Visiting Fellow, Research School of Biological Sciences, Australian National University, Canberra
When we plant physiologists are asked...to justify public support for our research, most of us would, I imagine, invoke its potential value to agriculture and horticulture...scratch a plant physiologist as many a sceptical review committee has done, and you ﬁnd an agronomist, plant breeder or horticulturist. (Evans 1977)
‘Adaptation in nature and performance in cultivation’ now emerge as connected themes for Plants in Action. As demonstrated here in Part I, successful adaptation in nature does not necessarily imply satisfactory performance in cultivation. This arises because selection in nature results in traits that do not coincide with the performance requirements of agriculture or other forms of intense cropping. Overall rates of carbon acquisition and the scale of photoassimilate partitioning into reproductive organs (harvest index) are often sacriﬁced in nature in favour of devices for survival. This is especially evident over much of Australia where natural selection pressures commonly relate to environmental stresses, and native plants have evolved accordingly. Adaptation in our post-Gondwanan flora to drought, ﬁre, nutrient stress and soil salinisation has attracted special attention from ecophysiologists.
Aboriginal Australians made extensive use of native species throughout millennia of occupation, and had long since come to terms with the vagaries and seasonal limitations of our endemic flora. Europeans were not so adjusted and their arrival provided an impetus for increased productivity of domesticated species. Initial efforts were based on poorly adapted exotic crop plants in drought-prone and nutrient-poor soils. In effect, both genotype and environmental issues had to be addressed, but problems faced by early settlers were not articulated in those terms at that time.
Early selection of genetic variants better adapted to local conditions was mercifully successful, but largely empirical. Explanation and extrapolation into new environments had to wait for an emerging plant science to deﬁne underlying processes and adaptive responses — processes in the sense of genetically determined workings of plants that enabled them to be ﬁtted to a given niche in nature, adaptive responses in the sense that requirements for successful growth and reproductive development had to ﬁt the environmental cues of a given location. Daylength, temperature and moisture stress proved to be important driving variables in this respect.
Development of plant science in Australia and New Zealand was shaped by issues of crop production, and a distinction in research philosophy gradually emerged between what might be termed process physiology and integrative plant science. Process physiology depends upon a reductionist approach to analysing the inner workings of plants at progressively ﬁner levels of organisation and contributes to our detailed ‘understanding’. Such understanding ﬁnds application in both natural and managed ecosystems via integrative research.
Reductionists commonly use well-deﬁned test systems with inherent properties that suit their analysis of particular processes such as ion uptake, photosynthetic electron flow or induction of flowering. They usually work within an established conceptual framework or paradigm, and deﬁne questions in a way that makes them amenable to test via experimentation with their test system. A well-deﬁned system helps minimise ambiguity. Working paradigms do not remain ﬁxed. Rather, they undergo often radical revision as new knowledge renders old paradigms untenable and a ‘crisis’ ensues (Kuhn 1970). A major revision of concepts pertaining to leaf gas exchange during the 1970s is a case in point. Discovery of C4 photosynthesis, deﬁnition of Rubisco function and an appreciation of photorespiration proved to be so highly congruent that a new paradigm emerged for gas exchange.
Whereas reductionist research implies an analysis of component parts at increasing levels of detail, integrative research implies a synthesis of interacting components to produce a model of plant function. Crop management models are built in this way, and cotton farming already depends closely on models used for decision-support systems. In that case, early attempts to account for variation in growth and reproductive development between seasons or across different locations were based on observation and inference. The resulting models ‘worked’, but were largely empirical and lacked a useful conceptual framework of component processes; they were of little use outside the reference frame within which they had been constructed. Current cotton models are more than empiric, being process based, and drawing upon an extensive knowledge of growth and develop-mental response to environmental inputs, especially water. As a result they are more generic and of wider predictive value.
A similar rationale applies to application of basic concepts in explaining adaptive features of any plant and, from that knowledge, predicting performance under deﬁned conditions. Plantation forests are a case in point where likely scenarios of tree growth as a function of site quality need to be explored well ahead of investment decisions. Such analyses necessitate validated models which in turn draw upon comprehensive data sets of genotype x environment interactions on the physiology of particular tree species (e.g. see Battaglia and Sands (1997) for Eucalyptus globulus).
As an aside, when simulation models in agriculture, horticulture or forestry are used to apply outcomes from process physiology to real-world situations, signiﬁcant gaps in basic understanding become apparent and can influence direction of future forest research. In this way, related streams of reductionist and integrative research also become interactive.
By analogy, Plants in Action seeks to engender such a two-way flow of information on all levels of organisation in vascular plants. Those levels stretch from gene expression during growth and reproductive development of individual plants to human and environmental selection pressures. Those unrelenting pressures shape genotypes and thus adaptation of wild species in nature, as well as the performance of domesticated plants in cultivation.
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