The Conservation Physiology of Bryophytes

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1		Marko S. Sabovljevic	--	2309	2022-05-16 10:43:23	\|
2	update layout and references	Rita Xu	Meta information modification	2309	2022-05-16 11:25:28	\|

This entry is adapted from the peer-reviewed paper 10.3390/plants11101282

mosses liverworts

1. Introduction

Conservation physiology is a rather new scientific discipline emerging over the last several decades with the aim of solving the conservation problems of different biological entities. This is an integrative approach applying physiological concepts and tools to gain new knowledge about the features of those targeted biological entities which are the subject of conservation. Once conservation is needed, researchers usually know very little about the entity (organisms, populations or ecosystems), and lack crucial data pertaining to the functional characteristics of the biological entity and its responses to environmental stressor or changes. Thus, in order to address conservation problems, data on the functional responses and, thus, survival strategies in different environmental backgrounds are urgently needed, and conservation physiology provides the opportunity to gain such knowledge directly and quickly through an experimental approach, since many biological entities are in need of urgent conservation and have no time to wait for data accumulation. Additionally, these data are necessary to develop good conservation policy, ecosystem restoration, population rebuilding and self-sustainability or simply to generate the support tools for decision-makers.

Recognition of the significance of physiology for conservation has increased considerably in recent decades, however, mostly in terms of big animal conservation, mainly mammals, and lately also for some plants. However, angiosperms are underrepresented in strict conservation physiological studies and this appears to be a general trend in conservation science ^[1]. Thus, this approach is missing among many other threatened biological entities (including bryophytes) and further development is both essential and urgent. Plants in general are primary producers, and their importance is indispensable for all other organisms. Van Kleunen science ^[1] reported 47% of all globally threatened organisms to be among the higher (vascular) plants. Bearing in mind that many plant scientists deal with the physiological responses of model organisms or crop plants, very little information on environmental response mechanisms can be found for wild and threatened plants. The situation with bryophytes (higher but non vascular plants) is even worse.

Thus, information on the mechanisms involved in how biological entities function is urgently needed for threatened taxa, and these include a wide range of areas, such as structure, resource acquisition, metabolic pathways, energy fluxes, regulation and homeostasis, adaption and the ability to tolerate environmental changes.

Some provenance trials on conservation physiology have been applied during ex situ conservation studies, as ex situ and conservation physiology can but do not overlap to a huge extent and are a compatible field in conservation science. Some of the published papers clearly fit into this view as independent research areas whose results support studied entity conservation (e.g., for bryophytes: ^[2]^[3]^[4]^[5]^[6]^[7]), although the history of ex situ conservation studies is relatively short ^[8]. Ex situ studies often focus on habitat variation limits and suitability for the target biological entity of high conservation interest (e.g., ^[9]).

The position of conservation physiology within conservation biology can, thus, be considered as an independent subdiscipline, but one which partly overlaps and intermingles with conservation ecology and genetics. Such a discipline is urgently needed for better conservation planning and management.

Bryophytes, a group of photosynthetic organisms which were among the first to colonize the terrestrial environment, are rather neglected in conservation initiatives world-wide as being of less economic importance. However, this group of 18,000–25,000 recent species has high significance in ecosystem functioning and also biotechnological potential, thus deserving greater attention in conservation initiatives.

Although they have many similarities with vascular plants, there are more dissimilarities and peculiarities of this heterogeneous group and the knowledge gained about vascular plant species often leads to misinterpretation or even incorrect conclusions.

The evolutionary distance as seen in years among certain species within the bryophyte group is bigger than that among remote entities of vascular plants. Thus, it can be inferred that even the extrapolation of knowledge among some bryological entities can be misleading. Considering that conservation physiology can include studies on a wide range of scales, from chemical contents or biomolecules through cells and special organs to whole organism and population biology, even more caution should be exercised when inferring measures for tentative species at survival risk.

Carey ^[10] stated that in addition to environmental changes in plant conservation physiology, special attention should also be paid to pathogen emergence, and researchers have almost no idea about bryophyte pathogens, thus indicating this need in the emerging field of bryophyte pathogen biology.

