Plant functional diversity effects on carbon and nitrogen storage: An empirical test in semiarid sandy grasslands
The trait-based approach shows that functional diversity is the most important driver of ecosystem properties. However the empirical evidence is still rather small about the role of plant functional diversity for carbon (C) and nitrogen (N) storage at ecosystem-level. Plant functional diversity consists of the most abundant functional trait values (community-weighted mean, CWM) and the variety of functional trait values (FD). The CWM effects may primarily be attributed to the biomass ratio hypothesis, while FD effects support the non-additive effects or the niche complementarity hypothesis. We measured the C an N storage in aboveground plant, litter, root and soil across four typical community types during degraded sandy grassland restoration in Horqin Sand Land, northern China. We also measured five plant traits in 45 species and then calculated the CWM traits, the functional divergence of each single trait (FDvar) and the trait dispersion of multiple traits (FDis). Using a stepwise multiple regression analysis, we tested the relative roles of CWM traits and FD to explain C and N storage.
We found that C and N storage were positively associated with CWMs of plant height and leaf carbon content and FDis, and were negatively associated with CWM of leaf nitrogen content. However, only CWM of plant height was retained as an important predictor of C and N storage in plant, litter, soil and total ecosystem in multiple models. CWMs of plant height and specific leaf area (SLA) best predicted soil C and N storage, as well as total ecosystem N storage. Relationship between FDis and total ecosystem C storage was positive. Two major components of plant functional diversity could contribute to explain C and N storage. Consistent associations were found between C or N storage and leaf traits related to the plant resource use strategy. What matters the most to C and N storage in these ecosystems is the relative abundance of plants with tall and larger SLA, while niche complementarity also promotes C storage. Thus, sustaining ecosystem C storage requires focusing on the dominance and diversity of traits in communities in sandy grassland ecosystems.