Plant root proliferation in nitrogen-rich patches confers competitive advantage

Plants respond to environmental heterogeneity, particularly below ground, w here spectacular root proliferations in nutrient-rich patches may occur. Su ch 'foraging' responses apparently maximize nutrient uptake and are now pro minent in plant ecological theory. Proliferations in nitrogen-rich patches are difficult to explain adaptively, however. The high mobility of soil nit rate should limit the contribution of proliferation to N capture. Many expe riments on isolated plants show only a weak relation between proliferation and N uptake. We show that N capture is associated strongly with proliferat ion during interspecific competition for finite, locally available, mixed N sources, precisely the conditions under which N becomes available to plant s on generally infertile soils. This explains why N-induced root proliferat ion is an important resource-capture mechanism in N-limited plant communiti es and suggests that increasing proliferation by crop breeding or genetic m anipulation will have a limited impact on N capture by well-fertilized mono cultures.