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Francisco Pugnaire/Functional Plant Ecology 7488_C000 Final Proof page xx 12.5.2007 2:00pm Compositor Name: JGanesan
1
Methods in Comparative
Functional Ecology
Carlos M. Duarte
CONTENTS
Development of Functional Plant Ecology ........................................................................... 1
Screening, Broad-Scale Comparisons, and the Development of Functional Laws ............... 3
References ............................................................................................................................. 5
DEVELOPMENT OF FUNCTIONAL PLANT ECOLOGY
The quest to describe the diversity of extant plants and the identification of the basic
mechanisms that allow them to occupy different environments have shifted scientists’ atten-
tion from ancient Greece to the present. This interest was prompted by two fundamental
aims: (1) a pressing need to understand the basic functions and growth requirements of plants
because they provide direct and indirect services to human kind and (2) the widespread belief
that the distribution of organisms was not random, for there was essential order in nature,
and that there ought to be a fundamental link between differences in the functions of these
organisms and their dominance in contrasting habitats. The notion that differences in plant
functions are essential components of their fitness, accounting for their relative dominance in
differential habitats, was, therefore, deeply rooted in the minds of early philosophers and,
later on, naturalists. While animal functions were relatively easy to embrace from a simple
parallel with our own basic functions, those of plants appeared more inaccessible to our
ancestors, and the concepts of ‘‘plant’’ and ‘‘plant functions’’ have unfolded through the
history of biology.
The examination of plant functions in modern science has largely followed a reduction-
istic path aimed at the explanation of plant functions in terms of the principles of physics and
chemistry (Salisbury and Ross 1992). This reductionistic path is linked to the parallel
transformation of traditional agricultural science into plant science and the technical develop-
ments needed to evolve from the examination of the coarser, integrative functions to those
occurring at the molecular level. While this reductionistic path has led us toward a thorough
catalog and understanding of plant functions, its limited usefulness to explain and predict the
distribution of plants in nature has been a source of frustration. This is largely because of the
multiple interactions that are expected to be involved in the responses of plants to a changing
environment (Chapin et al. 1987). Yet, the need to achieve this predictive power has now
transcended the academic arena to be a critical component of our ability to forecast the large-
scale changes expected from on-going climatic change. For instance, increased CO
2
concen-
trations are expected to affect the water and nutrient requirements of plants, but resource
availability is itself believed to be influenced by rising temperatures. Such feedback effects
cannot be appropriately predicted from knowledge of the controls that individual factors
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1
exert on specific functions. Moreover, the changes expected to occur from climate change are
likely to derive mostly from changes in vegetation and dominant plant types rather than from
altered physiological responses of extant plants to the new conditions (Betts et al. 1997).
Failure of plant physiology and plant science to provide reliable predictions of the
response of vegetation to changes in their environment likely derives from the hierarchical
nature of plants. The response of higher organizational levels is not predictable from the
dynamics of those at smaller scales, although these set constraints on the larger-scale responses
of hierarchical systems. Component functions do not exist in isolation, as the dominant
molecular approaches in modern plant physiology investigate them. Rather, these individual
functions are integrated within the plants, which can modulate the responses expected
from particular functions, leading to synergism, whether amplifying the responses through
multiplicative effects or maintaining homeostasis against external forcing.
Recognition of the limitations of modern physiology to provide the needed predictions at
the ecological scale led to the advent of plant ecophysiology, which tried to produce more
relevant knowledge by the introduction of larger plant components, such as plant organs
(instead of cells or organelles), as the units of analysis. Plant ecophysiology represented,
therefore, an effort toward approaching the relevant scale of organization, by examining
the functions of plant organs. Most often, however, practitioners of the discipline laid
somewhere between the molecular approaches dominant in plant physiology and the more
integrative approaches championed by plant physiological ecology. Because of the strong
roots in the tradition of plant physiology, the suite of plant functions addressed by plant
ecophysiology still targeted basic functions (e.g., photosynthesis, respiration, etc.) that can be
studied through chemical and physical laws (Salisbury and Ross 1992). As a consequence,
plant ecophysiology failed to consider more integrative plant functions, such as plant growth,
which do not have a single physiological basis, but which are possibly the most relevant
function for the prediction of plant performance in nature (cf. Chapter 3).
