Diversity–productivity relationships: Initial effects, long-term patterns, and underlying mechanisms

Abstract

A common pattern emerging from studies on the relationship between plant diversity and ecosystem functioning is that productivity increases with diversity. Most of these studies have been carried out in perennial grasslands, but many lasted only two growing seasons or reported data from a single year. Especially for perennial plant communities, however, the long-term effects of diversity are important. The question whether interactions between few species or among many species lead to increased productivity remained largely unanswered. So far, the main mechanism addressed is the increased input of nitrogen by nitrogenfixing legumes. We report that other mechanisms can also generate strong increases of productivity with diversity. Results from 4 consecutive years of a plant diversity experiment without legumes show that a positive relationship between plant species richness and productivity emerged in the second year and strengthened with time. We show that increased nutrient use efficiency at high species richness is an important underlying mechanism. This mechanism had not been discussed in earlier studies. Furthermore, our results suggest that complementary nutrient uptake in space and time is important. Together, these mechanisms sustain consistently high productivity at high diversity.biodiversity ͉ niche complementarity ͉ nitrogen use efficiency ͉ ecosystem functioning T he notion that the current loss of biodiversity may be detrimental to ecosystem functioning has led to major experiments in the last decade. Studies investigating the relationship between biodiversity and ecosystem functioning focused on the effects of losses of plant diversity on productivity (as a measure of ecosystem functioning) in grasslands. In these studies, productivity often declined with diversity loss (1), although several different patterns have been reported, including no response and idiosyncratic differences as plant diversity decreases (see ref. 2 for a review).Both the patterns and the underlying mechanisms have been hotly debated (3-5, †, ‡). A positive relationship between diversity and productivity could arise through causal mechanisms such as facilitation or complementary resource use (6, 7). However, the same relationship between productivity and diversity could also be generated by chance, through a sampling or selection effect. More diverse plant communities have a higher chance of including a highly productive species that dominates the community (3, 4, 7). Complementarity and sampling effects may operate simultaneously, but can be separated by using the additive partitioning equation (8).A positive effect of diversity on productivity was reported by several experiments, but most of these studies have been short term (Ͻ3 years) or reported results from a single growing season (9-18). In perennial grasslands, interactions between species occur over multiple years, but only three experiments reported results from a period Ͼ3 years. They showed that the positive effects of diversity increased several years after the st...

Plant genotypic diversity reduces the rate of consumer resource utilization

“…Because plant phenotypic traits such as biomass [34,35], C : N ratio [36,37] and chemical defences against herbivores [38] can change when plants are grown in diverse compared with homogeneous communities, we first hypothesized that individual plant resistance (and therefore consumption) could change when genotypes grow in monocultures versus polycultures. Alternatively, owing to the high mobility of P. japonica within plant patches (see §3), we hypothesized that sequential feeding on different genotypes in polyculture compared with sequential feeding on different plants of the same genotype in monoculture could alter rates of consumption.…”

Impacts of plant diversity on biomass production increase through time because of species complementarity

“…Second, many, if not most, of the experiments reviewed by recent metaanalyses have been short-term, run for only a small number of growing seasons or a few generations of the focal organisms (9). Of those experiments that have run for multiple generations or growing seasons, most find that diversity effects and their underlying mechanisms change through time as species interactions structure experimental communities (21)(22)(23)(24)(25)(26). This raises the possibility that past interpretations of diversity-function relationship have been heavily influenced by studies that have yet to allow population dynamics.…”

Relationship between Diversity and Productivity at Ratargul Fresh Water Swamp Forest in Bangladesh

“…It has been demonstrated in other plant related studies that productivity increases with increasing TD, FD and PD (Tilman et al 1997;Petchey et al 2004;Ruijven and Berendse 2005;Paquette and Messier 2011;Zuo et al 2012;Cadotte 2013;Genung et al 2014). The mechanism behind such result is resource use complementarity (Tilman et al 1997;Petchey 2003;Cadotte 2013).…”

“…Many experiments measured species richness or species diversity explaining diversity-ecosystem functioning relationship (Tilman et al 2001;Hedlund et al 2003;Ruijven and Berendse 2005;Zuo et al 2012). But species diversity cannot explain similarities or variation of functional traits among species (Hooper et al 2002) which has made FD a better predictor than TD in explaining productivity (Petchey et al 2004;Roscher et al 2012).…”