Xing Suna,
Qin Liu†
*b,
Gengmao Zhaoc,
Xiang Chen†b,
Tongtong Tang†b and
Yuyong Xianga
aSchool of Biological Science and Food Engineering, Chu Zhou University, 239000, Chuzhou, China. E-mail: xsun@chzu.edu.cn; xyy10657@sohu.com
bInstitute of Soil Science, Chinese Academy of Sciences, 210008, Nanjing, Jiangsu Province, China. E-mail: qliu@issas.ac.cn; xchen@issas.ac.cn; tttang@issas.ac.cn; Fax: +86 25 86881263; Tel: +86 25 86881388
cCollege of Resources and Environmental Sciences, Nanjing Agricultural University, 210095, Nanjing, China. E-mail: seawater@njau.edu.cn
First published on 29th November 2017
In this study, the carbon (i.e., C) bio-sequestration within phytoliths (PhytOC) in 51 rice cultivars was evaluated to breed cultivars with a high efficiency of carbon sequestration in phytoliths and high productivity. The phytolith extraction from rice plants was achieved through wet digestion procedures, and the C content of phytoliths was determined using an Elemental Analyzer 3000. The phytolith contents in the rice organs ranged from 9.69 to 175.52 mg g−1, with significant differences in the phytolith contents in the different organs of each rice cultivar. The estimated PhytOC fluxes of rice plants in 51 rice cultivars were approximately 0.006–0.035 Mg-e-CO2 per ha per year. High variation coefficients of phytoliths and contents of phytoliths of plant in indica and japonica rice cultivars implied considerable variation among these rice cultivars. Additional results showed no correlation between the phytolith contents and the C content of phytoliths (R = 0.170, p > 0.05), and the C content of phytoliths was significantly correlated with the PhytOC content in dry plant weight (R = 0.804, p < 0.01). However, the estimated PhytOC flux was significantly correlated with the phytolith content (R = 0.651, p < 0.01), with the C content of phytoliths (R = 0.512, p < 0.01) and with the PhytOC content in dry plant weight (R = 0.727, p < 0.01). Selected rice cultivars herein with a high efficiency of C sequestration in phytoliths and high productivity, therefore, played important roles in controlling the C sink and Si biogeochemical cycle in soil-rice systems.
Some studies have considered that PhytOC is derived through photosynthesis,3,8,18–20 of which 1–6% is typically occluded within phytolith.19 The phytolith content in plant matter varied greatly among different crop types (0.37–8.38%, average 3.68%) and even among crop species of the same crop types.20 Recent studies have shown that the global CO2 sequestration in rice phytoliths is 1.97 × 107 Mg-e-CO2 per year,6 and this value is slightly lower compared with wetland plants (4.39 × 107 Mg-e-CO2 per year)7 and higher compared with bamboo leaf litter (1.56 × 107 Mg-e-CO2 per year),21 sugarcane leaves (0.72 × 107 Mg-e-CO2 per year),22 and millet (2.37 × 106 Mg-e-CO2 per year).4 After plants return to the soil, decomposition through microorganisms is initiated, and phytoliths in straws are released directly into the soil.23–25 Phytoliths can tolerate extreme environments, such as earthquakes, dust storms, floods, forest fire erosion, etc., and are often retained in the in situ environment.10,26–30 The phytolith decomposition rate depends on the solubility of these molecules, which is similar to amorphous Si (10−2.74) and falls between Si glass (10−2.71) and quartz (10−4.00).31 Thus, because of the stability of phytolith, the C occluded within phytoliths is relatively stable and persists in the soil for a millennium, reflecting a strong resistance to decomposition, compared with other organic matter fractions. Indeed, PhytOC can be retained for a thousand years,19,27,28,32,33 and phytoliths can contribute 15–37% of long-term biogeochemical C sequestration.19 Thus, PhytOC plays a major role in the soil C cycle,19 and the importance of this molecule in relation to climate change has been emphasized.3,8,18,34–36
Rice is a staple crop grown on nearly every continent worldwide, with a global rice-planting area of approximately 1.64 × 108 ha in 2014.14 As a Si accumulator, contains several phytoliths and can occlude more organic C in its organs compared with other plants.3 China, as one of the largest crop-producing countries worldwide, has approximately 1.60 × 108 ha of crop lands,37 of which 3.03 × 107 ha is rice cropland.38 Thus, the PhytOC of rice croplands may represent the magnitude of the C sink in cropland ecosystems.3,19 According to the correlations between the phytolith content and the PhytOC content in crops, these results showed that the PhytOC content of plants can be increased by crop species or cultivar optimization.6,20,39 However, the variability of phytolith and PhytOC accumulation within more cultivars of rice has not previously been examined. In the present study, we evaluated PhytOC produced in the rice plants of 51 rice cultivars. The aim of the present study was to select rice cultivars with a high efficiency of C sequestration in phytoliths and high productivity, to increase the C long-term sequestration in phytoliths, reduce CO2 emissions and relieve the environmental stress resulting from greenhouse gas emissions.
