Soil carbon pool changes following semi-arid lands planting programs

Highlights

• We studied soil carbon following semi-arid lands planting programs.

• Soil carbon stock significantly changed based on the type of the species.

• Seedlings density had a significant effect on soil carbon in the short-term.

• The most carbon change was observed in the of 0–30 cm soil depth.

Abstract

Success in carbon sequestration projects (CSPs) is a challenging issue in semi-arid regions, therefor the objective of this report was to monitor soil carbon stock (SCS) through tree planting programs (TPPs) in Iran’s central lands. We monitored SC pool changes in rhizosphere of Haloxylon persicum Bunge, Atriplex canescens (Pursh) Nutt., Nitraria schoberi L. and Amygdalus scoparia Spach planted in pure form under densities of 200 plants/ha (Den₁) and 275 plants/ha (Den₂) every two years 2004 to 2018. Results demonstrated carbon sequestration (CS) depends strongly on the type of species and its density at the early stage of TPPs (P < 0.01). Also under Den_2, the rate of CS changes had an erratic trend under TPPs and the maximum biennial rate was 23.0, 18.5, 13.7 and 17.0% for H. persicum, A. canescens, N. schoberi and A. scoparia, respectively. Interestingly this report, significant increase of 271.19, 222.00, 138.90 and 206.40 kg h⁻¹, respectively has occurred in 0.3 m soil depth after 14 years’.

Introduction

Soils hold the largest stock of terrestrial organic carbon (C) in the biosphere (Franzluebbers, 2012, Palosuo et al., 2016) and play an important role in the global C (Alidoust et al., 2018, Pattanayak et al., 2005). On one hand, C is intricately interconnected with numerous ecosystem services for human wellbeing and nature conservation (Ghosh et al., 2019). However, huge quantities of Earth's stored C are lost (Mukhopadhyay et al., 2016) and therefore, C concentrations in the atmosphere have increased and leading to an increase in temperature (Backéus et al., 2005). Until now various actions have been evaluated to reduce C emission (Morgan et al., 2010) and carbon sequestration (CS) in soil and plant biomass is the most effective method (Srinivasarao et al., 2012). Therefore, land management programs can maintain the soil carbon (SC) storage or lead to increased CS (Akpa et al., 2016) even at regional scales (Han et al., 2017).

CS describes long-term storage that removes C from the atmosphere and depositing it in reservoirs in soils and plant biomass (GCCA, 2010, Chatterjee et al., 2018, Hemamali et al., 2020) which is the simplest and most economically practical solution to reduce atmospheric C (Emmerich, 2003, Andrew, 2010, Hahn et al., 2005, Yazdanshenas et al., 2018). However, there are uncertainties in the spatial pattern of carbon stocks (Fang et al., 2019) and the rate of CS depends on land cover characteristics, soil physical and biological conditions, previous C stock in soil and management methods (Schuman et al., 2002, Ferreira et al., 2016, Alidoust et al., 2018).

Due to high stand-level productivity and C storage potential, trees plantation (TP) is first selected method for CS (Kelty, 2006, Yuan et al., 2016) but it’s potential varies according to the species planted, soil characteristic and management methods (Mortenson et al., 2004, Bahrami et al., 2013, Corbeels et al., 2020). On the other hand, although globally terrestrial SC is higher than plant biomass C (PBC) and atmosphere C (Mukhopadhyay et al., 2016, Scharlemann et al., 2014) but any soil has potential for CS (IPCC, 2007, Solomon et al., 2007, Ontl et al., 2020). Therefore, the type and diversity of soil and vegetation should be noted for CS programs (Derner and Schuman, 2007).

Along to the soil, plants have a great impact on CS. They are the major contributors to CS and SC in most systems (Krna and Rapson, 2013). Due to the changing in soil under different vegetation types, the amount and stability of SC will be changed (Gu et al., 2019). Therefore, CS is different based on plants vegetation characteristics (Chauhan et al., 2010, Cierjacks et al., 2010). I.e. in some cases, grassland and cropland that have low biomass are converted into forests trough TPPs for more CS (Nave et al., 2013, Roshetko et al., 2007).

Therefore, capturing C by TP or avoiding deforestation is thought to be a cost effective way to reduce atmospheric C (Grace et al., 2010, Naseri et al., 2014). Regarding, adoption of improved crop and soil management practices improve soil quality and reduce the rate of enrichment of atmospheric C (Schuman et al., 2001) therefore, soils and plants with high potential for CS must be identified for TPPs (IEA, 2010, Orgill et al., 2017, Stavi and Argaman, 2014).

According to the above, in recent years, combating desertification and CS programs (CSPs) through TPPs have become increasingly important in arid and semi-arid regions. Despite of the doing many TPPs, CS potential of different TTPs is rarely understood (Yuan et al., 2016). In Iran also, due to geographical location, more than 90 percent of the land areas are classified as arid or semi-arid lands and desertification control and rehabilitation programs i.e. TPPs (CS projects) are of the most important strategy for living people. In these areas, TPPs have begun for more than 50 years and soil carbon sequestration programs (SCSPs), especially have been carried out for more than 20 years in country. But, until now, no monitoring program has been done through TTPs for serving soil and plant C stock changes through the time. Therefore, the purpose of this study was to monitor and estimate the rate of CS in TPPs under cultivation of Haloxylon persicum Bunge, Atriplex canescens (Pursh) Nutta, Nitraria schoberi L. and Amygdalus scoparia Spach in Iran’s central semi-arid lands during 2004–2018.

Our study will address the following questions that what is the temporal pattern of the rates of C stock changes under TPPs through years? How much C can be sequestrated every two years in each TP type? We hypothesize that different types of TPPs have different effects on improving SC pool; in addition, rates of SC will increase with land restoration under all TPPs types through time.