Effects of environmental factors on gross caloric values of three life-forms aquatic plants on the Qinghai-Xizang Plateau,China

Aims Gross caloric value (GCV) reflected plants’ capability of converting solar energy. It provided a reliable indicator of plants’ adaptations to environments in perspective of energy conversion and fixation. The aims of this study were (1) to illustrate the characteristics of GCV of aquatic plants on the Qinghai-Xizang Plateau, (2) to explore the geographical and environmental patterns and (3) to discuss the underlying mechanisms in forming the patterns.
Methods In July and August 2015, we collected 533 samples of aquatic plants’ leaves in 143 field sites on the Qinghai-Xizang Plateau, and measured their GCV using SDACM-4000 oxygen bomb calorimeter. Together with mean annual temperature (MAT) of climatic factor and properties of water body, this study compared the differences of GCV among submerged, emergent and floating-leaved plants by analysis of variance (ANOVA) and Tukey’s HSD. We further regressed GCV of submerged and emergent plants against geographical and climatic factors and properties of water body by simple regression to explore the relative effects of environmental factors on GCV.
Important findings On the Qinghai-Xizang Plateau, the mean GCV was (15.95 ± 3.90) kJ·g^-1. Among the three life forms, the rank of GCV was the emergent plants (18.10 kJ·g^-1) > the floating-leaved plants (16.77 kJ·g^-1) > the submerged plants (14.31 kJ·g^-1). With an increasing latitude, the GCV of emergent and submerged plants increased. Only GCV of emergent plants decreased with increasing altitude and temperature. The GCV of emergent and submerged plants increased with increased water salinity. Dissolved oxygen had significant negative effects on emergent plants, while pH value had no significant effects.