Fig. 1 SEM images of phytoliths extracted from the rice samples using the wet ashing method according to Zuo (2011) and Sun (2016). |
In addition, the C contents of phytoliths substantially varied in different rice cultivars. The C contents of phytoliths ranged from 0.43 to 15.46 mg g−1 (Fig. 3), and the PhytOC content in dry organs weight ranged from 0.017 to 0.97 mg g−1 (Fig. 4). The phytolith content in plant matter greatly varied among different crop types (0.37–8.38%, average 3.68%) and even among crop species of the same crop types.20 The similar results and trends were reported by many researchers.6,8,14 Many studies analysing the physical and chemical properties of phytoliths have shown that the phytoliths can occlude C to levels ranging from 2 to 58 mg g−1.34 The occlusion of C within phytoliths has been retained in soils for more than a millennium, generating an important long-term terrestrial C fraction.28,38–40 Thus, appropriate measures can improve the phytolith content of crops through enhancing soil available Si contents,39 aboveground net primary productivity,44 cultivar selection,4,21,22 nitrogen application,43 and basalt powder amendment,8 etc. Its mechanism will be considered in future work.
The production of PhytOC fluxes in rice organs are depends primarily on the dry weight, phytolith content, C content of phytolith of various plant parts and the total dry biomass.6,14 According to the before data, we estimated PhytOC fluxes in rice, and these results showed different fluxes of PhytOC in 51 rice cultivars (from 0.12 to 8.95 kg-e-CO2 per ha per year) (Fig. 5). The estimated PhytOC fluxes of different organs (root, stem, sheath, leaf and grains) ranged from 0.12 to 8.95 kg-e-CO2 per ha per year, 0.43 to 1.55 kg-e-CO2 per ha per year, 1.28 to 6.24 kg-e-CO2 per ha per year, 1.20 to 5.69 kg-e-CO2 per ha per year, 0.44 to 6.57 kg-e-CO2 per ha per year, respectively. The estimated PhytOC fluxes of stem were lowest of the rice organs.
Cultivars | Phytolith content (mg g−1) | C content of phytoliths (mg g−1) | PhytOC content in dry plant weight (mg g−1) | Estimated PhytOC fluxes (Mg–CO2 per ha per year) |
---|---|---|---|---|
a Data obtained from the Changshu Agroecological Experimental Station, Chinese Academy of Sciences. | ||||
Zhonghan 35 | 59.47 ± 6.45ab | 5.09 ± 3.96ab | 0.31 ± 0.24abc | 0.011–0.023 |
Guichao 2 | 53.83 ± 14.76b | 4.06 ± 2.35abc | 0.21 ± 0.09bc | 0.012–0.025 |
Xinliangyou 6 | 60.31 ± 5.13ab | 1.21 ± 0.02c | 0.09 ± 0.01c | 0.007–0.015 |
