Journal of
Plant Ecology VOLUME 3, NUMBER 4, PAGES 279–284 DECEMBER 2010 doi: 10.1093/jpe/rtq015 Advanced Access published on 30 May 2010 available online at www.jpe.oxfordjournals.org
Effects of biological soil crusts on profile distribution of soil water, organic carbon and total nitrogen in Mu Us Sandland, China Shuqin Gao1,2, Xuehua Ye1, Yu Chu1 and Ming Dong1,* 1
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China 2 Graduate University of Chinese Academy of Sciences, Yuquanlu, Beijing 100049, China *Corresponding address: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China. Tel/Fax: +86 10 82594676; E-mail:
[email protected]
Abstract Aims Biological soil crusts (BSCs) can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems. Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer. Thus, little is known about effects of BSCs on properties throughout the soil profile. In the current study, we assessed the effects of BSCs on the distribution of soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) throughout the soil profile as well as the influence of water conditions on the effects of BSCs. Methods In a field investigation in Mu Us Sandland, North China, soil samples were taken from plots with and without BSCs on 13 and 28 September 2006, respectively. On the two sampling dates, average soil gravimetric water content was 3.83% (61.29%) and 5.08% (60.89%), respectively, which were regarded as low and high water conditions. Soil samples were collected every 5 cm to a depth of 60 cm, and SW, SOC and STN were measured in the laboratory.
INTRODUCTION Biological soil crusts (BSCs) occur widely in arid and semiarid regions of the world (Eldridge and Greene 1994). BSCs are soil surface communities consisting of differing proportions of cyanobacteria, algae, lichens, mosses, microfungi and other bacteria (Belnap and Lange 2003). BSCs are the main sources of nitrogen and carbon in some ecosystems (Billings et al. 2003; Lange et al. 1992) and have many ecological functions including altering hydrological processes (Belnap 2006; Belnap et al.
Important Findings (i) BSCs affected profile distribution of SW, SOC and STN. In addition, water conditions within the plots significantly modified BSCs’ effects on the profile distribution of SW, but marginally affected the effects on SOC and STN. (ii) Under high water conditions, SW in the surface soil layer (0–10 cm) was higher in soils with BSCs compared to those without BSCs, while the opposite was true in the deep soil layer (30–55 cm). (iii) Under low water conditions, SW was lower with BSCs compared with no BSCs in near-surface (5–20 cm) and deep (25–40 cm) soil layers. (iv) BSCs affected SOC and STN only in the surface soil layer (0–5 cm) and were modified by plot water conditions. Keywords: biological soil crusts d plot water condition distribution d soil organic carbon d soil total nitrogen water
profile soil
Received: 8 November 2009 Revised: 16 April 2010 Accepted: 3 May 2010
2005) and influencing carbon and nitrogen dynamics (Hawkes 2003; Veluci et al. 2006). Water is a limiting factor for vegetation in arid and semiarid regions (Johnson and Asay 1993). Much previous work has investigated the function of BSCs on water dynamics, but results have been contradictory. For instance, BSCs have been found to enhance (Eldridge 1993) or reduce (Li et al. 2002) water infiltration and lessen (Brotherson and Rushforth 1983) or increase (Liu et al. 2005) soil water evaporation. Alternatively, water infiltration may not be affected by BSCs but by physical
Ó The Author 2010. Published by Oxford University Press on behalf of the Institute of Botany, Chinese Academy of Sciences and the Botanical Society of China. All rights reserved. For permissions, please email:
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characteristics of soil (Eldridge et al. 1997). In general, discrepancies are related to crust taxonomy (Brotherson and Rushforth 1983), soil types and stages of vegetation succession (Belnap and Lange 2003), while initial soil water content (SW) is also important. Nitrogen is another limiting factor in arid and semiarid regions (Peterjohn and Schlesinger 1990). Much is known about nitrogen fixation and carbon acquisition by BSCs and their contribution to the surface soil fertility (Evans and Ehleringer 1993; Evans and Johansen 1999; Housman et al. 2006; Johnson et al. 2007). Much is also known about the horizontal distance that fixed carbon and nitrogen can move (Green et al. 2008). Most nitrogen fixed by BSCs is immediately released and can be used by vascular plants or be transferred directly from BSCs to plants (Harper and Belnap 2001; Harper and Pendleton 1993; Mayland and McIntosh 1966; Pendleton et al. 2003). Carbon fixed by BSCs contributes to soil stabilization (Guo et al. 2008) and limits the nitrogen fixation rate by BSCs (Bergman et al. 1997). However, little is known about the effects of BSCs on soil organic carbon content (SOC) and soil total nitrogen content (STN) below the soil surface including the depth to which BSCs can influence these soil properties. In semiarid regions, precipitation is usually unevenly distributed in both space and time (Wei et al. 2005), and this type of pulse-like water supply may strongly drive an infiltration process of water (Schwinning and Sala 2004), influencing the effects of BSCs on the profile distribution of soil properties. To examine the influences of BSCs on the distribution of soil properties throughout the soil profile and their modification due to pulse-like rainfall, we conducted a field investigation at Mu Us Sandland in semiarid North China. We measured SW, SOC and STN along 60-cm profiles in soil covered with and without BSCs before and after a rain event.
