[show abstract][hide abstract] ABSTRACT: a b s t r a c t It was hypothesized that litter with higher N concentration would decompose faster than that with lower N concentration and that increased soil nutrient availability would stimulate litter decomposition. To examine the interspecific differences in decomposition rate of leaf litter in relation with differences in litter chemistry and soil nutrient availability, senescent leaves of four species Pennisetum flaccidum, Artemisia scoparia, Chenopodium acuminatum and Cannabis sativa, and soil samples with different fertilization treatments (no fertilization, N, P, and N þ P fertilizations, respectively) were collected from a sandy grassland in Northeast China and incubated under laboratory conditions. The decomposition rate of leaf litter was determined by measuring the CO 2 emission during decomposition of litter. We found remarkable interspecific differences in leaf decomposition rates. Moreover, rates of litter decomposition at different incubation stages were correlated with different litter quality indices. The rate of litter decomposition was positively correlated with initial litter N concentration in the initial stage of the incubation, whereas it was negatively correlated with litter N and P concentrations in the late stage. Responses of litter decomposition to soil nutrient availability differed among species. Our results suggest that both indirect changes in litter quality through shifts of species composition/dominance and direct changes in soil nutrient availability under nutrient addition conditions could affect litter decomposition and consequently C and nutrient cycling of grassland ecosystems.
Journal of Arid Environments - J ARID ENVIRON. 04/2011; 75(9).
[show abstract][hide abstract] ABSTRACT: Nitrogen (N)-fixing species have a function to enrich N in soil. Mixing N-fixing shrub species into poplar stands can be assumed as a measure to increase productivity while improving soil fertility. To verify this assumption and to understand the temporal influences of N-fixing shrub species mixed into poplar plantations on soil fertility, we investigated selected soil chemical and microbial properties in pure poplar (Populus × xiaozhuanica W. Y. Hsu et Liang) and mixed poplar–seabuckthorn (Hippophae rhamnoides L.) stands at ages of five and 15 years in a semi-arid region of Northeast China. Both stands at age of five have similar values of aboveground biomass, total soil organic C concentration, total N concentration, microbial biomass C, and metabolic quotient; however, at age of 15, these values except for soil metabolic quotient are significantly greater in mixed poplar–seabuckthorn stand than in pure poplar stand. The soil metabolic quotient is lower in the former stand than in the latter stand. Our results suggest that, in semi-arid regions, mixing N-fixing shrub species into poplar plantations can improve soil fertility in a long run rather than in a short term; therefore, mixing N-fixing shrub species into poplar stands is an option to improve soil fertility and increase productivity in a long run.
[show abstract][hide abstract] ABSTRACT: Soil microbial properties play a key role in belowground ecosystem functioning, but are not well understood in forest ecosystems
under nitrogen (N) enrichment. In this study, soil samples from 0–10cm and 10–20cm layers were collected from a Dahurian
larch (Larix gmelinii Rupr.) plantation in Northeast China after six consecutive years of N addition to examine changes in soil pH, nutrient concentrations,
and microbial biomass and activities. Nitrogen addition significantly decreased soil pH and total phosphorus, but had little
effect on soil total organic carbon (TOC) and total N (TN) concentrations. The NO3−-N concentrations in the two soil layers under N addition were significantly higher than that in the control, while NH4+-N concentrations were not different. After six years of N addition, potential net N mineralization and nitrification rates
were dramatically increased. Nitrogen addition decreased microbial biomass C (MBC) and N (MBN), and MBC/TOC and MBN/TN in
the 0–10cm soil layer, but MBC/MBN was increased by 67% in the 0–10cm soil layer. Soil basal respiration, microbial metabolic
quotient (qCO2), and β-glucosidase, urease, acid phosphomonoesterase and nitrate reductase activities in the two soil layers showed little change
after six years of N addition. However, soil protease and dehydrogenase activities in the 0–10cm layer were 41% and 54% lower
in the N addition treatment than in the control, respectively. Collectively, our results suggest that in the mid-term N addition
leads to a decline in soil quality in larch plantations, and that different soil enzymes show differentiated responses to
Larix gmelinii Rupr.-Microbial biomass-Microbial metabolic quotient-Nitrogen enrichment-Temperate plantation forest