Rongyou 463 | 67.04 ± 1.56ab | 4.11 ± 0.31abc | 0.29 ± 0.03abc | 0.013–0.027 |
Tianyou 998 | 77.15 ± 17.96a | 7.21 ± 5.28a | 0.50 ± 0.30a | 0.018–0.035 |
Yueyou 9114 | 74.63 ± 18.71 ab | 3.13 ± 0.72bc | 0.24 ± 0.05bc | 0.011–0.022 |
Gangyou 188 | 59.48 ± 2.17ab | 1.80 ± 0.17bc | 0.11 ± 0.01c | 0.009–0.019 |
IIyou 1259 | 60.32 ± 5.23ab | 2.05 ± 0.40bc | 0.13 ± 0.01c | 0.012–0.025 |
IIyou 501 | 72.45 ± 11.83 ab | 1.94 ± 0.31bc | 0.15 ± 0.04b | 0.012–0.024 |
Fuyou 21 | 64.89 ± 14.85 ab | 3.43 ± 1.47bc | 0.24 ± 0.15bc | 0.018–0.035 |
Chuannong 1 | 60.21 ± 2.86ab | 1.54 ± 0.30bc | 0.10 ± 0.01c | 0.009–0.018 |
Zhongyou 7 | 61.86 ± 6.44ab | 1.40 ± 0.40bc | 0.10 ± 0.03c | 0.009–0.019 |
Yixiang 2079 | 68.96 ± 4.43ab | 1.46 ± 0.11bc | 0.11 ± 0.00c | 0.010–0.021 |
IIyou 1313 | 60.06 ± 3.87ab | 1.29 ± 0.11bc | 0.09 ± 0.01c | 0.008–0.017 |
Yixiang 725 | 74.17 ± 18.94 ab | 1.36 ± 0.40bc | 0.12 ± 0.06c | 0.010–0.020 |
Nenyou 8015 | 64.18 ± 7.53ab | 1.85 ± 0.40bc | 0.14 ± 0.03c | 0.011–0.022 |
Qianyou 0508 | 82.00 ± 21.83a | 2.28 ± 0.27bc | 0.17 ± 0.04ab | 0.014–0.027 |
Tenuo 2072 | 60.41 ± 9.32ab | 1.64 ± 0.46bc | 0.11 ± 0.04c | 0.009–0.018 |
Zhenzhunuo | 64.73 ± 4.75ab | 2.32 ± 1.03bc | 0.16 ± 0.08bc | 0.012–0.025 |
Cultivars | Phytolith content (mg g−1) | C content of phytoliths (mg g−1) | PhytOC content in dry plant weight (mg g−1) | Estimated PhytOC fluxes (Mg–CO2 per ha per year) |
---|---|---|---|---|
a Data obtained from the Changshu Agroecological Experimental station, Chinese Academy of Sciences. | ||||
Huaidao 5 | 62.96 ± 6.02abc | 4.17 ± 1.38ab | 0.27 ± 0.07abc | 0.010–0.021 |
Xindao 18 | 46.80 ± 13.99bc | 5.02 ± 2.89a | 0.23 ± 0.10bcde | 0.006–0.013 |
Wuyunjeng 7 | 65.55 ± 6.53abc | 4.04 ± 1.68abc | 0.27 ± 0.10abcd | 0.012–0.024 |
Xindao 20 | 53.37 ± 2.83abc | 3.55 ± 1.36abcde | 0.20 ± 0.06bcdef | 0.010–0.019 |
Shengdao 16 | 64.54 ± 1.23abc | 2.11 ± 0.44def | 0.15 ± 0.03bc | 0.008–0.015 |
Huaidao 11 | 78.06 ± 9.66ab | 2.10 ± 0.34def | 0.18 ± 0.05bcdef | 0.009–0.018 |
Zhendao 99 | 54.24 ± 3.42abc | 1.96 ± 0.33def | 0.12 ± 0.02def | 0.006–0.012 |
Lianjing 11 | 62.86 ± 9.66abc | 2.17 ± 0.43cdef | 0.15 ± 0.03bc | 0.009–0.018 |
Yanjing 47-12 | 65.55 ± 3.87 abc | 2.26 ± 0.50cdef | 0.16 ± 0.05cdef | 0.010–0.019 |
Wuyunjing 21 | 69.43 ± 8.45 abc | 1.91 ± 0.32def | 0.15 ± 0.04cdef | 0.008–0.016 |
Zhengdao 18 | 45.64 ± 1.01c | 2.19 ± 0.70cdef | 0.11 ± 0.03ef | 0.006–0.012 |
Jin G2 | 78.89 ± 21.24a | 3.65 ± 1.50abcd | 0.31 ± 0.20 ab | 0.018–0.035 |
Zhonghua 11 | 58.80 ± 17.19 abc | 2.39 ± 0.15bcdef | 0.15 ± 0.04cdef | 0.012–0.024 |
Ribenqing | 53.82 ± 11.19 abc | 2.41 ± 1.21bcdef | 0.15 ± 0.10cdef | 0.006–0.013 |
Fengguan 16 | 53.90 ± 9.69 abc | 2.09 ± 0.17def | 0.13 ± 0.02def | 0.007–0.015 |
Gangyouguba | 78.40 ± 22.26 ab | 2.21 ± 0.97cdef | 0.21 ± 0.14bcdef | 0.011–0.022 |
Longjing 38 | 63.56 ± 6.31 abc | 2.09 ± 0.24def | 0.14 ± 0.03cdef | 0.011–0.021 |
Longdao 12 | 57.63 ± 6.65 abc | 1.62 ± 0.25ef | 0.11 ± 0.01ef | 0.007–0.014 |
Longjing 21 | 48.45 ± 2.80 abc | 1.76 ± 0.11def | 0.10 ± 0.01ef | 0.006–0.012 |
Longjing 36 | 56.10 ± 10.32abc | 1.80 ± 0.04def | 0.11 ± 0.02ef | 0.008–0.016 |
Suidao 3 | 48.38 ± 5.18abc | 1.54 ± 0.35f | 0.09 ± 0.02ef | 0.007–0.013 |
Jixidao 1 | 54.67 ± 17.18abc | 1.44 ± 0.13f | 0.09 ± 0.03ef | 0.006–0.012 |
Nanjing 5055 | 52.41 ± 9.31abc | 1.29 ± 0.11f | 0.08 ± 0.01f | 0.006–0.012 |
Nanjing 46 | 53.44 ± 8.36abc | 1.51 ± 0.19f | 0.09 ± 0.01ef | 0.006–0.012 |
Xiushui 09 | 52.75 ± 5.98abc | 1.68 ± 0.14ef | 0.10 ± 0.01ef | 0.008–0.016 |
Zhejing 88 | 64.21 ± 5.42abc | 2.02 ± 0.26def | 0.14 ± 0.01cdef | 0.09–0.019 |
Xiushui 134 | 65.50 ± 3.65abc | 1.51 ± 0.68f | 0.11 ± 0.04ef | 0.008–0.017 |
8you 682 | 63.84 ± 9.29abc | 2.61 ± 0.58bcdef | 0.18 ± 0.06bcdef | 0.011–0.022 |
Zheyou 12 | 68.42 ± 4.61abc | 1.62 ± 0.19ef | 0.12 ± 0.01def | 0.010–0.019 |
Wuxiangnuo 8333 | 72.17 ± 3.99abc | 5.05 ± 2.88a | 0.38 ± 0.22a | 0.011–0.023 |
Sujingnuo 1 | 66.11 ± 9.83abc | 1.92 ± 0.52def | 0.14 ± 0.05cdef | 0.008–0.017 |
Zhenuo 65 | 51.84 ± 12.49abc | 1.78 ± 0.32def | 0.10 ± 0.01ef | 0.007–0.014 |
In the present study, we estimated that the C fluxes of the rice plants were 0.006 and 0.035 Mg-e-CO2 per ha per year in terms of the PhytOC in rice plant material on a dry weight basis.45 However, Li, Z. et al.6 and Prajapati et al.14 reported that the flux of the rice PhytOC is 0.03–0.13 Mg-e-CO2 per ha per year, and 0.05–0.12 Mg-e-CO2 per ha per year, which was higher than the results obtained in the present study.6 The differences between these results might reflect (i) the number of tested cultivars (i.e., this manuscript tested 51 rice cultivars, and Li et al.6 tested only 5 rice cultivars); (ii) the Si content of the paddy field, for example, previous studies have demonstrated that soil with high Si could enhance the phytolith content in crops;46–48 and (iii) the tested measure (i.e., this manuscript examined a revision to the wet digestion method, and Li et al. examined the microwave digestion method6). But still it is likely that breeding for high PhytOC rice cultivars would result in more amount of securely bio-sequestered C in rice crops.
Varieties | n | Phytolith content (mg g−1) | C content of phytoliths (mg g−1) | PhytOC content in dry plant weight (mg g−1) | Estimated PhytOC fluxes (Mg–CO2 per ha per year) |
---|---|---|---|---|---|
a Data obtained from the Changshu Agroecological Experimental Station, Chinese Academy of Sciences. | |||||
Indica rice | 3 | 57.87 ± 3.52a | 2.90 ± 1.39a | 0.21 ± 0.11a | 0.010–0.021 |
Indica three line hybrid rice | 14 | 67.21 ± 6.00a | 2.46 ± 1.10a | 0.19 ± 0.12a | 0.012–0.024 |
Indica glutinous rice | 2 | 62.57 ± 3.06a | 2.10 ± 0.46a | 0.13 ± 0.03a | 0.011–0.022 |
Japonica rice | 27 | 59.63 ± 9.35a | 2.54 ± 0.91a | 0.15 ± 0.06a | 0.009–0.017 |
Japonica three line hybrid rice | 2 | 67.52 ± 5.20a | 2.32 ± 0.68a | 0.15 ± 0.02a | 0.010–0.021 |
Japonica glutinous rice | 3 | 63.38 ± 10.44a | 3.09 ± 1.86a | 0.21 ± 0.15a | 0.009–0.018 |
Parameters | Phytolith content (mg g−1) | C content of phytoliths (mg g−1) | PhytOC content in dry plant weight (mg g−1) | Estimated PhytOC fluxes (Mg–CO2 per ha per year) |
---|---|---|---|---|
Panel A: indica rice cultivars | ||||
Minimum value | 53.38 | 1.44 | 0.09 | 0.007 |
Maximum value | 77.15 | 7.21 | 0.51 | 0.018 |
Range | 23.32 | 5.77 | 0.42 | 0.010 |
Mean | 65.25 | 2.62 | 0.19 | 0.011 |
Standard deviation | 6.38 | 1.44 | 0.11 | 0.003 |
Coefficient of variation (%) | 9.78 | 55.02 | 60.57 | 24.01 |
Panel B: japonica rice cultivars | ||||
Minimum value | 45.64 | 1.56 | 0.08 | 0.006 |
Maximum value | 78.89 | 5.24 | 0.38 | 0.018 |
Range | 33.25 | 3.68 | 0.30 | 0.012 |
Mean | 60.47 | 2.58 | 0.16 | 0.009 |
Standard deviation | 9.26 | 0.98 | 0.07 | 0.003 |
Coefficient of variation (%) | 15.32 | 38.04 | 44.50 | 29.16 |
Variables | Phytolith content | C content of phytoliths | PhytOC content in dry plant weight | Estimated PhytOC fluxes |
---|---|---|---|---|
a Correlation is significant at the 0.01 level (2-tailed). | ||||
Phytolith content | 1 | |||
C content of phytoliths | 0.170 | 1 | ||
PhytOC content in dry plant weight | 0.505a | 0.804a | 1 | |
Estimated PhytOC fluxes | 0.651a | 0.512a | 0.727a | 1 |
In fact, the C contents of phytoliths primarily depended on the efficiency of the C occluded within phytoliths during plant growth. Genetic and physiological differences within rice cultivars could also affect the formation and efficiency of the C occluded within phytoliths.48 However, the C contents of phytoliths was significantly correlated with the PhytOC content in dry plant weight in the 51 rice cultivars (R = 0.804, p < 0.01) (Table 5) and with the PhytOC content in dry plant weight in 6 rice varieties (R = 0.864, p < 0.05) (Table 6). Similarly Guo et al., Li et al. and Prajapati et al. reported that the PhytOC content in dry plant weight was the significantly correlated with the content of phytoliths and the C content of phytoliths, implying that the PhytOC content in dry plant weight depends not only on the content of phytolith but also on the C content of phytolith.6,8,14 Thus, how to increase phytolith content and the C content of phytoliths will require further in-depth study.
Variables | Phytolith content | C content of phytoliths | PhytOC content in dry plant weight | Estimated PhytOC fluxes |
---|---|---|---|---|
a Correlation is significant at the 0.01 level (2-tailed). | ||||
Phytolith content | 1 | |||
C content of phytoliths | −0.392 | 1 | ||
PhytOC content in dry plant weight | −0.076 | 0.864a | 1 | |
Estimated PhytOC fluxes | −0.042 | −0.630 | −0.670 | 1 |
The global rice-planting area was approximately 1.64 × 108 ha in 2014.14 Considering that the largest PhytOC flux of rice plants was 0.035 Mg-e-CO2 per ha per year, globally, 5.74 × 106 Mg-e-CO2 would have been occluded within the phytolith of rice plants per year,6 although the annual CO2 occlusion within the rice phytoliths of the unit area is likely lower than that of other plants, such as bamboo leaf litter (1.56 × 107 Mg-e-CO2 per year)30 and wetland plants (4.39 × 107 Mg-e-CO2 per year),8 and grasslands (4.14 × 107 Mg-e-CO2 per year),3 and higher than millet (2.37 × 106 Mg-e-CO2 per year)5 and sugarcane leaf (0.72 × 107 Mg-e-CO2 per year).31 In this study we had showed that estimated PhytOC fluxes in rice cultivars varied considerably between different rice cultivars. So the selection of high phytOC rice cultivars became one of effective measure to improve securely bio-sequestered C in rice crops.
Footnote |
† Present/permanent address: Institute of Soil Science, Chinese Academy of Sciences, 71 East Beijing Road, Nanjing, Jiangsu Province, 210008, P. R. China. |
This journal is © The Royal Society of Chemistry 2017 |