Journal of Plant Ecology
genes squarrosa, Chenopodium aristatum and Ixeris gracilis existed. We selected five 10 3 10 m2 sample plots in the fixed dunes and set up six 1 3 1 m2 quadrats in plant interspaces in every plot. Three quadrats were covered with BSCs and three were not. We used a soil corer with a diameter of 5 cm to collect soil samples. After removing BSCs, we collected soil samples every 5 cm to a depth of 60 cm from the soil surface. Soil samples from plots without BSCs were collected in the same manner after removing litterfall. Part of the soil sample was used to measure SW, and the remaining sample was air-dried and passed through a 2-mm sieve to remove plant material. Samples were subsequently pulverized in a grinder and passed through a 0.2-mm sieve. These samples were analyzed for SOC and STN. Samples collected on 13 September 2006 were regarded as having low SW (before rainfall; average soil gravimetric water content of the soil profile = 3.83% 6 1.29%), and those on 28 September 2006 had high SW (after rainfall; average soil gravimetric water content of the soil profile = 5.08% 6 0.89%). SW was measured using the oven-drying method (Top and Ferre 2002). SOC was measured using H2SO4–K2Cr2O7 wet oxidation followed by titration with FeSO4 with the Walkley– Black procedure (Nelson and Sommers 1982), and STN was determined using micro-Kjeldahl digestion (Nelson and Sommers 1980) followed by colorimetric analysis (Hook et al. 1991).
Statistical analyses We used one-way analysis of variance to test effects of BSCs on SW, SOC and STN. All statistical analyses were performed using SPSS 13.0 (SPSS, Chicago, IL, USA).
RESULTS Effect of BSCs on SW
The field investigation was conducted at the National Research Station for Ordos Grassland Ecosystems, Institute of Botany, Chinese Academy of Sciences, located in Mu Us Sandland (37°27#–39°22#N and 107°20#–111°30#E), Inner Mongolia, China. The dominant soil type in this area is aeolian sandy soil, having a complete C horizon and sometimes a thin A horizon. It is a semiarid area with a typical continental climate and mean annual precipitation of 250–450 mm, most of which (60–70%) occurs between July and September. The annual mean temperature is 6.2°C –8.5°C, with monthly means of 22°C in July and 11°C in January. Annual mean sunshine hour is 2800–3100 hours, and annual total solar radiation is 138–150 kcal cm 2 (Li 2001; Zhang 1994).
BSCs affected profile distribution of SW, and water conditions modified effects of BSCs (Tables 1 and 2; Fig. 1). Under high water conditions, there were differences in SW between soils covered with and without BSCs at some soil layers, but there was no effect (P = 0.209) of BSCs on SW for the whole soil profile (0–60 cm). SW in the top 10 cm was significantly higher in soil covered with BSCs than that without BSCs, while the difference decreased with increasing soil depth (Table 1). On the contrary, SW at 30–55 cm was significantly lower in soils covered with BSCs, while no difference was observed at 55–60 cm (Table 1; Fig. 1A). Under low water conditions, BSCs decreased SW for the whole soil profile (0–60 cm) (P < 0.001). SW in the top 5 cm was low in plots with and without BSCs. At depths of 5–20 cm and 25–40 cm, SW was significantly lower in plots covered with BSCs than in those without BSCs. BSCs had no effect on soil moisture at depths of 40–60 cm (Table 2; Fig. 1B).
Sampling design and measurements
Effect of BSCs on SOC
Fixed dunes dominated by Artemisia ordosica were chosen as plots for sampling. In the communities, Eragrostis pilosa, Cleisto-
BSCs affected profile distribution of SOC, and water conditions slightly modified the effects of BSCs (Tables 1 and 2; Fig. 2).
MATERIALS AND METHODS Study site
Gao et al.
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Effect of BSCs on soil property profile distribution
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Table 1: effects of BSCs on soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) at different depths under high water conditions (n = 15) SW (%) Soil depth (cm) df 0–5
F
SOC (%) P
df
F
STN (%) P
df
F
P
1,28 23.214
