Prescribed burning is projected to be adopted more frequently with intensifying climate change; thus, a long-term study is necessary to understand the burning impacts on forest productivity and carbon (C) and nitrogen (N) cycling. Litter fall production rate can be used to indicate burning impacts on forest productivity, whereas N concentration, and C and N isotope composition (δ13C and δ15N) can be used to infer burning impacts on C and N cycling in plant-soil system.
Materials and methodsIn this study, the impacts of low-intensity prescribed burning on litter production, N concentration, and C and N isotope compositions were continuously investigated for 6 years at five study sites in a natural eucalypt forest of subtropical Australia.
Results and discussionHigher leaf litter production rate, N concentration and δ15N, and lower δ13C could be seen shortly after prescribed burning. The higher leaf litter N concentration and lower δ13C were likely due to the ease of competition for soil N and moisture from understory vegetation in the short term by prescribed burning. Leaf δ15N and N concentration were closely correlated, and seasonal changes in leaf litter production rate, δ13C and δ15N were observed. Burning season and related severity might determine the suppression degree of understory vegetation. Time since fire (TSF) was a significant impact factor influencing the litter fall production rate, N concentration, δ13C and δ15N of leaf litter fall for a decade following prescribed burning. However, monthly rainfall and temperature were less consistent in their impacts.
ConclusionsNitrogen limitation was enhanced by prescribed burning through the removal of litter and understory vegetation in the N poor forest and might be responsible for the long-term burning impacts. Low-intensity prescribed burning might have a long-lasting impact on forest litter productivity in nutrient poor forests in subtropical Australia.
相似文献This study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.
Materials and methodsIn situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L?1 NO3?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3?-N in the top 5 cm soil before and after the incubation, and δ15N of NO3?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.
Results and discussionThe significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.
ConclusionsThe δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.
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