Do soil depth and plant community composition interact to modify the resistance and resilience of grassland ecosystem functioning to drought?

Abstract

While the effect of drought on plant communities and their associated ecosystem functions is well studied, little research has considered how responses are modified by soil depth and depth heterogeneity. We conducted a mesocosm study comprising shallow and deep soils, and variable and uniform soil depths, and two levels of plant community composition, and exposed them to a simulated drought to test for interactive effects of these treatments on the resilience of carbon dioxide fluxes, plant functional traits, and soil chemical properties. We tested the hypotheses that: (a) shallow and variable depth soils lead to increased resistance and resilience of ecosystem functions to drought due to more exploitative plant trait strategies; (b) plant communities associated with intensively managed high fertility soils, will have more exploitative root traits than extensively managed, lower fertility plant communities. These traits will be associated with higher resistance and resilience to drought and may interact with soil depth and depth heterogeneity to amplify the effects on ecosystem functions. Our results showed that while there were strong soil depth/heterogeneity effects on plant‐driven carbon fluxes, it did not affect resistance or resilience to drought, and there were no treatment effects on plant‐available carbon or nitrogen. We did observe a significant increase in exploitative root traits in shallow and variable soils relative to deep and uniform, which may have resulted in a compensation effect which led to the similar drought responses. Plant community compositions representative of intensive management were more drought resilient than more diverse “extensive” communities irrespective of soil depth or soil depth heterogeneity. In intensively managed plant communities, root traits were more representative of exploitative strategies. Taken together, our results suggest that reorganization of root traits in response to soil depth could buffer drought effects on ecosystem functions.

Vertical distribution of bacterial community diversity in the Greater Khingan Mountain permafrost region

“…Microorganisms in permafrost, particularly bacteria, can adjust to cryoenvironments and play a vital role in the decomposition and mineralization of soil organic matter, the circulation and transformation of soil nutrients (Fry et al, 2021). Permafrost areas in the northern hemisphere account for 24% of the land surface area (Graham et al, 2012).…”

Root traits of grasslands rapidly respond to climate change, while community biomass mainly depends on functional composition

“…A larger RLD in the upper soil layer underlines that resource uptake by the plant community mainly occurred in the soil subsurface (Mommer et al, 2010). While grasslands grown in shallow mesocosms usually have larger RLD (Fry et al, 2021), due to reduced availability of soil volume and thus of resources that will be rapidly depleted, we posit that urban grasslands also have high RLD because the lack of space forces roots to become increasingly exploitative, especially in periods of water scarcity.…”

“…Moreover, because our experiment represented first-year grassland communities and the soil volume was not yet fully exploited by the roots, we cannot rule out that biennial and perennial forbs would develop deeper roots over time and change root allocation across the soil profile, with a rather increasingly exploitative strategy (e.g. higher root mass and length per unit soil volume, higher root to shoot ratio) allowing for optimized use of limited resources in the overall shallow soil profile of the mesocosms (Fry et al, 2021).…”

Long‐term subtropical grassland plots take a long time to change: Replacement is more important than richness differences for beta diversity

“…It is frequently assumed that there will be increased β diversity on deeper soils because they contain more species than shallow soils by supplying space for increased belowground niche partitioning (e.g., Baer et al, 2016 ; Belcher et al, 1995 ; Braun et al, 2022 ; Martorell et al, 2015 ). However, β diversity may decline through trade‐offs for a few highly productive species, leading to reduced diversity on deep soils (Abrams & Hulbert, 1987 ; Braun et al, 2022 ; Fry et al, 2021 ; Gibson & Hulbert, 1987 ).…”