Agriculture, Ecosystems and Environment 142 (2011) 213–221 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment jo ur n al homepage: www.elsevier.com/lo cate/agee Impact of elevated CO 2 on utilization of soil moisture and associated soil biophysical parameters in pigeon pea (Cajanus cajan L.) Saurav Saha a , Debashis Chakraborty a,∗ , Lata b , Madan Pal c , Shantha Nagarajan a a Division of Agricultural Physics, Indian Agricultural Research Institute, New Delhi, India b Division of Microbiology, Indian Agricultural Research Institute, New Delhi, India c Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi, India a r t i c l e i n f o Article history: Received 15 August 2010 Received in revised form 3 May 2011 Accepted 5 May 2011 Available online 8 June 2011 Key words: Elevated CO2 Pigeon pea Crop water use Water use efﬁciency Root growth Active carbon pools a b s t r a c t An experiment was conducted with two genotypes of pigeon pea (Cajanus cajan L.) grown in an allu- vial sandy loam soil (belonging to Holambi series, a mixed hyperthermic family of typic Haplustept) in open top chambers (OTCs) installed in the ﬁeld. The objective was to ﬁnd out the effect of elevated CO 2 (580 ppm) on soil moisture changes, crop water use, root growth characteristics and status of active car- bon pools in soil. Soil temperatures at 9:00 and 16:00 h were similar till 94 days after sowing (DAS), and were marginally less thereafter in the CO 2 chambers. Proﬁle moisture content was consistently lower in CO 2 chambers, indicating greater water use by the crop. An exponential relationship was obtained between crop biomass and its water use. Greater biomass led to higher water use efﬁciency by the crop, though genotypic differences were evident only in pod yields. Root characters at two growth stages (72 and 110 DAS) showed a signiﬁcant increase in its weight density, length density and surface area at 0–15 and 15–30 cm layers for plants grown under elevated CO 2 . Signiﬁcantly higher amount of roots with smaller diameter (<0.1 mm) under elevated CO 2 possibly contributed in greater soil moisture absorption. There was no appreciable change in the soil physical properties (bulk density, hydraulic conductivity and mean weight diameter); but different active carbon pools (oxidizable, carbohydrate, labile, micro- bial biomass and total) in the soil increased signiﬁcantly due to CO 2 exposure. Dehydrogenase and FDA hydrolysis enzymes also increased substantially and were found to have a highly positive correlation with all C fractions indicating the role of active carbon pools in stimulating microbial population, leading to better biological activity in soil near the root zone under CO 2 enrichment. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The change in climate over the years has usually been thought of as a natural phenomenon. However, its rapid and ‘unnatural’ changes, and the spatial and temporal variabilities have assumed greater importance in recent years over the world. These have been attributed mostly to anthropogenic factors, in sharp contrast to the natural course of change in climate. There is growing evidence of increase in atmospheric CO 2 concentration from a base value of 280 to a level of 379 l l -1 (IPCC, 2007). During the last 12 years, its increase has been 1.9 l l -1 year -1 and is predicted to be as high as 570 l l -1 by the middle of this century. Accordingly, as a conse- quence of this rise in CO 2 , a warmer earth (rise in earth’s average temperature from 2.0 to 4.5 ◦ C; IPCC, 2007) is predicted. This might ∗ Corresponding author. Tel.: +91 11 25841178; fax: +91 11 2584 2321; mobile: +91 9868316785. E-mail addresses: debashisiari@hotmail.com, debashis@iari.res.in, debashisiari@gmail.com (D. Chakraborty). possibly exert in a signiﬁcant impact on agricultural productivity (Aggarwal and Sinha, 1993). Under conditions of non-limiting soil water and elevated atmospheric CO 2 , a reduction in stomatal conductance and a concomitant decline in transpiration were observed in many herba- ceous plants (Morison, 1998). Transpiration, a vital component in soil–water–plant relationship is of particular importance in study- ing possible interactions of elevated CO 2 and water supply in terms of plant water use. It has been envisaged that the evapotranspira- tion and water use efﬁciency of crop will be altered with climate change (Mo et al., 2007; Thomas, 2008), as inﬂuenced by elevated CO 2 . This has far-reaching implications, particularly in arid and semi-arid regions, where water availability has always been a crit- ical consideration. Root biomass normally increases under elevated CO 2 , but detailed study of root growth and functions are lacking (Rogers et al., 1994). An increase in below-ground plant productivity and metabolism with increased atmospheric CO 2 have been observed, suggesting that a signiﬁcant portion of extra carbon (C) is trans- ferred to root systems, and ultimately to the soil microbial 0167-8809/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2011.05.008