In general, bryophytes have a larger area or occupancy, i.e., range compared to vascular plants, but being haploid organisms and highly specialized, they are attached to microhabitats and react easily to minor environmental changes. That is why they have a high indicative potential for environmental changes. On the other hand, this can provide the opportunity to study the variation of physiological traits over large spatial and temporal scales. Chown et al. ^[11] defined this approach as macrophysiology, which is important in mitigating population decline and plasticity to cope with environmental changes. This is crucial when choosing individuals for studies as well as for captivity and ex situ conservation programs.

In organisms other than bryophytes, accumulated physiological knowledge has allowed for the generation of management models of target entity. Moreover, it has become possible to predict the response to changes, to test and develop conservation strategies, i.e., to reach the goal of desirable conservation outcomes ^[1].

The approach to various threatened taxa cannot be the same bearing in mind that some suffer from habitat changes and degradation and others from rather low fitness. Although the study of such taxa can be the same, the conservation programs may differ to achieve the same goal.

It should be stated that conservation physiological studies should not be solely directed at environmental changes, but also antropogenically induced impacts and the responses of bryophytes to them. It should be highlighted that conservation physiology and its approach do not include only threatened taxa and abiotic stressors, but also the study of the functions and mechanisms of taxa which may threaten natural ecosystems and native species, such as alien or invasive species.

The conservation physiology of bryophytes faces numerous constraints. There are not very many bryophyte scientists and few of them deal with the experimental approach. The plant material is rather hard to recognize and find in relevant developmental phases, and the known habitat can be very distant and not easily accessible, especially for priority and/or targeted species. In vitro and ex situ collections are rather rare and hard to establish, and the asexual reproduction of haplotypes can be problematic when considering the genetic loss or structure of the population for conservation. Nevertheless, there are also advantage such as the small size of bryophytes compared to other plants, demanding less laboratory space and lower costs.

The developmental traits of bryophytes are not the same for some growth phases and some developmental stages will be absent even when the optimal conditions for vegetative growth are achieved. Thus, studies of the various physiological responses of different growth phases (e.g., sex organ development) are needed as well as the variability of functional traits, referred to as physiological diversity of biological entities. Physiological diversity seems to be extremely important for establishing self-sustainable populations and reintroduction programs in general. Thus, the discovery of the mechanistic basis should lead to functional patterns, which can be achieved through the experimental approach in conservation physiology. The overlapping of data from realized niches usually studied in distributional investigation should be strengthened by the data gathered in fundamental niche studies, hence improving the prediction of survival in a changing environment. Suffering the fitness consequences, but still with some survival rate, is due to a poor understanding of environmental thresholds and organisms’ tolerance of extremes, synergisms and antagonisms of both biotic and abiotic factors in areas of survival but of lower habitat quality.

Physiological tools are useful in defining the areas of the highest functional, and not only structural basis, and so take priority in spatial protection since protecting all habitats is impossible and unrealistic even for the most threatened and/or the rarest species.

Future environmental change scenarios include multiple stressors and physiological approaches and experimental tests enable valid prediction and timely protection. Additionally, physiological tools allow the study of potential pollutants and bryophyte responses to them, thus identifying the potential thresholds for those emerging or long-term present in potential or native habitats.

Although ex situ conservation efforts are often a last resort for the conservation of highly endangered species, they remain an important safeguarding tool. However, many problems and disadvantages emerge when dealing with bryophytes ex situ: limited material availability, a lack of information on biology and ecology, unknown, undeveloped or underdeveloped biotechnological procedures for propagation or appropriate morphological development and desired developmental stage achievement. Additional problems include germplasm formation and maintenance, spore production and storage, unknown spore biology (e.g., dormancy) and nutritional or species-specific requirements. Lack of knowledge about natural enemies, and interaction with other organisms or chemical constitutions make in vitro tests and collection unavoidable when dealing with bryophyte conservation physiology and compiling protection action plans, which include minimized stress and maximized survival.

2. Some Examples of Incidental and Intentional Bryophyte Conservation Physiological Approaches in Europe

The conservation of bryophytes is usually conducted through an assessment of species and their populations in their areas of occupancy, resulting in red data books or red lists e.g., ^[12] or regional or national legislation. There are fewer examples which include the organized monitoring of local populations of target species, and the number where the experimental approach is applied, either via field or laboratory experiments, is even lower. However, bryophyte scientists and enthusiasts are aware of the significance of the experimental approach and experimental evidence when dealing with tentative or sensitive species remaining in small numbers in nature. Thus, in many red-list, red-book and conservation programs, the urgent need for such data on the target species is highlighted. There have been very few experimental approach examples during ex situ conservation, and these tend to identify new problems instead of offering explanations and solutions.

