Why plant science matters


Over the last 25 yr New Phytologist has roughly doubled in size. Over the same period the world population has increased by c. two billion people, a 40% rise. The rise in world population poses some exceptionally difficult challenges for the planet and for our species; the parallel increase in scientific knowledge, exemplified by this journal’s output, is one of the key levers that we have to help us meet those challenges.

Currently c. one billion people subsist on < $1 a day. Over the next 30 yr population growth will probably double that number unless serious action is taken to improve their living standards. The likely growth in population in the least developed countries is equivalent to creating a new city of one million people every 5 d. If these people are to have acceptable standards of living, then their rate of consumption, particularly of food and energy, needs to increase. This achievement, which has so far proved elusive, needs to occur at a time when a range of indicators, such as planetary boundaries being crossed (Rockström et al., 2009), ecological footprints being exceeded (Ewing et al., 2010) and ecosystem services being degraded (Millennium Ecosystem Assessment, 2005), all point to the fact that global levels of consumption are excessive and unsustainable.

The single biggest problem we face is how to feed the 9–10 billion people who will live on the planet in 30–50 yr time (Beddington, 2010). Historically we have achieved large increases in food production both by intensification and by bringing new land into cultivation. Expansion of the farmed area will not work as a strategy for the next phase both because the amount of suitable unfarmed land is small and because we now understand the consequences for biodiversity and planetary systems of converting much more of it into cropland (Midgley & Thuiller, 2005; Brussaard et al., 2010; Phalan et al., 2011). The problem is exacerbated both by the inevitable loss of productive farmland to urbanization and the high current rate of degradation of soils in many parts of the world (Lal, 2007). There are currently seven billion people living off 1.5 billion hectares of farmland, which means that each of us should have access to just over 2100 m2, or c. 45 m × 45 m – in reality, of course, some of us use the products of a much larger area. If population grows to 9.3 billion by 2050 [the United Nations (UN) medium projection] and we continue to lose c. 0.4% of that land each year to urbanization, salinization and other forms of land loss or degradation, the area available will then be under 1400 m2 per person (c. 37 m × 37 m): your personal square of land is shrinking by c. 20 cm yr−1. In consequence, productivity will have to rise by c. 50% just to keep pace with the current availability of food and the consequences of inequity in distribution will be even more stark.

How can we do this? Some improvement in productivity is achievable by using known science and simple technology, notably in large parts of Africa where yields are often low and farmers cannot afford even basic inputs to boost them. New science will play its part too: exciting developments in the understanding of how the devastating parasitic weed Striga attaches to and damages its host have opened new avenues for its control (Cissoko et al., 2011; Jamil et al., 2011). Raising agricultural yields in Africa above their current low levels is therefore wholly achievable. However, the massive yields delivered by intensive agriculture are probably not sustainable, because of the energy costs of nitrogen (N) fertilizers and the decreasing supplies of phosphate (Cordell et al., 2009), and certainly not deliverable globally by that route. Nevertheless, big improvements are possible. Where the key limitation is soil fertility, N-fixing symbioses can be effective, perhaps by bringing new crop species into play. However, using mycorrhizal fungi to enhance crop phosphorus (P) acquisition is more challenging, though probably essential, and will be best achieved by effective agronomic practices (Verbruggen et al., 2010) and there is building evidence that these symbionts may play an important role in the N cycle too (Leigh et al., 2009; Hodge & Fitter, 2010). If fertilizer is available then it needs to be used cleverly, as in precision agriculture (Gebbers & Adamchuk, 2010).

On many soils, however, making nutrients more available will do little because the problems are drought or toxicity, including salinity. Drought is an especially challenging problem because of the absolute scarcity of water in many parts of the world and because humans currently intercept c. 60% of all run-off following precipitation and use 80% of that for agriculture. There is real concern that one of the biggest impacts of climate change will be to increase the frequency, severity and global scale of drought (Romm, 2011). Using drought resistant plants as novel crops will help – for example, Crassulacean Acid Metabolism (CAM) species such as Agave have some potential (Borland et al., 2011) – and that will require a better understanding of the variety of ways that plants have evolved to cope with drought (McDowell et al., 2008), but attention has also been given to the possibility of engineering drought resistance.

There has been great hope that genome knowledge can be used to improve crops and the plethora of new technologies (next generation sequencing, transcriptomics, phenomics) gives grounds for enhanced expectations (Jackson et al., 2011). One GE Shangri-la has been the creation of a N-fixing cereal, either by transferring the genetic pathways for symbiotic fixation from legumes (Oldroyd et al., 2009) or by direct transfer of the nitrogenase enzyme system to chloroplasts or mitochondria (Beatty & Good, 2011). The effort being put into this programme is large and it seems likely that progress will eventually be made, but it is not a risk-free approach: an N-fixing cereal could potentially become a major weed in other crops or invasive in unmanaged ecosystems, and if N-fixation were to be transferred to a crop with wild relatives, the ability might become more widespread with wholly unpredictable consequences for natural ecosystems and the global N cycle.

Relying too heavily on genetic manipulations is always going to be a dangerous strategy. To date the technology has largely been used to counter weeds and pests, despite abundant evidence that plant pathogens and competitors can evolve rapidly to counter any clever defences we erect. Intelligent combinations of approaches can help to make bred or engineered resistance more durable, as shown by Brun et al. (2010), but a proper long-term solution may require a very different approach: ‘One idea is to re-engineer the agroecosystem to increase overall host diversity, at the species level as well as at the gene level, to reduce directional selection and present an evolutionary dilemma to the pathogen’ (MacDonald, 2010; pp. 3–5). In other words, we need to re-think the way we organize production systems.

A more sustainable agriculture will use both the technological innovations of plant science and the ecosystem thinking that derives from ecology. The ecosystem is a relatively young concept (Currie, 2011) and is only now beginning to have an impact outside its core discipline, especially with the adoption of the concept of ecosystem services, the free services that we get from the natural world and on which we depend (Millennium Ecosystem Assessment, 2005; EASAC, 2009). The problem with intensive agriculture is that it uses land for a single purpose – food production; all other services that land might deliver are minimized, including soil formation, carbon storage (for climate control), water storage (for flood control) and water purification. Since we need to preserve and promote all these services, we are going to have to develop cleverer ways of managing land, whether in agriculture or elsewhere, that ensure that we get both sufficient food and a habitable planet. What is needed to attain that goal is better collaboration between plant scientists, ecologists, agronomists, social scientists and others to develop integrated and sustainable agricultural systems. New Phytologist will remain a forum for publication of the innovative fundamental plant science (Grierson et al., 2011) and ecology that underpins that development.