Elsevier

Pedosphere

Volume 32, Issue 3, June 2022, Pages 393-401
Pedosphere

Net ecosystem carbon exchange for Bermuda grass growing in mesocosms as affected by irrigation frequency

https://doi.org/10.1016/S1002-0160(21)60017-6Get rights and content

ABSTRACT

Intensification of grazed grasslands following conversion from dryland to irrigated farming has the potential to alter ecosystem carbon (C) cycling and affect components of carbon dioxide (CO2) exchange that could lead to either net accumulation or loss of soil C. While there are many studies on the effect of water availability on biomass production and soil C stocks, much less is known about the effect of the frequency of water inputs on the components of CO2 exchange. We grew Bermuda grass (Cynodon dactylon L.) in mesocosms under irrigation frequencies of every day (I1 treatment, 30 d), every two days (I2 treatment, 12 d), every three days (I3 treatment, 30 d), and every six days (I6 treatment, 18 d, after I2 treatment). Rates of CO2 exchange for estimating net ecosystem CO2 exchange (FN), ecosystem respiration (RE), and soil respiration (RS) were measured, and gross C uptake by plants (FG) and respiration from leaves (RL) were calculated during two periods, 1–12 and 13–30 d, of the 30-d experiment. During the first 12 d, there were no significant differences in cumulative FN (mean ± standard deviation, 61 ± 30 g C m-2, n = 4). During the subsequent 18 d, cumulative FN decreased with decreasing irrigation frequency and increasing cumulative soil water deficit (W), with values of 70 ± 22, 60 ± 16, and 18 ± 12 g C m-2 for the I1, I3, and I6 treatments, respectively. There were similar decreases in FG, RE and RL with increasing W, but differences in RS were not significant. Use of the C4 grass growing in a C3-derived soil enabled partitioning of RS into its autotrophic (RA) and heterotrophic (RH) components using a 13C natural abundance isotopic technique at the end of the experiment when differences in cumulative W between the treatments were the greatest. The values of RH and its percentage contributions to RS (43% ± 8%, 42% ± 8%, and 8% ± 5% for the I1, I3, and I6 treatments, respectively) suggested that RH remained unaffected across a wide range of W and then decreased under extreme W. There were no significant differences in aboveground biomass between the treatments. Nitrous oxide (N2O) emission was measured to determine if there was a trade-off effect between irrigation frequency and increasing W on net greenhouse gas emission, but no significant differences were found between the treatments. These findings suggest that over short periods in well-drained soil, irrigation frequency could be managed to manipulate soil water deficit in order to reduce net belowground respiratory C losses, particularly those from the microbial decomposition of soil organic matter, with no significant effect on biomass production and N2O emission.

Section snippets

INTRODUCTION

Conversion of non-irrigated grasslands to high-intensity grazing systems with irrigation is a major land-use change in dryland areas of New Zealand to increase feed supply for cattle during periods with low rainfall (MacLeod and Moller, 2006). However, despite increased aboveground production (Condron et al., 2014), there is increasing evidence that irrigation in grazed grasslands of New Zealand leads to a decrease (Houlbrooke et al., 2008; Mudge et al., 2017) or no change (Condron et al., 2014

Mesocosm preparation and experimental design

Topsoil (0–150 mm depth) was collected from a grazed grassland site dominated by perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) from the Lincoln University Demonstration Farm (43° 65′ S, 172° 48′ E, 34 m above sea level). The soil was classified as a Typic Immature Pallic Soil (Hewitt, 2010) or a Typic Haplustept (Soil Survey Staff, 2014). The soil was mixed and sieved (≤ 4 mm), with all visible plant material removed, prior to storage at 4 °C. Soil total C and N

Soil water content and cumulative W

As anticipated, soil θv values decreased gradually during the period when no water was applied and then returned to a value between 0.32 and 0.35 m3 m-3 immediately after water was applied (Fig. 1). The minimum values reached for θv decreased with decreasing irrigation frequency to 0.23, 0.20, 0.18, and 0.08 m3 m-3 in the I1, I2, I3, and I6 treatments, respectively. The pronounced effects of the I6 treatment on CO2 exchange components following the lack of response in the I2 treatment after the

