Soil type and temperature determine soil respiration seasonal dynamics in dairy grassland

Soil respiration rates (Rs) were measured in New Zealand dairy grassland. Both season and soil type significantly affected Rs. Soil temperature and soil type dominated overall Rs.Soil respiration (R s), the CO2 release from root respiration and microbial metabolism, affects global soil carbon storage and cycling. Only few studies have looked at R s in the southern hemisphere, especially regarding the interaction between soil type and environmental factors on R s in dairy grassland. We investigated the relationship between R s and soil temperature (T s), soil water content (SWC), soil type, and other environmental factors based on summer and winter measurements at four sites in New Zealand. Across sites, soil respiration rates ranged from 0.29 to 14.58 with a mean of 5.38 +/- 0.13 (mean +/- standard error) mu mol CO2 m-2 s-1. Mean summer R s was 86.5% higher than mean winter R s, largely driven by organic/gley and pumice soils while ultic soils showed very little seasonal temperature sensitivity. Overall mean R s in organic/gley soils was 108.0% higher than that in ultic soils. The high R s rate observed in organic/gley was likely due to high soil organic matter content, while low R s in ultic and pallic soils resulted from high clay content and low hydraulic conductance. Soil temperature drove overall R s. Our findings indicate that soil type and soil temperature together best explain R s. This implies that a mere classification of land use type may be insufficient for global C models and should be supplemented with soil type information, at least locally.