Long-Term Stochasticity Combines With Short-Term Variability in Assembly Processes to Underlie Rice Paddy Sustainability.

Wenjing Liu,Emily B Graham,Linghao Zhong,Jianwei Zhang,Xiangui Lin,Shijie Li,Youzhi Feng

doi:10.3389/fmicb.2020.00873

Abstract

Revealing temporal patterns of community assembly processes is important for understanding how microorganisms underlie the sustainability of agroecosystem. The ancient terraced rice paddies at Longji provide an ideal platform to study temporal dynamics of agroecosystem sustainability due to their chronosequential records of soil physicochemistry and well-archived microbial information along 630-year rice cultivation. We used statistical null models to evaluate microbial assembly processes along the soil chronosequences of Longji rice paddies through time. Stochastic and deterministic assembly processes jointly governed microbial community composition within successional eras (less than 250 years), and within-era determinism was mainly driven by soil fertility and redox conditions alone or in combination. Conversely, across successional eras (i.e., over 300 years), stochasticity linearly increased with increasing duration between eras and was eventually predominant for the whole 630 years. We suggest that the impact of stochasticity vs. determinism on assembly is timescale-dependent, and we propose that the importance of stochastic assembly of microbial community at longer timescales is due to the gradual changes in soil properties under long-term rice cultivation, which in turn contribute to the sustainability of paddy ecosystem by maintaining a diverse community of microorganisms with multi-functional traits. In total, our results indicate that knowledge on the timescales at which assembly processes govern microbial community composition is key to understanding the ecological mechanisms generating agroecosystem sustainability.

Highlights

Agroecosystem sustainability can be defined as meeting society’s current needs for food without compromising the needs of future generations (Tilman et al, 2011; Liu et al, 2015a)
We found that deterministic assembly processes in all successional eras were governed by soil fertility and/or redox conditions linked to anthropogenic land use practices (Table 4)
We find that deterministic and stochastic processes simultaneously govern community assembly through successional time but that the influence of each varies both with successional era and with the duration of the time period examined

Summary

Introduction

Agroecosystem sustainability can be defined as meeting society’s current needs for food without compromising the needs of future generations (Tilman et al, 2011; Liu et al, 2015a). Soil fertility is the basis of sustainability in agroecosystems because it is central in maintaining crop productivity while minimizing the need for fertilizer application that has deleterious effects on environmental. Microbes play critical roles in soil fertility due to their contribution to, for example, organic matter decomposition, nutrient cycling and contaminant pools. It soil microbial communities should have direct implications for sustainability of crop yields (van der Heijden et al, 2008; Hall et al, 2018). Scientists conceptually link higher microbial diversity and function to greater agroecosystem sustainability (Cardinale et al, 2002; Bell et al, 2005; Patsch et al, 2018)

Methods

Results

Discussion

Conclusion