A comparison of soil respiration, carbon balance and root carbon use efficiency in two managed Moso bamboo forests in subtropical China

Xiaolu Tang,Lianghua Qi,Manyi Du,Shaohui Fan,Wenhui Su,Fengying Guan

doi:10.15287/afr.2016.497

Abstract

Moso bamboo forest (Phyllostachys heterocycla [Carr.] Mitford cv. Pubescens) is an important forest type in subtropical China and comprises an important pool in the global carbon cycle. Understanding the effects of the stand management, such as understory removal, on soil respiration (RS) will help to provide a more accurate estimation of carbon cycling and predict future climate change. The study aimed to compare RS and net ecosystem production (NEP) in two Moso bamboo forests managed by the application of herbicide (AH) and conventional hand-weeded (HW) treatment, and further examine their root carbon use efficiency (RCUE). Trenching and litter removal were used to partition the source components of RS and one-year field measurement was conducted. Maximum-minimum approach was used to estimate fine root production. NEP was determined by the balance between NPP of vegetation and heterotrophic respiration (RH) of soil. RCUE was calculated using an indirect method. In both stands, soil temperature and soil moisture at 5 cm depth were the main driving forces to the seasonality of RS. Annual RS was 31.6 t CO2 ha-1 for the stand AH and 33.9 t CO2 ha-1 for the stand HW, while net ecosystem production (NEP) were 21.9 and 21.1 t CO2 ha-1, respectively, indicating that the both Moso bamboo stands acted as carbon sinks in the scenarios of current climate change. The RCUE was 30.6% for the stand AH, which was significantly lower than that for the stand HW (58.8%). This result indicates that different stand management practices can alter RCUE and the assumed constant universal carbon use efficiency (CUE) of 50% is not appropriate in Moso bamboo forests. This study highlight the importance of partition the source components of RS and accurate estimation of RCUE in modelling carbon cycling in Moso bamboo forests.

Highlights

Soil respiration (RS), a primary CO2 exchange process between soil and atmosphere, is the second largest carbon (C) flux in global C cycling after gross primary productivity (Raich & Schlesinger 1992)
RS in the stand application of herbicide (AH) ranged from 0.60 μmol CO2 m-2 s-1 in February to 4.24 μmol CO2 m-2 s-1 in June with an annual average of 2.27 μmol CO2 m-2 s-1, while RS in the stand HW changed from 0.76 μmol CO2 m-2 s-1 in February to 4.42 μmol CO2 m-2 s-1 in June with an annual average of 2.44 μmol CO2 m-2 s-1 (Fig. 2 a)
The highest rates of RL occurred in June for the stand AH and August for the stand HW, while the lowest rates were found in February for both stands (Fig. 2 c)

Summary

Introduction

Soil respiration (RS), a primary CO2 exchange process between soil and atmosphere, is the second largest carbon (C) flux in global C cycling after gross primary productivity (Raich & Schlesinger 1992). C release from RS is estimated to be 98 Pg C per year in 2008 (1 Pg C=1015 g C) (Bond-Lamberty & Thomson 2010). This amount is more than 10 times of that from fossil fuel combustion (IPCC 2007). A minor change in RS could significantly affect the atmospheric CO2 concentrations and an understanding of the belowground C process is becoming increasingly important to estimate global C budget (Wu et al 2014b). Moisture and substrate quality are important environmental factors driving the changes of RS (Subke & Bahn 2010, Wang et al 2010)

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