The efforts of plant ecophysiology proved, therefore, to be insufficient to achieve the
prediction of how plant function allows the prediction of plant distribution and changes in
plant abundance in a changing environment. Realization that the knowledge required to
effectively address this question would be best achieved through a more integrative approach
led to the advent of a new approach, hereafter referred to as ‘‘Functional Plant Ecology,’’
which is emerging as a coherent research program (cf. Duarte et al. 1995). Functional plant
ecology is centered on whole plants as the units of analysis, the responses of which to external
forcing are examined in nature or under field conditions. Functional plant ecology, therefore,
attempts to bypass the major uncertainties derived from the extrapolation of responses to
nature (tested in isolated plant organs maintained under carefully controlled laboratory
conditions) and to incorporate the integrated responses to multiple stresses displayed by
plants onto the research program.
Although centered in whole plants, functional plant ecology encompasses lower
and higher scales of organization, including studies at the organ or cellular level (e.g.,
Chapter 8), as well as the effect of changes in plant architecture or functions (e.g., Chapters
4 and 5), and the importance of life history traits (e.g., Chapters 15 and 16), interactions with
neighbors (e.g., Chapters 17 and 18), and those with other components of the ecosystem (e.g.,
Chapter 19). In fact, this research program is also based on a much broader conception of
plant functions than hitherto formulated. The plant functions that represent the core of
present efforts in functional plant ecology are those by which plants influence ecosystem
functions, particularly those that influence the services and products provided by ecosystems
(Costanza et al. 1997). Hence, studies at lower levels of organization are conducted with the
aim of being subsequently scaled up to the ecosystem level (e.g., Chapter 10).
Because of the emphasis on the prediction of the consequences of changes in vegetation
structure and distribution for the ecosystem, functional plant ecology strives to encompass
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2 Functional Plant Ecology
the broadest possible range of functional responses encountered within the biosphere.
Yet, the elucidation of the range of possible functional responses of plants is not possible
with the use of model organisms that characterize most of plant (and animal) physiology.
Functional plant ecology arises, therefore, as an essentially comparative science concerned
with the elucidation of the range of variations in functional properties among plants and the
search for patterns and functional laws accounting for this variation (Duarte et al. 1995).
While practitioners of functional plant ecology share the emphasis on the comparative
analysis of plant function, the approaches used to achieve these comparisons range broadly.
These differences rely largely on the breadth of the comparison and the description of the
subject organisms in the analysis. The implications of these choices have not, however, been
subject of explicit discussions despite their considerable epistemological implications and
their impact on the power of the approach.
SCREENING, BROAD-SCALE COMPARISONS, AND THE DEVELOPMENT
OF FUNCTIONAL LAWS
The success and the limitations of comparative functional plant ecology depend on the
choices of approach made, involving the aims and scope of the comparison, as well as the
methods to achieve them. The aims of the comparisons range widely, from the compilation of
a ‘‘functional taxonomy’’ of particular sets of species or floras to efforts to uncover patterns
of functional properties that may help formulate predictions or identify possible controlling
factors. Many available floras incorporate considerable knowledge, albeit rarely quantitative,
on the ecology of the species, particularly as to habitat requirements. An outstanding example
is the Biological Flora of the British Isles (cf. Journal of Ecology), which incorporates
some functional properties of the plants (e.g., Aksoy et al. 1998). The likely reason why
‘‘functional’’ floras are still few is the absence of standardized protocols to examine these
properties while ensuring comparability of the results obtained. A step toward solving this
bottleneck was provided by Hendry and Grime (1993), who described a series of protocols to
obtain estimates of selected basic functional traits of plants in a comparable manner. Unfor-
tunately, while exemplary, those protocols were specifically designed for use within the
screening program of the British flora conducted by those investigators (Grime et al. 1988),
rendering them of limited applicability in broader comparisons or comparisons of other
vegetation types.
The screening approach may, if pursued further, generate an encyclopedic catalog
of details on functional properties of different plants. Some ecologists may hold the hope
that, once completed, such catalogs will reveal by themselves a fundamental order in the
functional diversity of the plants investigated, conforming to a predictive sample similar to a
‘‘periodic table’’ of plant functional traits. While I do not dispute here that this goal may
be eventually achieved, the resources required to produce such catalogs are likely to be
overwhelming, since, by definition, such a screening procedure is of an exploratory nature,
where the search for pattern is made a posteriori. Provided the number of elements to be
screened and the potentially large number of traits to be tested, the cost-effectiveness of the
approach is likely to prove suboptimal. A screening approach to functional plant ecology is,
therefore, unlikely to improve our predictive power or to uncover basic patterns unless driven
by specific hypotheses. Moreover, a hypothesis-driven search for pattern is likely to be most
effective if based on a comparative approach, encompassing the broadest possible relevant
range of plants. It is not necessary to test every single plant species to generate and test such
general laws.
