Effects of sampling method on foliar δ13C of Leymus chinensis at different scales

Stable carbon isotope composition (C-13) usually shows a negative relationship with precipitation at a large scale. We hypothesized that sampling method affects foliar C-13 and its response pattern to precipitation. We selected 11 sites along a precipitation gradient in Inner Mongolia and collected leaves of Leymus chinensis with five or six replications repeatedly in each site from 2009 to 2011. Additionally, we collected leaves of L. chinensis separately from two types of grassland (grazed and fenced) in 2011. Foliar C-13 values of all samples were measured. We compared the patterns that foliar C-13 to precipitation among different years or different sample sizes, the differences of foliar C-13 between grazed and fenced grassland. Whether actual annual precipitation (AAP) or mean annual precipitation (MAP), it was strongly correlated with foliar C-13 every year. Significant difference was found between the slopes of foliar C-13 to AAP and MAP every year, among the slopes of foliar C-13 to AAP from 2009 to 2011. The more samples used at each site the lower and convergent P-values of the linear regression test between foliar C-13 and precipitation. Furthermore, there was significant lower foliar C-13 value in presence of grazed type than fenced type grassland. These findings provide evidence that there is significant effect of sampling method to foliar C-13 and its response pattern to precipitation of L. chinensis. Our results have valuable implications in methodology for future field sampling studies.