Soil Organic Carbon Accumulation in Intensively ... - Springer Link

Bot. Rev. (2011) 77:296–303 DOI 10.1007/s12229-011-9071-2

Soil Organic Carbon Accumulation in Intensively Managed Phyllostachys praecox Stands Guomo Zhou1,2,3 & Shunyao Zhuang1,2,4,5 & Pekun Jiang1,2,3 & Qiufang Xu1,2,3 & Hua Qin1,2,3 & Minghung Wong4,5 & Zhihong Cao1,2,4,6 1

Joint Laboratory for Forest Soil and the Environment, Institute of Soil Science, CAS, Nanjing 210008, China 2 School of Environment Science and Technology, Zhejiang A & F University, Hangzhou 311300, China 3 Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystem and Carbon Sequestration, Zhejiang A & F University, Hangzhou 311300, China 4 Joint Laboratory for Soil and Environment, Institute of Soil Science, CAS, Nanjing 210008, China 5 Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, People’s Republic of China 6 Author for Correspondence; e-mail: [email protected] Published online: 15 June 2011 # The New York Botanical Garden 2011

Abstract Area of bamboo forest (Phyllostachys praecox) has rapidly increased in southern China during the last 20 years due to its high economic value. Aims of this study were to analyse the temporal and spatial variations of soil organic matter (SOM) in heavily winter mulched bamboo stands and to estimate potential for carbon sequestration. Total of 60 soil profiles with 0–15 years of bamboo plantation were sampled from three towns in Lin’an County. Results showed that with increased plantation years, SOM decreased slightly at the beginning (1–5 years), and then rose up steadily. Based on the average of the three locations, the highest SOM content of 75.82 g/kg was the surface layer (0–10 cm) of the 15 years. As plantation year increased, the variation of SOM in the surface layer (0–10 cm) was represented by a parabolic shape, and in the second layer (10–20 cm), it was a similar mode, but less vigorous. Soil organic carbon (SOC) storage significantly increased during 5 to 15 years after it reached full production, and the calculated annual SOC increment in 0–40 cm soil profile was about 6.3 tC/ha/year. Therefore, extended Phyllostachys praecox forests can be considered as one option for countering CO2 emissions and regional climate change. Keywords Phyllostachys Praecox . Winter Mulch . Soil Organic Matter . Carbon Sequestration

Introduction Phyllostachys Praecox stands which are planted for both vegetable bamboo shoots and timber with higher economic value are mainly distributed in Lin’an, Anji and

Soil Organic Carbon Accumulation in Intensively Managed

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Deqing areas of Zhejiang Province, and also in Jiangsu, Anhui, Jiangxi province (Fang et al., 1994). Bamboo shoots growing are promoted up under mulching covering in winter which was discovered by a teacher in the Sankou town of Lin’an in 1988. With the help of experts from Zhejiang Agriculture and Forestry University, during 3~4 years of experiments and demonstration, intensive cultivation management with heavier winter mulching (rice straw and rice hull) plus over fertilizing, a new technology has been developed. The purpose of it is to promote the early growth of bamboo shoots and higher output, thus significantly increasing the income of bamboo farmers and providing tender, delicious bamboo shoots to the markets during the winter season (Wang et al., 1995). Carbon dioxide emissions per capita of China is low, however in total, CO2 emissions has surpassed those of the USA and has ranked No. 1 in the world since 2006 (Raupach et al., 2007). Removing atmospheric carbon (C) and storing it in terrestrial biosphere is one of the options to counter anthropogenic greenhouse gas emission and global warming. Forestry and agricultural lands are considered to be one of the major C sinks. It was estimated that the total soil C pool was about 2500 GT which is 3.3 times of the size of the atmospheric C pool (Lal, 2004). Reforestation or afforestation in China has been successful during the last 30 years in increasing the amount of C stored in living biomass, while bamboo forests in China have been expanding significantly. Bamboos are some of the fastest growing plants in the world, and can grow 1 m/day during the rapid elongation period. Bamboos are found in diverse climates, from cold mountains to warm subtropical and hot tropical regions which are mostly distributed in East Asia and the Pacific region (Bystriakova et al., 2003). Efficient photosynthesis of bamboo groves allows accumulation of large biomass and organic C. Gratani Loretta et al. (2008) have reported C sequestration of 14 kg CO2/a/culm by bamboo stands (Phyllostachy pubescens) in the Botanical Garden of Rome. Bamboo is also a plant with a higher C biogeochemical sequestration potential via phytolith occlude C (PhytOC) and this could be further improved by genetic engineering (Parr & Sullivan, 2005; Parr et al., 2010; Christer Jansson et al., 2010). The results of previous research on Phyllostachys Praecox stands showed that winter mulching raised the soil temperature due to mulched organic matter decomposing and being fermented by microbes (Hu et al., 1996), while some argued that the main reason for the higher soil temperature was due to thick mulch over the surface of soil which isolated thermal energy lost from the soil and prevented access for the cold wind into soil (Jiang et al., 1999). Total soil organic carbon (SOC) accumulation of Phyllostachys Praecox stands were significantly increased by winter mulching practices (Jiang et al., 2002). The total SOC pool under Phyllostachys Praecox stands was similar to that of natural Pinus massoniana stands, but was significantly higher than that of Castnea mollissima stands, and in the meantime soil microbial biomass carbon was decreased by intensive management (Jiang et al., 2002). However, there is no systemic data on the dynamic variation of SOC in Phyllostachys Praecox stands under 15 years of continuous intensive cultivation practices. The purposes of this study were 1) to determine the spatial (locations and soil profile layers) and temporal (0 to 15 years) variation of SOM/SOC; 2) to measure SOC accumulation in Phyllostachys Praecox stands of different