The comparisons attempted may differ greatly in scope, from comparisons of variability
within species to broad-scale comparisons encompassing the broadest possible range of
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Methods in Comparative Functional Ecology 3
phototrophic organisms, from the smallest unicells to trees (e.g., Agustı
´
et al. 1994, Nielsen
et al. 1996). Experience shows, however, that the patterns obtained at one level of analysis
may differ greatly from those observed at a broader level (Duarte 1990), without necessarily
involving a conflict (Reich 1993). The scope of the comparison depends on the question that
is posed. However, whenever possible, progress in comparative functional plant ecology
should evolve from the general to the particular, thereby evolving from comparisons at the
broadest possible scales to comparisons within species or closely related species. In doing so,
we shall first draw the overall patterns, which yield the functional laws that help identify the
constraints of possible functional responses in organisms.
The simplest possible comparison involves only two subjects, which are commonly
enunciated under the euphemism of ‘‘contrasting’’ plant types. Such simple comparisons
between one or a few subject plants are very common in the literature. These simple
comparisons are, however, deceiving, for they cannot possibly be conclusive as to the nature
of the differences or similarities identified. The implicit suggestion in these contrasts is that
the trait on which the contrast is based (e.g., stress resistance vs. stress tolerance) is the cause
underlying any observed differences in functional traits. This is fallacious and at odds with the
simplest principles of method in science. Hence, contrasts are unlikely to be an effective
approach to uncover regular patterns in plant function, since the degrees of freedom involved
are clearly insufficient to venture any strong inferences on the outcome of the comparison.
Broad-scale comparisons involving functional responses across widely different species
are, therefore, the approach of choice when the description of general laws is sought. The
formulation of the comparative analysis of plant functions at the broadest possible level has
been strongly advocated (Duarte et al. 1995), on the grounds that it will be most likely to
disclose the basic rules that govern functional differences among plants. Broad-scale com-
parisons are most effective when encompassing the most diverse range of plant types possible
(e.g., Agustı
´
et al. 1994, Niklas 1994). In addition, they are most powerful when the functional
properties are examined in concert with quantification of plant traits believed to influence the
functions examined, for comparisons based on qualitative or nominal plant traits cannot be
readily falsified and remain, therefore, unreliable tools for prediction. Hence, the develop-
ment of broad-scale comparisons requires that both the functional property examined and the
plant traits, which account for the differences in functional properties among the plants, are
to be tested and carefully selected.
Broad-scale comparisons must be driven by a sound hypothesis or questions. Yet, this
approach is of a statistical nature, often involving allometric relationships (e.g., Niklas 1994),
so that observation of robust patterns is no guaranty of underlying cause and effect relation-
ships, which must be tested experimentally. Nevertheless, the functional laws developed
through broad-scale comparative analysis may hold predictive power, irrespective of whether
they represent direct cause–effect relationships. This use requires, however, that the inde-
pendent, predictor variable be simpler than the functional trait examined, if the law is to have
practical application. Examples of such functional laws are many (e.g., Niklas 1994, Agustı
´
et al. 1994, Duarte et al. 1995, Enrı
´
quez et al. 1996, Nielsen et al. 1996) and have been
generally derived from the compilation of literature data and the use of plant cultures in
phytotrons or the use of the functional diversity found, for instance, in botanical gardens
(e.g., Nielsen et al. 1998). This choice of subject organisms is appropriate whenever the
emphasis is on the functional significance of intrinsic properties. However, the effect of
environment conditions can hardly be approached in this manner, and functional ecologists
must transport the research to the field, which is the ultimate framework of relevance for this
research program.
The comparative approach is also a powerful tool to examine the effect of environmental
conditions in situ. Gradient analysis, where functional responses are examined along a
clearly defined environmental gradient, has proven a powerful approach to investigate the
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4 Functional Plant Ecology
relationship between plant function and environmental conditions (Vitousek and Matson
1990). Gradient analysis is particularly prone to spurious relationships where the relationship
between the gradient property and the functional response reflects a functional relationship to
a hidden factor covarying with that nominally defining the gradient. Inferences from gradient
analysis are, therefore, also statistical in nature and have to be confirmed experimentally to
elucidate the nature of underlying relationships.
