Ecosphere (Nov 2021)
Intraspecific trait variation improves understanding and management of cover crop outcomes
Abstract
Abstract Understanding links between functional trait diversity and ecosystem services can inform more sustainable management of agroecosystems. The use of cover crops (i.e., non‐harvested crops) is a key strategy for increasing plant functional trait diversity in crop rotations. Variation in functional traits can be assessed in multiple ways—within a species (intraspecific), across species (interspecific), and across communities (community trait metrics). Recent evidence from the field of trait‐based research suggests that the role of intraspecific trait variation (ITV) in explaining ecological dynamics deserves greater attention. We conducted a systematic literature review to determine whether this also applies to cover crops. While fewer than one‐third of the 30 studies we reviewed explicitly tested intraspecific trait questions, together they demonstrated that significant ITV occurs across populations and in response to environmental and management conditions. ITV is thus an understudied yet important aspect of cover crop performance. To address research gaps identified by the literature review, we conducted a complementary field experiment to evaluate cover crop functional trait variation and assess relationships between traits and ecosystem services. Significant ITV occurred among three cover crop species (buckwheat, cowpea, and sorghum sudangrass) planted alone and in mixtures, indicating that interactions between functionally diverse species in mixtures induced trait plasticity. We expected that traits such as plant height, root:shoot ratio, shoot C:N ratio, and specific leaf area (SLA) would be positively related to cover crop nitrogen (N) assimilation. Using community‐weighted means per common practice, our hypothesis was supported for the former three traits, while SLA was unexpectedly negatively associated with N assimilation. However, ITV revealed that this unexpected relationship was driven by higher SLA and lower N assimilation values of the broadleaf compared with the grass species. Across treatments, SLA for the grass species was positively related to N assimilation, as expected. In sum, we demonstrate that assessing ITV is critical for refining understanding and management of cover crop outcomes.
Keywords
