Effects of prolonged drought on plant-soil feedbacks and implications for plant community dynamics

Abstract

Plant-soil feedback (PSFs) refers to the ability of a given plant to alter soil physicochemical properties in ways that modify the growth of a plant subsequently grown in the same soil. It is well established that PSFs influence plant community structure and dynamics, plant succession and invasion process. There is also evidence that change in climate will affect PSFs impacting plant community dynamics and, through this, ecosystem functioning and stability. However, our knowledge about the effects of climate change, specifically prolonged drought, on PSFs and its role in shaping plant community dynamics under natural conditions is limited. Therefore, in this thesis, I (i) experimentally assessed shifts in PSFs in response to prolonged drought legacies across plant species, functional types, and community level under laboratory condition; (ii) investigated drought induced shifts in plant-soil feedbacks under field conditions utilizing an experimental rainfall manipulation in a mesic grassland; (iii) assessed the effects of a foliar herbivore on PSFs in monocultures and mixtures in soils with prolonged drought legacies; (iv) investigated the role of long-term drought soil legacies on the performance of two globally recognized notorious foliar herbivores, and their influence on PSFs; (v) assessed the contribution of potential belowground mechanisms, specifically changes in litter decomposition, belowground carbon allocation and competition for nitrogen, to shifts in the strength and direction of PSFs under prolonged drought using stable isotope (13C and 15N) labelling; and (vi) conducted a literature review quantifying shifts of PSFs in response to drought and warming using a meta-analytical approach and identify key future knowledge gaps. I conclude that drought effects on PSFs are context-dependent and may differ within and among plant functional types. Belowground biota, such as plant-parasitic nematodes, arbuscular mycorrhizal fungi (AMF) and bacteria, contribute to shifts in PSFs between ambient rainfall and drought. Aboveground biota, such as foliar herbivores, are likely to be key drivers involved in altering PSFs under prolonged drought through affecting plant foliar N and CN ratio and herbivore-induced shifts in plant-soil biotic interactions, including beneficial relationships with rhizobia. Belowground mechanisms, such as litter decomposition, significantly contributed to shifts in PSFs in drought. Moreover, changes in relative belowground carbon allocation and competition for nutrients are also likely to contribute to contrasting outcomes under drought conditions; additional analyses of archived samples will provide further insight into the role of these mechanisms.

Date of Award	2021
Original language	English