Experimental investigations on bryophytes are avoided because of the problems involved in in treatments and bryophyte material collection and propagation. The studies of in vitro cultures are conducted, but on a small number of species which serve as models (e.g., Physcomitrium patens (Hedw.) Mitt., Marchantia polymorpha L. or Ceratodon purpureus (Hedw.) Brid.). A similar approach is rarely seen for other species (Figure 1). The reasons for this are manifold: from problems in establishing axenic cultures and growth control, to the slow growth of bryophytes, to difficulties in finding a sufficient quantity of clean (free of other cohabitants) target species and their identification. The problems of in vitro culturing bryophytes as well as some solutions and procedures are addressed in some studies e.g., ^[13]^[14]^[15]^[16] and the references therein. Additionally, more details on procedures and strategies can be found in Sabovljević et al. ^[14].

Figure 1. Some examples of moss species applied in conservation physiology programs: (A). Anacamptodon splachnoides (origin from Hungary) from in vitro culture anchored to the natural wooden substrate; (B). Anomodon rostratus (origin from Serbia) from in vitro culture anchored to the limestone rocks by the application of egg white; (C). Calliergon giganteum (origin from Croatia) in vitro propagation; (D). Dicranum viride (origin from Hungary) in vitro propagation; (E). Hamatocaulis vernicosus (origin from Romania) xenic condition propagation and acclimation; (F). Physcomitrium eurystomum (origin from Croatia) propagation in in vitro controlled conditions and sporophyte development with viable spores; (G). Tayloria froelichiana (origin from Slovakia), xenic propagation and acclimation; (H). Zygodon forsterii (origin from Hungary) anchoring to wooden substrate and gametophore induction in xenic conditions.

Studies which directly address bryophyte conservation problems are rare, but significant contributions can be found. In this chapter, researchers provide an overview of some of the most interesting instances.

The development of bryophytes is often directed by inner and outer signals, although very little information is available on the developmental physiology of bryophytes. Most extrapolations are based on the knowledge accumulated about vascular plants and a few are derived from the study of moss model species Physcomitrium patens (Hedw.) Bruch & Schimp. A review of plant growth regulators in bryophytes can be found in Sabovljević et al. ^[17]. Very little is known about the differences among species of bryophytes groups and some tests in various species seem to show rather different developmental patterns and functions. This is to be expected considering that the phylogenetical distance between different groups and species can be very great. The absence of vascular systems is common, and the effects of exogenously applied plant growth regulators may serve as developmental triggers ^[13]^[18]^[19]. They can also act as elicitators or blockers depending on the concentrations applied and on the synergistic/antagonistic effects with other tested factors (i.e., chemicals, light conditions or temperature). These findings can be a good starting point in testing the biological features of rare species. This means firstly applying such tests on more common species (counterparts), further developing the tests and then using them on the target species. The selection of counterparts should be in accordance with ecological, physiological or morpho-anatomical characteristics, which should be similar or like those of the target species based on the information available for the target species (elaborated in ^[14]). Such tests were conducted in Atrichum undulatum (Hedw.) P. Beauv. ^[20], Bryum argenteum Hedw. ^[18], Dicranum scoparium Hedw. ^[21], Hypnum cupressiforme Hedw. ^[22] and Thamnobryum alopecurum Nieuwland ex Gangulee ^[23]. These were later applied to target rare or threatened species, such as Bruchia vogesiaca Schwaegr. ^[24], Calliergon giganteum (Schimp.) Kindb. ^[25], (Figure 1C), Entosthodon hungaricus (Boros) Loeske ^[26] and Molendoa hornschuchiana (Hook.) Limpr. ^[27], to achieve good development and propagation in laboratory conditions prior to testing in outdoor environments.

References

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1. Introduction

2. Some Examples of Incidental and Intentional Bryophyte Conservation Physiological Approaches in Europe

References