Broad-scale comparisons often entail substantial uncertainty—typically in the order-of-
magnitude range—in their predictions, which is a result of the breadth—typically four or
more orders of magnitude—in the functions examined. This imprecision limits the applic-
ability of these functional laws and renders their value greatest in the description of general,
large-scale patterns, over which the effect of less-general functional regulatory factors, both
intrinsic and extrinsic, is superimposed. Hence, multiple factors that constrain the functional
responses of plants are nested in a descending rank of generality, whereby the total number of
traits involved in the control is very large and only a few of them are general across a broad
spectrum of plants.
The nested nature of the control of functional responses implies uncertainties when
scaling functional laws, either toward lower or higher levels of organization (Duarte 1990).
There is, therefore, no guaranty that the patterns observed at the broad-scale level will apply
when focusing on particular functional types. Changes in the nature of the patterns when
shifting across scales have prompted unnecessary disagreement in the past (Reich 1993).
A thorough investigation of functional properties of plants should include, whenever pos-
sible, a nested research program, whereby the hypotheses on functional controls examined are
first investigated at the broadest possible scale, to focus subsequently on particular subsets of
species or functional groups, along environmental gradients.
The chapters in this volume provide a clear guide to functional ecology with examples,
emphasizing the nested nature of the research program both within the chapters and in the
manner in which they have been linked into different parts. The chapters also provide an
overview of the entire suite of approaches available to address the goals of functional ecology,
providing, therefore, a most useful tool box for prospective practitioners of the research
program. The resulting set provides, therefore, a heuristic description of functional ecology,
which should serve the dual role of providing a factual account of the achievements of
functional ecology while endowing the reader with the tools to design research within this
important research program.
REFERENCES
Agustı
´
, S., S. Enrı
´
quez, H. Christensen, K. Sand-Jensen, and C.M. Duarte, 1994. Light harvesting
among photosynthetic organisms. Functional Ecology 8: 273–279.
Aksoy, A., J.M. Dixon, and W.H.G. Hale, 1998. Capsella bursa-pastoris (L.) Medikus (Thlapsi bursa-
pastoris L., Bursa bursa-pastoris (L.). Shull, Bursa pastoris (L.) Weber). Journal of Ecology 86:
171–186.
Betts, R.A., P.M. Cox, S.E. Lee, and F.I. Woodward, 1997. Contrasting physiological and structural
vegetation feedbacks in climate change simulations. Nature 387: 796–799.
Chapin III, F.S., A.J. Bloom, C.B. Field, and R.H. Waring, 1987. Plant responses to multiple environ-
mental factors. Bioscience 37: 49–57.
Costanza R., R. d’Arge, R. de Groo, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R.V.
O’Neill, J. Paruelo, R.G. Raskin, P. Sutton, and M. van der Belt, 1997. The value of the world’s
ecosystem services and natural capital. Nature 387: 253–260.
Duarte, C.M., K. Sand-Jensen, S.L. Nielsen, S. Enrı
´
quez, and S. Agustı
´
, 1995. Comparative functional
plant ecology: Rationale and potentials. Trends in Ecology and Evolution 10: 418–421.
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Methods in Comparative Functional Ecology 5
Enrı
´
quez, S., S.L. Nielsen, C.M. Duarte, and K. Sand-Jensen, 1996. Broad-scale comparison of
photosynthetic rates across phototrophic organisms. Oecologia (Berlin) 108: 197–206.
Grime, G.P., J.G. Hodgson, and R. Hunt, 1988. Comparative plant ecology. Unwin Hyman,
Boston, MA.
Hendry, G.A.F. and J.P. Grime, 1993. Methods in Comparative Plant Ecology. A Laboratory Manual.
Chapman and Hall, London.
Nielsen, S.L., S. Enrı
´
quez, and C.M. Duarte, 1998. Control of PAR-saturated CO
2
exchange rate in
some C
3
and CAM plants. Biologia Plantarum 40: 91–101.
Nielsen, S.L., S. Enrı
´
quez, C.M. Duarte, and K. Sand-Jensen, 1996. Scaling of maximum growth rates
across photosynthetic organisms. Functional Ecology 10: 167–175.
Niklas, K.J., 1994. Plant Allometry. The Scaling of Form and Process. The University of Chicago Press,
Chicago, IL.
Salisbury, F.B. and C.W. Ross, 1992. Plant Physiology, 4th edn. Wadsworth, Belmont, CA.
Vitousek, P.M. and P.A. Matson, 1990. Gradient analysis of ecosystems. In: J.J. Cole, G. Lovett, and
S. Findlay, eds. Comparative Ecology of Ecosystems: Patterns, Mechanisms, and Theories.
Springer-Verlag, NY, pp. 287–298.
