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• Alder expansion reduced soil P pool in the 0–40 cm depth. • Total P concentration increased in surface soils but reduced in deep soils after alder expansion. • Alder expansion increased plant-available P fractions by elevating acid phosphatase activity. • Alder expansion caused about ninefold increase in aboveground plant biomass. Dinitrogen (N 2)-fixing woody plants, mainly alder (Alnus) species, have widely expanded to boreal peatlands. However, little is known about the effect of N 2 -fixing plant expansion on soil phosphorus (P) dynamics and its potential mechanisms in these ecosystems. To clarify the response of soil P status to N 2 -fixing plant expansion, we compared the differences in aboveground plant biomass, soil total P pool, acid phosphatase activity, P sorption index, and four bioavailable P fractions (CaCl 2 , citrate, phosphatase enzyme, and HCl extractable P fractions) in the 0–10 cm, 10–20 cm, and 20–40 cm depths between A. sibirica islands and adjacent open peatlands in a boreal peatland, Northeast China. While alder expansion hardly affected bulk density and associated volume of the peats, it strongly decreased total P pool in the 0–40 cm soil depth because of approximately ninefold increases in aboveground plant biomass and associated P transfer from soils to plants. Soil total P concentration increased in the 0–10 cm depth, but declined in the 10–20 cm and 20–40 cm depths. At each depth, alder expansion increased soil acid phosphatase activity, and CaCl 2 and enzyme extractable P fractions, despite unchanged P sorption index and citrate extractable P fraction. Both CaCl 2 and enzyme extractable P fractions correlated positively with acid phosphatase activity, indicating that increased P bioavailability was primarily caused by elevated microbial mineralization of organic P. These findings highlight the contrasting responses of soil P pool and bioavailability to N 2 -fixing tree expansion, and suggest that N 2 -fixing tree expansion would reduce soil P pool via enhanced P bioavailability and subsequently increased plant P uptake in boreal peatlands. [ABSTRACT FROM AUTHOR]

Abstract: Dicranopteris is a common fern distributed throughout tropical and subtropical regions of the world. It often forms a mat-like understory, especially in open areas. A forest floor dominated by Dicranopteris plays an important role in ecosystem dynamics, but is often overlooked in ecological research. We conducted an experiment by removing overstory or understory Dicranopteris to compare their effects on soil microclimate, litter decomposition, soil decomposer food web and ecosystem nutrient cycling. Results of our field study showed that removal of a Dicranopteris-dominated understory leads to increased soil temperature and reduced soil moisture, subsequently, altering the components of the soil food web (microbial community, nematode and microarthropod densities) and reducing ecosystem processes of litter decomposition. When present, Dicranopteris forms a dense understory layer in subtropical and tropical regions, which is favorable for sustaining soil microclimates and acts as the major driver of soil biota and ecological processes in intensive forest ecosystems. [Copyright &y& Elsevier]

Abstract To study how the understory vegetation influences the catalytic properties of extracellular hydrolases, we established a paired treatment experiment, with understory vegetation and litter removed from one treatment (understory removal, UR) and litter removed and the understory vegetation left intact in the other (control, CK), in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. We used fluorescent substrates to determine the maximum velocity (V max), the affinity of hydrolases to the substrates (K m), and the catalytic efficiency (V max /K m) of three extracellular hydrolases (β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP)). We found that the V max values for βG and NAG were 23.0% and 16.8% lower, respectively, in the UR treatment than in the CK treatment, and that the V max for AP was similar in both treatments. The K m and V max /K m for all the three hydrolases remained steady after the understory vegetation was removed. The soil C and N contents and the bacterial and fungal biomass were generally positively correlated with the V max values. Thus, understory vegetation had more influence on the activities (V max) than on the substrate affinities of extracellular hydrolases (K m). Microbes tended to concentrate on maintaining the catalytic efficiency when the SOC contents were between 15.8 and 20.3 g kg−1 when the understory vegetation was removed from a subtropical Chinese fir forest, and the catalytic efficiency could decrease under extremely low soil C contents. We suggest that understory vegetation should be maintained to sustain the potential microbial activity in subtropical Chinese fir forests. Highlights • The V max of βG and NAG, but not AP, decreased when understory vegetation was removed. • The K m and V max / K m values did not change when understory vegetation was removed. • Soil C and N and microbial biomass were mainly positively related to the V max. • Understory vegetation should be maintained to sustain potential microbial activity. [ABSTRACT FROM AUTHOR]

Edible mushroom cultivation is an important industry in intensively managed forest understories. However, proper disposal of spent mushroom substrate (SMS) presents a challenge to its sustainable development. Biochar derived from SMS could be used to improve soil quality while providing a solution for SMS disposal. But SMS biochar pyrolyzed at different temperatures may alter carbon dioxide (CO 2) and nitrous oxide (N 2 O) emissions associated with global warming, especially under the context of nitrogen (N) addition and warming. We conducted a factorial incubation study to examine greenhouse gas emissions and N transformations in moso bamboo forest soil amended with SMS-biochar (control vs. pyrolyzed at 300, 450 or 600 °C) in different N-addition (0 or 100 mg N kg-1 soil) and temperature (20, 25 or 30 °C) treatments. Pyrolysis temperature affected pH, C and N of SMS-biochars. N-transformations depended on the interaction of pyrolysis temperature, N-addition, and incubation temperature but were generally lower with 450 °C biochar addition. Soil N 2 O emissions increased with N-addition and they were more sensitive to incubation temperatures without biochar. Soil CO 2 emissions increased with incubation temperature or biochar pyrolyzed at lower temperatures. Pyrolysis temperature might have regulated the effects of SMS-derived biochar on N 2 O emissions via changes in dissolved C, N, pH and associated changes in soil microbial community compositions. Because of the importance of sustainable development of this understory industry, amending soils with biochar produced at higher temperatures may be the best strategy for both the disposal of SMS and the mitigation of greenhouse gas emissions. Image 1 • PH of spent mushroom substrate (SMS) biochar increased with pyrolysis temperature. • SMS-biochar reduced the temperature sensitivity of soil N 2 O emission rates. • Lower pyrolysis temperature SMS-biochar increased CO 2 emissions. • Spent mushroom substrate biochar pyrolyzed at 450 °C decreased nitrification rate. [ABSTRACT FROM AUTHOR]