COS 280-6 - Water availability and diversity drive rooting strategies in herbaceous plants: insights from a biodiversity experiment

Abstract: Plant communities are faced with a plethora of anthropogenic global changes including biodiversity loss and changes in precipitation. Rooting strategies may offer valuable insight into how plants will respond, and acclimate, to global-change stressors. Recently, more work has gone into quantifying root traits, but we still lack a deep understanding of the role that plant root trait plasticity plays in the responses of different species to biotic and abiotic changes. Here, we quantified a suite of root traits across species richness and water availability to understand 1) how individuals change their strategies in response to changes in community richness and water availability and 2) draw connections between individual-level trait-responses to community-level performance. We conducted an experiment in which plant species richness (1 to 12 species) was crossed with watering (no additional water, +100% average rainfall) and sampled individuals from 11 native-Texas grassland species across monoculture and 12-species plots. A total of 396 individuals were sampled from March to May in 2022. Root systems were digitized and analyzed using RhizoVision software to quantify traits such as specific root length (SRL), average fine root diameter, root tissue density, and rooting depth. Our results show that across species richness and water availability, individuals significantly changed their rooting strategies at the species level. SRL was higher (p = 0.009) in 12 species plots (30.4 ± 21.8 m/g) compared to monoculture plots (26.2 ± 19.5 m/g) and higher (p = 0.009) in watered plots (30.3 ± 22.5 m/g) compared to the ambient treatment (26.2 ± 18.7 m/g). Fine root diameter was higher (p = 0.003) in monocultures (01.44 ± 0.700 mm) compared to 12 species plots (1.31 ± 0.634 mm) but was not different across water availability (p = 0.31). Rooting depth was higher (p < 0.001) in monocultures (202 ± 95.1 mm) than in 12 species plots (179 ± 82.4 mm) but showed no difference across the watering treatment (p = 0.31). Interestingly, productivity increased with species richness (R² = 0.07, p = 0.001), but surprisingly did not vary across water availability (R² = 0.08, p = 0.34). In conclusion, we show that productivity in these plant communities is resilient to the effects of changes in precipitation (but not biodiversity loss), and that this community-level resilience is mediated in part by individual-level root trait plasticity. These results offer insight regarding how plants respond belowground to biotic and abiotic changes to maintain productivity under stress.