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plantation ages, and to estimate the potential of carbon sequestration in the soil system of Phyllostachys Praecox stands under such intensive management practices.

Materials and Method Ecological Condition of Sampling Locations Sankou town (119°42′E, 30°14′N.) is the earliest and main Phyllostachys praecox bamboo cultivation area in Lin’an, China. Hengban town is located in the northeastern part of Lin’an (119°46′E, 30°21′N), and Xitianmu town is located in the middle part of Lin’an (119°27′E, 30°21′N). The ecological conditions of the study area are: annual temperature around 15.9°C, 1420 mm of annual rainfall, with 236 day of no frost periods and terrace fields distributed on hill areas of about 100– 250 m above sea level. They are all naturally hilly areas which were previously used for rice cultivation before the cultivation of Phyllostachys Praecox stands. The paddy soils here are all developed from red soils or Ultisols (USDA, 1999). Fertilization and Winter Mulching Traditionally, the broadcasting and turning fertilizers into deeper (10–20 cm) soil layers three times per year are adapted. This was first applied at the end of May to mid- June after the complete harvesting of bamboo shoots in order to promote the development of underground stems. The second application of fertilizer took place in mid-September after the autumn rain season to increase the breakup of bamboo shoots. The third occurred in mid-November to early December before the start of winter mulching so that it can accelerate the growth of shoots. The main sources are of complex fertilizer (16-1616) with a rate of 2.25 tha/year plus urea of 1.125 tha/year, which some farmers may supplement with barnyard manure or other organic materials. On average the first fertilization is the main dose consisting of about half of the total rate and the other two are about one fourth each. Heavy winter mulching and over fertilization started at the fifth year of bamboo garden set up, and only small amounts of fertilizers were used during the initial 5 years. Meanwhile winter mulching was added in early December with 40 tha/ year of rice straw underneath and 55 tha/year of rice hull on the top. The thickness of rice straw layer was about 15 cm and the rice hull layer on the top was also 15 cm. The rice straw was almost completely decomposed during the winter season; this should be a major source of increased soil organic carbon. While in the top layer of the rice hull, only about one third was decomposed per year. Rice hull that were not decomposed rice hull were taken out from bamboo stands during mid-March, and stored in the field for reuse in the following years, so that they could be totally cycled in 3 years. Sampling and Analysing Method In September 2005 before the second fertilization,1 year, 5 years, 10 years and 15 years plantation of bamboo stands and 0 year (paddy field nearby as control) were selected from each location having similar topography, altitude, and management conditions. With four replications for bamboos of each age, a total


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of 20 profiles were explored in each town, namely surface (0–10 cm), subsurface (10–20 cm) and bottom (20–40 cm) layers of soil were sampled from each profile. Soil samples were air-dried indoors for 1 week. Soil organic matter and other properties were analysed according to Chinese Soil Science Society standard methods edited by (Lu, 1999). Microsoft Office-Excel software and DPS software (Tang & Feng, 1997) were used for data statistics analysis

