Abstract
Abstract. Semi-arid woodlands, which are characterised by patchy vegetation interspersed with bare, open areas, are frequently exposed to wildfire. During summer, long dry periods are occasionally interrupted by rainfall events. It is well known that rewetting of dry soil induces a flush of respiration. However, the magnitude of the flush may differ between vegetation patches and open areas because of different organic matter content, which could be further modulated by wildfire. Soils were collected from under trees, under shrubs or in open areas in unburnt and burnt sandy mallee woodland, where part of the woodland experienced a wildfire which destroyed or damaged most of the aboveground plant parts 4 months before sampling. In an incubation experiment, the soils were exposed to two moisture treatments: constantly moist (CM) and drying and rewetting (DRW). In CM, soils were incubated at 80 % of maximum water holding capacity (WHC) for 19 days; in DRW, soils were dried for 4 days, kept dry for another 5 days, then rewetted to 80 % WHC and maintained at this water content until day 19. Soil respiration decreased during drying and was very low in the dry period; rewetting induced a respiration flush. Compared to soil under shrubs and in open areas, cumulative respiration per gram of soil in CM and DRW was greater under trees, but lower when expressed per gram of total organic carbon (TOC). Organic matter content, available P, and microbial biomass C, but not available N, were greater under trees than in open areas. Wild fire decreased the flush of respiration per gram of TOC in the open areas and under shrubs, and reduced TOC and microbial biomass C (MBC) concentrations only under trees, but had little effect on available N and P concentrations. We conclude that the impact of wildfire and DRW events on nutrient cycling differs among vegetation patches of a native semi-arid woodland which is related to organic matter amount and availability.
Highlights
Semi-arid woodlands are widespread in regions with Mediterranean climate where, in summer, long dry periods are occasionally interrupted by heavy rainfall events
Rewetting of dry soil induces a flush of respiration, which has been explained by increased substrate availability due to death of part of the microbial biomass, release of osmolytes accumulated during the dry period, and exposure of previously occluded organic matter (Fierer and Schimel, 2002; NavarroGarcia et al, 2012; Kim et al, 2012; Borken and Matzner, 2009; Birch, 1958)
total organic carbon (TOC) content was higher under trees than in open areas or under shrubs
Summary
Semi-arid woodlands are widespread in regions with Mediterranean climate where, in summer, long dry periods are occasionally interrupted by heavy rainfall events. Rewetting of dry soil induces a flush of respiration, which has been explained by increased substrate availability due to death of part of the microbial biomass, release of osmolytes accumulated during the dry period, and exposure of previously occluded organic matter (Fierer and Schimel, 2002; NavarroGarcia et al, 2012; Kim et al, 2012; Borken and Matzner, 2009; Birch, 1958). The respiration pulse upon rewetting may contribute a significant proportion of the total annual CO2 flux from surface soils (Fierer and Schimel, 2003; Jarvis et al, 2007). Sun et al.: Response of soil respiration to drying and rewetting
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