Effects of Drying and Re-Wetting on Litter Decomposition and Nutrient Recycling: A Manipulative Experiment

Beatrice Palmia,Claudio Ferrari,Alex Laini,Rossano Bolpagni,Pierluigi Viaroli,Marco Bartoli

doi:10.3390/w11040708

Abstract

Climate change and water abstraction may change stream flow from perennial into intermittent lotic systems, modifying their abiotic and biotic benthic environment and impacting ecosystem processes such as nutrient turnover. We conducted a microcosm experiment to investigate the interactive effect of water intermittency, macrofauna and leaf size (Populus nigra leaves) on nutrient mineralization and recycling. Leaf disks (1 or 5 cm diameter) were incubated for 40 days with or without the leaf-consumer, Potamophylax cingulatus larvae (Trichoptera, Limnephilidae) and with or without an intervening, 10-days simulation of stream drying and subsequent rewetting. Nutrient fluxes, residual leaf biomass and leaf elemental composition were measured to evaluate how intermittency, macrofauna and leaf size affect organic matter mineralization rates and stoichiometry. Results suggest that drying slows decomposition rates, impacting both the microbial and setting to zero macrofauna activities. The presence of macrofauna increases mineralization and nutrient (C, N and P) regeneration rates. Our findings also suggest that leaf disks with higher diameter display higher microbial activity and NH4+ regeneration. During the experiment, the C:N:P ratios of residual litter changed, as the leaf material became enriched with N and P. Our study suggests that increasingly frequent dry events might slow mineralization rates and downstream nutrient transport.

Highlights

In many areas of the world, climate change and water abstraction exceeding water availability are expected to change the timing, extent and frequency of drying that will alter the hydrology of many freshwater environments [1]
The experiment described in the present work has two main elements of novelty: it considers simultaneously three interplaying factors: drying, presence of macrofauna and leaf size and it combines a traditional, static approach with an approach based on process rates measurement
This study demonstrates interesting combined effects of a short-term drying event, the presence of macrofauna and leaf size, on leaf litter mineralization and its elemental composition

Summary

Introduction

In many areas of the world, climate change and water abstraction exceeding water availability are expected to change the timing, extent and frequency of drying that will alter the hydrology of many freshwater environments [1]. Shifts from perennial to intermittent flow regimes modify the abiotic characteristics of benthic systems, plant, animal and microbial communities, nutrient concentrations and availability [3,4], food webs [5] and ecological processes [6], resulting in changes of benthic ecosystem functioning. Especially in forested regions, strongly depend on leaf litter inputs as sources of nutrients and energy for downstream sectors [7]. In these systems, upstream organic matter processing is a key ecosystem process [8]. The efficiency of organic matter breakdown, microbial use, and biogeochemical transformations are highly dependent on

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