Results and Discussion Soil Fertility of Phyllostachys Praecox Stands with Different Plantation Years Fertility characteristics of surface layer soils varied with different plantation ages of Phyllostachys Praecox stands under intensive management as shown in Table 1. Results indicated that as the plantation time prolonged, soil acidity (pH) decreased from 5.5 to 4.3, which was mainly due to the change in land use from rice paddy fields to upland (Cao et al., 2004), over fertilization and heavy organic materials mulch which induced acidification (Jiang et al., 2001). Soil total phosphorus (p) and available P were both significantly increased after 15 years of bamboo plantation. The very high available P level would certainly pose a potential risk for surface water pollution (Hart et al., 2004), however, fortunately, the bamboo stands under investigation were surrounded by rice ridges (former rice fields) and only occasional heavy storms caused the lost of P via run off (Zhang et al., 2003; Sharpley et al., 2008). Soil total potassium (K) did not change, but available K increased after 10 years of cultivation using over fertilization. A fertilizer adjustment regime should be implemented to markedly reduce P input. Temporal Variation of SOM Variation of SOM is an important index for both evolution of soil quality and soil carbon pool. Table 2 shows the dynamics of SOM contents (n=4) in Phyllostachys Praecox stands under intensive management in Sankou town. It changed to a curved Table 1 Fertility Status of Surface Layer (0–10 cm) with Different Planting Years of Phyllostachys Praecox Stands Age\Index

pH

TN (g•kg-1)

TOM (g•kg-1)

TP (g•kg-1)

TK (g•kg-1)

Avail. P (mg•Kg-1)

Avail. K (mg•Kg-1)

0a

5.47

2.02b*

33.8b

0.50d

11.1a

7.10d

40.5c

1a

5.37

1.86b

28.1c

0.74c

11.5a

38.3cd

62.3bc

5a

4.76

1.77b

31.1c

0.74c

12.4a

54.1c

10a

4.33

2.07b

44.5b

1.28b

11.1a

171.8b

110.8ab

15a

4.32

4.61a

75.8a

2.01a

11.0a

457.6a

131.9a

75.9abc

TN, TOM, TP, TK are total soil nitrogen, organic matter, phosphorus and potassium; Avail. P, Avail. K is soil available phosphorus and potassium. *Means within a column followed by the same letter are not significantly different at level of (P) 0.05 (n=12)

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shape during 15 years in surface (0–10 cm) and second (10–20 cm) layers. During first 5 years it had decreased from 33.79 g/kg for the control to 26.35 g/kg after 5 years although there was no statistical difference. This indicated that mineralization of SOM had accelerated under anaerobic condition in the wetland rice paddy and subsequently changed to aerobic condition in dry land for bamboo stands. During this time, the land was not heavily fertilized,, no winter mulch was used and there was no high output of bamboo shoots yet. After 5 to 10 years and up to 15 years, there was a fast increase to 33.07 and 79.24 g/kg, respectively. It was 26% higher in 10 year stand than in 5 year stand and 140% higher in 15 year than in 10 year stand. The dramatic increase of SOM was certainly due to very heavy winter mulch of organic materials and over fertilization, as well as very higher biomass production and litter fall after bamboo stands (Phyllostachys Praecox) were fully set up (Jiang et al., 2002). SOM content in the third layer (20–40 cm) gradually increased from 7.91 g/kg in the control to 18.14 g/kg in 15 year stands. However, there were no statistically significant differences from 0 year to 10 years, but there were significant differences from 10 years to15 years. This indicated that the SOC increases resulted from the balance between losses of SOM via leaching after the land use was changed from wetland rice paddy to bamboo forests dry land, and partly due to anthropogenic activities such as ploughing and the digging of bamboo shoots. The increase of SOM was due to heavy winter mulch and more organic fertilizers, as well as increased litter fall. After 10 years of bamboo plantation there was a dramatic positive increase. Spatial Variation of SOM Variation of SOM with Soil Depth SOM distribution under Phyllostachys Praecox stands varied with different layers. Generally, it decreased from top down to the deeper layers in all ages and locations. For example, the average (n=4) SOM content in three soil layers in Sankou town is shown in Fig. 1. The SOM content in all ages of bamboo forests was in the following order: top layer > second layer > third layer. SOM variation was the most vigorous in surface layer followed by the second layer, however, there was a very gentle, but steady increase in the third layer. It was obvious that intensive management practices affected the top 20 cm layer soil, but not much on the bottom layer (20–40 cm). Table 2 Variation of SOM (g/kg) with Plantation Age and Soil Depth of Phyllostachys Praecox Stands Age\Depth

0–10 cm

10–20 cm

20–40 cm

0a

30.96 b*

23.40 b

7.95 b

1a

25.55 c

23.29 b

11.17 b

5a

26.35 c

25.19 b

14.73 b

10a

33.07 b

26.91 b

15.85 b

15a

79.24 a

37.47 a

19.73 a

*Means within a column followed by the same letter are not significantly different at level of (P) 0.05. (n=4)


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Fig. 1 Average SOM (g/kg) distribution in three soil layers under Phyllostachys Praecox stands in Sankou town (n=4)

