Growth & Development

Plant economics spectrum theory holds true within ferns

Plants usually have limited resources in one way or another. There is only so much nutrient in the soil. How best to use it? The plant economics spectrum theory integrates the coordination of plant functional traits along a resource acquisition–conservation trade-off axis. The need for acquisition might vary with competition for resources. There’s plenty of evidence that supports the theory in seed plants, but Dunmei Lin and colleagues wondered if the same was true for ferns. If it was, then the same traits should also influence litter decomposition among coexisting ferns.

Plants have varying traits in terms of morphology (shape) and physiology (innards) that can change to cope with various biological or physical challenges. However, these traits do not all vary independently. As an example, Lin and colleagues refer to the leaf economics spectrum, a collection of traits that vary together and act as a trade-off between acquiring and conserving resources.

The authors examined the leaf and root functional traits of twelve coexisting fern species in a subtropical forest in China. They aimed to see if there were clear dimensions of leaf and root variation, if these related to each other, and if they could also predict how litter decomposed. 

“Because the conditions of light, nutrient availability and water vary strongly at the hectare scale in our study site…, we hypothesized that the variation in leaf and root traits of fern species should represent different resource use strategies along a major resource acquisition–conservation trade-off axis.” write the authors. “This is because fern species are thought to be relatively well adapted to a wide range of biotic and abiotic conditions…, and may present a wide range of variation in their functional traits to cope with various environmental conditions.”

Diagram of plant spectrum theory for ferns.

Schematic diagram depicting the hypothetical leaf economics spectrum and root economics spectrum and their afterlife effects on litter decomposition within ferns. Source: Lin et al. 2020.

“We also examined whether fern species with trait syndromes reflecting an acquisitive resource strategy would decompose faster than those with trait syndromes reflecting a conservative resource strategy. Specifically, we expected that species at the acquisitive end of the spectrum present high leaf and root nutrient concentrations, high SLA [specific leaf area] and SRL [specific root length], and exhibit higher litter decomposition rates, whereas species at the conservative end of the spectrum are characterized by low nutrient concentrations, high DMC [dry matter contents] and lignin concentration, and exhibit low litter decomposition rate.”

The team did indeed find that plant economics spectrum theory did correlate with much of what they saw in ferns. “[D]ifferent species were relatively well segregated along the first PCA axis, for each plant organ considered. Fern species found at the positive side of the first PCA axis presented traits linked to resource acquisition, i.e. with high SLA and leaf N and P concentrations, and high root pH and P concentration… Fern species located at the negative side of the first PCA axis presented a rather conservative resource-using strategy, i.e. with high leaf DMC, C concentration and C:N:P ratios, along with high root DMC, C:P ratio, C, cellulose and lignin concentrations.”

The authors also found that there was a correlation between where the ferns lay on the trade-off axis, and how their litter decomposed. Lin and colleagues say that might have consequences for human activity. “[O]ur results highlight that changes in fern communities caused by anthropogenic disturbance or other environmental factors may have important consequences on C and nutrient cycling through changes in plant functional traits and afterlife effects during the decomposition process. This also underscores the necessity for plant community conservation as a major policy priority for maintaining biogeochemical cycling in sub-tropical forests.”