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 (Rₛ), the CO₂ release from root respiration and microbial metabolism, affects global soil carbon storage and cycling. Only few studies have looked at Rₛ in the southern hemisphere, especially regarding the interaction between soil type and environmental factors on Rₛ in dairy grassland. We investigated the relationship between Rₛ and soil temperature (Tₛ), 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) µmol CO₂ m⁻² s⁻¹. Mean summer Rₛ was 86.5% higher than mean winter Rs, largely driven by organic/gley and pumice soils while ultic soils showed very little seasonal temperature sensitivity. Overall mean Rₛ in organic/gley soils was 108.0% higher than that in ultic soils. The high Rₛ rate observed in organic/gley was likely due to high soil organic matter content, while low Rs in ultic and pallic soils resulted from high clay content and low hydraulic conductance. Soil temperature drove overall Rₛ. Our findings indicate that soil type and soil temperature together best explain Rₛ. 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. (Figure presented.)