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6 Functional Plant Ecology
2
Opportunistic Growth
and Desiccation Tolerance:
The Ecological Success of
Poikilohydrous Autotrophs
Ludger Kappen and Fernando Valladares
CONTENTS
Poikilohydrous Way of Life ................................................................................................ 8
Poikilohydrous Constitution versus Poikilohydrous Performance:
Toward a Definition of Poikilohydry .............................................................................. 8
Ecology and Distribution of Poikilohydrous Autotrophs ............................................... 13
Does Poikilohydry Rely on Specific Morphological Features? ....................................... 15
Exploiting an Erratic Resource ........................................................................................... 16
Different Modes of Water Uptake and Transport .......................................................... 17
Problems of Resuming Water Transport......................................................................... 20
Retarding Water Loss...................................................................................................... 22
Preventing Damage and Tolerating Stresses ....................................................................... 24
Desiccation Tolerance...................................................................................................... 24
Cellular and Physiological Changes during Desiccation.................................................. 25
Synthesis of Proteins and Protective Substances ............................................................. 28
Photoprotection of the Photosynthetic Units .................................................................. 29
Desiccation Tolerance: An Old Heritage......................................................................... 32
Tolerance to Extreme Temperatures: A Property
Linked to Poikilohydry.................................................................................................... 33
Limits and Success of Poikilohydry .................................................................................... 34
Photosynthesis ................................................................................................................. 34
Lichens and Bryophytes............................................................................................... 34
Vascular Plants ............................................................................................................ 39
Different Strategies .......................................................................................................... 41
Opportunistic Metabolic Activity in situ ......................................................................... 42
Place in Plant Communities............................................................................................. 46
Primary Production of Poikilohydrous Autotrophs ........................................................ 47
Acknowledgments ............................................................................................................... 48
References ........................................................................................................................... 48
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7
POIKILOHYDROUS WAY OF LIFE
Poikilohydry, or the lack of control of water relations, has typically been a subject studied by
lichenologists and bryologists. For many years, much was unknown about poikilohydrous
vascular plants, and evidence for their abilities was mostly anecdotal. A small number of these
plants were studied by a few physiologists and ecologists who were fascinated by the capability
of these ‘‘resurrection plants’’ to quickly switch from an anabiotic to a biotic state and vice
versa (Pessin 1924, Heil 1925, Walter 1931, Oppenheimer and Halevy 1962, Kappen 1966,
Vieweg and Ziegler 1969). Recently, a practical demand has released an unprecedented
interest in poikilohydrous plants. The increasing importance of developing and improving
technologies for preserving living material in the dry state for breeding and medical purposes
has induced tremendous research activity aimed at uncovering the molecular and biochemical
basis of desiccation tolerance. Poikilohydrous plants have proven to be very suitable for
exploring the basis of this tolerance with the target of genetic engineering (Stewart 1989,
Oliver and Bewley 1997, Yang et al. 2003, Bernacchia and Furini 2004, Alpert 2006).
Consequently, much of the current literature discusses poikilohydrous plants mainly as a
means of explaining basic mechanisms of desiccation tolerance (Hartung et al. 1998, Scott
2000, Bartels and Salamini 2001, Rascio and Rocca 2005) instead of exploring their origin, life
history, and ecology (Raven 1999, Porembski and Barthlott 2000, Belnap and Lange 2001,
Ibisch et al. 2001, Proctor and Tuba 2002, Heilmeier et al. 2005).
Many new resurrection plants have been discovered during the last 25 years, especially in
the Tropics and the Southern Hemisphere (Gaff 1989, Kubitzki 1998, Proctor and Tuba
2002). This has provided new insights into the biology of these organisms. In this chapter,
structural and physiological features of poikilohydrous autotrophs and the different strat-
egies in different ecological situations are discussed. As desiccation tolerance itself is the
most—but not only—striking feature, our goal is to assess in addition the life style and the
ecological success of poikilohydrous autotrophs. We give attention to the productivity of
poikilohydrous autotrophs, how they manage to live in extreme environments, the advantage
of their opportunistic growth, and what happens to structure and physiology during desic-
cation and resurrection.
