**3.2 Biochar**

*Advances in Forest Management under Global Change*

was positively correlated with pH (*R*<sup>2</sup>

negatively correlated with pH (*R*<sup>2</sup>

with decreasing pH (5.57–7.06) (*R*<sup>2</sup>

(lime amelioration) under NO3

when soil acidification happened.

reducing soil exchangeable H+

high-dose levels (1 or 2 g kg<sup>−</sup><sup>1</sup>

**3. Sustainable forest management**

*2.3.2 Shifts in microbial communities and abundance*

was negatively correlated with soil pH (3.7–8.0) (*R*<sup>2</sup>

the potential of N2O production in acid soils [26].

*2.3.3 Microbes increased resistance to soil acidification*

Generally, the abundance of AOB was lower in soil pH < 5.5 than that in neutral soil pH. Here, nitrification was weak and almost disappears at soil pH < 4 [66]. However, AOA could mediate the process of ammonia oxidation in extremely strong acidity soil (pH: 4.2–4.47) [43]. Another study reported that the abundance of AOB

acid paddy soil (pH 5.6), while AOB dominated in alkaline soil (pH 8.2) [68]. Previous research indicated that fungi were the main microbial community that mediated N2O emissions in acid soil [69, 70]. Additionally, fungi-mediated denitrification accounted for 70% soil N2O emissions from a 100-year-old tea plantation (soil pH 3.8) [71]. In acid soils, the activity of N2O reductase was inhibited, leading to higher N2O emissions in lower soil pH [72]. Indeed, there was a positive correlation between the abundance of *nirS*, *nirK*, or *nosZ* and soil pH (4.0–8.0) and a negative correlation between N2O/(N2O + N2) and soil pH [73]. In agreement, N2O/(N2O + N2)

addition decreased N2O/(N2O + N2) [74]. The ratio of N2O/(N2O + N2) increased

tively correlated with N2O/N2 [76]. Intensive management consistently decreased soil pH and increased the ratio of N2O/(N2O + N2) [77]. Increasing dolomite dosage increased soil pH and hence increased the transcription of *nosZ* genes and reduced

Laboratory study showed that the potential of soil N2O emissions was increased

with decreasing pH (soil pH ranging from 2.96 to 6.26) from tea plantations in Japanese [78]. In addition, higher soil N2O emissions and lower abundance of *nosZ* genes were observed in soil pH at 3.71 (control) than in pH at 5.11, 6.19, and 7.41

100-year-old tea plantation [79]. Field study found a negative correlation between soil N2O emissions and pH (pH 3.6–5.9) (N2O-N = 636.6\* e<sup>−</sup>0.8028 \* pH, *R* = −0.93) from *Betula pendula* Roth forest [80]. Thus, denitrifying microorganisms may have been adapted extremely to acid soil environments, resulting in high N2O emissions

Soil amelioration (e.g*.*, application of lime, biochar nitrification inhibitors, and urease inhibitors) plays an important role in mitigation of soil acidification and N2O

Lime as an ameliorant was often used to amend acid soils in southern China due to increasing soil pH. It can relieve the toxic effect of soil Al3+ on plant growth by

tion [82]. In addition, application of lime can reduce soil N2O emissions [40]. For example, under 60% WFPS or flooded conditions, dolomite addition at medium- or

scription of *nosZ* genes (N2O → N2) by increasing acid soil pH from a rice-rapeseed

= 0.2807), while the abundance of AOA was

= 0.759, *P* < 0.001), and lime

) from a

= 0.2141) [67]. For example, AOA dominated in

= 0.82) [75]. Consistently, soil pH was nega-

<sup>−</sup>-N fertilization (50, 200, and 1000 mg kg<sup>−</sup><sup>1</sup>

[81]. Lime addition increased soil pH and salt satura-

soil) can reduce N2O emissions and increase the tran-

**8**

emissions.

**3.1 Lime**

Biochar was stable in the soil from Amazon basin of Brazil, and biochar input improved soil fertility [85]. This discovery accelerated the development of technologies for biochar application in soil amelioration.

Biochar is a carbon (C)-rich solid material by pyrolyzing of organic biomass such as crop straw, forestry by-products, urban waste, industrial by-products, animal manure, and urban sludge at low oxygen and high temperature (250–700°C) condition [86]. Biochar has been characterized by a high pH, specific surface area, degree of aromatization, and porosity. In addition, biochar is rich in C-containing functional groups (e.g., C–H, C–O, C=C and C=O) and relatively stable organic C. The physicochemical properties of biochar were mainly determined by pyrolysis temperature [87].

Presently, biochar was widely used as a soil ameliorant in agriculture and forestry field. For example, our previous studies reported that *C. oleifera* fruit shells are ideal feedstock for producing biochar as they are rich in C and N [1, 88]. Biochar includes the following advantages:

