Date Published: September 16, 2013
Publisher: Public Library of Science
Author(s): Zhaoliang Song, Jeffrey F. Parr, Fengshan Guo, Senjie Lin.
The occlusion of carbon (C) by phytoliths, the recalcitrant silicified structures deposited within plant tissues, is an important persistent C sink mechanism for croplands and other grass-dominated ecosystems. By constructing a silica content-phytolith content transfer function and calculating the magnitude of phytolith C sink in global croplands with relevant crop production data, this study investigated the present and potential of phytolith C sinks in global croplands and its contribution to the cropland C balance to understand the cropland C cycle and enhance long-term C sequestration in croplands. Our results indicate that the phytolith sink annually sequesters 26.35±10.22 Tg of carbon dioxide (CO2) and may contribute 40±18% of the global net cropland soil C sink for 1961–2100. Rice (25%), wheat (19%) and maize (23%) are the dominant contributing crop species to this phytolith C sink. Continentally, the main contributors are Asia (49%), North America (17%) and Europe (16%). The sink has tripled since 1961, mainly due to fertilizer application and irrigation. Cropland phytolith C sinks may be further enhanced by adopting cropland management practices such as optimization of cropping system and fertilization.
Present understanding of the global carbon (C) cycle and climate feedbacks is limited by uncertainty over terrestrial C balance –. As one of the largest terrestrial ecosystems deeply influenced by human activities, the croplands cover an area of 15.33×108 hm2 globally and may play a significant role in terrestrial C balance , . Although croplands were traditionally considered to be the largest biospheric source of C lost to the atmosphere in most areas of the world –, they may also be significant C sinks under proper management , , –.
Relative to the liable biomass C sink, the phytolith C sink in croplands is certain and stable, and can be sustained for several hundreds or thousands of years in most regions of the world. The phytolith sink of global croplands is a stable net sink of 26.35±10.22 Tg CO2 yr−1, and may play a significant role in global cropland C balance for 1961–2100. The high phytolith sinks in Asia, North America and Europe can be attributed to the relatively high production of rice, maize, and wheat, respectively. The total phytolith C sink of global croplands has tripled since 1961 mainly due to fertilization, irrigation and cropland expansion. Taking an average phytolith C sink rate of 0.03 Pg CO2 yr–1, the total phytolith C sink of global croplands during 1961 and 2100 is 4.2±1.9 Pg CO2 yr–1, 40±18% of the total net soil C sink. Our data suggest that the cropland phytolith C sinks may be further enhanced by adopting cropland management practices such as optimization of cropping system and fertilization.