Soil microbial respiration responses to changing temperature and substrate availability in fertile grassland

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From: Australian Journal of Soil Research(Vol. 48, Issue 5)
Publisher: CSIRO Publishing
Document Type: Report
Length: 7,145 words

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Abstract :

A relationship between soil respiration rate ([R.sub.s]) and temperature ([T.sub.s]), has been understood to be predicated on carbon (C) substrate availability. However, unlike [T.sub.s], C availability in soils is not a state variable that can be readily measured. The C in soils has come from plants, so the C supply rate can be affected by the weather and nutrient supply. We studied a fertile soil beneath pasture, measuring [R.sub.s] across a temperate--climate range of [T.sub.s]. Our objectives were to: (1) quantify the synchrony of diurnal changes in [T.sub.s] and [R.sub.s] beneath pasture under conditions favourable for plants, (2) quantify responses of microbial respiration ([R.sub.m]) to the removal of plants and depletion of C supply over time at various [T.sub.s], and (3) determine if [R.sub.m] was related to water-soluble (WSC, 20[degrees]C) and hot-water-soluble C (HWSC, 80[degrees]C) contents. At a grassland site, [R.sub.s] increased with Ts as predicted by an Arrhenius type relationship. Sampled soil was incubated at 3[degrees], 9[degrees], and 24[degrees]C and [R.sub.m] was measured over 14 days. In addition soil samples were pre-incubated at 3[degrees] or 9[degrees]C for both 5 and 14 days, then incubated at 24[degrees]C for 1 day and [R.sub.m] was measured. On day 2, [R.sub.m] was less than predicted at 24[degrees] and 9[degrees]C, respectively, suggesting a C availability limitation. The time courses of [R.sub.m], revealed that at 24[degrees]C, [R.sub.m] utilised C that was not utilised at lower [T.sub.s], indicating that evidently recalcitrant C was available to microbes at a warmer temperature. The responses of [R.sub.m] at 24[degrees]C after the pre-incubation treatments were identical for the 3[degrees]C and 9[degrees]C pre-incubation treatments, although significantly more C was respired during pre-incubation at 9[degrees]C. The WSC and HWSC contents were unaffected by [T.sub.s], so did not provide useful measures of the C substrate available for [R.sub.m]. Additional keywords: carbon, pasture, water soluble carbon, soil temperature.

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Gale Document Number: GALE|A237453368