POIKILOHYDROUS CONSTITUTION VERSUS POIKILOHYDROUS PERFORMANCE:
T
OWARD A DEFINITION OF POIKILOHYDRY
According to Walter (1931), poikilohydry in plants can be understood as analogous to
poikilothermy in animals. The latter show variations of their body temperature as a function
of ambient temperature, whereas poikilohydrous autotrophs (chlorophyll-containing organ-
isms) exhibit variations of their hydration levels as a function of ambient water status (Walter
and Kreeb 1970). The term autotroph is used here to comprise an extensive and heterogenous
list of autotrophic unicellular and multicellular organisms (cyanobacteria, algae, bryophytes,
and vascular plants), including the lichen symbiosis. Poikilohydrous performance (from the
Greek words poikilos, changing or varying, and hydor, water) is applied to organisms that
passively change their water content in response to water availability (‘‘hydrolabil’’; Stalfelt
1939), eventually reaching a hydric equilibrium with the environment. This fact does not
necessarily imply that the organism tolerates complete desiccation (Table 2.1). There is no
general consensus on the definition of poikilohydrous autotrophs. The Greek word poikilos
also means malicious, which, figuratively speaking, may apply to the difficulty of comprising
the outstanding structural and functional heterogeneity of this group of organisms.
It is difficult to be precise about the vast number of poikilohydrous nonvascular
taxa, comprising 2000 Cyanophyta, c.23,000 Phycophyta, c.16,000 Lichenes, and c.25,000
Bryophyta. The number of poikilohydrous vascular plant species could be almost 1500 if the
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8 Functional Plant Ecology
TABLE 2.1
Desiccation Tolerance of Isolated Chloroplasts and of Poikilohydr
ous Autotrophs
a
Species
Degree of Desiccation Survived
Time of Drought Survived
Reference
Isolated chloroplasts (
Beta
)
15% RWC
Until equilibrium
Santarius 1967
Nostoc
and Chlorococcum
Air-dry
73 years
Shields and Durrell 1964
Lichens
Lichens (50 species)
2%–9% d.wt.
38–78 week air-dry
Lange 1953
24–56 week P
2
O
5
Pseudocyphellaria dissimilis
45%–65% rh
8–10 h until equilibrium
Green et al. 1991
Bryophytes
Ctenidium molluscum
Varying between
<10% rh and
>
60% rh
40 h
Dircksen 1964
Dicranum scoparium
<10% rh in winter,
>50% in summer
40 h
Dircksen 1964
Epiphytic mosses (14 species)
0%–30% rh
Until equilibrium
Hosokawa and Kubota 1957
Fissidens cristatus
Varying between
<10% rh and
>60% rh
40 h
Dircksen 1964
Mnium punctatum
<25% rh in winter and
>80% rh in summer 40 h
Dircksen 1964
Rhacomitrium lanuginosum
32% rh
239 days
Dilks and Proctor 1974
Sphagnum
sp.
Air-dry
<5 days
Wagner and Titus 1984
Exormetheca holstii
Air-dry
8 months
Dinter 1921 (S. Hellwege et al. 1994)
Riccia canescens
(bulbils)
Air-dry
7 year
Jovet-Ast 1969
Pteridophytes
Selaginella lepidophylla
Air-dry
About 1 year
Eickmeier 1979
Isoetes australis
0% rh
Until equilibrium
Gaff and Latz 1978
Asplenium ruta-muraria
5%–10% RWC
1–3 days H
2
SO
4
(winter) Kappen 1964
Asplenium septentrionale
7%–20% RWC
1–3 days H
2
SO
4
(winter) Kappen 1964
Asplenium trichomanes
7%–15% RWC
1–3 d H
2
SO
4
(winter)
Kappen 1964
Camptosorus rhizophyllus
(gametophyte)
H
2
SO
4
Picket 1914
Cheilanthes
(8 species)
2%–20% rh
Until equilibrium
Gaff and Latz 1978
Hymenophyllum tunbridgense
43%
15 days
Proctor 2003
Hymenophyllum wilsonii
20%
30 days
Proctor 2003
Notholaena maranthae
6% RWC
Iljin 1931
Paraceterach
sp.
15% rh
Until equilibrium
Gaff and Latz 1978
Pellea
(2 species)
2%–30% rh
Until equilibrium
Gaff and Latz 1978
Pleurosorus rutifolius
2% rh
Until equilibrium
Gaff and Latz 1978
Polypodium polypodioides
3% RWC
50 h
Stuart 1968
Polypodium vulgare
3%–10% RWC
10 D P
2
O
5
(winter)
Kappen 1964
Polystichum lobatum
7%–10% RWC
24 h (air) winter
Kappen 1964
Gametophytes of ferns (5 species)
20–65 rh
36 h
Kappen 1965
(continued
)
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Opportunistic Growth and Desiccation Tolerance 9