Responses of CO2 exchange components to irrigation frequency

The threshold values of W for the broken-stick model below which FN, FG, and RE remained constant at the maximum values were similar regardless of treatment and ranged from 47 to 57 mm, suggesting similar threshold values for photosynthesis and ecosystem respiration. The lack of any treatment differences in cumulative FN, FG, and RE during the first 12 d demonstrated that these processes were insensitive to mild increases in W up to 30 mm. This coincides closely with the breakpoints between no

CONCLUSIONS

The findings from growing Bermuda grass in mesocosms showed that decreases in net ecosystem CO2 exchange (FN) with increasing cumulative soil water deficit (W) were moderated by the offset between a strong decrease in gross C uptake by plants (FG) and a less sensitive response in ecosystem respiration (RE). However, this did not result in changes in aboveground biomass production with increasing W. Although cumulative RS did not increase with increasing W, the use of a 13C natural abundance

ACKNOWLEDGEMENTS

This work was funded by the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) and National Natural Science Foundation of China (No. 32101431) to support Yuan Li. The authors especially thank Roger Cresswell, Kethsiri Alwis, Emily Huang at Lincoln University, New Zealand for laboratory analyses. We thank Alan Stewart at PGG Wrightson Seeds, New Zealand for providing grass seeds. We are grateful to Neil Smith, Graeme Rogers, Trevor Hendry, Brent Richards, Andrea Leptin, David Rex,

References (52)

  • V O Sadras et al.

    Soil-water thresholds for the responses of leaf expansion and gas exchange: A review

    Field Crops Res

    (1996)
  • C Scheer et al.

    Nitrous oxide emissions from fertilized, irrigated cotton (Gossypium hirsutum L.) in the Aral Sea Basin, Uzbekistan: Influence of nitrogen applications and irrigation practices

    Soil Biol Biochem

    (2008)
  • D Whitehead et al.

    Management practices to reduce losses or increase soil carbon stocks in temperate grazed grasslands: New Zealand as a case study

    Agric Ecosyst Environ

    (2018)
  • X H Zhou et al.

    Similar responses of soil carbon storage to drought and irrigation in terrestrial ecosystems but with contrasting mechanisms: A meta-analysis

    Agric Ecosyst Environ

    (2016)
  • N Balaine et al.

    Soil gas diffusivity controls N2O and N2 emissions and their ratio

    Soil Sci Soc Am J

    (2016)
  • S Burri et al.

    Effects of plant productivity and species richness on the drought response of soil respiration in temperate grasslands

    PLOS ONE

    (2018)
  • S P Chen et al.

    Dependence of carbon sequestration on the differential responses of ecosystem photosynthesis and respiration to rain pulses in a semiarid steppe

    Global Change Biol

    (2009)
  • L M Condron et al.

    Long-term irrigation effects on soil organic matter under temperate grazed pasture

    Eur J Soil Sci

    (2014)
  • F De Mendiburu

    Agricolae: Statistical procedures for agricultural research. R package version 1

  • L Fuchslueger et al.

    Experimental drought reduces the transfer of recently fixed plant carbon to soil microbes and alters the bacterial community composition in a mountain meadow

    New Phytol

    (2014)
  • A Heinemeyer et al.

    Partitioning of soil CO2 flux components in a temperate grassland ecosystem

    Eur J Soil Sci

    (2012)
  • A E Hewitt

    New Zealand Soil Classification

    (2010)
  • D J Houlbrooke et al.

    Effect of irrigation and grazing animals on soil quality measurements in the North Otago Rolling Downlands of New Zealand

    Soil Use Manag

    (2008)
  • J E Hunt et al.

    Carbon budgets for an irrigated intensively grazed dairy pasture and an unirrigated winter-grazed pasture

    Biogeosciences

    (2016)
  • G L Hutchinson et al.

    Improved soil cover method for field measurement of nitrous oxide fluxes

    Soil Sci Soc Am J

    (1981)
  • T E Huxman et al.

    Precipitation pulses and carbon fluxes in semiarid and arid ecosystems

    Oecologia

    (2004)
  • Cited by (0)

    View full text