Tradeoffs between resource allocation and growth across life history strategies: A quantitative comparison of traits between annual and perennial congeneric species

Background/Question/Methods

A tradeoff between longevity and reproductive effort is expected as long living plants need to allocate resources away from reproductive tissues to resource acquisition and storage structures. The existence of this tradeoff becomes relevant in light of the increasing pressure on agriculture to meet demands for food, feed, and biomass for energy, while limiting negative environmental impacts. In fact, perennial crops may reduce soil erosion and nutrient leaching, and access larger water and nutrient stores thanks to their higher root allocation. It is thus important to explore to what extent this tradeoff occurs across different genera, and how it is impacted by human-driven selection. Also, the existence of this tradeoff raises the question as to whether staple crops can be selected or engineered to achieve perennial habit and adequate yields, a combination that appears unfeasible from the perspective of plant resource economy. To address these questions, key traits relative to congeneric annual and perennial pairs were collected from nearly 50 published studies. Overall, the dataset encompasses 25 genera, covering a number of naturally occurring grasses and herbs as well as staple grain crops, their perennial relatives, and new hybrids.

Results/Conclusions

Confirming previous expectations, our meta-analysis shows that perennials allocate more resources to roots but less in reproductive structures than annuals, although the extent of the difference in resource allocation between life histories is impacted by genus and previous history of domestication. Furthermore, perennials are characterized by a higher assimilation rate per unit leaf area, thicker leaves, and lower relative growth rate. Patterns of nitrogen allocation and use are less clear due to limited data availability. When focusing on recently selected grain crops (e.g., wild and domesticated species and new hybrids from the genera Oryza and Triticum), an inverse correlation is apparent between seed production and ability to survive beyond one year, thus suggesting that current hybridization efforts are succeeding in increasing longevity at the cost of yield reduction.