Insights into plant size-density relationships from models and agricultural crops

• DOI: 10.1073/pnas.1205663109
• Publication Date: 2012-05-15T05:56:30Z
• Authors: Jianming Deng; Wenyun Zuo; Zhiqiang Wang; Zhexuan Fan; Mingfei Ji; Genxuan Wang; Jinzhi Ran; Changming Zhao; Jianquan Liu; Karl J. Niklas; Sean T. Hammond; James H. Brown
• Keywords: Crops, Agricultural; Population Density; 0106 biological sciences; 2. Zero hunger; Plant Development; 15. Life on land; Models, Biological; 01 natural sciences; Trees; Biomass; Algorithms; Ecosystem

There is general agreement that competition for resources results in a tradeoff between plant mass,M, and density, but the mathematical form of the resulting thinning relationship and the mechanisms that generate it are debated. Here, we evaluate two complementary models, one based on the space-filling properties of canopy geometry and the other on the metabolic basis of resource use. For densely packed stands, both models predict that density scales asM−3/4, energy use asM0, and total biomass asM1/4. Compilation and analysis of data from 183 populations of herbaceous crop species, 473 stands of managed tree plantations, and 13 populations of bamboo gave four major results: (i) At low initial planting densities, crops grew at similar rates, did not come into contact, and attained similar mature sizes; (ii) at higher initial densities, crops grew until neighboring plants came into contact, growth ceased as a result of competition for limited resources, and a tradeoff between density and size resulted in critical density scaling asM−0.78, total resource use asM−0.02, and total biomass asM0.22; (iii) these scaling exponents are very close to the predicted values ofM−3/4,M0, andM1/4, respectively, and significantly different from the exponents suggested by some earlier studies; and (iv) our data extend previously documented scaling relationships for trees in natural forests to small herbaceous annual crops. These results provide a quantitative, predictive framework with important implications for the basic and applied plant sciences.