedish ones but provided less detail. All these indicators are appropriate for managers to initiate monitoring of genetic biodiversity.

Effect of genotypic richness, drought, and mycorrhizal associations on productivity and functional traits of a dominant C4 grass

Article

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Mar 2022
J PLANT ECOL-UK

Aims While the relationship between genetic diversity and plant productivity has been established for many species, it is unclear whether environmental conditions and biotic associations alter the nature of the relationship. To address this, we investigate the interactive effect of genotypic diversity, drought and mycorrhizal association on plant productivity and plant traits. Methods Our mesocosm study was set up at the Konza Prairie Biological Research Station, located in the south of Manhattan, Kansas. Andropogon gerardii Vitman, the focal species for our study, was planted in two levels of genotypic richness treatment: monoculture or three-genotype polyculture. A rainout shelter was constructed over half of the experimental area to impose a drought and Thiophanate-methyl fungicide was used to suppress arbuscular mycorrhizal fungi in selected pots within each genotypic richness and drought treatment. Important Findings Genotypic richness and mycorrhizal association did not affect above-ground biomass of A. gerardii. Drought differentially affected the above-ground biomass, the number of flowers and bolts of A. gerardii genotypes, and the biomass and the functional traits also differed for monoculture versus polyculture. Our results suggest that drought and genotypic richness can have variable outcomes for different genotypes of a plant species.

Human Domination of Earth’s Ecosystems

Article

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Jul 1997

Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.

Ecosystem Consequences of Changing Biodiversity

Article

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Jan 1998
BIOSCIENCE

Productivity and Sustainability Influenced by Biodiversity in Grassland Ecosystem

Article

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Feb 1996
NATURE

THE functioning and sustainability of ecosystems may depend on their biological diversity1-8. Elton's9 hypothesis that more diverse ecosystems are more stable has received much attention1,3,6,7,10-14, but Darwin's proposal6,15 that more diverse plant communities are more productive, and the related conjectures4,5,16,17 that they have lower nutrient losses and more sustainable soils, are less well studied4-6,8,17,18. Here we use a well-replicated field experiment, in which species diversity was directly controlled, to show that ecosystem productivity in 147 grassland plots increased significantly with plant biodiversity. Moreover, the main limiting nutrient, soil mineral nitrogen, was utilized more completely when there was a greater diversity of species, leading to lower leaching loss of nitrogen from these ecosystems. Similarly, in nearby native grassland, plant productivity and soil nitrogen utilization increased with increasing plant species richness. This supports the diversity-productivity and diversity-sustainability hypotheses. Our results demonstrate that the loss of species threatens ecosystem functioning and sustainability.

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge: Ecological Monog

Article

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Nov 2004

Biodiversity and ecosystem stability in a decade-long grassland experiment

Article

Jun 2006

Human-driven ecosystem simplification has highlighted questions about how the number of species in an ecosystem influences its functioning. Although biodiversity is now known to affect ecosystem productivity, its effects on stability are debated. Here we present a long-term experimental field test of the diversity–stability hypothesis. During a decade of data collection in an experiment that directly controlled the number of perennial prairie species, growing-season climate varied considerably, causing year-to-year variation in abundances of plant species and in ecosystem productivity. We found that greater numbers of plant species led to greater temporal stability of ecosystem annual aboveground plant production. In particular, the decadal temporal stability of the ecosystem, whether measured with intervals of two, five or ten years, was significantly greater at higher plant diversity and tended to increase as plots matured. Ecosystem stability was also positively dependent on root mass, which is a measure of perenniating biomass. Temporal stability of the ecosystem increased with diversity, despite a lower temporal stability of individual species, because of both portfolio (statistical averaging) and overyielding effects. However, we found no evidence of a covariance effect. Our results indicate that the reliable, efficient and sustainable supply of some foods (for example, livestock fodder), biofuels and ecosystem services can be enhanced by the use of biodiversity.

Biodiversity and Ecosystem Stability in a Decade-Long Grassland Experiment

Article