Variation of SOC with Sampling Locations Soil organic matter contains about 58% organic carbon. Figure 2 shows the total SOC converted from SOM in three layers from three locations with different ages of Phyllostachys Praecox stands. The data indicated that spatial variation of SOC had the same mode of SOM variation in all layers. When comparing the different locations, a more vigorous change was observed in Sankou town than in Hengban and Xitianmu towns, but the latter two locations had similar SOC spatial variation mode as that of Sankou town. The highest data of SOC in 15 years stands was found in Sankou which reflected management differences. The economy and industries in Sankou is relatively underdeveloped compared with Hengban and Xitainmu. Bamboo growers in Sankou take great care for bamboo groves since their income depends mainly on selling bamboo shoots. At the beginning, SOC was a little lower in Sankou than in the other two towns, and fell more during the first 5 years. However, farmers of Sankou town applied greater amounts of organic fertilizers and with better quality of winter mulch materials as well as pulled out those remaining top rice hull in time after harvest and prevented disease development in advance etc.. These efforts not only resulted in a high income (more than 150000 RMB/ha/year), but also the highest SOC of 57 g/kg storage in soils though it was the lowest at the beginning (Fig. 2). Bamboo growers in Hengban and Xitianmu towns have other sources (business or industry) of income and their management was careless and winter mulching was even discontinued during later years. Estimate the Potential of Carbon Sequestration by Soil Pools Bamboo has an inherently fast growth rate and massive size. For example, they can reach full production stage after only 5 years. The average yield of fresh bamboo shoots is about 45 tha/year and of bamboo trunk is about 11.25 tha/year (Fang et al., 1994). A large amount of C is certainly fixed by this efficient photosynthesis. Based on the results of the SOC data for Phyllostachys Praecox stands, the calculated average annual C increments in different soil layers from 5 year to 15 years (full production stage) at three locations were 3.89, 1.75, 0.65 tC/ha in surface, second and bottom layers, respectively. The total increment of C storage in

Fig. 2 Variation of total organic carbon in surface layer (0–10 cm) soils under Phyllostachys praecox stands with different planting years in three locations (n=4)

G. Zhou et al.

Total Soil Organic Carbon (g••Kg-1)

302

50

Sankou town

40

Henban Town Xitianmu Town

30 20

10 0

0

1

5 10 Year of Bamboo forests plantation

15

0–40 cm soil layer was 6.29 tC/ha/year. This shows great potential for C sequestration to meet the challenges of global warming. Bamboos provide an ever green canopy, good for soil and water conservation, wind protection and desert fixation as well as for aesthetic decorations. Its timber and branches serve as raw materials for many types of industries such as construction, and its edible bamboo shoot is considered a delicious vegetable. Therefore, bamboo such as Phyllostachys Praecox stands is not only a highly valuable economic plant, but also a potential C sequestrates. An important fact is that bamboo forests can be harvested without destruction of the grove or stand and could be maintained for over a hundred years. This technology of heavy winter mulch reported here is one way of reusing rice straw and hull which are usually just burned in the fields or remain in the surface water both causing another pollution problem. Both rice straw and rice hull used for winter mulch are rich in rice phytolith which is also a kind of phytOC and may remain in the soil for several thousands years (Parr & Sullivan, 2005). This intensive management technique not only added fresh organic materials to increase SOC, but also added part of phytOC into soils of Phyllostachys Praecox stands too.

Conclusions The results indicated that Phyllostachys Praecox stands managed with intensive cultivation and characterized by heavy winter mulching of rice straw and hull, caused a rapid increase in SOM. For an average of three locations, the highest SOM content in the surface (0–10 cm) layer of 15 year old stands was 75.82 g/kg, which was twofold the SOM content in the control. Therefore, with regards to SOC accumulation and storage, it significantly increased from 5 years to 15 years and the increment in 0–40 cm soil layers reached 6.3 tC/ha/year. The total SOC pool of studied Phyllostachys Praecox stands was significantly higher than that of Castnea mollissima stands and similar to that of natural Pinus massoniana stands; however, Phyllostachys Praecox stands is much more sustainable for production and has a higher economic value than other forests in subtropical region of China. Therefore, there is a great potential for C sequestration by intensively cultivating Phyllostachys Praecox stands to counter climate change on a regional scale.


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Acknowledgements We wish to express our gratitude to Miss R.R. Cai, Miss F. Huang, Mr. X.B. Qian, and Mr. J.S. Wu, and the financial support from Zhejiang A & F University and Institute of Soil Science CAS, Nanjing. We also sincerely thank Dr. Anna O.W. Leung for English editing of this paper.

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